Photochemical Transformation of Monochloramine Induced by Triplet State Dissolved Organic Matter

Qingqing Kong; Liaoliao Yao; Lei Ye; Yanheng Pan; Yanchun Deng; Zijie Tan; Yangjian Zhou; Guojing Shi; Xin Yang

doi:10.1016/j.jhazmat.2024.134366

Photochemical Transformation of Monochloramine Induced by Triplet State Dissolved Organic Matter

J Hazard Mater. 2024 Jun 5:471:134366. doi: 10.1016/j.jhazmat.2024.134366. Epub 2024 Apr 24.

Authors

Qingqing Kong¹, Liaoliao Yao¹, Lei Ye¹, Yanheng Pan², Yanchun Deng¹, Zijie Tan¹, Yangjian Zhou¹, Guojing Shi³, Xin Yang⁴

Affiliations

¹ Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China.
² School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia.
³ Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia.
⁴ Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China. Electronic address: yangx36@mail.sysu.edu.cn.

PMID: 38678708
DOI: 10.1016/j.jhazmat.2024.134366

Abstract

The photoexcited dissolved organic matter (DOM) could produce reactive intermediates, affecting chemical oxidant transformation in UV based advanced oxidation processes (AOPs). This study confirmed the critical role of triplet state DOM (³DOM*), generated from DOM photoexcitation, in the transformation of monochloramine (NH₂Cl), a commonly used chemical oxidant and disinfectant in water treatment. NH₂Cl (42.25 μM, as Cl₂) was decayed by 17.4-73.4 % within 60 min, primarily due to ³DOM* , in DOM (2-30 mg_C L^-1) solutions irradiated by 365 nm, where NH₂Cl has no absorption. The second-order quenching rate constants of triplet state model photosensitizers by NH₂Cl were determined to be 0.95(± 0.04)-4.49(± 0.04)× 10⁸ M^-1 s^-1 by using laser flash photolysis. As a reductant, ³DOM* reacted with NH₂Cl through one-transfer mechanism, leading to amino radical (NH₂^•) generation, which then transferred to ammonia (NH₄⁺, pKa 9.25) through H-abstraction by the phenolic moieties in DOM. Additionally, the intermediate product of ³DOM* oxidized by NH₂Cl or those triplet state quinones can hydrolyze to form phenolic moieties, elevating NH₄⁺ yield to higher than 99% upon 365 nm irradiation. These findings suggest that the widespread DOM can be applied to convert NH₂Cl via ³DOM* with minimal toxic risks.

Keywords: Advanced oxidation processes; Monochloramine (NH(2)Cl); Photoexcited dissolved organic matter; Reactive nitrogen species; Water treatment.