Modification of S-doped g-C3N4 with CDs and brown TiO2-x: Impressive S-scheme photocatalysts with QDs sizes for degradation of pollutants and disinfection of bacteria

Background: It has been reported that defect engineering in TiO2 via the generation of mid-band gap states and elemental doping in g-C3N4 can improve the characteristics of TiO2 and g-C3N4 semiconductors, resulting in boosted photocatalytic ability for removal of contaminants. Methods: In this research, for the first time, S-doped g-C3N4 (denoted as S-GC) was modified with CDs and brown TiO2-x (denoted as TOX) by a facile scalable procedure, and the resultant QDs sized nanocomposites were utilized for detoxifying water contaminants, containing metronidazole (MNZ) and tetracycline (TC) (as pharmaceutical pollutants), malachite green (MG), fuchsine (FS), and methylene blue (MB) (as organic pollutants), and disinfection of two bacteria, containing Staphylococcus aureus and Escherichia coli upon visible light. Findings: Among the photocatalysts, the binary S-doped g-C3N4/TiO2-x (1:2) and ternary S-doped g-C3N4/TiO2-x/CDs (3 mL) photocatalysts presented superior activity. The photocatalytic activity of S-doped g-C3N4/TiO2-x/CDs (3 mL) nanocomposite against TC degradation was 1335 × 10‒4 min‒1, which was respectively 134, 16.0, 88.1, 31.1, and 3.41 times faster than g-C3N4, S-doped g-C3N4, TiO2, TiO2-x, and S-doped g-C3N4/TiO2-x (1:2) photocatalysts. The facile charges transfer among the S-doped g-C3N4 and TiO2-x components via CDs mediator along with the provided active sites played a significant role in the promoted activity, which was confirmed by EIS, PL, and BET analyses. Besides the catalyst stability tests, the plant toxicity studies were conducted through the growth of wheat seeds in a polluted solution with TC after detoxification, and the results showed that the treated system has less toxicity for using in agricultural purposes. © 2024 Taiwan Institute of Chemical Engineers