The Preparation Of Graded Porous Carbon And The Study Of Capacitor Desalination Performance

Recently,the deionization capacitor has become a nexw-emerging and energy-saving technique for desalination,which relies on the electric double layer capacitor.The capacitive deionization(CDI)has got more and more attention because of its low cost,low energy consumption and environment-friendliness.Porous carbons are the most widely used as electrode materials for deionization capacitors because of its wide source of raw materials,low cost,adjustable pore structure,large specific surface area and stable physical and chemical properties.In porous carbon,micropore can provide large specific surface area for carbon materials,which is conducive to the increase of desalination,but the size of micropore is small,which is not conducive to ion transport.Mesoporous carbon has large pore size and small ion diffusion resistance,which is conducive to rapid desalination.The utilization rate of surface area is high,but the specific surface area of mesoporous carbon is small,which limit the desalination amount.The specific surface area of macropore is limited,and its contribution to desalination can be neglected.However,macropore can reduce the ion transport path and accelerate the desalination speed.Therefore,hierarchical porous carbon with micropore-mesopore-macropore has both high desalination capacity and fast desalination rate.In this paper,three different hierarchical porous carbons were prepared by template and activation method,and their capacitive desalination properties were investigated,the details are as follows:(1)Using citric acid as carbon precursor and nickel acetate as template,porous carbon nanofibers with high mesoporous content and carbon shell surface were prepared by electrospinning,curing,carbonization and pickling.When the mass ratio between citric acid and nickel acetate is 1:1.5,the average diameter of porous carbon nanofibers is 88.7 nm,and the specific surface area,pore volume and mesoporous porosity are 218 m2/g,0.40 cm3/g and 84.90%respectively;the single cycle deionization capacity and deionization capacity of per specific surface area reach 6.28 mg/g and 0.089 mg/m2,respectively.(2)Using ferric citrate as carbon precursor and KOH as activation agent,hierarchical porous carbon has been synthesized through the one-step carbonization strategy?carbonization-activation strategy and nitric acid surface modification of activated carbon with ferric citrate.The pore size distribution of porous carbon increased to about 16 nm after activation;and the specific surface area,pore volume and mesoporous porosity are 2140 m2/g,2.89 cm3/g and 82.87%respectively;the single cycle deionization capacity and deionization capacity of per specific surface area of AC reach 6.13 mg/g and 0.0089 mg/m2,respectively.After surface oxidation,the hydrophilicity of porous carbon was effectively improved,and the contact angle was reduced to 104.4 °;the specific surface area,pore volume and mesoporous porosity are 1960 m2/g,2.28 cm3/g and 78.07%respectively;the single cycle deionization capacity and deionization capacity of per specific surface area of AC-N reach 7.47 mg/g and 0.0118 mg/m2,respectively.It is founded that mesoporous carbon is more conducive to capacitive desalination than microporous carbon.(3)Through one-step KOH activation and acid pickling of high sulfur petroleum coke,hierarchical porous carbon with different sulfur content was prepared.When the mass ratio between petroleum coke and KOH is 1:2,the specific surface area,pore volume,mesoporous rate and sulfur content reach 1051 m2/g,0.56 cm3/g,35.71%and 1.07%respectively,the single cycle deionization capacity and deionization capacity of per specific surface area reach 5.00 mg/g and 0.015 mg/m2,respectively.It is founded that sulfur functional groups can effectively improve the desalination of samples.