Boosting photocatalytic rate via internal electric field on g-C3N4/CNT/ZnIn2S4-X S-scheme heterojunction nanocomposites

The synergistic regulation of internal electric fields by cocatalysts and sulfur vacancies facilitates the construction of an emerging step-scheme (S-scheme) heterostructures, thereby achieving effective charge separation and utilization while extending operational lifespan. In this study, g-C3N4/CNT/ZnIn2S4 (denoted as CN/CNT/ ZIS) S-scheme heterojunction composites were synthesized via hydrothermal methods and thermal treatment. The loading amounts of the cocatalysts CNT and ZIS were meticulously designed and optimized to enhance the photocatalytic rate of CN nanosheets. The photocatalytic performance of the CN/CNT/ZIS S-scheme heterojunction composite for the photodegradation of methyl orange (MO) and the photocatalytic reduction of Cr (VI) was evaluated under visible light irradiation. The results indicated that the photocatalytic degradation rate of MO for the CN/CNT/ZIS-2 composite was 24.57 times, 15.64 times, and 4.53 times greater than that of pure CN, CN/CNT, and ZIS, respectively; simultaneously, the rates for the photocatalytic reduction of Cr (VI) were 5.75 times, 3.83 times, and 2.56 times higher, respectively. Furthermore, the interfacial electric field was tested and analyzed using photo-electro-chemistry and KPFM. The significant enhancement in the photocatalytic rate of CN is attributed to the ability of the co-catalyst CNT to improve visible light absorption and the synergistic modulation of the interfacial electric field by sulfur vacancies, thereby confirming that the photocatalytic reaction system meets the criteria for an emerging S-scheme hierarchical heterostructure. This research provides valuable insights into the enhancement of photocatalytic performance through the regulation and design of S-scheme heterojunction photocatalysts via internal electric fields.