Size Effect of Gold Nanoparticles in Catalytic Reduction of p-Nitrophenol with NaBH4

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 2O 3 support to prepare Au/Al 2O 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 2O 3 while avoiding the growth of Au NPs. Au NPs and Au/Al 2O 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.