Highly effective bromate reduction by liquid phase catalytic hydrogenation over Pd catalysts supported on core-shell structured magnetites: Impact of shell properties

Abstract

Liquid phase catalytic reduction of bromate with supported noble metals as the catalysts is a promising method to remove bromate in water. Magnetic supports provide a feasible way to recover catalysts whose surface properties also strongly influence the catalytic efficiency. In this study, Pd nanoparticles supported on core-shell structured magnetites with varied shells (e.g., carbon, SiO2, polypyrrole, polyaniline, polydopamine and chitosan) were prepared and catalytic reduction of bromate on the catalysts was investigated. The results showed that in comparison with other catalysts Pd/(Fe3O4@polyaniline) exhibited a higher catalytic efficiency due to its higher point of zero charge and surface hydrophilicity. In parallel, bromate reduction on Pd/(Fe3O4@polyaniline) followed the Langmuir-Hinshelwood model, confirming the crucial role of bromate adsorption. At pH 5.6 and a catalyst dosage of 0.05 g/L, 0.4 mM bromate could be completely reduced into bromide within 120 min. Furthermore, the magnetic catalysts could be effectively separated and recovered under an external magnetic field within 3 min. The results of catalyst reuse showed that after five consecutive catalytic reduction cycles Pd/(Fe3O4@polyaniline) retained 87% of its fresh catalyst activity. The present findings indicate that Pd/(Fe3O4@polyaniline) with polyaniline as the shell is a highly active, stable and recyclable catalyst for liquid phase catalytic hydrogenation of pollutants in water.