Engineering And Characterization Of Surfactants Treated Carbon-based Electrodes With Respect To Capacitive Deionization Performance

Capacitive deionization（CDI）is an emerging desalination technology based on the electrical double layer（EDL）concept,whereby salts ions in the saline water are reversibly held into EDL of polarized electrodes.When electrodes become saturated with ions,the polarity is reversed and ions are released back into the brine stream.In essence,the performance of the CDI system relies on electrode,cell architecture,and operational parameters.Nevertheless,ideally,optimized electrodes hold the lion’s share of contributing factors to the CDI performance.As such,electrode materials and design strategies play a pivotal role on the CDI advancement.Since the beginning of CDI development,activated carbon（AC）has been the workhorse material for electrode fabrication.Along the way,optimization of electrode properties towards ideality has been the research hotspot of this promising technology.Several modification methods and concoctions of AC with various modifiers have been reported with improved and versatility attributes for broadening the scope of applications,by meeting necessary features of electrodes for a given CDI cell configuration.Study dual surfactants（ionic and non-ionic）to enhance the electrochemical performance of the inverted CDI（i-CDI）electrode,in order to exert the synergistic effect of non-ionic surfactants and surfactants to improve the desalination function and broaden the application of the surfactant catalog range.Using Tween-80 to improve the sol-gel process,study the influence of directional synthesis on the electrochemical capacitance performance of composite materials,and explore the practical value of composite materials in CDI applications.This thesis presents the tradeoff in carbon-based electrode design;engineering and characterization of surfactants treated carbon-based electrodes with respect to CDI performance,and perspectives.First,the beneficial and detrimental effects of modifiers on AC electrodes,classification of CDI cells architectures,and interdependence between electrode aspects and CDI cell configuration are discussed.Using physical and chemical methods to study the interfacial aggregation of mixed surfactants,the results show the treated carbon gained a good wettability,where contact angle decreased from 124.63° to76.61° and pH_PZC shifted from 4.2 to 6.3.The zeta potential revealed an increase of surface charge density.Moreover,the stability testing unveiled a reinforced adsorption,where AC-T80-HDTMA exhibited a relatively low detachment（0.32%）compare with AC-HDTMA（1.32%）after 500 cycles.The enhanced surface activity of porous carbon with respect to water treatment can attributed to the surfactants synergism via interface aggregation on the carbon surface.It explains that hydrophobic effect and steric stability are the main keys to the synergy,and describes the hypothetical synergistic mechanism of surfactant adsorption on the carbon surface.Further,synergistic effects of surfactants（HDTMABr,SDS and T80）treatment on AC activity for inverted CDI（i-CDI）were elucidated.The pecific capacitance of ionic and dual surfactants treated electrodes at 0.8 V in 1M NaCl were 127.3 and 171 Fg^-1,respectively.The AC-T80-HDTMA/AC-T80-SDS system exhibited a higher salt removal capacity(7.5 mg g^-1)at 1.2V(in 750 mg L^-1 of NaCl solution)with extended cyclic stability（38%）compare with AC-HDTMA/AC-SDS(5.2mg g^-1).The loss of performance stability linked on degradation mechanism caused by redox reactions and co-ion expulsion triggered the development of a new CDI generation named i-CDI which operates in the opposite manner of conventional CDI,whereby salt ions are desorbed and adsorbed during charging and discharging,respectively.The reported utilization is only limited to the ionic catalog.A dual surfactants-treatment was employed in order to reap the benefits of synergy of nonionic with ionic surfactants.The profitable effects suggest that a properly chosen combination of surfactants can be a suitable functionalizing agent of i-CDI electrodes.Lastly,the thesis disclose a novel strategic approach of carbon and titania（TiO₂）composites concoction via Tween 80-assisted sol-gel process using titanium（IV）isopropoxide（TTIP）as Titania precursor.The specific capacitances of AC/TiO₂ and AC-T80/TiO₂ at the scan rate of 10m Vs^-1 and a potential of 1.6 V are 215.3 and 265 Fg^-1,respectively,where the electrode resistance of surfactant-treated composite（0.8Ω）is smaller than that of surfactant-free composite（1.2Ω）.Further,AC-T80/TiO₂//AC-T80/TiO₂ composite delivered the salt adsorption capacity（SAC）of 17.1mgg^-1（26%higher than surfactant-free composite）at 1.4 V,with outstanding capacity retention（87%）over 150 cycles in oxygen saturated saline water（10 m M）.The joint effects of homogeneously deposited layers of TiO₂ and interfacial activity of Tween 80 resulted to a superior electrochemical performance.This cooperative interaction between carbon material,surfactant and TTIP along with induced homogeneous concoction and reduced surface tension owing to the hydrophilic domains of Tween 80 is essential for carbon-based electrode design.As such,the hybridization resulted to enhanced capacitive behaviors with additional practical values,focusing on the essential role of surfactant on the holistic state of the composite with respect to the CDI performance.Through deployment of synthesis aid agent,Tween 80 acts as a steric stabilizer,wetting,and capping agent,with a remarkable ability to control the particles undergoing modification and homogeneous bonding.In short,this work presents the fundamental aspects of surfactants utilization in carbon-based electrode development with respect to CDI performance.