水資源短缺已成為全球關注的議題。電容去離子(CDI)是一種新興的離子去除技術，用於去除水中離子。有機物的存在會阻塞CDI電極並導致CDI效能下降。本研究中，使用三種電極材料：粒狀活性碳電極(GAC)、經硫酸改質的粒狀活性碳(SGAC)、抗阻塞膜/粒狀活性碳電極(PVDF /GAC或PES/GAC)，探討有機物(腐殖酸(HA)或天然有機物(NOM))對CDI系統的影響。
    實驗結果顯示有機物的存在會顯著降低GAC電極的電吸附能力。由於NOM的化學結構比HA更複雜，因此NOM對CDI效能的負面影響更大。在HA或NOM存在的情況下， GAC電極的平均電吸附容量分別從3.88 mg/g降至3.04或2.94 mg/g，分別降低了21.6％或24.2％。
    經過硫酸改質後之粒狀活性碳(SGAC)，SGAC電極的平均電吸附量提高到4.44 mg/g。在HA或NOM存在的情況下，平均電吸附量分別降低至3.62或3.36 mg/g，相當於降低了18.5％或24.3％。
    GAC電極上的抗組塞膜(PVDF或PES)可以減輕有機物阻塞的影響。特別是PVDF/GAC電極，不僅提高了平均電吸附容量，而且抑制了HA或NOM對CDI效能的影響。應用於CDI系統的PVDF/GAC電極的平均電吸附容量為4.83 mg/g。即使溶液中存在HA或NOM，平均電吸附容量仍可以保持在較高的水平(4.55或4.26 mg/g)。研究成果顯示PVDF或PES膜的親水特性可有效防止有機物阻塞。

Water shortage has become a global concern. Capacitive Deionization (CDI) is an emerging ion separation technology for removal of ions from water. The presence of organic matters will foul on the CDI electrode and lead to the decline of the CDI performance. In this study, three kinds of electrode materials: granular activated carbon electrode (GAC), granular activated carbon modified by sulfuric acid electrode (SGAC), antifouling membrane/granular activated carbon electrode (PVDF/GAC or PES/GAC) were used in CDI systems to investigate the impact of organic matters (humic acid (HA) or NOM) on CDI system.
   Our results showed that the presence of organic matters can significantly reduce the electrosorption capacity of GAC electrode. NOM has more adverse impact on CDI performance due to more complex chemical structures than that of HA. The average electrosorption capacity of GAC electrode during CDI processes decreased from 3.88 mg/g to 3.04 or 2.94 mg/g in the presence of HA or NOM, respectively, which corresponding to 21.6% or 24.2% reduction.
   With sulfuric acid modification, the average electrosorption capacity of SGAC electrode was improved to 4.44 mg/g. In the presence of HA or NOM, the average electrosorption capacity diminished to 3.62 or 3.36 mg/g, respectively, which corresponding to 18.5% or 24.3% reduction. 
   The antifouling membrane (PVDF or PES) coating on GAC electrode can mitigate the impact of organic matters fouling. Especially for PVDF/GAC electrode, not only the average electrosorption capacity was raised, but also the impact of HA or NOM on CDI performance was damped. The average electrosorption capacity of PVDF/GAC electrode applied to CDI system was 4.83 mg/g. Even with HA or NOM presented in the solution, the average electrosorption capacity can remain at high level (4.55 or 4.26 mg/g). The hydrophilic characteristics of PVDF or PES membrane were proved to effectively prevent the fouling of organic matters.

Table of contents
Chapter 1 Introduction	1
1.1	Motivation	1
1.2	Objectives	2
Chapter 2 Literature Review	3
2.1	Desalination	3
2.2	Capacitive deionization (CDI)	5
2.3	Activated carbons (AC) as electrode in capacitive deionization	6
2.4	Activated carbon modified with strong acid	8
2.5	Organic matters	12
2.6	The impact of organic matters on CDI system	14
2.7	Polymer membrane	16
Chapter 3 Material and Methods	18
3.1	Experimental structure	18
3.2	Experimental drugs and materials	20
3.2.1	Experimental drugs	20
3.2.2	Experimental instruments	21
3.3	Electrodes material	22
3.3.1	GAC pre-treatment	22
3.3.2	GAC modification by sulfuric acid (SGAC)	22
3.4	Electrode preparation	23
3.4.1	GAC electrodes and SGAC electrodes	23
3.4.2	Antifouling membrane coating on GAC electrode	23
3.5	Experimental analysis method	24
3.5.1	Scanning electron microscope (SEM)	24
3.5.2	Pore size and specific surface area analysis (BET)	24
3.5.3	Fourier transform infrared spectroscopy (FT-IR)	25
3.5.4	Contact angle	25
3.5.5	Cyclic voltammetry (CV)	26
3.5.6	Electrochemical impedance spectroscopy (EIS)	26
3.6	Organic matters analysis method	27
3.6.1	Ultraviolet-visible spectrophotometer (UV)	27
3.6.2	Detection of total organic carbon in water (TOC)	27
3.6.3	Fluorescence spectrometry	28
3.7	Capacitive deionization (CDI)	29
3.7.1	CDI system	29
Chapter 4 Results and Discussions	30
4.1	The impact of organic matters on capacitive deionization using GAC electrodes	30
4.1.1	Surface characteristics analysis of GAC	30
4.1.2	Electrochemical characteristics analysis of GAC	37
4.1.3	Impact of organic matters on the electrosorption capacity of GAC electrodes	44
4.1.4	Physical adsorption or electrosorption of organic matters on GAC electrodes	48
4.1.5	Capacitive deionization application for effluent from sewage treatment plant	54
4.2	The impact of organic matters on capacitive deionization using sulfuric acid modified GAC (SGAC) electrodes	59
4.2.1	Surface characteristics analysis of SGAC	59
4.2.2	Electrochemical characteristics analysis of SGAC	66
4.2.3	Impact of organic matter on the electrosorption capacity of SGAC electrodes	72
4.2.4	Physical adsorption or electrosorption of organic matters on SGAC electrodes	76
4.2.5	Capacitive deionization application for effluent from sewage treatment plant	82
4.2.6	Caparisons between GAC and SGAC	86
4.3	The impact of organic matters on capacitive deionization using PVDF/GAC or PES/GAC electrodes	91
4.3.1	Surface characteristics analysis of PVDF/GAC and PES/GAC	91
4.3.2	Electrochemical characteristics analysis of PVDF/GAC and PES/GAC.	96
4.3.3	Impact of organic matters on the electrosorption capacity of PVDF/GAC and PES/GAC electrodes.	105
4.3.4	Physical adsorption or electrosorption of organic matters on PVDF/GAC and PES/GAC electrodes.	109
Chapter 5 Conclusions and suggestions	120

 
List of Figure
Figure 3.1.1.1 Schematic experimental structure for CDI system…………….............17
Figure 4.1.1.1 SEM images of GAC (a) x1,000, (b) x5,000, (c) x20,000 and (d) x50,000.  …………………………………………………………………………...30
Figure 4.1.1.2 N2 adsorption (●)/desorption(○) isotherms of the GAC…………...31
Figure 4.1.1.3 Pore size distribution of the GAC…………………………………….31
Figure 4.1.1.4 Optical micrograph of the contact angles on the surface of GAC……33
Figure 4.1.1.5 The FT-IRspectra of GAC…………………………………………….34
Figure 4.1.2.1 Cyclic voltammograms of GAC electrode in 1 M NaCl……………...37
Figure 4.1.2.2 Cyclic voltammograms of GAC electrode in 1 M NaCl containing 10 mg/L HA……………………………………………………………………………...37
Figure 4.1.2.3 Cyclic voltammograms of GAC electrode in 1 M NaCl containing 10 mg/L NOM…………………………………………………………………………...38
Figure 4.1.2.4 Cyclic voltammograms of GAC electrode in different electrolytes at scan rate of 1 mV/sec………………………………………………………………………38
Figure 4.1.2.5 Specific capacitance (F/g) at different scan rates of GAC electrode…...39
Figure 4.1.3.1 The changes of conductivity in the CDI systems with feed water containing (a) 300 mg/L NaCl (●), (b) 300 mg/L NaCl and 10 mg/L HA (△) and (c) 300 mg/L NaCl and 10 mg/L NOM (□)……………………………………………...43
Figure 4.1.3.2 Removal efficiency based on conductivity using GAC electrodes in CDI systems containing sodium chloride with/without organic matters in solution within three cycles. (●) 300 mg/L NaCl, (△) 300 mg/L NaCl and 10 mg/L HA and (□) 300 mg/L NaCl and 10 mg/L NOM………………………………………………………..44
Figure 4.1.4.1 Variation of HA concentration as electrosorption (▲) and physical  adsorption (△) using GAC electrodes applied to CDI systems……………………….48
Figure 4.1.4.2 Variation of NOM concentration as electrosorption (■) and physical adsorption(□) using GAC electrodes applied to CDI systems……………………….48
Figure 4.1.4.3 The concentration changes of organic matters in sodium chloride solution with 10 mg/L HA (▲) or NOM (■) during physical adsorption for five hours and CDI electrosorption and desorption for three cycles…………………………….…………49
Figure 4.1.4.4 Electrosorption capacity of GAC electrode in the sodium chloride solution with/without organic matters (HA or SRNOM)……………………...………50
Figure 4.1.5.1 The changes of the conductivity to different water compositions in CDI systems. Feed water contained (a) 300 mg/L NaCl and 10 mg/L HA (▲) and (b) 300 mg/L NaCl and 50 mg/L HA (△), and (c) effluent from sewage plant (◆)…………...53
Figure 4.1.5.2 Removal efficiency based on conductivity using GAC electrodes in different concentrations of HA in sodium chloride solution and effluent from sewage plant within three cycles. Symbols: (▲) 300 mg/L NaCl and 10 mg/L HA, (△) 300 mg/L NaCl and 50 mg/L HA, and (◆) effluent from sewage plant……………….…..54
Figure 4.1.5.3 Variation of removal efficiency based on organic concentrations of 10 mg/L HA (▲) and 50 mg/L HA (△) and TOC of effluent from sewage plant (◆) using GAC electrodes applied to CDI systems…………………………………………..….55
Figure 4.2.1.1 SEM images of SGAC (a) x1,000, (b) x10,000, and (c) x50,000…….58
Figure 4.2.1.2 N2 adsorption (●)/desorption(○) isotherms of the SGAC…………..59
Figure 4.2.1.3 Pore size distribution of the SGAC…………………………….……..59
Figure 4.2.1.4 Optical micrograph of the contact angles on the surface of SGAC…..61
Figure 4.2.1.5 The FT-IR spectra of SGAC………………………………….………62
Figure 4.2.2.1 Cyclic voltammograms of SGAC electrode in 1 M NaCl……………65
Figure 4.2.2.2 Cyclic voltammograms of SGAC electrode in 1 M NaCl containing 10 mg/L HA……………………………………………………….……………………..65
Figure 4.2.2.3 Cyclic voltammograms of SGAC electrode in 1 M NaCl containing 10 mg/L NOM…………………………………………………………..……………….66
Figure 4.2.2.4 Cyclic voltammograms of SGAC electrode in different electrolytes at scan rate of 1 mV/sec…………………………………………..…………………….66
Figure 4.2.2.5 Specific capacitance (F/g) at different scan rates of SGAC electrode….67
Figure 4.2.3.1 The change of the conductivity in the CDI system with feed water containing (a) 300 mg/L NaCl (●), (b) 300 mg/L NaCl and 10 mg/L HA (△), and (c) 300 mg/L NaCl and 10 mg/L NOM (□) and (d) comparisons of threes water compositions………………………………………………………………………….70
Figure 4.2.3.2 Removal efficiency based on conductivity using SGAC electrodes in CDI systems containing sodium chloride with/without organic matters in solution within three cycles. (●) 300 mg/L NaCl, (△) 300 mg/L NaCl and 10 mg/L HA and (□) 300 mg/L NaCl and 10 mg/L NOM……………………………………………...71
Figure 4.2.4.1 Variation of HA concentration in CDI process (▲) and physical  adsorption (△) using SGAC electrodes applied to CDI systems……………………..75
Figure 4.2.4.2 Variation of NOM concentration in CDI process (■) and physical adsorption (□) using SGAC electrodes applied to CDI systems………………….….75
Figure 4.2.4.3 The concentration changes of organic matters in sodium chloride solution with 10 mg/L HA (▲) or NOM (■) during physical adsorption for five hours and followed with CDI electrosorption and desorption for four cycles……………………76
Figure 4.2.4.4 Electrosorption capacity of SGAC electrode in the sodium chloride solution with/without 10 mg/L organic matters (HA or NOM)……………………….77
Figure 4.2.5.1 The changes of the conductivity to different water compositions in CDI systems. Feed water contained (a) 300 mg/L NaCl and 10 mg/L HA (▲), (b) 300 mg/L NaCl and 50 mg/L HA (△), (c) effluent from sewage plant (◆), and (d) comparisons of threes water compositions…………………………………………………...……..80
Figure 4.2.5.2 Removal efficiency based on conductivity using SGAC electrodes in different concentrations of HA in sodium chloride solution and effluent from sewage plant within three cycles. Symbols: (▲) 300 mg/L NaCl and 10 mg/L HA, (△) 300 mg/L NaCl and 50 mg/L HA, and (◆) effluent from sewage plant………………...…81
Figure 4.3.1.2 SEM images of PES/GAC (a) x150, (b) x300, (c) x1,000, (d) x3,000…84
Figure 4.3.1.3 Optical micrograph of the water contact angles on the surface of (a) (b) PVDF and (c) (d) PES……………………………………………………………..….85
Figure 4.3.1.4 Water permeation flux of PVDF (■) or PES (▲) membrane under different pressures…………………………………………………………………….86
Figure 4.3.2.1 Cyclic voltammograms of PVDF/GAC electrode in 1 M NaCl………..90
Figure 4.3.2.2 Cyclic voltammograms of PES/GAC electrode in 1 M NaCl………….90
Figure 4.3.2.3 Cyclic voltammograms of PVDF/GAC electrode in 1 M NaCl containing 10 mg/L HA…………………………………………………………………………..91
Figure 4.3.2.4 Cyclic voltammograms of PES/GAC electrode in 1 M NaCl containing 10 mg/L HA………………………………………………………..…………………91
Figure 4.3.2.5 Cyclic voltammograms of PVDF/GAC electrode in 1 M NaCl containing 10 mg/L NOM………………………………………………………………………..92
Figure 4.3.2.6 Cyclic voltammograms of PES/GAC electrode in 1 M NaCl containing 10 mg/L NOM………………………………………………………………………..92
Figure 4.3.2.7 Specific capacitance (F/g) at different scan rates of PVDF/GAC electrode.
………………………………………………………………………………….…….93
Figure 4.3.2.8 Specific capacitance (F/g) at different scan rates of PES/GAC electrode.
………………………………………………………………………………………..93
Figure 4.3.3.1 Variation of conductivity in 300 mg/L NaCl solution during electrosorption and desorption for three cycles using GAC (●), PVDF/GAC (□), and PES/GAC (△) electrodes applied to CDI cells………………………………………97
Figure 4.3.3.2 Variation of conductivity in 300 mg/L NaCl solution containing 10 mg/L HA during electrosorption and desorption for three cycles using GAC (●), PVDF/GAC (□), and PES/GAC (△) electrodes applied to CDI cells…………………………….98
Figure 4.3.3.3 Variation of conductivity in 300 mg/L NaCl solution containing 10 mg/L NOM during electrosorption and desorption for three cycles using GAC (●), PVDF/GAC (□), and PES/GAC (△) electrodes applied to CDI cells………………..99
Figure 4.3.4.1 Variation of HA concentration during CDI processes using GAC (●), PVDF/GAC (■), and PES/GAC (△) electrodes applied to CDI cells…………….106
Figure 4.3.4.2 Variation of NOM concentration during CDI processes using GAC (●), PVDF/GAC (■), PES/GAC (△) electrodes applied to CDI cells……….…..106
Figure 4.3.4.3 The concentration of HA in NaCl solution containing HA during physical adsorption for five hours and following with CDI processes for three cycles. GAC (●), PVDF/GAC (■), PES/GAC (△) electrodes……………………….…..107
Figure 4.3.4.4 The concentration of NOM in NaCl solution containing NOM during physical adsorption for five hours and following CDI processes for three cycles. GAC (●), PVDF/GAC (■), PES/GAC (△) electrodes…………………………...…….107
Figure 4.3.4.5 Electrosorption capacity of PVDF/GAC electrodes in the sodium chloride solution containing organic matters (HA or NOM)…………………….…108
Figure 4.3.4.6 Electrosorption capacity of PES/GAC electrodes in the sodium chloride solution containing organic matters (HA or NOM)………………………………….108
Figure 4.3.4.7 Excitation-emission matrix fluorescence spectra of (a) original 300 mg/L NaCl containing 10 mg/L HA, and (b) 300 mg/L NaCl containing 10 mg/L HA after CDI process with PVDF/GAC electrodes…………………………………….……..110
Figure 4.3.4.8 Excitation-emission matrix fluorescence spectra of (a) original 300 mg/L NaCl containing 10 mg/L NOM and (b) 300 mg/L NaCl containing 10 mg/L NOM after CDI process with PVDF/GAC electrodes…………………….……………………..110

 

List of Table
Table 3.2.1.1 Manufactures and purity of experimental chemicals………….…..…18
Table 3.2.2.1 Manufacturers and models of equipment……………………………19
Table 4.1.1.1 Pore characteristics of the GAC…………………………….……….32
Table 4.1.1.2 FT-IR wavenumber with corresponding functional groups………….34
Table 4.1.2.1 Specific capacitance at different scan rate of GAC………….……….39
Table 4.1.3.1 Removal efficiency and electrosorption capacity of different solutions using GAC electrode for each cycle……………………………………………..44
Table 4.1.5.1 Removal efficiency of different water compositions using GAC electrode for each cycle…………………………………………………………...…..54
Table 4.2.1.1 Pore characteristics of the SGAC……………………………………60
Table 4.2.1.2 FT-IR wavenumber with corresponding functional groups………….62
Table 4.2.2.1 Specific capacitance at different scan rates of SGAC electrode….…..67
Table 4.2.3.1 Removal efficiency and electrosorption capacity of different solutions using SGAC electrode for each cycle…………………………………………………71
Table 4.2.5.1 Removal efficiency based on conductivity of different water compositions using SGAC electrode for each cycle……………….………………….81
Table 4.3.1.1 Water permeation flux of PVDF or PES membrane under different pressures…...…………………………………………………………………………86
Table 4.3.2.1 Specific capacitance at different scan rate of PVDF/GAC…………….94
Table 4.3.2.2 Specific capacitance at different scan rate of PVDF/GAC……………..94
Table 4.3.3.1 Removal efficiencies of different water compositions using three electrodes applied to CDI system for each cycle………………………………….…100

Table 4.3.4.1 The average electrosorption capacity (mg/g) of GAC, PVDF/GAC and PES/GAC electrodes applied to CDI systems……………………………………..109

Reference
Chen, L., et al. (2018). "Investigation of the long-term desalination performance of membrane capacitive deionization at the presence of organic foulants." Chemosphere 193: 989-997.
	
de Melo, B. A. G., et al. (2016). "Humic acids: Structural properties and multiple functionalities for novel technological developments." Materials Science and Engineering: C 62: 967-974.
	
Donohue, M. and G. Aranovich (1998). "Classification of Gibbs adsorption isotherms." Advances in colloid and interface science 76: 137-152.
	
El-Dessouky, H. T., et al. (1999). "Multi-stage flash desalination: present and future outlook." Chemical Engineering Journal 73(2): 173-190.
	
Green, N. W., et al. (2015). "Suwannee River natural organic matter: isolation of the 2R101N reference sample by reverse osmosis." Environmental Engineering Science 32(1): 38-44.
	
Hatzell, K. B., et al. (2015). "Effect of oxidation of carbon material on suspension electrodes for flow electrode capacitive deionization." Environmental science & technology 49(5): 3040-3047.
	
Huang, W., et al. (2014). "Desalination by capacitive deionization process using nitric acid-modified activated carbon as the electrodes." Desalination 340: 67-72.
	
Jia, B. and L. Zou (2012). "Wettability and its influence on graphene nansoheets as electrode material for capacitive deionization." Chemical Physics Letters 548: 23-28.
	
Kalfa, A., et al. (2020). "Capacitive deionization for wastewater treatment: Opportunities and challenges." Chemosphere 241: 125003.
	
Khezami, L., et al. (2005). "Production and characterisation of activated carbon from wood components in powder: Cellulose, lignin, xylan." Powder Technology 157(1-3): 48-56.
	
Lee, K. P., et al. (2011). "A review of reverse osmosis membrane materials for desalination—development to date and future potential." Journal of Membrane Science 370(1-2): 1-22.
	
Liang, S., et al. (2019). "Integrated ultrafiltration–capacitive-deionization (UCDI) for enhanced antifouling performance and synchronous removal of organic matter and salts." Separation and Purification Technology 226: 146-153.
	
Liu, F., et al. (2011). "Progress in the production and modification of PVDF membranes." Journal of Membrane Science 375(1-2): 1-27.
	
Liu, X., et al. (2018). "Mechanisms of humic acid fouling on capacitive and insertion electrodes for electrochemical desalination." Environmental science & technology 52(21): 12633-12641.
	
Mossad, M. and L. Zou (2013). "Study of fouling and scaling in capacitive deionisation by using dissolved organic and inorganic salts." Journal of hazardous materials 244: 387-393.
	
Niu, R., et al. (2015). "An insight into the improved capacitive deionization performance of activated carbon treated by sulfuric acid." Electrochimica Acta 176: 755-762.
	
Pavlik, J. W. and E. M. Perdue (2015). "Number-average molecular weights of natural organic matter, hydrophobic acids, and transphilic acids from the Suwannee River, Georgia, as determined using vapor pressure osmometry." Environmental Engineering Science 32(1): 23-30.
	
Sadrzadeh, M. and T. Mohammadi (2008). "Sea water desalination using electrodialysis." Desalination 221(1-3): 440-447.
	
Schnitzer, M. (1977). Recent findings on the characterization of humic substances extracted from soils from widely differing climatic zones. Soil organic matter studies.
	
Silverstein, R. M. and G. C. Bassler (1962). "Spectrometric identification of organic compounds." Journal of Chemical Education 39(11): 546.
	
Simon, P., et al. (2014). "Where do batteries end and supercapacitors begin?" Science 343(6176): 1210-1211.
	
Supply, W. U. J. W., et al. (2015). Progress on sanitation and drinking water: 2015 update and MDG assessment, World Health Organization.
	
Thorn, K. A., et al. (1989). "Characterization of the International Humic Substances Society standard and reference fulvic and humic acids by solution state carbon-13 (13C) and hydrogen-1 (1H) nuclear magnetic resonance spectrometry." Water-Resources Investigations Report 89: 4196.
	
Wang, C., et al. (2015). "Parameter optimization based on capacitive deionization for highly efficient desalination of domestic wastewater biotreated effluent and the fouled electrode regeneration." Desalination 365: 407-415.
	
Wang, S., et al. (2015). "In-situ combined dual-layer CNT/PVDF membrane for electrically-enhanced fouling resistance." Journal of Membrane Science 491: 37-44.
	
Wang, T., et al. (2020). "Scaling behavior of iron in capacitive deionization (CDI) system." Water research 171: 115370.
	
Welgemoed, T. and C. F. Schutte (2005). "Capacitive deionization technology™: an alternative desalination solution." Desalination 183(1-3): 327-340.
	
Yang, K. and J. T. Fox (2018). "Adsorption of humic acid by acid-modified granular activated carbon and powder activated carbon." Journal of Environmental Engineering 144(10): 04018104.
	
Yeh, C.-L., et al. (2015). "Improved performance in capacitive deionization of activated carbon electrodes with a tunable mesopore and micropore ratio." Desalination 367: 60-68.
	
Yin, C., et al. (2007). "Review of modifications of activated carbon for enhancing contaminant uptakes from aqueous solutions." Separation and Purification Technology 52(3): 403-415.
	
Yoo, J., et al. (2016). "Role of polarity fractions of effluent organic matter in binding and toxicity of silver and copper." Journal of hazardous materials 317: 344-351.
	
Zou, L., et al. (2008). "Using activated carbon electrode in electrosorptive deionisation of brackish water." Desalination 225(1-3): 329-340.