Mechanochemical mechanism of rapid dechlorination of hexachlorobenzene.
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.
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.
Shanshan
S
Deng
BCEG Environmental Remediation Co. Ltd.,No.6 Jingshun East Street, Chaoyang District, Beijing 100015, China.
Shaoguo
S
Kang
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.
Nannan
N
Feng
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.
Jianxin
J
Zhu
Institute of Nuclear and New Energy Technology, Tsinghua University,Haidian District, Beijing 100084, China.
Bo
B
Yu
Institute of Nuclear and New Energy Technology, Tsinghua University,Haidian District, Beijing 100084, China.
Xiaofeng
X
Xie
Institute of Nuclear and New Energy Technology, Tsinghua University,Haidian District, Beijing 100084, China.
Jing
J
Chen
Dechlorination mechanism; Density functional theory (DFT); Free radical reaction; Hexachlorobenzene (HCB); Mechanochemical treatment