Study On Construction And Capacitive Deionization Applications Of Carbon Based Porous Materials

The shortage of drinking water resource has been a threat to human survival and social development.Many efforts have been made to explore the appropriate solution.Desalination of salt water and removal of pollutants are considered as the most effective solution.There are many kinds of water treatment technologies such as reverse osmosis,electrodialysis,distillation,adsorption,etc.However,these methods still have shortcomings such as high cost,low removal efficiency,secondary pollution during material’ regeneration process and so on.The electric double layer capacitor（EDL）based capacitive deionization（CDI）technology is recognized as the most promising water treatment technology with the advantages of high efficiency,low cost,easy regeneration and no secondary pollution.However,the development of this technology is not mature with some problems need to be solved such as lacking of effective electrode material,the study of mechanism is not deep enough,and the reasonable operating mode remains to be further improved.This paper mainly focuses on three aspects:（1）The design of electrode materials and explore the correlation between the material structure,composition and performance;（2）The integration of various technologies to promote the portable application of CDI technology;（3）The application of CDI technology to seawater desalination and remove pollutants from water.The following achievements have been made in this paper:1.Synthesis of nitrogen doped porous carbon materials and its application in electrode materialsThe three-dimensional nitrogen doping porous carbon（3D-NPC）was obtained by a directly pyrolysis of the mixture of sodium chloride and sodium glutamate.The ideal target product exhibits the coexistence of micropores and mesopores that is conducive to the transport of protons and electrons,and provide large adsorption specific surface area（1481 m2 g-1）and high heteroatom doping（nitrogen content:4.93%）which will contribute to the enhancement of the material’s pseudo-capacitance and wettability,thus together achieving the improved desalination performance.The target material showed excellent desalination ability（adsorption capacity:21.0 mg g-1）.In view of the above characteristics of the material,3D-NPC can also be used as cathode catalyst for Zn-air battery,showing excellent catalytic performance and open circuit voltage of 1.34 V.Therefore,this study realized the synthesis of three-dimensional nitrogen doping porous carbon and apply the same material to both CDI and Zn-air batteries.2.Synthesis of kelp derived hierarchical porous carbon materials and its application in capacitive electrode materialsIn the process of heat treatment,the salt ions（NaCl,CaCl2,etc）in the kelp can act as pore-forming agent to form the mesoporous,and a richer pore structure can be obtained by further KOH activation.A series of experiments were conducted to determine the appropriate calcination temperature and activator dosage.The ideal sample possessed the coexisting microporous and mesoporous pore structure,high specific surface area（2613.7 m2 g-1）,splendid desalination capacity（27.2 mg g-1）and the capacitor energy storage capacity（202 F g-1）.If the material was assembled into soft package battery to replace the DC power to supply CDI device,the portable application of CDI was realized.The above results are particularly important for the CDI application under special conditions（remote areas without electric power,man-made or natural disasters）.3.Tetracycline removal by porous carbon assembled CDI electrodeIn this chapter,the symmetric electrode CDI device assembled with kelp derived hierarchical porous carbon was firstly applied to the removal of tetracycline（TC）for the first time.The removal ability of TC can be improved by introducing CDI technology（Langmuir fitting result:925.3 mg g-1）.What’s more,the TC removal efficiency shows no obvious changes in the presence of other coexisting ions（Cl-,Ca2+,Mg2+,Na+ and K+）.Meanwhile,the opposite charged contaminant ions such as Ca2+,Mg2+,Na+ and K+ will also be adsorbed on the other side of the CDI electrode,achieving the purpose of purifying water.This study proves that CDI technology has a great application in removing TC and enriched metal ions.4.Arsenic removal with graphite carbon nanotubes（GCN）loaded Fe/Fe3C and porous carbon assembled asymmetric CDI electrodeIn this part,FeCl3·6H2O and fumaric acid were selected as precursor to synthesis porous graphite carbon nanotubes（GCN）loaded Fe/Fe3C materials（Fe/Fe3C-GCN）.The Fe/Fe3C-GCN materials and kelp derived hierarchical porous carbon materials are respectively used as the cathode and anode electrode materials to assemble an asymmetric CDI.The adsorption rate and adsorption capacity of As（Ⅲ）in CDI process（Freundlich adsorption isotherm fitting result:97.73 mg g-1）are higher than those of symmetrical electrode（double layer adsorption）composed of multistage porous carbon materials.This is because the asymmetric electrode can combine the double layer electric adsorption of GCN and the chemical adsorption characteristics of Fe/Fe₃C.It is important that the highly toxic As（Ⅲ）compound could be oxidezed into the less toxic As（Ⅴ）at the anode and removed from the waste water by this method in one step.The whole removal process is clean and efficient,which provides a new research idea for the removal of pollutants in water.