水資源匱乏問題日益受到世界各地關注，由於海水蘊藏量豐富，因此海水淡化技術的開發逐漸受到重視。電容去離子 (capacitive deionization, CDI)是新穎的海水淡化技術，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，具有操作及維護簡便、無二次性污染、低能耗以及可逆性等優勢。電極材料是影響CDI性能的最主要因素之一，因此本研究著重於電極材料特性之探討。
本研究所使用的電極材料為石墨烯(graphene, rGO)，石墨烯擁有極佳的電導率及電化學穩定性，故非常適合應用於電容去離子。但由於石墨烯屬於略為疏水的材質，較不利於水處理程序，因此本研究主要是利用強酸與強鹼改善石墨烯之親疏水性問題。
以混合酸HNO3:H2SO4= 2:1處理石墨烯電極後，其接觸角由78.09°下降至19.45°，親水性明顯提升；同時，其比電容亦從原本的39.06 F/g，提升至145.81 F/g，約為3.73倍。以強鹼改質部分，以KOH改質後之石墨烯，接觸角由78.09°下降至21.97°，由於親水性的提升，比電容亦從原本的39.06 F/g上升至56.83 F/g，約為1.46倍；兩種處理方法相較，以酸處理之整體效應優於鹼處理的方式，其中又以HNO3:H2SO4= 2:1比例處理的石墨烯，於電容去離子技術之應用深具潛力。

The shortage of potable water has become one of the major issues nowadays. In order to relieve this condition, desalination technologies has become more important. Capacitive deionization (CDI) is a novel technology for desalination, which is an electrosorption process. It works by attracting salt ions to the surface of electrodes where ions are held in electrical double layers (EDLs) when the electrodes are charged, then releases the ions when potential is removed. There are several advantages of CDI system, including easy to install and maintain, no secondary pollution, energy efficiency and easy to regenerate. 
The electrode material is the most important factor to affect CDI performance, so this study focuses on the characteristics of electrode materials. In this study, we use graphene (rGO) for the electrode. Graphene is a carbon material with unique mechanic and electronic properties, which is very suitable for the electrode for CDI system. We use strong acid or strong base to improve the wettability of graphene to enhance the CDI performance.
When graphene was treated with mixed acid HNO3: H2SO4 = 2: 1 (volume ratio), the contact angle decreased from 78.09° to 19.45°, which indicating the wettability was improved. The specific capacitance was also increased around 3.73 times from 39.06 F/g to 145.81 F/g. 
After graphene was modified by KOH, the contact angle of graphene decreased from 78.09° to 21.97°, and the specific capacitance increased around 1.46 times from 39.06 F/g to 56.83 F/g. 
Comparison between these two treatment processes, acid modification is much better than strong base treatment. With acid treatment, the graphene treated by HNO3: H2SO4 = 2: 1 is the most suitable for CDI system.

目錄
第一章	緒論	1
1.1	研究緣起	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(Multi-effect Distillation, MED)	5
2.1.2	多級閃化法(Multi-Stage Flash, MSF)	7
2.1.3	逆滲透(Reverse Osmosis, RO)	9
2.1.4	電透析(Electrodialysis, ED)	9
2.1.5	電容去離子法(Capacitive Deionization, CDI)	10
2.2	電容去離子技術	11
2.2.1	電容去離子簡介	11
2.2.2	電容去離子之原理	11
2.2.3	電容去離子與其他技術之成本比較	15
2.3	電容去離子之電極種類	18
2.3.1	活性碳(Activated Carbons)	18
2.3.2	碳氣凝膠(Carbon Aerogel)	19
2.3.3	奈米碳管(Carbon Nanotubes)	20
2.3.4	石墨烯(Graphene)	22
2.4	碳材之改質	25
2.4.1	以強酸改質碳材	25
2.4.2	以強鹼改質碳材	32
2.5	非對稱電容去離子技術(Asymmetric CDI)	35

第三章	材料與方法	39
3.1	實驗架構	39
3.2	實驗藥品與設備	41
3.2.1	實驗藥品	41
3.2.2	實驗設備	42
3.3	電極材料之製作	43
3.3.1	氧化石墨烯(Graphene oxide, GO)之製作	43
3.3.2	石墨烯 (Reduced Graphene Oxide, rGO)之製備	45
3.3.3	強酸改質石墨烯	46
3.3.4	強鹼改質石墨烯	48
3.4	實驗分析方法	49
3.4.1	X射線繞射分析(X-ray Diffraction, XRD)	49
3.4.2	掃描式電子顯微鏡分析(SEM)	49
3.4.3	穿透式電子顯微鏡分析(TEM)	49
3.4.4	接觸角測定實驗(Contact angle)	50
3.4.5	傅立葉轉換紅外線光譜儀(FT-IR)	50
3.4.6	循環伏安法(cyclic voltammetry, CV)	51
3.4.7	計時電位法(Chronopotentiometry, CP)	51
3.4.8	計時電流法 (Chronoamperometry, CA)	51
3.4.9	電化學組抗譜分析(EIS)	53
3.5	電容去離子技術(Capacitive deionization, CDI)	53
3.5.1	電容去離子系統(CDI system)	53
3.5.2	非對稱電容去離子系統(Asymmetric CDI system)	53
第四章	結果與討論	55
4.1	以強酸改質之石墨烯電極進行電容去離子脫鹽之研究	55
4.1.1	以強酸改質之石墨烯電極表面特性之分析	55
4.1.2	以強酸改質之石墨烯電化學分析	64
4.1.3	以強酸改質之石墨烯電極應用於電容去離子技術	75
4.2	以強鹼改質之石墨烯電極進行電容去離子脫鹽之研究	78
4.2.1	以強鹼改質之石墨烯電極表面特性之分析	78
4.2.2	以強鹼改質之石墨烯電化學實驗之分析	87
4.2.3	以強鹼改質之石墨烯電極應用於電容去離子技術	95
4.3	以非對稱電極應用於電容去離子技術	98
4.4	不同改質電極材料之電容去離子效率比較	101
第五章	結論與建議	102
Reference	104

 
List of Figure
Figure 2.1.1 Global desalination technologies share by capacity.	4
Figure 2.1.1.1 Schematic diagram of the MED plant at PSA.	6
Figure 2.1.2.1 Schematic diagram of a MSF plant with feed mixing and cooling.	8
Figure 2.2.2.1 Purification (a) and regeneration (b) processes in CDI	13
Figure 2.2.2.2 The double layer model of H. Helmholtz and J. Parrin	14
Figure 2.2.3.1 Worldwide water resources per capita and level of rainfall as a function of continent.	16
Figure 2.3.3.1 SEM image of AC electrode.	21
Figure 2.3.3.2 Structural models of a SWCNT and an MWCNT.	21
Figure 2.3.4.1 SEM images of PG (a, b) and NG (c, d) at low and high magnification.	23
Figure 2.3.4.2 Typical CV curves of (a) PG and (b) NG at different scan rates in 1 M NaCl aqueous solution.	23
Figure 2.4.1.1 FTIR spectra of the original and the modified ACs.	26
Figure 2.4.1.2 Electrosorption/desorption profiles of the original and the modified AC electrodes.	28
Figure 2.4.1.3 FTIR spectra of the original and the modified ACs.	28
Figure 2.4.1.4 CV curves of FAC at various scan rates..	30
Figure 2.4.1.5 Ｍass normalized specific capacitance of AC and FAC with respect to the scan rates.	30
Figure 2.4.1.6 Conductivity transients of AC and FAC at 1.2 V in NaCl solution with an initial conductivity of 50 µS cm-1.	31
Figure 2.4.1.7 The regeneration of FAC electrode in NaCl solution with initial conductivity of 100µS cm-1.	31
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.	33
Figure 2.4.2.2 The kinetic constants for CDI process at about 1.3 V.	33
Figure 2.4.2.3 C1s XPS spectra of non-treated carbon cloth (a), chemically modified carbon cloth in 1 M KOH (b), and 1 M HNO3 solution (c).	34
Figure 2.4.2.4 Cyclic voltammogram for activated nano-porous carbon cloths in 0.5 M NaCl at 5 mV/s.	34
Figure 2.5.1 Normalized differential capacitance curves of ACF and ACF-HNO3.	37
Figure 2.5.2 CDI performance of (a) 0-CDI and (b) N-CDI at different voltages.	37
Figure 2.5.3 The change in sodium ion concentrations in three consecutive electrosorption/ regeneration cycles by symmetric and asymmetric electrode materials in continuous flowing solutions.	38
Figure 3.1.1 Schematic experimental structure for CDI system.	40
Figure 3.3.1.1 Graphene oxide (GO) preparation procedure.	44
Figure 3.3.2.1 Graphene (rGO) preparation procedure.	45
Figure 3.3.3.1 Strong acid treated graphene preparation procedure.	47
Figure 3.3.4.1 Strong base treated graphene preparation procedure.	48
Figure 3.4.8.1 Charge- discharge curve of applied potential from -0.4 V to 0.8 V.	52
Figure 3.5.2.1 Schematic diagram of the CDI setup.	54
Figure 4.1.1.1 XRD patterns of (a) graphene oxide, (b) graphene and (c) nitric acid-treated graphene.	56
Figure 4.1.1.2 SEM images of (a, b) pristine graphene and (c, d) acid treated (HNO3:H2SO4 = 2:1) graphene.	57
Figure 4.1.1.3 TEM images of (a) pristine graphene and (b) acid treated (HNO3:H2SO4 = 2:1) graphene.	59
Figure 4.1.1.4 Optical micrographs of the water contact angles on the surface of (a) pristine graphene and (b) acid treated (HNO3:H2SO4 = 2:1) graphene.	60
Figure 4.1.1.5 The FT-IR spectra of (a) rGO, (b) rGO-HNO3 (c) rGO-2:1 (d) rGO-1:1 (e) rGO-1:2 and (f) rGO-H2SO4.	62
Figure 4.1.2.1 Cyclic voltammograms of (a) graphene, (b) HNO3, (c) 2:1, (d) 1:1, (e) 1:2 and (f) H2SO4 at various scan rates.	65
Figure 4.1.2.2 Cyclic voltammograms of graphene and acid-treated graphene at scan rate of 50 mV/s.	66
Figure 4.1.2.3 Mass normalized specific capacitance of graphene and acid-treated graphene with respect to the scan rates.	68
Figure 4.1.2.4 Charge-discharge curves of (a) graphene, acid- treated graphene with (b) HNO3, (c) 2:1, (d) 1:1, (e) 1:2 and (f) H2SO4.	70
Figure 4.1.2.5 Charge-discharge curves of graphene or acid-treated graphene at current density of 1 A/g.	71
Figure 4.1.2.6 The current-time response obtained at applied cyclic potential on graphene and acid-treated graphene.	73
Figure 4.1.2.7 The electrochemical impedance spectra (EIS) measured at frequency range of 100 kHz to 0.01 Hz for original, HNO3, 2:1, 1:1, 1:2, H2SO4 modified graphene electrode, respectively.	74
Figure 4.1.3.1 Conductivity transients of rGO and 2:1 acid treated rGO at 1.0 V in 50 ppm NaCl solution.	76
Figure 4.1.3.2 Electrosorption/desorption profiles of the 2:1 acid treated rGO electrode in 50 ppm NaCl solution.	77
Figure 4.2.1.1 XRD patterns of (a) pristine graphene and (b) KOH-treated graphene.	79
Figure 4.2.1.2 SEM images of (a, b) pristine graphene and (c, d) KOH-treated graphene.	80
Figure 4.2.1.3 TEM images of (a) pristine graphene and (b) KOH-treated graphene.	82
Figure 4.2.1.4 Optical micrographs of the water contact angles on the surface of (a) pristine graphene and (b) KOH-treated graphene.	83
Figure 4.2.1.5 FT-IR of (a) pristine, (b) KOH and (c) NaOH treated graphene.	85
Figure 4.2.2.1 Cyclic voltammograms of (a) graphene, (b) KOH, (c) NaOH, and (d) CV of graphene and graphene modified by different strong bases at scan rate of 50 mV/s.	88
Figure 4.2.2.2 Mass normalized specific capacitance of graphene and base-treated graphene with respect to the scan rates.	89
Figure 4.2.2.3 CP of (a) graphene, (b) KOH, (c) NaOH and (d) CP of graphene at current density of 1 A/g.	91
Figure 4.2.2.4 The current-time response obtained at applied cyclic potential on graphene and base-treated graphenes.	93
Figure 4.2.2.5 The electrochemical impedance spectra (EIS) measured at frequency range of 100 kHz to 0.01 Hz for original, KOH and NaOH treated graphene, respectively.	94
Figure 4.2.3.1 Conductivity transients of rGO and KOH treated rGO at 1.0 V in 50 ppm NaCl solution.	96
Figure 4.2.3.2 Electrosorption/desorption profiles of the KOH treated rGO electrode in 50 ppm NaCl solution.	97
Figure 4.3.1 Conductivity transients of 2:1 and Fe@C treated rGO at 1.0 V in 50 ppm NaCl solution.	99
Figure 4.3.2 Electrosorption/desorption profiles of the 2:1 acid and Fe@C treated rGO electrode in 50 ppm NaCl solution.	100

 
List of Table
Table 2.2.3.1 Approximate ranges of energy demands for various desalination technologies	17
Table 3.2.1.1 Manufacturers and purity of experimental chemicals	41
Table 3.2.2.1 Manufacturers and model of instrument.	42
Table 3.3.3.1 The ratio of strong acid.	47
Table 4.1.1.1 Contact angle of graphene treated by different ratio of strong acid.	60
Table 4.1.1.2 FT-IR wavenumber with corresponding functional groups.	63
Table 4.1.2.1 Mass normalized specific capacitance (F/g) of graphene and acid-treated graphene with respect to the scan rates.	68
Table 4.1.3.1 Removal efficiency and electrosorption capacity of rGO and 2:1 acid treated electrode.	76
Table 4.2.1.1 Contact angle of graphene and graphene treated by strong base	83
Table 4.2.1.2 FT-IR wavenumber with corresponding functional groups.	86
Table 4.2.2.1 Mass normalized specific capacitance (F/g) of graphene and base-treated graphene with respect to the scan rates.	89
Table 4.2.3.1 Removal efficiency and electrosorption capacity of rGO and KOH treated electrode.	96
Table 4.3.1 Removal efficiency and electrosorption capacity of rGO and 2:1 and Fe@C treated electrode.	99
Table 4.4.1 Overview of salt adsorption performance reported for different electrode materials applied for CDI.	101
Table 5.1 Removal efficiency and electrosorption capacity of each electrode.	103

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