Photocatalytic transformation fate and toxicity of ciprofloxacin related to dissociation species: Experimental and theoretical evidences

Si Li; Taobo Huang; Penghui Du; Wen Liu; Jiangyong Hu

doi:10.1016/j.watres.2020.116286

Photocatalytic transformation fate and toxicity of ciprofloxacin related to dissociation species: Experimental and theoretical evidences

Water Res. 2020 Oct 15:185:116286. doi: 10.1016/j.watres.2020.116286. Epub 2020 Aug 9.

Authors

Si Li¹, Taobo Huang², Penghui Du², Wen Liu³, Jiangyong Hu⁴

Affiliations

¹ Beijing Key Laboratory of Farmland Soil Pollution Prevention and Remediation, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China; Department of Civil & Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore.
² College of Environmental Sciences and Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China.
³ College of Environmental Sciences and Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China; The Beijing Innovation Center for Engineering Science and Advanced Technology (BIC-ESAT), Peking University, Beijing, 100871, China. Electronic address: wen.liu@pku.edu.cn.
⁴ Department of Civil & Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore. Electronic address: ceehujy@nus.edu.sg.

PMID: 32818732
DOI: 10.1016/j.watres.2020.116286

Abstract

Chemical speciation of ionizable antibiotics greatly affects its photochemical kinetics and mechanisms; however, the mechanistic impact of chemical speciation is not well understood. For the first time, the impact of different dissociation species (cationic, zwitterionic and anionic forms) of ciprofloxacin (CIP) on its photocatalytic transformation fate was systematically studied in a UVA/LED/TiO₂ system. The dissociation forms of CIP at different pH affected the photocatalytic degradation kinetics, transformation products (TPs) formation as well as degradation pathways. Zwitterionic form of CIP exhibited the highest degradation rate constant (0.2217 ± 0.0179 min^-1), removal efficiency of total organic carbon (TOC) and release of fluoride ion (F^-). Time-dependent evolution profiles on TPs revealed that the cationic and anionic forms of CIP mainly underwent piperazine ring dealkylation, while zwitterionic CIP primarily proceeded through defluorination and piperazine ring oxidation. Moreover, density functional theory (DFT) calculation based on Fukui index well interpreted the active sites of different CIP species. Potential energy surface (PES) analysis further elucidated the reaction transition state (TS) evolution and energy barrier (ΔE_b) for CIP with different dissociation species after radical attack. This study provides deep insights into degradation mechanisms of emerging organic contaminants in advanced oxidation processes associated to their chemical speciation.

Keywords: Ciprofloxacin; Density functional theory; Dissociation species; Photocatalysis; Transformation intermediates.

MeSH terms

Anti-Bacterial Agents / toxicity
Ciprofloxacin* / analysis
Ciprofloxacin* / toxicity
Kinetics
Oxidation-Reduction
Water Pollutants, Chemical* / analysis
Water Pollutants, Chemical* / toxicity

Substances

Anti-Bacterial Agents
Water Pollutants, Chemical
Ciprofloxacin