Synthesis of gold nanoparticles stabilized with poly(N-isopropylacrylamide)-co-poly(4-vinyl pyridine) colloid and their application in responsive catalysis

The copolymer of poly(N-isopropylacrylamide)-co-poly(4-vinylpyridine) was synthesized by free radical copolymerization of 4-vinylpyridine and N-isopropylacrylamide. The copolymer synthesized with the feed monomer ratio of 4-vinylpyridine/N-isopropylacrylamide equal to 1/3 was associated to form thermoresponsive colloid in neutral water at room temperature, the average size and the cloud-point temperature of which were 40 nm and 32 °C, respectively. The thermoresponsive colloid was used as scaffold to load 2-nm Au nanoparticles to form the responsive catalyst of colloid-stabilizing gold nanoparticles. The catalysis in the model reduction of 4-nitrophenol with NaBH₄ suggested that the catalytic reduction could be modulated due to the thermoresponsive phase-transition of the colloid-stabilizing gold nanoparticles. That was, the catalytic reduction firstly accelerated with the increase in temperature below the cloud-point temperature and then decelerated with the increase in temperature above the cloud-point temperature of the thermoresponsive colloid-stabilizing Au nanoparticles.