Essential Explanation of the Strong Mineralization Performance of Boron-Doped Diamond Electrodes

• Published in: Environmental science & technology Vol. 42; no. 13; pp. 4914 - 4920
• Main Authors: Zhu, Xiuping, Tong, Meiping, Shi, Shaoyuan, Zhao, Huazhang, Ni, Jinren
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.07.2008
• Subjects: Applied sciences; Boron - chemistry; Chromatography, High Pressure Liquid; Diamond - chemistry; Diamonds; Electrochemistry - methods; Electrodes; Exact sciences and technology; Mineralization; Minerals - chemistry; Oxidation; Oxidation-Reduction; Phenols; Phenols - chemistry; Pollution; Remediation and Control Technologies; Studies; VOCs; Volatile organic compounds; Cresol; Phenol; Mineralization; Adsorption capacity; Phenols; Hydroxyl radicals; Oxidation; Electrochemical reaction; Free radical
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es800298p

Electrochemical oxidation of p-nitrophenol was examined using different anodic materials, including Ti/boron-doped diamond (BDD), Ti/SnO2−Sb/PbO2, and Ti/SnO2−Sb anodes. The results demonstrated that Ti/BDD anodes had a much stronger mineralization performance than the other two anodes. Furthermore, it was found that hydroxyl radicals could mainly exist as free hydroxyl radicals at BDD anodes, which could react with organic compounds effectively. This implied that the dominant mechanism for a much higher mineralization capacity of BDD anodes would be attributed to the existence of free hydroxyl radicals in the BDD anode cell rather than adsorbed hydroxyl radicals on the BDD anode. To further corroborate this hypothesis, electrochemical oxidation of p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) was examined at the Ti/BDD, Ti/SnO2−Sb/PbO2, and Ti/SnO2−Sb anodes, respectively. The study revealed that for Ti/BDD electrodes, the degradation rate of p-substituted phenols (k) increased with the increase of Hammett’s constant (σ), which confirmed the dominance of free hydroxyl radicals at BDD anodes and its effective reaction with organics therein. For Ti/SnO2−Sb/PbO2 electrodes, the degradation rate of p-substituted phenols (k) increased with the increase of initial surface concentration Γ (representing the adsorption capacity of phenols to electrode surface), which indicated that organic compounds mainly reacted with adsorbed hydroxyl radicals at PbO2 anodes. For Ti/SnO2−Sb electrodes, however, k increased with the increase of the integrated parameter S (representing the effects of both σ and Γ), which implied that organic compounds reacted with both adsorbed hydroxyl radicals and free hydroxyl radicals at SnO2 anodes.