Efficient photo-oxidation of bisphenol a and tetracycline through sulfur-doped g-C₃N₄/CD heterojunctions

The synergistic effects of sulfur-doped g-C₃N₄ (SCN) and carbon dots (CD) in nanocomposite photocatalysts were explored for the degradation of contaminants of emerging concern (CECs), particularly phenolic pollutants such as bisphenol A (BPA) and tetracycline (TC). Various SCN/CD nanocomposites were synthesized via thermal polymerization by mixing with different CD concentrations with thiourea (1, 2, 3, and 4 by wt%), denoted as SCN/CD1, SCN/CD2, SCN/CD3, and SCN/CD4, respectively. The embedded CD functions as an intrinsic surface modifier on the surface of the SCN which facilitated the suppression of electron-hole recombination and promoted photocatalytic activity. Among the synthesized catalysts, SCN/CD3 exhibited remarkable efficiency, degrading a 50-ppm solution of BPA to 92.5% and TC to 90.7% within 60 minutes, utilizing 50 mg of catalyst. Moreover, SCN/CD3 demonstrated exceptional reusability over five cycles without significant degradation in efficiency. Radical scavenging experiments identified holes (h⁺) and superoxide radicals (O₂˙⁻) as the primary radical species responsible for pollutant degradation. This work highlights the potential of SCN/CD composite photocatalysts in solving water pollution concerns by elucidating a promising photocatalytic degradation process for CECs.