Photoreduction of U(VI) from Real Nuclear Wastewater by Sulfur Vacancies Engineered TAPP/CdS Heterojunction under Air without Sacrificial Agents

Photocatalytic technology has been proposed as an effective method for treating uranium-containing wastewater due to its high efficiency, low energy consumption, and environmental friendliness. Herein, a novel sulfur-vacancy-enhanced direct Z-scheme heterojunction photocatalyst was synthesized in situ via the combination of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and cadmium sulfide (CdS) for the photoreduction removal of U(VI) from real uranium mine wastewater. Compared to pristine CdS and TAPP, the optimized TAPP_0.01/CdS heterojunction has stronger visible-light absorption, photoreduction ability, and electrochemical performance. Under visible-light irradiation, TAPP_0.01/CdS exhibited a superior photoreduction efficiency for U(VI), achieving an ultrahigh removal rate of 99.96% under air without sacrificial agents. Even for the treatment of real uranium mine wastewater under the same conditions, the removal rate for U(VI) remained at 94.41%. Meanwhile, TAPP_0.01/CdS demonstrated high selectivity for U(VI) in the presence of multiple cations, maintaining a removal rate of 81.96% after five consecutive cycles. The reduced U(IV) was deposited on the CdS surface in the form of UO_2.34. The e^- and ^·O₂^- free radicals were the determining factors in the U(VI) photoreduction process. The design of sulfur vacancies engineered direct Z-scheme heterojunction in this work provides a feasible strategy for the efficient recovery of uranium from nuclear wastewater.