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A novel approach for the fabrication of double-shelled, sandwiched, and nanostructured hollow spheres was proposed, using hydrotherm reaction and calcination. The negatively charged nanoparticles (e.g., Au, Ag, and Pt) could be adsorbed successively onto the positively charged hollow spheres (e.g., TiO2, ZnO, and ZrO2). The resulted nanocomposites (TiO2@Au, as a proof-of-concept) were dispersed in glucose solution under hydrothermal conditions. After calcination, uniform double-shelled and sandwiched TiO2@Au@C hollow spheres were obtained and Au nanoparticles were sandwiched between the shell wall of TiO2 and C. The samples were characterized by SEM, TEM, XRD, XPS, BET, and UV-vis DRS. The photocatalytic activity for the degradation of 4-nitroaniline was in the order of TiO2@Au@C > TiO2@C > TiO2/Au > P25. The visible-light photodegradation rate of 92.65% for 4-nitroaniline was achieved by TiO2@Au@C, which exhibited an increase of 75% compared to Degussa P25 TiO2. Furthermore, no deactivation occurred during catalytic reaction for three times, i.e., the TiO2@Au@C microspheres exhibited superior photocatalytic stability. TiO2@Au@C microspheres could also enhance the photocatalytic activity for hydrogen generation from methanol/water solutions. The synergistic effect of coupling TiO2 hollow spheres with Au nanoparticles and C shell on photocatalytic performance was proved by us. The photoexcited electrons from Au nanoparticles could be captured by the conduction band of TiO2 and then the electron-hole separation was improved. Moreover, both the visible light absorption and the affinity between TiO2 and pollutants could be improved by the coexistence of carbonaceous materials, which could facilitate the photocatalytic interface reaction.

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).

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