title: Atrazine degradation using chemical-free process of USUV: analysis of the micro-heterogeneous environments and the degradation mechanisms.
abstract: The effectiveness of sonolysis (US), photolysis (UV), and sonophotolysis (USUV) for the degradation of atrazine (ATZ) was investigated. An untypical kinetics analysis was found useful to describe the combined process, which is compatible to pseudo first-order kinetics. The heterogeneous environments of two different ultrasounds (20 and 400 kHz) were evaluated. The heterogeneous distribution of ATZ in the ultrasonic solution was found critical in determining the reaction rates at different frequencies. The presence of NaCl would promote/inhibit the rates by the growth and decline of "salting out" effect and surface tension. The benefits of combining these two processes were for the first time investigated from the aspect of promoting the intermediates degradation which were resistant in individual processes. UV caused a rapid transformation of ATZ to 2-hydroxyatrazine (OIET), which was insensitive to UV irradiation; however, US and USUV were able to degrade OIET and other intermediates through •OH attack. On the other hand, UV irradiation also could promote radical generation via H2O2 decomposition, thereby resulting in less accumulation of more hydrophilic intermediates, which are difficult to degradation in the US process. Reaction pathways for ATZ degradation by all three processes are proposed. USUV achieved the greatest degree of ATZ mineralization with more than 60% TOC removed, contributed solely by the oxidation of side chains. Ammeline was found to be the only end-product in both US and USUV processes.
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. Electronic address: xulijie827@gmail.com.
authors.forename: L J
authors.initials: LJ
authors.lastname: Xu
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. Electronic address: cewchu@polyu.edu.hk.
authors.forename: W
authors.initials: W
authors.lastname: Chu
authors.affiliation: Department of Civil and Environmental Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. Electronic address: n.graham@imperial.ac.uk.
authors.forename: Nigel
authors.initials: N
authors.lastname: Graham
mesh_terms: D001280:Atrazine / Q000737:chemistry / Q000528:radiation effects*; D006540:Herbicides / Q000737:chemistry / Q000528:radiation effects*; D045423:Microbubbles; D010084:Oxidation-Reduction; D010782:Photolysis; D012965:Sodium Chloride / Q000737:chemistry; D013010:Sonication; D014227:Triazines / Q000737:chemistry; D014466:Ultraviolet Rays; D018508:Water Purification / Q000379:methods*
chemical_list: D006540:Herbicides; D014227:Triazines; D012965:Sodium Chloride; C000089:ammeline; D001280:Atrazine
keywords: Atrazine; Mechanism; Salt effect; UV; Ultrasound