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  • 學位論文

利用電洞捕捉劑(EDTA/檸檬酸/水楊酸)於連續式光觸媒結合電透析程序光催化還原 Cr(VI) 之研究

Degradation of Chromium(VI) with different hole scavengers (EDTA / Citric acid / Salicylic acid) by fluidized TiO2 photocatalysis combining electrodialysis process

指導教授 : 陳孝行
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摘要


本研究利用 TiO2 所具備同步氧化還原之特性併同處理工業廢水中常見之 Cr(VI) 及有機污染物,此外,本研究所選用之有機物皆為易與金屬複合之羧酸,因此為了避免所產生之複合物阻塞光觸媒表面活性位置及降低電流效率,於模廠中另增設電透析薄膜程序以提升去除效率。目的為探討不同電洞捕捉劑在光催化反應中對 Cr(VI) 還原效率之影響。 於光催化系統中結合電透析薄膜程序避免複合物阻塞光觸媒活性位置提升了 Cr(VI) 及有機物併同處理之效果。由實驗結果得知,當電流密度為 4.0 mA/cm2 可達到最佳去除效率,而在不同電洞捕捉劑的存在下,對 Cr(VI) 之去除率提升約 4.4 % ~ 14.8 %,有機物去除率約提升 16.0 % ~ 21.7 %,在實驗中可發現金屬複合物的存在,無論是何種電洞捕捉劑,皆大約形成 20 % 左右之金屬複合物,因此隨著光催化時間的增加,效率的提升會受到限制。在光催化系統中,降低 pH 值、增加 HRT、增加光照強度及增加電洞捕捉劑初始濃度下對於 Cr(VI) 及有機物的去除效果皆能提升。在 pH 值部分,pH 值越低去除效果越佳,但所需的時間越長。在各操作條件下,電洞捕捉劑羧基團數目越多之有機酸,對 Cr(VI) 還原效率越佳。另外,由於水楊酸具芳香族之特性,使其在鹼性條件下對 Cr(VI) 的還原效果比 EDTA 及水楊酸佳;此外,芳香族之水楊酸在有 Ar 的條件下,對 Cr(VI) 的還原效果優於Air 及 O2。在有機物去除率方面,在光催化降解的過程中經一連串反應後會不斷有 OH•產生,此強氧化劑的存在使有機物氧化之效果遠優於 Cr(VI) 之還原。由 TOC 分析可得知有機物最終礦化產物為 CO2,而中間產物由 GC / MS 結合 MOPAC 軟體所計算之表面電荷密度 (FED) 進行分析。 在光催化系統中結合電透析薄膜程序並選用適當之有機物做為電洞捕捉劑能有效降解目標污染物,在固定 Cr(VI) = 0.001 M、current density = 4.0 mA/cm2、light intensity = 2.5 W/m2、TiO2 = 1.0 g/L、ED-CEM、NaCl = 1000 mg/L 條件下,以 EDTA 為電洞捕捉劑,在 pH = 3.0、EDTA / Cr(VI) 莫耳比 = 2.0、曝 Air、HRT = 4.0 hr的條件下對 Cr(VI) 可得到 96.9 % 的最佳去除效率,而 EDTA降解效率為 73.8 %;以檸檬酸為電洞捕捉劑,在 pH = 3.0、檸檬酸 / Cr(VI) 莫耳比 = 8.0、曝 Air、HRT = 4.0 hr的條件下對 Cr(VI) 可得到 97.7 % 的最佳去除效率,而檸檬降解效率為 59.8 %。

並列摘要


A novel technology of commercial Degussa P-25 TiO2 with UV light photocatalysis combining electrodialysis was proposed for simultaneous oxidization of organic compounds/reduction of Cr(VI) by electron-hole pairs. The goal of this work is to study the effects of different hole scavenger reduced Cr(VI) in photocatalysis process. Application of cation-exchange membrane (CEM) combining electrolysis in the photocatalysis system to avoid metal complexes that block the active sites of the catalyst increase the effect of simultaneous degradation of pollution. The result showed that the best removal efficiency occurred when the current density was set on 4.0 mA / cm2. The Cr(VI) removal efficiency enhanced from 4.4 % to 14.8 % and organic compounds enhanced from 16.0 % to 21.7 % in different hole scavengers. Furthermore, there was formation of the metal compounds in photocatalysis process to influence the degradation efficiency. The result have shown that the lower pH value, increasing HRT, higher light intensity and the denser initial concentration of hole scavenger enhance the removal efficiency of Cr (VI) and organic compounds in the photocatalytic system. It is worth mentioning that the lower pH values can enhance the removal efficiency but requires a relatively longer time. No matter under what operating conditions, with the used of organic compounds having a large number of carboxyl group, the removal efficiency of Cr (VI) markedly increased. Salicylic acid used in the alkaline condition to reduce of Cr(VI) was better than EDTA and citric acid due to the characteristics of salicylic acid being an aromatic acid. In addition, conditions with Argon was better in reducing Cr(VI) than those in Oxygen and Air. As for the removal efficiency of organic compounds, formation of hydroxyl radical from degradation process of organic compounds lead to a far better oxidation of organic compounds than the reduction of Cr(VI). Beside, the final mineralization product is carbon dioxide during the oxidation of organic compounds in the photocatalysis combing electrodialysis system. The intermediate products were indenfied by GC/MS analysis. The photocatalytic degradation reaction pathway were proposed, on the basis of detected intermediate species and calculated frontier electron densities of organic compounds structure by MOPAC system. Under a operating conditions of Cr(VI) = 0.001 M, current density = 4.0 mA/cm2, light intensity = 2.5 W/m2, TiO2 = 1.0 g/L, ED-CEM, the best removal efficiency is obtained with EDTA as a hole scavenger, the organic/Cr(VI) mole ratio being 2.0 and also Air in the system. The best removal efficiency is obtained with citric acid as a hole scavenger, the organic / Cr(VI) mole ratio being 8.0 and also Argon in the system.

參考文獻


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被引用紀錄


林秉蓮(2012)。探討還原性物質於連續式光催化系統氧化非類固醇抗發炎藥劑影響之研究〔碩士論文,國立臺北科技大學〕。華藝線上圖書館。https://doi.org/10.6841%2fNTUT.2012.00482

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