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

- Hydrazine-grafted robust membrane having porous architecture has been developed.
- High amount of Pd0 (124 ± 1 mg g−1) could be loaded in hydrazine-grafted membrane.
- Pd NPs in neutral and ionic membranes were studied for catalyzing U(VI)-reduction.
- Pd NPs in neutral membrane exhibited high activity but not in ionic membrane.
- High intensity sonication enhanced U(VI)-reduction with formic acid significantly.

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 Pd0 in the hydrazine grafted membrane above which reduction occurred in a significant rate. It was observed that kinetic of reduction at lower amount of Pd0 was controlled by pseudo-second-order kinetics. On increased amount of Pd0, 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.

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