Optimizing Pd and Au-Pd decorated Bi2WO6 ultrathin nanosheets for photocatalytic selective oxidation of aromatic alcohols

Abstract

Ultrathin semiconductor nanosheets decorated with metallic nanoparticles (NPs) are promising in photocatalysis due to the multi-component interactions. The materials with a series of monometallic Pd and bimetallic Au-Pd NPs anchored on Bi2WO6 ultrathin nanosheets were synthesized and developed as photocatalysts for selective oxidation of aromatic alcohols to aromatic aldehyde. By optimizing the metallic contents, a typical sample of Au(0.25)Pd(0.25)-Bi2WO6 exhibited the highest photocatalytic activity among all the prepared photocatalysts including Au(0.5)-Bi2WO6, Pd(x)-Bi2WO6, Au(x)Pd(x)-Bi2WO6 (x represents the weight percentage of metal in the photocatalyst), along with the improved selectivity for producing benzaldehyde. The extended absorption in visible range, higher efficiency for the transfer and separation of photogenerated charge carriers, and the superior ability for generating active radicals of Au(0.25)Pd(0.25)-Bi2WO6 were demonstrated by DRS spectra, photoelectrochemical measurements, and ESR detection. The effect of the active species for selective oxidation of aromatic alcohols was proved to follow the order of h+ + O2− > h+ >> O2−. Accordingly, a possible mechanism based on the interfacial cooperation between bimetallic Au-Pd NPs and Bi2WO6 ultrathin nanosheets was proposed to illustrate the photocatalytic process, where the holes accumulated in Bi2WO6 ultrathin nanosheets and O2− produced on metallic NPs synergistically promote the selective oxidation of aromatic alcohols.