Enhanced photocatalytic degradation of sulfamethazine by Bi-doped TiO2 nano-composites supported by powdered activated carbon under visible light irradiation

Abstract

The antibiotic sulfamethazine (SMT) has emerged as a water pollutant that is recalcitrant to conventional water treatment process. A number of technologies based on hydroxyl radical or sulfate radical induced SMT degradation have been described, but photo-induced degradation is not widely examined. Herein, photocatalysts of Bi-doped TiO2 nano-composites supported by powdered activated carbon (PAC) were prepared, with variable molar ratios of Bi/Ti (0.06:1(6%), 0.08:1(8%), 0.1:1(10%) and 0.12:1(12%)) by a sol-hydrothermal method. The ratio of 10% (Bi-Ti/PAC (10%)) was most efficient to degrade SMT. Experimental variables during photocatalytic degradation were optimized for solution pH, catalyst dosage, initial SMT concentration, and coexisted anions. Under optimal conditions of 1.0 g/L catalyst, 20 mg/L initial SMT concentration, pH 6.0 and visible light irradiation at 400–780 nm, the degradation rate reached 81.18% in 300 min. Compared to Bi-Ti(10%) nano-composite without PAC, pure TiO2 or commercially available P25, Bi-Ti/PAC(10%) was superior for SMT degradation with a degradation kinetic rate of 0.00531 min−1. The properties of the prepared photocatalysts were characterized by X-ray powder diffraction, scanning electron microscope, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and ultraviolet-visible diffuse reflection spectroscopy. This revealed that Bi-Ti/PAC (10%) had a smaller crystal size, larger specific surface area, larger pore size, stronger visible light absorption ability and lower band gap energy than pure TiO2. Ten intermediates of SMT were identified and a possible degradation pathway was proposed.