Influencing factors and chlorinated byproducts in electrochemical oxidation of bisphenol A with boron-doped diamond anodes

• Published in: Electrochimica acta Vol. 246; pp. 1121 - 1130
• Main Authors: Li, Hongna, Long, Yujiao, Zhu, Xiuping, Tian, Yunlong, Ye, Jing
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 20.08.2017; Elsevier BV
• Subjects: Anodes; Bisphenol A; Boron; Boron-doped diamond; Byproducts; Chloride ions; Chlorination; Chlorine; chlorine evolution; Chloroform; Chromatography; Current density; Current efficiency; Degradation; degradation mechanism; Diamonds; Electrochemical oxidation; Electrolysis; Ethane; factor analysis; Gas chromatography; Hydroxyl radicals; Independent variables; Mass spectrometry; Oxidation; Response surface methodology; Studies; Toxicity; Water treatment; chlorine evolution; factor analysis; bisphenol A; degradation mechanism; Boron-doped diamond
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2017.06.163

•First systematic factor analysis on BPA degradation and chlorinated byproducts.•Optimized condition (maximized k, CE; minimized ΔCl): BDD superior than Pt.•Chlorine evolution and Cl-DBPs were first analyzed concretely with BDD.•The entire toxicity was reduced with more varieties of chlorinated intermediates. The influencing factors and formation of chlorinated byproducts in electrochemical oxidation of bisphenol A (BPA) with the boron-doped diamond (BDD) were systematically investigated using response surface methodology (RSM). The initial BPA concentration, chloride concentration, pH, and current density were studied as independent variables and the degradation rate of BPA (k), current efficiency (CE) and amount of Cl consumed (ΔCl) were selected as responses. The results showed that current density was the most influential factor on both k and ΔCl, and there were strong interactions between the influencing factors for all three responses, attributable to their effects on active chlorine, hydroxyl radicals and the state of BPA in this system. Based on the criteria of achieving the effective degradation of estrogenic BPA with relatively higher current efficiency and less generation of chlorinated byproducts, a final solution with 0.06mM BPA and 40mM NaCl (pH 8) and a current density of 15mAcm−2 optimized through RSM was proved to give a BPA degradation rate of 0.318min−1, a CE of 54.93% and ΔCl of 3.55mM. This showed great advantages compared with Pt anodes under the optimized conditions. The specific orientation of different forms of chlorine was also analyzed under different operation condition. Active chlorine, chloroform, and perchlorate showed similar variation trends with the operating factors. The amount of chlorine consumed in 240min was 5.03mM for BDD anode (while only 0.30mM for Pt under similar conditions), indicating more varieties and amounts of chlorinated byproducts in the BDD system compared to Pt system due to its stronger oxidizing ability. This was further demonstrated through identification of different forms of chlorine and gas chromatography–mass spectrometry analysis. Besides generation of more perchlorate, chlorinated intermediates such as 1,1,2,2-tetrachloro-ethane, 2,2-bis(chloromethyl)-1-propanol, 1,1,1-tris(chloromethyl)-ethane, 2,3,4,6-tetrachloro-phenol, and pentachloro-phenol were specifically detected in the BDD cell. Although the entire toxicity of the whole BPA solution decreased obviously, the formation of these byproducts should be cautiously concerned during the electrolysis. Hereby, electrochemical oxidation should be conducted under lower current density in weakly alkaline electrolyte for actual water treatment projects polluted with organics and inevitable chloride ions.