Egg-shell membrane mimicking synthetic polymer membrane supported palladium nanoparticles for catalyzing reduction of uranyl(VI) ions

To develop an efficient, robust and recyclable heterogeneous catalyst, the palladium nanoparticles (Pd NPs) were formed by spontaneous reduction of Pd2+ ions with hydrazine covalently attached via glycidyl units to the pore wall of poly(propylene) membrane. After the formation of Pd NPs, the hydrazine grafted membrane was characterized for porosity, through-pores distribution, basicity, elemental mapping and Pd NPs sizes and distribution in the matrix. It was observed that there was a significant reduction of UO22+ ions by formic acid in the presence of Pd embedded hydrazine grafted membrane; but no reduction of UO22+ ions by formic acid was observed in the presence of Pd NPs embedded cation-exchange membrane under similar conditions. The analyses of kinetics of reduction of UO22+ ions by formic acid revealed a threshold amount of Pd-0 in the hydrazine grafted membrane above which reduction occurred in a significant rate. Itwas observed that kinetic of reduction at lower amount of Pd was controlled by pseudo second-order kinetics. On increased amount of Pd, the reduction process switched to diffusion controlled indicating matrix effect on the reduction kinetics. Therefore, the high intensity ultrasonication was used to overcome the diffusion barrier affecting the kinetics of UO22+ ions reduction in the Pd NPs embedded neutral membrane matrix. This resulted in a switching of kinetic of the reduction from diffusion controlled process to pseudo-first-order kinetics leading to very high catalytic activity of Pd NPs. The catalytic activity of Pd NPs in the hydrazine grafted poly(propylene) membrane samples did not deteriorate during the five cycles, and after storing for three months suggesting a long shelf-life. (C) 2016 Elsevier B.V. All rights reserved.