Self-regulated S-scheme heterojunction for synergistic removal of tetracycline and hexavalent chromium: Synergistic mechanism of trivalent chromium

The limitation of conventional photocatalysts in simultaneously removing Tetracycline (TC), hexavalent chromium (Cr (VI)) and trivalent chromium (Cr (III)) were addressed in mixed pollution treatment. The S-scheme heterojunction of titanate nanotubes/Bi2WO6 (TNTs/BWO) was successfully constructed to achieve efficient removal of TC, Cr (VI), and Cr (III). The theoretical calculations (DFT) demonstrated that TNTs’ ion exchange properties led to the partial replacement of interlayer Na+ by Cr (III), optimizing the S-scheme heterojunction during the photocatalytic reaction. Experimental results revealed that the coexistence of TC, Cr (VI), and Cr (III) had a mutual promotion effect, as evidenced by the apparent rate constant of Cr (VI) reaching 0.7 min−1, which was 87.5 times higher than that of the single pollutant system, while maintaining a high apparent rate constant for TC. The likely intermediate products, degradation pathways, and photocatalytic mechanism were also elucidated using DFT molecular orbitals and Fukui index analysis. This work provides new insights and strategies for simultaneously removing pollutants and contributes to wastewater purification.