Dual-defect-driven triple built-in electric fields to facilitate charge rapid separation of ZnIn2S4-Vs/TMC-Vo core-shell S-scheme heterojunction for boosting machine vision-assisted photothermal H2 evolution

Abstract

Built-in electric fields play a crucial role in enhancing the charge separation efficiency. The ZIS-R/TMC-Vo core–shell S-scheme heterostructures with different vacancy concentrations were prepared by NaBH₄ reduction and TAA content adjustment. The presence of S, O dual-defect was confirmed by HRTEM, EPR, and XPS characterization. The unique structure enables catalysts to fully utilize the visible light and convert it into thermal energy, with a high center temperature of 116.9 °C in 90 s. Dual defects can be used as electron traps, efficiently promoting charge separation. The high vacancy concentration resulted in a highly uneven distribution of electrons, which contributed to the formation of inner electric fields within the semiconductors, expanding the Fermi energy level (E_f) and increasing the interfacial electric field strength, thereby constructing the triple built-in electric fields and greatly enhancing the driving force of charge separation. The catalysts exhibited excellent water purification and hydrogen evolution performance under visible light, and the photothermal catalytic degradation was assisted by machine vision to improve the accuracy of the degradation process. 20ZT-R degraded RhB up to 99.7 % in 40.4 min, and the removal of Cr(Ⅵ) by 20ZT-R reached 99.6 % in 20.3 min. Meanwhile, hydrogen evolution up to 44,500 μmol g-1 in 6 h, the PHE rate of 20ZT-R was 7420 μmol g^-1h⁻¹ of 20ZT-R, which was 157.9 and 24.4 times more than TMC and ZIS-P, respectively. It is shown that higher vacancy concentration can significantly improve the rapid charge separation. This work provides new insights into the modulation of vacancy concentration to construct and enhance built-in electric fields in S-scheme heterojunction for water purification and H₂ evolution.