Modulating the Catalytic Activity of Gold Nanoparticles through Surface Tailoring

The present work describes the catalytic activity of gold nanoparticles towards the reduction of 4-nitrophenol and their modulation through surface tailoring using various organic ligands. One step protocol is used to prepare CTAB capped gold nanoparticles of size 15 +/- 2 nm and the catalysis reaction using these particles simultaneously follow both zero-order and first-order reaction kinetics. The zero-order rate constant, k(0)=0.418 mol lit(-1) min(-1) and first-order rate constant, k(1)=0.938 min(-1) is achieved just by using 8 nM of gold catalyst. On the other hand citrate capped gold nanoparticles of similar sizes (13 +/- 3 nm) follow only the first-order kinetics with k(1)=0.243 min(-1), which is about four times less compared to CTAB capped gold nanoparticles. Moreover, the reaction kinetics is changed to zero-order rate with k(0)=0.345 mol lit(-1) min(-1) simply by replacing citrate with CTAB on the gold nanoparticles surface. On the other hand, replacing the citrate with PVP on the nanoparticles surface, the reaction rate still follows the first-order kinetics, but with two-fold increase in the rate constant with k(1)=0.587 min(-1). Further, silica coating of the CTAB capped gold nanoparticles and their use as catalyst for 4-nitrphenol reduction exclusively follows the zero-order kinetics with k(0)=0.305 mol lit(-1) min(-1) and are better recyclable upto five cycles without affecting their conversion efficiency.