Highly visible-light-active sulfur and carbon co-doped TiO₂ (SC-TiO₂) heterogeneous photocatalysts prepared by underwater discharge plasma

To promptly and simply create highly crystalline S/C co-doped TiO₂ (SC-TiO₂) photocatalysts at room temperature and atmospheric pressure, we suggest a novel plasma-assisted sol-gel synthesis method. This method is a simultaneous synthetic process, in which an underwater plasma undergoes continuous reactions to generate high-energy atomic and molecular species that enable TiO₂ to achieve crystallinity, a large surface area, and a heterogeneous structure within a few minutes. In particular, it was demonstrated that the heterogeneously structured TiO₂ was formed by doping that sulfur and carbon replace O or Ti atoms in the TiO₂ lattice depending on the composition of the synthesis solution during underwater plasma treatment. The resultant SC-TiO₂ photocatalysts had narrowed bandgap energies and extended optical absorption scope into the visible range by inducing the intermediate states within bandgap due to generation of oxygen vacancies on the surface of TiO₂ through synthesis, crystallization, and doping. Correspondingly, SC-TiO₂ showed a significant degradation efficiency ([k] = 6.91 h⁻¹) of tetracycline (TC, antibiotics) under solar light irradiation, up to approximately 4 times higher compared to commercial TiO₂ ([k] = 1.68 h⁻¹), resulting in great water purification. Therefore, we anticipate that this underwater discharge plasma system will prove to be an advantageous technique for producing heterostructural TiO₂ photocatalysts with superior photocatalytic efficiency for environmental applications.