Structural Regulation Of Biomass Carbon Materials And Their Application In Capacitive Deionisation

Water is the material basis of human existence.However,the freshwater resources on the earth are decreasing day by day and pollution is a serious problem.Compared with the scarce fresh water resources,the earth’s seawater resources are extremely abundant,accounting for 97%of the total water resources on the earth.Therefore,desalination of seawater and brackish water,especially at low energy consumption,is an effective means to solve the shortage of fresh water resources.At present,multi-stage flash distillation,multi-effect distillation,reverse osmosis,electrodialysis and other technologies are widely used in seawater desalination.But their energy consumption and cost are high,and they also have secondary pollution.In contrast,capacitive deionisation（CDI）has attracted much attention due to its low energy consumption,simple operation and good reproducibility.The principle of CDI is based on the formation of double electric layer capacitors（EDLs）at the electrode/electrolyte interface,which adsorb ions in solution onto the electrode surface by electrostatic adsorption.Obviously,electrode materials are the core of CDI technology and play a crucial role in achieving high desalination performance of CDI process.Among various electrode materials,carbon materials have attracted much attention due to their advantages such as large specific surface area,high chemical resistance,good conductivity,and easy availability.However,the desalting capacity and rate of carbon materials are low,which hinders the further application of carbon electrodes.This is mainly due to the slow kinetics of ion diffusion due to poor pore structure and limited surface area,the reduction of ion accessible sites due to poor hydrophilicity,and the simple physical adsorption process.Therefore,it is urgent to develop advanced carbonaceous materials with good porosity,good hydrophile and strong pseudocapacitance to achieve high desalting performance.In this paper,banana peel and basswood were used as carbon sources to prepare two kinds of carbon material electrodes with different morphology and structure,and the capacitive deionization performance and mechanism of carbon material electrodes were deeply studied.The main research contents and conclusions are summarized as follows:（1）By optimizing the drying method of banana peel,adjusting the carbonation temperature and chemical activation,the carbon material(a-n PC₈₀₀)with graded porous structure was prepared.The graded porous structure of the carbon material was verified by specific surface area test and scanning electron microscope.In addition,ammonium borate was used as a dopant to perform a one-step B and N double element co-doping(a-n PC₈₀₀-B/N_x)on the graded porous carbon,and the doping results were verified by X-ray energy spectroscopy and X-ray photoelectron spectroscopy.B,N co-doping optimizes the chemical composition of carbon materials,improves the hydrophilicity of carbon materials,increases the pseudocapacitance performance of carbon materials,and can effectively improve the salt removal performance of carbon materials.In addition,through electrochemical kinetic analysis and density functional theory calculation,the mechanism of pore structure and B,N co-doping synergistically improving the desalting performance was elucidated.（2）Self-supporting electrodes are prepared by directly carbonizing basswood（CW）.Compared with coated electrodes,self-supported electrodes do not need binders,which can avoid the problem of further deterioration of hydrophilicity caused by binders.After carbonized wood,its own pore structure provides a channel for ion adsorption and transport.Using nickel as a catalyst,carbon nanotubes（CW/CNT）were grown on the surface and inside the pores of the self-supported electrode by chemical vapor deposition to construct a continuous channel for ion transport inside the electrode.Subsequently,nitrogen doping was used to further improve the wetted property of CW/CNT,effectively improve the utilization rate of CW/CNT electrode,and then improve its salt removal performance.