Photocatalytic reduction of uranium over a novel Z-scheme Ni-MOF/g-C3N4 heterojunction

The graphite phase carbon nitride (g-C₃N₄) was enhanced by constructing a heterojunction strategy. CN/Ni-MOF composites were synthesized using a solvothermal method, and the catalytic performance of photoreduced uranium were investigated. The photocatalytic reduction experiment demonstrated the reduction efficiency of the optimal CN/Ni-MOF(300) was 94.24 % and the rate constant was 0.0877 min⁻¹ after 20 min illumination. Notably, the photocatalytic reduction of uranium exhibited good activity in various catalyst dosages, pH, and concentrations of uranium solution. Furthermore, after 5 cycles of experiments, the reduction efficiency of 93.02 % was still sustained. The characterization results indicated that the main reactive substances involved in the reaction were e^- and ∙O₂^–, and the final reaction product was (UO₂)O₂·4H₂O. An analysis of the bandgap structure of the catalyst facilitated the examination of the electron transfer mechanism, resulting in the proposal of a plausible reaction mechanism. When CN is integrated with Ni-MOF, e^- may migrate from CN to Ni-MOF, accelerating the migration at the contact interphase, thereby enhancing the photocatalytic performance of the composite catalyst.