Facile and ecofriendly approach of using Calotropis procera fruit for the surface modification of TiO₂ for enhanced photocatalytic oxidation of methylene blue with irradiation of natural sunlight

This study explores the potential of modifying bulk TiO₂ through wet chemical processes to enhance its photocatalytic properties for environmental applications. The approach focuses on cost-effectiveness and environmental sustainability, aiming to address challenges such as pollutant degradation, including dyes and organic contaminants in water. By applying varying volumes of Calotropis procera fruit extract (2, 4, 6, and 8 mL) during wet chemical treatment, significant changes were observed in particle sizes, surface properties, crystallinity, and optical characteristics. The modified TiO₂ sample with 8 mL of extract (sample 4) demonstrated the lowest optical band gap at 2.59 eV and improved crystalline properties compared to unmodified TiO₂. Photocatalytic tests using methylene blue (MB) degradation under natural sunlight showed that sample 4 achieved a 97 % dye removal rate at a dye concentration of 1.60 × 10⁻⁵ M within 30 min. This superior performance was attributed to the reduced band gap, which enhanced the absorption of near-visible photons and minimized electron-hole recombination. Further analysis under varying conditions, including catalyst concentration, pH, and initial dye concentration, confirmed the efficiency of sample 4, achieving an outstanding rate constant of 1.8 × 10⁻⁵ min⁻¹ at pH 9. Radical trapping experiments identified holes as the primary active species in MB degradation, with hydroxide and superoxide radicals playing secondary roles. Cycling stability tests over five cycles confirmed the satisfactory stability of sample 4. These findings suggest that the modification of TiO₂ with the extract significantly enhances its photocatalytic efficiency and stability, making it a promising candidate for environmental applications such as wastewater treatment.