Sio2-Mediated High-Efficiency Enrichment Of 5 Nm Gold Nanoparticles And Their Catalytic Activity

Gold nanoparticles (Au NPs), smaller than 10 rim, have a high ratio of surface area to volume, and therefore have excellent catalytic activity. They are widely used in the field of catalysis. The concentration of small particle sized Au NPs synthesized by traditional wet chemical method is too low, and further enrichment is needed in order to meet the experimental requirements. However, small particle sized Au NPs are prone to aggregate during the concentration process and lose the catalytic activity. It is a challenge to concentrate the small Au NPs while keeping their catalytic activities. In this work, 500 nm silanized SiO2 particles which are covered by positive charges were used to adsorb 5 nm Au NPs through electrostatic interaction, and self-assemble to form Au NPs@SiO2 composite at room temperature. The loaded efficiency of Au NPs can reach 99.5% and the amount of Au NPs particles loaded on each SiO2 particle reached 800-1000, which greatly increased the effective concentration of Au NPs in the local area. Moreover, Au NPs enriched on the surface of SiO2 were bound by electrostatic action and uniformly distributed on the surface of SiO2 without agglomeration. The results showed that the catalytic activity of AuNPs@SiO2 was greatly enhanced by increasing the local concentration of AuNPs, and the catalytic activity was 3 times higher than that of AuNPs at the same concentration. After 5 times of reuse, the catalytic conversion efficiency remained at about 80%. The Au NPOSiO2 composite could be preserved for one month with the same structure and catalytic activity. Moreover, by adjusting the molar ratio of SiO2 and Au NPs, the assembly density of Au NPs at SiO2 can be precisely regulated, and the catalytic activity of Au NPOSiO2 can also be changed precisely. This work provides a simple method for preparing small sized Au NPs with high concentration and greatly improves the catalytic activity of Au NPs. The method has wide application in enriching other small sized nanoparticles.