www.sciencedirect.com/science/article/pii/S1381116909004993

Synthesis of size-controlled Au nanoparticles for aerobic alcohol oxidation within a porous, chelating and intelligent hydrogel of poly(N-isopropylacrylamide)-co-poly[2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxypropyl ester] (PNIPAM-co-PMACHE) is studied. The PNIPAM-co-PMACHE hydrogel is demonstrated to be a suitable scaffold, within which Au nanoparticles with size ranging from 2.6 to 6.3 nm are synthesized by reducing the Au precursor of HAuCl4 with different reducing agents. The synthesized composite of the hydrogel and the encapsulated Au nanoparticles is thermoresponsive, which can reversibly deswell/swell at the volume-phase-transition temperature (VPTT) at 27 °C. The encapsulated Au nanoparticles keep stable during the reversible deswelling/swelling of the thermoresponsive hydrogel/Au composite. The catalysis of the thermoresponsive composite is tested employing aerobic alcohol oxidation as model reaction and it is found that the catalytic activity of the thermoresponsive composite is strongly dependent on the size of the encapsulated Au nanoparticles. Besides, it is found that the thermoresponsive composite is catalytically efficient for aerobic alcohol oxidation partly since the reactant of alcohol is highly concentrated within the hydrogel matrix through the reversible deswelling and partly since the reactant of alcohol can be activated through the strong hydrogen bonding between the alcohol molecules and the poly(N-isopropylacrylamide) segment. And furthermore, the reversible deswelling/swelling of the thermoresponsive composite provides great convenience for catalyst recycling.