Study On The Modification Of Carbon Nanotubes Electrode Material And Its Inhibitive Performance On The Co-ion Effect Of Capacitive Deionization Process

In this papper,the chemical modification method was adopted to treat the carbon nanotubes(CNT)including sulfonation treatment with sulfanilic acid and ammoniation treatment with triethoxysilane to graft the sulfonated and ammoniated groups on the surface of CNT.And a series of methods were used to confirm the successful grafting of the functional groups.The contact angle analysis showed that the rate of contact angle change of the midified material was much higher than that of the prinstine CNT,which confirmed that the modification has improved the wettablity of the material.The results of electrochemical tests showed that the specific capacitance of sulfonated and ammoniated CNT electrode was about 1.6-1.7 times that of the CNT electrode and the charging reisitance for the sulfonated and ammoniated CNT electrode was dramatically reduced by 25%.The potential of zero charge(Epzc)for the three electrodes displayed that compared to the prinstine CNT electrode,the Epzc of sulfonated and ammoniated CNT electrode has shifted to 0.2 V and-0.1 V respectively,which further confirmed the effective modification of the charge characterization on the surface of CNT.By pairing the two modified electrodes with the CNT electrode,seven cells were assembled to study the effects of electrode assembling patterns on the desalination performance of the CDI process concerning about the aspects of the saturated adsorption,the electrosorption kinetics and the potential distribution.The saturated adsorption results showed that among the seven cells,cell N-S displayed the largest adsorption capacity with the value of 61.84 mg/g and the highest desalination efficiency of 18.38%.And the results of electrosorption kinetics showed that the electrosorption rate constant and the correlation coefficient of the cell N-S were the largest,indicating that the electrosorption rate was the fastest.It is also found that the effective driving force of the cathode and anode for the cell N-S was the largest among the seven cells and almost no potential loss was found.The above results indicated that the cell N-S can achieve the optimized electrode assembly.To test the stability of the modified electrodes,multiple CV tests and cyclic adsorption/desoprption tests were performed.And the results of 100 times CV test s showed that the decrease of the capacitance for the sulfonated and ammoniated CNT electrode were only 5.6% and 6.1%,while the decrease for the CNT electrode reached to 53.33%.It indicated that the modified electrode had the advantage over the CNT electrode in keeping the electrochemical stability of materials.What's more,the shift of the Epzc for the modified electrode was much smaller than that of the CNT electrode,which confirmed the ability of modified electrode in inhibiting the process of oxidation.The cyclic adsorption/desoprption tests showed that after 10 times cycles,the cell N-S displayed the largest adsorption capacity and the least decrease in adsorption performance and the shift of the Epzc in cathode and anode was the least.Meantime,the research for the inhibition mechanism of co-ion effect also indicated that cell N-S could achieve the largest degree of inhibition for the co-ion.These results demonstrated that the proper electrode assembly can maintain the electrochemical and desalination stability of the cell and inhibit the co-ion effect in a large degree.