Response surface methodology-based fabrication of boron-doped diamond electrodes for electrochemical degradation of guaifenesin in aqueous solutions

• Published in: Journal of the Taiwan Institute of Chemical Engineers Vol. 123; pp. 124 - 133
• Main Authors: Huang, Kuo-Lin, Chao, Peng-Jyun, Kuo, Yi-Ming, Chi, Kun-Yueh, Cheng, Hei Man, Wu, Rui-Zhe, Huang, Tai-Yu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2021
• Subjects: Boron doped diamond electrode; Degradation pathway; Free radical; Guaifenesin (guaiacol glyceryl ether); Response surface methodology; Guaifenesin (guaiacol glyceryl ether); Boron doped diamond electrode; Response surface methodology; Free radical; Degradation pathway
• ISSN: 1876-1070; 1876-1089
• DOI: 10.1016/j.jtice.2021.05.035

•The optimal deposition parameters of BDD electrode fabrication are chosen by RSM.•Complete guaiacol glyceryl ether (GGE) and TOC removal are achieved on BDD.•BDD structure and solution pH influence the GGE (guaifenesin) degradation.•GGE is degraded by direct and indirect oxidation processes (•OH, SO4•−, or S2O82−).•Intermediates are identified to draw GGE degradation pathways. In this study, a boron doped diamond (BDD) electrode (RSM2), fabricated at a boron/carbon (B/C) ratio = 0.75%, a carbon/hydrogen (C/H) ratio = 1.00%, and a reaction chamber pressure (P) = 5.00 torr, exhibited the best performance in terms of electrochemical degradation of guaifenesin [guaiacol glyceryl ether (GGE)] and total organic carbon (TOC) removal among 11 BDD electrodes prepared according to the response surface methodology (RSM). Associated with the B/C, C/H, and P parameters, BDD's diamond crystallite structure, graphite-sp2 C, and grain size influenced the performance of the fabricated BDD electrodes. At 0.125 A cm−2 and 25 °C, the pseudo-first order reaction rate constants of the GGE and TOC removals were 0.33 and 0.031 min−1, respectively, and such removals were better in 0.5 M Na2SO4 than in real hospital wastewater. Both direct and indirect oxidation of GGE occurred during electrolysis. Solution pH affected the indirect oxidation of GGE by •OH, SO4•−, or persulfate electrochemically generated during electrolysis. Several intermediates, including guaiacol, quinones, (aromatic and aliphatic) acids, and hexane-2,5-dione were detected and used to picture the GGE degradation pathways. [Display omitted]