以摻硼鑽石電極電高級氧化降解水中2-苯基苯並咪唑-5-磺酸

Electrodegradation of aqueous 2-phenylbenzimidazole-5-sulfonic acid by electro-advanced oxidation with boron-doped diamond electrodes

鄭希敏(Cheng Hei Man)

指導教授 ： 黃國林

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2022年)

https://doi.org/10.6346/NPUST202200220

摘要

由於防曬乳成分2-苯基苯並咪唑-5-磺酸(2-phenylbenzimidazole-5-sulfonic acid, PBSA)於多種水生環境中被檢測到，且對水中生物造成一定危害，是一種新興污染物，不易被傳統廢水處理程序有效去除，所以需要開發去除水溶液中PBSA之方法。本研究使用自製摻硼鑽石(boron doped diamond, BDD)電極(Nb/BDD)於電高級氧化程序(electrochemical advanced oxidation process, EAOP)降解PBSA，探討操作參數，包括電解質類型、電解質濃度、電流密度、陽極陰極面積及陰極材質對降解之影響及比能耗，並與NeoCoat及Diachem兩種商用電極進行比較。
研究結果顯示，X-射線繞射(X-ray diffractometry, XRD)分析證實自製BDD電極存在鑽石結構，並具有(111)及(200)晶向。於拉曼(Raman)光譜中出現500 cm−1與1220 cm−1附近之特徵峰伴隨1332 cm−1鑽石特徵峰左移及減弱之特徵及於X射線光電子能譜 (X-ray photoelectron spectroscopy, XPS)中發現具B-C鍵，進一步確認硼原子己經摻入鑽石晶格。與NeoCoat及Diachem電極相比，自製BDD電極硼濃度高達1.41×1021 cm-3，導致sp2石墨增加及晶粒細化。透過超高解析度熱場發射掃描式電子顯微鏡(field emission scanning electron microscope, FE-SEM)分析，得到鑽石晶粒平均粒徑為259 nm，晶粒細化導致晶界缺陷增加從而影響電極的電性能。循環伏安法(cyclic voltammetry, CV)及線性掃描伏安法(linear sweep voltammetry, LSV)分析表示自製BDD電極與商用Diachem電極之電化學窗口範圍一致(-1.7 ~ 2.0 V)但較商用NeoCoat電極窄(-1.7 ~ 2.8 V)，計算電化學活性表面(Electrochemical Active Surface, ECS)面積發現相比於兩種商用BDD電極，自製BDD電極具有較高ECS面積，為9.82 cm2。
CV結果顯示PBSA於自製BDD電極上之氧化還原特性為不可逆且PBSA能被直接及間接電氧化，其電化學氧化為擴散控制過程。使用硫酸鈉電解質比氯化鈉具有較好之PBSA及總有機碳(total organic compound, TOC)降解效率及反應速率。提高電流密度及電解質濃度可以加速PBSA及TOC降解。陽極面積增加會增加PBSA及TOC降解效率且有助於去除部分硝酸鹽氮，但比能耗亦隨之增加。相反的，增加陰極面積會呈現相反趨勢。比較不同陰極之降解效果，發現以鈦(Ti)板為陰極之硝酸鹽氮去除率較佳。電氧化降解PBSA之較佳實驗參數為4 cm2 Nb/BDD作陽極、4 cm2 Ti板作陰極、電解質濃度為0.1 M Na2SO4、電流密度為0.5 A/cm2。自製BDD電極與商用電極以較佳條件於純水及生活廢水中電氧化解降PBSA，發現各BDD電極之PBSA與TOC電降解趨勢及降解效率皆相似，PBSA去除率為100 %，TOC 去除率≥98%，k值分別相差2.63 × 10-4及1.42 × 10-4，R2 > 0.97，比能耗相似僅相差2.43 Wh/mg-TOC。
紫外-可見(UV-Vis)光譜分析顯示PBSA之三個特徵峰(205 nm、241 nm及300 nm)於電解60 min 時消失，表示PBSA之環狀結構被完全破壞。電子自旋共振 (electron spin resonance, ESR)光譜顯示，使用5,5-二甲基-1-吡咯啉-n-氧化物(5,5-dimethyl-1-pyrroline-n-oxide, DMPO)作為自旋陷阱(spin traps)於NaCl、Na2SO4、HClO4及H2SO4電解質中透過自製BDD陽極電活化可形成氫氧自由基(•OH)，且於酸性環境下較有利於形成•OH。電氧化降解PBSA之主要降解途徑為裂解咪唑環，中間產物主要為2-苯基-1H-苯並咪唑(2-phenyl-1H-benzimidazole, PBI)(m/z 193)、苯甲脒(benzamidine, BZD)(m/z 121)、苯甲酰胺(benzamide, BD)(m/z 122)、對苯二酚(hydroquinone)(m/z 111)、1,4-苯醌(1, 4-benzoquinone)(m/z 114)、馬來酸(maleic acid)、草酸(oxalic acid)及富馬酸(fumaric acid)。

關鍵字

電高級化學氧化法 ； 摻硼鑽石電極 ； 2-苯基苯並咪唑-5-磺酸 ； 自由基 ； 比能耗 ； 表面表徵

並列摘要

2-phenylbenzimidazole-5-sulfonic acid (PBSA), a component of sunscreen agent and one of emerging contaminants, has been detected in various aquatic environments, having the potential to pose a risk on aquatic biota. However, conventional wastewater treatment processes usually cannot effectively remove PBSA, so it is necessary to develop techniques for PBSA removal from waters. In this study, a lab-made boron-doped diamond electrodes (Nb/BDD) electrode was used in an electrochemical advanced oxidation process (EAOP) for degrading PBSA in sodium sulfate and sodium chloride solutions. Two commercial electrodes (NeoCoat and Diachem) were also tested for comparison. Operating parameters such as electrolyte, electrolyte concentration, current density, anode/cathode area ratio, and cathode material were studied in order to determine their effects on the degradation efficiencies of PBSA and total organic compound (TOC) and specific energy consumption.
The analysis of X-ray diffraction showed that the lab-made BDD had diamond crystalline with (111) and (200) reflections. The characteristic of B-doped diamond lattice was also reflected in Raman spectra the band at ~500 and 1220 cm-1 and that downshift at 1332 cm-1. In addition, the analysis of X-ray photoelectron spectroscopy (XPS) for B 1s spectra indicates the presence B-C bonds. The boron concentration (1.41×1021 cm-3) of lab-made BDD electrode was greater than those of the two commercial electrodes, causing the increase of sp2 graphite (associated with the D band and G band in Raman spectra) and the decrease of crystalline size. The average crystalline size was 259 nm based on field emission scanning electron microscope (FE-SEM) examination. The decrease of crystalline size led to structural imperfections and affected the electrical properties of electrodes, consistent with the result of cyclic voltammogram (CV) that the lab-made BDD electrode exhibited a potential window narrower than those of the two commercial eletrodes in 0.1 M Na2SO4 solution, the lab-made BDD also had higher electrochemical active surface (ECS) area (9.82 cm2).
CV analysis also showed that an electrochemically irreversible characteristic of PBSA on the lab-made BDD, although PBSA can be directly oxidized (diffusion control) on the BDD. The removal efficiency or degradation rate of PBSA or TOC was higher in Na2SO4 than in NaCl solution. In addition, the degradation rate of PBSA or TOC increased with an increasing current density or electrolyte concentration. Increasing anode area also increased the rate of PBSA or TOC degradation and nitrate-nitrogen removal, although the specific energy consumption increased. On the other hand, increasing the ratio of cathode area obtained an opposite result.
Among the cathodes, Ti exhibited the best removal of nitrate-nitrogen. The better conditions for PBSA degradation were determined as 4 cm2 Nb/BDD anode, Ti cathode, electrolyte = 0.1 M Na2SO4, and current density = 0.5 A/cm2. The rate of PBSA or TOC degradation (≥98% TOC removal) and specific energy consumption of lab-made BDD electrode were similar to those of commercial electrodes. The specific energy consumption of electrolysis using the lab-made BDD electrode (13.75 Wh/mg-TOC) was higher than that using the Diachem electrode (12.42 Wh/mg-TOC) but lower than that using the NeoCoat electrode (13.87 Wh/mg-TOC). The results of electrodegradation of PBSA in domestic wastewater were similar to the results in pure water.
The three peaks (205 nm, 241 nm, and 300 nm) shown in UV-Vis spectroscopy analysis totally disappeared after 60-min electrolysis, indicating that rings of PBSA were completely opened. The lab-made BDD could produce hydroxyl radicals (•OH) in NaCl, Na2SO4, HClO4, or H2SO4 solution based on electron spin resonance (ESR) analysis using 5,5-dimethyl-1-pyrroline-n-oxide (DMPO) as a spin trap. The main possible electrodegradation pathway of PBSA was imidazole ring cleavage. The major intermediates of PBSA were 2-phenyl-1H-benzimidazole (m/z 193), benzamidine (m/z 121), benzamide (m/z 122), hydroquinone (m/z 111), 1,4-benzoquinone (m/z 114), maleic acid, oxalic acid and fumaric acid.

並列關鍵字

electrochemical advanced oxidation processes ； boron-doped diamond electrode ； 2-phenylbenzimidazole-5-sulfonic acid ； free radicals ； specific energy consumption ； surface characterization

參考文獻

Abdelraheem, W. H., He, X., Komy, Z. R., Ismail, N. M., and Dionysiou, D. D., 2016, “Revealing the mechanism, pathways and kinetics of UV254nm/H2O2-based degradation of model active sunscreen ingredient PBSA,” Chemical Engineering Journal, Vol. 288, No. pp. 824-833.

Akrout, H. and Bousselmi, L., 2012, “Chloride ions as an agent promoting the oxidation of synthetic dyestuff on BDD electrode,” Desalination and Water treatment, Vol. 46, No. 1-3, pp. 171-181.

Al-Anazi, A., Abdelraheem, W. H., Han, C., Nadagouda, M. N., Sygellou, L., Arfanis, M. K., Falaras, P., Sharma, V. K., and Dionysiou, D. D., 2018, “Cobalt ferrite nanoparticles with controlled composition-peroxymonosulfate mediated degradation of 2-phenylbenzimidazole-5-sulfonic acid,” Applied Catalysis B: Environmental, Vol. 221, No. pp. 266-279.

Altuntepe, A. and Zan, R., 2021, “Permanent boron doped graphene with high homogeneity using phenylboronic acid,” Journal of Molecular Structure, Vol. 1230, No. p. 129629.

Ammar, H. B., Brahim, M. B., Abdelhédi, R., and Samet, Y., 2016, “Green electrochemical process for metronidazole degradation at BDD anode in aqueous solutions via direct and indirect oxidation,” Separation and Purification Technology, Vol. 157, No. pp. 9-16.