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Glutaraldehyde cross-linked chitosan was loaded with palladium and then reduced by means of an in situ hydrogen generation procedure (Zn in sulfuric acid solution) to prepare a chitosan-supported palladium catalyst. This catalyst was successfully used to degrade nitrophenol in dilute solutions in the presence of sodium formate as the hydrogen donor. The optimum initial pH was below pH 4. The pH strongly increased during the reaction. The influence of the initial concentration of nitrophenol and sodium formate was studied in order to determine the minimum molar ratio between these compounds to achieve the complete conversion of the nitrogenous product. The pseudo-first-order equation was shown to fit degradation kinetics in most cases; however, in some cases it was necessary to use a variable-order equation in order to model the kinetics. Decreasing catalyst particle size increased degradation rate; the kinetic parameter varied linearly with the reciprocal of the diameter, indicating that film diffusion may partially contribute to the kinetic control of the reaction. The kinetic parameter linearly increased with catalyst dosage, while increasing the palladium loading in the catalyst slightly increased degradation kinetics but the catalytic activity did not increase proportionally. Catalytic activity appears to be restricted to external catalyst layers.

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Chitosan has proved efficient at removing platinum in dilute effluents. The maximum uptake capacity reaches 300 mg g-1 (almost 1.5 mmol g-1). The optimum pH for sorption is pH 2. A glutaraldehyde cross-linking pretreatment is necessary to stabilize the biopolymer in acidic solutions. Sorption isotherms have been studied as a function of pH, sorbent particle size, and the cross-linking ratio. Surprisingly, the extent of the cross-linking (determined by the concentration of the cross-linking agent in the treatment bath) has no significant influence on uptake capacity. Competitor anions such as chloride or nitrate induce a large decrease in the sorption efficiency. Sorption kinetics show also that uptake rate is not significantly changed by increasing either the cross-linking ratio or the particle size of the sorbent. Mass transfer rates are significantly affected by the initial platinum concentration and by the conditioning of the biopolymer. Gel-bead conditioning appears to reduce the sorption rate. While for molybdate and vanadate ions, mass transfer was governed by intraparticle mass transfer, for platinum, both external and intraparticle diffusion control the uptake rate. In contrast with the former ions, platinum does not form polynuclear hydrolyzed species, which are responsible for steric hindrance of diffusion into the polymer network.

International audienc

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