| With the increasing seriousness of water pollution, water shortage is one of the major problem faced in China, and the desalination technology used in seawater and wastewater is an important way to solve this problem. Electro-adsorption desalination has become one of the most important desalination methods due to its low energy consumption and lesser pollution to the environment. While, the key to the desalination efficiency lies in the properties of the electrode materials, such as the surface area and pore structure. Therefore, the preparation method for electrode materials with high specific surface area and rich pore structure has been the focus of scientific research in.Using peanut shell biocar as the precursor, porous carbon material for the desalination electrode was obtained by KOH activation. The effects of the ratio of KOH and biomass, activation temperature and activation time on the specific surface area and pore structure of porous carbon were studied. The adsorption behavior of obtained porous carbon for methylene blue from solution were also discussed, and the basic parameters, such as adsorption capacity, kinetics and thermodynamics, were calculated. Then, the electrochemical performance of the porous carbon electrode was studied in detail. On this basis, the nitrogen doping porous carbons were prepared and its electrochemical performance were preliminary studied. The mainly conclusions were as followed:(1) The adsorptive capacity of the porous carbon for methylene blue was found to be highest with preparation conditions at1.5:1of the impregnation ratio (vKOH/mbiomass),800℃of activation temperature, and90min of activation time. Results shown that the surface area of the porous carbon obtained at optimum conditions was597.93m2·g-1, higher than peanut shell biocar (12.28m2·g-1). In the adsorption test, factors of the solution pH value, the initial concentration and the temperature were effected the adsorption of methylene blue from solution, and the porous carbon appeared to have better adsorption capacity than the peanut shell biochar with the value of144.55mg·g-1. When the pH value was6, the adsorption of methylene blue by porous carbon was best. With the increase of the initial concentration of methylene blue, the removal rate was decreased gradually. When the initial concentration of methylene blue increased from100mg·L-1to400mg·L-1, the equilibrium time increased from100min to500min, the removal rate decreased from99.25%to54.35%.(2) The porous carbon prepared under the optimum conditions showed better electro-adsorption properties in cyclic voltammetry analysis. Higher the scan rate, the smaller the electrode capacitance. With the increasing of the salt concentration, the electrode capacitance and the ion adsorption capacity were also increased. Smaller the ionic radius and bigger the electric charge, better the electro-adsorption performance. The impedance test shown that the resistance of porous carbon electrodes was lower than the peanut shell bio-char electrodes, showed better electric conductive. Constant current charge-discharge test found that the porous carbon electrodes had good stability and circulation regeneration. When the concentration of NaCl solution was20ppm, the desalting efficiency of the peanut shell biochar electrode was around25%, while the he desalting efficiency of the porous carbon electrode could reach98%. With the increase of the concentration of NaCl solution, the electrical conductivity of water increases gradually, the desalting efficiency was gradually reduced.(3) The nitrogen doping porous carbon electrodes were prepared by taking the melamine as raw materials. XPS characterization shown that the nitrogen content of the porous carbon was increased after melamine dropping. The specific capacitance of nitrogen doped porous carbon electrode was53.8F·g-1, which was higher than the porous carbon electrode41.6F·g-1, and the desalination tests shown that desalting performance of the nitrogen doping porous carbon electrodes was also improved. |
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