奈米鐵/石墨烯複合材料應用於電容去離子技術

隨著氣候變遷及新興與發展中國家的經濟及人口增長，全球水資源風險日益上升，對許多原本就缺乏淡水的國家而言，海水淡化成為重要開發技術，近年來出現一種新穎的海水淡化技術-電容去離子(capacitive deionization, CDI)，是一種利用電吸附程序去除水中離子的技術，相較於其他傳統海水淡化技術，具低成本，低耗能等優勢，其基本原理是在兩電極間施加一電場，使帶電荷之離子吸附於相反電荷之電極表面，藉以達到去除水中離子的目的。　　石墨烯特殊的二維結構於奈米技術領域，被視為具有吸引力之材料之一；鐵奈米顆粒於環境工程已有廣泛應用，若能結合環境友善的鐵與良好導電性之石墨烯，可用以提升電容去離子效率。本研究中鐵奈米顆粒成功摻雜於石墨烯中，利用X-ray繞射儀、掃描式電子顯微鏡、穿透式電子顯微鏡以及接觸角測定儀來觀察複合材料表面特性，並進一步運用電化學儀器測試(循環伏安法、計時電位法、計時電流法以及阻抗分析)分析複合材料之電化學特性。　　氧化石墨烯(graphene oxide (GO))以改良式Hummer’s法製備，選用還原劑Dithionite還原GO生成rGO。研究中添加環境友善之鐵金屬，使用水熱合成法(Ex-situ)、In-situ 原位合成與Fe@C奈米核殼材料三種方法改質石墨烯；水熱合成法(Ex-situ)為使用已還原好之石墨烯加入鐵鹽，並在高溫高壓下製成Fe/rGO複合材料；In-situ法則是使用氧化石墨烯於不添加還原劑情況下，利用亞鐵離子被氧化，而氧化石墨烯同步被還原為石墨烯形成Fe/rGO複合材料；此外，添加Fe@C核殼顆粒形成Fe@C/rGO複合材料，三種方法皆可提升電極之比電容，比電容與未改質的rGO相比，從原始rGO的 42.19 F/g，三種方法在最佳配比狀況下，分別提升至169.3 F/g、141.56 F/g、186.88 F/g，而比電容的增加主要是因為鐵金屬的法拉第虛擬電容(Faradic pseudocapacitance)所貢獻，最後將三種複合材料應用於CDI系統，進行鹹水中NaCl之離子分離研究。

關鍵字

電容去離子；鐵；石墨烯

並列摘要

Due to climate change and population growth in developing countries, the risk of lacking water resource is increasing globally. For many water-scarce countries, seawater desalination has become an important technology. In recent years, there is a novel desalination technology ─ capacitive deionization (CDI), which is a technique for removing ions from water by electrosorption. Compared with other traditional seawater desalination technology, it has advantages of low cost and low energy consumption. The basic principle of CDI is to apply an electric field between two electrodes, so that the charged ions can be adsorbed on the opposite charge of the electrode surface to achieve the removal of water ions. Graphene with unique two-dimensional structure is one of the attractive material in nanotechnology . The iron nanoparticles have been widely used in environmental engineering. If graphene could combine with environmentally benign iron, it will enhance the efficiency of capacitive deionization. In this study, iron nanoparticles were successfully doped within graphene, and the surface characteristics of the composites were observed by X-ray diffraction, Scanning Electron Microscope, Transmission Electron Microscopy and contact angle. The electro-chemical properties of the composites were also analyzed by electrochemical analyzer (Cyclic Voltammetry, Chronopotentiometry, Chronoamperometry and Electrochemical Impedance Spectroscopy). Graphene oxide (GO) was prepared by modified Hummer's method, and reduced by Dithionite to produce graphene (rGO). The additions of environmental friendly iron with graphene were synthesized by hydrothermal method (Ex-situ), In-situ synthesis and mixing with Fe@C core-shell nanoparticles. For hydrothermal synthesis (Ex-situ), graphene and iron salt with high temperature and pressure were synthesized to yieldFe/rGO composite materials; For In-situ method, the preparation of iron nanoparticles/graphene composites was conducted with ferrous serving as reductant to reduce GO. In this in-situ procedure, ferrous is oxidized to ferric and GO is reduced to rGO simultaneously. In addition, the addition of Fe@C core-shell particles to graphene to prepare Fe@C/rGO composites. Three methods with the best ratio can enhance the specific capacitance from 42.19 F/g (original rGO) to 169.3 F/g (ex-situ), 141.56 F/g (in-situ), 174.04 F/g (Fe@C). The increase of specific capacitance is due to the ferrous metal faradic pseudocapacitance contribution. Finally, desalination with three composites in CDI System were compared.

並列關鍵字

Capacitive Deionization(CDI) ； Iron ； Graphene

參考文獻

AlMarzooqi, F. A., Al Ghaferi, A. A., Saadat, I., & Hilal, N.(2014). Application of Capacitive Deionisation in water desalination: A review. Desalination, 342, 3-15.

Bao, Q., Zhang, D., & Qi, P. (2011). Synthesis and characterization of silver nanoparticle and graphene oxide nanosheet composites as a bactericidal agent for water disinfection. Journal of colloid and interface science, 360(2), 463-470.

Cai, P. F., Su, C. J., Chang, W. T., Chang, F. C., Peng, C. Y., Sun, I. W., . . . Wang, H. P. (2014). Capacitive deionization of seawater effected by nano Ag and Ag@C on graphene. Marine pollution bulletin, 85(2), 733-737.

Chaudhari, S. (2013). 1-Dimensional porous α-Fe2O3 nanorods as high performance electrode material for supercapacitors. RSC Advances, 3(47), 25120.

Choi, J.-H. (2010). Fabrication of a carbon electrode using activated carbon powder and application to the capacitive deionization process. Separation and Purification Technology, 70(3), 362-366.

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奈米鐵/石墨烯複合材料應用於電容去離子技術

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