Bandgap Regulation Engineering of MXene Ti ₃ C ₂ by Radioactive Cesium Uptake and Sustainable Photocatalytic Production of H ₂ O ₂ in Real Seawater

Photocatalytic H2O2 production in seawater offers a novel and sustainable route for the substitution of freshwater consumption. However, this strategy is limited by the complexity and cost resulting from electron–proton donors and pure O2 dependency. Simultaneously, adsorption, a frequently used method to treat radionuclide wastewater, latently causes issues of adsorbent-caused waste and pollution. In this work, we designed a sustainable system based on recycling MXene Ti3C2 adsorbent after radioactive cesium (Cs+) uptake and further used it in photocatalytic H2O2 production from seawater. The adsorptive performance and behavior of Ti3C2 were evaluated for model nuclear wastewater with different Cs+ concentrations. Cs+ was uniformly adsorbed on the layer surface of Ti3C2 and promoted the delamination of Ti3C2. Cs+ uptake also improved e––h+ pair separation and photogenerated electron transfer on the Ti3C2 matrix. Without using an organic electron–proton donor and pure O2, Ti3C2 adsorbed Cs+ achieved 892.43 μmol·g–1·h–1 H2O2 productivity in real seawater, which was 1.84 times higher than that over pristine Ti3C2. It also obtained 12.44% apparent quantum yield (AQY) at 550 nm, and 6 cycles of reusability. Enhancement in photocatalytic performance was attributed to the regulation of the bandgap of Ti3C2 by the adsorbed Cs+ from 1.51 eV to a semiconductor range of 2.00 eV. Further, the conduction band (CB) of Ti3C2 was shifted to a more negative potential, facilitating the two-electron reduction of O2 to generate more H2O2. This study opened avenues for the sustainable use of spent adsorbents and resolved freshwater reliance.