Fabrication of Reduced Graphene Oxide Decorated with Nonmetal-Doped Nanotitania: An Efficient Visible Light–Driven Photocatalyst and Sterilizing Agent for Microbial Cells

The present study pertains to the fabrication of a visible light-responsive nanocomposite of nitrogen and sulfur-doped TiO₂ anchoring reduced graphene oxide (NSNTG) using a facile microwave method for enhanced photocatalytic activity. Two other nanocomposites, TiO₂/rGO (NTG) and nitrogen-doped TiO₂/rGO (NNTG), were also synthesized by using the same method. X-ray diffraction (XRD) and Raman spectroscopy were employed to confirm the presence of the crystalline anatase TiO₂ phase. Elemental composition and formation of a homogeneous dispersion of modified TiO₂ on the GO surface were explored using Field-emission scanning electron microscopy (FESEM) with energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) studies revealed surface composition, chemical state, and the presence of oxygen vacancy defects. A lower bandgap energy and stronger absorption in the visible region were confirmed by UV-visible diffuse reflectance spectroscopy (DRS) analysis. Mott-Schottky analysis revealed the flat band potentials and band alignment of NTG, NNTG, and NSNTG, indicating n-type semiconductor behaviors with flat band potential values of -0.50, -0.60, and -0.68 V, respectively, providing insights into their charge transfer processes. The high photocurrent response in NSNTG facilitates efficient charge migration by inhibiting charge recombination, aligning with the results from PL and EIS measurements. In addition, the large surface area (233.0 m²/g) and a small pore size distribution (7.8 nm) of NSNTG nanocomposites were confirmed using N₂ adsorption-desorption analysis, supporting enhanced adsorption of organic pollutants. The photocatalytic activity of the synthesized nanocomposites was studied by the degradation of organic dyes under visible light; NSNTG exhibited higher removal rates, 97 and 90% within 35 and 60 min, for methylene blue (MB) and rhodamine B (RhB), respectively. The optimal conditions for degradation were pH 8, dye concentration of 50 mg/L, and photocatalyst dosage of 50 mg. Mineralization rates evaluated from TOC analysis were 85.21 and 82.30% for MB and RhB, respectively. The key reactive species involved in photocatalytic degradation were identified as photogenerated hydroxyl radicals, holes, and superoxide radicals. The synthesized nanocomposites were also tested for their antimicrobial efficacy against Gram-negative and Gram-positive bacteria, by the disc diffusion method, NSNTG exhibited a maximum zone of inhibition against <i>Bacillus subtilis</i> and <i>Staphylococcus aureus</i>, comparable to gentamycin. This study outlines the potential of NSNTG as a cost-effective, high-yield, and reusable material for environmental applications.