以非均質陰離子交換層塗佈之碳電極提升薄膜電容去離子技術之磷酸去除率

Abstract

電容去離子(Capacitive deionization, CDI)為一新穎的電化學技術，能夠藉由電場的作用分離水中帶電荷之物質與離子，達到去除鹽類或是污染物質的目的。近年來，離子交換材料(Ion exchange materials)廣泛應用於電容去離子技術，成為薄膜電容去離子(Membrane capacitive deionization, MCDI)系統來提升電容去離子技術的脫鹽效率，已有許多研究致力於開發具有高效能、低成本及環境友善性的離子交換複合式電極。在本研究中，運用簡易且快速的方法製成非均質陰離子交換碳電極(heterogeneous anion-exchange carbon electrode, AE-AC)，使得電極具有陰離子交換膜的特性以及活性碳的多孔性，來提升脫鹽過程當中的磷酸離子選擇性與吸附量。電極特性分析分為表面分析及電化學特性分析兩部分，其中表面特性藉由如掃描式電子顯微鏡(SEM)、X射線光電子能譜(XPS)等方式來分析其物理及化學性質；電化學分析實驗如循環伏安法(CV)，分析測試電極之電容特性與充放電表現，而結果顯示，活性碳電極經塗佈陰離子交換層後，一樣具有出色的電容表現。在批次式薄膜電容去離子系統之脫鹽實驗部分，將陰離子交換碳電極(AE-AC)作為陽極，能有效提升磷酸的電吸附量達0.0716 mmol/g-carbon。研究之實驗參數包含：離子電吸附電壓、離子脫附之反向電壓、溶液pH值影響以及磷酸根離子與氯離子之競爭性。經由不同電壓測試脫鹽效果，可得知薄膜電容去離子系統之最佳吸附及脫附電壓；而pH與競爭性實驗則是使用不同進流水樣，探討磷酸根物種個別的吸附量以及磷酸根離子受氯離子的影響程度。最後，在連續式薄膜電容去離子實驗中，運用非均質陰離子交換碳電極之磷酸電吸附量可達0.1235 mmol/g-carbon，約為活性碳電極的3.5倍。此結果顯示，非均質陰離子交換層塗佈於碳電極後，相當具有應用於薄膜電容去離子技術去除/分離水中磷酸鹽之潛力。

Capacitive deionization (CDI) has been developed as a promising electrochemical technology for removing ionic species. Recently, ion-exchange based materials have been widely introduced into the CDI, constituting a membrane capacitive deionization (MCDI) system to further enhance the ion removal efficiency. Many researchers have developed the high exchange capacity, low cost and environmental friendly ion-exchange electrodes. In this study, the heterogeneous anion-exchange composite electrodes were prepared to increase the phosphate removal from water. The heterogeneous anion-exchange carbon electrode (AE-AC) was integrated with anion-exchange resin (AE) and activated carbon (AC) via a facile approach. The surface analyses were implemented to characterize the physical and chemical behaviors of the electrodes, such as scanning electron microscope and X-ray photoelectron spectroscopy. Besides, as resulted by electrochemical measurements (e.g., cyclic voltammetry), the carbon electrode coated with anion-exchange layer has good capacitive properties for ion storage. The batch-mode desalination performance of MCDI using the AE-AC electrode as anode material showed superior phosphate electrosorption capacity of 0.0716 mmol/g-carbon. The optimal charging and discharging potentials were determined by the electrosorption-desorption cycling experiments. The effects of pH and competition with other ions on phosphate removal were also tested. Importantly, the phosphate electrosorption capacity of AE-AC electrode in the single-pass CDI experiment is 0.1235 mmol/g-carbon, which is about 3.5 times more than that of the activated carbon electrode. One can conclude that the heterogeneous anion-exchange layer coated carbon electrode has the great potential for enhanced phosphate removal in MCDI process.