Optimization of Benzodiazepine Drugs Removal from Water by Heterogeneous Photocatalysis Using TiO2/Activated Carbon Composite

Widely consumed benzodiazepine drugs are emerging contaminants, some of them being endocrine disruptors. Although many of these drugs remain in wastewater even after conventional treatment, innovative treatability studies are still sparse. The aim of this study was to investigate the efficiency of heterogeneous photocatalysis using synthesized composites based on TiO2 and activated carbon (TiO2/AC) as catalysts under sunlight-simulated irradiation. Different ratios and calcination temperatures were tested for the synthesis, and the composite with the best photocatalytic efficiency (based on methylene blue dye removal from water solution) was the one formed by 10% AC calcined at 400 °C (TiO2/AC10%). This composite was applied in heterogeneous photocatalysis to remove bromazepam, clonazepam, and diazepam at environmentally relevant concentrations (100 μg/L). Such treatment approach has not been reported in the literature to date. Independent variables such as catalyst concentration, pH, and sunlight-simulated irradiation were studied using design of experiments (DoE) to find conditions that provide maximum removal efficiency. TiO2/AC10% powder was characterized by SEM, XRD, BET, and diffuse reflectance. Under feasible optimized conditions, the efficiency of TiO2/AC10% to remove benzodiazepine drugs from water was > 97.5%, which is much higher than the removal obtained with commercial catalyst and all controls.