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An experimental and theoretical study on the degradation of clonidine by hydroxyl and sulfate radicals

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  • Ruiyang Xiao, Central South University, Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution
  • ,
  • Lei He, Central South University, Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution
  • ,
  • Zonghao Luo, Central South University, Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution
  • ,
  • Richard Spinney, The Ohio State University
  • ,
  • Zongsu Wei
  • Dionysios D. Dionysiou, University of Cincinnati
  • ,
  • Feiping Zhao, Central South University, Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution

Emerging contaminants such as pharmaceuticals that cannot be completely removed by traditional biological treatments are ubiquitously present in water bodies with detected concentrations ranging from ng L−1 to mg L−1. Advanced oxidation technologies (AOTs) are promising, efficient, and environmentally friendly for the removal of these pharmaceuticals. In this study, we investigated the degradation kinetics of a model pharmaceutical, clonidine (CLD), via hydroxyl radical ([rad]OH) in UV/H2O2 and sulfate radical (SO4 •−) in UV/peroxydisulfate (PS) systems for the first time. The second−order rate constants (k) of protonated cationic CLD with [rad]OH and SO4 •− were measured to be (2.15 ± 0.07) × 109 M−1 s−1 and (1.12 ± 0.03) × 109 M−1 s−1, respectively. We also calculated the pKa value of CLD and thermodynamic behaviors for reactions of CLD/HCLD+ with [rad]OH and SO4 •− at M05–2X/6–311++G**//M05–2X/6–31+G** level with SMD solvation model. The pKa value was calculated to be 8.14, confirming the literature value. H atom abstraction pathway was the most favorable pathway for both [rad]OH and SO4 •−, while single electron transfer pathway was thermodynamically feasible only for SO4 •− for CLD but not for HCLD+. In addition, the reactivities of both tautomeric forms of CLD (i.e., amino and imino CLD) with both radicals were also investigated. This study contributed to a better understanding on the degradation mechanisms of CLD and proposed the possibilities of the elimination of pharmaceuticals by applying AOTs during wastewater treatment processes.

OriginalsprogEngelsk
Artikelnummer136333
TidsskriftScience of the total Environment
Vol/bind710
Antal sider10
ISSN0048-9697
DOI
StatusUdgivet - 2020

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