負載銅二氧化鈦光催化處理含鉻廢水之生命週期評估

Life cycle environmental performance of photocatalytic removal process for chromium wastewater by Cu/TiO2

黃教程(Chiao-Cheng Huang)

指導教授 ： 闕蓓德

共同指導教授 ： 劉雅瑄(Ya-Hsuan Liou)

國立臺灣大學/工學院/環境工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601902

摘要

鉻(Chromium) 常應用於電鍍業、金屬表面處理業的製程中且在環境中主要以三價與六價氧化態存在，傳統的含鉻廢水處理方式為化學混凝法，此方法操作成本低但後續會產生大量的含鉻污泥，若未進行妥善處理，可能由掩埋場滲漏至土壤及地下水中造成嚴重的鉻污染。二氧化鈦異相光催化因化學穩定性、熱穩定性、低毒性以及低成本等優點，近年來廣泛應用於環境有機污染物或重金屬處理。
本研究以光沉積法製備負載銅二氧化鈦(Copper loading titanium dioxide, Cu/TiO2)作為光觸媒去除合成廢水中的鉻。結果顯示在中性條件下改質後的0.5 wt% Cu/TiO2 照光使鉻去除效率有顯著的提升。藉由BET、XRD 以及界達電位儀分析改質後觸媒的表面特性，且利用XANES 對光催化前後的觸媒表面鉻的氧化態與表面結構進行分析，證明六價鉻在暗吸附期間吸附於觸媒內部孔隙，而光催化期間銅會以CuO 及微量Cu2O 形式沉澱於觸媒表面，三價鉻則會以Cr2O3 物種形態於觸媒表面與銅形成共沉澱顆粒。另外，針對化學混凝法、電凝法、銅鐵雙金屬以及本研究之光催化試驗進行生命週期評估，以TRACI 2.1 衝擊評估方法量化四個案例的環境衝擊並進行比較，結果顯示銅鐵雙金屬以及光催化法的衝擊較化學混凝法及電凝法高，單向得點結果顯示衝擊熱點來自於材料製備程序中的電力消耗。敏感度分析結果顯示，一次觸媒產量提升兩倍，光催化法整體衝擊得點變動率47%，提升觸媒產量可有效降低光催化法整體衝擊得點。本研究依據綠色化學的原則，以儀器分析結果歸納光催化處理含鉻廢水的機制，並且以生命週期評估結果提供未來應用於實廠設計之參考。

關鍵字

鉻 ； 負載銅二氧化鈦 ； 異相光催化 ； 生命週期評估 ； X 光近邊緣結構

並列摘要

Chromium is commonly used in electroplating and metal surface treatment process and mainly exists in the environment in the form of trivalent chromium and hexavalent chromium. Traditional treatment for chromium containing industrial wastewater is chemical coagulation, which is a low-cost method in operation. However, chromium containing sludge created in this process may cause significant chromium pollution through leaching from landfill to soil and groundwater if it was not properly disposed of. A potential alternative is the use of heterogeneous photocatalysis with TiO2, which has been widely applied for organic pollution degradation and heavy metal removal in recent years due to its chemical and thermal stability, low toxicity and low cost. This study aimed to remove chromium metal from synthetic wastewater with Cu/TiO2 prepared by photodeposition method. The results show that the 0.5 wt% Cu/TiO2 has a
much better chromium removal efficiency than TiO2 under neutral condition. BET, XRD and Zeta Potential Analyzer were used to measure catalyst surface property. XANES was used to measure the surface structure and the oxidation state of chromium adsorbed inside the catalyst pore. The results clearly prove that a trace amount of Cr(VI) was adsorbed by catalyst during dark adsorption period. During photocatalysis, Copper deposit on the surface mainly in the form of CuO with trace amount of Cu2O and Cr(III) form codeposition with copper on catalyst surface mainly in the form of Cr2O3. Life cycle assessment of this study used TRACI 2.1 impact assessment model to quantify and compare the environmental impact of chemical coagulation, electrochemical coagulation, copper-iron bimetallic and photocatalysis process which was conducted
previously. The results show that copper-iron bimetallic and photocatalysis process have a higher impact than chemical coagulation and electrochemical coagulation. The
single point results show that the impact hotspot was mainly attributed to the electricity consumption of catalyst production process. The results of sensitivity analysis show doubling catalyst yield leads 47% variation to the total impact of photocatalysis process, which shows increasing catalyst yield could effectively reduce the total impact of photocatalysis process. This investigation was conducted based on the principles of green chemistry, summarizing the mechanism of photocatalytic process for chromium removal from wastewater. LCA results provide suggestions for future application to full-scale plant.

並列關鍵字

Chromium ； Copper loading TiO2 ； Heterogeneous photocatalysis ； Life cycle assessment (LCA)；X-ray adsorption near edge structure (XANES)

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