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

Gold nanoparticles (Au NPs) were prepared by reducing HAuCl4with NaBH4. Their average particle sizes could be tuned in the range of 1.7 and 8.2 nm, by adjusting the amount of NaBH4used during synthesis. The obtained Au NPs (colloids) were then loaded onto a commercial Al2O3support to prepare Au/Al2O3catalysts 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 Al2O3while avoiding the growth of Au NPs. Au NPs and Au/Al2O3catalysts were tested in the reduction ofp-nitrophenol with NaBH4. 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.