Size Effect of Gold Nanoparticles in Catalytic Reduction of p-Nitrophenol with NaBH(4)

Gold nanoparticles (Au NPs) were prepared by reducing HAuCl(4) with NaBH(4). Their average particle sizes could be tuned in the range of 1.7 and 8.2 nm, by adjusting the amount of NaBH(4) used during synthesis. The obtained Au NPs (colloids) were then loaded onto a commercial Al(2)O(3) support to prepare Au/Al(2)O(3) catalysts with tunable Au particle sizes. An optimal pH value (5.9) of the Au colloid solution was found to be essential for loading Au NPs onto Al(2)O(3) while avoiding the growth of Au NPs. Au NPs and Au/Al(2)O(3) catalysts were tested in the reduction of p-nitrophenol with NaBH(4). Interestingly, the catalytic activity depended on the size of Au NPs, being the highest when the average size was 3.4 nm. Relevant characterization by UV-Vis, TEM, and XRD was conducted.