Development of S-Ca-codoped TiO2 hybrid nanostructures for the efficient photodegradation of crystal violet and tetracycline effluents: Experimental and DFT study

Abstract The photocatalytic efficiency of pristine titanium dioxide nanoparticles (TiO2 NPs) remains suboptimal due to its poor visible light absorption and rapid charge carrier recombination, necessitating fine structural tuning. In this study, we report the synthesis of a novel photocatalyst, sulfur (S) and calcium (Ca) co-doped titanium dioxide (S-Ca-codoped TiO2) hybrid nanostructures using a sol–gel method. By using state-of-the-art techniques, the prepared pristine TiO2 NPs and co-doped hybrid nanostructures were characterized for their structural, morphological, textural, and optical properties. The Raman spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses confirm the successful synthesis of anatase TiO2 NPs and the hybrid nanostructures. The optical properties of the prepared samples were examined by UV–Vis diffuse reflectance (DRS) spectroscopy and photoluminescence (PL). The surface areas of TiO2 NPs and the hybrid nanostructures were calculated using the Brunauer–Emmett–Teller (BET) method and were found to be 49.5 and 72.2 m2g−1, respectively. Density Functional Theory calculations were performed to determine the electronic properties of pure anatase TiO2, single (S-doped TiO2, Ca-doped TiO2) and co-doped (S-Ca-codoped TiO2) systems. The single and co-doped substitution significantly reduce the band gap energy and increases charge mobility, thereby enhancing the light absorption capability and photocatalytic performance of doped materials. The prepared TiO2 NPs and hybrid nanostructures were tested for the degradation of tetracycline (TC) and crystal violet dye (CV) under both sunlight and ultraviolet (UV) irradiation. The S-Ca-codoped TiO2 hybrid nanostructures achieved exceptional photocatalytic performance, degrading 99.6% of TC in 120 min and 99.26% of CV in 90 min under sunlight, significantly surpassing pristine TiO2 NPs (77.4% for TC, 77.17% for CV). This enhanced activity was also consistent under UV irradiation , with S-Ca-codoped TiO2 hybrid nanostructures reaching 99.25% degradation for TC and 96.4% for CV, compared to only 72.8% and 82.3%, respectively, for the pristine TiO2 NPs. The photocatalytic efficiency of the prepared materials were optimized by tuning key reaction parameters, confirming the excellent potential of the S-Ca-codoped TiO2 nanomaterial in comparision of TiO2 NPs for real-world water treatment. Graphical abstract