SnS2-covalent organic framework Z-scheme van der Waals heterojunction for enhanced photocatalytic reduction of uranium (VI) in rare earth tailings wastewater.

[Display omitted] • The SnS 2 -covalent organic framework van der Waals heterojunction (SnS 2 COF) was constructed. • With good photoelectric properties, SnS 2 COF can realize separation and transfer of electron-hole. • The electron flow path of heterojunction conforms to Z-scheme by experimental study and theoretical calculation. • SnS 2 COF can effectively reduce and remove U (VI) from rare earth tailings wastewater under UV/Vis light. Uranium removal by photocatalytic reduction is one of the most promising methods to reduce radioactive contamination in wastewater. Herein, a Z-scheme van der Waals heterojunction photocatalyst (SnS 2 COF) was synthesized in situ by combining covalent organic frameworks (COF) with semiconductor (SnS 2) for U (VI) reduction in rare earth tailings wastewater. The synthesis method of van der Waals heterojunction is simple and solves the problem of no hanging bond in composite components. In this heterojunction, large areas of van der Waals interaction form high-speed electron transport channels. In addition, it is deduced that SnS 2 COF fits the Z-scheme heterojunction electron transport mode through the theoretical calculation of the ground state and excited state electron density difference and the related band structure. Under the photoexcitation, the direction of electron flow is reversed, which further promotes the separation of the photogenerated electron (e−)-hole (h+) under the action of the built-in electric field, maintains the high reducibility of the conduction band, and avoids the photocorrosion of SnS 2. Compared with inorganic-inorganic heterojunction, SnS 2 COF has a wider light absorption range, more active sites, and higher e−-h+ separation and transfer efficiency. Therefore, it had a higher U (VI) reduction removal capacity, up to 1123.3 mg g−1, far surpassing the SnS 2 and COF counterparts under ultraviolet/visible light. And the U (VI) removal rate reached 98.5 % in rare earth tailings wastewater. The design concept of organic–inorganic heterojunction materials provides an alternative strategy for improving the photocatalytic performance. [ABSTRACT FROM AUTHOR]