Enhanced and selective phototransformation of chlorophene on aluminum hydroxide-humic complexes. (1st April 2021)

• Record Type: Journal Article
• Authors: Wang, Xinghao; Pu, Lirong; Liu, Cun; Gao, Juan; Gu, Cheng
• Is Part Of: Water research. Volume 193(2021)
• Publication Date: 2021-04-01
• Subjects: Mineral-associated organic matter -- Selective reaction -- Superoxide anions -- Photodegradation -- Hydroxylation process -- Oligomerization; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.116904
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Photodegradation of CP was significantly enhanced with mineral-humic complexes. Production of high local concentrations of ROS was observed in HA-HAO system. Higher adsorption of CP to HA-HAO contributed to the enhanced degradation. Hydroxylated intermediates were the primary products in HA-HAO system. The adsorbed CP tends to be hydroxylized due to the hydrogen bonding interaction. Abstract: Mineral-humic complexes, known as mineral-associated organic matter (MAOM), are ubiquitous in natural waters. However, the interaction between organic pollutants and MAOM remains elusive, which may affect their degradation process. In this study, photochemical transformation of chlorophene (CP) in the presence of MAOM, prepared by coating aluminum hydroxide with humic acid (HA-HAO), was investigated. Our results showed that the degradation of CP was significantly enhanced in the presence of HA-HAO, and the degradation rate constant was ~5 times as that with HA only. It was because the adsorption of CP to HA-HAO particles was greatly enhanced, and concentration of reactive oxygen species (ROS) was increased on HA-HAO surfaces, which further promoted the reactions between CP and ROS. The quenching experiments combined with EPR technology confirmed that superoxide anion (O2 ·– ) was the primary reactive radical on CP photodegradation. More importantly, the degradation of CP with HA-HAO followed a hydroxylation process, rather than the oligomerization reaction with HA only. Spectroscopic analysis provided direct evidence for the formation of hydrogen bonding between CP phenolic hydroxyl group and surface oxygen of HAO, which would suppress the reactivity of phenolic hydroxyl group, consequently the ortho- and meta-positions of CP became more facile for the hydroxylation reaction. This study shows the importance of MAOM in altering the photochemical behavior and transformation pathway of organic contaminants. Graphical abstract: Image, graphical abstract