Enhanced visible-light photocatalytic degradation of methylene blue using TiO₂/g-C₃N₄ composites synthesized via co-calcination

A straightforward synthetic approach was employed to fabricate TiO₂–g-C₃N₄ (denoted as T-g-CN) composites and investigate their photocatalytic performance during the degradation of methylene blue. In this method, technical-grade urea, used as a precursor for graphitic carbon nitride (g-C₃N₄), was introduced into a TiO₂ suspension immediately after the hydrothermal treatment (conducted at 180 °C for 3 h). The synthesis was finalized by 30 min of sonication, followed by calcination at 500 °C for 2 h. Three T-g-CN composites were prepared with varying TiO₂/g-C₃N₄ mass ratios of 1:2, 1:3, and 1:4, labelled as T-g-CNA, T-g-CNB, and T-g-CNC, respectively. The physicochemical properties of the resulting composites were characterized using FTIR, XRD, UV–Vis diffuse reflectance spectroscopy (DRS), N₂ adsorption–desorption, TEM, and XPS. FTIR analysis revealed a shift in the characteristic triazine ring vibration of g-C₃N₄ from 810 cm −1 to 806 cm −1 in the T-g-CN composites, suggesting interfacial interaction between TiO₂ and g-C₃N₄. The XRD patterns confirmed the anatase phase of TiO₂, with the most intense peak corresponding to the (200) plane, while the g-C₃N₄ spectrum exhibited signatures of stacked aromatic layers and repeating triazine units. Notably, the T-g-CN composite displayed a reduced band gap of about 2.64–2.72 eV, reflecting an enhanced visible-light absorption. The Brunauer–Emmett–Teller (BET) specific surface area of the composites ranged from 27.43 to 31.06 m 2 /g, with T-g-CNB exhibiting the highest value (31.06 m 2 /g). Among all samples, T-g-CNC demonstrated the best photocatalytic efficiency, achieving 95% degradation of methylene blue within 100 min under combined LED and UV irradiation. Furthermore, the T-g-CNC composite maintained its catalytic performance over three consecutive reuse cycles, highlighting its stability and reusability.