title: Synergetic effect of alkaline earth metal oxides and iron oxides on the degradation of hexachlorobenzene and its degradation pathway.
abstract: The degradation of hexachlorobenzene (HCB) was carried out over physical mixtures of a series of alkaline earth metal oxides (MO: M=Mg, Ca, Sr, Ba) and iron oxides with different crystal types (Fe(x)O(y):Fe(2)O(3) or Fe(3)O(4)) at 300°C. These physical mixtures all showed a synergetic effect toward the degradation of HCB. A range of degradation products were identified by various methods, including tri- to penta-chlorobenzenes by gas chromatography/mass spectrometry (GC-MS), tri- to penta-chlorophenols, tetrachlorocatechol (TCC) and tetrachlorohydroquinone (TCHQ) by GC-MS after derivatization, and formic and acetic acids by ion chromatography. Two degradation pathways, hydrodechlorination and oxidative degradation, appear to occur competitively. However, more sequential chlorinated benzene and phenol congeners were formed over mixed MO/Fe(3)O(4) than over mixed MO/Fe(2)O(3) under the same conditions. The oxidative reaction dominated over mixed MO/Fe(2)O(3) and was promoted as the major reaction by the synergetic effect, while both the oxidative and hydrodechlorination reactions were important over mixed MO/Fe(3)O(4), and both pathways are remarkably promoted by the synergetic effect. The enhanced hydrodechlorination may be attributed to free electrons generated by the transformation of Fe(3)O(4) into Fe(2)O(3), and hydrogen provided by water adsorbed on the MO.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. gjsu@rcees.ac.cn
authors.forename: Guijin
authors.initials: G
authors.lastname: Su
authors.forename: Yexuan
authors.initials: Y
authors.lastname: Liu
authors.forename: Linyan
authors.initials: L
authors.lastname: Huang
authors.forename: Yali
authors.initials: Y
authors.lastname: Shi
authors.forename: Aiqian
authors.initials: A
authors.lastname: Zhang
authors.forename: Lixia
authors.initials: L
authors.lastname: Zhang
authors.forename: Wenbin
authors.initials: W
authors.lastname: Liu
authors.forename: Lirong
authors.initials: L
authors.lastname: Gao
authors.forename: Minghui
authors.initials: M
authors.lastname: Zheng
mesh_terms: D004785:Environmental Pollutants / Q000737:chemistry*; D052918:Environmental Restoration and Remediation; D006581:Hexachlorobenzene / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008673:Metals, Alkaline Earth / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*
chemical_list: D004785:Environmental Pollutants; D008673:Metals, Alkaline Earth; D010087:Oxides; D006581:Hexachlorobenzene; D007501:Iron