Spatial microenvironment enhanced photocatalytic reduction of uranyl ions under solar light irradiation

Photocatalytic reduction of uranyl ions (UO₂²⁺) is an environmentally friendly, energy efficient, and highly effective method for uranium-containing wastewater treatment and uranium recovery. Herein, a novel photocatalytic material CH-8 @NNFO-4 with abundant oxygen vacancies was synthesize by growing Ca(OH)₂ on the surface of Fe doped NaNbO₃ in situ. The Ca(OH)₂ synergizes with the oxygen vacancies, creating a microenvironment that narrows the bandgap and extends the light response range. At the same time, the Ca-O enhance carrier transport rates and reduce the electron-hole recombination rate. Under solar irradiation, over 93.68 % UO₂²⁺ is rapidly reduced to insoluble U(IV) without protectants or free radical scavengers, which is sixteen times that of pure NaNbO₃, with a theoretical reduction capacity reached to 826.45 mg·g⁻¹. After five cycles, the removal efficiency remains at 88.77 %. The CH-8 @NNFO-4 possesses excellent recyclability, acid and alkali resistant, anti-interference of anions and cations and chemical stability, Furthermore, the charge transfer in CH-8 @NNFO-4 revealed through DFT calculations, and an enhanced mechanism for the Ca-O synergizes spatial microenvironment photocatalytic reduction of U(VI) was proposed. This work provides a new catalytic reaction design strategy for the efficient reduction of U(VI).