Adsorptive removal of technetium‐99 using macroporous poly(GMA‐co‐EGDMA) modified with diethylene triamine

The possibility of sorption of technetium‐99 in the form of pertechnetate anion (TcO₄^?) and the sorption kinetics for removing TcO₄^? from aqueous solution by chelating polymers based on glycidyl methacrylate (GMA) were investigated. Two samples of macroporous crosslinked poly(glycidyl methacrylate‐co‐ethylene glycol dimethacrylate) (PGME), with different amount of the crosslinker (ethylene glycol dimethacrylate, EGDMA), were synthesized by suspension copolymerization and functionalized with diethylene triamine (deta). We propose that nonspecific sorption of pertechnetate anion via electrostatic interactions takes place at the protonated amino groups of macroporous crosslinked copolymer. The results of batch experiments performed at pH 1–14 showed fast sorption kinetics for removing TcO₄^? by amino‐functionalized PGME‐deta in a wide range of pH, that is, from 1.0 to 9.0. Almost complete removal of TcO₄^? (91–98%) was reached within 180 min in the stated pH range (1.0–9.0), with the sorption half‐times of under 25 min. The partitioning coefficients of linear adsorption isotherms, with 180‐min equilibrium time, reach the high values of 2130 mL g^?1 and 1698 mL g^?1 for the two samples of synthesized PGME‐deta. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Sorption of textile dye from aqueous solution by macroporous amino‐functionalized copolymer

Macroporous poly(glycidyl methacrylate‐co‐ethylene glycol dimethacrylate) (PGME) was synthesized by suspension copolymerization and functionalized with diethylene triamine (PGME‐deta). The effect of pH, contact time, and sorbent mass on sorption efficiency of initial and functionalized copolymer sample for removal of Acid Orange 10 dye from aqueous solutions was studied. No dye was sorbed by nonfunctionalized copolymer, indicating that sorption of Acid Orange 10 by PGME‐deta is specific, through amino groups. The isotherm data are best fitted by Langmuir model, indicating homogeneous distribution of active sites in PGME‐deta as well as monolayer sorption. Sorption kinetics study showed that the sorption of Acid Orange 10 by PGME‐deta obeys the pseudo‐second‐order kinetic model. It was shown that PGME‐deta selectively sorbs Acid Orange 10 from binary solution with Bezaktiv Rot reactive dye. The comparison of sorption characteristics of PGME‐deta with activated carbon showed that this functionalized copolymer might be used as an alternative sorbent for textile dyes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Effects of ethylene glycol on the synthesis of ampicillin using immobilized penicillin G acylase

The effects of organic cosolvents on the synthesis of ampicillin from phenylglycine methyl ester (PGME) and 6‐amino penicillanic acid (6‐APA) using immobilized Bacillus megaterium penicillin G acylase have been examined. Several cosolvents were tested for their influence on the enzyme in terms of enzyme stability and hydrophobicity. Among the cosolvents tested, ethylene glycol was found to increase the yield of ampicillin by 39–50%. The effects of ethylene glycol on the pK_a of PGME, the hydrolysis of ampicillin and PGME, and synthetase/amidase and esterase/amidase ratios were also studied. Experimental data indicated that ethylene glycol inhibited more the hydrolysis of the ampicillin than the hydrolysis of the PGME and the synthetase/amidase ratio varied from 0.2 to 0.88 when the concentration (v/v) of the cosolvent increased from 0 to 40%. The enhancement of the synthesis yield was mainly caused by the reduction in the hydrolysis of acyl donor (PGME) and product (ampicillin) in the water–cosolvent system. © 2003 Society of Chemical Industry     

Removal of Cr (VI) from aqueous solution by newspapers

The potential to remove Cr (VI) ions from aqueous solution using newspapers was investigated in the present study. The effects of relevant parameters such as solution pH, adsorbent concentration, and reaction temperature on Cr (VI) adsorption were examined. The adsorption of Cr (VI) ions onto newspapers was found to be highly pH-dependent and the highest uptake occurred at pH 1.0. The sorption equilibrium data were correlated to the Langmuir, Freundlich, Redlich-Peterson and Dubinin-Radushkevich equations. Five different non-linear error functions were examined and the result indicated that the Freundlich and Redlich-Peterson equations better fitted the equilibrium data than Langmuir isotherm. The maximum sorption capacity was found to be 55.06 mg/g at pH 1.0, adsorbent concentration 4 g/L and reaction temperature of 30 °C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) were also evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The kinetic experimental data were well fitted by the pseudo-second order, external film diffusion and diffusion models allowing the corresponding parameters to be evaluated. The sorption capacity increased with the decrease of adsorbent concentration.     

Application of Chattim tree (devil tree,Alstonia scholaris) saw dust as a biosorbent for removal of hexavalent chromium from contaminated water

“Devil tree saw dust”; a novel biosorbent has been utilised successfully for the removal of hexavalent chromium from contaminated water. Batch adsorption procedure is utilised to test the ability of saw dust as an adsorbent for hexavalent chromium (reduction coupled adsorption). The contribution of various parameters on sorption, such as contact time, sorbate concentration, pH of the medium and temperature were estimated and maximum uptake of hexavalent chromium from contaminated water was 333.33 mg g^?1 at pH 2.0 and temperature of 35°C. Hexavalent chromium uptake from contaminated water followed the pseudo‐first‐order rate expression. The standard free energy change (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰) have also been evaluated and it has been concluded that the sorption was feasible, spontaneous and endothermic in nature. The process follows well Langmuir isotherm. Fourier Transform Infra‐Red (FTIR) spectroscopy and scanning electron microscopy (SEM) of hexavalent chromium loaded and unloaded saw dust were performed, SEM clearly indicates chromium adsorption. FTIR spectroscopy revealed the involvement of carbonyl, hydroxyl and amide groups on the cell surfaces in chromium binding. Very good adsorption capacity and low cost or cost free of devil tree saw dust makes this biosorbent as one of the best adsorbents for removal of hexavalent chromium from contaminated water. © 2012 Canadian Society for Chemical Engineering     

Cr(VI) reduction by bio and bioinorganic catalysis via use of bio‐H2: a sustainable approach for remediation of wastes

Use of biologically‐produced hydrogen (bio‐H₂) as an electron donor for Cr(VI) reduction by native and palladized cells of Desulfovibrio vulgaris NCIMB 8303 was demonstrated. The bio‐H₂ was produced fermentatively by Escherichia coli HD701 (a strain upregulated with respect to formate hydrogenlyase expression) using glucose solution or two industrial confectionery wastes as fermentable substrates. Maximum Cr(VI) reduction occurred at the expense of bio‐H₂ using palladized biomass (bio‐Pd(0)), with negligible residual Cr(VI) remaining from a 0.5 mmol dm^?3 solution after 2.5 h. Use of bio‐H₂ as the electron donor for Cr(VI) reduction by agar‐immobilized bio‐Pd(0) in a continuous‐flow system gave 90% reduction efficiency at a flow residence time of 0.7 h, which was maintained for the duration of bio‐H₂ evolution by E. coli HD701. This study shows the potential to remediate toxic metal waste at the expense of food processing waste, as a sustainable alternative to landfilling. Copyright © 2007 Society of Chemical Industry     

Immobilization of catalase on a novel polymer support,crosslinked polystyrene ethylene glycol acrylate resin: Role of the macromolecular matrix on enzyme activity

Crosslinked polystyrene ethylene glycol acrylate resin (CLPSER) was developed for the immobilization of the enzyme catalase by the introduction of a crosslinker, O,O′‐bis(2‐acrylamidopropyl) poly(ethylene glycol)₁₉₀₀, to styrene. The crosslinker was prepared by the treatment of acryloyl chloride with O,O′‐bis(2‐aminopropyl) poly(ethylene glycol)₁₉₀₀ in the presence of diisopropylethylamine. The resin was characterized with IR and ¹³C‐NMR spectroscopy. The catalytic activity of the catalase‐immobilized system of CLPSER was compared with divinylbenzene‐crosslinked polystyrene, ethylene glycol dimethacrylate crosslinked polystyrene, and 1,4‐butanediol dimethacrylate crosslinked polystyrene systems. Crosslink levels of 2, 8, and 20 mol % were evaluated. Among these crosslinked systems, the 2 mol % system was found to be most suitable to support catalytic activity. When a long flexible hydrophilic poly(ethylene glycol) crosslink, introduced between the polystyrene (PS) backbone and functional groups was used for immobilization, the extent of coupling and enzyme activity increased. Depending on the nature of the support, the catalytic activity of the system varied. The hydrophilic CLPSER support was most efficient for immobilization compared to the other PS‐based supports. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 8–19, 2005     

Effects of experimental variables on the synthesis of porous matrices

Macroporous beads, poly(ethylene glycol dimethacrylate‐co‐acrylic acid) [poly(EGDMA‐co‐AAc)], and poly(ethylene glycol dimethacrylate‐co‐hydroxyethyl methacrylate) [poly(EGDMA‐co‐HEMA)] were prepared by the suspension polymerization technique in the presence of a porogen agent. Different experimental conditions such as amount of initiator, porogen type, and temperature were studied to optimize the polymerization systems. These hydrophilic copolymers were characterized by IR spectroscopy, scanning electron microscopy, specific surface area, and swelling in water. A new parameter, H, defined as the ratio between the equilibrium weight swelling ratio (q_w) and equilibrium volume swelling ratio (q_v), allowed to select the reaction conditions from which matrices with high capacity of water sorption and low stretching degree were reached. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 920–927, 2001     

Sorption and desorption parameters of water or ethanol in light‐cured dental dimethacrylate resins

Two cycles of sorption/desorption of water or ethanol by light‐cured dental resins of bisphenol A glycol dimethacrylate (Bis‐GMA), bisphenol A ethoxylated dimethacrylate (Bis‐EMA) urethane dimethacrylate (UDMA) triethylene glycol dimethacrylate and decanediol dimethacrylate (D₃MA) were studied. The experimental curves m_t = f(t) taken for the first water sorption by poly‐Bis‐GMA, poly‐Bis‐EMA and poly‐UDMA showed a maximum. A maximum was also observed in the curve obtained for first sorption of ethanol by poly‐Bis‐GMA. In all other cases, the curves for sorption or desorption of water or ethanol showed Fickian behavior. The experimental data obtained for first sorption of water or ethanol were perfectly fitted to a new proposed equation, which predicts water or ethanol sorption with simultaneous extraction of unreacted the monomer. This equation gave us the possibility for the determination of the diffusion coefficient of the extraction of the unreacted Bis‐GMA during the water and ethanol sorption, as well as the diffusion coefficient of the extraction of the unreacted Bis‐EMA and UDMA during the water sorption. The maximum water or ethanol absorbed at equilibrium and the diffusion coefficient are determined from the second sorption/desorption cycle during which the extraction of the monomer is negligible. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Behaviors of polyelectrolyte AAm/AMPS/bentonite composite hydrogels in uptake of uranyl ions from aqueous solutions

Uranyl ion (UO₂²⁺) sorption properties of polyelectrolyte composite hydrogels made by the polymerization of acrylamide (AAm) with 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) and clay such as bentonite (Bent) were investigated as a function of composition to find materials with swelling and uranyl ion sorption properties. Highly swollen AAm/AMPS hydrogels and AAm/AMPS/Bent composite hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with AMPS as co‐monomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4 butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. The influence of AMPS content in hydrogels was examined. Uranyl ion adsorption from aqueous solutions was studied by batch sorption technique at 25°C. The effect of uranyl ion concentration and mass of AMPS on the uranyl ion adsorption were examined. Finally, adsorption capacity (the amount of sorbed uranyl ion per gram of dry hydrogel) (q) was calculated to be 0.67 × 10⁻³–2.11 × 10⁻³ mol uranyl ion per gram for the hydrogels. Removal effiency of uranyl ions (RE%) was changed range 9.05–29.92%. The values of partition ratio (K_d) of uranyl ions was calculated to be 0.10–0.43 for AAm/AMPS hydrogels and AAm/AMPS/Bent composite hydrogels, respectively. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Porous microparticles based on methacrylic copolymers and gellan as drug delivery systems

Two types of porous microparticles based on glycidyl methacrylate, dimethacrylic monomers (ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and triethylene glycol dimethacrylate) and gellan were prepared by two methods. The first method was aqueous suspension polymerization in the presence of N‐butyl acetate as porogenic agent when the crosslinking and grafting reactions were achieved in a single step. The second method was based on the reaction between hydroxyl groups belonging to gellan and the epoxy groups situated on the surface of porous microparticles based on glycidyl methacrylate and dimethacrylic monomers in basic medium. The microparticles with and without gellan were characterized by Fourier transform infrared spectroscopy, SEM, AFM and TGA. Also, the porous structure was investigated in terms of pore volume, porosity and specific surface. The swelling behaviour in aqueous solution with different pH values as well as sorption studies of cefuroxime sodium salt onto porous microparticles were investigated. The presence of gellan in the structure of the microparticles leads to porous materials characterized by higher specific surface areas (S_sp = 78–140 m² g^–1), higher swelling capacities (S_w = 162%–365%) and higher sorption capacities of the drug (q_e = 101–147 mg g^–1) compared to microparticles without gellan in their structures (S_sp = 73–85 m² g^–1; S_w = 139%–209%; q_e = 70–110 mg g^–1). © 2019 Society of Chemical Industry     

Coals as sorbents for the removal and reduction of hexavalent chromium from aqueous waste streams

The aim of this study is to demonstrate the potential of coals as a low-cost reactive barrier material for environmental protection applications, with the ability to prevent leaching of toxic Cr(VI) and other transition metals. Depending upon the type of ion and the surface functionalities, the uptake can involve ion sorption, ion exchange, chelation and redox mechanisms with the surface functionalities being considered as partners in electron transfer processes. The capacity for Cr(VI) uptake of low rank coals and oxidized bituminous coals has been found to lie within the range 0.2-0.6 mM g⁻¹. Air oxidation of bituminous coals can increase their Cr(VI) removal capacities. The effect of air oxidation of coals on uptake capacity was more pronounced for Cr(VI) than Cr(III), but less than for Hg(II) and the other ions (Ca²⁺, Ba²⁺, Zn²⁺, Cd²) investigated. As previously found for Hg(II), redox mechanisms play an important role in Cr(VI) uptake, with sorption of the resultant Cr(III) being aided by the functionalities arising from oxidation of the coal surface. In acidic media, much of the resultant Cr(III) is exchanged back into solution by hydrogen ions, but some of the sorbed chromium is irreversibly bound to the coal. The reduction of Cr(VI) alone is often considered a satisfactory solution in view of Cr(III) being essentially non-toxic.     

Reduction of hexavalent chromium by Bacillus sp. isolated from chromite mine soils and characterization of reduced product

BACKGROUND: The reduction of highly mobile and toxic hexavalent chromium by bacterial strains is considered to be a viable alternative to reduce Cr(VI) contamination, in soils and water bodies, emanating from the overburden dumps of chromite ores and mine drainage. The present study reports the isolation of Cr(VI) resistant bacterial strains from an Indian chromite mine soil and their potential use in reduction of hexavalent chromium. RESULTS: Among the isolates, a bacterial strain (CSB‐4) was identified as Bacillus sp. based on standard biochemical tests and partial 16SrRNA gene sequencing, which was tolerant to as high as 2000 mg L^?1 Cr(VI) concentration. The strain was capable of reducing Cr(VI) to Cr(III) in different growth media. Under the optimized conditions pH ～7.0, 100 mg L^?1 Cr(VI), 35 °C temperature and stirring speed 100 rpm, CSB‐4 reduced more than 90% of Cr(VI) in 144 h. The time course reduction data fitted well an exponential rate equation yielding rate constants in the range 3.22 × 10^?2 to 6.5 × 10^?3 h^?1 for Cr(VI) concentration of 10–500 mg L^?1. The activation energy derived from temperature dependence rate constants between 25 and 35 °C was found to be 99 kJ mol^?1. The characterization of reduced product associated with bacterial cells by SEM‐EDS, FT‐IR and XRD was also reported. CONCLUSION: Reasonably high tolerance and reduction ability of indigenous Bacillus sp. (CSB‐4) for Cr(VI) under a wide range of experimental conditions show promise for its possible use in reclamation of chromite ore mine areas including soils and water bodies. Copyright © 2010 Society of Chemical Industry     

Water and dye sorption studies of novel semi IPNs: Acrylamide/4‐styrenesulfonic acid sodium salt/peg hydrogels

In this study, it has been investigated that the incorporation of poly(ethylene glycol), (PEG) and 4‐styrenesulfonic acid sodium salt, (NaSS) into acrylamide, (AAm) hydrogel during free radical solution polymerization synthesis. Poly (ethylene glycol)dimethacrylate, (PEGDMA) was used as a multifunctional crosslinker in polymerization. The main purpose of this study was to combine both monomers and a polymer in a new polymeric system. Dye sorption properties of hydrogels and semi IPNs were investigated by using cationic dye such as Union Green B (Janus Green B, UGB). Swelling and sorption studies were carried out at 25°C. For structural characterization, FTIR analysis was made. The equilibrium percentage swelling (S_eq%) ranges are 660–1330% for AAm/NaSS hydrogels and 580–1310% for AAm/NaSS/PEG semi IPNs. To determine the sorption behaviors of cationic dye UGB, some sorption parameters such as sorption capacity (q), adsorption percentage (Ads%) and partition coefficient (K_d) of the hydrogels were investigated. Binding characterization has been studied by Langmuir linearization method. The sorption capacity values of the hydrogel systems were changed between 1.24 × 10^?4 and 4.05 × 10^?4 mol g^?1. The values of Ads% of the hydrogels were changed among 18?67%, and the values of K_d of the hydrogels were between 0.22 and 2.02. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

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     

Direct synthesis of surface molecularly imprinted polymers based on vinyl–SiO2 nanospheres for recognition of bisphenol A

Molecularly imprinted polymers (MIP) with high performance in selectively recognizing bisphenol A (BPA) were prepared by using a novel and facile surface molecular‐imprinting technique. Vinyl‐functionalized, monodispersed silica spheres were synthesized by a one‐step emulsion reaction in aqueous solution. Then, BPA surface molecularly imprinted polymers (SMIP) were prepared by polymerization with 4‐vinylpyridine as the functional monomer and ethylene glycol dimethacrylate as the crosslinker. Maximal sorption capacity (Q_max) of the resulting SMIP was up to 600 μmol g^?1, while that of nonimprinted polymers was only 314.68 μmol g^?1. Kinetic binding study showed that sorption capacity reached 70% of Q_max in 20 min and sorption equilibrium at 80 min. SMIP had excellent accessibility and affinity toward BPA, for the selectivity coefficients of SMIP for BPA in respect to phenol, p‐tert‐butylphenol, and o‐phenylphenol were 3.39, 3.35, and 3.02, respectively. The reusage process verified the SMIP owning admirably stable adsorption capacity toward BPA for eight times. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Relaxational behavior and swelling‐pH master curves of poly[(diethylaminoethyl methacrylate)‐graft‐(ethylene glycol)] hydrogels

Poly[(diethylaminoethyl methacrylate)‐graft‐(ethylene glycol)] hydrogels were prepared with a molar ratio of 10:1 of diethylaminoethyl methacrylate to poly(ethylene glycol) of number‐average molecular weights (M_n) 200, 400 and 1000 g mol^?1 using tetra(ethylene glycol) dimethacrylate to give a crosslinking ratio between 0.5 and 4.0 %. Glucose oxidase and catalase were immobilized in the matrix during polymerization. The maximum enzyme loading used was 6.6 × 10^?4 g of glucose oxidase per g of polymer. The equilibrium and dynamic swelling properties of these hydrogels were investigated. The pH‐dependent equilibrium swelling characteristics showed a sharp transition between the swollen and the collapsed state at pH 7.0. The dynamic response of the hydrogel discs to pH was analyzed in pulsatile pH conditions. The effects of particle size, crosslinking and molecular weight of poly(ethylene glycol) (PEG) on the dynamic swelling response were investigated. The pulsatile nature of the response was analyzed using Boltzmann superposition. Swelling–pH master curves were obtained. Copyright © 2004 Society of Chemical Industry     

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     

Dilute gelling systems: copolymers of styrene and glycol dimethacrylates

Gelation properties of the copolymers of styrene with various proportions of ¹⁴C labelled ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and polyethylene glycol (MW = 400) dimethacrylate have been studied. The thermal copolymerizations were carried out in 15% (v/v) solution in toluene. The rates of polymerization were found to increase with larger proportions of dimethacrylate cross-linking agents. The conversion at the gel point was surprisingly constant over a wide range of crosslinker concentration. The fraction of crosslinker saturated at both ends was found to increase in the order ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and polyethylene glycol 400 dimethacrylate. The proportion of completely reacted crosslinker increased only slowly with conversion. At very high concentrations of crosslinker, the onset of inhomogeneity was observed as described previously by Storey³ and Dusek¹⁸.