Synthesis of TiO₂@WO₃/Au Nanocomposite Hollow Spheres with Controllable Size and High Visible-Light-Driven Photocatalytic Activity

A new nanocomposite was reported as a good-performance photocatalyst, i.e., double-shelled, positively and negatively charged, nanostructured hollow spheres with supported Au nanoparticles (NPs). TiO₂, WO₃, and Au NPs were coated successively onto the functionalized polystyrene (PS) template spheres. The as-synthesized product PS@TiO₂@WO₃/Au nanocomposites were calcined at elevated temperature and then intact double-shelled TiO₂@WO₃/Au hollow spheres were obtained. The dispersity, morphology, size, and lattice of TiO₂@WO₃/Au hollow spheres were investigated by SEM and TEM. The presence of TiO₂ hollow sphere and WO₃/Au shell was proved by HAADF-STEM and XRD images. The photodegradation activity for rhodamine B and trimesic acid (i.e., color and colorless aromatic pollutants) in decreasing order were TiO₂@WO₃/Au, TiO₂–WO₃, P25. Under visible-light irradiation, the photodegradation rate of rhodamine B and trimesic acid for TiO₂@WO₃/Au was 94% and 95%, respectively, which exhibited a significant increase of 62% and 80% as compared with P25. The synergistic effect of coupling TiO₂ hollow spheres with WO₃ shell and Au NPs on photocatalytic performance was proved by this article. First, Au NPs deposited in WO₃ shell and loaded on TiO₂ shell separately act as electron trap site and surface plasmon resonance-sensitizer, respectively, and hence the photogenerated electron–hole separation rate was improved. Second, the visible-light absorption of TiO₂ hollow spheres was increased by the coexistence of WO₃ and Au and unique hierarchical mesoporous architectures of TiO₂@WO₃/Au. Finally, the surface charge of TiO₂@WO₃/Au and rhodamine B was negative and positive, respectively, the affinity between them could be improved by electrical attractions, and then the major bottleneck in heterogeneous photocatalysis (i.e., poor affinity between pollutants and photocatalyst) could be broken. The optimal hollow sphere size of TiO₂@WO₃/Au was 450 nm, which was proved by the photodegradation of aromatic pollutants and photoreduction of Cr­(VI)