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Reductive Dehalogenation of Chlorinated Methanes by Iron Metal
Abstract
Reduction of chlorinated solvents by fine-grained iron metal was studied in well-mixed anaerobic batch systems in order to help assess the utility of this reaction in remediation of contaminated groundwater. Iron sequentially dehalogenates carbon tetrachloride via chloroform to methylene chloride. The initial rate of each reaction step was pseudo-first-order in substrate and became substantially slower with each dehalogenation step. Thus, carbon tetrachloride degradation typically occurred in several hours, but no significant reduction of methylene chloride was observed over 1 month. Trichloroethene (TCE) was also dechlorinated by iron, although more slowly than carbon tetrachloride. Increasing the clean surface area of iron greatly increased the rate of carbon tetrachloride dehalogenation, whereas increasing pH decreased the reduction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corrosion) of the iron through a largely diffusion-limited surface reaction.
... Mechanistic information regarding the operating mode of Fe 0 /H2O systems is conflicting. For example, Matheson and Tratnyek (1994) used slowly stirred batch experiments (≤ 15 rpm) to suggest that chlorinated carbons (RCl) are removed from aqueous solution mostly via reductive degradation mediated by electrons from Fe 0 . Weber (1996) reported to have confirmed that reductive transformation by Fe 0 is a surface-mediated process while using 4-aminoazobenzene as a probe contaminant and a completely different experimental design. ...
... Gillham and O'Hannesin (1994) to 33.7 % for Schreier and Reinhard (1994). Table 1 also reflects the fact that the reductive transformation concept was favoured (Section 1) as Gillham and O'Hannesin (1994) and Matheson and Tratnyek (1994) were roundly referenced 10 times more than Lipczynska-Kochany et al. (1994) and Schreier and Reinhard (1994). Another important feature reflected in Table 1 is that only a tiny fraction of published articles have referenced the original mechanistic works. ...
... As evident from Eq. 3 and Eq. 5, Fe 0 corrosion consumes H + and induces a significant increase in the pH value of the solution. A concomitant decline in solution redox potential (Eh) has been documented (Matheson andTratnyek 1994, Singh et al. 2023). In other words, irrespective of the presence of any contaminant, the immersion of Fe 0 in a system may lead to the development of highly reducing conditions. ...
Permeable reactive barriers (PRBs) containing metallic iron (Fe0) as reactive materials are currently considered as an established technology for groundwater remediation. Fe0 PRBs have been introduced by a field demonstration based on the fortuitous observation that aqueous trichloroethylenes are eliminated in Fe0-based sampling vessels. Since then, Fe0 has been tested and used for treating various biological (e.g., bacteria, viruses) and chemical (organic and inorganic) contaminants from polluted waters. There is a broad consensus on the view that "reactivity loss" and "permeability loss" are the two main problems hampering the design of sustainable systems. However, the view that Fe0 is a reducing agent (electron donor) under environmental conditions should be regarded as a distortion of Corrosion Science. This is because it has been long established that aqueous iron corrosion is a spontaneous process and results in the Fe0 surface being shielded by an oxide scale. The multi-layered oxide scale acts as a conduction barrier for electrons from Fe0. Accordingly, "reactivity loss", defined as reduced electron transfer to contaminants must be revisited. On the other hand, because "stoichiometric" ratios were considered while designing the first generation of Fe0 PRBs (Fe0 as reductant), "permeability loss" should also be revisited. The aim of this communication is to clarify this issue and reconcile a proven efficient technology with its scientific roots (i.e., corrosion science).
... Instead, mean chloroform, dichloromethane, and methane concentrations were plotted over time, and trends were compared visually. (Gillham & O'Hannesin, 1994) or 72 h (Matheson & Tratnyek, 1994) in aqueous solution. Feng and Lim (2005) found the reduction of chloroform (~1.5 mgL −1 ) in~50 and 1 h by microscale Fe 0 and nanoscale Fe 0 in ultrapure water at pH 7, respectively. ...
... Generated electrons reduce chlorinated compounds (denoted as RCl) such as chloroform, using them as electron acceptors (reduction half-reaction). The coupling of both half-reactions mediates the overall process (Equation 1) of reductive dechlorination by Fe 0 (Matheson & Tratnyek, 1994). ...
... Produced Fe 2+ itself is a reductant and excessive Fe 0 (also in our study; see the section on stoichiometry, kinetics, and pathway of chloroform transformation below) can also react with water under anaerobic conditions to produce trace amounts of hydrogen gas (H 2 ), another reductant and Fe 2+ (Equation 2). These reductants might be involved in the reductive dechlorination of chloroform (denoted as RCl in Equations 3 and 4) in our study (Matheson & Tratnyek, 1994;Rodríguez-Fernández et al., 2018). ...
... Transport of pesticides in environment depends upon their electrical potentials, adsorption and complex-formation abilities [13][14][15][16][17][18][19][20][21][22] . Atr previously has been the theme of dechlorination by using of zero valent metal ions and theoretical metal complex studies [16][17][18][19][20][21][22][23][24] . ...
... In literature, extensive analysis on dechlorination of chlorinated compounds through zero valent metals has been reported [21][22][23][24][25][26][27][28] . All the studies have demonstrated that dechlorination process enhanced at low pH values from 2 to 5, where, zero-valent metal ions get oxidized [24][25][26][27][28][29] . ...
... In literature, extensive analysis on dechlorination of chlorinated compounds through zero valent metals has been reported [21][22][23][24][25][26][27][28] . All the studies have demonstrated that dechlorination process enhanced at low pH values from 2 to 5, where, zero-valent metal ions get oxidized [24][25][26][27][28][29] . In the literature, there are detailed studies about the dechlorination of various organic compounds and atrazine have been reported [5][6][7][8][9][10][11][12][13][14][15] . ...
Atrazine is a broad spectrum herbicide of triazine family. It is a chlorine-containing molecule and it can persist in environment. Chemical and biochemical techniques are the main techniques used to decompose the chemicals. In pre-sent study, the dechlorination of atrazine (Atr) via reaction with Sn(II) ion under aqueous media at neutral pH condi-tions was studied. The observed dechlorinated metabolite was 4-Ethylamino-6-isopropylamino-[1,3,5]triazin-2-ol. Identification of dechlorinated product of Atr was performed by using spectroscopic (FTIR) and mass (ESI-MS) spectrometric analysis. The kinetics of the dechlorination of Atr was measured by using pseudo-first order kinetics. The observed reaction constants was, kobs = 6.11x10-2 (at 430 mg/ L of Atr), and kobs = 6.14 x10-2 (at 215 mg/ L of Atr). The calculated half-life (t1/2) period was, t1/2 = 0.204 d (at 430 mg/ L of Atr), and t1/2 = 0.205 d (at 215 mg/ L of Atr).
... These pesticides are organo-chlorinated compounds frequently, which means in their arrangement one or more chlorine atoms are present in addition to nitrous and/or carboxylic groups (Marussi and Vione, 2021;Yang et al., 2019b). In the start of the 1990 s, early research carried out and for an massive number of ecological scientists attractive material continuous to be a ZVI due to its non-poisonous, inexpensive, and influential reducing features (O'Hannesin, 1994;Matheson, 1994). nZVI used as an effective substitute for the specific remediation of chlorinated derivatives that put difficulties towards the atmosphere by their venomousness and harmful effects in soil and water. ...
... Apart from nanoparticles, to degrade insecticides there are various information on the use of nanotubes and nanostructures as well as thin films. TiO 2 nanotubes and TiO 2 (Matheson, 1994;Midik Ertosun et al., 2019) thin films were utilized for atrazine degradation and of organochlorine pesticides degradation respectively (Marussi and Vione, 2021;Yang et al., 2019b). Titania changed graphite anode by electro-oxidation management was efficaciously employed for the degradation of 2,4-dichlorophenol (Midik Ertosun et al., 2019;Rojas et al., 2015). ...
... There are mainly two schools; the clear discrepancies between them are identified by Noubactep (2015). The first school supports that Fe 0 is a strong reducing agent for contaminant reductive transformation: degradation of organics and/or precipitation of inorganics (Matheson and Tratnyek 1994, Weber 1996, Blowes et al. 1997. The second school subscribes that contaminants are adsorbed onto the surface of in situ generated iron corrosion products and/or are enmeshed within their matrix (Noubactep 2007, Noubactep 2008, Jiao et al. 2009, Noubactep 2009e, Ghauch et al. 2010, Noubactep 2010a, Noubactep 2011a, Noubactep 2012, Gheju et al. 2016, Noubactep 2022. ...
... Adsorption proceeds effectively by means of the electrostatic forces in a situation where the adsorbent and adsorbate are oppositely charged. The adsorption/co-precipitation concept (Noubactep 2007, Noubactep 2008 was clearly introduced as an extension of the reductive transformation concept (Matheson andTratnyek 1994, Weber 1996). However, its validity is widely questioned by investigators as expressed in five representative responses to recent comments authored by Noubactep (Elsner et al. 2007, Ghauch 2008, Kang and Choi 2008, Tratnyek and Slater-Blanc 2010, Napgal et al. 2012. ...
The concept that metallic iron (Fe0) is a reducing agent under environmental conditions has urged the large-scale application of Fe0 filters for environmental remediation and water treatment. During the past two decades, some 3,000 scientific articles have widely discussed the importance of processes yielding water treatment in Fe0/H2O systems. The current state-of-the-art knowledge is that Fe0 is the generator of (i) contaminant scavengers (iron hydroxides/oxides), and (ii) reducing agents (e.g. H/H2, FeII, green rusts, Fe3O4). In other words, contaminant reductive transformation in the presence of Fe0 is not mediated by electrons from the metal body (direct reduction).
The realization that Fe0 is not the reducing agent in Fe0/H2O systems has redirected fundamental researches on the operating mode of Fe0 filters. In this effort, a cationic azo dye (methylene blue, MB) has been presented as reactivity indicator to characterize changes in Fe0/H2O systems. The present study investigates the impact of contact time on the efficiency of Fe0/H2O systems. The research questions are "is there any direct relationship between experimental duration and system's efficiency?" If yes, how is the efficiency modified in the presence of natural additives such as manganese oxides (MnO2) and sand? Both research questions are justified by the evidence that the Fe0 surface is constantly shielded by an oxide scale which has been reported to mediate a 'reactivity loss' of Fe0 materials.
The methodology consists of (i) varying the experimental duration, and (ii) modifying the Fe0/H2O system by amending it with various amounts of MnO2 and sand. The efficiency of Fe0/sand/MnO2 systems for water treatment is characterized using methylene blue (MB) as reactivity indicator. Batch experiments using various weight ratios of Fe0 and the two additives were performed for up to six weeks (47 days). The impact of the intrinsic reactivity of MnO2 was characterized by using different types of MnO2. The MB discoloration process was investigated both under shaking and non-disturbed conditions.
The results clearly demonstrate the impact of increased contact time on the extent of MB discoloration in all tested systems (Fe0, Fe0/sand, Fe0/MnO2 and Fe0/sand/MnO2). As a rule, MB discoloration was improved by increased experimental duration. It was noted that the extent of MB discoloration is influenced by the diffusive (or advective) transport of MB from the solution to the reactive materials at the bottom of the test tubes. Without shaking, more time is needed for the transport of MB to the particles of tested materials. For experiments lasting for longer times, sand addition prevented Fe0 particles from compaction (cementation) at the bottom of the test-tubes. This enabled the long-term generation of iron hydroxides (new iron corrosion products) for the discoloration of MB by adsorption and co-precipitation. The same observation was made for Fe0/MnO2 systems. In other words, the addition of non-expansive materials (e.g. MnO2, sand) is necessary to sustain the efficiency of Fe0 filters. Shaking the test tubes increased the extent of MB discoloration by two different mechanisms: (i) speeding up the mass transport of MB solution towards the adsorptive materials, and (ii) speeding up the kinetics of Fe0 corrosion, creating new corrosion products. Discoloration processes occur due to MB diffusion and advection which are accelerated during the shaking operation. The results clearly delineate the complexity of the Fe0/MnO2/sand system and suggest that varying the experimental conditions will give more opportunities to discuss the efficiency of Fe0/H2O systems.
... The corrosion of ZVI drives reduction reactions that mitigate various contaminants; however, interactions with solutes in groundwater influence these reactions and affect the performance and reliability of the PRB in remediating pollutants (Zachara et al., 1987;Matheson and Tratnyek, 1994;Gillham and O'Hannesin, 2009). Table 2 presents several pathways of iron and standard reduction potentials for families of contaminants based on specific treatment pathways, which render these pollutants to less harmful forms. ...
... While it is true that co-precipitation, chemisorption, electrostatic physisorption, and size exclusion are all processes that occur, the extent to which these processes play a role in groundwater remediation depends on the interactions between the contaminant and iron species, which is highly pH-dependent. The seminal work of Cutler (1987), Gillham and O'Hannesin (1994), Matheson and Tratnyek (1994) provides evidence for direct electron transfer and the corrosion of ZVI in contact with chlorinated hydrocarbons; particularly the reductive dechlorination that occurs in steel sampling vessels and steel pipe lacking moisture or oxygen. By ignoring the role of electron transfer from the ZVI matrix within a particle to the contaminant, the arguments of Noubactep and colleagues appear to focus on the role of electron transfer from ferrous species and neglect the fact that the low Eh, production of dihydrogen, and oxidation of ZVI suggest that the corrosion of ZVI is what continues to drive reduction reactions for many years after application. ...
Permeable reactive barriers (PRBs) are used for groundwater remediation at contaminated sites worldwide. This technology has been efficient at appropriate sites for treating organic and inorganic contaminants using zero-valent iron (ZVI) as a reductant and as a reactive material. Continued development of the technology over the years suggests that a robust understanding of PRB performance and the mechanisms involved is still lacking. Conflicting information in the scientific literature downplays the critical role of ZVI corrosion in the remediation of various organic and inorganic pollutants. Additionally, there is a lack of information on how different mechanisms act in tandem to affect ZVI-groundwater systems through time. In this review paper, we describe the underlying mechanisms of PRB performance and remove isolated misconceptions. We discuss the primary mechanisms of ZVI transformation and aging in PRBs and the role of iron corrosion products. We review numerous sites to reinforce our understanding of the interactions between groundwater contaminants and ZVI and the authigenic minerals that form within PRBs. Our findings show that ZVI corrosion products and mineral precipitates play critical roles in the long-term performance of PRBs by influencing the reactivity of ZVI. Pore occlusion by mineral precipitates occurs at the influent side of PRBs and is enhanced by dissolved oxygen and groundwater rich in dissolved solids and high alkalinity, which negatively impacts hydraulic conductivity, allowing contaminants to potentially bypass the treatment zone. Further development of site characterization tools and models is needed to support effective PRB designs for groundwater remediation.
... It should be noted that secondary competing reactions can take place at electrode surfaces which can lower the efficiency of the EOIF system. For example, depending on the system pH, hydrolysis or oxidation of Fe þ2 ðaqÞ can lead to the formation of either aqueous ferric (Fe þ3 ðaqÞ Þ or ferrous hydroxide (Fe OH ð Þ 2ðsÞ Þ precipitates 58,73 . Chloride ions can also react at the anode to form chlorine gas or are adsorbed at the anode by the surface polarization 74,75 . ...
Achieving net-zero emissions by 2050 requires the development of effective negative emission techniques, including ocean-based approaches for CO 2 sequestration. However, the implementation and testing of marine CO 2 removal (mCDR) techniques such as ocean iron fertilization (OIF) or ocean alkalinity enhancement (OAE) face significant challenges. Herein, a novel self-operating electrochemical technology is presented that not only combines OIF and OAE, but also recovers hydrogen gas (H 2 ) from seawater, hence offering a promising solution for achieving quantifiable and transparent large-scale mCDR. Experimental results show that the electrochemical OIF (EOIF) can not only increase the concentration of ferrous iron (Fe ⁺² ) by 0–0.5 mg/L, but also significantly increases the seawater pH by 8% (i.e., a 25% decrease in the hydrogen ions concentration). The release of iron (Fe ⁺² /Fe ⁺³ ) can be regulated by adjusting the magnitude of the electric current and its form (e.g., pulsed current and polarity reversal), as well as by optimizing the electrode material and geometry. In certain ocean regions, enhanced iron concentrations stimulate the naturally occurring biological carbon pump (BCP), leading to increased phytoplankton growth, CO 2 uptake, and subsequent export of carbon to the deep ocean. Simultaneously, the system increases seawater alkalinity and the buffer capacity, enhancing CO 2 solubility and storage in the shallow ocean through the solubility pump. The obtained measurements demonstrate the scalability of EOIF and its ability to operate using solar energy at a lower cost. Overall, the proposed EOIF technology offers a practical, effective, and sustainable solution for addressing climate change on a large scale.
... standard redox potential) [7]. Due to its environmentally friendly and cost-effective nature [8], ZVI shows a promising functional material for the reductive removal of various persistent pollutants in the environment, including HOCs [9], nitroaromatic hydrocarbons [10], dyes [11], phenolic compounds [12], HMs [13], etc. However, the widespread application of ZVI has been hindered by several limitations [14]. ...
Zero Valent Iron (ZVI), an ideal reductant treating persistent pollutants, is hampered by issues like corrosion, passivation, and suboptimal utilization. Recent advancements in nonmetallic modified ZVI (NM-ZVI) show promising potential in circumventing these challenges by modifying ZVI's surface and internal physicochemical properties. Despite its promise, a thorough synthesis of research advancements in this domain remains elusive. Here we review the innovative methodologies, regulatory principles, and reduction-centric mechanisms underpinning NM-ZVI's effectiveness against two prevalent persistent pollutants: halogenated organic compounds and heavy metals. We start by evaluating different nonmetallic modification techniques, such as liquid-phase reduction, mechanical ball milling, and pyrolysis, and their respective advantages. The discussion progresses towards a critical analysis of current strategies and mechanisms used for NM-ZVI to enhance its reactivity, electron selectivity, and electron utilization efficiency. This is achieved by optimizing the elemental compositions, content ratios, lattice constants, hydrophobicity, and conductivity. Furthermore, we propose novel approaches for augmenting NM-ZVI's capability to address complex pollution challenges. This review highlights NM-ZVI's potential as an alternative to remediate water environments contaminated with halogenated organic compounds or heavy metals, contributing to the broader discourse on green remediation technologies.
... Moreover, the mats developing at NTE and SI develop really close or directly on waste steel chains and ballast from previous HOV descents. These anthropogenically introduced elements could release H 2 due to their reaction with surrounding seawater (11,(71)(72)(73), explaining the highest abundances of ZetaOTU 9 at these sites. ...
Zetaproteobacteria have been reported in different marine and terrestrial environments all over the globe. They play an essential role in marine iron-rich microbial mats, as one of their autotrophic primary producers, oxidizing Fe(II) and producing Fe-oxyhydroxides with different morphologies. Here, we study and compare the Zetaproteobacterial communities of iron-rich microbial mats from six different sites of the Lucky Strike Hydrothermal Field through the use of the Zetaproteobacterial operational taxonomic unit (ZetaOTU) classification. We report for the first time the Zetaproteobacterial core microbiome of these iron-rich microbial mats, which is composed of four ZetaOTUs that are cosmopolitan and essential for the development of the mats. The study of the presence and abundance of different ZetaOTUs among sites reveals two clusters, which are related to the lithology and permeability of the substratum on which they develop. The Zetaproteobacterial communities of cluster 1 are characteristic of poorly permeable substrata, with little evidence of diffuse venting, while those of cluster 2 develop on hydrothermal slabs or deposits that allow the percolation and outflow of diffuse hydrothermal fluids. In addition, two NewZetaOTUs 1 and 2 were identified, which could be characteristic of anthropic iron and unsedimented basalt, respectively. We also report significant correlations between the abundance of certain ZetaOTUs and that of iron oxide morphologies, indicating that their formation could be taxonomically and/or environmentally driven. We identified a new morphology of Fe(III)-oxyhydroxides that we named “corals.” Overall, our work contributes to the knowledge of the biogeography of this bacterial class by providing additional data from the Atlantic Ocean, a lesser-studied ocean in terms of Zetaproteobacterial diversity.
IMPORTANCE
Up until now, Zetaproteobacterial diversity studies have revealed possible links between Zetaproteobacteria taxa, habitats, and niches. Here, we report for the first time the Zetaproteobacterial core microbiome of iron-rich mats from the Lucky Strike Hydrothermal Field (LSHF), as well as two new Zetaproteobacterial operational taxonomic units (NewZetaOTUs) that could be substratum specific. We highlight that the substratum on which iron-rich microbial mats develop, especially because of its permeability to diffuse hydrothermal venting, has an influence on their Zetaproteobacterial communities. Moreover, our work adds to the knowledge of the biogeography of this bacterial class by providing additional data from the hydrothermal vent sites along the Mid-Atlantic Ridge. In addition to the already described iron oxide morphologies, we identify in our iron-rich mats a new morphology that we named corals. Finally, we argue for significant correlations between the relative abundance of certain ZetaOTUs and that of iron oxide morphologies, contributing to the understanding of the drivers of iron oxide production in iron-oxidizing bacteria.
... The coprecipitation procedures are highly efficient and straightforward chemical processes that can be used to synthesize IONPs in substantial amounts. 22 IONPs have gained a great deal of interest in various fields such as food preservation, 23 ferrofluids, antibacterial activity, 24 biosensor, 25 magnetic refrigeration for MRI, 26 cell sorting, 27 targeted drug delivery, 28 and hyperthermic cancer treatments, 29 because of their specific properties. Recently, resistant bacterial strains have emerged, making it imperative to develop new antibacterial agents from a wide range of areas. ...
Proper management and control measurements are needed to stop the spread of highly pathogenic E. coli isolates that cause urinary tract infections (UTI) by developing new antibacterial agents to ensure the safety of public health. Therefore, the present investigations were used to achieve the synthesis of iron oxide nanoparticles (IONPs) via a simple coprecipitation method using ferric nitrates Fe (NO3)3 as the precursor and hydrazine solution as the precipitator and to explore the antibacterial activity against eradicating Uropathogenic Escherichia coli (E. coli). The synthesized IONPs were further studied using a UV–vis spectrophotometer, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopic (SEM) analysis. The maximum surface plasmon resonance peak was observed as absorption at 320 nm in a colloidal solution to validate the synthesis of IONPs. The FT-IR analysis was used to identify different photoactive functional groups that were responsible for the reduction of Fe (NO3)3 to IONPs. The crystalline nature of synthesized IONPs was revealed by XRD patterns with an average particle size ranging as 29 nm. The SEM image was employed to recognize the irregular morphology of synthesized nanoparticles. Moreover, significant antibacterial activity was observed at 1 mg/mL stock solution but after (125, 250, and 500 μg/mL) dilution, the synthesized IONPs showed moderate activity and became inactive at lower concentrations. The morphological and biochemical tests were used to confirm the presence of E. coli in the samples. Furthermore, the minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) were carried out to determine the inhibitory concentrations for the isolated bacteria. The isolated E. coli were also subjected to antibiotic sensitivity testing that showed high resistance to antibiotics such as penicillin and amoxicillin. Thus, the findings of this study were to use IONPs against antibiotic resistance that has been developed in an inappropriate way.
... It has been recognized as the main pathway of contaminant transformation by Fe0 in the subsurface. In the presence of oxygen, the contaminants can also be oxidized by hydroxyl radical and the other oxidants generated during the corrosion process of FeO [26,27]. The bactericidal action of Escherichia coli by zero-valent iron nanoparticles could be due to the infiltration of the small particles (ranging from 10 -80 nm) into E. coli membranes. ...
Silica coated superparamagnetic Iron Oxide Nanoparticles (SPIONPS) have plenty of applications in biomedical engineering particularly drug delivery systems due to their unique efficiency and very negligible side effects. SPIONPS was synthesized rapidly using an aqueous fruit extract of Ficus carica. Single step green biosynthetic method was adapted to prepare SPIONPS in an environmentally friendly approach. The synthesized SPIONPS was subjected to different analytical studies. Results observed from UV-Visible spectroscopy and powder X-ray diffraction analysis confirms the formation of iron oxide nanoparticle. Further, the vibrating sample magnetometer confirms the paramagnetic character of the prepared sample. Particle size and scanning electron microscope analysis validate the formation of the nanoparticle. The antioxidant activity and phytochemical analysis of fruit extract and SPIONPS were analyzed to explore the presence of biomolecules, which are responsible for the reduction and stabilization of SPIONPS. In addition to the excellent superparamagnetic properties of SPIONPS are antibacterial activity against E.coli and B.stearothermophilus species. The biocompatibility of SPIONPS with the HepG-2 cell line shows its potential usefulness in drug delivery applications.
... Three possible dechlorination mechanisms of chloroorganics by Fe have been proposed: (i) the direct transfer of electrons from Fe (ii) reduction by H 2 ; (iii) reduction by Fe 2+ . Both Fe 2+ and H 2 are produced from the corrosion of Fe (Lien and Zhang, 2007;Matheson and Tratnyek, 1994). In this study, we conducted experimental tests to evaluate these three mechanisms and identify the true mechanism underlying Fe's role in the dechlorination of 2,4-DCP. ...
Abstract: The basic structural unit of palygorskite (P) consists of rod-shaped crystals with a diameter ranging from 20 to 70 nm. However, due to strong hydrogen bonding and electrostatic forces, most palygorskite rod crystals tend to aggregate, limiting its nanomaterial properties in practical application. To address this limitation, the study focused on dissociating palygorskite aggregates and incorporating them into nanorod palygorskite-loaded Fe/Ni bimetallic nanoparticles (nP-nFe/Ni) synthesis. This approach facilitated the dissociation of palygorskite aggregates and enabled the dispersion of Fe/Ni nanoparticles by palygorskite nanorods. The results revealed that the BET specific surface area of nP-nFe/Ni was significantly higher at 86.17 m2/g compared to 33.62 m2/g for nFe/Ni. Consequently, the dechlorination efficiency of nP-nFe/Ni for 2,4-dichlorophenol (2,4-DCP) at 120 min was 22.4% higher than that of nFe/Ni, despite nP-nFe/Ni containing only 35.1% of the Fe content found in nFe/Ni at the same dosage. Moreover, it was observed that acidic conditions favor maximum dichlorination, while higher temperatures enhance the dechlorination rate. The action mechanism of Fe was identified as the generation of H2, which is catalyzed by Ni to form active hydrogen (H*) that attack the C-Cl bonds of 2,4-DCP for hydrodechlorination. Ni played a vital role in catalyzing H2 conversion to H*, accelerating H2 production by Fe, and inhibiting Fe passivation. These findings are crucial for the application of nano iron technology and nano-scale palygorskite in water and wastewater treatment.
... Reductive dechlorination of CF using ZVI is well known [58][59][60][61][62][63][64] and there is also extensive literature on the catalytic hydrodechlorination of CF over palladium, rhodium, and other catalysts, pure or on different supports, alone or bi-metallic, and both, in gas and liquid phase reactions [7,8,[65][66][67][68][69][70][71][72][73][74][75][76][77][78][79]. Typically, those studies focus on the degradation in terms of the catalysts' activities, selectivities, the role of grain sizes and support materials, and on the long-term performance of the catalysts. ...
Water pollution is calling for a sustainable remediation method such as the use of metallic iron (Fe ⁰ ) to reduce and filter some pollutants, yet the reactivity and hydraulic conductivity of iron filters decline over time under field conditions. Here we review iron filters with focus on metallic corrosion in porous media, flaws in designing iron filters, next-generation filters and perspectives such as safe drinking water supply, iron for anaemia control and coping with a reactive material. We argue that assumptions sustaining the design of current Fe ⁰ filters are not valid because proposed solutions address the issues of declining iron reactivity and hydraulic conductivity separately. Alternatively, a recent approach suggest that each individual Fe ⁰ atom corroding within a filter contributes to both reactivity and permeability loss. This approach applies well to alternative iron materials such as bimetallics, composites, hybrid aggregates, e.g. Fe ⁰ /sand, and nano-Fe ⁰ . Characterizing the intrinsic reactivity of individual Fe ⁰ materials is a prerequisite to designing sustainable filters. Indeed, Fe ⁰ ratio, Fe ⁰ type, Fe ⁰ shape, initial porosity, e.g. pore size and pore size distribution, and nature and size of admixing aggregates, e.g. pumice, pyrite and sand, are interrelated parameters which all influence the generation and accumulation of iron corrosion products. Fe ⁰ should be characterized in long-term experiments, e.g. 12 months or longer, for Fe dissolution, H 2 generation and removal of contaminants in three media, i.e., tap water, spring water and saline water, to allow reactivity comparison and designing field-scale filters.
Quiescent batch experiments were conducted to evaluate the influences of Cl–, F–, HCO3–, HPO42–, and SO42– on the reactivity of metallic iron (Fe0) for water remediation using the methylene blue (MB) method. Strong discoloration of MB indicates high availability of solid iron corrosion products (FeCPs). Tap water was used as an operational reference. Experiments were carried out in graduated test tubes (22 mL) for up to 45 d, using 0.1 g of Fe0 and 0.5 g of sand. Operational parameters investigated were (i) equilibration time (0 to 45 d), (ii) 4 different types of Fe0, (iii) anion concentration (10 values), and (iv) use of MB and Orange II (O-II). The degree of dye discoloration, the pH, and the iron concentration were monitored in each system. Relative to the reference system, HCO3– enhanced the extent of MB discoloration, while Cl–, F–, HPO42–, and SO42– inhibited it. A different behavior was observed for O-II discoloration: in particular, HCO3– inhibited O-II discoloration. The increased MB discoloration in the HCO3– system was justified by considering the availability of FeCPs as contaminant scavengers, pH-increase, and contact time. The addition of any other anion initially delays the availability of FeCPs. Conflicting results in the literature can be attributed to the use of inappropriate experimental conditions. The results indicate that the application of Fe0–based systems for water remediation is a highly site-specific issue which has to include the anion chemistry of the water.
During the last century, large scale production of halogenated organic compounds and heavy
metals, specifically by industrial processes, and the inappropriate management of those products caused
a wide spreading of a variety of hazardous contaminants into the environment including a massive
contamination of the groundwater. Their presence and persistence have significantly influenced human
health and the environment. Recently, many technologies have been employed in order to reduce their
impacts. However, the majority of those technologies did not achieve the target, because of their high cost
and low efficacy in the reduction of contaminants. Nevertheless, a new technology of synergetic
interactions of (nZVI) zero-valent iron nanoparticles with two types of anaerobic bacteria; the
organohalide respiring bacteria (OHRB) and sulfate-reducing bacteria (SRB), have been investigated as
a promising technology for in-situ groundwater remediation. This powerful technique was successfully
utilized for the reduction of pollutants and converted to environmentally benign forms. This article
reviews and emphasizes the coupling effect of (nZVI-OHRB) and (nZVI-SRB) on the remediation process
of contaminated sites, in addition to a detailed illustration of the mechanism of the integration of (nZVIOHRB) and (nZVI-SRBs), and discussion of the influencing factors on the integrated system. Actually,
the technology presented here, though proven successfully, needs more case studies to better
understanding of the interactions between microorganisms and nZVI, as well as with the surrounding
environment for a better efficacy and finding the best solutions.
Metallic iron (Fe0) is readily available worldwide and it has shown promise for water treatment in filtration systems. Fe0 filters remove physical contamination (e.g. colloids, suspended particles), pathogens (e.g. bacteria, viruses), and micro-pollutants (e.g. arsenic, nitrate, pesticides, pharmaceuticals) from polluted waters. Accordingly, Fe0 filters can be used for water treatment applications where other materials (e.g. activated carbon, biochar, bone char) are economically or logistically infeasible. Therefore, Fe0 filters are a good candidate to help low-income communities in their efforts to achieve universal access to safe drinking water by 2030. The objective of this chapter is to summarize available knowledge on the design of Fe0 filters in order to booster their large scale application at household and small community levels. Optimal conditions for Fe0 filters include the rational choice of the used materials building the reactive zone (Fe0 and other aggregates), the Fe0 ratio in the reactive zone, the Fe0 mass (e.g. size of the filter or number of filters in series), and the contact time (flow velocity). The proper combination of these design parameters is discussed. Results show that: (i) all reactive Fe0 can be used for efficient water filters, (ii) only porous Fe0 materials are suitable for sustainable water filters, (iii) well-designed hybrid Fe0/aggregate systems are also sustainable, (iv) the major limitation of Fe0 filters is the lack of knowledge on the long-term corrosion rate. Future research efforts should last for months or years.
Advances in Drinking Water Purification
Small Systems and Emerging Issues
1st Edition - January 17, 2024
Editor: Sibdas Bandyopadhyay
Paperback ISBN: 9780323917339
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eBook ISBN: 9780323972024
Description
Advances in Drinking Water Purification: Small Systems and Emerging Issues captures the knowledge and impact on the performance of various types of water purification technologies and identities the need for further development with a view to carry forward the SDG global targets of achieving safe and affordable drinking water. The book bridges the knowledge gap between various types of treatability options which is essential for selection of suitable treatment systems and augmentation in the desirable levels of specific contaminants. It focuses on providing the scope of selecting location specific technology options by presenting multiple approaches for treatment of most crucial toxic contaminants/pathogens.
In addition, it provides insights into the effect of nature of impurities and selection of treatment options on the global quality of drinking water, comprising its possible impacts on the efficiency of the techniques used and thus on the safety of drinking water. This information is indispensable in identifying the appropriate technology depending on the socioeconomic conditions to address the problem of decontamination in drinking water.
The rheological behavior of a xanthan gum (XG) suspension with Fe-based nanoparticles (Fe-NPs), e.g., nanoparticles of zerovalent iron (nZVI) and Fe3O4 (nFe3O4), needs to be understood for better injection of Fe-NPs for groundwater remediation. In this study, the rheological behavior of a XG suspension of nZVI and nFe3O4 was investigated at different particle concentrations. The Ostwald, Sisko, Williamson, and Cross models were employed to fit the rheological behavior of the suspensions for quantitatively describing the effect of the particles. The results showed that the viscosity of the XG solutions decreased with increasing particle concentrations and they maintained shear thinning properties. The Cross model was the best among the four models to describe the shear thinning behavior of the XG solution in the presence of the particles. According to Cross model analysis, increasing particle concentrations increased the degree of shear thinning behavior, as indicated by the increase of the power index (n). Also, the relaxation time (λ) decreased with increasing particle concentrations, which indicated an increase of molecule movement of XG. Compared with nFe3O4, nZVI resulted in a larger decrease in viscosity and a larger increase in the degree of shear thinning behavior. There was a good linear relation between n and λ for the suspensions (R2 = 0.85), which indicated that increasing molecule movement of XG was an important mechanism for the particles to intensify the shear thinning rheological behavior of the XG suspension of Fe-NPs. This study added insight into the knowledge of the rheological properties of the XG suspension of Fe-NPs, which is of importance for the field injection effort.
Sulfated zero-valent iron (SZVI) has shown promising applications in wastewater treatment. However, the rapid decline in the reactivity of SZVI with time limits its real practice. To mediate this problem, partial aging was proposed to improve the reactive durability of SZVI. Taking Cr(VI) as the target contaminant, we found that the aged ZVI (AZVI) gradually lost reactivity as aging time increased from 0.5 to 2 d. Counter-intuitively, the partially aged SZVI (ASZVI) showed greater reactivity than SZVI when exposed to oxygenated water for a period ranging from 0.5 to 14 d. In addition, the ASZVI with 0.5 d of aging time (ASZVI-0.5) not only maintained reactivity in successive runs but also increased the Cr(VI) removal capacity from 9.1 mg/g by SZVI to 19.1 mg/g by ASZVI-0.5. Correlation analysis further revealed that the electron transfer from the Fe ⁰ core to the shell was mediated by the conductive FeS and FeS 2 in the subshell of ASZVI. Meanwhile, the lepidocrocite and magnetite on the surface of ASZVI facilitated Cr(VI) adsorption and subsequent electron transfer for Cr(VI) reduction. Moreover, the iron (hydr)oxide shell could retain the conductive FeS and FeS 2 in the subshell, allowing ASZVI to reduce Cr(VI) efficiently and sustainably. In general, partial aging can enhance the reactive durability of ZVI when coupled with sulfidation and this synergistic effect will be beneficial to the application of SZVI-based technology for wastewater treatment.
From a physical‐chemical viewpoint, every polymeric ion exchange resin bead is a crosslinked polyelectrolyte that is insoluble in water. Today, tens of ion exchange resin manufacturers around the world produce hundreds of different products. As different as they may appear, these ion exchangers are well defined and the specific interactions are well characterized by five independent composition variables, namely, matrix, functionality, crosslinking, pore structure and physical configuration. In addition to the diverse groups of ion exchangers characterized by these five composition variables, a new class of polymeric‐inorganic ion exchangers has been synthesized. Here, a dispersed phase of metal or metal oxide nanoparticles (MNPs or MONPs) is embedded in the ion exchanger phase; together they offer a synergy not available otherwise. The resulting new materials are heterogeneous, even at the sub‐10 nm scale, and termed “Hybrid Ion Exchangers” or HIX. In such a material, the host (i.e. polymer beads) improves the hydraulic permeability in the flow‐through systems with no apparent influence on the behavior of the metal and metal oxide nanoparticles. This article emphasizes how the choice of the functional groups of the polymeric host materials can be harnessed to alter (enhance or diminish) the intrinsic properties of the nanomaterials.
Chloroform (CF) is a widely used chemical reagent and disinfectant and a probable human carcinogen. The extensive literature on halocarbon reduction with zerovalent iron (ZVI) shows that transformation of CF is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. In this study, an alternative method of ZVI modification─involving simultaneous sulfidation and nitridation through mechanochemical ball milling─was developed and shown to give improved degradation of CF (i.e., higher degradation rate and inhibited H2 evolution reaction). The composite material (denoted as S-N(C)-ZVI) gave synergistic effects of nitridation and sulfidation on CF degradation. A complete chemical reaction network (CRN) analysis of CF degradation suggests that O-nucleophile-mediated transformation pathways may be the main route for the formation of the terminal nonchlorinated products (formate, CO, and glycolic polymers) that have been used to explain the undetected products needed for mass balance. Material characterizations of the ZVI recovered after batch experiments showed that sulfidation and nitridation promoted the formation of Fe3O4 on the S-N(C)-ZVI particles, and the effect of aging on CF degradation rates was minor for S-N(C)-ZVI. The synergistic benefits of sulfidation and nitridation on CF degradation were also observed in experiments performed with groundwater.
Granular metallic iron (gFe0) materials have been widely used for eliminating a wide range of pollutants from aqueous solutions over the past three decades. However, the intrinsic reactivity of gFe0 is rarely evaluated and existing methods for such evaluations have not been standardized. The aim of the present study was to develop a simple spectrophotometric method to characterize the intrinsic reactivity of gFe0 based on the extent of iron dissolution in an ascorbic acid (AA-0.002 M or 2 mM) solution. A modification of the ethylenediaminetetraacetic acid method (EDTA method) is suggested for this purpose. Being an excellent chelating agent for FeII and a reducing agent for Fe III , AA induces the oxidative dissolution of Fe0 and the reductive dissolution of FeIII oxides from gFe0 specimens. In other words, Fe0 dissolution to FeII ions is promoted while the further oxidation to FeIII ions is blocked. Thus, unlike the EDTA method that promotes Fe0 oxidation to FeIII ions, the AA method promotes only the formation of FeII species, despite the presence of dissolved O2. The AA test is more accurate than the EDTA test and is considerably less expensive. Eight selected gFe0 specimens (ZVI1 through ZVI8) with established diversity in intrinsic reactivity were tested in parallel batch experiments (for 6 days) and three of these specimens (ZVI1, ZVI3, ZVI5) were further tested for iron leaching in column experiments (for 150 days). Results confirmed the better suitability (e.g. accuracy in assessing Fe0 dissolution) of the AA test relative to the EDTA test as a powerful screening tool to select materials for various field applications. Thus, the AA test should be routinely used to characterize and rationalize the selection of gFe0 in individual studies.
Purification of wastewater that contains residual chlorinated phenolic compounds is important for water conservation. [email protected] bimetallic materials have the capability of degrading chlorinated phenolic pollutants, but the processes of electron transfer and active species generation have not been verified directly. In this work, the [email protected] bimetallic material, of which copper exhibits a special surface, obtained by a facile displacement reaction, was applied for 2,4-dichlorophenol (2,4-DCP) degradation. The degradation efficiency of 2,4-DCP, which is highly related to H2O2 generation and •OH production, can reach 100% at 30 min with an [email protected] dosage of 2 g/L in ambient atmosphere. The porous shell structure of [email protected] provides convenient channels for iron ion release and electron transport and transformation. According to DFT (density functional theory) calculations, Cu2O (1 1 1) on the surface of particles and Cu (1 1 1) with Fe doping possess higher selectivity and catalytic activity for H2O2 in situ generation through the 2e⁻ oxygen reduction reaction (ORR) than Cu (1 1 1). The ⋅OH, which was the following product of *OOH and H2O2, was a strategic radical for 2,4-DCP degradation. The coexistence of •OH and •H in the Fe-Cu degradation system was directly proven. The intermediate products of 2,4-DCP degradation were identified, and the degradation intermediates revealed that the degradation function for 2,4-DCP mainly resulted from the synergistic action of ⋅H and ⋅OH. The highly efficient self-catalyst [email protected] can be a promising material for chlorinated phenolic compound removal in wastewater purification.
The environmental and health hazards created by industrial chemicals and consumer products must be minimized. For safer products to be designed, the relationships between structure and toxicity must be understood at the molecular level. Green chemistry combined with free radical research has the potential to offer innovative solutions to such problems.
Some solutions are "greener then others", and many necessitate significant financial investment. New technology will only be adopted if real benefit can be shown and sometimes adaptation of existing methods is the best option. The efficiency of processes must be assessed, not only in terms of the final yield, but also cost, environmental impact and waste toxicity.
This practical and concise guide showcases the sustainable methods offered by green free radical chemistry and summarizes the fundamental science involved. It discusses the pros and cons of free radical chemistry in aqueous systems for synthetic applications. All transformation steps are covered including initiation, propagation, and termination. Useful background knowledge is combined with examples, including industrial scale processes for pharmaceuticals and fine chemicals.
The book helps chemists to choose appropriate methods for achieving maximum output using a modern, environmentally conscious approach. It shows that, armed with an elementary knowledge of kinetics, an understanding of the mechanistic and technical aspects, and some common sense, it is possible to harness free radicals for use in a broad range of applications.
Streamlining Green Free Radical Chemistry is aimed at chemists, engineers, materials scientists, biochemists and biomedical experts, as well as undergraduate and postgraduate students. It encourages readers to question conventional methods and move towards the "Benign-by-Design" approach of the future. References to further reading are provided at the end of each chapter.
Chloroform, a probable human carcinogen, is mainly produced anthropogenically for industrial use and may be released to the environment from a large number of sources related to its manufacture and use, including pulp and paper mills, hazardous waste sites, and sanitary landfills. Remediation of chloroform through conventional technologies has been met with limited success due to the conditions required and the formation of hazardous substances such as dichloromethane. The objective of this study was to investigate chloroform reduction in multicontaminated fine‐textured soil using zero‐valent iron (Fe0) in anaerobic microcosms. Four amended matrices were tested: simple matrix control (glass beads), soil matrix control (glass beads + soil), Fe0 in a simple matrix (glass beads + Fe0), and Fe0 in a soil matrix (soil + Fe0). Headspace chloroform and its transformation products dichloromethane, chloromethane, and methane were measured over 230 days and during short intervals in the initial 3 days. Chloroform (~0.3 mM initial mass) persisted in both control microcosms but was completely transformed in microcosms containing soil + Fe0 by 12 h and glass beads + Fe0 by 48 h. Reductive dechlorination of chloroform occurred with simultaneous production of dichloromethane (~0.11 to 0.14 mM mass) and chloromethane (~0.02 to 0.13 mM mass). Little methane (~0.07 to 0.26 μM mass) production as an end product of chloroform reduction was observed in microcosms amended with Fe0. Produced dichloromethane and chloroform almost disappeared by 230 days. The results showed a complete chloroform transformation pathway that has good potential for the remediation of chlorinated compounds in fine‐textured soil. The role of soil clay minerals in redox reactions can be further investigated to improve the reductive dechlorination of chlorinated compounds in contaminated environments.
Reductive hydrodechlorination is an effective approach to enhance the degradation rate of chlorinated herbicides such as alachlor, which are frequently detected in ground and surface water. In this study, a cobalt porphyrin complex with eight triazole units and alkyl chains, CoPor8T, was synthesized to catalyze the reductive hydrodechlorination of alachlor. Mechanistic study was performed using a combination of voltametric, spectroscopic, and electrospectroscopic techniques. A conversion yield of 84 % at −1.8 V vs. Fc/Fc⁺ and chloride ion concentration of 96 % was obtained after electrocatalysis. This work provides a new avenue of using molecular catalysts for electrocatalytic chlorinated herbicide remediation.
Ball milling is an effective technique to not only activate and reduce the size of commercial microscale zero valent iron (mZVI) but also to mechanochemically sulfidate mZVI. Yet, little is known about the difference between how chlorinated ethenes (CEs) interact with ball milled mZVI (mZVIbm) and mechanochemically sulfidated mZVI (S-mZVIbm). We show that simple ball milling exposed the active Fe0 sites, while mechanochemical sulfidation diminished Fe0 sites and meanwhile increased S2- sites. Mechanochemical sulfidation with [S/Fe]dosed increased from 0 to 0.20 promoted the particle reactivity most for TCE dechlorination (∼14-fold), followed by PCE and 1,1-DCE while it diminished the reactivity for trans-DCE (∼0.4-fold), cis-DCE (∼0.02-fold) and VC (∼0.002-fold) compared to simple ball milling. Sulfidation also improved the electron efficiency of CE dechlorination, except for cis-DCE and VC. The kSA of cis-DCE, VC and trans-DCE dechlorination positively correlated with surface Fe0 content, suggesting their dechlorination was mainly mediated by Fe0 site or reactive atomic hydrogen. The kSA of TCE dechlorination positively correlated with surface S2- content and the dechlorination mainly occurred on S2- sites via direct electron transfer. Increased sulfidation favored direct electron transfer mechanism. The kSA of PCE and 1,1-DCE was not dependent on either parameter and their dechlorination was equally achieved through either mechanism.
Zero-valent iron (ZVI) is one of the most widely used engineered materials for the remediation of chlorinated ethenes in the subsurface environment. The material has been widely used in various in situ remediation technologies including Fe-permeable reactive barriers (Fe-PRB) and subsurface injection of nanoscale zero-valent iron (nZVI) for contaminant plume attenuation and source zone remediation. However, there are two serious drawbacks when ZVI is used for the remediation of chlorinated ethenes: (i) ZVI tends to undergo rapid passivation which undermines its longevity for remediation applications, and (ii) ZVI has low dechlorination reactivity in the absence of catalyst additives. Bimetallic nanoparticles (BNPs), prepared by doping a small amount of catalytic metals (e.g., Pd or Ni), can significantly enhance the particles’ dechlorination reactivity. However, BNPs suffer rapid deactivation when exposed to groundwater media, and the BNPs deactivation mechanisms are still poorly understood.
The first part of this dissertation aims to investigate Ni-Fe BNPs and Pd-Fe BNPs deactivation mechanisms when exposing them to common groundwater solutes. Aging experiments were conducted by pre-immersing fresh prepared BNPs in solutions containing different groundwater solutes for 24 h prior to reacting the particles with trichloroethene (TCE) to assess their dechlorination reactivity. Analyses of reaction kinetics and product distribution and stable carbon isotope fractionation measurements suggest that Pd-Fe BNPs were sensitive to solute-induced deactivation, particularly in solutions containing chloride, bicarbonate, nitrate or sulfite ions. Although Ni-Fe BNPs possess higher electrochemical stability than Pd-Fe BNPs in the aqueous media, strong deactivation was observed in sulfate, nitrate, and phosphate solutions. Multiple modes of BNP deactivation were proposed for the two types of BNPs.
To overcome the intrinsic limitations of conventional and bimetallic ZVI materials, the second part of this dissertation aims to develop a new form of ZVI with higher dechlorination reactivity without the use of catalyst additives and a greater resistance to environmental passivation. A surface sulfidation treatment was designed and optimized for laboratory-made nZVI and commercial ZVI. The sulfided nZVI demonstrates remarkable improvements in dechlorination rates for chlorinated ethenes. Aging experiments indicated that sulfided nZVI possesses greater stability and maintains its dechlorination reactivity over long-term aging processes. Applying sulfidation treatment to commercial iron results in more efficient tetrachloroethene (PCE) and TCE degradation. Sulfidation treatment therefore represents a simple yet promising approach to increase the reactivity of ZVI using earth-abundant reagents in place of precious catalyst metals.
This article summarizes and systematizes the current understanding of abiotic and biotic chemistry of halogenated aliphatic compounds. Knowledge of abiotic transformations can provide a conceptual framework for understanding biologically mediated transformations. Most abiotic transformations are slow, but they can still be significant within the time scales commonly associated with ground water movement. In contrast, biotic transformations typically proceed much faster, provided that there are sufficient substrate and nutrients and a microbial population that can mediate such transformation. Recent studies, which describe transformations of halogenated aliphatic compounds in microbial and mammalian systems, are also discussed. These studies reveal broad patterns of transformation in biological systems in general. 114 references, 8 figures, 12 tables.
This article discusses some of the changes which can occur at interfaces due to reaction or annealing. For chemically unstable interfaces, the atomic recombinations result in formation of new phases, which can even be amorphous in the initial stages. When no further chemical evolution takes place, physical rearrangement can have important consequences on the structure and properties. Examples are drawn from work on Ti-Si, Pt-GaAs, Ti-Si-O-N, Al-Si and TiSi2-Si.
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@inproceedings{OPL:8147053,author = {Sinclair,R. and Ko,D. H. and Konno,T. J. and Nolan,T. P.},title = {Reactions at Solid Interfaces},booktitle = {Symposium Cb – Structure and Properties of Interfaces in Materials},series = {MRS Proceedings},volume = {238},year = {1991},doi = {10.1557/PROC-238-269},URL = {http://journals.cambridge.org/article_S1946427400454813},}
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Reactions at Solid Interfaces
R. Sinclair,D. H. Ko,T. J. Konno and T. P. Nolan (1991).
MRS Proceedings , Volume 238 , 1991, 269
http://journals.cambridge.org/action/displayAbstract?aid=8147053
The code will display like this
Reactions at Solid Interfaces
R. Sinclair,
D. H. Ko,
T. J. Konno
and T. P. Nolan 1991
MRS Proceedings,
,Volume238,
1991,
269
http://journals.cambridge.org/abstract_S1946427400454813
R. Sinclair,
D. H. Ko,
T. J. Konno
and T. P. Nolan
(1991).
Reactions at Solid Interfaces.
MRS Proceedings,
238,
269
doi:10.1557/PROC-238-269.
0Comments
The reaction sequence between a chlorinated solvent, 1,1,1-trichloroethane, and aluminum is explained and a proposed reaction mechanism is given. The addition of a proper inhibitor to the solvent stops the vigorous solvent-metal interaction and allows solvent use in aluminum metal cleaning applications. Twenty-two compounds were evaluated as inhibitors, at reflux temperatures, of the reaction of aluminum with 1,1,1-trichloroethane. Minimum concentrations needed to inhibit the reaction are tabulated. Certain structure-activity relationships of the tested inhibitors are examined. It is suggested that the inhibitor competes with the solvent for the aluminum chloride produced at micro corrosion sites. Successful inhibition involves complexing of the chemisorbed aluminum chloride product with electronegative groups of the inhibitor. The resultant complex is insoluble in the solvent and acts as a plug or cover over the original reaction site.
The transformation of volatile chlorinated hydrocarbons in aqueous phase containing free ferrous and sulfide ions with and without light irradiation were investigated to evaluate the effect of these reducing ions on the dechlorination of chlorinated hydrocarbons. In the presence of the ferrous ion alone, 84% of the original carbon tetrachloride (CT) was transformed to chloroform within 33 days, and a removal efficiency of 99% was reached when the solution was irradiated by visible light. However, carbon tetrachloride did not appear to be reactive in other media containing sulfide and/or bound ferrous ions. 1,1,1-trichloroethane and tetrachloroethylene were less susceptible than carbon tetrachloride to the reductive dechlorination. No transformation was observed for these two compounds in different types of media in 33 days. Oxidationreduction potential (ORP) measurements showed that carbon tetrachloride could be depleted only when ORP of the environment was below 360 mV (relative to standard hydrogen electrode). This study indicates that free ferrous ion is an active reducing agent for the dechlorination of CT, but has little effect on the transformation of 1,1,1-trichloroethane and tetrachloroethylene, whereas, free sulfide and bound ferrous ions do not appear to have the capability of dechlorination for these heavily chlorinated hydrocarbons.
Further observations on the reaction show that vacuum treatment of aluminum decreases the induction time from 70 to about 5 min. This may be a consequence of removing water and perhaps also oxygen from the oxide film. Vacuum treatment has no effect on the long induction time for 2.43 per cent Mg‐Al alloy.
Corrosion products in reduce to zero the induction time of pure aluminum. It was found that is responsible, and that ferric chloride acts similarly. These chlorides, however, have no effect on the corrosion rate.
Reaction of aluminum with carbon tetrachloride vapor is similar to its behavior in boiling liquid, the induction time and corrosion rates being approximately the same.
It is concluded that reaction is initiated by formation of active free radicals or atoms whose formation is accelerated with time, until the rate of generation equals the rate of destruction. The corrosion rate is then constant. Oxygen and water, whether in the solvent or in the aluminum oxide film, increase the induction time by reacting with free radical species responsible for initiating the reaction. Various organic compounds are corrosion inhibitors for the same reason. Alloyed magnesium presumably also reacts preferentially with free radical species, thereby prolonging the induction time independent of water or oxygen. , on the other hand, decreases the induction time, presumably forming a complex which dissociates into free radical species.
It is proposed that the free radical and the complex take prominent part in the chain reaction producing the observed major final corrosion products and . Side reactions also occur, as is common with organic reactions of this type. increases the corrosion rate by reaction with aluminum to form A1Cl plus active H, the latter in turn reacting with to form and again . is hydrolyzed by water to form ; this explains why a small amount of water in can effectively increase attack after the induction time is exceeded.
Alloys containing manganese or magnesium react rapidly after the induction period, then more slowly, finally reaching a limiting weight loss. Their behavior, unlike pure aluminum, is caused by a protective reaction‐product layer forming only after corrosion products reach a minimum concentration in . The limiting weight loss depends, therefore, on the ratio of volume to area of aluminum exposed. It is also dependent on alloy composition. By analysis, the protective film is either mostly aluminum chloride with smaller quantities of complexed lower halides of aluminum, or a complex of aluminum chloride with various chlorinated hydrocarbons.
Quantitative adsorption studies, temperature-programmed desorption, Auger spectroscopy, and sputter depth profile methods have been used to study the interaction of CClâ with Fe(110) at 90 and 300 K. Irreversible dissociative adsorption of CCLâ occurs at 300 K, and the only desorption product which is observed is the high-temperature iron chloride species. Auger spectroscopy shows that small coverages of chlorine remain on the surface of the crystal even after heating to > 1,070 K while the carbon diffuses into the bulk of the crystal at â¼ 600 K. Correlations between the observed surface processes and tribology (the study of friction and wear) investigations are presented.
The adsorption of H2O and its decomposition on clean Fe(100) have been studied using low-energy electron diffraction (LEED), temperature programmed desorption (TPD), and high-resolution electron energy loss spectroscopy (EELS). Water adsorbs molecularly on the surface at 100 K and desorbs from three states at 165, 220, and 310 K. EELS and TPD data suggest that the Fe(100) surface interacts sequentially with water, forming hydrogen-bonded molecular clusters at low temperature and low coverage. As the surface is warmed, wetting occurs as the clusters break apart, and molecular water begins to dissociate. Dissociation is complete at a temperature of 250 K, forming a p(1 × 2)-OH overlayer, with the OH bond tilted from the surface normal. The hydroxyl overlayer disproportionates or decomposes resulting in water or hydrogen desorption near 310 K. Oxygen remaining on the surface following this desorption is bound in the fourfold hollow site, as has been observed for oxidation of this surface by O2.
The title book covers coordination chemistry of the hydrous oxide-water interface; surface charge and the electric double layer; adsorption; chemical weathering phenomena; homogeneous and heterogeneous nucleation and precipitation; particle-particle interaction; carbonate reactivity; redox processes mediated by surfaces; photochemistry; and trace element transport. It can be used as a source book for teaching and for professionals in geochemical and environmental disciplines.
Laboratory tests were conducted to examine zero-valent iron as an enhancing agent in the dehalogenation of 14 chlorinated methanes, ethanes, and ethenes. All compounds were tested by batch procedures in which 10 g of 100-mesh electrolytic iron was added to 40 ml hypovials. Aqueous solutions of the respective compounds were added to the hypovials, and the decline in concentration was monitored over time. Substantial rates of degradation were observed for all compounds tested with the exception of dichloromethane. The degradation process appeared to be pseudo first-order with respect to the organic compound, with the rate constant appearing to be directly proportional to the surface area to volume ratio and increasing with increasing degree of chlorination. Column tests showed the process to proceed under flow conditions with degradation rates indpendent of velocity and consistent with those measured in the batch tests. When normalized to 1 m2/ml, the t50 values ranged from 0.013 to 20 hr, and were about 5 to 15 orders of magnitude lower than values reported for natural rates of abiotic degradation. The results indicate abiotic reductive dechlorination, with iron serving as the source of electrons; the mechanism is, however, uncertain. Based on the rapid rates of degradation, both in situ and aboveground applications for remediation of contaminated ground water are proposed.
We consider recent data on dissociative electron transfer reactions in which the electron transfer causes practically concerted
dissociation of the chemical bond in the reagent. We discuss considerable experimental data on reactions in the gas phase
and in solutions, and also existing theoretical models for describing the kinetics of these complex processes.
In this communication, a comprehensive review on halocarbon adsorption on solid surfaces is presented. The physical and chemical properties of surfaces, for which adsorbed halocarbons readily dissociate, are dominated by the respective halogens, hence, the published data on halogen adsorption on surfaces are also presented in a tabulated form. A complete reference list on halogen overlayers is provided. The adsorption of halocarbons is discussed with reference to their surface chemistry while technological as well as some environmental aspects are also mentioned. The available results are discussed according to the substrate surfaces used. In general, one can distinguish between substrates where some halocarbons adsorb molecularly or with partial fragmentation and those surfaces where the halocarbons dissociate completely and the atomic fragments remain adsorbed or absorb in the selvedge. The former class of substrates includes those which catalyse elimination reactions in the adsorbed phase (e.g. platinum). The latter case has been observed for iron surfaces, where after CFCI3 adsorption, a pronounced effect on the geometry and stability of the surface layer composed of chlorine atoms by the absorbed fragments (i.e. carbon and fluorine) has been noted. This vertical interaction of the coabsorbed (absorbed) atomic species in the selvedge is more pronounced than the effect of the lateral interaction in the adsorbed layer and might be of general importance in more complicated adsorption systems. We cannot offer an explanation for the physical basis of these vertical interaction effects, but these effects clearly demonstrate that, in certain systems, a separation between surface and solid state chemistry is arbitrary.
The reaction of a reduced iron (II) porphyrin with a series of chlorinated methanes and ethanes was examined under neutral conditions in buffered aqueous solutions containing an excess of the reducing agent. Carbon tetrachloride, chloroform and 1,1,1-trichloroethane were reduced to lower chlorinated homologs, while methylene chloride, 1,1,2-trichloroethane and 1,1-dichloroethane did not appear to be degraded in this system.
A simple and versatile method is described for the rapid determination of iron in natural waters using the chromogen Ferrozine. The method is capable of analysing samples with concentrations from less than 5 mg m−3 to 3 g m−3 routinely, with high precision. While the method was intended for the determination of total soluble iron, the distinction between ferrous and ferric iron is also possible.
The purpose of this review is to compare and discuss recent experimental and theoretical results in the field of H2O-solid interactions. We emphasize studies of low (submonolayer) coverages of water on well-characterized, single-crystal surfaces of metals, semiconductors and oxides. We discuss the factors which influence dissociative versus associative adsorption pathways. When H2O adsorbs molecularly, it tends to form three-dimensional hydrogen-bonded clusters, even at fractional monolayer coverages, because the strength of the attractive interaction between two molecules is comparable to that of the substrate-H2O bond. The template effect of the substrate is important in determining both the local orientation and long-range order of H2O molecules in these clusters. The influence of surface additive atoms (e.g., O, Br, Na, K) and also surface imperfections (e.g. steps and defects) on the surface structure and chemistry of H2O is examined in detail. Some results on single-crystal substrates are compared with earlier measurements of H2O adsorption on high-area materials.
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