A new bioinorganic process for the remediation of Cr(VI)

Palladised biomass of Desulfovibrio desulfuricans ATCC 29577 (bio‐Pd(0)) effected reduction of Cr(VI) to Cr(III) under conditions where biomass alone or chemically‐prepared Pd(0) were ineffective. Reduction of 500 µmol dm^?3 Cr(VI) by 0.4 mg cm^?3 bio‐Pd(0) (Pd : biomass ratio of 1:1) was achieved from 1 mol dm^?3 formate/acetate buffer at pH 1–7 at room temperature; the optimum pH was 3.0. The ratio of mass of Pd : dry mass of biomass, and the need for finely ground bio‐Pd(0) were important parameters for optimal Cr(VI) reduction, with a ratio of 1:1 giving 100% reduction of 500 µmol dm^?3 Cr(VI) within 6 h at room temperature, decreasing to 30 min following heat treatment of the Pd(0)‐loaded biomass. The reduced Cr was recovered quantitatively as soluble Cr(III) at pH 3.0 with no poisoning of the bioinorganic catalyst with respect to continued reduction of Cr(VI). © 2002 Society of Chemical Industry     

Reduction of Cr(VI) by palladized biomass of Desulfovibrio vulgaris NCIMB 8303

Palladized biomass of Desulfovibrio vulgaris (Bio‐Pd(0)) reduced Cr(VI) to Cr(III) at an initial rate four‐fold higher than chemically‐prepared Pd(0) metal. Optimal Cr(VI) reduction by suspended Bio‐Pd(0) occurred at pH 3, whereas pH did not affect the rate of Cr(VI) reduction by Bio‐Pd(0) immobilized in agar beads. The rate of Cr(VI) reduction was concentration‐dependent below 300 µmol dm^?3, and application of enzyme kinetics, considering Bio‐Pd(0) as an ‘artificial enzyme’, gave an apparent K_m (K_mapp) of approx. 650 µmol dm^?3 and V_max of 1667 nmol h^?1 mg Pd(0) for suspended Bio‐Pd(0). The potential of Bio‐Pd(0) as a method for the treatment of Cr(VI)‐wastes is discussed. Copyright © 2005 Society of Chemical Industry     

Use of Desulfovibrio and Escherichia coli Pd‐nanocatalysts in reduction of Cr(VI) and hydrogenolytic dehalogenation of polychlorinated biphenyls and used transformer oil

BACKGROUND: Desulfovibrio spp. biofabricate metallic nanoparticles (e.g. ‘Bio‐Pd’) which catalyse the reduction of Cr(VI) to Cr(III) and dehalogenate polychlorinated biphenyls (PCBs). Desulfovibrio spp. are anaerobic and produce H₂S, a potent catalyst poison, whereas Escherichia coli can be pre‐grown aerobically to high density, has well defined molecular tools, and also makes catalytically‐active ‘Bio‐Pd’. The first aim was to compare ‘Bio‐Pd’ catalysts made by Desulfovibrio spp. and E. coli using suspended and immobilized catalysts. The second aim was to evaluate the potential for Bio‐Pd‐mediated dehalogenation of PCBs in used transformer oils, which preclude recovery and re‐use. RESULTS: Catalysis via Bio‐Pd_{D.desulfuricans} and Bio‐Pd_E.coli was compared at a mass loading of Pd:biomass of 1:3 via reduction of Cr(VI) in aqueous solution (immobilized catalyst) and hydrogenolytic release of Cl^? from PCBs and used transformer oil (catalyst suspensions). In both cases Bio‐Pd_{D.desulfuricans} outperformed Bio‐Pd_E.coli by ～3.5‐fold, attributable to a ～3.5‐fold difference in their Pd‐nanoparticle surface areas determined by magnetic measurements (Bio‐Pd_{D.desulfuricans}) and by chemisorption analysis (Bio‐Pd_E.coli). Small Pd particles were confirmed on D. desulfuricans and fewer, larger ones on E. coli via electron microscopy. Bio‐Pd_{D.desulfuricans}‐mediated chloride release from used transformer oil (5.6 ± 0.8 µg mL^?1) was comparable with that observed using several PCB reference materials. CONCLUSIONS: At a loading of 1:3 Pd:biomass Bio‐Pd_{D.desulfuricans} is 3.5‐fold more active than Bio‐Pd_E.coli, attributable to the relative catalyst surface areas reflected in the smaller nanoparticle sizes of the former. This study also shows the potential of Bio‐Pd_{D.desulfuricans} to remediate used transformer oil. Copyright © 2012 Society of Chemical Industry     

Novel hexamethylene diamine‐functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly[(glycidyl methacrylate)‐co ‐(ethylene glycol dimethacrylate)] (PGME ) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME‐HD ) were tested as potential Cr(VI ) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI ) sorption was investigated in the temperature range 298–343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI ) sorption obeys the pseudo‐second‐order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g^?1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰) and entropy change (ΔS ⁰) and activation energy of sorption (E _a), were calculated. The Cr(VI) adsorption onto PGME‐HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME‐HD sample GMA 60 HD was easily regenerated with 0.1 mol L^?1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed. © 2016 Society of Chemical Industry     

Reduction of Cr(VI) to Cr(III) and removal of total chromium from wastewater using scrap iron in the form of zerovalent iron(ZVI): Batch and column studies

This work experimentally investigates Cr(VI) reduction to Cr(III) using waste scrap iron in the form of zerovalent iron (ZVI) collected from the mechanical workshop of the Institute, both in batch and continuous operation. The reduction of Cr(VI) to Cr(III) was found to be complete (～100%) depending on the experimental conditions. Lower pH values favour Cr(VI) reduction. Two concurrent reactions take place, that is reduction of Cr(VI) by Fe⁰ (ZVI) and by Fe²⁺ generated due to H⁺ corrosion of iron. Maximum around 22%, 11% and 2% Cr(III) remained dissolved in solution while the experiments were carried out at initial pH of 2, 4.67 and 7. Higher ZVI loading increases Cr(VI) reduction rate, however, consumption of iron is noted to be higher. The results indicate that the bed is exhausted rapidly at higher pH, initial Cr(VI) concentration and flow rate. This is attributable to predominance passivation of ZVI surface forming Cr(III)–Fe(III)‐oxide layer. SEM analysis of ZVI before and after the experiments confirms formation of passive oxide on iron surface is responsible for deterioration of Cr(VI) reduction efficiency due to its blanketing effect.     

Biological Cr(VI) reduction in a trickling filter under continuous operation with recirculation

BACKGROUND: Hexavalent chromium (Cr(VI)) is toxic to humans, animals and plants. Conventional treatment technologies reduce Cr(VI) to the less toxic and mobile Cr(III), but these methods are usually expensive and generate secondary waste. Microbial Cr(VI) reduction has recently gained attention as a detoxification process, since it enables Cr(VI) reduction through relatively cheap and simple methods. The aim of this work was to investigate the mechanism and the performance of biological Cr(VI) reduction using mixed cultures originated from industrial sludge under continuous operation with recirculation in a pilot‐scale trickling filter. RESULTS: Biological Cr(VI) reduction was studied using a pilot‐scale trickling filter filled with plastic media under continuous operation with recirculation and the use of indigenous bacterial population. The effect of the organic carbon (electron donor) concentration was examined for constant Cr(VI) influent concentration at about 5.5 mg L^?1 and volumetric flow rates ranging from 60 to 900 mL min^?1. The highest reduction rate achieved was 1117 g Cr(VI) m^?2 d^?1 for a volumetric flow rate of 900 mL min^?1. The system's reduction capacity was significantly affected by chromate loadings, resulting in frequent backwashing of the filter. The determination of the reduction mechanism was also studied using batch cultures of free suspended cells and culture supernatant. CONCLUSION: The high reduction rates combined with the low operating cost indicate that the above technology can be a viable solution for the treatment of industrial chromate effluents. Copyright © 2008 Society of Chemical Industry     

The role of sulfide in the immobilization of Cr(VI) in fly ash geopolymers

The use of fly ash-based geopolymer binders to immobilize chromium is investigated in detail, with particular regard to the role of the sulfide ion as a reductant for Cr(VI) treatment. In the absence of sulfide, Cr added as Cr(VI) is highly leachable. However, addition of a small quantity of Na₂S reduces the Cr to Cr(III), and enables leaching efficiencies in excess of 99.9% to be reached after 90 days' exposure to deionized water, Na₂CO₃ or MgSO₄ solutions. Leaching in H₂SO₄ is somewhat greater than this, due most probably to the oxidation of the Cr(III) present. Addition of the Cr(VI) as a highly soluble salt is preferable to its addition as a sparingly soluble salt, because a higher salt solubility means the Cr(VI) is more available for reduction prior to geopolymeric setting. The potential value of geopolymer technology as an immobilization process for problematic heavy metal waste streams is highlighted by these results, and the need for a full understanding of binder chemistry in any immobilization system outlined.     

Transport of Chromium(VI) through a Supported Liquid Membrane Containing Tri-n-octylphosphine Oxide

ABSTRACT

In this study the transport of chromium(VI) from aqueous solutions of pH 2–4 through a supported liquid membrane (SLM) with tri-n-octylphosphine oxide (TOPO) dissolved in kerosene as a mobile carrier was investigated. The transport flux of Cr(VI) increased with an increase in the concentrations of Cr(VI) in the feed phase and of TOPO in the membrane phase, but with a decrease in pH of the feed phase. Considering the equilibria of various Cr(VI) species in the aqueous phase and of the Cr(VI)—TOPO complexes formed in the membrane phase, a permeation model including the aqueous film diffusion of HCrO₄ ^? and Cr₂O₇ ^2? toward the membrane, the interfacial chemical reaction between them and TOPO, and the membrane diffusion of the Cr(VI)—TOPO complexes (H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃) was proposed to describe the transport of Cr(VI) through the SLM. By best fitting the transport flux equations of Cr(VI) with the experimental data using the Rosenbrock method, the apparent mass-transfer coefficients of HCrO₄ ^? and Cr₂O_7^. across the aqueous film, and those of H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃ across the membrane phase, were obtained. This work helps to clarify the transport mechanism of Cr(VI) through an SLM.     

2,2′‐(Methylimino)bis(N,N‐dioctylacetamide) (MIDOA), A New Tridentate Extractant for Technetium(VII), Rhenium(VII), Palladium(II), and Plutonium(IV)

2,2′‐(Methylimino)bis(N,N‐dioctylacetamide) (MIDOA) was developed as a new extractant for technetium. MIDOA has a similar backbone to TODGA, N,N,N′,N′‐tetraoctyldiglycolamide, where the nitrogen atom bearing a methyl group replaces the ether oxygen in TODGA. MIDOA is highly lipophilic and ready to use in the HNO₃–n‐dodecane extraction system. The distribution ratio (D) for Tc(VII) is extremely high. In addition, Cr(VI), Re(VII), Mo(VI), W(VI), Pd(II), and Pu(IV) are well extracted by MIDOA. MIDOA has high selectivity toward certain oxometallates. The D(Tc) values decrease gradually with HNO₃, H⁺, and NO₃ ^? concentrations, and the log D vs log [MIDOA] dependence indicates the species extracted to be the 1:1 metal‐ligand complex. It is clear that MIDDA [2,2′‐(methylimino)bis(N,N‐didodecylacetamide)] and IDDA [2,2′‐(imino)bis(N,N‐didodecylacetamide)], which have structures analogous to MIDOA, have similar extraction behavior to that of MIDOA.     

Photo‐reduction and adsorption in aqueous Cr(VI) solution by titanium dioxide,carbon nanotubes and their composite

BACKGROUND: This study compared the removal of aqueous Cr(VI) by multi‐walled carbon nanotubes (CNTs) modified by sulfuric acid, titanium dioxide (TiO₂) and composite of CNTs and TiO₂. RESULTS: More than 360 h contact time was needed to completely adsorb 3 mg L^?1 of Cr(VI) by CNTs, indicating that the rate of adsorption by CNTs alone was slow. The reaction time approaching equilibrium depended on the Cr(VI) concentration. XPS analysis of CNTs after adsorbing Cr(VI) showed that the Cr(VI) on the surface of CNTs was partially reduced to Cr(III). A 3 mg L^?1 solution of Cr(VI) was fully photocatalyzed by commercial TiO₂ (Degussa P25) in less than 0.5 h under UV irradiation. Unlike P25, reduction by another commercial TiO₂ (Hombikat UV100) took 4 h and more than 2 h were necessary for reduction by the composite. Thus the efficiency of Cr(VI) photo‐reduction by the composite was lower than by TiO₂, but higher than that by CNTs. XPS analysis of TiO₂ and composite showed the existence of both Cr(VI) and Cr(III) on their surfaces. CONCLUSION: In contrast to TiO₂, the reduction rate of aqueous Cr(VI) using CNTs as adsorbent was slow. P25 had a markedly higher photocatalytic efficiency than the composite or UV100 alone. Using P25 to reduce aqueous Cr(VI) has a higher potential for practical application. The diameters of TiO₂ and CNTs and the ratio of TiO₂/CNTs are key problems in the preparation of TiO₂/CNTs composite. Copyright © 2011 Society of Chemical Industry     

Gold nanoparticle formation using Shewanella oneidensis: a fast biosorption and slow reduction process

BACKGROUND: The metal respiring bacterium Shewanella oneidensis has previously been used for reduction of Pd(II) into Pd(0) nanoparticles. This study investigated whether Shewanella oneidensis could also perform the reduction of Au(III) to Au(0). The kinetics of both the biosorption and reduction of Au(III) were studied. RESULTS: Biosorption of Au(III) was a fast and efficient process, and depended on the presence of an electron donor, the pH and the medium used. The reduction process, however, appeared to be a slow process, requiring the presence of an electron donor. As reduction also occurred in heat‐killed cells, it is suggested that the reduction is non‐enzymatic. At a concentration of 100 mg L^?1 Au(III), the nanoparticles were mainly smaller than 10 nm and precipitated intracellularly. With H₂ as the electron donor, it was shown that the location of the particles and the size could be steered by changing the concentration of Au(III). CONCLUSIONS: After a fast biosorption and slow reduction process, Au(0)‐nanoparticles were formed inside the cells or on the cell wall of Shewanella oneidensis. In most cases, these particles had interesting properties, such as small size and a narrow size distribution, which can make them suitable for applications in, for example, catalysis. Copyright © 2010 Society of Chemical Industry     

Electroreduction of hexavalent chromium by polyaniline

BACKGROUND: A plate‐gap model interpretation of enzymatic reaction kinetics and rotating disc voltammetry were applied for evaluation of the nature of the reaction of the electroreduction of Cr(VI) (as dichromate ions) on a polyaniline (PANI)‐modified glassy carbon (GC) electrode. RESULTS: The kinetic parameters (the maximal current (V_max) and Michaelis constant (K_M)) for electroreduction of Cr(VI) on the PANI‐modified GC electrode were determined as V_max = 0.34 × 10^?7 mol cm^?3 s^?1 and K_M = 0.47 × 10^?6 mol cm^?3. The reduction of dichromate is intensified by PANI film growth. CONCLUSION: To characterise the electroreduction of Cr(VI) on a PANI‐modified GC electrode, the kinetic parameters of the reaction were determined using a plate–gap model interpretation of enzymatic reaction kinetics and rotating disc voltammetry. The catalytic nature of Cr(VI) electroreduction on the PANI‐modified electrode has been shown. Copyright © 2009 Society of Chemical Industry     

Fabrication of supported Pd–Ir/Al2O3 bimetallic catalysts for 2‐ethylanthraquinone hydrogenation

A series of χ wt % Pd‐(1‐χ) wt % Ir (χ = 0.75, 0.50, and 0.25) catalysts supported on γ‐Al₂O₃ have been prepared by co‐impregnation and calcination‐reduction, and subsequently employed in the hydrogenation of 2‐ethylanthraquinone—a key step in the manufacture of hydrogen peroxide. Detailed studies showed that the size and structure of the bimetallic Pd–Ir particles vary as a function of Pd/Ir ratio. By virtue of its small metal particle size and the strong interaction between Pd and Ir, the 0.75 wt % Pd–0.25 wt % Ir/Al₂O₃ catalyst afforded the highest yield of H₂O₂, some 25.4% higher than that obtained with the monometallic 1 wt % Pd catalyst. Moreover, the concentration of the undesired byproduct 2‐ethyl‐5,6,7,8‐tetrahydroanthraquinone (H₄eAQ) formed using the Pd–Ir bimetallic catalysts was much lower than that observed with the pure Pd catalyst, which can be assigned to the geometric and electronic effects caused by the introduction of Ir. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3955–3965, 2017     

Use of polyethylene films photografted with 2‐(dimethylamino)ethyl methacrylate as a potential adsorbent for removal of chromium (VI) from aqueous medium

A new polymeric adsorbent material based on polyethylene (PE) was prepared by photografting of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) as a positively chargeable monomer to a PE film. The effects of the experimental parameters, such as the pH value, temperature, and grafted amount on adsorption of chromium(VI) (Cr(VI)) ions were investigated for the DMAEMA‐grafted PE (PE‐g‐PDAMEMA) films. The maximum adsorption capacity was obtained at the initial pH value of 3.0 for a PE‐g‐PDMAEMA film with 1.8 mmol/g and the maximum adsorption capacity obtained was higher than or compatible to those of many of the other polymeric adsorbents prepared for Cr(VI) ions. The adsorption kinetics obeyed the mechanism of the pseudo‐second order kinetic model and adsorption of Cr(VI) ions on PE‐g‐PDMAEMA films was well expressed by the Langmuir isotherm model. A high Langmuir adsorption constant suggests that the adsorption of Cr(VI) ions occurs between protonated dimethylamino groups and ions mainly through the electrostatic interaction. Cr(VI) ions adsorbed were successfully desorbed from a PE‐g‐PDMAEMA film in solutions of NaCl, NH₄Cl, NH₄Cl containing NaOH, and NaOH and a PE‐g‐PDMAEMA film was regenerated and repeatedly used for adsorption of Cr(VI) ions without appreciable loss in the adsorption capacity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43360.     

Photocatalytic reduction of chromium and oxidation of organics by polyoxometalates

The photocatalytic reduction of Cr(VI) to the less toxic Cr(III) is presented in the presence of the polyoxometalates (POM) PW₁₂O₄₀³⁻ or SiW₁₂O₄₀⁴⁻ as photocatalyst and an organic substrate (salicylic acid or propan-2-ol) as electron donor. Cr(VI), as dichromate, is reduced to Cr(III), according to the 6:1 stoichiometry of PW₁₂O₄₀⁴⁻ versus Cr₂O₇²⁻ indicated from experiments in the dark. Increase of POM or salicylic acid (SA) concentration accelerates, till a saturation value, both the reduction of metal and the oxidation of the organic, suggesting that these two conjugate reactions act synergistically. The photocatalytic action of POM is not so important in the case of highly concentrated solutions of organics that exhibit direct photochemical reduction of Cr(VI), i.e. propan-2-ol (i-prOH), while it becomes important at low concentrations of i-prOH, especially for organics that do not react directly photochemically with Cr(VI), such as SA. Increase of Cr(VI) concentration enhances consumption of SA and Cr(VI) till an optimum value, due to inner filter effect. The method is suitable for a range of chromium concentration from 5–100 ppm achieving complete reduction of Cr(VI) to Cr(III) up to non-detected traces (>98%). The presence of oxygen does not influence the efficiency of SA and Cr(VI) consumption. In contrast to the semiconductor-based heterogeneous photocatalysis, the POM-based homogeneous process seems superior in the frame that: (i) it remains catalytic throughout illumination by providing more active sites and (ii) among the two POM used, the one that is more efficient in the degradation of the organic, that is PW₁₂O₄₀³⁻ compared to SiW₁₂O₄₀⁴⁻, is also more efficient in reducing Cr(VI), due to a kinetic effect, and a compromise is not needed.     

Reduction of hexavalent chromium by copper

The galvanic reaction of metallic copper in Cr(VI)-laden aqueous solutions of varying pH was examined by in situ u.v.–visible spectrophotometry, rotating disc electrode chronopotentiometry and cyclic voltammetry. The galvanic reaction in 0.2 M H₂SO₄ solutions was pseudo first order in Cr(VI) concentration. Experiments with both magnetically stirred solutions and a copper mesh or a copper film in a rotating disc electrode configuration revealed the reaction to be diffusion-controlled with respect to Cr(VI) transport to the copper surface. Finally, cyclic voltammetry data in Cr(VI)-laden media of varying pH underline the important role of protons in the galvanic reaction.     

Simultaneous phenol removal and biological reduction of hexavalent chromium in a packed‐bed reactor

BACKGROUND: Phenol and hexavalent chromium are considered industrial pollutants that pose severe threats to human health and the environment. The two pollutants can be found together in aquatic environments originating from mixed discharges of many industrial processes, or from a single industry discharge. The main objective of this work was to study the feasibility of using phenol as an electron donor for Cr(VI) reduction, thus achieving the simultaneous biological removal/reduction of the two pollutants in a packed‐bed reactor. RESULTS: A pilot‐scale packed‐bed reactor was used to estimate phenol removal with simultaneous Cr(VI) reduction through biological mechanisms, using a new mixed bacterial culture originated from Cr(VI)‐reducing and phenol‐degrading bacteria, operated in draw–fill mode with recirculation. Experiments were performed for feed Cr(VI) concentration of about 5.5 mg L^?1, while phenol concentration ranged from 350 to 1500 mg L^?1. The maximum reduction/removal rates achieved were 0.062 g Cr(VI) L^?1 d^?1 and 3.574 g phenol L^?1 d^?1, for a phenol concentration of 500 mg L^?1. CONCLUSION: Phenol removal with simultaneous biological Cr(VI) reduction is feasible in a packed‐bed attached growth bioreactor. Phenol was found to inhibit Cr(VI) reduction, while phenol removal was rather unaffected by Cr(VI) concentration increase. However, the recorded removal rates of phenol and Cr(VI) were found to be much lower than those obtained from previous research, where the two pollutants were examined separately. Copyright © 2008 Society of Chemical Industry     

Adsorption of Cr(VI) ions onto poly(ethylene glycol dimethacrylate‐1‐vinyl‐1,2,4‐triazole)

Poly(ethylene glycol dimethacrylate‐1‐vinyl‐1,2,4‐triazole) [poly(EGDMA‐VTAZ)] beads (average diameter = 150–200 μm) were prepared by copolymerizing ethylene glycol dimethacrylate (EGDMA) with 1‐vinyl‐1,2,4‐triazole (VTAZ). Poly(EGDMA‐VTAZ) beads were characterized by swelling studies and scanning electron microscope (SEM). The adsorption of Cr(VI) from solutions was carried at different contact times, Cr(VI) concentrations, pH, and temperatures. High adsorption rates were achieved in about 240 min. The amount of Cr(VI) adsorbed increased with increasing concentration and decreasing pH and temperature. The intraparticle diffusion rate constants at various temperatures were calculated. Adsorption isotherms of Cr(VI) onto poly(EGDMA‐VTAZ) have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The pseudo first‐order kinetic model was used to describe the kinetic data. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes. The dimensionless separation factor (R_L) showed that the adsorption of metal ions onto poly(EGDMA‐VTAZ) was favorable. It was seen that values of distribution coefficient (K_D) decreasing with Cr(VI) concentration in solution at equilibrium (C_e) indicated that the occupation of activate surface sites of adsorbent increased with Cr(VI). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Capacity of Cr(VI) reduction in an aqueous solution using different sources of zerovalent irons

Zerovalent iron (ZVI) has drawn intense interest as an effective and inexpensive tool to enhance degradation of various environmental contaminants. Reduction of Cr(VI) to Cr(III) by ZVI merits environmental concern as a hazardous species is transformed into a non-hazardous one. Objectives of this research were to assess kinetics and capacity of Cr(VI) reduction by different sources of ZVIs, of which chemical parameters can base in situ application of ZVI to treat Cr(VI) contaminated water. Reduction kinetics were first-order and rapid showing that 50% of the initial Cr(VI) was reduced within 7.0 to 347 min depending on Cr(VI) concentration, temperature and ZVI source. The reduction rates were increased with decreasing the initial Cr(VI) concentrations and increasing the reaction temperatures. The J ZVI (Shinyo Pure Chemical Co., Japan) was more effective in Cr(VI) reduction than PU (Peerless Metal Powders, USA). The maximum reduction capacities of J and PU ZVIs at 25°C were 0.045 and 0.042 mmol g⁻¹ Fe⁰, respectively. A relatively higher value of the net reaction energy (E _a ) indicated that Cr(VI) reduction by ZVI was temperature dependent and controlled by surface properties of ZVI. Chemical parameters involved in the Cr(VI) reduction by ZVI such as temperature quotient, kinetic rates, and stoichiometry indicated that the ZVI might be effective for in situ treatment of the Cr(VI) containing wastewater.     

Improved Stability and Catalytic Activity of Palladium Nanoparticle Catalysts using Phosphine‐Functionalized Imidazolium Ionic Liquids

Palladium nanoparticles (Pd NPs) stabilized by 6 different phosphine‐functionalized ionic liquids (PFILs) were synthesized in imidazolium‐based ionic liquids (ILs) using H_2(g) (4 bar) as a reductant. Characterization showed well‐dispersed particles of ∼3 nm (TEM) and confirmed the PFIL stabilization of the NPs (XPS). The PFILs were composed of an imidazolium functionality separated from the phosphine group by a propyl or undecyl chain. The counter anions for both FILs and IL solvents were chosen from N‐bis(trifluoromethanesulfonyl)imide (Tf₂N⁻), trifluoromethanesulfonate (TfO⁻) or hexafluorophosphate (PF₆⁻). Colloidal suspensions of the Pd NPs were employed as biphasic hydrogenation catalysts for the reduction of the olefinic bond in styrene under mild conditions (50 °C, 4 bar H_2(g), 1.5 h). The PFIL‐stabilized Pd NPs were effective hydrogenation catalysts and showed superior activity and recyclability over NPs synthesized in the absence of PFILs. Poisoning tests of the Pd NP catalysts and characterization of the electronic properties of the phosphine were also performed.