Carbon Nanotube Prepared From Waste Face Masks And Application Of Supercapacitor Energy Storage

The outbreak and the continued epidemic of COVID-19 have caused a rapid increase in the consumption of medical face masks.The traditional treatments of waste face masks by landfilling and incinerating seriously undermine the sustainable development of the environment and resources.Facing the increasing demand for disposal of waste face masks and the severe situation,it is of great significance to develop efficient and environmentally friendly technologies for the recycling remanufacturing of waste face masks.Faced with the severe situation of the surge in the number of waste face masks and the difficulty of disposal,the waste face masks were treated by catalytic carbonization method to prepare high value-added carbon nanotubes and explore its application in the field of supercapacitor energy storage in this study,which provide a new method for the recycling and reuse of waste face masks.The discarded polypropylene face masks and activated carbon face masks were selected as the research objects,and prepared as hollow carbon nanotubes,bamboo-like carbon nanotubes,and activated carbon/carbon nanotube hybrid materials with different sizes and structures were obtained by different catalytic systems and preparation methods.The effects of different catalysts and reaction conditions on the morphology,structure,and energy storage performance of carbon nanotubes were investigated.The main research results are as follows:Taking waste polypropylene masks as the research object,the polypropylene mask-based carbon nanotubes were successfully fabricated by Ni-X（X=Mo,Mn）bimetallic catalyst combined with catalytic carbonization method.The effects of catalyst Ni/X molar ratio and carbonization temperature on the morphology,size and electrochemical performance of carbon nanotubes were investigated.The results show that adjusting the molar ratio of Ni/X can effectively reduce the diameter of carbon nanotubes and improve its yield,graphitization degree,crystallinity,and electrochemical performance of carbon nanotube electrode materials.CNT-Ni Mo5 and CNT-Ni Mn5 have the minimum average diameters of 12.4 nm and 14.6 nm,and the specific capacitance of which can reach 45.99 F/g（1 A/g）and 40.32 F/g（1 A/g）,respectively,when the molar ratio of Ni/X is 5 and at a carbonization temperature of 900℃.In order to obtain carbon nanotubes with excellent electrochemical performance,bamboo-like carbon nanotubes were successfully prepared by Ni-Fe bimetallic catalytic carbonization of waste polypropylene face masks.The effects of different Ni/Fe molar ratios and carbonization temperature on the growth of bamboo structure and electrochemical performance of carbon nanotubes were investigated.The results show that the interaction between Fe and Ni can form Fe Ni₃ alloy at 800～900℃to promote the growth of carbon nanotubes and obtained bamboo-like carbon nanotubes with regular structure,small diameters,high degree of graphitization,and large specific surface area.At a carbonization temperature of 900℃,when the molar ratio of Ni/Fe is 3,the CNT-Ni Fe3 has the minimum diameter of 15-20 nm,and the specific capacitance reaches 56.04F/g（1 A/g）.Its capacitance retention rate reaches 85.41%,after 10,000 charge-discharge cycles.The symmetric supercapacitor assembled based on CNT-Ni Fe3 has an energy density of 4.78Wh/kg（900 W/kg）,and the capacitance retention rate is 71.40%after 10,000 charge-discharge cycles.Taking waste activated carbon face masks as the research object,activated carbon/carbon nanotubes（AC/CNT）hybrid materials were prepared by nickel nitrate impregnation method with one-step and stepwise carbonization methods.The effects of catalytic carbonization methods and catalyst impregnation solution concentration on hybrid materials were studied.The results show that the stepwise carbonization method is beneficial to the preparation of AC/CNT hybrid materials.The specific capacitance of the AC/CNT-S/0.1 electrode material is 101.12 F/g（1 A/g）when the concentration of the impregnation solution is 0.1 mol/L.The capacitance retention and coulombic efficiency are 97.20%and 98.49%after 10,000 charge-discharge cycles,respectively.Meanwhile,the energy density of the assembled supercapacitor reaches 7.07 Wh/kg（900 W/kg）.