Palladium Nanoparticles Hosted in Poly(ethylenimine) and Poly(ethylene glycol methacrylate phosphate) Anchored Membranes for Catalyzing Uranyl Ions Reduction and Mizoroki–Heck Coupling Reaction

The poly(ethylenimine) (PEI) and poly(ethylene glycol methacrylate phosphate) (poly(EGMP)) functionalized microporous poly(propylene) membrane have been developed to host the palladium (Pd) nanoparticles (NPs) for catalyzing the inorganic and organic reactions. These functionalized membranes are characterized for their porosities and pore-size distributions. Field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-rays spectrometry (EDX) attached to FE-SEM, and small-angle X-rays scattering (SAXS) have been used to study the Pd NPs size distributions and homogeneous distributions in the membrane matrixes. The average size of Pd NPs has been found to be ≈2 nm in all the membranes by SAXS experiments, and elemental mappings by EDX suggest uniform distributions of Pd NPs. However, a very small number of bigger particles have been formed in the membrane having lowered pore-filling due to lower network elasticity in some region that allowed agglomeration to some extent. The in situ generated H2 during the decomposition of formic acid on Pd surface is used for the reduction of UO22+ to U4+. It has been observed that the primary, secondary, and tertiary amine groups on PEI facilitate the formic acid decomposition preferentially to form H2. However, the Pd NPs hosted in the poly(EGMP) seem to be less efficient in reducing uranyl ions that bind strongly with the phosphate groups. The effect of physical structure of membrane matrix on catalyzing the uranyl ion reduction is also studied. The Pd2+ and Pd NP-loaded PEI and poly(EGMP) membranes are also studied for their catalytic activities in the representative Mizoroki–Heck cross-coupling reaction of iodobenzene with ethyl acrylate in the presence of base at 100 °C without any solvent. In this case also, the Pd NPs embedded PEI-membrane has given better yield (76%) in comparison with the poly(EGMP) membrane (65%) with the same amount of Pd NPs and under similar conditions. However, there have been also marginally higher catalytic activities of the Pd NP-loaded membranes as compared to Pd2+ ions loaded in the same host membrane. It has been observed from X-ray photoelectron spectroscopy (XPS) that Pd2+ ions are reduced to Pd0 that actually catalyze the Mizoroki–Heck cross-coupling reaction.