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

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.