A comparative study on the degradation of carbamazepine by UV laser/chlorine and UV laser/PS processes: Performance and mechanisms

Abstract

Residual carbamazepine (CBZ) in water is difficult to remove through conventional treatment processes, threatening the safety of drinking water. Ultraviolet-based advanced oxidation processes (UV-AOPs) have shown promise in removing refractory organic pollutants, while the low energy and efficiency of traditional mercury lamps hinder their practical applications. In this study, the performance and mechanism of an intensive-energy light source, UV laser, were systematically explored in UV-AOPs (laser/chlorine, laser/persulfate (PS)). It was found that UV laser exhibited a significantly activating ability for chlorine and PS due to its precise wavelength and high pulse energy. When exposed to UV laser (266 nm, 4.2 mW/cm2) combined with 200 μM chlorine and PS, the kinetic rate constants for the degradation of 10 μM CBZ were determined to be 3.160 × 10-3 and 1.227 × 10-3 s−1, respectively. The degradation of CBZ was dominated by hydroxyl radicals (60.98 %) and sulfate radicals (23.15 %) in laser/PS system, while in laser/chlorine system, hydroxyl radicals (54.90 %), chlorine radicals (27.43 %), and chlorine oxide radicals (13.81 %) were primary reactive species. Furthermore, both the laser/chlorine and laser/PS systems demonstrated compatibility with a wide pH range of 5.0–9.0 and high resistance to anionic interference. Moreover, the electrophilic and nucleophilic sites of CBZ and energy barrier of the initial reaction were calculated based on the density functional theory (DFT). Additionally, the degradation pathways of CBZ and the toxicity of transformation products in laser/chlorine and laser/PS processes were proposed and evaluated. These results demonstrated that the UV laser-based processes exhibited promising prospects in eliminating refractory organic pollutants in water treatment.