Preparation Of Biomass Porous Carbon Electrode Materials By Plant Absorption Of Nano-polystyrene

In the background of the energy crisis,it is particularly important to develop environmentally friendly and green energy storage technology.Supercapacitors have attracted extensive attention because of their high power density,long cycle life,good safety and reliability.As a key component of supercapacitors,electrode materials are the decisive factors that affect the electrochemical performance of supercapacitors.In the selection of electrode active materials,biomass carbon has been widely used because of its low cost,wide source,and good conductivity.The main disadvantage of traditional carbon-based supercapacitors is low energy density,and excellent electrode materials can be obtained by modification.At present,thse study of micro-nano plastics in academic circles is mostly in the aspects of environment,biological toxicity and so on.It is killing two birds with one stone to recycle and reuse such pollutants in a closed loop form.In this master’s thesis,Eichhornia crassipes and Pistia stratiotes are selected as biomass precursors,and nano-plastics in water environment are recovered by plant absorption.Carbon-based materials are prepared by pyrolysis/carbonization at high temperature and applied to supercapacitors.The main research contents are as follows:(1)Eichhornia crassipes is a floating aquatic plant with well-developed roots and unique hollow gourd-shaped stems,which is widely studied as an energy plant.In this chapter,two kinds of nano-polystyrene with different particle sizes are prepared(49nm and 240 nm),and Eichhornia crassipes is used as adsorbent to absorb nano-polystyrene in water environment.The absorption of nano-plastics by Eichhornia crassipes is confirmed by laser confocal microscope and ultraviolet-visible absorption spectrum.The growth status of plants exposed to different concentrations(12.5/25/50/100 μg/m L)of nano-plastic solutions is compared,and it is found that nano-plastics will affect the normal development of plants in the process of being absorbed by plants.When Eichhornia crassipes and nano-plastic are co-carbonized,plastic particles will make holes in the carbon material,which further affects the electrochemical properties of the material.The electrochemical performance of the carbonized material is tested by three-electrode system.By comparison,the capacity of the sample with the best performance was 519 F/g at 0.5 A/g which is nearly doubled compared with that of the control group.The device is charged and discharged for 10,000 cycles at 1 A/g current density,and the capacity retention rate of the device is 77 %.(2)Pistia stratiotes has obvious advantages such as fast growth and reproduction,easy fishing,and great potential for absorbing and accumulating various pollutants.Choosing Pistia stratiotes to absorb nano-polystyrene with different charges.Due to the different electrostatic interaction between plant roots and nano-plastics with positive/negative charges,the particle concentration in different plant organs(roots/shoots)is also different.The structural changes of carbon materials in roots/leaves of nano-polystyrene after co-carbonization with plants are investigated.SEM,BET,XPS and other methods proved that nano-plastics can optimize the structure of Pistia stratiotes root carbon materials.Tested by three-electrode system,the material has good electrochemical performance.The specific capacitance of the sample with the best performance is 252 F/g at 0.5 A/g,and the capacity remains stable compared with the initial value after 10,000 cycles of 1 A/g charging and discharging.The experimental results show that nano-polystyrene will play a positive role in improving the electrochemical properties of root carbon materials,and the specific capacitance and cycle stability of the materials have been comprehensively improved.Although Eichhornia crassipes and Pistia stratiotes are both aquatic plants,the electrochemical properties of the prepared electrode materials are different due to the different plant structures.The unique gourd-shaped stem of Eichhornia crassipes gives plants a looser and more porous structure,and it is more efficient for the transportation and accumulation of nano-plastics.The electrode material obtained by carbonization of this precursor also has a higher specific capacitance.The dense structure of the root of Pistia stratiotes leads to the lower specific surface area of electrode materials after carbonization,and the lower capacity value after co-carbonization with nano-plastics.The low density structure of leaves ensures the smooth stomata of Pistia stratiotes,so the specific surface area of carbonized materials is large.