Synergistic effect of double Schottky potential well and oxygen vacancy for enhanced plasmonic photocatalytic U(VI) reduction

Plasmonic photocatalysis is an effective strategy to solve radioactive uranium hazards in wastewater. A plas-monic photocatalyst Bi/Bi2O3_x@COFs was synthesized by in-situ growth of covalent organic frameworks (COFs) on Bi/Bi2O3_x surface for the U(VI) adsorption and plasmonic photoreduction in rare earth tailings wastewater. The presence of oxygen vacancy in Bi/Bi2O3_x and Schottky potential well formed by Bi and Bi2O3_x interface increased the number of free electrons, which induced localized surface plasmon resonance (LSPR) and enhanced the light absorption performance of composites. In addition, oxygen vacancy improved the Fermi level of Bi/Bi2O3_x, leading to another potential well between Bi2O3_x and COFs interface. The electron transport direction was reversed, thus increasing the electron density of COFs layer. COFs was an N-type semiconductor with specific binding U(VI) groups and suitable band structure, which could be used as an active reaction site. Bi/ Bi2O3_x@COFs had 1411.5 mg g_ 1 removal capacity and high separation coefficient for U(VI) due to the synergistic action of photogenerated electrons and hot electrons. Moreover, the removal rate of uranium from rare earth tailings wastewater by regenerated Bi/Bi2O3_x@COFs was over 93.9%. The scheme of introducing LSPR and Schottky potential well provides another way to improve the photocatalytic effect.

Automated summary

Plasmonic photocatalysis using Bi/Bi2O3_x@COFs as the catalyst effectively removes radioactive uranium from rare earth tailings wastewater. The presence of oxygen vacancy and Schottky potential well in Bi/Bi2O3_x enhances the light absorption performance and electron density of the COFs layer. The synergy between photogenerated electrons and hot electrons enables Bi/ Bi2O3_x@COFs to have high removal capacity and separation coefficient for U(VI). The introduction of localized surface plasmon resonance and Schottky potential well provides a new approach to improve photocatalytic efficiency.