Ingenious Design of Ternary Hollow Nanosphere with Shell Hierarchical Tandem Heterojunctions Toward Optimized Visible-light Photocatalytic Reduction of U(VI)

TiO2 based photocatalytic reduction has been regarded as a promising technology for flexibility of uranium recovery from seawater, however, the use of sacrificing agents and protection gas are two major challenges for practical application. Herein, a ternary hybrid TiO2@CdS@Au hollow nanosphere (TCA) was designed and synthesized for highly efficient photocatalytic reduction of U(VI). The designed ternary hollow nanosphere is composed of double heterojunctions: type-Z heterojunction generated between TiO2 with CdS and metal-semiconductor junction between CdS and Au NPs, which is contributive for the spatial separation and diffusion of photogenerated charges. Therefore, compared with loaded Pt or GOQDs, the superior photocatalytic reduction efficiency of TCA2 (Au NPs content of 0.8%) for U(VI) achieves 99.7% within 25 min and remains unchanged after five cycles in the presence of 3 mmol.L-1 NaHCO3 under air condition. Its photoreduction rate constant is 5.7 and 4.1 times as much as the CdS and hollow TiO2@CdS nanosphere. Additionally, in the absence of any protective gases and holes sacrificial agent, the soluble U(VI) adsorbed on the photocatalyst is reduced to insoluble alpha-U3O8 by photogenerated electrons and superoxide radical, which has been recognized as one of the most effective strategy for the separation and recovery U(VI) from polluted environment.