Construction of a Hierarchical Core–Shell Z-Scheme Two-Dimensioanl/Two-Dimensional ZnIn2S4@TpBpy Heterostructure for Photocatalytic Reduction of U(VI)

The essential nature of the photocatalytic process is charge transfer. To optimize the spatial separation of photogenerated electron–hole (e^–-h⁺) pairs for high-performance catalytic efficiency, in this work, we have successfully prepared hierarchical core–shell two-dimensional (2D)/2D ZnIn₂S₄@TpBpy (ZIS@TpBpy) with well-matched Z-scheme interfacial charge transfer channels for uranium (U(VI)) photoreduction. The Z-scheme electron transfer configuration was confirmed by internal electric field (IEF) formation analysis, XPS characterization, and DMPO spin-trapping EPR spectroscopy. With large specific surface area and abundant active sites, the ZIS@TpBpy composite achieved a U(VI) extraction rate of 94.08%. In addition, the removal rate constant of ZIS@TpBpy (0.0137 min^–1) was 2.05 and 4.28 times higher than those of TpBpy (0.0067 min^–1) and ZnIn₂S₄ (0.0032 min^–1), respectively. First, the combination of organic and inorganic components expanded the range of visible light absorption and utilization. Afterward, under visible-light irradiation, more photogenerated e^–-h⁺ pairs dissociated and migrated to the ZnIn₂S₄ surface driven by the IEF and Z-scheme heterostructure. Simultaneously, the synergistic effect between the polarization potential generated by the IEF in the ZIS@TpBpy composite and abundant active sites (N and O atoms) in the TpBpy framework further accelerated the depletion and translocation of photogenerated e^–-h⁺ pairs, which significantly improved the efficiency of photocatalytic reduction of U(VI).