Preparation Of Bagasse-based Phosphorus-doped Activated Carbon And Its La³⁺ Electrosorption Properties

This work designed a strategy for preparing phosphorus doping activated carbon and MnO₂-loaded phosphorus-doped activated carbon,using bagasse as raw materials and phytic acid as activator and phosphorus dopant.The effects of activation temperature and impregnation ratio on the iodine adsorption value,methylene blue adsorption value,La³⁺adsorption capacity and electrochemical performance of phosphorus-doped activated carbon were discussed.To reveal the active sites and mechanism of phosphorus-doped activated carbons,the pore structure,binding form and hydrophilicity of phosphorus-doped activated carbons were characterized by nitrogen adsorption-desorption isotherm,SEM,XPS,FT-IR and contact angle measuring instrument,etc.The theoretical will support for the electrosorption of phosphorus-doped nanoporous carbons to remove rare earth elements.The research contents and results are as follows:（1）Phosphorus doped activated carbon（PAC）was prepared with bagasse as biomass carbon source,phytic acid as P source and activator.The results show that under the activation and doping of phytic acid,the adsorption capacity and specific surface area of activated carbon have been greatly improved,and phosphorus doping is also achieved;the introduction of P-containing functional groups such as C-O-P,C-P-O and C-P=O C-O-P,C-P-O and C-P=O,the hydrophilicity of activated carbon is improved,and the active sites required for pseudocapacitive reaction are provided,thereby improving its electrochemical performance;the capacitive behavior of activated carbon is mainly affected by pseudocapacitive and electric double layer reactions.When the activation temperature and impregnation ratio were 900℃and1.5,respectively,the specific surface area was 1733.81 m²·g^-1,the iodine adsorption value was 1321 mg·g^-1,the methylene blue adsorption value was 255 mg·g^-1,and the specific capacitance was 222 F·g^-1,all of them reaching the maximum;the capacitance retention rate is still as high as 98.77%after 9000 cycles,indicating that PAC-900-1.5 has the potential to be used as a supercapacitor electrode.（2）P-doped activated carbon electrode was used for electrosorption separation of La³⁺in solution.The results show that the La³⁺electrosorption capacity of P-doped activated carbon electrode increases first and then decreases with the increase of activation temperature and impregnation ratio.The P-doped activated carbon prepared under the condition of activation temperature of 900℃and impregnation ratio of 1.5 has the best La³⁺electrosorption performance,which is as high as 88.89mg·g^-1 at 1.8 V operating voltage,86%higher than that of un-doped carbon.The activation of phytic acid is conductive to enhance EDLs adsorption and introduce Faraday adsorption active sites such as C-P-O,C-P=O and P-O-P;Driven by the electric field,La³⁺can not only enter the pore structure of PAC-900 to form EDLs,but also form P₂-O-(La³⁺)and La-O-P with surface groups through Faraday reaction.Furthermore,PAC has also excellent selective behavior for La³⁺in the La³⁺/Na⁺and La³⁺/Ca²⁺co-existence system,and the selection rate can reach 94.08%and 90.98%.（3）The MnO₂-loaded phosphorus-doped activated carbon composites（1/2-MnO₂@PAC-900-1.5）was prepared by redox precipitation method for electrosorption of La³⁺in solution.The results show that La³⁺electrosorption performance of 1/2-MnO₂@PAC-900-1.5 is greatly enhanced after loading MnO₂,which reaches 93.02 mg·g^-1 at 1.2 V,45.34%higher than PAC-900-1.5;After 10adsorption-desorption cycles,the adsorption capacity and retention rate were 50.82mg·g^-1 and 54.64%,respectively;La³⁺enters into the pore structure of1/2-MnO₂@PAC-900-1.5 under the action of electric field driving force during the electrosorption process to form an electric double layer,and further undergoes a Faradaic adsorption reaction with MnO₂ through surface adsorption and intercalation.