The synthesis of lactic-acid-based telechelic prepolymers

We have studied how different catalysts and diols affect the properties of low-molecular-weight (M_w (GPC) < 49800 g/mol) lactic-acid-based telechelic prepolymers. The catalysts and diols were tested separately in our previous studies. In this study, we used the best previously tested diols and catalysts together in order to prepare different types of telechelic prepolymers (for example, crystalline or amorphous). All condensation polymerizations were carried out in the melt, using different diols and different catalysts. The prepolymers were characterized by differential scanning calorimetry, gel permeation chromatography, titrimetric methods, and ¹³C nuclear magnetic resonance (¹³C-NMR). According to NMR, the resulting polymers contained less than 1 mol % of lactic acid monomer and less than 5.1 mol % of lactide. Dibutyltindilaurate, like tin(II)octoate, produced quite good molecular weights, but the resulting prepolymers contained exceptionally high amounts of D-lactic acid structures, and, therefore, these prepolymers were totally amorphous. Antimony(III)oxide produced a high-molecular-weight prepolymer when the diol used was aliphatic. Like DBTL, Sb₂O₃ produced amorphous prepolymers, which contained a lower amount of D-lactic acid structures than DBTL prepolymers. 1,8-dihydroxyanthraquinone produced a different kind of chain structure with Ti(IV)bu and Ti(IV)iso because one prepolymer had high crystallinity, and the other showed only a slight crystallinity. Sulphuric acid produced a very high-molecular-weight prepolymer with aliphatic 2-ethyl-1,3-hexanediol; and with aromatic diols, it produced quite good molecular weights, except with 1,8-dihydroxyanthraquinone. High-molecular-weight prepolymers produced with H₂SO₄ also showed high crystallinity; and, according to ¹³C-NMR, they did not contain lactide and D-lactic acid structures. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1011–1016, 1998     

Rheological properties of new polymer compositions for sand consolidation and water shutoff in oil wells

The rheological properties of some newly developed polymer compositions have been investigated with and without crosslinking. These polymer compositions were developed as a water shutoff and sand consolidation treatment agents for producing oil and gas wells. The effects of several variables on the rheology of the compositions were evaluated over a wide range of temperatures (25–110°C), shear rates (0–500 s^?1), brine percentages (0–15%), crosslinker types and concentrations (0–3%), and polymer concentrations (6–50%). It was found that increasing the shear rate from 0 s^?1 to 100 s^?1 caused shear thinning and reduction of the viscosity of the dilute solutions (6–13%) from 25 cP to ～ 3 cP at 80°C. In contrast, for the concentrated solutions (20–50%), the viscosity dropped slightly in the shear rate range 0–10 s^?1, and subsequently decreased more slowly up to shear rates of 500 s^?1. The viscosities of all polymer solutions dropped by a factor of 2 as the brine concentration increased from 0% to 15%. Finally, aging time coupled with shear rates and higher percentages of crosslinkers accelerate the buildup of viscosity and gelation time of the polymer compositions. For concentrated solutions, shear rates ranging within 0–200 s^?1 accelerated gelation time from 9.75 h to 2–3 h, when they were sheared at 80°C. The polymeric solutions exhibited Newtonian, shear‐thinning (pseudo‐plastic), and shear‐thickening (dilatant) behavior, depending on the concentration, shear rate, and other constituents. In most cases, the rheological behavior could be described by the power law. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The hydrogenation of HO-terminated telechelic polybutadienes in the presence of a homogeneous hydrogenation catalyst based on tris(triphenylphosphine)rhodium chloride

The hydrogenation kinetics of multiple bonds in HO-terminated telechelic polybutadienes was investigated using two types of these prepolymers prepared by the anionic and radical polymerization. The rate of addition of hydrogen to the π-bonds of these polydienes in the presence of tris(triphenylphosphine) rhodium chloride as a homogeneous hydrogenation catalyst was determined by the chemical structures of the starting polydienes, their concentration in the solvent, the partial hydrogen pressure, the concentration of the catalyst, and the temperature. The effect of kinetic parameters given above on the rate of hydrogenation reaction can be interpreted in the sense of Wilkinson's reaction mechanism of the hydrogenation of alkenes in the presence of the Rh(I)-complex. Due to the predominant 1,2-structural units, the anionic prepolymer reacted twice as quickly with hydrogen (k = 0.093 mol^?1 dm³ s^?1) compared with the radical prepolymer (k = 0.045 mol^?1 dm³ s^?1). During the hydrogenation of multiple bonds there is a partial loss of hydroxy groups in modified telechelic prepolymers; the extent of this reaction depends on reaction conditions of the hydrogenation reaction.     

Effect of an electric field on the transport of Th(IV) in the presence of Eu(III) and U(VI) through supported liquid membrane containing di‐2‐ethylhexylphosphoric acid

This paper investigates the transport of Th(IV) ions in nitric acid media through a supported liquid membrane (SLM) impregnated with di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene using an electric field. The transport was carried out in a three compartment cell fitted with microporous cellulose nitrate (SLM) and cation exchange membrane (Nafion). The effect of different parameters including nitric acid concentration in the feed solution, HDEHP concentration in the membrane, and HCl concentration were studied. The optimal conditions for Th(IV) transport were 0.1 mol dm^?3 HDEHP, 10^?3 mol dm^?3 HNO₃ in the feed solution, 1 mol dm^?3 HCl in compartment 2 and 1 mol dm^?3 HCl in compartment 3 at 25 °C. Under the optimal conditions of Th(IV) transport the recovery factor after 90 min was 0.25 without applying an electrostatic field, compared with 0.9 when the electric field was applied. The effect of electric current on the flux of Th(IV) through the membrane was also studied. The flux increased as the current density increased from 10 to 30 mA cm^?2 to reach a maximum value at 30 mA cm^?2 (8 × 10^?9 g eq cm^?2 s^?1). The transport percentages of 0.3 g dm^?3 Th(IV) in the presence of 0.1 g dm^?3 Eu(III) and 1 g dm^?3 U(VI) were 66, 84 and 15%, respectively. The determined selectivities of U(VI)–Th(IV) and Th(IV)–Eu(III) were 0.12 and 0.3, respectively, after 90 min. Therefore, the order of selectivity of this system is Eu(III) > Th(IV) > U(VI). © 2001 Society of Chemical Industry     

Capillary extrusion of elastomeric emulsion crosslinked interpenetrating networks

The rheological properties of an elastomeric emulsion thermosetting (EMSET) interpenetrating network (IPN) of poly(ethyl acrylate) (70 percent) and polystyrene (30 percent) were studied using a capillary rheometer to test if the submicron thermoset particles, persumably the flow units, could flow as a thermoplastic matrix. The IPN exhibited power law behavior over a wide range of shear rates (0.05 to 500 s^?1), with a power law exponent of approximately 0.18 over a large range of temperatures (80 to 200°C), without a yield stress or a Newtonian plateau evident. The flow activation energies were found to be comparable with most processable thermoplastic materials at 4 kcal/mole for constant shear rates, and 20 kcal/ mole for constant shear stresses. The effect of a roll mill shear modification step prior to extrusion indicated stability of the flow units. The pervasive rippling melt fracture and the significant slip velocity at the wall emphasized the importance of slip in the flow mechanism of this elastomeric EMSET IPN.     

Separation and Spectrophotometric Determination of Osmium(IV) and Ruthenium(III) with O-methoxyphenyl Thiourea as Chromogenic Legand: Sequential Separation of Osmium(IV), Ruthenium(III), and Platinum(IV)

A precise and selective method has been developed for extraction spectrophotometric determination of osmium(IV) and ruthenium(III) using o-methoxyphenyl thiourea (OMePT) as a chromogenic ligand. The basis of the proposed methods are osmium(IV)-OMePT complex was formed in 0.8 mol L^?1 at room temperature while ruthenium(III)-OMePT complex was formed in 3.4 mol L^?1 aqueous hydrochloric acid media after 5.0 min heating in boiling water bath. The osmium(IV)-OMePT and ruthenium(III)-OMePT complex were measured at 518 and 640 nm against the reagent blank, respectively. Complexes were also extracted in 10 mL chloroform and showed comparable absorbance values. Beer’s law was obeyed up to 110.0 μg mL^?1 for osmium(IV)-OMePT complex and up to 50.0 μg mL^?1 for ruthenium(III)-OMePT complex. Molar absorptivity and Sandell’s sensitivity of osmium(IV)-OMePT and ruthenium(III)-OMePT complexes were 2.12 × 10³ L mol^?1 cm^?1, 0.089 μg cm^?2 and 2.34 × 10³ L mol^?1 cm^?1, 0.043 μg cm^?2, respectively. The stoichiometry of osmium(IV)-OMePT and ruthenium(III)-OMePT complex was 1:1 and 1:2, respectively. Stability of osmium(IV)-OMePT complex was > 8 days and that of ruthenium(III)-OMePT complex was > 48 h. The proposed method was successfully applied for determination of osmium(IV) and ruthenium(III) from synthetic mixtures corresponding to platinum-osmium alloy and fissium alloy, respectively. The method was successfully applied for sequential separation of osmium(IV), ruthenium(III), and platinum(IV).     

Unvernetzte epoxid-amin-additionspolymere, 16. HPLC-analyse und 13C-NMR-spektroskopie von telechelen (diglycidylether-bisphenol A)-anilin-prepolymeren

Synthesis and properties of telechelic diglycidyletherbisphenol A (DGEBA)-aniline prepolymers with aminoalcohol endgroups are reported. The composition of the prepolymer mixtures obtained by addition polymerization was analyzed by means of HPLC using a LiChrosorb RP-18 column with water/acetonitrile gradient elution mode. The prepolymers represent a series of homologous oligo(aminodiols) 2 , n = (1), 2, 3, 4 ... which are separated into diastereomers. The average value n? depends on the molar ratio of the monomers and is varied between 1,0 and 14,0 resulting in M?_n (vapor pressure osmometry) 500–6000 g · mol^-1. C, H, N elemental analysis and ¹³C-NMR spectroscopy were used to estimate the chemical structure of the prepolymer mixtures.     

Construction and Performance Characteristics of Modified Screen Printed and Modified Carbon Paste Sensors for Selective Determination of Cu(II) Ion in Different Polluted Water Samples

Four new ion-selective electrodes (ISEs), based on N,N′-bis(salicylaldehyde)-p-phenylene diamine (SPD) as ionophore, are constructed for the determination of copper(II) ion. The modified carbon paste (MCPEs; electrodes I and II) and modified screen-printed sensors (MSPEs; electrodes III and IV) exhibit good potentiometric response for Cu(II) over a wide concentration range of 1.0 × 10^?6 – 1.0 × 10^?2 mol L^?1 for electrodes (I and II) and 4.8 × 10^?7–1.0 × 10^?2 mol L^?1 for electrodes (III and IV) with a detection limit of 1.0 × 10^?6 mol L^?1 for electrodes (I and II) and 4.8 × 10^?7 mol L^?1 for electrodes (III and IV), respectively. The slopes of the calibration graphs are 29.62 ± 0.9 and 30.12 ± 0.7 mV decade^?1 for electrode (I) (tricresylphosphate (TCP) plasticizer) and electrode (II) (o-nitrophenyloctylether o-NPOE plasticizer), respectively. Also, the MSPEs showed good potentiometric slopes of 29.91 ± 0.5 and 30.70 ± 0.3 mV decade^?1 for electrode (III) (TCP plasticizer) and electrode (IV) (o-NPOE plasticizer), respectively. The electrodes showed stable and reproducible potentials over a period of 60, 88, 120, and 145 days at the pH range from 3 to 7 for electrodes (II), (III), and (IV) and pH range from 3 to 6 for electrode (I). This method was successfully applied for potentiometric determination of Cu(II) in tap water, river, and formation water samples in addition to pharmaceutical preparation. The results obtained agree with those obtained with the atomic absorption spectrometry (AAS).     

Kinetic study of anionic polymerization of butadiene in a polar solvent

The kinetics of the propagation reaction for the polymerization of butadiene initiated by cumyl potassium in tetrahydrofuran solution at several temperatures have been studied. Kinetic data and electrolytic behaviour indicate that polybutadienyl free ions assume the whole of the propagation reaction. At 0°C, the respective rate constants for ion-pairs and free ions are 1 l mol^?1 s^?1 and 4.8 × 10⁴ l mol^?1 s^?1 respectively. The ionic dissociation constant is 7.8 × 10^?9 mol/l. The activation energy of the propagation reaction for free ions is 6.5 kcal/mol.     

Molecular orientation of polydimethylsiloxane induced by elongational and shearing strains

A study examining the molecular orientation of poly(dimethylsiloxane) for different combinations of elongational and shear strains is presented. Three different cases were studied: (1) pure elongational strain; (2) increasing shear and decreasing elongational strains; (3) increasing shear and increasing elongational strains. The experiments were performed in a converging flow cell (at room temperature), where elongational and shearing strain rates achieved values of 370 s^?1 and 640 s^?1 respectively. Values of the Hermans orientation function were obtained from measurements of birefringence and polarization angles while strain rates were estimated from laser Doppler anemometry velocity measurements. Prospects for predicting molecular orientation from the stress-optical laws and rheological flow models are outlined and commented on.     

Estimation of crosslinking of diallyl phthalate prepolymer. An investigation by infrared spectroscopy

The cure of the dially phthalate prepolymer was studied by means of infrared spectroscopy. It was found that the C?C stretching band of the allyl group, which appears at 1647 cm^?1 in diallyl phthalate monomer, splits into two bands at 1645 and 1651 cm^?1 in both of the prepolymers and cured resins derived therefrom, the split band being found to be mostly useful to investigate the highly cured resin system of diallyl phthalate. On the basis of the split band, α is defined as a new parameter expressing a degree of residual unsaturation of diallyl phthalate prepolymers as well as highly crosslinked polymers, as revealed experimentally. Further, α proved to correlate closely with other parameters such as the iodine value measured for the prepolymers, and swelling weight ratio or Barcoal hardness (hot) measured for the cured resins, it becoming evidently a convenient parameter to examine the degree of crosslinking of diallyl phthalate resin system. The effect of metal molds employed upon cure of prepolymers was also elucidated from the measured α values.     

Ceric ion‐induced graft copolymerization of acrylamide on cationic guar gum at low temperature

The solution polymerization of acrylamide (AM) on cationic guar gum (CGG) under nitrogen atmosphere using ceric ammonium sulfate (CAS) as the initiator has been realized. The effects of monomer concentration and reaction temperature on grafting conversion, grafting ratio, and grafting efficiency (GE) have been studied. The optimal conditions such as 1.3 mol of AM monomer and 2.2 × 10^?4 mol of CAS have been adopted to produce grafted copolymer (CGG1‐g‐PAM) of high GE of more than 95% at 10°C. The rates of polymerization (R_p) and rates of graft copolymerization (R_g) are enhanced with increase in temperature (<35°C).The R_p is enhanced from 0.43 × 10^?4 mol L^?1 s^?1 for GG‐g‐PAM to 2.53 × 10^?4 mol L^?1 s^?1 for CGG1‐g‐PAM (CGG1, degree of substitute (DS) = 0.007), and R_g from 0.42 × 10^?4 to 2.00 × 10^?4 mol L^?1 s^?1 at 10°C. The apparent activation energy is decreased from 32.27 kJ mol^?1 for GG‐g‐PAM to 8.09 kJ mol^?1 for CGG1‐g‐PAM, which indicates CGG has higher reactivity than unmodified GG ranging from 10 to 50°C. Increase of DS of CGG will lead to slow improvement of the polymerization rates and a hypothetical mechanism is put forward. The grafted copolymer has been characterized by infrared spectroscopy, thermal analysis, and scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3715–3722, 2007     

Comparative study of the determination of platinum by extraction with Cyanex 923 and Cyanex 471X from bromide media

The extraction equilibrium study of Pt(IV) was carried out with Cyanex 923 and Cyanex 471X in toluene from hydrobromic acid media to investigate their extraction capacity, since they have different donor atoms, ‘O’ and ‘S’. Their distribution equilibria were studied as a function of extractant concentration, diluents, hydrobromic acid concentration and the effect of temperature on extraction. Pt(IV) was quantitatively extracted with 0.1 mol dm^?3 Cyanex 923 in toluene from 5.0–8.0 mol dm^?3 HBr media and was stripped with 4.0 mol dm^?3 perchloric acid. However it was also quantitatively extracted with 0.1 mol dm^?3 Cyanex 471X (with 0.1 mol dm^?3SnCl₂) in toluene from 6.0–8.0 mol dm^?3 HBr media and was stripped with 1.0 mol dm^?3 stabilized sodium thiosulfate solution at pH 9.0. The slope analysis method indicated metal complex species of 1:1 for Pt(IV) with Cyanex 923 and Cyanex 471X in toluene from HBr media. These methods were successfully applied to the analysis of platinum in real samples. © 2001 Society of Chemical Industry     

Viscosity of polydimethylsiloxane gum: Shear and temperature dependence from dynamic and capillary rheometry

The rheology of Dow Corning polydimethylsiloxane gum (PDMS/silicone gum) was studied over a time range of 10^?2 to 10⁵ s^?1 and a temperature range of 23–150°C using both capillary and dynamic rheometry. A low shear Newtonian region is observed at room temperature below 0.01 rad/s (increasing to 0.1 rad/s at 150°C) for which an Arrhenius activation energy for a viscous flow of 13.3 kJ/mol was determined. The Cox–Merz rule for merging of shear and complex viscosities is found to be valid up to 10 s^?1. Viscosity is found to be independent of temperature above 100 s^?1, where terminal power‐law flow is encountered. This is exhibited in the dynamic data as equal plateau moduli for the various temperature curves. Gross wall slippage is seen in capillary flows above approximately 100 s^?1, corresponding to a stress value of 70–100 kPa. Slip‐stick (spurt) flow is not observed. The viscosity data are best fitted by the Carreau–Yasuda model with a fitting parameter a of 0.7, a power‐law index n of 0.05 (low because of slip effect), and a zero shear viscosity of 32 kPa s at 23°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2533–2540, 2002     

Response of an HMX based explosive to dynamic loading by the Hopkinson split bar technique

The dynamic compression and localized adiabatic shear in samples of an HMX based explosive was studied using the split Hopkinson bar technique. Dynamic compression tests were performed at strain rates of (0.3–2.0) · 10³ s^?1. Fracture of the explosive samples was found to occur at stresses of 60–80 MPa. The behavior of HMX based samples was also studied in localized shear tests at different strain rates (200–2500 s^?1). The initiation of explosive transformations under the dynamic loads is discussed.     

Comparison of superimposed effects in high‐shear‐rate capillary rheology of polystyrene,polypropylene, and linear low‐density polyethylene melts

Polymer melts exhibit unique rheological behaviors at high shear rate up to 10⁶ s^?1, which is a common phenomenon in micro‐injection molding. Both online and commercial capillary rheometers, which were modified to allow regulation of back pressure, were used for measuring the melt shear viscosities of polystyrene (PS), polypropylene (PP), and linear low‐density polyethylene (LLDPE) under high shear rates. The rheological characteristics of the three melts were compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6 × 10⁵, 8.0 × 10⁵, and 2.8 × 10⁶ s^?1 for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS > PP > LLDPE. It seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 10⁵ s^?1 for the PS melt among the three melts. POLYM. ENG. SCI., 55:506–512, 2015. © 2014 Society of Plastics Engineers     

Extraction separation of Ir(III) and Rh(III) with Cyanex 923 from chloride media: a possible recovery from spent autocatalysts

Liquid–liquid extraction of Ir(III) and Rh(III) with Cyanex 923 from aqueous hydrochloric acid media has been studied. Quantitative extraction of Ir(III) was observed in the range of 5.0–8.0 mol dm^?3 HCl with 0.1 mol dm^?3 Cyanex 923, while Rh(III) was extracted quantitatively in the range of 1.0–2.0 mol dm^?3 HCl with 0.05 mol dm^?3 Cyanex 923 in toluene along with 0.2 mol dm^?3 SnCl₂. The Ir(III) was back extracted with 4.0 mol dm^?3 HNO₃ quantitatively from the organic phase while Rh(III) was stripped with 3.0 mol dm^?3 HNO₃. The extraction of Rh(III) with Cyanex 923 was not quantitative without use of SnCl₂. However in the extraction of Ir(III) a negative trend was observed in the presence of SnCl₂. Varying the temperature of extraction showed that the extraction reactions of both the metal ions are exothermic in nature, and the stoichiometric ratio of Ir(III)/Rh(III) to Cyanex 923 in organic phase was found to be 1:3. The methods developed were applied to the recovery of these metal ions from a synthetic solution of similar composition to that from leaching of spent autocatalysts in 6.0 mol dm^?3 HCl. © 2002 Society of Chemical Industry     

Design,synthesis and characterization of a novel self‐doped polyaniline derivative

A type of self‐doped polyaniline derivative was successfully synthesized using an oxidative coupling polymerization approach. The structure of the electroactive polymer was investigated using Fourier transform infrared and ¹H NMR spectroscopy and gel permeation chromatography. Its thermal and spectral properties were characterized using thermogravimetric analysis and UV‐visible spectroscopy. The electrochemical activity of the polymer was studied using cyclic voltammetry (CV) in 1.0 mol L^?1 H₂SO₄ solution with various scan rates. The peak current increases linearly with scan rate from 10 to 120 mV s^?1, which indicates that the electrode reaction is controlled by a surface process. In addition, the self‐doped characteristic was investigated using CV in 1.0 mol L^?1 KCl solution with pH value changing from 1 to 12, and the results indicate that the polymer has excellent electrochemical activity even in neutral and alkaline environments. Copyright © 2010 Society of Chemical Industry     

Porous Ni/ZrO2 Cermet from Highly Concentrated Composite Colloid

Rheology and shaping of concentrated cermet suspensions consisting of nickel (Ni) and yttria‐stabilized zirconia (YSZ) nanoparticles in water have been examined over a broad range of volumetric solids concentration (? = 0.1–0.4) and Ni fraction (f_Ni = 0.15–0.45). Preferential adsorption of pyrogallol‐poly(ethylene glycol) polymer (i.e., Gallol‐PEG) on surface of the Ni and YSZ particles imparts steric hindrance between the suspending particles so that fluidity can be obtained under shear stress. The cermet suspensions exhibit shear‐thinning flow behavior under steady‐shear measurement over shear rates of 10⁰–10³ s^?1. Yield stress and yield strain of the suspensions appear to vary pronouncedly with ? and f_Ni under oscillatory shear over a shear‐strain range of 10^?1–10³%. With the Gallol‐PEG adsorption, an apparent viscosity less than 6 × 10^?1 Pa.s at a shear rate of 10² s^?1 has been obtained for the highly concentrated composite suspension with ? of 0.40 and f_Ni of 0.25. A high solids concentration effectively prohibits phase segregation during wet‐shaping processes. Uniform green compacts have been obtained from slip casting of the concentrated cermet mixture (? = 0.30) without use of binder and are then fired at 1200°C under reducing atmosphere to form porous Ni/YSZ compacts. Relative sintered density increases from 65% to 75% of the theoretical value when f_Ni was increased from 0.15 to 0.45, due mainly to the lower sintering temperature required for the Ni phase.     

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