Tuning Of Photoelectric Properties Of Carbon Nanotubes And Its Application In Molecular Sieving Of Light-polluted Gases

Carbon nanotubes（CNTs）are one of the most widely studied materials in nanomaterials,and their unique one-dimensional porous structure and unique properties make them have broad application prospects in adsorption-separation,energy storage devices,catalysis,luminescent materials and other fields.Among them,the electronic structure and chemical properties of the precious metal and nitrogen doped carbon nanotubes are changed,so that they have better electrochemical performance,catalytic performance and magnetic properties.In this paper,the first-principles method of density functional theory was used to regulate the properties of carbon nanotubes by using nitrogen and precious metal doping to form adsorbents,and theoretical simulation is carried out on the regulated substrate structure for a variety of gases.The main contents of the research work are as follows:（1）In this thesis,the（8,0）type SWNTs were selected,and two different types of defective carbon nanotubes with single vacancy and double vacancy were constructed,as well as nitrogen doped composite structures at different defect locations.The optical properties of carbon nanotubes with different structures were calculated theoretically.It is found that the degeneracy of electronic band is significantly reduced by single and double vacancy defects,the band structure of the nitrogen-doped composite defect structure is significantly changed,the light absorption and reflection characteristics of the system are weakened,and there are different degrees of red shift or blue shift.The results show that the composite structure formed by nitrogen atom and vacancy has a significant effect on the regulation of optical properties of carbon nanotubes.（2）The electronic structure and reflection properties of ideal carbon nanotubes,nitrogen-containing single-pore defect carbon nanotubes（N₃-CNT）and platinum-nitrogen co-doped carbon nanotubes（Pt N₃-CNT）were investigated.The results show that,compared with the electronic structure diagram of CNTs,N₃-CNT forms a semi-full impurity band near the Fermi level,and Pt N₃-CNT forms an impurity band near the Fermi level with a positive electron mobility.Moreover,the bond length and bond Angle of the Pt N₃-CNT structure changed,and the N₃ group acted as the electron active center to withdraw electrons from the carbon tube and Pt atoms.Simultaneous density of states（DOS）and projected density of states（PDOS）,deformable charge（DCD）,ab initio molecular dynamics（AIMD）simulation,and the D-band center structure and position of Pt N₃-CNT and Pt C₃-CNT show that Pt atoms and nitrogen-containing deficient carbon nanotubes form chemical adsorption.Compared with Pt C₃-CNT system,it is more conducive to gas adsorption,and the adsorption capacity of gas molecules is effectively enhanced.（3）In this thesis,the density functional method was used to analyze the main components of air（N₂,O₂,H₂O,CO₂）and the most common air pollutants（NO_x,SO_x,CO,O₃,NH₃,H₂S）and other 12 kinds of gas molecules in platinum atoms modified nitrogen the adsorption behavior and electronic structure on the surface of doped（8,0）single-walled carbon nanotubes were investigated to study their air purification performance.By studying the geometry,adsorption energy and charge transfer of the adsorption system,it is shown that the coordination energies between Pt and the coordination atoms（C,N,O,and S atoms）in the gas molecules can stably adsorb these gases,and the adsorption energies range from-0.81～-4.28e V.The calculated DOS and PDOS diagrams further support the strong adsorption of Pt N₃-CNT on gas molecules.At the same time,the calculation of the recovery time of each adsorbed molecule at different temperatures shows that CO₂,H₂O and N₂ can be gradually desorbed at 298～498K,while the toxic gas is always stably adsorbed on the surface of Pt N₃-CNT.AIMD proves that Pt N₃-CNT has good thermal stability at high temperature up to 1000 K,which is very suitable as an adsorbent to remove toxic gases and achieve the purpose of air purification.The results of this study have certain reference value for the development of carbon-based air purification adsorbents with good adsorption performance and recovery performance.