| 摘要: | 電-芬頓程序(electro-Fenton)屬於高級氧化程序之一種，本研究中將此法應用於苯環類化合物之破壞處理上，以electro-Fenton處理含不同取代基之苯環化合物，藉此瞭解取代基特性對苯環類化合物電解氧化破壞行為之影響。主要原理是利用電解反應使有機物在電解槽中離子化，或在陽極直接電解氧化，在此同時，鐵離子可於陰極被電解還原成亞鐵離子，並立即與過氧化氫反應，進行Fenton反應氧化有機物質。
主要研究項目包括：(1)進行直接電解氧化試驗，以釐清電流對污染物氧化分解之貢獻程度，(2)比較electro-Fenton氧化期間不同操作因子對硝基苯及苯胺去除率之影響情形，其中各項操作因子包括起始pH、亞鐵離子及過氧化氫添加濃度等操作參數以作為後續之相關研究基礎，(3)比較亞鐵與三價鐵離子在electro-Fenton系統中之污染物去除效率，(4)觀察陰離子對electro-Fenton系統的影響情形，(5)比較electro-Fenton與傳統Fenton程序氧化硝基苯及苯胺之相異性。
實驗結果顯示，硝基苯因含氧結構官能基陰電性為3.5，較苯胺的含氫結構官能基陰電性為2.1，更易在電解系統中，吸引電子與其發生進行直接電解氧化反應，使得硝基苯較苯胺易於在直接電解氧化反應系統中，被電解氧化而去除。於操作參數方面發現，硝基苯在起始pH值2.0 ~ 3.5的範圍中，去除率不會因pH值的改變而產生明顯影響，但在苯胺系統中影響卻較為明顯，於pH為2.5 ~ 3.5範圍間時，系統之去除效率依序為pH 3.5＞3.0＞2.5＞2.0；亞鐵離子的濃度為1.43 ×10-3 M時，便已足夠將硝基苯氧化分解，但於苯胺系統，廢水中的亞鐵離子濃度需至5.40 ×10-3 M才可將苯胺完全分解；氫氧自由基雖具強氧化力可氧化污染物，但若系統中的過氧化氫濃度過量，便會使氫氧自由基與過氧化氫產生反應，或產生自身合成過氧化氫反應，降低系統中之去除效率，本系統之最適加藥劑量為1.90 M。並挑選三組與二價鐵離子相同濃度之鐵離子進行三價鐵離子濃度添加試驗，比較二者對污染物去除成效之差異度，但因三價鐵離子因催化過氧化氫產生氫氧自由基的能力較亞鐵離子差，故需添加相當於5倍的二價鐵離子濃度，才能達到近似的處理成效。此外，於觀察陰離子對electro-Fenton系統的影響情形中發現，於硝基苯系統，氯離子、硝酸根及過氯酸根對電解氧化反應並無抑制情形，反而可促進污染物質氧化，在反應進行10分鐘後，便可將污染物完全分解氧化，但在磷酸根部分，則會對系統產生不良的抑制反應，故不建議使用磷酸根作為電解氧化系統之輔助電解質；此外，在苯胺系統中，對所有陰離子均會對污染物的氧化產生抑制反應，造成去除率下降，故不適合作為苯胺系統的輔助電解質使用，顯示陰離子對於electro-Fenton反應的影響與化學物質本身具有及密切的關係。最後，當實驗條件控制為 [C6H5NO2] = 1.0 ×10-2 M、Fe2+ = 1.8 x 10-3 M、H2O2 = 1.9 M、initial pH＝2.0、電流密度＝33.33 A/m2、反應時間為10分鐘時，經electro-Fenton法處理之硝基苯去除率高於傳統Fenton法約40%可知，電流確實可有效增進硝基苯與苯胺於Fenton系統氧化分解污染物之速率。
Electro-Fenton process is one of advanced oxidation processes; it was employed to the treatment of benzene compounds in the dissertation. Electrochemical destruction of the nitrobenzene and aniline were conducted to examine the influence of benzene substituents characteristics on the electrochemical oxidability of benzene compounds. In this study, a novel electrochemical method for treating wastewater containing benzene compounds was investigated. In the electrolytic cell, the organic compound was ionized or was oxidized by direct electrolysis on the anode. Meanwhile, this method applied H2O2 and ferrous ion to produce hydroxyl radical for oxidizes the contaminants, in which ferrous ion is regenerated via the reduction of ferric ion on the cathode.
The objectives of this study included：(1) to identify the ability of direct electrolysis in oxidizing pollutant; (2) to determine the influences of initial pH, ferrous ion and hydrogen peroxide concentration on the oxidation of benzene compounds; (3) to compare the catalyzing ability of ferrous and ferric ions; (4) to identify the effects of inorganic anions on the electro-Fenton process; (5) to compare the oxidation efficiency of the electro-Fenton and Fenton processes.
Results showed that the experimental conditions were controlled as follows, [C6H5NO2] = 0.01 M, [C6H5NH2] = 0.01 M, Fe2+ = 1.8 x 10-3 M, H2O2 = 1.9 M, initial pH＝2.0, current density＝33.33 A/m2, after electrolyzing for 10 min, the removal efficiencies increased 40% compared of those Fenton treatment. The oxygen atom is strongly electronegative. It has tendency to attract electrons. Therefore direct electrolysis of aniline is more difficult than nitrobenzene. The oxidation rates of made oxidation of nitrobenzene no significant effect at low initial pH (pH=2.0 ~ 3.5). However, for the oxidation of aniline, the highest rate can be found at initial pH 3.5. When applying Fe3+ to electro-Fenton system, it needed five times of Fe3+ dosage to get the same oxidation efficiency compared to the system with Fe2+. This study selected four anions, namely H2PO4-, Cl-, NO3- and ClO4- to explore their effect on the process. Phosphate ions suppressed the nitrobenzene and aniline decomposition. The main reason for the suppression of phosphate ions is that will produce a complex reaction with ferrous ions and ferric ions, which lowers its ability to catalyze hydrogen peroxide. |
