| At present,activated carbon has been widely used in petrochemical,food,medicine,aerospace and other fields,and rice husk contains more than 40%carbon,which is a potential carbon source for the preparation of activated carbon.The pore structure of activated carbon with high specific surface area obtained by the existing activated carbon preparation methods is mainly micropores.However,mesoporous activated carbon is also very important in some application fields of activated carbon.Therefore,two-stage activation is used in this paper to prepare mesoporous activated carbon with high specific surface area.In this paper,rice husk was used as the raw material,phosphoric acid activation was first carried out,and then alkali activation experiment was carried out to obtain mesoporous activated carbon products with high specific surface area.The specific surface area was more than 3000 m2/g,and the mesoporous in proportion was more than 80%.Finally,the adsorption performance of liquid phenol and the electrochemical performance of supercapacitor were investigated.Firstly,various parameters in the phosphoric acid activation experiment of rice husk were explored and analyzed to obtain the optimal phosphoric acid activation process parameters:the impregnation ratio of phosphoric acid was 1.8:1;the activation temperature was 550℃;and the activation time was 60 min.The yield,methylene blue adsorption value,iodine adsorption value and specific surface area of phosphoric acid activation product were34.6%,291.8 mg/g,1078 mg/g and 1314 m2/g,respectively.After desilication,the ash content of activated phosphoric acid decreased significantly,and the specific surface area and mesopore volume also increased,indicating the beneficial effect of desilication process.However,the specific surface area after desilication did not reach 2000 m2/g,which did not reach the target of activated carbon with high specific surface area in this paper.According to the elemental analysis before and after desilication,the content of C increased by 25.36%after desilication.In infrared analysis,the peak value of chemical bonds or functional groups related to Si O2 decreased obviously after desilication.Raman spectroscopy showed that the disorder degree of carbon structure increased after desilication.Then the alkali activation process parameters of the phosphoric acid activation product and its desilication samples were studied and analyzed.The optimal two-stage activation process parameters were no desilication,the ratio of agent to material was 4:1,the activation temperature was 850℃,and the activation time was 120 min.The total yield,specific surface area and mesopore in proportion were 15.77%,3055 m2/g and 81.46%,respectively.The pore structure parameters reached the expected value in this paper.It was found that the specific surface area of the two activation products was very similar to that of the direct alkali activation products of rice husk coke,but the mesopore ratio was very different,which provided samples for the influence of the mesopore in proportion difference on the application results in the future investigation.Through the elemental analysis of RHC,P-RH,K-RH and PK-RH samples,it can be seen that the carbon content of PK-RH is the highest,while the oxygen content is the lowest.The peak area of PK-RH oxygen-containing functional group was also lower than that of K-RHC.Raman analysis showed that the carbon structure of PK-RH was less disordered than that of K-RHC.In addition,the adsorption performance of each sample in phenol was studied.In the phenol adsorption test,it was found that the adsorption performance of PK-RH was the best,followed by K-RHC and P-RH,and the adsorption performance of RHC ranked the last.The adsorption value of PK-RH in 2 g/L high concentration phenol solution was as high as 437.02mg/g,which was higher than that of K-RHC by more than 20%.The reason can be attributed to that mesopores,as molecular channels,can provide more paths in the adsorption process and have a positive influence on the adsorption process,which is more obvious in the adsorption of high concentration of pollutants.When the p H of phenol solution is 6,the adsorption performance of activated carbon is the best.Through the analysis of adsorption kinetics,it was concluded that the adsorption test of phenol could be well described by the Langmuir model and the pseudo-second order kinetic model,which indicated that the adsorption of phenol was an exothermic process and was mainly controlled by chemisorption.The adsorption of phenol by activated carbon is mainly through"donor-acceptor effect"and"π-πdispersion interaction"to the inner surface.Lastly,the electrochemical performance of supercapacitors prepared from several carbon materials was analyzed.It was found that the specific capacitance of PK-RH was the highest,up to 358.8 F/g,followed by K-RHC,the value of which was 278.4 F/g.The minimum value of P-RH was only 138.0 F/g.The trend of specific capacitance obtained by GCD curve is the same.The alternating current impedance test shows that the resistance of electrolyte ion movement of PK-RH capacitor is the least.In addition,the relationship between power density and energy density was analyzed.When the power density increased to more than 3times,the energy density only decreased by 22.55%,indicating that PK-RH is an excellent electrode material for preparing supercapacitors. |
