Synergistic N-Vacancy and S-Scheme Engineered CaF2/g-C3N4 Heterojunction for Photocatalytic Aromatic Phenol Degradation: DFT, Phytotoxicity, and Environmental Impact

Abstract Advanced oxidation technology using photocatalysis is widely regarded as a promising strategy for removing pollutants from wastewater. However, developing efficient visible-light-driven photocatalysts for practical applications remains a significant challenge. In this study, a novel, recyclable S-scheme heterojunction, g-C3N4/CaF2 (GCN/CF), was successfully synthesized via a hydrothermal method. The unique charge-transfer pathway in GCN/CF facilitates enhanced charge separation while retaining the robust redox properties of the composite materials. UV, PL, and TRPL analyses confirmed the generation of an increased number of photoinduced carriers. The GCN/CF composite exhibited significantly improved degradation rates, with kinetic constants 10 times higher than those of the no-catalyst system and 4 times greater than those of pure GCN. Remarkably, 40-GCN/CF achieved degradation efficiencies of 69–74%, 46–56%, and 40% for pollutants in tap water, pond water, and Hooghly River water, respectively. The introduction of nitrogen vacancies improved charge-carrier mobility and promoted oxygen adsorption at N-vacancy sites, as supported by experimental results. Furthermore, the generation of reactive species such as O2–• and OH• played a critical role in pollutant degradation. LC-MS analyses identified intermediate products and degradation pathways. This study provides valuable insights for designing advanced S-scheme photocatalysts for real wastewater treatment applications.