電容去離子對陰離子之選擇性研究

The Selectivity of Anions in Capacitive Deionization (CDI)

郝康旭(Kang-Syu Hao)

指導教授 ： 彭晴玉

淡江大學/工學院/水資源及環境工程學系碩士班/碩士(2020年)

https://doi.org/10.6846/TKU.2020.00922

摘要

電容去離子(Capacitive Deionization, CDI)是深具潛力的低能耗脫鹽技術，透過在兩個電極之間施加電壓從水溶液中去除離子。當溶液中存在多種離子時，CDI系統對每種離子的去除率不同，即CDI系統對離子之電吸附選擇性不同。本研究，利用三種電極材料：粒狀活性碳(GAC)、石墨烯/粒狀活性碳(rGO/GAC)和聚苯胺/粒狀活性碳(PANI/GAC)應用於CDI系統中，探討四種環境中常見陰離子(Cl-、NO3-、SO42-、H2PO4-)之電吸附情形。
研究發現離子價數顯著影響電吸附選擇性，離子價數越高，離子被CDI系統電吸附效果越好。在具有相同離子價的離子混合時，則是以水合比(hydration ratio即水合半徑與離子半徑的比)顯著影響電吸附選擇性，低水合比的離子表現出較高的電吸附選擇性，但研究中也發現磷酸不符合上述的規則。此外，初始濃度較高之離子，在電吸附初期，離子被電吸附的效率較高。
比較三種電極材料應用於CDI系統去除四種陰離子之吸附當量時，吸附當量由高至低的順序為SO42- > NO3- > Cl- > H2PO4-，符合離子價數高者電吸附效果較好(二價優於一價)，且水合比低者電吸附效果較好(水合比NO3- : 1.87、Cl- :1.99 )，但H2PO4-並不符合水合比原則，且在三種電極材料系統中電吸附表現皆為最差。
PANI/GAC複合材料，提高原GAC的比電容值(96.33 F/g)，且將中孔比率提升至91.74%，組成非對稱電容去離子系統後，針對SO42-和Cl-有較優異的電吸附表現，但對NO3-和H2PO4-去除效果不好，表示PANI/GAC複合材料對不同陰離子之電吸附選擇性。

關鍵字

電容去離子 ； 陰離子 ； 石墨烯 ； 聚苯胺 ； 電吸附選擇性 ； 水合比

並列摘要

Capacitive deionization (CDI) is an emerging low-energy desalination technology that removes ions from aqueous solutions by applying a voltage between two electrodes. When there are multiple ions in the solution, the removal efficiency of each ion by the CDI system is different, that is, the electrosorption selectivity of the CDI system for ions is different. In this study, three electrode materials employed: granular activated carbon (GAC), graphene/granular activated carbon (rGO/GAC) and polyaniline/granular activated carbon (PANI/GAC) were applied to CDI systems to explore the electrosorption of common anions (such as Cl-, NO3-, SO42-, H2PO4-) in the environment.
This study found that the ionic valence significantly affects the electrosorption selectivity. The higher the ionic valence, the better the ion electrosorption effect of the CDI system. When ions with the same ionic valence are mixed, the hydration ratio has significant impact on the electrosorption selectivity. Ions with low hydration ratios exhibit a higher electrosorption selectivity, but our study also found that phosphoric acid does not meet the above mentioned rules. In addition, the higher the initial concentration of ions, the higher the removal efficiency of the ion in the early stage of electrosorption.
In comparison of three electrode materials employed in CDI systems to remove four anions, the order of electrosorption equivalent from high to low is SO42- > NO3- > Cl- > H2PO4-. Divalent ion has better performance than that of monovalent ion, and those with lower hydration ratio have better electrosorption effect (hydration ratio NO3-: 1.87, Cl-: 1.99). However, H2PO4- does not agree with the principle of hydration ratio, and the electrosorption performance of H2PO4- is the worst among four anions.
Addition of PANI to GAC can improve the specific capacitance of the original GAC (96.33 F/g), and increase the mesopore ratio to 91.74%. An asymmetric PANI/GAC//GAC CDI system showed that it had excellent electrosorption performance for SO42- and Cl, but the removal efficiency of NO3- and H2PO4- was not good, indicating the electrosorption selectivity of PANI/GAC composites to different anions.

並列關鍵字

Capacitive Deionization ； Anion ； Graphene ； Ployaniline ； Electrosorption selectivity ； Hydration ratio

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