Band gap engineering of titanium dioxide (TiO2) nanoparticles prepared via green route and its visible light driven for environmental remediation

• Green Synthesis is used for the preparation of Titanium dioxide nanoparticles. • Croton macrostachyus is used as stabilizing and reducing agent. • Doping of calcium with TiO 2 is used for transformation and decrease in the band gap of the nanoparticles. • Photocatalytic degradation is mostly important in clean environment. The present study investigates the green synthesis and characterization of Calcium-doped titanium dioxide nanoparticles (Ca-TiO 2 NPs) for their potential application in the degradation of organic pollutants under visible light. The nanoparticles were prepared using a simple phytosynthesis method and characterized by various spectroscopic and microanalytical techniques for structural and optical properties. From UV spectroscopic result it is observed that the energy band gap of pure titanium dioxide (TiO 2 ) is decreased from 3.1 eV to 2.52 eV, 2.45 eV and 2.35 eV for 2 %, 5 % and 9 % Ca-doped which shows the transformation from UV to Visible light absorbance. The results obtained suggested that, the introduction of calcium significantly enhanced visible light absorption, thereby extending the photocatalytic activity into the visible spectrum. In this study, the degradation potential of Ca-TiO 2 NPs was assessed through the degradation of 4-Nitro phenol and Congo red organic pollutant dyes under visible light spectrum. Results show a substantial improvement in visible light degradation compared to undoped TiO 2 , indicating the phenomena of calcium-doped titanium dioxide nanoparticles as efficient visible light-responsive photocatalysts for environmental remediation.