The Synthesis Of Coal-based Carbon Materials For Capacitive Deionization

With the aggravation of environmental pollution and the explosion of population,water crisis problem has become a serious problem facing humanity.Therefore,converting abundant seawater and brackish water into fresh water is an important way to realize the increase of water resources and solve the water crisis.At present,brackish water treatment technologies mainly include reverse osmosis,membrane desalination,electrodialysis,multi-effect distillation and multi-stage flash evaporation,but these technologies have the disadvantages of high energy consumption,secondary pollution,and high cost.Capacitive deionization(CDI),as a new electrical desalination technology,has been widely concerned by researchers due to its advantages of low energy consumption,environmental friendliness,and high efficiency.As the core component of CDI technology,the performance of electrode materials plays a vital role to improving the desalination capacity of the CDI system.Hence,finding electrode materials with high adsorption capacity,fast adsorption rate,and low energy loss is a key technical problem to be solved urgently by CDI technology.In this paper,a series of porous carbon materials were designed and prepared by controling the pore structure and composition by using coal resources with abundant reserves in Xinjiang.The relationship between the sample morphology,composition and structure and its CDI performance were systematically studied,which provided a new idea for the design and preparation of high-performance CDI electrode materials.The main research content and results are summarized as follows:(1)The coal-based hierarchical porous carbons(HPC)were prepared by sol-gel method and activation method,and the influence of KOH dosages on the morphology,structure,and CDI performance were studied.The results show that the HPC obtained after KOH activation has a three-dimensional interconnected hieratchical porous structure.Its specific surface area and total porous volume have reached 2168 m² g^-1 and 1.079 cm³g^-1,respectively.Large specific surface area provides abundant adsorption sites for ion adsorption;3D interconnected hierarchical prous structure and high mesoporous volume provide fast channels for ion transmission;high heteroatom content makes the material have good wettability.Through the synergistic effect of composition and structure,the desalination capacity of the sample HPC_1.5:1 21.56 mg g^-1,and showed good desalting rate and desalination stability.(2)Mesoporous carbon nanofiber fabric(MCNF)with large accessible surface area was prepared by electrospinning using ferrocene as pore former and coal-based graphene quantum dots as raw materials.The good mechanical properties of MCNF allow it to be used directly as a filtration membrane to filter sandy simulated brackish water,with a water flux of 2960 L m^-2 h^-1.Thanks to abundant edge sites and strong polar surface,MCNF exhibit good hydrophilicity.Under the optimal conditions,the specific surface area and mesoporous volume of the MCNF-5 reached 922 m² g^-1 and 0.32 cm³ g^-1,respectively.Its desalination capacity was 19.34 mg g^-1 in 500 mg L^-1 Na Cl solution,and the desalination capacity showed a linear relationship with the cumulative specific surface area with pore diameter greater than 0.65 nm.(3)The core-shell structure(CNF_ZIF)carbon nanofibers@porous carbon nanosheets was constructed by in-situ growth of zeolitic imidazolate framework-8(ZIF-8)nanosheets on electrospun nanofibers.The addition of coal-based graphene quantum dots in electrospun fibers provides abundant anchor points for the in-siut generation of ZIF-8,which effectively avoids the agglomeration of ZIF-8 during the growth process,ZIF-8derived carbon nanosheets with well-defined micro-mesopores and abundant defects provide large amounts of adsorption sites and reduce the ion transmission resistance.Furthermore,high N-content of CNF_ZIF effectively improves the surface wettability and electrochemical performances.As a result,the obtained CNF_ZIF-10 exhibits a high salt adsorption capacity of 16.89 mg g^-1 and desalting rate of 1.82 mg g^-1 min^-1 in a 500 mg g^-1 Na Cl solution,respectively.Meanwhile,in KCl,CaCl₂,and MgCl₂ solutions of 500mg L^-1,the salt adsorption capacity of CNF_ZIF-10reached 20.53 mg g^-1,18.25 mg g^-1,and17.58 mg g^-1,respectively.