Solar light-active S-scheme TiO2/In2S3 heterojunction photocatalyst for organic pollutants degradation

Heterojunction TiO2/In2S3 composite photocatalyst was prepared using a simple low-temperature one-step hydrothermal method. In2S3 nanosheets with a thickness of 1–5 nm were decorated with 20–30 nm TiO2 nanoparticles, forming a stable heterojunction. The electron transfer mechanism and band alignment between TiO2 and In2S3 was studied using X-ray photoelectron spectroscopy and UV–visible spectroscopy, which suggested the formation of an S-scheme heterojunction in TiO2/In2S3 composite. The TiO2/In2S3 composite with a 1:1 mole ratio showed 99.9% photocatalytic degradation of Rhodamine B within 20 minutes of solar light irradiation, which was better than the results for pristine TiO2, pristine In2S3, and their physical mixture, as well as any other previously reported materials of the same kind. The as-prepared TiO2/In2S3 composite showed excellent stability (98% for Rhodamine B) even after five successive reuse cycles. This excellent performance of TiO2/In2S3 was attributed to the S-scheme heterojunction because of an internal electric field, columbic attraction, and band bending. A radical trapping study showed that superoxide radicals O2·- contribute the most to the photocatalytic degradation of Rhodamine B followed by hydroxyl radicals (OH) and holes (hVB+). The use of a low synthesis temperature and a simple, one-step formation method, with no secondary pollutants generated, makes this process an environmentally friendly and sustainable solution for cost-effective wastewater treatment, highlighting its future commercial applications.