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年度	107	專案性質	實驗性質
專案類別	研究專案	研究主題	整治
申請機構	國立臺灣大學	申請系所	環境工程學研究所
專案主持人	侯嘉洪	職等/職稱	副教授
專案中文名稱	電催化/電吸附同步去除砷之技術開發
中文關鍵字	電催化,電吸附,砷,地下水整治
專案英文名稱	Removal of arsenic from groundwater using simultaneous electrocatalysis and electrosorption process
英文關鍵字	Electrocatalysis, Electrosorption, Arsenic, Groundwater Remediation
執行金額	919,930元
執行期間	2018/1/10 至 2018/11/30
計畫中文摘要	環境中大多數的砷係以無機砷的型態存在，若長期暴露將對人體健康及生態環境直接或間接地造成威脅，因此，砷被國際癌症研究組織列為第一級致癌物。無機砷分為三價砷及五價砷，分別以不帶電荷之亞砷酸鹽及帶電荷之砷酸鹽存在。傳統上針對地下水中砷污染所因應的處理技術包括化學氧化法、薄膜法、吸附法、離子交換法及化學混凝法等。傳統之砷處理技術，多有能源需求較高、操作成本較高、薄膜表面易積垢、無法有效處理含低濃度污染物之水質、需添加化學藥劑及產生二次污染物的問題。本研究團隊過去執行104年度「以電容去離子技術移除地下水中砷之研究」及105年度「建構電容去離子系統整合模組處理含砷地下水之先驅試驗」之研究計畫，成功證實電容去離子技術(capacitive deionization, CDI)應用於分離地下水中砷之潛力。CDI技術原理係施加外部電場於多孔性碳電極，基於電吸附機制，藉由庫倫靜電力吸附水中之帶電離子，達到分離貯存離子與淨水的目的。值得一提的是，環境水體中五價砷物種皆屬於帶電離子，可透過電吸附機制去除，反之，三價砷物種在水體中不具有帶電性，故無法直接透過電吸附機制去除。本研究目的係以電催化材料修飾活性碳(activated carbon, AC)電極材料，針對較難處理的亞砷酸鹽(三價砷)，透過電催化反應，將三價砷氧化成五價砷，再以電吸附的方式將其移除，從而增加CDI對於含砷地下水的整體去除效能。研究計畫內容主要利用循環伏安法將過渡金屬之鈷氧化物(cobalt oxide, CoOx)，以電沉積方式與多孔性活性碳結合，作為複合電極。複合電極會進一步透過物化、電化學及表面型態特性分析，評估複合電極對三價砷的電催化活性及砷物種的電吸附容量，最後以CDI批次實驗進行驗證，完成同步電催化/電吸附分離砷之技術開發。本研究利用循環伏安之電沉積法成功製備CoOx/AC複合電極，CoOx的修飾改變AC電極的比表面積及孔徑分布，提升助於離子傳輸的中孔分布比例。並由表面型態及化學鍵結形態分析證實CoOx實際沉積於AC電極，且係以Co(II)及Co(III)之混合價態存在。再者，證實CoOx/AC複合電極對三價砷物種具有優異的電催化氧化活性，且複合電極可維持良好的電容表現及電化學穩定性。於電催化/電吸附同步除砷的CDI批次試驗中，三價砷的電吸附容量為4.77 mg g−1，係AC電極之三倍。同時，本研究成功驗證CoOx/AC複合電極對砷物種具有較佳的轉換效率，三價砷物種催化成五價砷物種的轉換效率為60.5%，砷總體的去除效率為AC電極的兩倍。說明CoOx/AC複合電極具電催化/電吸附的機制，係可同時去除三價砷及五價砷，進而提高砷整體的去除效能。本研究完成電催化/電吸附同步分離水中砷物種之試驗，研究成果對於電化學處理技術於地下水體中無機砷的去除，可有相當顯著的貢獻。
計畫英文摘要	Arsenic (As) contamination in groundwater has been a serious worldwide problem that endangers the health of human beings. Especially, inorganic arsenic compounds have been identified as a form of carcinogen to humans by the International Agency for Research on Cancer (IARC). Inorganic arsenic compounds can be classified as arsenate (pentavalent arsenic, As(V)) and arsenite (trivalent arsenic, As(III)). Noteworthy, extreme weather conditions caused by climate change increase the risk of water shortages. For that reason, the demand for withdrawing groundwater for agriculture or industry increased. Negative effects of As in groundwater used for irrigation water in the agricultural production system are of great concern in Taiwan. Many localized groundwater sources have been identified as a potential problem, in which the arsenic concentration is higher than the irrigation water quality standard of 0.05 mg L−1. Therefore, it is essential to develop the effective, energy-saving, and environmental friendly separation techniques for the removal of arsenic from groundwater. Capacitive deionization (CDI), regarded as a promising water-purification technology, has powerful advantages such as low operating pressure, low energy consumption, no chemical additive, no secondary waste, and easy regeneration. CDI, to remove ionic species from aqueous solutions, is based on the charge separation using nanoporous carbon electrodes for capacitive electrical double-layer storage. It is worth noting that as compared with traditional water treatment processes, CDI is especially suitable for the removal of arsenic at low concentrations in groundwater. Under the assistance of electric field, arsenic can be electrostatically separated from water and stored in the EDL. The main purpose of this study is to enhance the removal of arsenic (i.e., As(III)) from aqueous solutions via simultaneous electrocatalysis and electrosorption in CDI. This study focuses on the modification of the activated carbon (AC) electrode using transition metal cobalt oxide (CoOx) as the electrocatalyst for CDI application. Surface morphology, pore characterization, and chemical properties of the resultant composite electrodes will be characterized in detail. The interaction between the composite electrode and arsenic species will be investigated by electrochemical measurement (e.g., cyclic voltammetry). Finally, a batch-mode CDI experiment will be carried out to determine the arsenic removal efficiency using the CoOx/AC composite electrode. Herein, As(V) with negative charge can be directly removed by the anode via electrosorption process at 1.2 V. While, the removal of As(III) involved in the oxidation of As(III) to As(V) and subsequent electrosorption of the As(V) onto the electrode surface of the anode. It is expected that the modified CoOx/AC composite electrode could significantly enhance the removal efficiency of As(III) through the electrocatalytic oxidation of As(III) species. In the present work, the CoOx/AC composite electrode modified by the electrodeposition method of cobalt oxide using cyclic voltammetry has been achieved. The physicochemical properties of the fabricated CoOx/AC composite electrode were characterized in detail. The SEM analysis of CoOx/AC composites demonstrates that CoOx nanoparticles uniformly exists on the surface of AC. The SEM images further support that the contents of electrodeposited CoOx films in the nucleation and growth process during the electrodeposition. The surface morphology, composition and chemical state of the CoOx/AC composite electrode show that the CoOx was successfully deposited on the surface of the AC matrix and existed as a mixed oxidation state of Co(II) and Co(III). The deposition of CoOx on the AC electrode enhance the proportion of mesoporosity which facilitates ion transport. The electrochemical properties were investigated by electrochemical impedance, galvanostatic, and cyclic voltammetry experiments. Especially, no significant difference in the specific capacitance and iR drop between the AC and CoOx/AC composite can be observed under the same conditions. Notably, the CoOx/AC composite electrode has the superior electrochemical performance with excellent cyclic stability and reversibility after 1000 cycles. This result proves that the introduction of CoOx has less influence on the internal resistance for ion diffusion and storage into the pore network of AC. Furthermore, the electrocatalysis/electrosorption performance of As removal was investigated using batch-mode CDI experiments at a working voltage of 1.2 V in a 50 mg L−1 As(III) or As(V) solution. The electrosorption capacity was 4.77 mg g−1 for 50 mg L−1 As(III), which is approximately 3-fold higher than that of the AC electrode (1.6 mg g−1). The conversion efficiency was 60.5% for the As(III) to As(V), and the removal efficiency of As is higher than that of the AC electrode. The obtained results verified that the CoOx/AC composite electrode has better electrocatalytic activity and electrosorption capacity, which provide useful information for the removal of arsenic by CDI technique in practical applications.