Nitrogen-doped TiO₂/AC bi-functional composite prepared by two-stage calcination for enhanced synergistic removal of hydrophobic pollutant using solar irradiation

Sol-gel method with the incorporation of two-stage calcination protocol was developed to synthesize a bi-functional composite, viz. nitrogen-doped titanium dioxide supported on activated carbon (N-TiO₂/AC). Various types of N-TiO₂/AC composites produced using different calcination conditions were characterized using XRD, porosimetry, XPS, SEM and TEM. All the N-TiO ₂/AC composites exhibited good adsorption of a hydrophobic pollutant (bisphenol-A (BPA) as model pollutant) in water. The effects of calcination conditions, light wavelength and composite dosage on photocatalytic degradation (PCD) performance were investigated. N-TiO₂/AC (400M-700T) composite produced from two-stage calcination (400 °C in air with subsequent 700 °C in NH₃/N₂ atmosphere) was comprised of anatase-rutile phase and this composite exhibited significant PCD efficiency for removing BPA under simulated solar irradiation, with initial pseudo first-order rate constant of ca. 0.67 h^-1. In addition, the N-TiO₂/AC composite exhibited satisfactory BPA removal performance over several series of reuse. Photostability of the N-TiO₂/AC composite was also examined to address its durability under prolonged exposure of UV irradiation. The amount of carbon being leached in water was found to be less than 0.1% after 6 h of UV irradiation.