Preparation Of Heteroatoms Doped New Structure Carbon Materials For Capacitive Deionization

With population growth,industrial development and climate change,the shortage of fresh water resources has become one of the biggest survival crises facing mankind.The desalination of seawater and brackish water,reuse of recycled water,deep purification of tap water,and treatment of salty wastewater can effectively solve this crisis.Compared with the traditional deionization process,capacitive deionization is a new high-efficiency deionization technology based on the electric double layer principle,featuring low cost,low energy consumption and prevention of secondary pollution.The key to this technology is the electrode material.In this paper,for the problems of low conductivity and poor wettability of common electrode materials,new structure carbon materials doped with heteroatoms are designed and used as capacitive deionization electrodes,which effectively improve the performance of capacitive deionization.The main research results are divided into the following aspects:?1?The 1,4-benzenedicarbocylic acid and triethyldiamine,were designed to coordinate with zinc to obtain the dual-ligand metal organic frameworks material as the carbon precursor.The nitrogen-doped rod-like porous carbon materials were obtained by pyrolysis of the dual-ligand metal-organic frameworks with nitrogen atmosphere at the high temperature.The rod-like porous carbon materials were used for the capacitive deionization electrodes,and its capacitive deionization performance was investigated.In this method,the 1,4-benzenedicarbocylic acid ligand can be used as a pore former to increase the specific surface area and pores of the carbon material,and the triethyldiamine ligand is used as a nitrogen doping source to increase the hydrophilicity and conductivity of the carbon material,thereby increasing the capacity of the carbon materials to remove ions.By adjusting the ratio of the two ligands,carbon materials with the optimal specific surface area and nitrogen doping can be obtained after carbonization,thereby achieving optimal capacitive desalination performance.According to the morphology and structure characterization,the obtained rod-shaped carbon materials have a high specific surface area(962 m² g^-1),a hierarchically porous nanostructure and moderate nitrogen doping?2.6%?.Electrochemical tests show that the electrodes have the electroadsorption capacity of 24.17 mg g^-1 in a 500 mg L^-1 NaCl solution at applied voltage of 1.2 V.In addition,the moderate nitrogen-doped rod-like porous materials also exhibit a faster salt adsorption rate and good regeneration performance.?2?The zeolitic imidazolate skeleton-8?ZIF-8?was first prepared as the structural template,then hexachlorocyclotriphosphazene?as nitrogen,phosphorus source?and 4,4?-dihydroxydiphenyl sulfone?as nitrogen,sulfur source?were polymerized in situ on the surface of ZIF-8,forming the nanocomposites of poly cyclotriphosphazene-co-4,4?-dihydroxydiphenyl sulfone?PZS?coated ZIF-8.By pyrolysis of the nanocomposites at high temperature under nitrogen atmosphere and further etching with hydrochloric acid,the nitrogen,phosphorus and sulfur co-doped hollow carbon polyhedral materials were finally obtained.It was used as capacitive deionization electrodes to investigate its capacitive deionization performance.The morphology and structural analysis show that the nitrogen,phosphorus and sulfur co-doped hollow carbon polyhedral materials have excellent hollow structure,high surface area(929 m² g^-1),enhanced conductivity and excellent hydrophilic surface.On account of the synergistic effect of above characteristics,the electrodes have lower internal resistance,larger specific capacitance and better cycle stability.From the capacitive desalination test,the electrodes show the high electroadsorption capacity of 22.19 mg g^-11 in 500 mg L^-1 NaCl solution at 1.2 V.What's more,the electrodes exhibit good stability and regeneration performance.?3?The fibers of polyacrylonitrile,4,4'-dihydroxydiphenyl sulfone and hexachlorocyclotriphosphazene were prepared by electrospinning technique and used as carbon precursor.The nitrogen,sulfur,and phosphorus co-doped carbon fiber materials were obtained by calcining the precursor materials at high temperature in an inert atmosphere.The nitrogen,sulfur,and phosphorus co-doped carbon fiber was used for the capacitive deionization electrodes,and its capacitive deionization performance was investigated.According to the morphology and structure analysis,the nitrogen,sulfur and phosphorus co-doped carbon fiber materials have a high specific surface area(816 m² g^-1)and large pore volume.Its electrochemical tests show that the electrode materials have a higher specific capacitance and a lower internal resistance.The nitrogen,sulfur and phosphorus co-doped carbon fiber materials exhibit a high electroadsorption capacity of 28.75mg g^-1 in a 500 mg L^-1 NaCl solution at a flow rate of 50 mL min^-1 at 1.2 V.Simultaneously,the nitrogen,sulfur and phosphorus co-doped carbon fiber materials exhibit faster electroadsorption rate and better regeneration performance.In summary,the method for preparing multi-heteroatoms co-doped carbon precursor materials by electrospinning technique is novel,simple and high-efficiency,and the obtained carbon materials exhibit great advantages in the field of deionization.It is promising electrode materials for capacitive deionization.