Immobilization of physicochemically stable Pd nanocatalysts inside uniform hydrogel microparticles

Abstract

Here, we report a facile method of immobilizing metal nanoparticles physicochemically and very stably in uniform hydrogel microparticles. This approach provides the high dispersity and physicochemical preservability of immobilized PdNPs inside the hydrogel microparticles at the same time. The synthesis of PVP (polyvinylpyrrolidone)-stabilized PdNPs was performed by microwave heating and the immobilization of PdNPs was preformed by using micromolding method with UV-curable hydrogel precursor. The immobilized PdNPs are physically stabilized by the trapping in the porous hydrogel networks and chemically stabilized by the hydrogen bonding induced between PVP, PEGDA (polyethylene glycol diacrylate) hydrogel matrix and PEG (polyethylene glycol). Furthermore, the formation of hydrogen bonding clearly confirmed enhances the stability against oxidation of the immobilized PdNPs. The catalytic performance of heterogeneous Pd nanocatalysts was evaluated by the hydrogenation of 4-nitrophenol. Compared with the direct use of PdNPs as catalysts, the mass transfer resistance caused by the porous structure of the hydrogel decreases the initial reaction rate, however, the Pd nanocatalysts immobilized inside hydrogel provide the advantages such as high reuse stability and easy separation. Furthermore, the effect of steric hindrance, due to hydrogen bonding, on the reaction is negligibly small, however, the stability of immobilized PdNPs as a heterogeneous nanocatalyst improves in both liquid phase reactions and long term storage.