Effect of copolymer chain length and additives on the catalytic efficiency of thermo-sensitive block copolymer stabilized gold nanoparticles

The reduction of toxic 4-nitrophenol (4-NP) into non-toxic 4-aminophenol (4-AP) is an important reaction and gold nanoparticles (GNPs) have been explored for catalyzing this reduction process. In this work, three amphiphilic poly(N-isopropylacrylamide)-b-poly(styrene-r-vinyl pyridine) copolymers having different chain length was used to cap GNPs as well as gold nano rods (GNRs) and the catalytic efficiency of these polymer-GNP conjugates was evaluated for the reduction reaction in water. Thermosensitive conformational changes of these block copolymers in aqueous medium renders non-Arrhenius type temperature-dependent catalytic efficiency due to change in accessibility of GNP surface. The catalytic efficiency of GNPs was also influenced by the length of the coated polymers, shape of the gold nanoparticles and presence of salt or surfactant in the solution, which was also attributed to the altered accessibility of the reactants to the catalyst surface. Nearly no loss of catalytic activity and initial rate constant on recycling confirmed the stability of the polymer coating. Hence, these new catalysts could be potentially very useful in industrial applications.