Preparation Of Novel Carbon Nanomaterial Electrodes And The Study On Their Desalination Performance In Capacitive Deionization

Capacitive deionization(CDI)has received much attention due to its significant advantages of efficient energy use and no secondary pollution.This paper prepared several carbon nanomaterials with charge characteristic,hierarchical porous structure and specific morphology and investigated their applications in CDI technology,which revealed the relationship between the structure of electrode materials and desalination performance.Firstly,carbon nanotubes(CNT)was modified by a novel sulfobutyl ether ?-cyclodextrin polymer with multi-sulfonic and multi-hydroxyl groups.The effects of functional group content on the morphology,structure,surface properties and electrochemical properties of the modified CNT were investigated.Based on the electroneutrality principle,the inhibitory effect of the modified CNT electrode on the co-ion effect during the adsorption process was explored when the modified CNT electrode was respectively used as the positive electrode and negative electrode of the asymmetric CDI cell.The results indicated that when the modified CNT electrode was used as the negative electrode,the saturation specific adsorption capacity of 6.48 mg/g and the average charge efficiency of 36.9% were achieved.After 50 cycles of the desalting tests,the specific adsorption capacity of the modified CNT electrode was only attenuated by 4.4%,exhibiting a good long-term stability.Secondly,hierarchically porous carbon(HPC)with a high fraction of mesopore was prepared by using silica sol as the template agent and ?-cyclodextrin as the carbon source.The effects of the amount of templating agent on the morphology,structure,electrochemical performance and desalination performance of HPC were investigated.Furthermore,the effects of traditional voltage mode and alternating polarization voltage mode on the desalination performance and stability of HPC electrode were investigated.And based on the potential of zero charge(PZC),the convex "arc" change trend of the desalination performance under the alternating polarization voltage mode was theoretically analyzed.The results indicated that after 100 cycles of the desalting tests,the attenuation rate of the specific adsorption capacity for the HPC electrode was 43.9% under the traditional voltage mode,while the value for the HPC electrode was slightly higher than that of the first cycle under the alternating polarization voltage mode.And when the PZC of the two electrodes was equal to E0(64th cycle),the desalination performance of the electrode reached the maximum value(14.04 mg/g)under the alternating polarization voltage mode.Thirdly,the composite electrode material was prepared by the hollow spherical carbon(HCS)and polypyrrole(PPy).Among them,the hollow spherical carbon was synthesized by using P123/SO as the soft template agent and glucose as the carbon source.The morphology,structure,electrochemical properties and desalting performance of two ion-doped HCS@PPy composite electrode materials were investigated.Furthermore,the tolerance of the HCS@PPy composite electrode was explored under different p H and temperature conditions.The results indicated that the saturation specific adsorption capacity of the HCS@PPy composite electrode was 38.24 mg/g,which was significantly higher than that of the HCS electrode(11.37 mg/g).The structure of the HCS@PPy composite electrode was destroyed under the alkaline and high temperature solution,leading to a significant decrease of the desalination performance.The saturation specific adsorption capacity of the HCS@PPy composite electrode under the acidic solution with p H=3 was still high at 32.73 mg/g,so the HCS@PPy composite electrode could be used in acidic solution.Finally,the N-doped hollow carbon sphere(NHCS)was prepared by using SiO₂ as the template agent and PPy as the carbon source.The effects of carbonization temperature on the structure and N-doped degree of NHCS were investigated.The flow electrode was constructed with NHCS-800 as the active material.The effects of active material content on the rheological properties,electrochemical performance and desalination performance of NHCS-800 flow electrode were investigated,and the charge permeation transfer process was also analyzed.The results indicated that the NHCS-800-30 wt% flow electrode possessed the best comprehensive performance,and its desalting efficiency and salt removal flux were 40.2% and 80.3 mg/min espectively under the optimum operating voltage of 1.2 V,the optimum ratio of the raw material liquid to the electrode slurry of 1:1.5 and the optimum raw material concentration of 1 g/L.