Design And Regulation Of Porous Carbon Materials For Capacitive Deionization

In current society with a low-carbon economy,capacitive deionization(CDI)has attracted huge interest as an emerging desalination technology due to its low energy consumption,high removal efficiency,low cost,and non-secondary pollution.Normally,the water desalination performance of CDI technology largely depends on the electrode materials properties.Therefore,rational design and regulation of the structure and composition of electrode materials to acquire high CDI performance is of great significance.In this thesis,from the standpoint of pursuing CDI electrode with outstanding desalination performance,several porous carbon nanomaterials with controllable porous structures and chemistry compositions were explored.Moreover,the structure-function relationship between the porous carbon nanomaterials and CDI performance were also profoundly investigated.The main research contents and conclusions are presented as follow.(1)To meet the demand of CDI technology,nitrogen-doped hierarchical porous carbon(N-HPC)was fabricated via pyrolysis of hypercrosslinked diblock copolymer(PEO113-b-PS192)with a nitrogen-enriched melamine.The resultant N-HPC has a 3D hierarchical porous network,in which macropores,mesopores and micropores are well interconnected.This unique structure is beneficial to facilitate the ions diffusion within the framework.Moreover,the electrochemistry property of the carbon material is improved by the nitrogen-doping modification.The specific capacitance of N-HPC electrode is 2.74 times higher than that of its undoped counterpart.The CDI test results suggest that N-HPC electrode has an enhanced CDI performance with high electrosorption capacity of 13.76 mg g-1,in 500 mg L-1 NaCl solution.N-HPC electrode also shows a good cycle stability over 6 adsorption-desorption cycles.(2)The nitrogen-doped hollow mesoporous carbon spheres(N-HMCSs)were prepared via a "silica-assisted" sol-gel strategy,and used as CDI electrode.To understand the effect of structure and composition on CDI performance,another two CDI electrode materials,i.e.,hollow mesoporous carbon spheres(HMCSs)and solid mesoporous carbon spheres(SMCSs)were prepared for comparison.The obtained N-HMCSs possess unique hollow cavity and excellent nitrogen doping property,resulting in fast ion diffusion,good charge transfers ability and fine wettability.The CDI test results suggest that N-HMCSs electrode exhibits an improved electrosorption capacity and rate,demonstrating the dependence of CDI performance on the combined effect of hollow structure and nitrogen doping property.N-HMCSs electrode also presents excellent cycle stability over 20 adsorption-desorption cycles.(3)Based on the results of N-HPC and N-HMCSs electrodes,the nitrogen-doped cluster-like porous carbons(NCPCs)with hierarchical hollow nanoarchitecture were rationally prepared by carbonizing the polydopamine/nano-ZnO composite and employed as CDI electrodes.The resultant NCPCs possess an interconnected hierarchical structure with a hollow cavity,nitrogen-doping property,high specific surface,large pore volume and good wettability.All these merits can ensure a huge accessible electrosorption interface for the very quick diffusion of ions so that achieve an excellent CDI performance.Particularly,the sample carbonized at 900?(NCPC-900)with the optimal porous structure and chemistry composition exhibits the highest electrosorption capacity of 17.20 mg g-1 in 500 mg L-1 NaCl solution.Besides,the NCPC-900 electrode shows a good cycle stability over 20 adsorption-desorption cycles.These results suggest that the unique cluster-like structure and nitrogen-doping property could boost the CDI performance,which is better than those of N-HPC and N-HMCSs electrodes.(4)The protic salt-derived porous carbons(PSCs)were synthesized via the direct pyrolysis of the protic salt,i.e.,p-phenylenediamine bisulfate([pPDA][2HSO4]),which was obtained by simply neutralizing p-phenylenediamine with sulfuric acid.The resultant PSCs possess large surface area,high nitrogen doping,good graphitization and large mesopores.All these intrinsic characteristics endow PSCs with excellent electrochemical properties and CDI desalination performance.The CDI test results suggest that the dependence of CDI performance on the balance between porous structure and chemical composition.Particularly,the carbon obtained at 900?(PSC-9)with optimal porous structure(1082 m2g-1)and chemical composition(5.2%N)exhibits the best CDI performance:a high electrosorption capacity of 20.20 mg g-1 in 500 mg L-1 NaCl solution and excellent electrosorption stability over 20 times of adsorption-desorption cycles.Due to the all-in-one properties,PSCs have achieved the best CDI performance among all as-prepared carbon CDI electrodes.Moreover,PSCs with high pyrolysis yeld have a simple preparation method,resulting in a promising prospect of engineering applications...