Study On The Capacitive Deionization Properties Of Graphene Electrodes Prepared By Different Reduction Conditions

Entering the 21 st century,the structure of water resources has undergone tremendous changes with the surge in population and industrial development.The increase in human demand,on the other hand,the environment is damaged by pollution,resulting in the reduction of freshwater resources.At present,many countries and regions are facing the crisis of water resources,and the demand for sustainable fresh water has brought insurmountable challenges to human beings.The lack of fresh water resources will seriously threaten the survival of human beings.Seawater desalination technology is a technology that scientific researchers are committed to using seawater,which accounts for a large proportion of the earth,for desalination treatment,in order to solve the global shortage of freshwater resources that humans are facing.More effective ways to ensure the availability of freshwater resources.The emergence of capacitive deionization(CDI)technology has emerged among many seawater desalination technologies with its unique advantages.As an emerging seawater desalination technology,its basic principle is to use electric double layer capacitance for ion adsorption.The driving energy of the desalination process requires no high.This technology is different from traditional desalination technology,and has outstanding comparative advantages: low energy consumption,renewable electrodes,green environmental protection,no secondary pollution,etc.,to a certain extent,avoids the problems of traditional desalination technology.In summary,its advantages in desalination technology are the outstanding performance has attracted many research interests,and has become the current research hotspot of desalination technology.As the key to the CDI module,the electrode material plays an important role in the adsorption process,and the quality of the material determines the performance of the CDI.Based on graphene’s excellent electrical properties,high specific surface area,and stable physical and chemical properties in many applications,it is very suitable as an ideal CDI electrode material and has broad application prospects in capacitive deionization technology.The research contents of this paper are as follows:Firstly,using graphene oxide dissolved in water as the raw material of the dispersion system solution,graphene was prepared by reduction with Lascorbic acid(vitamin C)at different temperatures from 40 to 90 °C.The morphology and structure of graphene at different reduction temperatures were explored by SEM,XRD,FT-IR,Raman and other testing methods;electrodes were fabricated,and the electrochemical behavior of the electrodes was tested and analyzed.The scanning speed showed a specific capacitance of 83.6 F/g,and the cycle stability was good;then the electrode was tested for capacitive deionization performance.As the reduction temperature increases,the oxygen-containing functional group responds more quickly to L-ascorbic acid,and the reaction is carried out in a better environment,the group removal is more thorough,and the electrical and CDI performance as an electrode is improved.The graphene electrode reduced at 80 °C achieves an ion removal rate of 29.5% and a desalination amount of 5.38 mg/g,which has good renewable performance.Secondly,on the basis of the reduction temperature in the previous chapter,L-ascorbic acid was used as the reducing agent to study the reaction of graphene oxide to prepare graphene from 20 to 120 minutes for different reduction times.The morphology and structure of graphene under different reduction time were explored by SEM,XRD,FT-IR,Raman and other test methods;then as an electrode material,the electrochemical properties of the material were explored in a three-electrode system,and the graphite under the reaction time of 120 minutes The specific capacitance of the alkene was 78.3 F/g at a scan rate of 5 m V/s,and the cycle stability was good;then the electrode was tested for capacitive deionization performance.With the increase of the reaction time,the oxygen-containing functional groups are in contact with L-ascorbic acid more fully,and the reaction is removed in more sufficient time.The reaction is completed,and the electrical and CDI performance as an electrode is improved.The graphene electrode reduced by reacting at 80 °C for 120 minutes has a desalination rate of 0.233 mg/(g min),a desalination efficiency of 32.1%,and a salt adsorption capacity of 5.35 mg/g,showing good renewable performance.Finally,based on the reduction temperature and reaction time in the previous two chapters,in order to improve the agglomeration of graphene sheets,carbon nanotubes were added before reduction,and the reduction reaction was carried out at the ratio of graphene : carbon nanotubes=n:1(where n = 20,15,10,8,5,and 2)to obtain effective composite graphene/carbon nanotube materials;SEM,XRD,FT-IR,Raman,etc.were used to analyze the morphology,morphological,Structural analysis,it was found that the microstructure was improved,the carbon nanotubes were successfully embedded in the graphene sheet,providing more pore sites,forming a better conductive network,and the stacking of the sheets was reduced;electrochemical analysis and testing of the composite material found that The addition of carbon nanotubes increases the specific capacitance of the composite structure(when the mass ratio of graphene :carbon nanotubes is 10:1,the specific capacitance reaches 144 F/g,which is 1.8 times that of graphene);then the electrode is subjected to capacitive deionization Performance test to explore the effect of applied voltage and carbon nanotube content on the desalination process of the electrode.It was found that the optimal adsorption effect was achieved under the condition that the mass ratio of graphene and carbon nanotubes was 10:1,the desalination efficiency was 47.5%,and the maximum adsorption capacity is 8.64 mg/g,which is 61% higher than that of graphene.The composite electrode was subjected to several complete electro-adsorption-desorption processes,showing good reproducibility,and the adsorption performance did not decrease significantly and remained stable.The electrode can be used continuously and repeatedly for desalination.