Removal of brilliant green dye by synergistic effect of adsorption and photocatalysis on B-TiO2

Abstract The escalating discharge of synthetic dyes, such as brilliant green (BG), into aquatic ecosystems poses severe environmental and health risks because of their toxicity, carcinogenicity, and bioaccumulation potential. This study reports the synthesis of black titanium dioxide (B-TiO 2 ) via the chemical reduction of commercial Degussa P25 TiO 2 using NaBH 4 at 300 °C under a N 2 atmosphere, aiming to enhance the visible-light photocatalytic activity for BG removal. Comprehensive characterization via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis DRS), Brunauer-Emmett-Teller (BET) analysis, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) confirmed the introduction of Ti 3 ⁺ defects and oxygen vacancies, resulting in a reduced bandgap (≈2.3 eV), extended visible-light absorption, increased surface area, and improved charge separation. Photocatalytic evaluations under visible-light irradiation ( λ > 420 nm) exhibited optimal BG removal (10 mg/L) at a catalyst load of 1 g/L and pH 11, achieving optimal removal in 30 min, adhering to pseudo-first-order kinetics ( k = 0.062 min −1 ). Radical-scavenging experiments identified superoxide radicals (O 2 •⁻ ) as the primary reactive species, with minor contributions from hydroxyl radicals (•OH) and holes (h⁺). The catalyst demonstrated good reusability, maintaining > 95% efficiency over four cycles. These findings underscore B-TiO 2 as a robust solar-driven photocatalyst for sustainable wastewater remediation, in alignment with the UN’s Sustainable Development Goals for clean water and health.