Modification Of Carbon Electrode For Inverted Capacitive Deionization

Due to population growth and increased water pollution caused by industrialization,the fresh water resources available on the earth are seriously deficient,which has caused serious contradictions between water supply and demand.The most reliable way to solve this problem is to convert the abundant seawater and brackish water on the earth into fresh water through desalination technology.Capacitive deionization(CDI)is a novel desalination technology based on the principle of electrosorption.Compared with traditional desalination technologies,CDI has the advantages of low cost,no pollution and low energy consumption,which has attracted widespread concern of many scientific researchers.Electrode has an important impact on the performance of CDI.Although the salt adsorption capacity(SAC)of the carbon material electrode needs to be improved,and the cycle performance also decreases seriously during long-term operation,it is inexpensive and is the first choice for industrial operation.In this dissertation,the surface modified activated carbon(AC)electrodes are subjected to the inverted capacitive deionization(i-CDI)operation to suppress the anodic oxidation reaction of the activated carbon electrode,which improves the salt adsorption capacity,cycle stability and charge efficiency.The main research contents and conclusions are as follows:(1)Activated carbon treated with nitric acid(N-AC)and modified with ionic liquid(P-AC)to introduce negatively charged carboxyl functional groups and positively charged bromonium groups on the surface of the activated carbon,which enhanced the the hydrophilicity and ion selectivity of carbon electrodes.The asymmetric CDI cell assembled with N-AC and P-AC electrodes can achieve a SAC of 9.6 mg/g in 500 mg/L NaCl under1.2/0 V voltage,and the SAC retention rate can still be maintained at 85.6% under 0.8/0 V voltage after 100 i-CDI cycles,which showing excellent cycle stability.(2)The hydrophilic binders carboxymethyl cellulose sodium(CMC),polyvinyl alcohol(PVA)and sulfonated carboxymethyl cellulose sodium(SCMC),quaternized polyvinyl alcohol(QPVA)were used to prepare the activated carbon electrodes,which further enhanced the hydrophilicity and ion selectivity of activated carbon electrodes.Applying the activated carbon electrodes prepared by the hydrophilic binder to the i-CDI test significantly improves the i-CDI performance of the activated carbon electrodes: The SAC of NC-CMC//PC-PVA and NC-SCMC//PC-QPVA are 13.81 mg/g and 16.61 mg/g in 500 mg/L NaCl under 1.2/0 V voltage,and the SAC retention rates are 89.95% and 94.18% under 0.8/0 V voltage after 100i-CDI cycles.In addition,the hydrophilic charged polymer binders can effectively inhibit theside reactions of anodic oxidation depending on its own charges,so that the conventional CDI cell assembled with untreated activated carbon also shows excellent desalination performance:The SAC of AC-CMC//AC-PVA and AC-SCMC//AC-QPVA are 14.58 mg/g and 17.39 mg/g in 500 mg/L NaCl under 1.2/0 V voltage,and the SAC retention rates are 89.95% and 94.18%under 0.8/0 V voltage after 100 conventional CDI cycles.