Modification Of Biochar Electrodes And Study Of Capacitive Deionisation Performance

The Earth is rich in water,but only 0.4%of freshwater resources are potable.The shortage of fresh water resources seriously affects the sustainable development of human society.Seawater desalination has been regarded as one of the most effective solutions.The traditional desalting methods include multi-effect distillation,multi-stage flash evaporation,electrodialysis and reverse osmosis.These technologies require a large amount of energy consumption,while Capacitive deionization（CDI）technology has been widely used in seawater desalination in recent years due to its low energy consumption,no secondary pollution and often use of low-cost electrode materials.Based on the working principle of double-layer electroadsorption,it is the focus of current research to prepare a kind of cheap and easily available electrode material with high specific surface area,suitable pore size distribution,excellent hydrophilicity and high conductivity.Prolifera biomass is a kind of algae growing in the ocean,because its cell wall structure contains special oxygen-containing functional groups,which is conducive to the formation of rich porous carbon after carbonization,so it can be used as a potential electrode material for capacitive deion desalination.In this thesis,Enteromorpha prolifera biomass as carbon source,select different activators to modify it to prepare the birth material porous carbon,and on the basis of its modification load manganese dioxide,study its characteristic structure and capacitance deion performance.The main research contents and results are as follows:（1）Taking Prolifhia morpha biomass as carbon source,the biomass porous carbon materials with different morphologic structures were prepared by using KOH,H₃PO₄ and Zn Cl₂ activators.Through the morphologic structure characterization,electrochemical performance test and capacitance deionization performance test,the results were obtained as follows:Among the three activation modes,the carbon material prepared by KOH activation has high specific surface area,appropriate pore size distribution and excellent specific capacitance,which can reach 217.75F g^-1 at 0.5A g^-1current density.In 60 m L Na Cl solution(500mg L^-1),the amount of salt removal can reach 25.29mg g^-1,indicating that K-AC carbon electrode（KOH modified biochar）is more suitable for capacitive deion desalination as electrode material.（2）The effects of KOH activation mode on the structure of biochar at different pyrolysis temperatures（800℃,900℃）and different amounts of activators（alkali-carbon mass ratio of 2:1,3:1 and 4:1）were further explored.The optimum activation conditions and CDI operating conditions were selected through the morphology and structure characterization,electrochemical performance testing and capacitive deionization testing of the samples.The results show that the specific capacitance of 4KPC-800 carbon electrode（activation temperature is 800℃,the ratio of alkali to carbon mass is 4:1）can reach 386.06F g^-1under the current density of 0.5A g^-1,and under the operating condition of 1.2V voltage and 10m L min^-1liquid flow rate,It showed the best electroadsorption capacity(27.33mg g^-1)for 60 m L Na Cl solution(500mg L^-1).（3）Using potassium permanganate and manganese sulfate as raw materials,manganese dioxide was synthesized under hydrothermal conditions.Biochar/Mn O₂ composites were prepared by loading manganese dioxide with 4KPC-800 porous material prepared in the previous chapter according to different dosage（mass ratio of Mn O₂ to biochar was 1:2,1:1 and 2:1）.The results of structural characterization,electrochemical performance test and capacitance deionization test are as follows:Doping of Mn O₂improves the pseudocapacitance and capacitance deionization performance of biochar.At 0.5A g^-1 current density,the specific capacitance of 0.5Mn O₂/AC carbon electrode（mass ratio of Mn O₂ to biochar is 1:2）can reach 595.25F g^-1.In 60 m L Na Cl solution(500 mg L^-1),the high salinity of 32.53mg g^-1 can be achieved.The results show that 0.5Mn O₂/AC electrode has the fastest adsorption response among the three composite electrodes.These studies not only realize the utilization of waste resources,but also provide strategies for the application of Enteromorpha biomass as a new environment-friendly material in seawater desalination.