Influence of Nitrite on Ultraviolet-Activated Peroxydisulfate Degradation of 2,4-Dichlorophenol
Xulei Zhao, Jingjing Gui, Peizeng Yang, Deyang Kong, Junhe Lu, Jean‐Marc Chovelon, Yuefei Ji
Abstract
Ultraviolet-activated peroxydisulfate (UV/PDS) oxidation has been considered as a promising technology for removing organic pollutants in wastewater. In this study, we investigated the abatement of 2,4-dichlorophenol (DCP) by UV/PDS, finding that the degradation can be attributed to both direct photolysis and sulfate radical (SO 4 •– ) oxidation. Intriguingly, the presence of trace levels of nitrite (NO 2 – ) increased the degradation rate and dramatically changed the degradation pathways. We propose that an in situ-generated reactive species, nitryl chloride (ClNO 2 ), was responsible for this effect. UV irradiation played a critical role in the generation of ClNO 2 because direct photolysis caused dechlorination of DCP. The released chloride (Cl – ) was further oxidized by SO 4 •– to a chlorine radical (Cl • ). At the same time, NO 2 – was oxidized by SO 4 •– to nitrogen dioxide radicals (NO 2 • ). Combination of Cl • and NO 2 • gave rise to ClNO 2 . This mechanism was not found in the heat-activated PDS system since SO 4 •– oxidation resulted in little dechlorination. As a strong nitrating agent, ClNO 2 reacted rapidly with DCP to form 2,4-dichloro-6-dinitrophenol (DCNP) as the primary transformation product. The yield reached 60.1% in 12 min in the presence of 50 μM NO 2 – . The bioluminescence inhibition assay revealed that DCNP is more toxic than DCP. This contribution indicates that the activation approach can significantly influence the degradation behavior of halogenated pollutants in PDS oxidation systems.