Fabrication of thermosensitive hydrogel-supported Ni nanoparticles with tunable catalytic activity for 4-nitrophenol

Abstract

Thermosensitive hydrogels displaying a high degree of swelling were successfully fabricated from cross-linked poly(N-isopropylacrylamide-co-2-acrylamido-2-methylpropanesulfonic acid) (P(NIPAM-co-AMPS)). The sulfonic acid groups in the copolymer networks strongly modulated the internal structure and swelling behavior of the P(NIPAM-co-AMPS), thereby lowering the critical solution temperature of the hydrogels. These groups acted as adsorption sites, enabling the in situ synthesis of Ni nanoparticles in P(NIPAM-co-AMPS) hydrogels. Significant changes in the average diameter and number of the Ni nanoparticles were observed when the concentration of AMPS was changed. The catalytic capability of P(NIPAM-co-AMPS)/Ni to act as a switched temperature reactor was demonstrated in a model reduction reaction. Kinetic data revealed that the adsorption of the reactants on the catalyst surface was the key factor in terms of the Langmuir–Hinshelwood model. The reaction rate of the P(NIPAM-co-AMPS)/Ni composite hydrogels did not increase monotonically; instead, the reaction rate decreased to some extent around the low critical solution temperature (LCST), demonstrating a thermally tunable catalytic activity. The P(NIPAM-co-AMPS)/Ni composites were also highly stable, and were usable after five cycles of use, retaining a high level of activity.