Synergistic rapid removal of U(VI) from radioactive wastewater by photoexcitation-driven Z-scheme heterojunction hydrogel

Abstract

The development of inexpensive and efficient semiconductor catalysts for uranium removal from wastewater via photoreduction remains challenging. Herein, we successfully synthesized Z-scheme heterojunction LaOCl-ZnO-1.5 photocatalyst by ultrasound-assisted in-situ deposition technology followed by immobilization in sodium alginate (SLZ-1.5) by an embedding strategy for the reductive removal of U(VI) from uranium-containing wastewater. The construction of a heterojunction achieves synergistic effects, improving optical response range and photocatalytic efficiency, reducing the loss of photocatalyst through immobilization in the gel structure, and simultaneously solving the difficulty of recycling powder catalysts. SLZ-1.5 demonstrated superior photocatalytic properties for the reduction of U(VI) and rapid reaction kinetics (120 min, 96.1 %) under visible-light irradiation by a xenon lamp. Through the synergistic effect of adsorption and photocatalysis, its optimal removal capacity for U(VI) reached 520.8 mg/g. SLZ-1.5 exhibited great recyclability and excellent selectivity (1.22 × 104 mL/g). In addition, the outstanding performance (98.6 %) of SLZ-1.5 in a dynamic adsorption column under visible-light irradiation validated its potential for practical applications. The photoreduction mechanism indicated that the excellent photocatalytic performance of LaOCl-ZnO-1.5 was enabled by its great light absorption capacity and appropriate bandgap. SLZ-1.5 heterojunction hydrogel is a successful example of a promising adsorption-reduction coupling material that can be applied for the purification and treatment of uranium-containing wastewater.