Bimodal N-doped P25-TiO ₂/AC composite: Preparation, characterization, physical stability, and synergistic adsorptive-solar photocatalytic removal of sulfamethazine

A novel nitrogen-doped P25-TiO ₂ of bimodal structure with activated carbon supported (N-P25-TiO ₂/AC) was synthesized via the modified sol-gel techniques. Besides adding urea as N-source, the N-doping could also be induced through calcination under mixed NH ₃/N ₂ atmosphere. The composite was characterized using XRD, porosimetry, UV-vis spectrophotometry, FTIR, XPS, SEM/EDX and TEM. The physical stability of the composite was examined through ultrasonication disruption, and the composite exhibited good physical stability. The synergistic effects of the adsorption-solar photocatalysis of sulfamethazine (SMZ) as exhibited by the composites were examined. The best performing bimodal composite was N-P25-TiO ₂ (25 + 10)/AC, which comprised 25% of N-P25 and 10% N-TiO ₂ (sol) by weight composition (wt%). The maximum adsorption capacity (S _max) for the N-P25-TiO ₂ (25 + 10)/AC, at pH 3.0, 6.0 and 10.0 was 183 ± 3, 194 ± 3, and 103 ± 2 mg g ^-1, respectively. The effects of the total loading of N-doped titania, sol-gel synthesis technique, weight distribution of N-P25 and N-TiO ₂ (sol), composite dosage, light wavelength spectrum and solution pH on the photocatalytic degradation (PCD) of SMZ were investigated. The N-P25-TiO ₂ (25 + 10)/AC composite exhibited enhanced PCD efficiency under solar irradiation with a pseudo first-order rate constant (k _app) of 0.48 h ^-1, as compared to other types of bimodal composites because its higher N-P25 content led to a greater photocatalytic activity.