Degradation of pharmaceutical contaminants by bubbling gas phase surface discharge plasma combined with g-C3N4 photocatalysis

Abstract

The feasibility of using gas phase surface discharge with microporous bubbling for the degradation of pharmaceutical contaminants was evaluated. After 25 min of treatment, 82% removal of ibuprofen (with an initial concentration of 60 mg L⁻¹) and 100% removal of tetracycline hydrochloride (with an initial concentration of 200 mg L⁻¹) was achieved. To utilize the UV and visible radiation produced in the discharge process, a g-C₃N₄ photocatalyst was added into the solution to enhance the degradation efficiency. Adding 75 mg L⁻¹ g-C₃N₄ can increase the removal of ibuprofen by 18% (initial concentration of 10 mg L⁻¹) and tetracycline hydrochloride by 10% (initial concentration of 100 mg L⁻¹) after 10 min of discharge treatment. The crystallinity of the used g-C₃N₄ became higher as the discharge treatment can planarize the g-C₃N₄ surface via oxidization. In addition, aqueous O₃, H₂O₂ and ˙OH radicals under different conditions were measured to investigate the reaction mechanisms. The aqueous O₃ reaches saturation after 30 min of discharge but H₂O₂ kept accumulating during the two hour discharge. The average ˙OH formation rate is 0.4191 mol L⁻¹ min⁻¹ in distilled water but 0.5640 mol L⁻¹ min⁻¹ with g-C₃N₄, which demonstrates the promotion of photocatalytic ˙OH generation. Therefore, combining the bubbling gas phase surface discharge plasma with g-C₃N₄ photocatalysis leads to an extraordinary performance for the treatment of pharmaceutical additives.