Molten Salt-assisted Activation For Synthesis Of Porous Carbon Materials And Their Performance

Porous carbon materials have great potential in adsorption and energy storage due to their large specific surface area,tunable pore structure,good conductivity and structural stability.Chemical activation method is a convenient and efficient method for the preparation of porous carbon materials,which mainly generates pores through the reaction of carbon atoms with the activation medium,and can significantly increase the specific surface area and pore volume.However,this method has the disadvantages of low yield of porous carbon,poor hydrophilicity,and the corrosiveness of most activation reagents to the environment.Based on this,a green molten salt assisted activation strategy was proposed to prepare porous carbon materials with large specific surface area and multi-stage pore structure.The effects of halide molten salt（Na Cl-KCl）,activator（K₂SO₄）and their synergistic effects on the composition,microstructure,adsorption properties and electrochemical properties of porous carbon materials were studied.The results are as follows:（1）Firstly,the effect of Na Cl-KCl molten salt on the structure and properties of porous carbon materials was studied.Phenolic resin was used as carbon source and Na Cl-KCl was used as auxiliary reagent for carbonization synthesis.In the roasting process,the volatilization characteristics of Na Cl-KCl molten salt played a pore-forming role,which was beneficial to the formation of pore structure.With the increase of Na Cl-KCl molten salt ratio,the specific surface area of porous carbon materials increase,the maximum specific surface area is 921 m²/g,and the pore size is 2.49 nm.The results of dye adsorption test showed that the prepared porous carbon materials showed good dye adsorption efficiency and cyclic stability.（2）The effect of single activator K₂SO₄ activated and the synergistic effect of K₂SO₄ activator and Na Cl-KCl molten salt on the composition,microstructure,yield and dye adsorption properties of the prepared porous carbon materials was studied.The results showed that the addition of oxygen-containing salt K₂SO₄ promoted the doping of sulfur and oxygen elements in carbon materials,which was conducive to enhancing the wettability of carbon materials and further promoting the adsorption of dye molecules and solution ions.But its strong oxidation reaction with carbon atoms can easily lead to the loss of carbon products（mass yield is 6.60%）.Under the synergistic effect of K₂SO₄ activator and Na Cl-KCl molten salt,due to the melting characteristics of Na Cl-KCl,it can promote the contact between precursor ions and improve the reaction rate.And reduce the product with gas loss,improve the quality yield（15.20%）.Finally,porous carbon materials with multi-stage pore structure were prepared,which have specific surface area of 1838 m²/g and pore volume of 1.18cm³/g.Compared with the single auxiliary reagent,the specific surface area increased significantly.And in the adsorption of rhodamine B can reach 99%removal rate,with excellent dye water cleaning effect.Multiple cyclic experiments further proved that it had cyclic stability in dye adsorption.（3）Based on the above experiments,the effect of carbonization temperature on the composition and structure of porous carbon materials was further studied,and its application in dye adsorption and supercapacitor was explored.The results show that the optimum preparation temperature of the S and O co-doped porous carbon material is 900°C.The prepared products had large specific surface area,and the pores were are mainly microporous and mesoporous.In the adsorption of rhodamine B dye,the product showed excellent dye removal rate.In the electrochemical test,the product was used as the active electrode material,and the optimized specific capacitance was296.7 F/g.And it still maintained a retention rate of 99.3%after 3500 cycles.The above results show that the porous carbon materials prepared by optimizing carbonization temperature have large specific surface area and good wettability,and have excellent performance in dye adsorption and supercapacitor.