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Heterogenization of copper catalyst for the oxidation of phenol, a common contaminant in industrial wastewater
Environmental Progress & Sustainable Energy
Abstract
Advanced oxidation process was employed as a pretreatment of industrial wastewater. For this purpose, the use of heavy metals as a catalyst is necessary but also complicated because homogeneous catalysts are difficult to recover after reaction process. The heterogenization of Cu(II) ions was proposed by taking advantage of the adsorptive characteristics of polymeric matrices. Crosslinked poly(4-vinylpyridine) of 2 and 25% and poly(D-glucosamine) were tested as supports of copper. Adsorption was employed to heterogenize Cu(II) by considering the influences of pH and temperature on the process. The catalysts were evaluated by their metal content, catalytic behavior for the oxidation of phenol and leaching degree after reaction. Poly(4-vinylpyridine) 2% was the best material for Cu(II) immobilization with an adsorption capacity of 90 mg g−1. Afterward, poly(4-vinylpyridine) 2%, Cu(II) achieved 64% of phenol conversion, which represents a favorable result for the oxidation of phenol as the model of industrial wastewater pretreatments.
... The Mnt easily interacts with metal ions (Bhattacharyya & Sen Gupta, 2008). It was observed previously that copper and iron ions bound to solid surfaces can exhibit high P-L activity (Castro et al., 2013;Wu et al., 2014;Pospiskova & Safarik, 2022). Thus, Mnt with bound metal ions may exhibit even higher P-L activity than native Mnt. ...
Montmorillonite (Mnt), belonging to the smectite group and representing a 2:1-type clay mineral with good cation-exchange and swelling capacities, is a common clay component of soils. It was observed that some Mnt preparations exhibit peroxidase-like (P-L) activity using N,N-diethyl-p-phenylenediamine sulfate salt as a substrate. Both native (non-swelling) and swelling Mnt exhibited similar P-L activity. Modification of Mnt with copper and iron influenced both P-L activity and phenol polymerization. Both free and textile-bound Cu-Mnt (Sigma-Aldrich) enabled phenol removal. Soil Mnt P-L activity is probably involved in lignin breakdown and decontamination of soils polluted with phenol-containing molecules.
... It converted 64% phenol, which is considered a promising outcome for phenol oxidation under harsh conditions. 122 The magnetic Fe 3 O 4 particles were another promising option of catalysts used for the catalysis of ozonation of drugs (sulfamethoxazole) by the ozone oxidation power. This catalyst's magnetic property encourages its function in catalysis even if it is not the core of the whole process. ...
Porous materials play an important role in creating a sustainable environment by improving wastewater treatment's efficacy. Porous materials, including adsorbents or ion exchangers, catalysts, metal–organic frameworks, composites, carbon materials, and membranes, have widespread applications in treating wastewater and air pollution. This review examines recent developments in porous materials, focusing on their effectiveness for different wastewater pollutants. Specifically, they can treat a wide range of water contaminants, and many remove over 95% of targeted contaminants. Recent advancements include a wider range of adsorption options, heterogeneous catalysis, a new UV/H2O2 procedure, ion exchange, Fenton oxidation, membrane activities, ozonation, membrane bioreactor, electrochemical treatment, wet air oxidation, and a carbon capture methodology utilizing various porous materials. A particular focus for innovative research is on developing technologies to synthesize porous materials and assess their performance in removing various pollutants from wastewater at varying experimental conditions. Porous materials can be essential in designing wastewater treatment systems to address the critical environmental issues of water stress and safe drinking water worldwide.
... From the treated water analysis by ICP-AES, it was found that approximately 60 % of the total copper was dissolved in the wastewater solution. Generally, the major fraction of copper will remain in the solution as cupric ion (Cu 2? ) under acidic conditions (pH \ 5) (Castro et al. 2013). However, the presence of other compounds and reaction conditions may affect the solubility of a metal in the aqueous solution. ...
Several process industries discharge wastewater with enormous amount of toxic phenolic compounds. Wet oxidation (WO) is considered among the potential cleaner treatment methods for such waste streams. The present study demonstrates the effectiveness of two homogeneous copper salts (nitrate and sulfate) as catalysts during batch WO process conducted under mild temperature and pressures (i.e., 120 °C and oxygen pressure = 0.5 MPa). The catalytic oxidation showed around 90 % reduction of phenol, chemical oxygen demand and total organic carbon from the wastewater within 2 h. The oxidation reaction pathway at mild conditions is also proposed based on the presence of intermediates/by-products. Fourier transform infrared spectroscopy confirmed the formation of polymerized compounds containing alcoholic/phenolic species. The inductively coupled plasma-atomic emission spectroscopy analysis revealed the presence of ~40 % of the total copper in sludge. The copper recovery from the treated wastewater and sludge and its reuse in the oxidation process should be studied in future.
Spherical copper powders and cobalt-modified copper powders were electroless plated with silver, respectively, to obtain two kinds of silver-plated copper powders. The composite powders were analysed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and thermogravimetric-differential scanning calorimetry. Effects of cobalt modification on surface morphology, silver reduction rate, particle size and anti-oxidisation resistance of composite powders were studied. The results indicate that surface morphology of silver-coated copper powders prepared by cobalt-modified copper powders was affected by cobalt, but the size, mass and the percent reduction of silver were significantly increased under the same conditions of electroless plating silver. And silver-coated copper powders prepared by cobalt-modified copper powders have better anti-oxidisation resistance than silver-coated copper powders prepared by copper powders.
The composites of graphite oxide (GrO) and HKUST-1 framework with different content of GrO including 1wt%, 3wt% and 5wt% were synthesized by typical solvothermal method and applied as heterogeneous catalysts for catalytic wet peroxide oxidation (CWPO) of phenol. Then XRD, FT-IR, Raman and SEM were conducted to characterize the samples. For catalytic oxidation of 150 mL 100 mg·L⁻¹ phenol, the dose of 30 mg (0.2 g·L⁻¹) catalysts and 0.46 mL H2O2 were kept constant. The GrO-3/HKUST-1 (3% content of GrO) showed higher catalytic activity than HKUST-1 framework and other GrO/HKUST-1 composite with 99% phenol conversion and 86% COD removal efficiency obtained at 50 °C after 30 min and 8 h. Then the effect of temperature (40-80 °C) and pH (4-9) on catalytic oxidation of phenol by GrO-3/HKUST-1 were investigated. The results showed that, the degradation of phenol was obtained optimum efficiency at 60 °C with complete phenol conversion and 93% COD reduction. Furthermore, the acid and alkali resistance ability were enhanced to a certain degree by the integration of GrO compared with the parent framework HKUST-1. Three successive runs were conducted in the natural pH (6.8) of 150 mL 100 mg·L⁻¹ phenol solution which indicated that the synthesized GrO-3/HKUST-1 composite had satisfactory reusability due to the prevention of carbon deposit and negligible Cu²⁺ leaching (8 ppm). The GrO/HKUST-1 composite could be a kind of promising heterogeneous catalysts for catalytic degradation of organic compounds. Similar to other catalysts, the catalytic oxidation of phenol also relies on the formation of hydroxyl radicals.
Two different porous copper metal-organic frameworks (Cu-MOFs) named as Cu3(BTC)2 and Cu(BDC) were synthesized and applied as heterogeneous catalysts for catalytic wet peroxide oxidation (CWPO) of simulated phenol wastewater (100 mg/L). The characterization including X-ray Powder Diffraction (XRD), Fourier Transform Infra-Red spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) were achieved. By comparison, Cu(BDC) exhibited better catalytic degradation performance. Then, Cu(BDC) was selected for further experiments. Several factors including temperature, H2O2 dose, catalyst dose and initial pH of phenol wastewater which could affect the catalytic degradation efficiency by Cu(BDC) were investigated. Under optimum conditions, phenol conversion of 99% and COD (Chemical Oxygen Demand) removal of 93% were achieved. The degradation on different concentration of phenol solution (100 to 1000 mg/L) was also conducted. No matter small or large concentration of phenol solution, satisfactory results with the phenol conversion of 99% and COD removal of over 90% were obtained. After reused twice, the Cu(BDC) could still keep well catalytic performance with phenol conversion of 99% and COD removal of over 85%. Like other copper catalysts, the mechanism of degradation process was also hydroxyl radical mechanism. The leaching of Cu2+ was also monitored by Inductively Coupled Plasma-Atomic Emission Spectrum (ICP-AES) with a negligible release of copper (7 ppm). Overall, Cu-MOFs could be a kind of promising heterogeneous catalyst for catalytic oxidation of phenol with H2O2 as oxidant.
Several process industries discharge wastewa-ter with enormous amount of toxic phenolic compounds. Wet oxidation (WO) is considered among the potential cleaner treatment methods for such waste streams. The present study demonstrates the effectiveness of two homogeneous copper salts (nitrate and sulfate) as catalysts during batch WO process conducted under mild tempera-ture and pressures (i.e., 120 °C and oxygen pressur-e = 0.5 MPa). The catalytic oxidation showed around 90 % reduction of phenol, chemical oxygen demand and total organic carbon from the wastewater within 2 h. The oxidation reaction pathway at mild conditions is also pro-posed based on the presence of intermediates/by-products. Fourier transform infrared spectroscopy confirmed the formation of polymerized compounds containing alcoholic/ phenolic species. The inductively coupled plasma-atomic emission spectroscopy analysis revealed the presence of *40 % of the total copper in sludge. The copper recovery from the treated wastewater and sludge and its reuse in the oxidation process should be studied in future.
In this work we describe the application of a new non-soluble and non-porous complex with copper ion based on ethylene glycol diglycidyl ether (EGDE), methacrylic acid (MAA) and 2-methylimidazole (2MI) in the decolorization of an azo dye Methyl Orange (MO) as a model pollutant at room temperature.The complex with copper ion was studied by ESR and SEM and was tested as a heterogeneous catalyst for H2O2 activation. A possible mechanism of interaction involves the production of hydroxyl radicals (confirmed by ESR), dioxygen and water.The Cu(II)-polyampholyte/H2O2 system acted efficiently in the color removal of MO. The adsorption and oxidative degradation of the azo-based dye followed pseudo-first-order kinetic profiles, and the rate constant for degradation had a second-order dependence on copper ion content in the mixture.A removal of MO higher than 90% was achieved in 20 min at pH 7.0, combining 0.8 mM of complexed copper ions in the mixture with 24 mM hydrogen peroxide.The dye adsorbed on the polyampholyte following a L4-type isotherm with 4.9 μmol g−1 maximum loading capacity and 3.1 μM dissociation constant for the first monolayer.
In this work, the degradation and mineralization of Orange II solutions (0.1 mM) using catalysts based on pillared saponite impregnated with several iron salts is reported. Oxidation is carried out in a batch reactor, in presence of various hydrogen peroxide concentrations, and in a wide range of temperature and pH values. Twelve samples are prepared, with three iron loads (7.5, 13.0 and 17.0 wt.%) and four iron salts as precursors, namely Fe(II) acetate, Fe(II) oxalate, Fe(II) acetylacetonate and Fe(III) acetylacetonate. The samples are characterized using X-ray diffraction, thermal analysis, infrared spectroscopy, energy dispersive spectroscopy and adsorption of nitrogen at 77 K. The catalytic results show that these solids present good properties for the degradation and mineralization of Orange II solutions, allowing to reach, in the best conditions and after 4 h of oxidation, 99% of dye degradation with 91% of total organic carbon (TOC) reduction (at 70 °C), using only ca. 90 mg of clay catalyst per litre of solution. Nevertheless, 96% of dye removal with 82% of mineralization are also reached at 30 °C. Besides, the amount of iron released into the final solution is lower than 1 ppm, in the worst of the cases, and 0.09 ppm in the best case.
Mixed (Al–Fe) pillared clays are very efficient solid catalysts for oxidation of organic compounds in water by hydrogen peroxide. We have shown that in rather mild experimental conditions (atmospheric pressure, T≤70°C) and with a low excess (20%) of hydrogen peroxide, phenol was rapidly converted, mainly to CO2, without significant catalyst leaching. The (Al–Fe) pillared clay catalyst (called FAZA) can be used several times without any change of its catalytic properties. According to the low leaching observed and a previous Mössbauer spectroscopy study, the iron species appear to be strongly bonded to the aluminium pillars.
[Cu(NCCH3)6][B(C6F5)4]2 and [Cu(NCCH3)6][B{C6H3(CF3)2}4]2 are immobilized on poly(4-vinylpyridine). Both resulting materials (Cu(II) complexes immobilized on polymer) are applicable as catalysts for the cyclopropanation of olefins at room temperature. The immobilized Cu(II) compounds are quite stable and recyclable for several catalytic runs, however with some decrease in the catalytic activity.
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An investigation on the use of chitosan for the removal of copper from aqueous solutions has been carried out. Both kinetic data and equilibrium isotherms were obtained. The effects of contact time, initial copper concentration, background electrolyte, and pH on the uptake capacity of copper were studied. Initial copper concentration and pH were found to have the greatest effects on uptake. The copper uptake of chitosan was quantitatively evaluated using sorption isotherms. Results indicated a capacity of 1.8–2.2 mmol/g of dry mass. The capacity increases when solutions contain high concentrations of chloride ions. The variation of pH leads to competition between coordination of copper with chitosan with the optimal range being 5.4 to 6.0.
4-Vinyl pyridine-N-vinyl pyrrolidone copolymers having various copolymer compositions and composition distribution were prepared. The latter was estimated by means of Spinner's equation. The copolymer prepared during the early stage of copolymerization was a random like copolymer, and the polymer polymerized completely was a blend like copolymer. Cu(II) complexes of the prepared copolymers had sufficient catalytic activity for the oxidation of hydroquinone, depending upon their composition distribution and the composition. The Cu(II) complex of the random like copolymer showed a higher catalytic activity than that of the blend like copolymer, even if the copolymers had a similar composition.
Polymer supported transition metal complexes of N,N′-bis (o-hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by anchoring its amino derivative Schiff base (AHPHZ) on cross-linked (6wt%) polymer beads and then loading iron(III), copper(II) and zinc(II) ions in methanol. The loading of HPHZ Schiff base on polymer beads was 3.436mmolg−1 and efficiency of complexation of polymer anchored HPHZ Schiff base for iron(III), copper(II) and zinc(II) ions was 83.21, 83.40 and 83.17%, respectively. The efficiency of complexation of unsupported HPHZ Schiff base for these metal ions was lower than polymer supported HPHZ Schiff base. The structural information obtained by spectral, magnetic and elemental analysis has suggested octahedral and square planar geometry for iron(III) and copper(II) ions complexes, respectively, with paramagnetic behavior, but zinc(II) ions complexes were tetrahedral in shape with diamagnetic behavior. The complexation with metal ions has increased thermal stability of polymer anchored HPHZ Schiff base. The catalytic activity of unsupported and polymer supported HPHZ Schiff base complexes of metal ions was evaluated by studying the oxidation of phenol (Ph) and epoxidation of cyclohexene (CH). The polymer supported metal complexes showed better catalytic activity than unsupported metal complexes. The catalytic activity of metal complexes was optimum at a molar ratio of 1:1:1 of substrate to oxidant and catalyst. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) in oxidation of phenol and epoxidation of cyclohexene was better with polymer supported metal complexes in comparison to unsupported metal complexes. The energy of activation for oxidation of phenol (22.8kJmol−1) and epoxidation of cyclohexene (8.9kJmol−1) was lowest with polymer supported complexes of iron(III) ions than polymer supported Schiff base complexes of copper(II) and zinc(II) ions.
Clay pillared with Fe-Al was synthesized as a catalyst for Fenton oxidation of phenol by hydrogen peroxide (H2O2). The pillaring process altered the basal space of clay, which is related to the amounts of aluminium and iron in the pillaring solution. The catalytic activity of the pillared clay was attributed to the accessible iron species, whose amount is regulated not only by the introduced iron species but also by the basal space that subsequently depends on the introduced aluminium species. The heterogeneous Fenton reaction exhibited an induction period followed by an apparent first order oxidation of phenol by H2O2. The induction period was proposed as an activation process of the surface iron species, which is thus enabled to complex with the reactants. The induction time (tI) depended on temperature (T) and pH condition but irrelevant to the concentrations of phenol and H2O2 and the amount of catalyst. The rate of the oxidation process was evaluated with respect to the concentrations of phenol and H2O2, the amount of catalyst, pH and temperatures. During the catalytic reaction the trend of iron leaching showed an ascending period and a descending period, which was related to the presence of ferrous ions and ferric ions. The Fe-Al pillared was recovered through two procedures, dry powder and slurry, which have different effect on the induction period.
A Fe on activated carbon catalyst has been prepared and tested for phenol oxidation with H2O2 in aqueous solution at low concentration (100mg/L). Working at 50°C, initial pH 3 and a dose of H2O2 corresponding to the stoichiometric amount (500mg/L) complete removal of phenol and a high TOC reduction (around 85%) has been reached. Oxidation of phenol gives rise to highly toxic aromatic intermediates which finally disappear completely evolving to short-chain organic acids. Some of these last showed to be fairly resistant to oxidation being responsible for the residual TOC. In long-term continuous experiments the catalyst undergoes a significant loss of activity in a relatively short term (20–25h) due to Fe leaching, this being related with the amount of oxalic acid produced. Deactivation may also be caused by active sites blockage due to polymeric deposits on whose formation some evidences were found. Washing with 1N NaOH solution allows to recover the activity although complete restoration was not achieved.
Various cross‐linked (4, 8, and 12%) gel‐type weak‐base poly(4‐vinylpyridine) (PVP) resins were studied for palladium recovery from nitric acid medium. The sorption of palladium was found to decrease with an increase in cross‐linkage of the resin. 8 and 12% PVP resins exhibited maximum D Pd(II) values at 2–6 M HNO3, whereas 4% PVP resin showed maximum D Pd(II) values at lower acidities (0.1 M HNO3). FT‐IR, SEM, and XPS techniques were used for the characterization of palladium‐loaded resins. Detailed studies were carried out with the resin of modest cross‐linkage i.e., 8% PVP resin. The sorption isotherm studies revealed that the maximum palladium loading approaches the theoretical capacity of the resin, presuming the sorption of palladium as divalent anion at 4 M HNO3. The pseudo‐second order kinetics model yielded the best fit for the experimental data of sorption kinetics. An increase in temperature accelerates the rate of palladium extraction and also the addition of chloride ions increases the palladium uptake. Column studies were performed using 4 and 8% PVP resins in 2 and 4 M nitric acid concentrations. The loaded palladium could be eluted efficiently with acidic thiourea solution.
Chitosan is a well-known biopolymer, whose high nitrogen content confers remarkable ability for the sorption of metal ions from dilute effluents. However, its sorption performance in both equilibrium and kinetic terms is controlled by diffusion processes. Gel bead formation allows an expansion of the polymer network, which improves access to the internal sorption sites and enhances diffusion mechanisms. Molybdate and vanadate recovery using glutaraldehyde cross-linked chitosan beads reaches uptake capacities as high as 7−8 mmol g-1, depending on the pH. The optimum pH (3−3.5) corresponded to the predominance range of hydrolyzed polynuclear metal forms and optimum electrostatic attraction. While for beads, particle size does not influence equilibrium, for flakes, increasing sorbent radius significantly decreases uptake capacities to 1.5 mmol g-1. Sorption kinetics are mainly controlled by intraparticle diffusion for beads, while for flakes the controlling mechanisms are both external and intraparticle diffusions. The gel conditioning increases the intraparticle diffusivity by 3 orders of magnitude: intraparticle diffusivities range between 10-13 and 10-10 m2 min-1, depending on the sorbent size and the conditioning.
A new amine-shielded cross-linking method of the chitosan hydrogel beads (CHBs) was investigated to improve the metal adsorption performance of the cross-linked beads. The CHBs were reacted with formaldehyde before the beads were cross-linked with EGDE, and, finally, the amine groups of cross-linked CHBs were released by HCl treatment. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy clearly showed that most of the amine groups in chitosan were converted to the −NCH2 groups after the formaldehyde treatment and they were not involved in the cross-linking reaction with EGDE, and the HCl treatment after the cross-linking reaction effectively released these shielded nitrogen atoms into the form of the primary amine again. Copper ion adsorption experiments confirmed that the CHBs cross-linked with the new method had significantly greater adsorption capacities than the beads cross-linked directly with EGDE. Mechanism study revealed that the increased adsorption performance was attributed to the large number of primary amine groups available on the surfaces of the cross-linked beads from the new cross-linking method.
A Hypersol-Macronet polymer, MN-600, and a weakly acidic ion exchanger, C-104E containing mainly carboxylic functionality, have been characterized to evaluate their performance for trace heavy metal removal. Characterization of these polymers in the form of scanning electron micrographs, Brunauer−Emmett−Teller (BET) and Langmuir surface area measurements, Fourier transform infrared spectroscopy analysis, X-ray photoelectron spectroscopy analysis, atomic composition measurement, elemental analysis, sodium capacity determination, and zeta potential measurements has been conducted. Density functional theory has been used to analyze the pore size distribution data of MN-600. The BET and Langmuir surface areas of MN-600 are 951 and 1118 m2 g-1, respectively. The zeta potentials of polymers at different pH values indicate zero crossover points at a pH of 1.2 and 1.8 for MN-600 and C-104E, respectively. The sodium capacity values of C-104E and MN-600 are 9.65 and 0.45 mequiv g-1, respectively. The oxygen content of C-104E is 42.12%, whereas MN-600 contains 15.37% oxygen in the polymer matrix. The higher sorption capacity of C-104E can be attributed to the presence of a greater number of oxygen-containing groups in the polymer (particularly carboxylic functionality). C-104E contains about 1.4% nitrogen, whereas MN-600 contains only 0.47% nitrogen. The applicability of surface complexation theory for the sorption of heavy metals onto these sorbents has been explored. The sorption of copper, nickel, and zinc ions from aqueous solution on these sorbents has been studied in batch equilibrium experiments for binary, ternary, and quaternary systems to determine the equilibrium parameters for modeling of ion-exchange equilibria. From the experimentally determined equilibrium parameters, ion-exchange equilibria have been calculated for a wide range of initial conditions. The experimental results for the Macronet polymer as well as the weakly acidic ion exchanger have been compared with the results obtained using the surface complexation model for the prediction of binary, ternary, and quaternary ion-exchange equilibria.
New polymeric structures obtained by chemical transformations of maleic anhydride/dicyclopentadiene copolymer with triethylenetetraamine, p-aminobenzoic acid, and p-aminophenylacetic acid were used for the removal Cu(II) ions from aqueous solutions. The experimental values prove the importance of the chelator nature and of the macromolecular chain geometry for the retention efficiency. The retention efficiency (ηr), the retention capacity (Qe), and the distribution coefficient of the metal ion into the polymer matrix (Kd) are realized by evaluation of residual Cu(II) ions in the effluent waters, by atomic adsorption. Also are discussed the influence of pH, the thermal stability of the polymer, and their polymer–metal complex, as well as the particular aspects regarding the contact procedure and the batch time. Based on the polymers and polymer–metal complexes characterization a potential retention mechanism is proposed. All polymer supports as well theirs metal–complexes are characterized by ATD and FTIR measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1397–1405, 2007
Mixed (Al-Fe) pillared clays, now prepared on pilot scale are very efficient solid catalysts for the oxidation of organic compounds with hydrogen peroxide in water. It is demonstrated in this study that in rather mild experimental conditions (atmospheric pressure, T≤70°C) and with a low excess (20%) of hydrogen peroxide, phenol was highly converted to CO2 without catalyst leaching. Indeed the (Al-Fe) pillared clay (called FAZA) was recycled and used several times without any change of their catalytic properties. Iron strongly bonded to aluminium in the pillars characterized by Mössbauer spectroscopy were suggested as the active sites in the phenol oxidation.
The interaction and thermal behavior of the poly(4-vinylpyridine-co-divinylbenzene)–Cu(II) complex were studied using infrared (IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The effect of pyridine ring–Cu2+ interaction on the motion and dipole moments of the PVP–DVB–Cu(II) complexes was estimated through the FTIR difference and deconvoluted spectra. The pyridine ring motion decreased with increasing Cu2+ ions content, whereas the dipole moments of the in-plane and out-of-plane ring C–H bending increased. The glass transition temperature (Tg) value of the PVP–DVB–Cu(II) complex was higher than that of the PVP–DVB copolymer, and increased with increasing Cu2+ ions content. The apparent activation energy (Ea) of the random scission within the PVP polymer chain in complex under air (∼187 kJ/mol) was higher than that in copolymer (120 kJ/mol). However, the value of Ea for the thermo-oxidative degradation (>400 °C) decreased with increasing Cu2+ ions content.
Series of heterogenized copper complexes are prepared by either coprecipitation or adsorption of Cu(II) on the bulk chitosan and composite supports (egg-shell type chitosan/SiO2 and chitosan/MCM-41systems). The morphology and properties of the catalysts are studied by FTIR, UV-Vis, SEM, and ESR methods, and the activity of the redox sites immobilized by the chitosan matrix is tested in oxidation of o- and p-dihydroxybenzenes in water. The estimate of the copper concentration derived from the ESR data shows that essentially all Cu(II) ions introduced in low-loaded samples (≤1.5 wt.% Cu) are ESR-visible, with the symmetry of isolated Cu2+-sites in chitosan approximating the square-planar coordination. Redox transformations of the active sites in the course of catalytic tests or prolonged boiling in water are not accompanied by copper leaching from the chitosan matrix, and the catalyst reoxidation by H2O2 leads to quantitative restoration of the Cu(II)-ESR signal. Thus, the matrix of chitosan is able to stabilize and retain isolated Cu2+ ions in highly coordinatively unsaturated state. In contrast with a homogeneous copper–chitosan system demonstrating copper–hydroquinone complexation that suppresses dramatically the yield of the oxidation products, the heterogenized samples are active and stable catalysts in the process of quinone formation. The binary composite system, with a thin film of low-loaded Cu–chitosan supported on macroporous SiO2, demonstrates significantly higher activity in oxidation of hydroquinone, as compared with the bulk Cu/chitosan sample. This approach to catalyst design opens up a promising way for synthesis of the supported chitosan catalysts with a very low content of noble metals.
In this review the authors intend to make a tutorial review on catalyst immobilisation from the viewpoint of the catalyst designer, emphasizing the use of promising concepts in this area, rather than trying to be exhaustive. The following topics are covered: 1 Introduction 2 Classic Ways of Immobilisation of Homogeneous Catalysts 3 General Remarks on Catalyst Heterogenisation on Polymeric Supports 3.1 Polymeric Supports 3.2 Polymer Supported Monodentate Phosphine Complexes 3.3 Polymer Supported Bidentate Phosphine Complexes 3.4 Phosphazene-Based Catalysts 3.5 Various Polymer Tethered Ligands with O or/and N as Metal Chelating Atoms 4 Recent Advances in Immobilisation of Chiral Catalysts
Progress towards environmentally responsible processing is marked by the elimination of waste and by-product generation and reduced dependence on hazardous chemicals. The key to both is often provided by catalytic as alternatives to stoichiometric processes.Heterogeneous catalysis, long established in bulk-chemicals processing, is beginning to make inroads into the fine-chemicals industry also. This tendency is helped by the availability of novel catalytic materials and modern techniques of creating and investigating specific active sites on catalyst surfaces. In this overview, examples from the areas of acid/base and redox catalysis are chosen to illustrate the trend from non-catalytic to catalytic processes.
This letter presents an original approach to the treatment of phenolic aqueous wastes using H2O2 with heterogeneous catalysts. The experimental results indicate that the system using Fe-ZSM-5 zeolite with MFI structure is promising since it allows total elimination of phenol and significant total organic carbon (TOC) removal under mild working conditions. Moreover, Fe-ZSM-5 remains active after after successive runs. Compared with processes using homogeneous catalysis, the possibility of induced pollution caused by the metal ions in the solution is avoided.
This review article was constructed around the first Algerian–French congress aimed on emerging materials which was held at Tamanrasset by the end of February 2003. The aim of this review is to point out that a lot of work has been done in heterogeneous catalysis to better understand the active sites responsible for the catalytic reactivity. Most of these researches were performed under reducible atmosphere, on metallic catalysts, to improve our knowledge about hydrocarbon reforming catalysts. Starting from this base which was recalled through various classes of important studies such as: (i) the dilution of the active sites, (ii) the use of bimetallics, (iii) the use of well-crystallised surfaces and (iv) the influence of the metal–support interactions; a development and an opening is made on the three-way catalysis and the DeNOx reactions. The objectives being to point out the very important influence of the experimental conditions and of the gas phase compositions which may induce very strong surface modifications of the initial metallic aggregates. Moreover, it will depend on the reactions, i.e. isomerisation, oxidation, reduction where the active site may also be composed of, in addition to the metallic crystallites, the participation of the oxygen of the support.A tentative for a general interpretation of the observed results is given by the use of the variations of the local density of states and of the “d” band centre energy.
The contamination of soils and waters by metals all over the world continues to present a serious danger to the environment and human health. The development of innovative metal clean-up technologies remains a challenge as current procedures have many limitations, such as being expensive, disruptive, and only efficient for certain concentrations. With high molecular weight and repetitive functional groups, biopolymers provide excellent chelating material for metals. Chitosan is a well-known and efficient metal chelator, but its practical use is limited due to the relatively high costs of constructing clean-up devices (filters) from chitosan alone. In the current study we attempt to find a more cost-effective solution by investigating a new adsorbent material based on chitosan immobilized on sand, namely, chitosan-coated sand (5% chitosan content). This new material was studied for its copper adsorption capacity at contact times of 2, 4, and 6 h and the equilibrium result was compared with copper adsorption capacities of chitosan and sand alone. Hopefully this concept will lead to an application as a large-scale permeable reactive barrier. Copper recovery from an adsorbent with the possible reuse of the adsorbent material was also evaluated in leaching tests. The equilibrium isotherms for Cu adsorption on chitosan-coated sand were described by the Langmuir model. These preliminary results indicate the possibility of using chitosan-coated sand to build inexpensive large-scale barrier filters for metal removal from moving contaminated groundwater plumes.
This study was to investigate the adsorption characteristics of Cu(II) onto spent activated clay (SAC) or so-called spent bleaching earth, a waste produced from an edible oil refinery company. Results of kinetic experiments showed that the Cu(II) adsorption rate was fast and more than 90% of Cu adsorption occurred within 5 min. Among the kinetic models tested, the adsorption kinetics was best described by the pseudo-second-order equation. The rate of adsorption decreased with increasing surface loadings. Results of equilibrium experiments showed that the solution pH was the key parameter affecting the adsorption characteristics. The adsorption of Cu(II) ions onto SAC occurs up to the precipitation pH, and then the precipitation of Cu ions starts. The Langmuir adsorption isotherm properly describes the equilibrium adsorption and the maximum adsorption capacities of SAC towards Cu(II) were determined to be 10.9, 11.5, and 13.2 mg/g, respectively at pH 5.0, 5.5, and 6.0. As temperature was increased from 4 to 50 °C, the adsorption capacity increased from 9.5 to 12.8 mg/g for solution pH of 5.0. Values of ΔG° ranging from −5.73 to −7.26 kcal/mol suggest that the adsorption process is spontaneous and mainly governed by specific surface interaction mechanism. The values of ΔH° and ΔS° were 3.47 kcal/mol and 33.2 cal/(mol K), respectively. Results of this study will be useful for future scale up for using this material as a low-cost adsorbent for the removal of Cu(II) from wastewater.
Chitosan is an optically active biopolymer that is characterized by a strong affinity for transition metals. The polymer can be used as a support for the preparation of heterogeneous catalysts in the form of colloids, flakes, gel beads, fibers (including hollow fibers), or immobilized on inorganic supports (alumina, silica, or other metal oxides). The conformation of the polymer (together with its flexibility) is an important advantage for this kind of application. The ease with which it can be modified physically and chemically opens up avenues for manufacturing a wide range of catalysts for applications in the fields of hydrogenation, oxidation, and fine chemical synthesis reactions. This review summarizes the main advances published over the last 15 years, outlining the procedures for preparing these materials, describing how they are tested in a series of reactions and discussing the main controlling parameters that should be taken into account in order to optimize their catalytic activity.
The adsorption of Cu(II) ions onto chitosan and cross-linked chitosan beads has been investigated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. Batch adsorption experiments were carried out as a function of pH, agitation period, agitation rate and concentration of Cu(II) ions. A pH of 6.0 was found to be a optimum for Cu(II) adsorption on chitosan and cross-linked chitosan beads. Isotherm studies indicate Cu(II) can be effectively removed by chitosan and cross-linked chitosan beads. Adsorption isothermal data could be well interpreted by the Langmuir equation. Langmuir constants have been determined for chitosan and cross-linked chitosan beads. The experimental data of the adsorption equilibrium from Cu(II) solution correlated well with the Langmuir isotherm equation. The uptakes of Cu(II) ions on chitosan beads were 80.71 mg Cu(II)/g chitosan, on chitosan-GLA beads were 59.67 mg Cu(II)/g chitosan-GLA, on chitosan-ECH beads were 62.47 mg Cu(II)/g chitosan-ECH and on chitosan-EGDE beads were 45.94 mg Cu(II)/g chitosan-EGDE. The Cu(II) ions can be removed from the chitosan and cross-linked chitosan beads rapidly by treatment with an aqueous EDTA solution and at the same time the chitosan and cross-linked chitosan beads can be regenerated and also can be used again to adsorb heavy metal ions.
The adsorption of Cu(II) ions from aqueous solutions by hazelnut shell activated carbon (HSAC) was studied in a batch adsorption system. Factors influencing copper adsorption such as initial copper ion concentration (25–200 mg L−1), pH (2–6), adsorbent dosage (0.5–3.0 g L−1) and temperature (293–323 K) were investigated. The adsorption process was relatively fast and equilibrium was established about 90 min. Maximum adsorption of Cu(II) ions occurred at around pH 6. A comparison of the kinetic models on the overall adsorption rate showed that the adsorption system was best described by the pseudo second-order kinetics. Desorption experiments were carried out to test the performance of the carbon and desorption efficiencies in four cycles were found to be in the range 74–79%. The adsorption equilibrium data fitted best with the Langmuir isotherm and the monolayer adsorption capacity of Cu(II) ions was determined as 58.27 mg g−1 at 323 K. Thermodynamic parameters were calculated for the Cu(II) ion–HSAC system and the positive value of ΔH (18.77 kJ mol−1) showed that the adsorption was endothermic and physical in nature.
The properties of copper-based pillared clays (Cu-PILC) have been studied and compared with those of the analogous iron-based clays (Fe-PILC) in the wet hydrogen peroxide catalytic oxidation (WHPCO) of model phenolic compounds (p-coumaric and p-hydroxybenzoic acids) and real olive oil milling wastewater (OMW). These two catalysts show comparable performances in all these reactions, although they show some differences in the rates of the various steps of reaction. In particular, Cu-PILC shows a lower formation of oxalic acid (main reaction intermediate) with respect to Fe-PILC. Both catalysts show no leaching of the transition metal differently from other copper-based catalysts prepared by wetness impregnation on oxides (alumina, zirconia) or ion-exchange of clays (bentonite) or zeolite ZSM-5. No relationship was observed between copper reducibility in the catalyst and the performance in WHPCO, as well as between the rate of copper leaching and catalytic behavior. Cu-PILC shows a comparable activity to dissolved Cu2+ ions, although the turnover number is lower assuming that all copper ions in Cu-PILC are active. Cu-PILC shows a high resistance to leaching and a good catalytic performance, which was attributed to the presence of copper essentially in the pillars of the clay. A high efficiency in H2O2 use in the first hour of reaction with the participation of dissolved O-2 in solution was also shown. For longer reaction times, however, the efficiency of H2O2 use considerably decreases. (c) 2006 Elsevier B.V. All rights reserved.
The adsorption characteristics of 2,4,6-trichlorophenol (TCP) on activated carbon prepared from oil palm empty fruit bunch (EFB) were evaluated. The effects of TCP initial concentration, agitation time, solution pH and temperature on TCP adsorption were investigated. TCP adsorption uptake was found to increase with increase in initial concentration, agitation time and solution temperature whereas adsorption of TCP was more favourable at acidic pH. The adsorption equilibrium data were best represented by the Freundlich and Redlich-Peterson isotherms. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. Boyd plot revealed that the adsorption of TCP on the activated carbon was mainly governed by particle diffusion. Thermodynamic parameters such as standard enthalpy (DeltaH degrees ), standard entropy (DeltaS degrees ), standard free energy (DeltaG degrees ) and activation energy were determined. The regeneration efficiency of the spent activated carbon was high, with TCP desorption of 99.6%.
The adsorption kinetics of methylene blue (MB) on the hazelnut shell with respect to the initial dye concentration, pH, ionic strength, particle size and temperature were investigated. The rate and the transport/kinetic processes of MB adsorption were described by applying the first-order Lagergren, the pseudo-second-order, mass transfer coefficient and the intraparticle diffusion models. Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model. Significant increases in initial adsorption rate were observed with the increase in temperature followed by pH and initial MB concentration. The intraparticle diffusion was found to be the rate-limiting step in the adsorption process. Adsorption activation energy was calculated to be 45.6kJmol(-1). The values of activation parameters such as free energy (DeltaG(*)), enthalpy (DeltaH(*)) and entropy (DeltaS(*)) were also determined as 83.4kJmol(-1), 42.9kJmol(-1) and -133.5Jmol(-1)K(-1), respectively.
Natural iron oxide-coated sand (NCS), extracted from the iron ore located in North-West of Tunisia, was employed to investigate its capacity to remove copper and nickel from aqueous solutions. The aim of this work was to characterize the considered sorbent (NCS) and to assess the possibility of removing nickel and copper from aqueous solutions by this sorbent. The effects of agitation time, pH, initial metal ion concentration and temperature on the removal of these metals were studied. In order to study the sorption isotherm, two equilibrium models, the Freundlich and Langmuir isotherms, were analyzed. The effect of solution pH on the adsorption onto NCS was studied in the pH range from 2 to 7 and 2 to 9 for copper and nickel respectively. The adsorption was endothermic and the computation of the parameters, DeltaH degrees, DeltaS degrees and DeltaG degrees, indicated that the interactions were thermodynamically favourable. Experiments with Cu and Ni adsorption measured together showed that Cu severely interfered with Ni adsorption to the NCS and vice versa under the conditions of the two coexisted ions adsorption.
The metal removal capability of prawn shell is evaluated in this study using copper as a model sorbate. A mild deacetylation method was used to convert chitin on the periphery of the shell to chitosan. The equilibrium and kinetic characteristics of copper adsorption on partially deacetylated prawn shell are studied in batch stirred-tank experiments. The extent of copper removal increases with an increase in pH. Both the Langmuir model with pH-dependent parameters and the extended Langmuir-Freundlich model with pH-independent parameters account very well for the measured equilibrium data. Modeling studies using two different second order surface reaction models demonstrate that transient profiles obtained experimentally for a range of initial metal concentrations (C0) and adsorbent dosage are in good agreement with calculated curves of both models. The two rate models can be used for an accurate description of measured kinetic data so long as their rate constants are properly correlated with the two system variables. In contrast, deviation exists between experimental data and theoretical curves calculated from a diffusion-based model.
Batch studies were carried out to investigate the adsorption of zinc(II) from fresh waters on an iron(III) hydroxide surface maintained at the pH of zero point of charge of hydroxide (ZPC, 6.85) and also on both the acidic (5.5) and alkaline (8.2) sides of pH of ZPC, at 15 and 35 degrees C. Zinc(II) adsorption on iron(III) hydroxide increased with an increase in pH. The rise in temperature from 15 to 35 degrees C increased zinc(II) adsorption at pH 5.5 and 6.85, but decreased it at alkaline pH (8.2). In none of the cases did adsorption attain a maximum adsorption density. The results indicate the presence of heterogeneous sites of varying affinity on the adsorbent. Zinc(II) adsorption followed Langmuir behaviour only at small adsorption densities (less than 10(-2.95) M Zn/kg at pH 5.5) and at higher adsorption densities, the availability of strongest binding sites decreased. Nonspecifically adsorbed zinc(II) (reversible to Ba(II)) decreased with the increase in pH and temperature. Sequential desorption experiments also revealed that desorption of adsorbed zinc(II) decreased with an increase in pH.
A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.
The adsorption of residue oil from palm oil mill effluent (POME) using chitosan powder and flake has been investigated. POME contains about 2g/l of residue oil, which has to be treated efficiently before it can be discharged. Experiments were carried out as a function of different initial concentrations of residue oil, weight dosage, contact time and pH of chitosan in powder and flake form to obtain the optimum conditions for the adsorption of residue oil from POME. The powder form of chitosan exhibited a greater rate compared to the flake type. The results obtained showed that chitosan powder, at a dosage of 0.5g/l, 15min of contact time and a pH value of 5.0, presented the most suitable conditions for the adsorption of residue oil from POME. The adsorption process performed almost 99% of residue oil removal from POME. Equilibrium studies have been carried out to determine the capacity of chitosan for the adsorption of residue oil from POME using the optimum conditions from the flocculation at different initial concentrations of residue oil. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms and isotherm constants. Equilibrium data fitted very well with the Freundlich model. The pseudo first- and second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step, i.e. chemisorption between residue oil and chitosan. The significant uptake of residue oil on chitosan was further proved by BET surface area analysis and SEM micrographs.
Cu(II) com-plex, highly active polymeric complex catalyst for the hy-droquinone oxidation
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Poly(4-vinyl-piridine-co-N-vinyl pyrrolidone)-Cu(II) com-plex, highly active polymeric complex catalyst for the hy-droquinone oxidation, Makromolekulare Chemie, Rapid Communications, 9, 705–708.
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