Biomass Derived Nitrogen Doped Activated Carbon Fiber For Capacitive Deionization

With the rapid expansion of modern industry and agriculture,the water crisis has begun to become a barrier to the development of human civilization.As is known to all,the water resource on our planet is very abundant,however,almost 98%of the water is saline water?seawater or brackish water?,which is not suitable for industrial and agricultural consumption.On the other hand,the freshwater is stored in the polar regions in the form of solids,which makes it more difficult to put to use.Thus,the desalination of seawater and brackish water has become the only solution that is expected to fundamentally solve the water crisis.Nowadays,various desalination technologies have been developed:from the most primitive distillation,ion exchange,to emerging membrane desalination technologies?reverse osmosis,electrodialysis?,and to distillation technology variants?membrane distillation,flash evaporation?etc.However,current desalination technologies all have their fatal flaws,including high energy consumption,low efficiency,membrane fouling,secondary pollution etc.Capacitance deionization?CDI?,as a new type of electro-driven technology,has attracted wide attention from the industry in the 1980s and has quickly become a major focus of researchers due to its low energy consumption,high efficiency,and no secondary pollution.Electrode material,as the key component of CDI,has been attracting the most attention.In this work,biomass?cocoon?derived carbon fibers were studied and used as electrode materials in the CDI.The relationship between the deionization performance of the capacitor and the structure and morphology of the material was systematically studied and further optimized.The thermodynamics,kinetics,and energy consumption of capacitive deionization were further analyzed,the result shows:1.The biomass derived nitrogen doped activated carbon fiber electrodes have excellent electrochemical performance(specific capacitance:236.03 F g^-1);2.The biomass derived nitrogen doped activated carbon fiber electrode have good electrosorption capacity(up to 16.56 mg g^-1 in 1000 mg L^-1 NaCl solution).3.Both electrochemical and electrosorption performances of the biomass derived nitrogen doped activated carbon fiber electrodes was significantly improved after the activation process,which is due to the increasement of surface area and the optimization of its pore size distribution.4.The electrosorption process of both od our materials follows the pseudo-first-order kinetics,and the adsorption rate constant?k?rises first and then decreases with the increase of applied voltage after 1.2 V.The reason for the rise of k is that the electric field strength increases with the voltage,while the decrease of k after 1.2 V is that the chemical reaction inhibits the rate of the electrosorption process;5.The electrosorption process can be fitted into Langmuir adsorption model,which shows that the adsorption process of ions is monolayer adsorption,and the adsorption process is mainly physical adsorption.6.The energy consumption analysis shows that voltage has a great influence on the energy consumption of CDI devices,especially after 1.2 V,which indicates that it is critical to control the voltage below that splitting voltage of water.