[[alternative]]Application of nano manganese/graphene composite for capacitive deionization (CDI)

碩士[[abstract]] 因人口增加、經濟發展與氣候變遷等因素，造成全球水資源匱乏。地球水資源中，海水佔97%，因此，海水淡化技術成為近年來各國重點開發之技術。電容去離子技術 (capacitive deionization, CDI) 是一種利用電吸附程序去除水中離子的電化學水處理技術，CDI具低成本、低能耗、無二次污染等優點，可應用於去除水中之鹽分。CDI 基本原理是將兩電極間施加電場，使帶電荷之離子吸附於相反電荷之電極表面，形成電雙層，藉以達到去除水子離子之目的。本研究目的為開發新穎電極材料，以應用於電容去離子技術。 電極材料為CDI系統之核心，比電容、導電性、比表面積及濕潤性等，都是良好電極材料之關鍵因素；石墨烯(graphene (rGO))為近年來倍受矚目之導電材料，因其具有高的比表面積、良好導電性及良好的化學惰性，所以適合應用於 CDI 系統。本研究中以X-ray繞射分析、掃描式電子顯微鏡、穿透式電子顯微鏡、比表面積分析儀(BET)、接觸角量測及電化學分析(循環伏安法、計時電位、計時電流、電極阻抗)等方法，探討電極材料表面特徵及電化學特性。 使用改良式Hummer法製備氧化石墨烯(graphene oxide (GO))，並以還原劑Dithionite進行還原GO生成rGO。並添加環境友善之錳金屬，使用Ex-situ、In-situ、Mn@C核殼材料三種方法改質石墨烯；Ex-situ法為使用已還原好之石墨烯加入奈米錳金屬，製成Mn/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，利用錳還原氧化石墨烯還原，錳同步被氧化為奈米錳並複合為Mn/rGO複合材料；此外，添加Mn@C核殼顆粒形成Mn@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178.23 F/g、179.64 F/g、107.33 F/g，而比電容的增加主要是因為錳金屬的法拉第虛擬電容(Faradic pseudocapacitance)所貢獻。 將三種複合材料應用於CDI系統，進行鹹水中NaCl之電吸附研究，使用還原劑Dithionite之石墨烯每克可吸附0.22毫克NaCl，而三種改質(Ex-situ、In-situ、Mn@C)分別為4.12 mg/g、1.54 mg/g、2.86 mg/g，吸附量皆大幅提升，而Ex-situ改質吸附量提升最多。[[abstract]] Because of population growth, economic development and climate change, global water resources are scarce. The oceans contain 97 percent of the Earth''s water, so desalination has become a key technology in recent years. Capacitive Deionization (CDI) is a technique for removing ions from water by electrosorption. The advantages of CDI system include low cost, low energy consumption and without secondary pollution. The basic principle of CDI is that an electric field is applied between two electrodes, so that the charged ions are electro-adsorbed on the electrode with opposite charge. The purpose of this study is to develop a novel electrode material for CDI system. The key factors for an outstanding electrode material are specific capacitance, specific surface, conductivity and wettability. Graphene is one of the most popular carbon based material in recent years. Due to its high specific surface area, great electrical conductivity and good chemical inertness, it is a good candidate for electrode material of CDI system. In this study, X-ray diffraction, scanning electron microscope , transmission electron microscope, surface area analyzer, contact angle analyzer and electrochemical analyzer (cyclic voltammetry, chronopotentiometry, chronoamperometry and electrochemical impedance spectroscopy) to observe the characteristics of electrode material. Graphene oxide (GO) was prepared by modified Hummer''s method, and then reduced by dithionite to produce graphene (rGO). The additions of environmental friendly manganese with graphene were synthesized by ex-situ method, in-situ synthesis and mixing with Mn@C core-shell nanoparticles. Ex-situ method mixed graphene and nano-manganese particles to form Mn/rGO composite.While for in-situ method, the preparation of manganese nanoparticles/graphene composites was conducted with manganese serving as reductant to reduce GO. In the in-situ procedure, manganese is oxidized and GO is reduced to rGO simultaneously. In addition, Mn@C/rGO composites were prepared by the addition of Mn@C core-shell particles to graphene. These three methods significantly enhance the specific capacitance of the electrode from 42.19 F/g (original rGO) to 178.23 F/g (ex-situ), 179.64 F/g (in-situ), and 107.33 F/g (Mn@C), respectively. The increase in specific capacitance is mainly due to the manganese Faradic pseudocapacitance contribution. Applying three kinds of composite materials to CDI system, study on the electroadsorption of NaCl in brackish water. Using of reduced by dithionite to produce graphene electrode presents a electrosorption capacity of 0.22 mg/g NaCl,three methods of MnO2/graphene (Ex-situ, In-situ, Mn@C) composite electrode presents a superior electrosorption capacity respectively 4.12 mg/g, 1.54 mg/g and 2.86 mg/g, the adsorption capacity increased greatly, and the adsorption capacity of Ex-situ was the highest.[[tableofcontents]]目錄 第一章 緒論.......................................................................................... 1 1.1 研究起源......................................................................................... 1 1.2 研究目的......................................................................................... 2 第二章 文獻回顧................................................................................... 3 2.1 海水淡化技術................................................................................. 3 2.1.1 多效蒸發法 (Multiple-effect distillation, MED)............................ 3 2.1.2 多級閃蒸法 (Multi-stage flash, MSF) ......................................... 5 2.1.3 逆滲透 (Reverse osmosis, RO)................................................. .6 2.1.4 電透析 (Electrodialysis, ED)....................................................... 7 2.1.5 電容去離子(Capacitive deionization, CDI).................................. 8 2.2 電容去離子技術(Capacitive Deionization, CDI)............................. 9 2.2.1 電容去離子技術之發展............................................................... 9 2.2.2 電容去離子技術之特色............................................................. 11 2.2.3 電容去離子技術之原理............................................................. 12 2.3 電雙層理論 (Electrical double layer, EDL) ................................ 13 2.4 電容去離子電極材料................................................................... 15 2.4.1 活性碳 (Activated Carbon, AC) .............................................. 15 2.4.2 活性碳纖維(布) (Activated Carbon Fiber(Cloth), ACF、 ACC).................................................................................................. 16 2.4.3 碳氣凝膠(Carbon aerogels) ..................................................... 19 2.4.4 奈米碳管 (Carbon nanotubes, CNTs) ..................................... 22 2.4.5 石墨烯 (Graphene) ................................................................. 24 2.5 電化學性能分析之原理................................................................ 28 2.5.1 循環伏安法(Cyclic Voltammetry, CV) ..................................... 28 2.6 金屬複合材料.............................................................................. 31 第三章 實驗材料與方法.................................................................... 32 3.1 實驗架構..................................................................................... 32 3.2 實驗藥品與設備.......................................................................... 34 3.2.1 實驗藥品.................................................................................. 34 3.2.2 實驗設備.................................................................................. 35 3.3 電極材料之製備.......................................................................... 36 3.3.1 氧化石墨烯製備....................................................................... 36 3.3.2 還原氧化石墨烯的製備........................................................... 38 3.3.3 Ex-situ 錳/石墨烯複合材料之製備 ......................................... 40 3.3.4 In-situ 錳/石墨烯複合材料之製備 .......................................... 42 3.3.5 Mn@C/石墨烯 ....................................................................... 44 3.4 電吸附電極之製作..................................................................... 46 3.5 電極材料儀器分析....................................................................... 46 3.5.1 X-ray Diffraction(XRD) ............................................................. 46 3.5.2 Scanning Electron Microscope(SEM) ...................................... 46 3.5.3 Transmission Electron Microscopy(TEM) ................................ 47 3.5.4 BET 孔徑與表面積分析 .......................................................... 47 3.5.5 Contact angle .......................................................................... 48 3.5.6 Cyclic Voltammetry ................................................................. 48 3.5.7 Chronopotentiometry .............................................................. 50 3.5.8 Chronoamperometry ............................................................... 50 3.5.9 Electrochemical Impedance Spectrum ................................... 50 3.6 電容去離子................................................................................. 51 第四章 結果與討論........................................................................... 53 4.1 Ex-situ 錳/石墨烯複合材料應用於電容去離子 .......................... 53 4.1.1 Ex-situ 錳/石墨烯複合材料表面特性分析 .............................. 53 4.1.2 Ex-situ 錳/石墨烯複合材料電化學分析 ................................. 61 4.1.3 複合材料用於電容去離子技術................................................ 71 4.2 In-situ 錳/石墨烯複合材料應用於電容去離子 .......................... 73 4.2.1 In-situ 錳/石墨烯複合材料表面特性分析 .............................. 73 4.2.2 In-situ 錳/石墨烯複合材料電化學分析 .................................. 82 4.2.3 複合材料用於電容去離子技術............................................... 93 4.3 Mn@C/石墨烯複合材料應用於電容去離子 .............................. 96 4.3.1 Mn@C/石墨烯複合材料表面特性分析 .................................. 96 4.3.2 Mn@C 複合材料電化學分析 .............................................. 101 4.3.3 複合材料用於電容去離子技術.............................................. 112 4.4 奈米錳/石墨烯複合材料之電吸附能力比較 ............................ 115 第五章 結論與建議........................................................................ 116 Reference ..................................................................................... 118 List of Figure Figure 2.1.1.1 Flow of steam from boiler to MED unit.(Sen et al., 2011) … 4 Figure 2.1.2.1 Schematic diagram of the evaporating section of an MSF desalination plant.(Choi, 2016) ................................................................... 5 Figure 2.1.3.1 Mechanism of reverse osmosis.(Gasmi et al., 2010) .......... 6 Figure 2.1.4.1 The schematic setup of ED stack.(Khan et al., 2017).......... 7 Figure 2.2.1.1 Timeline of developments of CDI (Porada et al., 2013)..... 10 Figure 2.2.3.1 Purification (a) and regeneration (b) processes in CDI (AlMarzooqi et al., 2014) ........................................................................... 12 Figure 2.2.3.1 (a) Helmholtz(b) Gouy and Chapman electric double layer mode.(C.H.Hamann, 1998) ....................................................................... 14 Figure 2.2.3.2 Stern electric double layer mode.(C.H.Hamann, 1998) ..... 14 Figure 2.4.2.1 SEM images of activated carbon cloth (a). Pore structures of non-treated carbon fiber (b), chemically modified carbon fiber in KOH (c), and HNO3 (d) solutions(Oh et al., 2006). ........................................... 17 Figure 2.4.2.2 Comparison of simulated isotherms with experimental data in the adsorption of NaCl on the ACC and Ti-ACC electrodes at 25 °C. Under an applied electric potential of 1.0 V.(Ryoo & Seo, 2003) ............ 18 Figure 2.4.2.3 Total surface area available on ZnO nanorods coated glass substrates over different precursor concentrations during hydrothermal process(Myint & Dutta, 2012). ................................................................ 18 Figure 2.4.3.1 Electrical conductivity of CSA and CA. The inset in the figure shows the variation of specific capacitance with respect to scan rate(Zuo et al., 2015). ............................................................................. 20 Figure 2.4.3.2 Cyclic voltammograms of (a) pyrolised and (b) activated carbon aerogels obtained recorded at 0.5 mV/s in the 0.1 M NaCl solution(Zafra et al., 2014). ..................................................................... 21 Figure 2.4.4.1 Electrochemical performance of different electrode materials tested in a two-electrode system in an aerobic 1 M Na2SO4 aqueous solution. CV curves of MnO2-CNT (6 h), pristine CNTs and MnO2 nanowires with a scan rate of 5 mVs-1 (Huang et al., 2015). ................ 23 Figure 2.4.5.1 C–V profiles of Gr/SnO2 15% at different scan rates and 1 M NaCl concentration(El-Deen et al., 2014). ............................................ 26 Figure 2.4.5.2 Cyclic voltammetry(Trinh et al., 2016) ........................... 26 Figure 2.4.5.3 CV curves of the MnO2-NRs@graphene electrodes at various scan rates(El-Deen et al., 2014). .......................................................... 27 Figure 2.5.1.1 Cyclic voltammetry circuit layout(Douglas A. Skoog 2007) ............................................................................................................... 29 Figure 2.5.1.2 Cyclic Voltammetry(Douglas A. Skoog 2007) ................ 30 Figure 2.5.1.3 Cyclic Voltammetry(Crow, 1994) ................................... 30 Figure 3.1.1 Schematic experimental structure for CDI system. .......... 33 Figure 3.3.1.1 Overall experimental flow chart for the fabrication of graphene oxide. .................................................................................... 37 Figure 3.3.2.1 Overall experimental flow chart for the fabrication of reduced graphene oxide. ...................................................................... 39 Figure 3.3.3.1 Experimental flow chart for the fabrication of ex-situ Mn/rGO. ............................................................................................... 41 Figure 3.3.4.1 Experimental flow chart for the fabrication of in-situ Mn/rGO. ............................................................................................... 43 Figure 3.3.5.1 Overall experimental flow chart for the fabrication of Mn@C/graphene.(Cai et al., 2014) ...................................................... 45 Figure 3.5.6.1 Schematic of the cyclic voltammetry test setup(Ji, Xu, Zhao, & Dai, 2014) ........................................................................................ 49 Figure 3.5.6.2 Cyclic voltanmmogram of an ideal capacitance. .......... 49 Figure 3.6.1 Schematic for the electrosorption experiment ................. 52 Figure 4.1.1.1 XRD patterns of the (a) graphene, (b) Mn：rGO (1：1), (c) Mn：rGO (1：1.5), and (d) Mn：rGO (1：2). ..................................... 55 Figure 4.1.1.2 FE-SEM images of the (a, b) graphene, (c, d, e) Mn：rGO (1：1.5) (f) EDS of the Mn：rGO (1：1.5). ......................................... 56 Figure 4.1.1.3 TEM images of the (a, b) graphene, (c, d) Mn：rGO (1： 1.5), (e) selected area electron diffraction (SAED) pattern of Mn：rGO (1：1.5), and (f) EDS of the Mn：rGO (1：1.5). ................................. 57 Figure 4.1.1.4 Pore volume distribution for (a) rGO, (b) Mn：rGO (1：1.5). ............................................................................................................ 58 Figure 4.1.1.5 Contact angle images of the (a) graphene, (b) Mn：rGO (1： 1), (c) Mn：rGO (1：1.5), and (d) Mn：rGO (1：2). ......................... 60 Figure 4.1.2.1 Cyclic voltammograms of (a) graphene, (b) Mn：rGO (1： 1), (c) Mn：rGO (1：1.5), and (d)Mn：rGO (1：2). ......................... 62 Figure 4.1.2.2 Cyclic voltammograms of the graphene, Mn：rGO (1：1), Mn：rGO (1：1.5), and Mn：rGO (1：2) at scan rate of 50 mV/s. . 63 Figure 4.1.2.3 Mass normalized specific capacitance of graphene and Mn/rGO with respect to the scan rates. ........................................... 64 Figure 4.1.2.4 Charge-discharge curves of (a) graphene, (b) Mn：rGO (1： 1), (c) Mn：rGO (1：1.5), and (e)Mn：rGO (1：2) under differentcurrent densities. ......................................................................................... 67 Figure 4.1.2.5 Charge-discharge curves for the graphene, Mn：rGO (1：1), Mn：rGO (1：1.5), and Mn：rGO (1：2) at current density of 1 A/g. ......................................................................................................... 68 Figure 4.1.2.6 The current-time response obtained at applied cyclic potential on graphene, Mn：rGO (1：1), Mn：rGO (1：1.5), and Mn：rGO (1：2). ............................................................................................. 69 Figure 4.1.2.7 The electrochemical impedance spectra (EIS) measured at frequency range of 100 kHz to 0.01 Hz for graphene, Mn：rGO (1： 1), Mn：rGO (1：1.5), Mn：rGO (1：2) electrode, respectively. ... 70 Figure 4.1.3.1 Representative desalination performance of the rGO and Mn / rGO(1:1.5) electrodes in 250 ppm NaCl with an applied voltage of 1.0 V. . 72 Figure 4.1.3.2 Electrosorption/desorption profiles of the Mn / rGO(1:1.5) composite electrode in 250 ppm NaCl (1.0 V). . ......................................................................................... 72 Figure 4.2.1.1 XRD patterns of the (a) graphene oxide (GO), (b) graphene generated by dithionite reduction, (c) Mn：GO (1：1), (d) Mn：GO (1：2), (e) Mn：GO (1：3). ............................................................. 76 Figure 4.2.1.2 FESEM images of the (a) graphene generated by dithionite reduction, (b, c) Mn：GO(1：2) (d) EDS of the Mn：GO (1：2)..... 77 Figure 4.2.1.3 TEM images of the (a, b) graphene generated by dithionite reduction, (c, d) Mn：GO (1：2), (e) Nano beam electron diffraction (NBED) of Mn：GO (1：2), (f) EDS of the Mn：GO (1：2). .......... 78 Figure 4.2.1.4 Pore volume distribution for (a) rGO, (b) Mn：GO (1：2). 79 Figure 4.2.1.5 Contact angle images of the (a) graphene generated by dithionite reduction, (b) Mn：GO (1：1), (c) Mn：GO (1：2) (e)Mn：GO (1：3). ............................................................................. 81 Figure 4.2.2.1 Cyclic voltammograms for the (a) graphene, (b) Mn：GO (1：1), (c) Mn：GO (1：2), (e) Mn：GO (1：3) at various scan rates. .............................................................................................................. 84 Figure 4.2.2.2 Cyclic voltammograms of graphene, Mn：GO (1：1), Mn： GO (1：2), and Mn：GO (1：3) at scan rate of 50 mV/s. ................. 85 Figure 4.2.2.3 Mass normalized specific capacitance of graphene and Mn/rGO composites with respect to the scan rates. ............................. 86 Figure 4.2.2.4 Charge-discharge curves of (a) graphene, (b) Mn：GO (1： 1), (c) Mn：GO(1：2), and (d) Mn：GO(1：3). ............................... 89 Figure 4.2.2.5 Charge-discharge curves of graphene or Mn/rGO composites at current density of 1 A/g. ................................................................... 90 Figure 4.2.2.6 The current-time response obtained at applied cyclic potential on graphene and Mn/rGO composites. ................................................ 91 Figure 4.2.2.7 The electrochemical impedance spectra (EIS) measured at frequency range of 100 kHz to 0.01 Hz for the obtained electrodes： graphene, Mn：GO(1：1), Mn：GO (1：2), and Mn：GO (1：3) electrode, respectively. ......................................................................... 92 Figure 4.2.3.1 Representative desalination performance of the rGO and Mn / GO electrodes in 250 ppm NaCl with an applied voltage of 1.0 V. ... 95 Figure 4.2.3.2 Electrosorption-desorption cycles of the Mn / GO composite electrode in 250 ppm NaCl (1.0 V).The change in solution conductivity. ......................................................................................... 95 Figure 4.3.1.1 XRD patterns of the (a) graphene oxide (GO), (b) graphene (rGO) generated by dithionite reduction, (c) Mn@C：rGO (1：5), (d) Mn@C：rGO (1：10), (e) Mn@C：rGO (1：50). .............................. 98 Figure 4.3.1.2 FESEM images of the (a) graphene generated by dithionite reduction, (b, c, and d) Mn@C：rGO (1：5)...................................... 99 Figure 4.3.1.3 Contact angle images of the (a) graphene generated by dithionite reduction, (b) Mn@C：rGO (1：1), (c) Mn@C：rGO (1： 5), (d) Mn@C：rGO (1：50). ........................................................... 100 Figure 4.3.2.1 Cyclic voltammograms for the (a) graphene, (b) Mn@C： rGO (1：5), (c) Mn@C：rGO (1：10), and (d)Mn@C：rGO (1：50). ............................................................................................................ 103 Figure 4.3.2.2 Cyclic voltammograms for the graphene, Mn@C：rGO (1： 5), Mn@C：rGO(1：10, Mn@C：rGO(1：50). ............................. 104 Figure 4.3.2.3 Capacitance retention of Mn@C/graphene in the potential range of 0~0.8 V at the scan rate of 1, 5,10, 50, 100 mV/s. ........................ 105 Figure 4.3.2.4 Charge-discharge curves of the (a) graphene, (b) Mn@C： rGO (1：5), (c) Mn@C：rGO (1：10), and (e)Mn@C：rGO (1：50) under different current densities. ....................................................... 108 Figure 4.3.2.5 Charge-discharge curves for the graphene, Mn@C：rGO (1：5), Mn@C：rGO (1：10), and Mn@C：rGO (1：50) at current density of 1 A/g. ................................................................................. 109 Figure 4.3.2.6 The current-time response obtained at applied cyclic potential on the surface of graphene, Mn@C：rGO (1：5), Mn@C：rGO (1： 10), and Mn@C：rGO (1：50). ........................................................ 110 Figure 4.3.2.7 The electrochemical impedance spectra (EIS) measured at frequency range of 100 kHz to 0.01 Hz for graphene, Mn@C：rGO (1：5), Mn@C：rGO (1：10), Mn@C：rGO (1：50) electrode, respectively. ....................................................................................... 111 Figure 4.3.3.1 Representative desalination performance of the rGO and Mn@C/rGO electrodes in 250 ppm NaCl with an applied voltage of 1.0 V. .................................................................................................. 114 Figure 4.3.3.2 Electrosorption-desorption cycles of the Mn@C/rGO composite electrode in 250 ppm NaCl (1.0 V). ....................................................................................... 114 List of Table Table 2.4.3.1 BET surface area and pore volume values derived from the nitrogen isotherms measured for the doped and non-doped aerogel samples(Zafra et al., 2014). .................................................................. 20 Table 3.2.1.1 Manufactures and purity of experimental medicines. ...... 34