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The destruction of organic pollutants under mild reaction conditions: A review
Abstract
A survey of the literature covering the destruction of organic pollutants accomplished under mild reaction conditions is presented. Technologies presented are segregated according to two main reaction pathways; oxidation and reduction. Sub-topics discussed are representative of the main component of the degradation system, including the following; electrochemical reactors, hydrogen as a reducing agent, zero-valent metals, biological based systems, photolytic processes, Fenton reaction, and a recently discovered process that is a form of room temperature and pressure oxygen activation.
... Many organic pollutions, such as pharmaceuticals and personal care products (PPCPs), pesticides, and organic dyes are toxic and refractory [1][2][3][4]. Various techniques have been developed to eliminate aqueous organic pollutants (e.g., extraction, adsorption, biological treatment, and advanced oxidation processes) [5][6][7][8][9]. Advanced oxidation processes (AOPs) are regarded as effective techniques for organic contaminants removal from water and wastewater [10][11][12][13][14]. ...
... Among various approaches to generate sulfate radicals via activation of additional sources of reactive species (such as peroxymonosulfate (PMS) and persulfate (PS)), the photo-activation in the presence of a heterogeneous catalyst is worth mentioning [65]. The general mechanism is presented in Equations (4)- (8). ...
... Among various approaches to generate sulfate radicals via activation of additional sources of reactive species (such as peroxymonosulfate (PMS) and persulfate (PS)), the photoactivation in the presence of a heterogeneous catalyst is worth mentioning [65]. The general mechanism is presented in Equations (4)- (8). ...
In recent decades, a growing number of organic pollutants released have raised worldwide concern. Graphitic carbon nitride (g-C3N4) has drawn increasing attention in environmental pollutants removal thanks to its unique electronic band structure and excellent physicochemical stability. This paper reviews the recent progress of g-C3N4-based composites as catalysts in various advanced oxidation processes (AOPs), including chemical, photochemical, and electrochemical AOPs. Strategies for enhancing catalytic performance such as element-doping, nanostructure design, and heterojunction construction are summarized in detail. The catalytic degradation mechanisms are also discussed briefly.
... The aim is not to give a complete review of almost 20 years intensive research. Comprehensive reviews on Fe 0 as remediation agent have been carried out recently (Tratnyek et al. 2003, Warner & Sorel 2003, Zhang 2003, Ebert 2004, Jambor et al. 2005, Li et al. 2006, Henderson & Demond 2007, Laine & Cheng 2007, Cundy et al. 2008, Thiruvenkatachari et al. 2008, Gillham 2010. The objective of the present work is to present a selection of key issues and questions which have not been properly addressed so far and which are essential for the further development of the technology. ...
... Accordingly, Fe 0 PRB is regarded as a reductive technology for organic contaminants (e.g. Laine & Cheng 2007, Thiruvenkatachari et al. 2008, Gillham 2010, Comba et al. 2011). ...
This thesis deals with the use of metallic iron (Fe0) for water treatment in general and the use of Fe0 for safe drinking water production in particular. The provision with safe drinking water is a real problem for 800 millions of people all over the world.Chapter 1 presents the concept of water treatment with Fe0 in a broader scientific context and
reveals research needs. Chapter 2 presents the 21 peer-reviewed journal articles on which the thesis is based in relation to their contribution to solve the problems from Chapter 1. Chapter 3 presents the same articles in the perspective of using Fe0 for safe drinking water production.Chapter 4 summarizes the major findings or the present work. An outlook is given in form of specific recommendations for future works. Chapter 5 gives an epilogue which is a sort of responses to the comments made by the referees on the submitted thesis. Chapter 6 lists cited references. The 21 papers on which this thesis is formulated are not appended to this version.
The experimental research was carried out at the Department of Applied Geology of the
University of Göttingen (Prof. Martin Sauter) between July 2005 and March 2009 and partly was financed by the German Research Foundation (DFG) under the Grant number DFG NO 626/2-1 and DFG NO 626/2-2.
I would like to thank Angelika Schöner, Paul Waofo and Sabine Caré for the scientific
collaboration during the study.
My acknowledgements also go to my colleagues of the Department of Applied Geology at the University of Göttingen, to my friends and collaborators for religious, cultural and sportive issues in Göttingen (and Krebeck), in Freiberg (Sachsen) and elsewhere. They provided the excellent atmosphere for this work.
Special thanks to: (i) my family for his endless support and (ii) Léonard Kwuida, Sabine Caré, and Ewa Lipczynska-Kochany for reading and re-reading the draft of this thesis.
... Typical methods of abatement of water pollutants are inadequate for degradation of THMs due to the recalcitrant nature of the latter and the formation of secondary pollutants [8] . Conversely, the reductive methods, aiming at the cathodic conversion of organic halides to the corresponding de-halogenated hydrocarbons, represent a more promising approach due to milder conditions, and a limited range of toxic by-products. ...
... Since neither mechanism is dominant, and the half-life of chloroform in studied conditions is over 10 0 0 years [80] , the influence of reactions (8) and (9) can be neglected. ...
Herein, we report, for the first time, application of Ag nanowire array electrodes for electrocatalytic reduction of chloroform in an aqueous solution of 0.05 M KClO 4. The activity of this electrode was compared with a bulk Ag electrode, and the peak potential shifted up to 280 mV to less negative values, suggesting improved catalytic properties toward the reduction of chloroform. The template-assisted po-tentiostatic electrodeposition of Ag nanowires from a cyanide-based solution was optimized. Particularly, the influence of working electrode potential and duration of electrodeposition on the length of nanowires, passed electric charge, pore-filling rate, and current efficiency was studied. A highly reproducible and fast fabrication of anodic alumina templates was achieved by optimizing operating parameters of the voltage pulse detachment and duration of wet chemical etching.
... La considération du Fe 0 comme donneur d'électrons pour la dégradation des contaminants organiques ou pour leur conversion en formes moins ou non toxiques (exemple: la dégradation réductrice, la précipitation réductrice) s'est propagée (Laine et Cheng 2007, Thiruvenkatachari et al. 2008, Gillham 2010, Comba et al. 2011, Obiri-Nyarko et al.2014, Colombo et al. 2015) à la suite de la publication, par Matheson et Tratnyek (1994), d'un papier expliquant l'élimination du tétrachlorométhane (CCl4) dans le système Fe 0 /H2O par la réduction chimique. Cependant, pour les contaminants inorganiques, la précipitation réductrice (Gu et al. 1998, Puls et al. 1999), la co-précipitation (Lackovic et al. 2000, Komnitsas et al. 2006, Noubactep et al. 2006 En fait, qu'un contaminant soit adsorbé, co-précipité ou réduit, il ne devrait pas pouvoir se remobiliser dans les conditions naturelles (Scherer et al. 2000). ...
... En réalité, il existe une grande diversité de processus conduisant à l'élimination des contaminants dans un filtre à lit de Fe 0 , mais les rapports sur ces processus restent très controversés dans la littérature (Noubactep 2015a. En réponse aux travaux qui contribuent à entretenir la controverse (Henderson et Demond 2007, Laine et Cheng 2007, Cundy et al. 2008, Guan et al. 2015, les résultats de cette étude et les travaux relatifs (Noubactep 2009c) indiquent que dans les conditions environnementales, l'élimination des contaminants pourrait initialement survenir en conjonction avec le processus non sélectif de précipitation des produits de corrosion. Ceci suggère que la réduction et l'oxydation devrait être regardées comme des processus conséquents en présence de la Fe 0 immergé en corrosion. ...
This thesis deals with metallic iron (Fe(0))for water treatment.
Steel wool was tested as Fe(0) source, and characterized for both its intrinsic reactivity (material screening) and efficiency (for water treatment) for the first time. Other achievements encompassed (I) testing the suitability of pozzolan as an alternative material to sand for the construction of metallic iron filters, and (II) testing the suitability of steel Fe(0)-based filters for water defluoridation. The work concludes that steel wool holds good promise as Fe(0)-bearing material for the construction of efficient, low-cost and reliable decentralized water treatment systems.
... Many governments have introduced legislation to set and limit emissions of pollutants in view of the rapid growth of public awareness of environmental problems ). In the mid-1990s, the United Nations Environment Programme successfully reached consensus on the production, use, and emissions of persistent organic pollutants (POPs) (Rodan et al. 1999;Laine and Cheng 2007). Halogenated organic compounds, also known as organic halogens, are prevalent organic pollutants, and many of them have been classified as POPs. ...
... Halogenated organic compounds, also known as organic halogens, are prevalent organic pollutants, and many of them have been classified as POPs. For example, various organochlorine insecticides, such as polychlorinated biphenyls (PCBs), polybrominated biphenyl ethers (PBDEs), and others, are used in the production of various commodities (Laine and Cheng 2007;Atashgahi et al. 2018). PCBs, which are widely and persistently present in the environment and accumulate through the food chain from aquatic organisms to fish and to humans, have adverse effects on various organisms and human beings (Beyer and Biziuk 2009;Zhang and Kelly 2018). ...
Halogenated organics are widely used in modern industry, agriculture, and medicine, and their large-scale emissions have led to soil and water pollution. Electrochemical methods are attractive and promising techniques for wastewater treatment and have been developed for degradation of halogenated organic pollutants under mild conditions. Electrochemical techniques are classified according to main reaction pathways: (i) electrochemical reduction, in which cleavage of C-X (X = F, Cl, Br, I) bonds to release halide ions and produce non-halogenated and non-toxic organics and (ii) electrochemical oxidation, in which halogenated organics are degraded by electrogenerated oxidants. The electrode material is crucial to the degradation efficiency of an electrochemical process. Much research has therefore been devoted to developing appropriate electrode materials for practical applications. This paper reviews recent developments in electrode materials for electrochemical degradation of halogenated organics. And at the end of this paper, the characteristics of new combination methods, such as photocatalysis, nanofiltration, and the use of biochemical method, are discussed.
... ADP is known for its ability to efficiently mineralize atrazine (Mandelbaum et al., 1995;Shapir et al., 1998;Silva et al., 2004). Remediation, however, is not limited to biological processes; abiotic processes are also important, such as low pHinduced chemical dissipation of triazines, oxidation-based destruction of organic pollutants, and reductive dehalogenation (Krutz et al., 2010;Laine and Cheng, 2007;. ...
... 1.9 ± 0.7 a,b 1.2 ± 0.1 a,b 3.6 ± 0.2 a,b 1.3 ± 0.1 a,b a) Hexazinone, no additive (343 days) 24.6 ± 2.0 b,c 24.3 ± 0.4 b,c 23.9 ± 1.1 b,c 24.0 ± 0.5 b,c b) Hexazinone, peat 5.0% (360 days) 11.8 ± 0.6 a,c 10.5 ± 6.1 a,c 13.8 ± 1.5 a,c 12.7 ± 2.1 a,c c) Hexaninone, CPS 15.0% (360 days) 14.8 ± 0.3 a,b 16.4 ± 1.4 a,b 15.9 ± 0.8 a,b 17.8 ± 1.5 a,b a) Dichlobenil, no additive (343 days pH values (157-270 days) (Kruskal-Wallis: A differ from AA) a) No additive 7.7 ± 0.3 AA,b 7.7 ± 0.4 AA,b 6.9 ± 0.7 A,b 7.0 ± 0.5 A,b b) Peat 5.0% 6.7 ± 0.3 AA,a,c 5.4 ± 0.4 AA,a,c 6.3 ± 0.6 A,a,c 5.6 ± 0.4 A,a,c c) CPS 15.0% 7.5 ± 0.1 AA,b 7.3 ± 0.3 AA,b 5.2 ± 0.3 A,b 7.1 ± 0.4 A,b and 2A-F; Tables 2-3), suggesting the reductive dehalogenation type of dissipation (Laine and Cheng, 2007). The reaction was faster than atrazine dissipation in the zero valent iron-amended slurries under aerobic conditions . ...
Pesticides leaching from soil to surface and groundwater are a global threat for drinking water safety, as no cleaning methods occur for groundwater environment. We examined whether peat, compost-peat-sand (CPS) mixture, NH4NO3, NH4NO3 with sodium citrate (Na-citrate), and the surfactant methyl-β-cyclodextrin additions enhance atrazine, simazine, hexazinone, dichlobenil, and the degradate 2,6-dichlorobenzamide (BAM) dissipations in sediment slurries under aerobic and anaerobic conditions, with sterilized controls. The vadose zone sediment cores were drilled from a depth of 11.3-14.6m in an herbicide-contaminated groundwater area. The peat and CPS enhanced chemical atrazine and simazine dissipation, and the peat enhanced chemical hexazinone dissipation, all oxygen-independently. Dichlobenil dissipated under all conditions, while BAM dissipation was fairly slow and half-lives could not be calculated. The chemical dissipation rates could be associated with the chemical structures and properties of the herbicides, and additive compositions, not with pH. Microbial atrazine degradation was only observed in the Pseudomonas sp. ADP amended slurries, although the sediment slurries were known to contain atrazine-degrading microorganisms. The bioavailability of atrazine in the water phase seemed to be limited, which could be due to complex formation with organic and inorganic colloids. Atrazine degradation by indigenous microbes could not be stimulated by the surfactant methyl-β-cyclodextrin, or by the additives NH4NO3 and NH4NO3 with Na-citrate, although the nitrogen additives increased microbial growth.
... In this context, the urgent need for efficient and economically viable new processes to degrade organic pollutants, especially EDCs, has attracted the scientific community's attention. Extensive researches have been made over the last years on several methods aiming to degrade organic pollutants by "green processes" in such a way that the chemicals used and the process itself doesn't generate as hazardous as -or even more than the pollutants treated -sludge and/or residue [2][3][4][5][6][7][8][9][10]. Particularly promising results have been obtained with the so-called advanced oxidation processes (AOPs) and electrochemical advanced oxidation processes (EAOPs), most of the latter based on Fenton's reaction [11,12]. ...
The two-electron pathway of the oxygen reduction reaction has been gaining attention from the scientific community due to its capability of forming radical hydroxyl. In addition, it is a promising way of removing emergent pollutants, like dyes, pharmaceuticals, hormones, pesticides, and endocrine disruptors from water bodies, a very serious problem that currently challenges scientists and grows at a global scale. Theoretical calculations have already guided, over the last decade, the development of better catalysts for the oxygen reduction reaction. However, this mechanism had usually been, until recently, taken as an unwanted process since the preferred route for energy generation and the main focus of these studies is the four-electron pathway. This review summarizes the recent progress on computational calculations from the hydrogen peroxide generation process point of view, specifically focused on carbon-based materials.
... The electroreduction of organic halides has played a key role in organic electrochemistry [1,2] since the early works of Winkel and Proske [3] and of von Stackelberg and Stracke [4] on the treatments of organic halocompounds. In the last thirty years, the removal of halogen groups from organic substrates has gained a strong attention due to the possibility of applying this process for environmental purposes, [5][6][7][8][9][10][11][12] being more effective than the most popular electrooxidative process of total degradation. The interest in oxidative processes is confirmed by recent reviews [13][14][15][16][17][18][19][20] and different papers on the mineralization of chlorophenoxy herbicides, [21][22][23] mono-and poly-halogenated phenolic wastes, [24][25][26] and other chlorinated organic compounds. ...
This work reports the electroreduction of a volatile organic halide (trichloromethane) from an airborn stream. In the past years we highlighted the role of polycrystalline silver as powerful electrocatalyst for the electroreductive hydrodehalogenation of volatile organic halides (VOH) in water/organic solvent mixtures, from 0 to 100% of the aqueous component. The successful conversion of trichloromethane and 1,1,1‐trichloethane to the relevant dehalogenated compounds, methane and ethane have prompted us to extend the investigations to the treatment of gaseous effluents, adopting a silver Gas Diffusion Electrode (Ag‐GDE) and the appropriate cell design. In the field of electroreduction processes the possibility of using GDE to treat gaseous effluents for the removal of volatile organic pollutants represents an electrochemical challenge, and the treatment of N 2 /CHCl 3 gas mixtures fed into the cathodic Ag‐GDE compartment demonstrates the feasibility of the electroreductive detoxification process. Our results will be presented and discussed in terms of CHCl 3 removal efficiency, selectivity and energy consumption in preparative electrolyses.
... In response to the search for safe and efficient techniques, photocatalysis, due to its potential for converting solar energy to pollutant degradation, has attracted the attention of researches due to the possibility of developing advanced "green" oxidation technologies, being used in studies aimed at water disinfection [21][22][23][24][25][26][27][28]. Besides, it shows benefits in relation to ozonization and disinfection of water by UV irradiation, which, although they are promising [29][30][31], they are substantially complex techniques due to the risk of formation of potentially harmful byproducts [32][33][34][35]. ...
In this article, we report the silver orthophosphate (Ag3PO4) photocatalytic inactivation properties on strains Gram-positive Saprophyte B. subtilis, a diploid fungus Candida albicans and Gram-negative Pseudomonas aeruginosa, using as irradiation source white-light-emitting diodes (WLEDs) with luminous flux (Φ v) of 1.3 × 103 Lumens and relative power density of 15 mW m−2. Microorganisms death curves and the kinetic constants (Kd) indicated that the inhibitory effect of the Ag3PO4 under WLEDs irradiation is well pronounced to C. albicans (6.6 × 10–2 min−1) in relation to P. augenosas (4.6 × 10–2 min−1) and B. subitilis (2.5 × 10–2 min−1). Decimal reduction time (Dt) were 34.4 min to C. albicans, 50.1 min P. augenosas and 92.1 min to B.subitilis. The micrographs obtained by scanning electron microscopy with field emission gun (SEM-FEG) demonstrated that there was cell wall permeability and consequently total rupture in the C. albicans, suggesting the lipid peroxidation phenomenon and protein oxidation promoted by the presence of reactive oxygen species (ROS). Furthermore, it was observed the Ag3PO4 when irradiated by WLEDs demonstrates important sporicidal activity in related to B. subtilis, promoting the endospore wall rupture.
... In response to the search for safe and efficient techniques, photocatalysis, due to its potential for converting solar energy to pollutant degradation, has attracted the attention of researches due to the possibility of developing advanced "green" oxidation technologies, being used in studies aimed at water disinfection [21][22][23][24][25][26][27][28]. Besides, it shows benefits in relation to ozonization and disinfection of water by UV irradiation, which, although they are promising [29][30][31], they are substantially complex techniques due to the risk of formation of potentially harmful byproducts [32][33][34][35]. ...
In this article, we report the silver orthophosphate (Ag 3 PO 4 ) photocatalytic inactivation properties on strains Gram-positive Saprophyte B. subtilis , a diploid fungus Candida albicans and Gram-negative Pseudomonas aeruginosa , using as irradiation source white-light-emitting diodes (WLEDs) with luminous flux (Φ v) of 1.3 x 10 ³ Lumens and relative power density of 15 mW m − 2 . Microorganisms death curves and the kinetic constants (K d ) indicated that the inhibitory effect of the Ag 3 PO 4 under WLEDs irradiation is well pronounced to C. albicans (6.6 x 10 − 2 min − 1 ) in relation to P. augenosas (4.6 x 10 − 2 min − 1 ) and B. subitilis (2.5 x 10 − 2 min − 1 ). Decimal reduction time ( D t ) were 34.4 min to C. albicans , 50.1 min P. augenosas and 92.1 min to B.subitilis The micrographs obtained by scanning electron microscopy with field emission gun (SEM-FEG) demonstrated that there was cell wall permeability and consequently total rupture in the C. albicans , suggesting the lipid peroxidation phenomenon and protein oxidation promoted by the presence of reactive oxygen species (ROS). Furthermore, it was observed the A g3 PO 4 when irradiated by WLEDs demonstrates important sporicidal activity in related to B. subtilis , promoting the endospore wall rupture.
... It has been demonstrated that TNT and most of its degradation products are toxic to human and animal even at a very low concentration (Adrian and Arnett 2007;Lee et al. 2003). Several methods have been used for decontamination of TNT from wastewater and contaminated soil such as biotreatment, phytoremediation, advanced oxidation, and adsorption (Agrawal and Tratnyek 1996;Laine and Chang 2007;Liou et al. 2004;Marcio et al. 2009). Chemisorption and physisorption are the most studied and highly effective methods and relatively low-cost techniques for water treatment (Oladipo and Gazi 2014;Oladipo et al. 2015). ...
Nano zerovalent iron (nZVI) impregnated reduced graphene oxide (nZVI-rGO) hybrid was prepared via gaseous hydrogen reduction of anhydrous iron(III) chloride (FeCl3) on the surface of thermally exfoliated reduced graphene oxide (rGO) nanosheets without using any toxic reducing agent, surfactant, or stabilizing agent. Characterization of prepared samples was carried out using various techniques. Morphological study showed that prepared rGO possesses a few-layered wrinkled paper-like structures and nZVI particles of ~ 30 nm size were homogeneously dispersed on the surface of rGO nanosheets. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry (EDS) analyses indicated that oxygen-containing functional groups decreased in the order of graphite oxide (GO) > rGO > nZVI-rGO. Removal studies of trinitrotoluene (TNT) were carried out using graphite (G), GO, rGO, and nZVI-rGO with the aid of high-performance liquid chromatography (HPLC). Kinetic models were applied to establish the rate and mechanism of adsorption of TNT on different adsorbents, and intraparticle diffusion model based on initial adsorption characteristics was employed to ascertain mechanism of film and intraparticle diffusion in the adsorption process. The removal rate and adsorption capacity was found to be highest for nZVI-rGO, which renders this adsorbent to be a potential futuristic adsorbent for removal of explosives.
Graphical Abstractᅟ
... This process allows to reduce considerably the effluent toxicity. The organochlorinated pollutant reacts with hydrogen, which leads to a chlorine-free hydrogenated compound and hydrochloric acid [5]. Moreover, the system can be operated under ambient conditions within a wide range of initial pollutant concentrations [6]. ...
This work aims to analyse the effectiveness of catalytic hydrodechlorination (HDC) for the degradation of the neonicotinoid pesticides listed in the EU Watch List (Decision 2018/840): acetamiprid (ACT), imidacloprid (IMD), clothianidin (CLT), thiacloprid (THC) and thiamethoxam (THM). With the exception of THC, all neonicotinoid pesticides (1000 μg L⁻¹) were completely removed in 30 min at 25 °C, using 0.25 g L⁻¹ of a commercial Pd/Al2O3 (1 wt. %) catalyst and 50 N mL min⁻¹ H2 flow rate. Strikingly, the micropollutant nature played a critical role on the activity and stability of the catalyst. The sulphur-bearing structures (CLT, THC and THM) showed the slowest degradation rates and led to a progressive deactivation of the catalyst. TEM/EDS and elemental analyses confirmed that the selective interaction of sulphur species on Pd active sites was the main reason for catalyst deactivation. The position of the heteroatom in the pesticide structure also influenced the catalytic deactivation. The catalyst showed a constant activity upon its sequential use in the HDC of ACT and IMD when these compounds were treated individually. Nevertheless, the interaction of the sulphur-containing compounds with the catalyst was remarkably favoured when the five micropollutants were treated in a mixture. A deactivation kinetic model in a long-term experiment was proposed with THC. To overcome catalyst deactivation, a regeneration procedure, based on a simple catalyst washing with a diluted NaClO solution, was developed. The process suitability was finally demonstrated in successive HDC-regeneration runs.
... A reduction percentage (23.4) for COD was achieved after treatment of sweet whey, major pollutant in dairy effluent, by aluminum sulphate and sodium alginate (Laine and Cheng, 2007). ...
This study was conducted to characterize the dairy industry wastewater and evaluate the efficiency of chemical coagulation and advanced oxidation process (AOPs) as pretreatment techniques. A composite sample was collected from diary industry plant at New Damietta City on March 2018 and characterized for some physico-chemical parameters to check the pollution potential of the effluents. Due to the high content of total suspended solids, chemical coagulation/precipitation process using lime, alum/lime and alum/polyacrylamide was applied for pretreatment of the collected sample and the optimum conditions were determined. Moreover, chemical coagulation using alum/lime followed by AOPs with Fenton's reagent was also assessed. The results showed that the concentration of COD is 112000 mg/L while for BOD is 78000 mg/L. In addition, the removal percentage of oil and grease, COD, total phosphorous (TP) and total Khejdal nitrogen (TKN) by Fenton's reaction after treatment with alum-lime are 86, 85, 99.35 and 99.03 %, respectively compared with that achieved by alum-lime (86.82, 73.11, 91.8 and 54.93 %, respectively). It was concluded that combining chemical coagulation/precipitation and AOPs was effective for the pretreatment of high organic load dairy wastewater.
... Advanced oxidation processes (AOPs) are usually used for water treatment and they operate under specific conditions of temperature, pressure, UV light and oxidizing agents (Glaze et al., 1987). This process is based on the in-situ generation of a strong oxidizing agent such as hydroxyl radicals (OH • ), which effectively treats contaminated water (Zaviska et al., 2009;Laine and Cheng, 2007;Bilińska et al., 2017). Various process technologies such as ozonation, Fenton, photo-Fenton, photocatalysis, electrochemical oxidation, ultrasound, plasma, and UV-based processes have been investigated as stand-alone or hybrid technologies for water treatment or wastewater treatment (Stefan, 2017). ...
Dye-containing wastewater should be treated effectively in order to prevent adverse effects on the environment and water resources. This review summarizes the recent dye removal technologies from wastewater, such as biological methods, advanced oxidation process (AOP), electrocoagulation, adsorption, and membrane technology and nano-technology. The performances, operating conditions, important process parameters, and the advantages and disadvantages of different treatment systems are reviewed. Besides, in order to achieve efficient color removal, a large number of researches have also focused on hybrid treatment technologies. Among the different hybrid treatments, the MBR (membrane bioreactor) and the PMR (photocatalytic membrane reactor) technologies have been discussed in this paper as promising methods for color removal from textile wastewater. Regarding effective factors in the PMR systems performance, photocatalytic nanoparticles have been discussed as a prominent factor. Since not many review papers focused on these methods, this paper has been prepared in a way to cover this deficiency and address mentioned methods more comprehensively.
... Furthermore, electrolyte would be consumed excessively under basic conditions which in turn reduces the solution conductivity. Also, H + ions prevent the decomposition of HO % under acidic conditions [50,51]. ...
Biological treatment of oily sludge wastes was studied using an isolated halo-tolerant strain Pseudomonas balearica strain Z8. An oily sludge sample was obtained from oil fields of south waste of Iran and was fully characterized. The initial TPH content was 44,500 mg kg−1. The ability of Pseudomonas balearica strain Z8 in production of biosurfactant was investigated using oil displacement method. Results demonstrated that isolated strain is a biosurfactant producing bacteria. The CMC and emulsification index [E24] of produced biosurfactant were 90 mg L−1 and 44% for crude oil. Effect of operational parameters including nitrogen source, sludge/water ratio and temperature were investigated against the time. The most TPH removal of 35% was observed for nitrogen source of NH4Cl, sludge/ water ratio of 1:7 and temperature of 40 °C.
... Adsorption of TNT onto adsorbents such as activated carbon or iron particles is another common technique. Nano zero valent iron (nZVI) particles have the capability to degrade TNT successfully (Hawari et al. 2000;Laine and Cheng 2007;Pennington and Patrick 1990). It has been reported that nano scale zero valent iron emulsion (EZVI) synthesized out of nZVI, immiscible substrate such as corn oil and surfactant can combinedly degrade TNT (Echols 2009). ...
Nitroaromatic explosives such as trinitrotoluene (TNT), dinitrotluene (DNT) and other metabolites present the greatest concern to the environment and public health due to their mutagenic properties and persistence. Remediation of soil contaminated by explosive residues has received increased interest in recent years in many countries due to their prolific use since the World War I and II. There is an urgent need to identify appropriate and effective technologies to attenuate/remediate TNT-contaminated sites and ensure safe environment. This article presents an overview of the technologies commonly adopted for remediation of TNT contaminated sites with particular emphasis on ways to enhance biodegradation especially with the addition of surfactants or biosurfactants.
... Glaze et al. (Glaze et al., 1987) gave a definition of advanced oxidation approaches; it works as water treatment method at room temperature and normal pressure and produces oxidizing agent such as hydroxyl radicals (•OH). Some significant research works are reported in this direction (Andreozzi et al., 1999;Herrmann et al., 1999;Tarr, 2003;Gogate and Pandit, 2004;Parsons, 2004;Brillas et al., 2006;Laine and Cheng, 2007;Zaviska et al., 2009). Various advanced oxidation approaches are depended on different chemical, photochemical, or electrochemical reactions. ...
The emerging organic pollutants including organochlorine pesticide, halo hydrocarbon, polybrominated diphenyl ethers, polycyclic aromatic hydrocarbons (PAHs), dyes, petrochemical products, etc. are of increasing environmental concern due to their devastating health effects. They are generally originated from intentional and unintentional industrial activities despite global ban on certain class of organic pollutants. Their chronic impact necessitates their prior monitoring as well as remediation. This chapter summarizes the status of method of detection and degradation of organic pollutants from water and soil. In particular biological, physical, chemical and advance oxidation processes for organic pollutants treatment are covered. Lately, e-waste sites are also contributing to increased level of POPs in environmental matrixes, which has been discussed. An emphasis has been given on understanding the physiochemical properties of these organic pollutants in presented matrix so as better solution can be opted out for their removal. Besides, sampling, extraction, storage methods, role of solvents, etc., are also discussed, which have key role in quantification and removal technique performance.
... Furthermore, electrolyte would be consumed excessively under basic conditions which in turn reduces the solution conductivity. Also, H + ions prevent the decomposition of HO % under acidic conditions [50,51]. ...
This work aimed to investigate the performance of biosurfactant, produced by a halotolerant bacterial strain, Pseudomonas aeruginosa PF2, for desorption of PAHs from soil, followed by electrokinetic oxidation of the desorbed solution using Magnetite Nanoparticles Modified Graphite (MNMG). Pyrene (PYR), anthracene (ANT) and phenanthrene (PHE) were used as contamination model. Produced and extracted biosurfactant was characterized as rhamnolipid with Critical Micelle Concentration (CMC) of 60 mg/L and emulsification index (E24) value of 60.2% for n-hexadecane, 58.4% for n-heptane and 55.6% for n-Hexane, respectively. Results of LC–MS/MS analysis indicated the presence of seven major peaks at m/z of 677.5, 531.1, 649.3, 528.9, 475.1, 359 and 503.2, which corresponded to the deprotonated molecules of RhaRhaC12C10, RhaC12C10, RhaRhaC10C10, RhaC12:1C10, RhaC8C10, Rha-C12:2 and RhaC10C10, respectively. The maximum desorption of PAHs was derived at pH value of 6, CMC of 3 and contact time of 24 h. Modification of graphite electrode enhanced the PAH degradation significantly. In electrokinetic oxidation of desorbed solution, the best results were observed at pH value of 5, contact time of 6 h, voltage of 3 V and electrolyte concentration of 25 mg/L, with the average removal efficiency of higher than 99% for all studied PAHs.
... It is noteworthy that such methodologies are economic, fast and very efficient. 10 Heterogenous catalysts such as TiO 2 and zinc oxide (ZnO) are widely employed for photocatalytic degradation of various organic pollutants. Among these, ZnO is a wide band gap semiconductor material used in many applications such as environmental remediation, water purification, sensors, decontamination, etc. ZnO is highly preferred because it does not cause secondary pollution. ...
BACKGROUND
Organophosphorus (OP) pesticides are widely used to prevent the destruction of crops by various pests, including insects and rodents, which can affect the yield. On the other hand, the use of OP pesticides is linked to various disorders in animals and humans who are exposed to pesticides directly or indirectly. The current study deals with the use of lanthanum (La)‐doped zinc oxide (ZnO) crystals grown on electrospun nanofibers for photocatalytic degradation of methyl parathion (MP), an important OP pesticide.
RESULTS
The electrospinning process was optimized using various parameters. Similarly, the crystal growth conditions such as La concentration, pH, temperature and time were optimized for further studies. Complete degradation was achieved at 150 min from the start and was supported by a reduction in photoluminescence of the reaction mixture. The total organic carbon content was used to decide the mineralization of the toxin. The degradation followed first‐order kinetics with rate constant 0.018 min⁻¹. Hence MP was successfully degraded using La‐ZnO/polyacrylonitrile (PAN) fibers, and the degraded by‐product was confirmed by gas chromatography/mass spectrometry (GC/MS) analysis.
CONCLUSION
Chemically modified La‐ZnO/PAN nanofibers were an efficient material to decontaminate the pesticide MP, achieving 100% efficiency. The process may be ecofriendly for upscaling photocatalytic degradation processes. © 2019 Society of Chemical Industry
... Previous studies showed that TCS could interfere with several hormones as endocrine disrupting chemical in various species and impair muscle contraction (Devito, 2007;Cherednichenko et al., 2012). Recently, more and more researchers focus their attention on removing the chlorinated organic compounds of water through electrochemical dechlorination method (Tsyganok, 2006;Laine and Cheng, 2007). The technology of electrochemical reductive detoxification and dechlorination of chlorinated organic compounds is called electrocatalytic hydrodehalogenation (ECH). ...
In this study, a new composite electrode of palladium (Pd) nanoparticles dispersed on polypyrrole-reduced graphene oxide (PPy-rGO) loaded on foam-nickel was achieved by galvanostatic method. Characterization of structures, morphology and crystallinity of the synthesized materials were investigated by scanning electron microscopes (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The results of XPS and XRD demonstrated Pd showed primarily as Pd0. From SEM and TEM results, we had seen that Pd nanoparticles were dispersible well on the composite electrode. Raman spectroscopy was used to show the state of graphene oxide and further demonstrated that PPy and rGO had existed of on the foam Ni matrix. The data of EIS also suggested the charge transfer of the new composite electrode decreased compared to Pd/PPy/foam-Ni and PPy/foam-Ni composite electrodes. The effect of the electropolymerization potential on Pd/PPy-rGO/foam-Ni electrode for removing triclosan (TCS) was examined. It was found that the removal efficiency of TCS on the composite electrode could reach 100% at electropolymerization potential of 0.7 V and reaction time of 100 min.
... Various techniques including biological, thermal, and chemical treatments have been developed for the degradation of chlorinated organic compounds (COCs) [1,2]. Among these techniques, electrocatalytic reductive dechlorination has been considered as a promising water treatment strategy for the detoxification of COCs, and has attracted more attention in recent years [3][4][5][6][7]. ...
In the present study, carbon black (CB), multi walled carbon nanotubes (MWCNTs), and granular activated carbon (GAC) were employed to support palladium (Pd) catalyst. The prepared Pd/CB, Pd/MWCNTs and Pd/GAC moveable catalysts were aimed to address the common issues (easy loss of catalyst and poor long-term performance) of normal fixed catalysts. The results of various characterizations (e.g., TEM, XRD, and XPS) clearly show that the Pd nanoparticles were successfully loaded onto the carbon-supports, especially CB and MWCNTs. And more importantly, the morphologies, Pd distribution, and chemical structure of these moveable catalysts were almost not changed after 3 h reaction. The moveable Pd/CB, Pd/MWCNTs, and Pd/GAC catalysts had good reactivity for 2,4-dichlorobenzoic acid (2,4-DCBA) dechlorination, and Pd/CB exhibited the best performance. The Pd/CB also shows the best adsorption capacity of 2,4-DCBA and dechlorination product (benzoic acid, BA), and the adsorption of BA was significantly inhibited in the presence of current due to the repulsion between the both negatively charged compounds and adsorbents. The removal of 2,4-DCBA and the generation rate of BA was improved with a pre-adsorption process, which was a promising strategy with higher dechlorination rate and shortened electrolysis time. Moreover, the loss of Pd catalyst was negligible during the 10 consecutive cycles experiment, and the improved longevity could be expected. These results suggested the good reactivity, stability, and reusability of moveable Pd/CB catalyst.
... In aqueous medium, advanced oxidation processes (AOPs) are very promising and could be applied to degrade contaminated and biologically refractory organic pollutants. The key advantage of AOPs is the in situ generation of hydroxyl radicals (HO•), which can act as highly oxidizing agents in water (Cheng et al., 2016a;Laine and Cheng, 2007;Oturan and Aaron, 2014). Under optimum conditions, it is capable of converting a variety of organic pollutants into smaller molecular weighted compounds or even into water and carbon dioxide as well. ...
This study reveals the optimization of ultrasonic-Fenton process for the treatment of sludge taken from a local municipal wastewater treatment plant after anaerobic digestion. Box-Behnken design (BBD), a common approach of response surface methodology (RSM), was applied to evaluate and optimize the individual and interactive effects of three process variables, namely Fe2+ dose, H2O2 amount and sonication time for Fenton-ultrasonication method. Five dependent parameters including total organic carbon (TOC), extracellular poly-meric substances (EPS), as LB-EPS and TB-EPS, and metals such as Zn and Cu were considered as the responses to investigate. According to the results of analysis of variances (ANOVA), five modelling equations are proposed that can be used to operate the design space with high regression coefficient R2. Modelling results suggest that Fenton parameters, such as: H2O2 and Fe2+ dosage had the significant effects on the overall removal of TOC; whereas, sonication improved the metal removal from the sludge sample. Based on response surface methodology, best performance is achievable under the following conditions: 36 mM of Fe2+, 320 mM H2O2 with 30 min of sonication respectively for all of the responses.
... It has been demonstrated that TNT and most of its degradation products are toxic to human and animal even at a very low concentration (Adrian and Arnett 2007;Lee et al. 2003). Several methods have been used for decontamination of TNT from wastewater and contaminated soil such as biotreatment, phytoremediation, advanced oxidation, and adsorption (Agrawal and Tratnyek 1996;Laine and Chang 2007;Liou et al. 2004;Marcio et al. 2009). Chemisorption and physisorption are the most studied and highly effective methods and relatively low-cost techniques for water treatment (Oladipo and Gazi 2014;Oladipo et al. 2015). ...
Nano zerovalent iron (nZVI) impregnated reduced graphene oxide (nZVI-rGO) hybrid was pre-pared via gaseous hydrogen reduction of anhydrous iron(III) chloride (FeCl3) on the surface of thermally exfoliated reduced graphene oxide (rGO) nanosheets without using any toxic reducing agent, surfactant, or stabilizing agent. Characterization of prepared samples was carried out using various techniques. (HPLC). Kinetic models were applied to establish the rate and mechanism of adsorption of TNT on different adsorbents, and intraparticle diffusion model based on initial adsorption characteristics was employed to ascertain mechanism of film and intraparticle diffusion in the adsorption process. The removal rate and adsorption capacity was found to be highest for nZVI-rGO, which renders this adsorbent to be a potential futuristic adsorbent for removal of explosives.
cal study showed that prepared rGO possesses a few-
layered wrinkled paper-like structures and nZVI parti-
cles of ~ 30 nm size were homogeneously dispersed on
the surface of rGO nanosheets. Fourier transform infra-
red (FTIR), X-ray diffraction (XRD), and energy dis-
persive X-ray spectrometry (EDS) analyses indicated
that oxygen-containing functional groups decreased in
the order of graphite oxide (GO) > rGO > nZVI-rGO.
Removal studies of trinitrotoluene (TNT) were carried
out using graphite (G), GO, rGO, and nZVI-rGO with
the aid of high-performance liquid chromatography
... catalyst concentration is an important parameter that limits the rate of Fenton reaction (1) to produce hydroxyl radicals and, therefore, affects the degree of mineralization of the organic contaminants. The decrease in the oxidation power of Fenton reaction is related to the competitive reaction between Fe 2+ and OH • (4) which can also be photolyzed [80], reaction (11). ...
This literature research, although not exhaustive, gives perspective to solar-driven photocatalysis, such as solar photo-Fenton and TiO2 solar photocatalysis, reported in the literature for the degradation of aqueous organic pollutants. Parameters that influence the degradation and mineralization of organics like catalyst preparation, type and load of catalyst, catalyst phase, pH, applied potential, and type of organic pollutant are addressed. Such parameters may also affect the photoactivity of the catalysts used in the studied solar processes. Solar irradiation is a renewable, abundant, and pollution-free energy source for low-cost commercial applications. Therefore, these solar processes represent an environmentally friendly alternative mainly because the use of electricity can be decreased/avoided.
... Decontamination of the non-conditioned pesticides is recommended to be carried out with the following three methods: burying, burning and plasmachemical destruction [15]. Burying pesticides on the landfill causes soil pollution. ...
The persistent organic pollutants placed at the largest (2700 tones) pesticide landfill (on the “Jagluja”) in Georgia in Marneuli District, contain the wide spectrum of substances of various chemical groups.
For their complete mineralization (deep oxidation up to CO2 and H2O) is offered nanoscale titania as photocatalyst within the visible spectral range of light.
... The use of ferric salts is economically advantageous and avoids handling problems with air sensitive Fe(II). Experiments with sludge containing Fe(III) yielded qualitatively positive results [96], but there is no indication on how such a result could be transferred to a large-scale process. However, it is important to note that Fe(III) ions react much slower than Fe(II) ions with H 2 O 2 : the apparent rate constant for the overall Reaction 8, i.e., (8a) + (8b), varies between 10 À2 and 10 À3 M À1 s À1 [110,120,179], values several orders of magnitude smaller than those of Reaction 7. If complexation of Fe (III) by H 2 O 2 (equilibrium 8a) is inhibited, the Fenton process is slowed down and may completely stop. ...
Among Advanced Oxidation Processes (AOPs), the Fenton process and the photochemically enhanced or assisted Fenton process, commonly called photo-Fenton, are considered to be among the most efficient for the oxidative degradation of a large variety of organic contaminants in aqueous systems. These processes, based on the generation of highly oxidizing species (hydroxyl radicals and possibly others) from hydrogen peroxide and Fe ions, may be counted among the few methods that are actually applied on a technical scale for an abiotic (pre-)treatment of wastewaters. With close to 5,000 articles published on this topic during the last decade, covering both fundamental aspects and applications, this chapter is restricted to a selective overview of the photo-Fenton process applied to water treatment. It briefly recalls the fundamentals of the Fenton reaction, describes the main lines of research for process enhancement and economic feasibility, summarizes the essentials determining the primary process parameters, and discusses the present state of technical development and its priorities.
... The adsorption of iron species by 417 zeolite Y could be excluded because of the negligible cation 418 exchange capacity of the sorbent with a SiO 2 /Al 2 O 3 ratio of 419200. Likely, the radical oxygenated species (mainly U OH and 420 U OOH,(Laine and Cheng, 2007)) cannot easily diffuse into the 421 sulfonamide-loaded zeolite. ...
High silica zeolite Y has been positively evaluated to clean-up water polluted with sulfonamides, an antibiotic family which is known to be involved in the antibiotic resistance evolution. To define possible strategies for the exhausted zeolite regeneration, the efficacy of some chemico-physical treatments on the zeolite loaded with four different sulfonamides was evaluated. The evolution of photolysis, Fenton-like reaction, thermal treatments, and solvent extractions and the occurrence in the zeolite pores of organic residues eventually entrapped was elucidated by a combined thermogravimetric (TGA–DTA), diffractometric (XRPD), and spectroscopic (FT-IR) approach. The chemical processes were not able to remove the organic guest from zeolite pores and a limited transformation on embedded molecules was observed. On the contrary, both thermal treatment and solvent extraction succeeded in the regeneration of the zeolite loaded from deionized and natural fresh water. The recyclability of regenerated zeolite was evaluated over several adsorption/regeneration cycles, due to the treatment efficacy and its stability as well as the ability to regain the structural features of the unloaded material.
... By consequence, as a suitable alternative method, advanced oxidation processes (AOPs) have been applied to remove FQs efficiently from water [9][10][11][12][13][14][15][16][17][18]. AOPs are characterized by the in-situ production of hydroxyl radical ( • OH) at ambient conditions [19,20]. ...
Solutions of 500mL 200mgL(-1) fluoroquinolone antibiotic levofloxacin (LEVO) have been degraded by anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2) and electro-Fenton (EF) processes using an activated carbon fiber (ACF) felt cathode from the point view of not only LEVO disappearance and mineralization, but also biodegradability enhancement. The LEVO decay by EF process followed a pseudo-first-order reaction with an apparent rate constant of 2.37×10(-2)min(-1), which is much higher than that of AO or AO-H2O2 processes. The LEVO mineralization also evidences the order EF>AO-H2O2>AO. The biodegradability (BOD5/COD) increased from 0 initially to 0.24, 0.09, and 0.03 for EF, AO-H2O2 and AO processes after 360min treatment, respectively. Effects of several parameters such as current density, initial pH and Fe(2+) concentration on the EF degradation have also been examined. Three carboxylic acids including oxalic, formic and acetic acid were detected, as well as the released inorganic ions NH4(+), NO3(-) and F(-). At last, an ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry was used to identify about eight aromatic intermediates formed in 60min of EF treatment, and a plausible mineralization pathway for LEVO by EF treatment was proposed.
... They also found that urban streams are more contaminated and contain higher concentrations of Malathion than agricultural streams. Furthermore, it was verified that Malathion can also contaminate the groundwater (Cox, 2003;Laine and Cheng, 2007). Studies performed by the U.S. Department of Agriculture (USDA, 2000), indicated that the application of Malathion near the water resources causes toxicity in aquatic organisms as vertebrates, amphibious and fishes. ...
Based on the concentration of Malathion used in the field, we evaluated the genotoxic potential of low concentrations of this insecticide on meristematic and F 1 cells of Allium cepa and on rat hepatoma tissue culture (HTC cells). In the A. cepa, chromosomal aberrations (CAs), micronuclei (MN), and mitotic index (MI) were evaluated by exposing the cells at 1.5, 0.75, 0.37, and 0.18 mg/mL of Malathion for 24 and 48 hr of exposure and 48 hr of recovery time. The results showed that all concentrations were genotoxic to A. cepa cells. However, the analysis of the MI has showed non-relevant effects. Chromosomal bridges were the CA more frequently induced, indicating the clastogenic action of Malathion. After the recovery period, the higher concentrations continued to induce genotoxic effects, unlike the observed for the lowest concentrations tested. In HTC cells, the genotoxicity of Malathion was evaluated by the MN test and the comet assay by exposing the cells at 0.09, 0.009, and 0.0009 mg/5 mL culture medium, for 24 hr of exposure. In the comet assay, all the concentrations induced genotoxicity in the HTC cells. In the MN test, no significant induction of MN was observed. The genotoxicity induced by the low concentrations of Malathion presented in this work highlights the importance of studying the effects of low concentrations of this pesticide and demonstrates the efficiency of these two test systems for the detection of genetic damage promoted by Malathion.
AOPs homogenized advanced oxidation process was studied in Fenton and Photo-Fenton on the treatment of artificial water from vegetable oil contaminants. Several variables were studied: time, pH, mixing speed, and a dose of catalysis (Fe2SO4.7H2O).The best conditions are obtained by studying experiments. Fenton and Photo-Fenton process work at an acidic medium (pH=3.5). The optimum mixing speed at (1000 rpm) for the Photo-Fenton process and (500 rpm) for the Fenton. When concentration of H 2 O 2 was (500 mg/L) obtained the concentration of Fe2SO4.7H2O for the photo-Fenton process = (50 mg/L), and for the Fenton process = (250 mg/L).
The Fenton process gave a maximum efficiency of removal of vegetable oils of 95.2% for Corn oil (COD from 12800 to 610 mg/L), 94.5% for Castor oil, while 57.5% for Coconut oil after the total reaction time (180 minutes).
The Photo- Fenton process gave an efficiency of removal: 93% for Corn oil (COD from 12500 to 870 mg/L), 83.8% for Castor oil, while 61.6% for Coconut oil.
As for the real wastewater, the treatment was acceptable and achieved an efficiency of 89.2%, and 83.8% for Fenton, and Photo-Fenton processes respectively.
The transfer hydrodehalogenation (THD) of halophenols is efficiently catalyzed by palladium supported on high surface ceria (Pd/CeO2) under mild conditions (65 °C) using isopropanol (iPrOH) as hydrogen source. The reactivity of 4-halophenols (4-X-PhOH) varies in the order 4-F-PhOH > 4-Cl-PhOH > 4-Br-PhOH >> 4-I-PhOH and appears to be controlled by the desorption of halides from the catalyst surface. Kinetic analysis of the reactions and temperature programmed surface reaction (TPSR) experiments indicate that oxidative addition of C-X bonds and H-abstraction from isopropoxide compete for the same active sites on Pd. The catalyst was able to conduct the THD of various hazardous pollutants and emerging contaminants (DDT, pentachlorophenol, pentafluorophenol and triclosan).
Organochlorine pesticides have raised considerable dangers to the environment by defiling of soil and groundwater. Thus, it is very important to establish proficient decontamination technique to overcome the risk effect on environment. The current work was assessed as an impetus for the photo degradation of toxin. A constant investigation was completed in the synthetic water test spiked with endosulfan and have demonstrated the efficiency of 96.5% at 45 min that was measured by HPLC and confirmed by GC-MS analysis. Phytotoxicological assessment of secondary metabolites of endosulfan was contemplated using Vigna radiata model. There is no much changes observed in phytotoxicological framework like endosulfan in agricultural system.
• Highlights
• La:ZnO/PAN nanofiber catalyst for the authentic period photocatalytic detection and degradation of endosulphan.
• Degradation efficiency of the nanomaterial was achieved as 96.5 % by utilizing simple photocatalytic reaction with the avail of developed nanomaterial.
• The developed material has excellent recyclable material and here no remote changes occurred after four successive cycles.
The CTAB-Pd/GAC catalyst was obtained by functionalizing palladium/granular activated carbon (Pd/GAC) with cetyltrimethylammonium bromide (CTAB), which was used for the electrocatalytic reductive dechlorination of 2,4-dichlorobenzoic acid (2,4-DCBA). The degradation rate of 2,4-DCBA by 40 mg g⁻¹ CTAB-Pd/GAC was 9.8×10⁻³ (min⁻¹ g⁻¹ Pd), which was 11 folds than that of Pd/GAC (0.9×10⁻³ min⁻¹ g⁻¹ Pd), and the value of qe, 2,4-DCBA/qe, BA was 2.33 as compared to 0.67 for Pd/GAC. The combined result of dechlorination and adsorption experiments suggested that the functionalization by CTAB would enhance the 2,4-DCBA concentration on the surface of CTAB-Pd/GAC, and accelerate the degradation rate. However, the removal efficiency of 2,4-DCBA would decrease when the CTAB load reached 80 mg g⁻¹, due to the excessive adsorption capacity for dechlorinated product. Density functional theory (DFT) calculations also proved that CTAB would increase adsorption capacity of catalyst and selective adsorption behavior of 2,4-DCBA, which accelerated the degradation rate of 2,4-DCBA.
Currently, graphitic carbon nitride (g-C3N4)-based materials are the centre of attention in chemistry and materials science because of their unique as well as fascinating properties, which are strongly desired for many technological applications. g-C3N4 is lamellar and composed of two-dimensional layers of carbon atoms naturally arranged in hexagonal networks. g-C3N4 is, therefore, analogous to graphene, but has nitrogen atoms bound through covalent bonds (sp²). This results in a stable, porous, heat-resistant polymeric semiconductor that is optically active under visible-light irradiation (and thus has excellent photocatalytic characteristics) as well as economically sustainable. The recent discovery of this new member of the graphene family is a crucial breakthrough, as there are only a few bi-dimensional organic solids. Hence, this chapter summarizes the current progress in the understanding of the synthesis and fundamental properties of g-C3N4-related materials.
In this paper, we report on the superior photocatalytic properties of silver orthophosphate (Ag 3 PO 4 ) sub-microcrystals prepared using different synthesis methods: precipitation (PM), precipitation-calcination (PM-C), and precipitation-hydrothermal (PM-H), on the degradation of Rhodamine B (RhB) cationic dye and methyl orange (MO) anionic dye using white-light-emitting diodes (WLEDs). The structure of the Ag 3 PO 4 sub-microcrystals obtained was investigated by X-ray diffraction (XRD), Rietveld refinement, micro-Raman (M-Raman), and Fourier transform infrared (FT-IR) spectroscopy. The X-ray photoelectron spectroscopy (XPS) was used to investigate the surface chemical composition and states. The shape, average crystal size, and morphological changes were observed using field emission scanning electron microscopy (FE-SEM). The results indicated that all samples have cubic body-centered, P 43´ n (218) space group, with the following crytallite size: PM (103.4 nm), PM-C (56.7 nm) and PM-H (123.8 nm). Also, it was observed the optical band gap values of 2.23, 2.15 and 2.16 eV of the samples PM, PM-C and PM-H, respectively. For both dyes, the PM-C sample has higher photodegradation efficiency (98%) and apparent quantum efficiency (φ x = 0.081) in relation to PM and PM-H samples. In addition, especially to RhB, the apparent quantum efficiency of samples practically remains unchanged by three photocatalytic cycles due to use of white light emitting diode (WLEDs) illumination.
The regioselectivity of electrochemical reduction of four trichlorobiphenyls (PCB 28–30 and PCB 37) was studied by cyclic voltammetry and bulk electrolysis. The number of stages and mechanism of electrochemical reduction of each of the examined substrate were inferred on the basis of the experimental electron transfer coefficients and calculated (DFT) bond lengths and potential energy surface sections. GC/MS analysis of the controlled potential electrolysis products showed that chlorine atom in the disubstituted ring of trichlorobiphenyls is reduced more readily than in the monosubstituted ring and that the rate of chlorine reduction changes in the series o-Cl > p-Cl > m-Cl.
Triclosan and chlorophene are chlorinated phenols used as antimicrobial agents. Both compounds are ordinarily detected in aquatic environments. The aim of this study is to prove the reactivity of three different metallic alloys used as common reductants such as Raney Al–Ni (50% Al–50% Ni), Devarda’s Al–Cu–Zn alloy (45% Al–50% Cu–5% Zn), and Arnd’s Cu–Mg alloy (60% Cu–40% Mg) for the hydrodechlorination of these agents in alkaline aqueous solution at ambient temperature and investigating such parameters as type and amount of reagents. The hydrodechlorination of triclosan was found to be completed when 5 molar equivalents of Al in the form of Raney Al–Ni alloy (0.27 g) and 20 equivalents of NaOH (0.8 g) per 1 mmol of triclosan were used and the reaction was performed at ambient temperature and pressure during 20 h of vigorous stirring. Chlorophene was completely dechlorinated using 2.5 equivalents of Al (0.14 g) and 10 equivalents of NaOH (0.4 g) per 1 mmol of chlorophene under the same conditions.
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Regioselectivity of the methanolysis of lower polychlorinated biphenyls with sodium methoxide in a mixture of methanol and DMSO at 100–130°С was studied. It was found that 2,4,4'-tricholobiphenyl is much more reactive than 2,4-dichlorobiphenyl. This results in different mechanisms of substitution. 2,4-Dichlorobiphenyl reacts with sodium methoxide by the elimination–addition mechanism to form four monosubstitution products in comparable quantities. 2,4,4'-Trichlorobiphenyl reacts with the methodixe ion by the classical SNAr mechanism, with preferential substitution of the 2-chlorine atom.
This study focuses on the hydrodechlorination of chlorinated arenes as well as polychlorinated biphenyls (PCBs) utilizing a resin-supported Pd(0) catalyst. Bearing in mind the dangers associated with toxic PCBs, treatment of the remnants of industrial wastes containing PCB congeners is indispensable. One such method is reductive hydrodechlorination. Instead of utilizing traditional sources of hydrogen, ammonium formate is used for in situ hydrogen generation. Moreover, palladium nanoparticles are supported on an anionic exchange resin which makes the process recyclable with a negligible change of yield after recycling experiments. The catalyst is demonstrated in the hydrodechlorination of a wide range of chlorinated compounds and PCB congeners including aroclors 1242, 1248 and 1254. Copyright
The utilization of ferrous ions (Fe(II)), one of the abundant metal ions in environments, as mediators for the electrochemical reductive transformation of 2-nitrophenol was studied in the cathode compartment of a microbial fuel cell (MFC). Two-chambered MFC measurements were performed to demonstrate that the no voltage output was observed in Fe(II)-only or 2-nitrophenol-only cathodic solution. In contrast, the presence of both Fe(II) ions and 2-nitrophenol solution in the cathode enabled the complete reductive degradation of 2-nitrophenol accompanied with energy generation. In addition, the elevated initial concentration of 2-nitrophenol and the complexation of Fe(II) species with an organic ligand significantly promoted voltage output, suggesting the increase in the reduction rate of 2-nitrophenol transformation. These findings show insights into the role of Fe(III)/Fe(II) electrochemical couple in the degradation of a reductive pollutant through the MFC technology.
Unique properties of ionic liquids make them green alternatives for conventional volatile organic compounds. Due to increased production and the high stability of these substances, they could be classified as persistent pollutants and could break through classical treatment systems into natural waters. A preliminary ionic liquid hydrolysis study demonstrated a pH dependent degradation profile with a significant decrease in hydrolysis efficiency as pH lowered from 10.0 to 2.8. In order to examine future prospects for ionic liquid removal, different advanced oxidation processes (TiO2 Degussa P25/H2O2, TiO2 Degussa P25, 7.2Fe/TiO2/H2O2, and H2O2) were studied for their applicability in the degradation of imidazolium-based ionic liquids in aqueous solution. These processes were conducted in the dark as well as in the presence of UVA and simulated sunlight (SS) radiation. Among the investigated dark processes, the 7.2Fe/TiO2/H2O2 system showed the highest efficiency, which can be attributed to a dark heterogeneous Fenton process. Otherwise, the most efficient among all the studied degradation processes was the UVA/TiO2 Degussa P25/H2O2 process. In order to make degradation processes more similar to that of the practical process SS radiation was used. Among studied processes, the 7.2Fe/TiO2/H2O2 system showed the greatest potential for the removal of ionic liquids. Also, it was observed that the impact of anions on the cation degradation efficiency was much more pronounced. Due to the possible fate of ionic liquids in the environment, for five different waters (pond, rain, tap, river, and condensate) degradations in the dark and under simulated sunlight were studied. For all processes, and all water types in the presence of SS radiation a remarkable positive effect of naturally dissolved organic matter on the degradation efficiency was observed. Also, in all experiments, the anion was less stable than the cation. The major photodegradation products identified using liquid chromatography-mass spectrometry (HPLC-MS/MS) techniques were hydroxylated compounds.
A new digestion method using UV-assisted Fe(0) Fenton reaction was developed for the determination of trace Cd in rice by hydride generation atomic fluorescence spectrometry. The proposed method integrated the advantages of simplicity, small dose of reagents, low cost and moderate reaction conditions, and was successfully utilized to analyze a Certified Reference Material (CRM) and real rice samples. A 1 mL mixture of the sample and reagents (0.0500 g rice powder, 0.2% (m/v) Fe(0), 0.75% (v/v) HNO3 and 18% (v/v) H2O2) was irradiated by UV-light for 50 min and then a clear solution was obtained by separating excess Fe(0) with a magnet prior to spectral analysis. The limit of detection (LOD) for Cd was found to be 0.02 mg kg(-1) and the relative standard deviation was better than 5.0% at a concentration level of 0.40 mg kg(-1). The recovery obtained by analyzing the CRM was 103% and spiked recoveries with 0.40 mg kg(-1) Cd in rice samples were 93% and 101%. The t-test proved that there is no significant difference between the certified value and the determined value of the CRM, and between the proposed method and microwave-assisted digestion coupled with inductively coupled plasma mass spectrometry (MWD-ICP-MS) at 95% confidence level.
The properties of zero-valent iron is useful in remediation of aromatic nitro compounds by reducing them to convert onto the amino products which may also lead to oxidize or mineralize them with the presence of persulfate anion (S 2O 82-). In practice, with the zero-valent iron, persulfate anion (E° = 2.01 V) may be activated to produce free sulfate radical (SO 4 - • ) with the higher standard reduction potential (E0 = 2.60 V). It is an active reagent for the mineralization of nitrobenzene in the studied samples. The activation process of persulfate in solution with zero-valent iron to produce SO4 - •, may be implemented by the following pathways: In the heterogeneous system the activation reaction was implemented on iron surface: Fe(0) + 2S 2O 82- → Fe 2+ + 2SO 4- • + 2SO 42-, In homogeneous case, the activation process was implemented in solution: Fe 2+ + S 2O 82- • → Fe 3+ + SO 4- • + SO 42- In the studied system zero-valent iron is a source producing Fe 2+ to keep the activation of persulfate anion. The free sulfate radical formed in situ oxidizes nitrobenzene causing the decrease of the total organic carbon in the samples. The experimental data have shown that the nitrobenzene concentration of 80 mg/L in the system consisting of 500 mg/L of Na2S2O8 and 1 g/L of zero-valent iron, pH = 5, the efficiency of nitrobenzene mineralization may reach for 98 % for 40 min. The nitrobenzene was first reduced with zero-valent iron then transported for the further oxidation with free sulfate radical, the mineralization nitrobenzene may reach for 95 % for 0.5 h. This means that amine products are easily oxidized than its nitro compounds. The obtained experimental data have suggested that the reduction of nitrobenzene by zero-valent iron may be combined with the oxidation process with persulfate activated with zero-valent iron to enhance the nitrobenzene degradation efficiency and the efficiency of zero-valent iron used. The factors such as ratios of persulfate/zero-valent iron/ nitrobenzene, pH, the addition of Fe 2+ influencing on the efficiency of nitrobenzene mineralization have been investigated.
Due to their highly persistent and biorefractory property in environment, halogenated organic contaminants (HOCs) possess the potential risk to ecological safety and human health after released into our surroundings so that their problems have attracted much attention in the concerned researches. Reductive hydrodehalogenation (HDH) by supported catalyst provides the practicable approach to decontaminate HOCs with mild reaction conditions, which forms the low toxic products easily for biodegradation or to recycle as chemical raw materials. So it has been in the spotlight of study on chemical treatment method for environment pollution. This paper reviews the degradation categories, HDH reaction pathway of HOCs with supported catalyst as well as the influential mechanisms of various relative factors. It is also introduced for the progress on these studies and further discussions about some remaining problems in the development of the catalytic HDH technology. In addition, the future trends for this method are prospected.
The chemical hydrogenation possesses the capacity of hydrodehalogenation, hydrodenitrification, hydrodesulfurization, and hydrodearomatization, which has been used environmentally to remove various typical organic or inorganic pollutants in gas or liquid phase. The pollutants treated by hydrogenation mainly include halogenated organic wastes, nitroarenes, organic sulfur compounds, polycyclic aromatic hydrocarbons, nitrates, sulfates, NO x, S0 2, and heavy metal ions. So this review presents the wide scale of the hydrogenation applications in the reductive destruction of environmental pollutants studied mainly within past five years. The destruction principles of the above pollutants by hydrogenation are introduced. The effects of the reaction conditions on the reduction efficiency are discussed such as catalysts and supports, hydrogen donors, and pH. The advantages of the reductive destruction for pollutants by hydrogenation are evaluated on the basis of green chemistry practices. Based on the requirements of industrial application, the research trends for the future are proposed in order to further improve hydrogenation efficiency and energy conservation.
Based on the concentration of Malathion used in the field, we evaluated the genotoxic potential of low concentrations of this insecticide on meristematic and F 1 cells of Allium cepa and on rat hepatoma tissue culture (HTC cells). In the A. cepa, chromosomal aberrations (CAs), micronuclei (MN), and mitotic index (MI) were evaluated by exposing the cells at 1.5, 0.75, 0.37, and 0.18 mg/mL of Malathion for 24 and 48 hr of exposure and 48 hr of recovery time. The results showed that all concentrations were genotoxic to A. cepa cells. However, the analysis of the MI has showed non-relevant effects. Chromosomal bridges were the CA more frequently induced, indicating the clastogenic action of Malathion. After the recovery period, the higher concentrations continued to induce genotoxic effects, unlike the observed for the lowest concentrations tested. In HTC cells, the genotoxicity of Malathion was evaluated by the MN test and the comet assay by exposing the cells at 0.09, 0.009, and 0.0009 mg/5 mL culture medium, for 24 hr of exposure. In the comet assay, all the concentrations induced genotoxicity in the HTC cells. In the MN test, no significant induction of MN was observed. The genotoxicity induced by the low concentrations of Malathion presented in this work highlights the importance of studying the effects of low concentrations of this pesticide and demonstrates the efficiency of these two test systems for the detection of genetic damage promoted by Malathion.
By learning how to balance natural resource limitations and pollution prevention with economic growth, green chemistry will become the central science of sustainability. The elimination of persistent pollutants is vital for a sustainable civilization. To achieve this, the most important guiding concept is that the elemental composition of technology should be shifted toward the elemental composition of biochemistry. Oxidation chemistry is currently a prolific producer of persistent pollutants. Many arise from the use of chlorine, hypochlorite, or chlorine dioxide in large-scale oxidation processes. Oxidation chemistry can be greened by replacing these with catalyzed alternatives based on Nature's oxidizing agent, hydrogen peroxide. TAML(R) (TetraAmidol/MacrocyclicLigand) iron catalysts, which were invented at Carnegie Mellon University are widely patented and are being developed to activate H2O2 for commercial applications. TAML activators are water-soluble, easy to use, function well from neutral to basic pH, are not dominated by nonselective Fenton-like reactivity, are straightforward to synthesize, work effectively in minute concentrations, enable peroxide processes to occur at temperatures well below those of the processes targeted for replacement, and are amenable to modification for capturing novel selectivities. TAML activators are "dial-a-lifetime" catalysts: an activator can be chosen exhibiting a lifetime commensurate with the desired task.
The activation of dioxygen by metal ions has both synthetic potential and biological relevance. Dioxygen is the cleanest oxidant for use in emission-free technologies to minimize pollution of the environment. The book gives a survey of those catalyst systems based on metal complexes which have been discovered and studied in the last decade. They activate molecular oxygen and effect the oxidation of various organic compounds under mild conditions. Much of the recent progress is due to a search for biomimetic catalysts that would duplicate the action of metalloenzymes. Mechanistic aspects are emphasized throughout the book. An introductonary chapter reviews the chemistry of transition metal dioxygen complexes, which are usually the active intermediates in the catalytic reactions discussed. Separate chapters are devoted to oxidation of saturated, unsaturated and aromatic hydrocarbons, phenols, catechols, oxo-compounds, phosphorus, sulfur and nitrogen compounds.
The capture and use of solar energy for the destruction of organic pollutants in aqueous media has been studied. The sunlight is captured by ferrioxalate which, in the presence of hydrogen peroxide, generates hydroxyl radicals. The latter reacts with and oxidizes organic molecules present in aqueous media. The efficiency of this new process for the destruction of organic molecules in tap water is at least 25 times greater than sunlight/TiO2/H2O2, which is a known process for solar detoxification.
A new method is presented for the continuous detection of the complete degradation of organic compounds during anodic oxidation. The oxidation of different model compounds was studied at lead dioxide anodes in undivided cells employing various current densities. Considerable differences in oxidizability of organic substances were found, e.g. between acetic and oxalic acid. Phenol, 4-hydroxycinnamic acid, glucose and oxalic acid could be mineralized at room temperature. Humic acid could be degraded nearly completely. A conventional DOC analyser was used as a reference standard.
The United Nations Environment Programme (UNEP) is currently coordinating negotiations to develop a binding global agreement by late in the year 2000 to prohibit, restrict, or reduce the production, use, or release of certain persistent organic pollutants (POPs). POPs are a small subset of organic chemicals whose characteristics of persistence in the environment, accumulation in biological organisms, and toxicity make them priority pollutants and environmental risks to humans and ecosystems. Under the UNEP negotiation, representatives are developing criteria and procedures for the addition of substances, guided by the initial list of 12 substances or substance groups selected for global action. It is therefore timely to investigate the scientific foundation for POPs screening criteria that have been used in other international, regional, and national programs, focusing on the properties of persistence, bioaccumulation, toxicity, and long-range transport in a policy context. The theoretical, empirical, and multimedia modeling approaches used reveal that guidance for setting POPs screening criteria can be developed using a combination of science and policy input. These approaches suggest that criteria adopted under regional POPs agreements in North America and Europe are reasonable and tend to isolate a limited number of clearly hazardous POPs from the majority of organic chemicals, while not being so stringent that the ability to respond to as yet unidentified risks is seriously compromised.
An electrochemical reduction system was studied for the destruction of persistent organic pollutants (POPs). A two-compartment electrochemical system separated by a cation exchange membrane was adopted. The anolyte was sodium hydroxide solution, which supplied sodium ions as cations to the cathode. The catholyte was a reaction mixture of 1,2,3-trichlorobenzene as the model POP, tetrahexylammonium bromide (THAB) as the electrolyte and acetonitrile as the solvent. The characteristic features of this system were the decrease in the amount of organic solvent used by about 50%, and the function of sodium ions as the mediator for electron transfer. The mechanism of dechlorination of the system was elucidated using cyclic voltammetry (CV) and a potentiostatic study, and the effect of sodium ions on the electrocatalytic destruction was also investigated.
The reduction of tetrachloroethylene (PCE) and trichloroethylene (TCE) catalyzed by vitamin B{sub 12} was examined in homogeneous and heterogeneous (B{sub 12} bound to agarose) batch systems using titanium(III) citrate as the bulk reductant. The solution and surface-mediated reaction rates at similar B{sub 12} loadings were comparable, indicating that binding vitamin B{sub 12} to a surface did not lower catalytic activity. No loss in PCE reducing activity was observed with repeated usage of surface-bound vitamin B{sub 12}. Carbon mass recoveries were 81-84% for PCE reduction and 89% for TCE reduction, relative to controls. In addition to sequential hydrogenolysis, a second competing reaction mechanism for the reduction of PCE and TCE by B{sub 12}, reductive {beta}-elimination, is proposed to account for the observation of acetylene as a significant reaction intermediate. Reductive {beta}-elimination should be considered as a potential pathway in other reactive systems involving the reduction of vicinal polyhaloethenes. Surface-bound catalysts such as vitamin B{sub 12} may have utility in the engineered degradation of aqueous phase chlorinated ethenes. 19 refs., 6 figs., 1 tab.
To date it does not appear to have been demonstrated in the literature that halogenated ethylenes can undergo reductive {beta}-elimination to alkynes under environmental conditions. The purpose of this paper is to provide experimental evidence that such pathways may be involved in the reaction of chloroethylenes with zero-valent metals as well as to speculate on the significance of the products that may result. Calculations indicate that reductive {beta}-elimination reactions of chloroethylenes are in fact comparable energetically to hydrogenolysis at neutral pH. Experiments were therefore initiated to assess whether {beta}-elimination reactions of chlorinated ethylenes could occur in the presence of two zero-valent metals, Fe and Zn. 76 refs., 3 figs., 1 tab.
Laboratory studies were conducted to determine the feasibility of injection and mixing hydrogen peroxide (H{sub 2}O{sub 2}) solutions into clay soils contaminated with trichloroethylene (TCE) to achieve in-situ chemical oxidation. Bench-scale slurry studies were conducted first using 0.3 L slurry reactors and TCE concentrations in the 1.9 to 34 mg/kg range. TCE reductions as high as 98% of the initial concentration were achieved with a H{sub 2}O{sub 2} dose of 28 g H{sub 2}O{sub 2}/kg soil. TCE degradation increased with increasing hydrogen peroxide strength and appeared independent of the initial TCE concentration. Column studies were conducted with an apparatus fabricated to simulate in-situ mixing and chemical oxidant injection. Stainless steel columns 20 cm in diameter and 23 cm long, which were packed with clay soil, were mixed with an auger blade while H{sub 2}O{sub 2} solutions were injected through orifices at the back of the mixing blade. The H{sub 2}O{sub 2} doses for the column studies were 1.2 and 2.5 g H{sub 2}O{sub 2}/kg soil, based on an injection concentration of 5% weight H{sub 2}O{sub 2} at volumetric additions of 5% and 10% of the soil volume treated. TCE reductions of 88% and 75% were achieved at the two dosing rates. Based on the results of these laboratory studies, in-situ chemical oxidation of contaminated soils appears to be a viable soil remediation technique that is dependent on the efficient delivery and distribution of H{sub 2}O{sub 2} throughout the region to be treated.
Hydrodechlorination of monochlorobenzene (MCB), 1,4-dichlorobenzene (DCB), and 1,3,5-trichlorobenzene (TCB) was carried out on palladium-supported gamma-alumina and alumina Lewis superacid catalysts at 298 K and ambient pressure in a stream of hydrogen, using a fixed bed flow reactor for the gas-phase reaction and a fixed bed semi-batch reactor for the liquid-phase reaction. Both catalysts showed higher activity for hydrodechlorination in the gas-phase reactions than the platinum catalysts supported on the same carriers. The completely hydrodechlorinated products consisted only of benzene and cyclohexane. Hydrodechlorination of MCB and DCB at 3900 g (.) h (.) mol(-1) resulted in conversions and cyclohexane yields of 100%, and for TCB the cyclohexane yield was also over 95% with a conversion of 90%. Slight activity decrease of the Pd catalysts due to chlorine accumulation on the catalyst was observed, but the chlorine amount was about one-fourth at 353 K compared to 298 K in spite of the remarkable increase in the number of reacted (dechlorinated) molecules, so catalyst deactivation was effectively reduced at higher reaction temperatures. Furthermore, even in the liquid-phase reactions at ambient temperature, which was lower than the reaction temperatures previously used, the palladium- supported catalysts had moderate activity for hydrodechlorination and formed benzene and cyclohexane. The hydrodechlorination of chlorobenzenes probably proceeded through reactions between the hydrogen atoms spilling over from the Pd surface to the alumina carrier surface and the chlorobenzenes adsorbed and activated on the Lewis acid sites of the alumina surface.
We have hypothesized that hydrogen gas intercalated in a palladium lattice is the powerful reducing agent that reductively dechlorinates chlorinated organic compounds that are adsorbed on the surface of palladized electrodes. We have shown that dechlorination of 4-chlorophenol to phenol occurs rapidly on palladized carbon cloth or pal ladized graphite electrodes. The reactions on the palladized carbon cloth and graphite depend on the adsorption of the chlorinated organic compound on the carbon surface and the reaction with hydrogen at the palladium/carbon interface. Palladium was much more effective in promoting the dechlorination reaction than platinum, probably because of its ability to intercalate hydrogen in its lattice.
A kinetic model is presented for the catalytic hydrodehalogenation of chlorinated ethylenes using Pd and H2 under water treatment conditions. All five chlorinated ethylenes, including tetrachloroethylene (PCE) and vinyl chloride, were completely removed from tap water within 10 minutes at room temperature by 0.5 g of 0.5% Pd on alumina and 0.1 atm H2. Ethane accounted for 55–85% of the mass balance in these systems. Ethene was a reactive intermediate whose maximum concentration accounted for less than about 5% of the initial substrate. Palladium on granular carbon was also an effective catalyst, although ethane yield for PCE was somewhat lower than with Pd-alumina (55% versus 85%). The transformation of PCE was first order with respect to both substrate and amount of metal, with a half-life of t12 = 9 min for 0.055 μmole Pd (583 μg of 1% Pd on powdered activated carbon). Addition of ∼10 mg/L of nitrite to the water decreased the rate constant by about 50%. The nitrite concentration decreased by about 25% over the course of the reaction. Addition of nitrate or sulfate had smaller effect on the rate of PCE transformation; chloride had no effect. The presence of oxygen greatly reduced the amount of ethane produced regardless of the catalyst support. Bisulf1de poisoned the catalyst.
To increase our understanding of the photocatalytic effects in the transformation of chlorinated organic compounds, the detailed mechanism of the direct photolysis of polychlorinated phenols has been established under aerobic and anaerobic conditions. The quantum yield of photolysis of 2,4,5-trichlorophenol (2,4,5-TCP) has been determined at different wavelenghts and pH values.It has been shown that direct photolysis of polychlorinated phenols is accompanied by chloride ion detachment from different positions of the benzene ring with the formation of 2,5-dichlorohydroquinone and dichlorocyclopentadiene derivatives in the case of 2,4,5-TCP, as well as polychlorinated dibenzodioxins (PCDD) and dibenzofurans (PCDF). Based on the 2,4,5-TCP direct photolysis products, it has been concluded that chlorophenol free radicals are formed as a result of CCl cleavage, which probably act as the origin of highly chlorinated PCDD and PCDF.To utilize visible light in the photocatalytic destruction of organic pllutants, we investigated the kinetics of transformation of polychlorinated phenols in systems involving singlet oxygen formation (dye-sensitized reactions with Rose Bengal, Methylene Blue and Eosin). It has been shown that superoxide radical is not reactive towards 2,4,5-TCP, whereas singlet oxygen results in the destructive oxidation of polychlorinated phenols without formation of PCDD and PCDF among the reaction products.The detailed mechanism of the interaction of singlet oxygen with 2,4,5-TCP has been investigated. It has been concluded that the initial trichlorophenol is dechlorinated and singlet oxygen interaction with 2,4,5-TCP proceeds via a mechanism with the formation of hydrogen peroxide without intermediate superoxide radicals.
Photocatalytic degradation of an odorous chemical, 2-mercaptobenzothiazole (MBT), in aqueous suspension was investigated using pure TiO2 and neodymium ion doped TiO2 (Nd3+−TiO2) catalysts. The photocatalytic activity of Nd3+−TiO2 was evaluated in the photocatalytic degradation of MBT in aqueous solution. The experimental results showed that the overall kinetic constant (k) of MBT degradation using Nd3+−TiO2 was significantly higher than that using TiO2 and an optimal content of neodymium ion doping was found to be 1.2% (molar ratio). The main intermediates during the MBT degradation were identified by LC/MS−MS, and the final products including sulfate ion, ammonium ion, and nitrate ion were also determined by ion chromatography. Only three main intermediates including benzothiazole, 2-hydroxybenzothiazole, and benzothiazole-2-sulfite were found during the MBT degradation using the TiO2 catalyst, while five main intermediates including benzothiazole, 2-hydroxybenzothiazole, benzothiazole-2-sulfonate, benzothiazole-2-sulfite, and anilinesulfonic acid were found during the MBT degradation using 1.2% Nd3+−TiO2. On the basis of analytical results, a possible pathway of MBT degradation in such a photocatalytic oxidation reaction was proposed and illustrated. It was concluded that the photodegradation of MBT and its intermediates can be enhanced owing to the neodymium ion doping.
The organophosphorus insecticide malathion was selected as an analog for the chemical nerve agent, VX. Degradation of 0.44 mM malathion in a 10 mL aqueous solution containing 0.50 g granular zero valent iron (ZVI) under ambient air and pressure was complete after 4 h to the detection limit of GC-FID. The degradation kinetics demonstrate the system to be pseudo-first-order with respect to malathion disappearance with a rate constant of 0.92 h−1. The only non-polar organic intermediates detected were diethyl succinate and malaoxon, of which malaoxon is degraded to below the limit of detection of the GC-FID after 12 h. Electrospray ionization mass spectral analyses show the final reaction products to be low molecular weight carboxylic acids (propionic, oxalic and iminodiacetic acid).
Catalytic dechlorination of chlorotoluene to toluene was carried out using several supported Rh-based catalysts in a 2-propanol solution of NaOH at ambient temperature (27°C). A carbon-supported Rh catalyst (Rh/C) showed high catalytic activity, although an induction period was involved in the reaction and the activity of the catalyst reduced during storage in air. The existence of Pt on the Rh catalyst was effective in overcoming the activity reduction by exposure to air and gave the reaction without any induction period. The composite Rh–Pt catalyst supported on TiO2 as well as on carbon was much more active for the reaction than the catalysts supported on SiO2, MgO and Al2O3.
Photocatalytic degradation of phenol, chlorinated phenols, and lindane was evaluated in a continuous flow TiO2 rotating disk photocatalytic reactor (RDPR). The RDPR operated at a hydraulic residence time of 0.25 day and at a disk angular velocity of 12rpm. At low molar feed concentrations (0.038mmol/l), the removal efficiencies for phenol and chlorinated phenols were in the order of 86% or higher, whereas the removal efficiency for lindane at a feed concentration of 0.016mmol/l was in the order of 63%.For 2,4,6-trichlorophenol (TCP), an increase in the molar influent concentration resulted in a decrease in removal efficiency but in an increase in removal rate. The degradation rate of 2,4,6-TCP followed a saturation type dependancy with the effluent concentration, suggesting a Langmuir–Hinshelwood (L–H) reaction rate equation. A L–H equation was employed to determine the reaction rate constant and the adsorption coefficient for 2,4,6-TCP. The photonic efficiency increased from 0.68% at an influent concentration of 0.13mmol/l to 2.06% at an influent concentration of 1.0mmol/l.
Formic acid, isopropanol and hydrazine were investigated as reductants for the Pd-catalyzed hydrodechlorination of chlorobenzene in water at ambient temperature. The intention was to find alternatives to molecular hydrogen with high water solubilities. Formic acid was found to be as reactive as H2 under acidic and neutral conditions, but less reactive under alkaline conditions. The observed kinetics imply two pH-controlled reaction mechanisms (possibly H-atom and hydride transfer). H-consumers, such as chlorinated compounds, strongly stimulate the decomposition of formic acid. The half-life of 5mgL−1 chlorobenzene in the presence of 1mgL−1 Pd is about 2min under optimal reaction conditions. Rh was found to be inactive in the formic acid driven hydrodechlorination. Isopropanol is less reactive by about five orders of magnitude than H2. Hydrazine is effective as a H-donor for the hydrodechlorination under alkaline conditions. However, the reaction is slower than with H2 by a factor of 30. From the technical and economic point of view, formic acid is a promising substitute for H2.
The deactivation of a 0.5wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene (TTCE), chlorobenzene (CBZ) and dichloromethane (DCM) in organic matrix in gas phase has been studied in this work. Experiments were carried out in a continuous fixed bed reactor, at a pressure range of 0.1–2MPa. It was found that the reactivity and stability of the catalyst increases as pressure increases. Different compounds present quite different deactivation patterns: fast initial deactivation followed by a plateau for DCM and CBZ, continuous moderate deactivation for TTCE.The effect of hydrogen chloride was studied by adding to the reactor feed different amounts of hydrogen chloride, working at 225–300°C.Fresh and used catalysts were characterised by nitrogen porosimetry, X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, thermogravimetry and temperature-programmed oxidation. Results indicate that carbonaceous deposits play a key role in the catalyst deactivation, being this phenomenon promoted by the presence of HCl.
Flow-through column tests were conducted to investigate the products of degradation of aqueous trichloroethene (TCE) in contact with granular iron metal. The results indicated the degradation process to be pseudo-first-order and the rate constant to be relatively insensitive to the initial concentration of TCE over the range from about 1.3 to 61 mg/L. The principal degradation product was ethene, followed by ethane with substantially smaller amounts of other C1−C4 hydrocarbons. About 3.0−3.5% of the initial TCE appeared as chlorinated degradation products, including the three dichloroethene isomers and vinyl chloride. Although the chloride mass balance was generally between 98 and 102%, a maximum of 73% of the carbon could be accounted for in the identified products. Based on the low concentrations of chlorinated degradation products in the solution phase, it is proposed that most of the TCE remains sorbed to the iron surface until complete dechlorination is achieved.
Deuterium isotope exchange was employed to investigate some of the reaction steps for the hydrodechlorination of CF3CFHCl and CH3CH2Cl on supported Pd catalysts. Hydrodechlorination rates for both compounds using D2 or H2 were identical. It is concluded that H or D species are not involved in the rate-determining step of the hydrodechlorination reaction. Experiments using a combined H2 and D2 feed for hydrodechlorination of CF3CFHCl showed that CF3CFH2 was preferentially formed over CF3CFHD. This experimental observation can be explained by isotope effects and is consistent with gas phase H2 in equilibrium with adsorbed H and a reaction step consisting of the combination of surface adsorbed CF3CFH species with adsorbed H. Deuterated product distributions of CF3CFHCl and CH3CH2Cl hydrodechlorination experiments with D2 were analyzed to explore the reaction steps beyond the kinetically relevant steps. The main product of CF3CFHCl hydrodechlorination was CF3CFHD, showing that the CCl bond is preferentially broken. In the case of CH3CH2Cl, substantial CH bond breaking accompanies the initial CCl scission. Deuterium exchange experiments with ethane on Pd/C and Pd/ZrO2 were also investigated and the results indicate that the CH3CH2Cl product distribution is not caused by re-adsorption and subsequent exchange reaction of ethane.
Large amounts of polychlorinated biphenyls (PCBs) had been produced in China. In order to dispose of them appropriately, a set of experimental PCB incinerators have been manufactured in China. The 2,3,7,8-substituted toxic polychlorinated dibenzodioxins and furans (PCDD/Fs) congeners in stack ash and bottom ash samples from the incinerator and technical products #1PCB and #2PCB (for the reason of comparison) were measured. In addition, the levels of these toxic congeners were converted to 2,3,7,8-TCDD TEQ. Moreover, levels of dioxin-like PCB congeners and 2,3,7,8-TCDD TEQ values in two types of commercial PCBs products and stack ash were determined.
Catalytically active membranes containing palladium nanoclusters of 3-5 nm were prepared from poly(ether-b-amide) (PEBA) and the catalyst precursor palladium diacetate in a solution-casting-reduction procedure. These membranes were used to simultaneously concentrate and react organics by catalytic pervaporation. The model reaction considered is the hydrogenation of 4-chlorophenol in aqueous solution using dissolved hydrogen as reducing agent. The reaction produced phenol and, in smaller yields, cyclohexanone and cyclohexanol were detected in the permeate but also in the feed solution. Conversion of 4-chlorophenol is up to 80% after 20 It of operation. However, a considerable amount of 4-chlorophenol passed the membrane unreacted. Pervaporative enrichment of the organics was by a factor of 100. The effectivity of the process was influenced by the palladium cluster size, feed temperature and permeate pressure. A significant conversion is realized only when employing the catalytic membrane in the pervaporation mode. (C) 2002 Elsevier Science B.V. All rights reserved.
The liquid-phase hydrodehalogenation of substituted chlorobenzenes has been carried out over palladium supported on AlPO4-SiO2. The hydrodehalogenation of the p-chlorobromobenzene undergo a consecutive reaction starting with the C-Br hydrogenolysis. For the other substituted chlorobenzenes, the reaction proceeds through the hydrogenolysis of the C-Cl bond. The reaction rate obtained for the substrates with electron-withdrawing substituents is lower than that of chlorobenzene while for the substrates with electron-releasing groups it is higher. This is related to a modification of the adsorption strength of the molecule and the surface reaction trough the inductive and mesomeric effects of the substituents. The Taft equation is used to correlate the hydrodechlorination catalytic activity of the p-substituted chlorobenzenes with inductive and mesomeric parameters of the substituents. These results seem to indicate that the reaction proceeds through an electrophilic attack. (C) 2002 Elsevier Science B.V. All rights reserved.
The kinetics of selective hydrodechlorination of 1,2-dichloroethane into ethylene over a Pd–Ag/SiO2 catalyst is studied. Kinetic data at 573, 596, and 647 K have been obtained by means of experimental designs in the space of the partial pressures of the four components influencing kinetics, that is, 1,2-dichloroethane, hydrogen, ethylene, and hydrogen chloride. One model among the numerous ones examined allows us to represent correctly the experimental data. It corresponds to the following mechanism: dechlorination of 1,2-dichloroethane into ethylene occurs on silver through dissociative adsorption with successive breaking of the two C–Cl bonds and desorption of C2H4. Thanks to its activation power of hydrogen by dissociative chemisorption, palladium present at the surface of the alloy supplies hydrogen atoms for regeneration of the chlorinated silver surface into metallic silver. The presence of hydrogen adsorbed on Pd also causes the undesired ethylene hydrogenation leading to a loss of olefin selectivity.
The electrochemical incineration of organic pollutants on a boron-doped diamond (BDD) thin film electrode was examined by bulk electrolysis, and the mechanism of oxidation was investigated. A comparative study with other electrodes such as Pt and glassy carbon (GC) electrodes revealed the superiority of the BDD over these electrodes. The extent of degradation of phenol and formate due to direct oxidation and hydroxyl radical-mediated oxidation were quantified by amperometric measurements. The extent of direct oxidation was found to decrease with increasing potentials due to the competing hydroxyl radical-mediated reactions. The extent of direct oxidation for formate was found to be higher than that for phenol, indicating the probability of higher adsorption of formate on the oxygen-terminated diamond surface. Finally, bulk electrolysis of phenol at the BDD resulted in the complete destruction of phenol to CO2 with a removal efficiency of 96%, indicating the promising use of BDD for electrochemical waste treatment applications.
A bench-scale Fenton electrochemical system was used to study the degradation of two widely used herbicides, atrazine and metolachlor. In this system the degradation of the herbicides occurs by attack of hydroxyl radicals which are produced from reaction of hydrogen peroxide with electrochemically generated ferrous iron. The goals of the study were to achieve degradation of the herbicides by optimizing reagent concentrations and to identify degradation pathways. Herbicide degradation was determined with respect to iron and hydrogen peroxide concentrations and their rate of addition. Effects of near-UV illumination and herbicide concentration on the degradation of the herbicides were also studied. Adding hydrogen peroxide in multiple smaller doses resulted in enhanced removal of the herbicides, especially metolachlor (greater than 99% degradation), as compared to adding it all at once at the beginning of the treatment. The degradation of atrazine, which was initially difficult, was enhanced (greater than 99% degradation) by using a small molar excess of hydrogen peroxide to iron (5:1) and maintaining the ratio for the entire period of treatment. Atrazine degradation in this system appears to be via N-dealkylation and dechlorination. Keywords: Atrazine; degradation; electrochemical; Fenton; herbicides; hydroxyl; radicals; metolachlor
The treatment efficiencies of an electrochemically mediated iron-hydrogen peroxide system and the classic Fenton reagent system have been investigated with the goal of developing simple accessible methods for treatment of pesticide-contaminated wastewater, such as pesticide rinsewater. These treatment methods were screened by applying them to aqueous solutions of alachlor, metolachlor, atrazine, cyanazine, and picloram. Electrochemically mediated iron precipitation, achieved by electrolyzing the pesticide solutions in the presence of sacrificial iron electrodes, studied as a control method, was not effective in removing the herbicides from their respective aqueous solutions. A modified Fenton system consisting of electrochemical generation of iron in the presence of hydrogen peroxide (electrochemical peroxide) was effective in removing/degrading the herbicides within a few hours, with 90% or greater efficiency in all cases except cyanazine. The classic Fenton system was effective in removing the herbicides within 1.5 h with greater than 99% efficiency. The final pH values of the electrochemical peroxide treated solutions ranged from 5 to 7.5, while the pH of the classic Fenton reagent treated solutions ranged from 2 to 3.2.
A number of structurally diverse organic and inorganic polydentate chelators were tested for their ability to solubilize Fe(III) at pH 6 and catalyze the oxidation of 0.1 mM (22 ppm) 2,4-dichlorophenoxyacetic acid (2,4-D) by 10 mM (340 ppm) hydrogen peroxide in aerated aqueous solution. Of 50 compounds tested, 20 organic compounds gave soluble complexes capable of oxidizing 2,4-D in periods ranging from minutes to less than 5 h. The reaction rate was proportional to the concentration of H2O2 and inversely proportional to the concentration of chelator. 2,4-Dichlorophenol was a transient intermediate. Chloride was released concurrently with 2,4-D disappearance. Activities of individual complexes toward 2,4-D transformation and hydrogen peroxide decomposition were similar. Several of the most active complexes gave about 80% mineralization of [ring-C-14]- or [carboxy-C-14]-2,4-D within 4 h. Additional supplements of H2O increased the extent of mineralization. All active organic ligands were themselves oxidized, but in many cases the resulting iron complexes remained solubilized and reactive, often more reactive than the original complex. From a practical perspective, degradation of the ligand may be viewed as desirable.
The system iron-ethylenediamine tetraacetate has been studied polarographically over the pH range 1-11. Waves corresponding to reversible reduction of the ferric complex to the ferrous state are obtained up to pH 9; in more alkaline solution the reaction proceeds irreversibly. The ferrous complex yields reversible anodic waves under proper conditions. The diffusion currents are proportional to concentration of the complex. The half-wave potential of the system is constant and equal to -0.13 v. vs. S.C.E. in the pH region 3.5-6.5; outside this range the half-wave potential is pH dependent. The stability constant of the ferric complex has been obtained from a spectrophotometric analysis of its dissociation equilibrium in 0.6-1 M perchloric acid. The value is dose to 6 × 10 23.
This work describes the reductive dehalogenation of carbon tetrachloride (CT) in a novel liquid-phase electrochemical reactor. The reactor consists of a cylindrical porous copper cathode with a concentric carbon-cloth anode wrapped around the cathode. The results show that CT destruction can be achieved, even in low conductivity solutions (i.e., deionized water), reaching 80% conversion of CT with a residence time of 10 min when a cathode potential of −0.4 V (versus a standard hydrogen electrode) is used. A mathematical model was formulated to simulate reactor performance. The model accounted for CT reductive dechlorination, hydrogen evolution on the cathode surface, and CT mass-transfer limitations. The equilibrium potential for CT reduction on the cathode surface was the only adjustable parameter. The model adequately represented experimental data under high-conductivity (2.2 S/m) and low-conductivity (0.05 S/m) conditions. The model results and experimental observations suggest that the entire cathode was active during CT reduction experiments, i.e., solution potential did not render portions of the cathode nonreactive, even in the low-conductivity experiments.
The complete destruction of separate mixtures of 1.1 mM 4-chlorophenol (aqueous) and 0.61 mM pentachlorophenol (aqueous slurry) take place in the presence of 0.5 g of iron particles in 10 mL of 0.32 mM ethylenediaminetetraacetic acid (EDTA) under ambient air under room temperature conditions. Under this reaction condition, the time required to reach complete disappearance to the detection limit of GC-FID for each compound was 4 h for 4-chlorophenol and 70 h for pentachlorophenol. Electrospray ionization mass spectral (ESI-MS) analysis of the 4-chlorophenol reaction mixture after its complete disappearance indicated non-chlorinated, primarily low molecular weight products; however, Cl- from 4-chlorophenol was not detected due to adsorption onto the iron or its corrosion products. Radical trap and control experiments suggest that the mechanism for destruction initiates with dioxygen activation, leading to the formation of reactive oxygen species (ROS) and ultimately ring opening of the phenolic compounds. This is the first example of an abiotic system capable of the complete destruction of an organic pollutant under room temperature and pressure conditions through dioxygen activation chemistry.
The oxidation of FeII(L) complexes by molecular oxygen is significantly enhanced by the presence of a chelating ligand L. The kinetics of this reaction was studied for L = ethylenediaminetetraacetate, N-(hydroxyethyl)ethylenediaminetriacetate, and diethylenetriaminepentaacetate as a function of [FeII(L)], [O2], pH, temperature, and pressure. All the observed kinetic relationships can be accounted for in terms of a mechanism in which O2 rapidly reacts with FeII(L) to produce FeII(L)O2, followed by three parallel reaction steps. These include spontaneous and acid-catalyzed electron transfer, as well as a reaction with FeII(L) to produce (L)FeIII-O22--FeIII(L). The results are discussed in reference to the available literature data for these and related oxidation processes.
The electrocatalytic hydrogenolysis of pentachlorophenol (PCP) was carried out under galvanostatic control, in an aqueous 1 M NaOH solution in which PCP is fully soluble, and on particles of palladium or rhodium supported on alumina (Pd(5%)/Al2O3 or Rh(5%)/Al2O3) and entrapped in a reticulated vitreous carbon (RVC) electrode. On Pd/Al2O3 and at 75 °C, the conversion was complete (>99%) after 16 mol of electrons per mol of substrate (16 F mol-1) were consumed, and phenol was the sole product formed in 98% yield (61% current efficiency). On Rh/Al2O3 and 25 °C, 100% conversion was reached after 24 F mol-1, and cyclohexanol was obtained in 98% yield with some 2% of cyclohexanone (62% current efficiency). The ease of electrocatalytic hyrogenolysis was found to increase in the following order: PCP < 2,6-dichlorophenol < 4-chlorophenol.
This research investigated the long-term performance of zero-valent iron aggregates for reductive dechlorination of trichloroethylene (TCE) and perchloroethylene (PCE). The effects of elapsed time, mass transfer limitations, and influent halocarbon concentration on reductive dechlorination rates were investigated using groundwater obtained from a field site contaminated with chlorinated organic compounds. Over the first 300 days of operation, reaction rates for TCE and PCE gradually increased due to increasing porosity of the iron aggregates. Although there was microbial growth in the column, biological activity did not measurably contribute to reductive dechlorination. Dechlorination rates were pseudo-first-order in reactant concentration for submillimolar halocarbon concentrations. TCE concentrations near aqueous saturation resulted in passivation of the iron surfaces and deviation from first-order reaction kinetics. However, this passivation was slowly reversible upon lowering the influent TCE concentration. Tafel polarization diagrams for an electrode constructed from the iron aggregates indicated that corrosion of the aggregates was anodically controlled. At all halocarbon concentrations, aggregate oxidation by water accounted for more than 80% of the corrosion. Throughout the course of the 3-yr column investigation, reaction rates for TCE were 2−3 times faster than those for PCE. However, current measurements with the aggregate electrode indicated that direct PCE reduction was faster than that for TCE. This disparity between amperometrically measured reaction rates and those measured in the column reactor indicated that halocarbon reduction may occur via direct electron transfer or may occur indirectly through reaction with atomic hydrogen adsorbed to the iron. Comparison of aggregate corrosion rates with those of fresh iron suggested that anodic control of corrosion leads to predominance of the indirect reduction mechanism. The faster reaction rate for TCE under anodically controlled conditions can therefore be attributed to its faster rate of indirect reduction as compared to PCE.
The disappearance of pentachlorophenol (PCP) from aqueous solutions in contact with zero valent metals (ZVMs) may be due to dechlorination reactions or sorption to ZVM-related surfaces. Previously reported results on PCP and zero valent iron measured only PCP loss from aqueous solutions and attributed this loss to reaction. In this study, the total amount of unreacted PCP, both that in aqueous solution and that sorbed to ZVM-related surfaces, was measured using a modified extraction method. PCP dechlorination was confirmed by following the appearance of tetrachlorophenol isomers. The results indicate that the rate of dechlorination is much slower than previously reported. In our experiments, electrolytic zero valent iron with a surface area of 0.12 m2/g resulted in an observed first-order rate constant (±95% confidence limits) of 3.9 (±0.7) × 10-3 h-1 or a half-life of approximately 7.4 days. Normalized to surface area, the rate constant (kSA) is 3.2 (±0.6) × 10-4 L m-2 h-1. Four amended irons prepared by coating iron with palladium (Pd/Fe), platinum (Pt/Fe), nickel (Ni/Fe), and copper (Cu/Fe) were also used and showed slower removal rates as compared to unamended iron (estimated half-lives of 36−43 days). Slower reaction rates obtained with amended irons as compared to iron have not been previously reported. Overall, this study conclusively demonstrates PCP dechlorination by iron and several bimetallic ZVMs and indicates that it is essential to separate reaction and sorption processes.
This research investigated the effectiveness of electrochemical reduction for removing trichloroethylene (TCE) and carbon tetrachloride (CT) from dilute aqueous solutions. The kinetics, reaction mechanisms, and current efficiencies for TCE and CT reduction were investigated using flow-through, iron electrode reactors and with amperometric measurements of reduction rates. The electrode reactors were operated over a range of flow rates, pH, ionic strength, dissolved oxygen concentration, and working electrode potentials. Typical reduction half-lives for TCE and CT in the iron reactor were 9.4 and 3.7 min, respectively. The addition of palladium as an electrocatalyst at a level of 1 mg of Pd per m2 of electrode surface area increased the reaction rates by a factor of 3. When operated continuously, reaction rates in the palladized-iron reactor were stable over a 9-month period of operation, indicating that there was no loss of palladium from the electrode. In both the iron and Pd−iron reactors, TCE was reduced primarily to ethane and ethene, while CT was reduced almost exclusively to methane. Under all operating conditions, chlorinated compounds accounted for less than 2% of the total reaction byproducts. Comparisons of amperometrically measured current efficiencies with those measured in the flow-through reactors and the weak effect of electrode potential on TCE reaction rates indicated that the primary pathway for TCE reduction by iron and palladized-iron electrodes is indirect and involves atomic hydrogen as the reducing agent. Direct reduction of TCE appeared to be inhibited by the preferential reduction of water. The finding that electrodes coated with a hydrophobic polymer to inhibit water reduction showed current efficiencies greater than 90% for direct TCE reduction supports this hypothesis. For CT, similar amperometric and analytically measured current efficiencies indicated that the primary mechanism for CT reduction is direct electron transfer. Carbon dioxide and bisulfide, which have been found to foul palladium in other catalytic systems, did not deactivate the catalyst. The fast reaction kinetics and electrode stability indicate that electrochemical reduction may be feasible for treating waters contaminated with chlorinated organic compounds.
Soil and water contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a serious environmental problem at several active and abandoned munitions production facilities. Zero-valent iron (Fe0) can effectively remediate RDX-contaminated soil and water. The objective of this study was to manipulate Eh and pH for enhanced Fe0-mediated destruction of RDX. This was accomplished by monitoring RDX destruction under controlled Eh-pH conditions (Eh: −300 to +150 mV; pH: 2−10). Decreasing Eh and pH increased RDX destruction in aqueous solution. Treating 20 mg of RDX L-1 (90 μM) under a static Eh of −150 mV and pH 7 with 20 g of Fe0 L-1 removed 95% of the RDX within 4 h; no RDX was detected after 8 h. Treating a soil slurry (20% solids; 510 mg RDX kg-1 soil) with 20 g of Fe0 L-1 at an Eh of −150 mV and pH 7 increased RDX destruction by 24% over the unbuffered control and resulted in 99% RDX destruction within 24 h. Adding 4.2 mM sodium sulfide (in lieu of a static Eh) under similar conditions resulted in 93% RDX loss within 24 h. Results indicated that lowering Eh and maintaining neutral pH during Fe0 treatment can increase RDX destruction in contaminated soil and water.
The photochemical reactions of the organochlorine pesticide DDT in aqueous solutions containing nonionic surfactant micelles (Brij 35, Brij 52, and Brij 72) were investigated and modeled. All photolytic experiments were conducted in a Rayonet RPR-200 merry-go-round photoreactor using a 253.7-nm mercury monochromatic ultraviolet (UV) lamps. Pseudo-first-order decay through photodechlorination was observed to be the dominant reaction pathway for DDT photodecay. The primary photoproducts include lesser chlorinated compounds (DDE and DDD) and hydrogen chloride. The photodechlorination of DDT involves two stages; the first is the fast aliphatic chlorine reduction, followed by a slow aromatic chlorine reduction. The photodecay rates of DDT were doubled in the Brij 52 micellar solution compared to that in water alone. A first-order parallel/consecutive model was developed and found useful to predict the photodecay of DDT and the generation of DDE/DDD in the micellar/aqueous system.
The reductive dechlorination of CCl4 and CHCl3 in the presence of the synthetic sulfate form of green rust (GRSO4), FeII4FeIII2(OH)12SO4yH2O, at pH 8 and room temperature was investigated. Reduction of CCl4 produces CHCl3 and C2Cl6 as main chloroaliphatic products, while GRSO4 is oxidized to magnetite (Fe3O4). The formation of C2Cl6 indicates a coupling reaction between trichloromethyl radicals in the suspension. Chloroform was much less susceptible than CCl4 to reductive dechlorination by GRSO4 showing reduction rates approximately 100 times less than for reduction of CCl4. The transformation of CCl4 by GRSO4 can be described by pseudo-first-order reaction kinetics with respect to formation of chloride. At room temperature the rate expression is given as: d[Cl-]/dt −d[CCl4]/dt = r·kobs[Fe(II)]GR, where kobs is in the range (0.47 × 10-5)−(2.18 × 10-5) s-1 for CCl4 concentrations above its aqueous solubility. This narrow range may be due to the constant CCl4(aq) concentration owing to buffering of the CCl4(aq) concentration by free phase CCl4(l) thereby indicating that the reaction takes place in solution. Experiments with initial CCl4 concentrations below its aqueous solubility support this theory. The reaction kinetics are compared with similar reactions where iron(0) is used as reductant of CCl4. The first-order rate constants for transformation of CCl4 with zerovalent iron and GRSO4, respectively, are found to be in the same range. Thus, GRs formed during corrosion of iron(0) under nonacid conditions may considerably contribute to the total reduction of CCl4 measured in iron(0) systems.
Information concerning the pathways and products of reaction of 1,1,1-trichloroethane (1,1,1-TCA) with zero-valent metals may be critical to the success of in situ treatment techniques. Many researchers assume that alkyl polyhalides undergo reduction via stepwise hydrogenolysis (replacement of halogen by hydrogen). Accordingly, 1,1,1-TCA should react to 1,1-dichloroethane (1,1-DCA), to chloroethane, and finally to ethane. Experiments conducted in laboratory-scale batch reactors indicate, however, that with zinc, iron, and two bimetallic reductants (nickel-plated iron and copper-plated iron) this simplistic stepwise scheme cannot explain observed results. 1,1,1-TCA was found to react rapidly with zinc to form ethane and 1,1-DCA. Independent experiments confirmed that 1,1-DCA reacts too slowly to represent an intermediate in the formation of ethane. In reactions with iron, nickel/iron, and copper/iron, cis-2-butene, ethylene, and 2-butyne were also observed as minor products. Product ratios were dependent on the identity of the metal or bimetallic reductant, with zinc resulting in the lowest yield of chlorinated product. For reactions with iron and bimetallic reductants, a scheme involving successive one-electron reduction steps to form radicals and carbenoids can be invoked to explain the absence of observable intermediates, as well as the formation of products originating from radical or possibly from carbenoid coupling.
Traditionally, destruction of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] for environmental remediation required high-energy processes such as incineration. Here, the capability of powdered zero-valent iron to dechlorinate DDT and related compounds at room temperature was investigated. Specifically, DDT, DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane], and DDE [2,2-bis(p-chlorophenyl)-1,1-dichloroethylene] transformation by powdered zero-valent iron in buffered anaerobic aqueous solution was studied at 20 °C, with and without the presence of nonionic surfactant Triton X-114. The iron was successful at dechlorinating DDT, DDD, and DDE. The rates of dechlorination of DDT and DDE were independent of the amount of iron, with or without surfactant. The rates with surfactant present were much higher than without. Initial first-order transformation rates for DDT, DDD, and DDE were determined. For example, the initial first-order rate of DDT dechlorination was 1.7 ± 0.4 and 3.0 ± 0.8 day-1 or, normalized by the specific iron surface area, 0.016 ± 0.004 and 0.029 ± 0.008 L m-2 h-1, without and with surfactant, respectively. A mechanistic model was constructed that qualitatively fit the observed kinetic data, indicating that the rate of dechlorination of the solid-phase (crystalline) reactants was limited by the rate of dissolution into the aqueous phase.
Hydroxypropyl-β-cyclodextrin (HP-β-CD) enhances the solubility of tetrachloroethylene (PCE) in water both in static and in flowing systems. HP-β-CD does not decrease the interfacial tension between PCE and water and, therefore, should not mobilize immiscible-phase PCE in the subsurface. Rates for the reaction of PCE with metallic iron were measured in HP-β-CD solutions under static conditions. In flowing systems, metallic iron removed PCE, and no other chlorinated ethylene species were observed in the column effluent. In several such systems, recycling of the HP-β-CD solution took place following the reaction with iron. No downward mobilization of the PCE pool in the generator column was observed. The solubility enhancement and reaction with metallic iron are consistent with reversible formation of a stoichiometric HP-β-CD/PCE complex. A theoretical treatment of the reaction rates of complexed PCE on an iron surface was developed. This treatment suggests that any material that enhances the solubility of low-solubility organic substances may slow down the rate of reaction in aqueous solution. In many cases, the rate retardation should equal the degree of solubility enhancement. The combination of HP-β-CD and iron metal appears to be a promising groundwater remediation technology.
The properties of iron metal that make it useful in remediation of chlorinated solvents may also lead to reduction of other groundwater contaminants such as nitro aromatic compounds (NACs). Nitrobenzene is reduced by iron under anaerobic conditions to aniline with nitrosobenzene as an intermediate product. Coupling products such as azobenzene and azoxybenzene were not detected. First-order reduction rates are similar for nitrobenzene and nitrosobenzene, but aniline appearance occurs more slowly (typical pseudo-first-order rate constants 3.5 × 10-2, 3.4 × 10-2, and 8.8 × 10-3 min-1, respectively, in the presence of 33 g/L acid-washed, 18−20 mesh Fluka iron turnings). The nitro reduction rate increased linearly with concentration of iron surface area, giving a specific reaction rate constant (3.9 ± 0.2 × 10-2 min-1 m-2 L). The minimal effects of solution pH or ring substitution on nitro reduction rates, and the linear correlation between nitrobenzene reduction rate constants and the square-root of mixing rate (rpm), suggest that the observed reaction rates were controlled by mass transfer of the NAC to the metal surface. The decrease in reduction rate for nitrobenzene with increased concentration of dissolved carbonate and with extended exposure of the metal to a particular carbonate buffer indicate that the precipitation of siderite on the metal inhibits nitro reduction.
The effect of the reducing potential on the reductive dehalogenation of the different HCH (hexachlorocyclohexane) isomers has not yet been studied. In the present study, the potential for dehalogenation of α-, β-, δ-, and γ-HCH isomers by the dithiothreitol (DTT) and titanium(III) citrate (reducing potential at pH 7, −0.33 and −0.48 V, respectively), with and without the addition of hydroxocobalamin was investigated. In the presence of DTT without catalyst, there was no disappearance of any of the HCH isomers studied after 1 h of treatment. However, disappearance of the γ- and α-HCH isomers was observed during the same time period when titanium(III) citrate was used as the reductant in the absence of catalyst (62.9 and 16.6% disappearance, respectively). Addition of the hydroxocobalamin to the DTT system favored mainly the disappear ance of γ- and α-HCH (92.9 and 30.8% disappearance after 1 h, respectively); disappearance of δ-HCH and β-HCH was small (11.9%) or negligible, respectively. Addition of the hydroxocobalamin to the titanium(III) citrate system favored the degradation of all HCH isomers under study: γ- and α-HCH completely disappeared to undetectable levels (<0.1%) after 1 and 2 min, respectively; degradation of δ-HCH and β-HCH was slower than that of the other two isomers, although they had almost completely disappeared (99.9 and 99.6% disappearance, respectively) after 10 and 60 min, respectively. The order of disappearance, γ-HCH > α-HCH > δ-HCH > β-HCH, coincided with a decreasing order of the axially positioned Cl atoms of these isomers (considering their thermodynamically most stable con figuration). This study is the first description of the rapid degradation of δ- and β-HCH under abiotic conditions, and the results demonstrate the effect of the reducing potential on the reductive dehalogenation of HCH isomers.
The reaction CH2O + xH2O2 → CO2 + (x + 1)H2O + [(x - 2)/2]O2 for x ≥ 2, in dilute aqueous formaldehyde waste solutions was found to be greatly accelerated with ferric ion as a catalyst. This reaction has similarities to the Fenton reaction (the oxidation of α-hydroxy acids to α-keto acids with hydrogen peroxide and ferrous salts) but is different in that the form of iron used is not oxidized but functions as a true catalyst. Ion chromatography results showed that the reaction proceeds in two steps: the oxidation of formaldehyde to formic acid followed by the oxidation of formic acid to carbon dioxide. 14C studies of the formaldehyde molecule showed that the reaction is complete (< 1 mg/L formaldehyde or formate) within a reasonable time frame at room temperature. Methyl alcohol, used as a stabilizer in the formaldehyde solutions, was oxidized producing formaldehyde, formic acid, and finally carbon dioxide.
A stable, conductive, bicontinuous microemulsion of surfactant/oil/water was evaluated as a medium for catalytic dechlorination of PCBs at constant current on lead cathodes. Biphenyl and its reduced alkylbenzene derivatives were the major products. Zinc phthalocyanine provided better catalysis than nickel phthalocyanine tetrasulfonate. Maximum current efficiency was 20% for 4,4′-DCB but increased to 42 % overall for the most heavily chlorinated PCB mixture. Nearly complete dechlorination of 100 mg of Aroclor 1260 (60% Cl) in 20 mL of microemulsion was achieved in 18 h, equivalent to the best previous result for Aroclor 1016 (48% Cl) on Hg cathodes in buffered surfactant dispersion. Advantages of the method include avoidance of added salts and buffers, decreased toxicity of the medium compared to polar organic solvents, and the use of lead cathodes in place of environmentally unacceptable Hg.
The present study was designedto further elucidate the potential of transition-metal coenzymes in biodehalogenation by systematically investigating the dechlorination of polychlorinated ethanes by vitamin B 12 and hematin
Kinetics studies of the indirect photooxidation of trace hydroxyl radical (+OH) probes in aqueous solutions were used to evaluate the nature and formation efficiency of the transient oxidants that are generated when hydrogen peroxide reacts with Fe(II) that is produced from photoreduction of Fe(III) (lambda = 436 nm). Results of studies of these "photo-Fenton reactions" under various test conditions are in good agreement with the hypothesis that Fe2+ and its oxalate, citrate, and phosphate complexes react with H2O2 efficiently to produce +OH in water at pH values ranging from 3 to 8. Such reactions involving Fe(II) and H2O2 provide a generally important pathway for oxidations in the environment and possibly for the treatment of contaminated waters.