Hierarchical yolk-shell WO3 microspheres with highly enhanced photoactivity for selective alcohol oxidations

Abstract Hierarchical WO3 microspheres with controllable interior structures from solid, yolk-shell, to hollow were synthesized through sonochemical precipitation and hydrogen ion-exchange routes followed by thermal treatment. During the photocatalytic selective oxidation of aromatic alcohols to their corresponding aldehydes in aqueous medium under light irradiation with full wavelengths, the yolk-shell WO3 microspheres exhibited much higher photocatalytic activity than those WO3 microspheres with solid and hollow structures, respectively. This superior activity of the yolk-shell WO3 microspheres can be attributed to the synergistic promoting effect of the following factors: firstly, the porous structure constructed by self-assembly of the interconnected nanosheets together with high surface area promoted the light harvesting and also facilitated the adsorption and diffusion of reactant molecules; secondly, the small crystallite size favored the rapid transfer of photoelectrons, which diminished the transfer distance of photoelectrons and thus inhibited their recombination with holes; thirdly, the yolk-shell structure enhanced light harvesting via multiple reflections in the yolk-shell chambers. Meanwhile, all the WO3 photocatalysts displayed excellent durability against structural collapse due to the robust hierarchical structures. This work identifies the important role of yolk-shell structure played in photocatalytic selective oxidation of aromatic alcohols.