Sulfur-doped g-C3N4/TiO2 S-scheme heterojunction photocatalyst for Congo Red photodegradation

Constructing step-scheme (S-scheme) heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials. In this work, a series of sulfur-doped g-C3N4 (SCN)/TiO2 S-scheme photocatalysts were synthesized using electrospinning and calcination methods. The as-prepared SCN/TiO2 composites showed superior photocatalytic performance than pure TiO2 and SCN in the photocatalytic degradation of Congo Red (CR) aqueous solution. The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure, but also from the S-scheme heterojunction. Furthermore, the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO2 across the interface of the SCN/TiO2 composites. The built-in electric field, band edge bending, and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light. Therefore, the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability. These results were adequately verified by radical trapping experiments, ESR tests, and in situ XPS analyses, suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism. This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future.