Mechanochemical mechanism of rapid dechlorination of hexachlorobenzene

Shanshan Deng; Shaoguo Kang; Nannan Feng; Jianxin Zhu; Bo Yu; Xiaofeng Xie; Jing Chen

doi:10.1016/j.jhazmat.2017.03.022

Mechanochemical mechanism of rapid dechlorination of hexachlorobenzene

J Hazard Mater. 2017 Jul 5:333:116-127. doi: 10.1016/j.jhazmat.2017.03.022. Epub 2017 Mar 12.

Authors

Shanshan Deng¹, Shaoguo Kang², Nannan Feng¹, Jianxin Zhu³, Bo Yu⁴, Xiaofeng Xie⁴, Jing Chen⁴

Affiliations

¹ Department of Solid Waste Treatment and Recycling, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences,18 Shuangqing Road, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² BCEG Environmental Remediation Co. Ltd.,No.6 Jingshun East Street, Chaoyang District, Beijing 100015, China.
³ Department of Solid Waste Treatment and Recycling, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences,18 Shuangqing Road, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: zhujx@rcees.ac.cn.
⁴ Institute of Nuclear and New Energy Technology, Tsinghua University,Haidian District, Beijing 100084, China.

PMID: 28342352
DOI: 10.1016/j.jhazmat.2017.03.022

Abstract

Recent researches indicate that mechanochemical treatment (MCT) is a promising method to degrade the environmental hazards, especially in the area of persistent organic pollutants (POPs) disposal. However, the mechanochemical dechlorination mechanism of POPs still needs to be further verified. In this mechanochemical process, hexachlorobenzene (HCB) was chosen as a model pollutant with aluminum and alumina (Al+Al₂O₃) powders as the co-milling regents. Both of the intermediate analysis and quantum chemical calculations were adopted to elucidate the free radical dechlorination mechanism of HCB. The solid residues were characterized by electron spin-resonance (ESR) spectroscopy, Fourier transform infrared (FTIR) spectra and X-ray photoelectron (XPS) spectra, which proposed that the radicals formed in the mechanochemical process were chlorinated phenoxyl radicals (CB-O). Four quantum chemical descriptors were selected in predicting the intermediates and reaction pathway: (i) atomic charge, (ii) electrostatic potential (ESP), (iii) frontier molecular orbitals (FMO) theory and (iv) dual descriptor. Then, a stepwise dechlorination mechanism based on CB-O was proposed. It was found that the intermediates and radical-related reactions in the mechanochemical dechlorination of HCB are quite different from that happen in a typical photocatalytic dechlorination process. Impacts of different radical reactions on the dechlorination of HCB were also compared at last.

Keywords: Dechlorination mechanism; Density functional theory (DFT); Free radical reaction; Hexachlorobenzene (HCB); Mechanochemical treatment.