First-principles Study On The Electronic Structure Regulation Of Graphyne And Its Adsorption Performance For CH₄

With the global warming,rising sea levels and serious air pollution,the search for cleaner and sustainable new energy has become an urgent issue.Due to its rich natural resources and low CO2 emissions,CH₄ molecules are considered to be an alternative fuel to traditional fuel gasoline and coal.Therefore,various natural gas adsorbent materials have been extensively studied.Graphyne materials have the characteristics of large specific surface area,abundant chemical bonds and pores structure,and they have huge application potential in natural gas storage.In this paper,firstly,the effect of metal modification on the adsorption properties of CH₄ by the graphdiyne(GDY)system was studied.The results revealed that the modification of the Ti atom can significantly improve the adsorption properties of GDY on CH₄.The macroporous position of the alkyne chain is the most stable adsorption position.GDY system modified by Ti atoms can adsorb up to 24 CH₄ molecules.The average adsorption energy is-0.223 eV,and the adsorption capacity is 0.552 g g-1.Between the CH₄ molecule and substrate,in addition to the is H orbital and the 3d Ti orbital hybridization,also includes electrostatic interaction.Ti atom is in a unique macroporous position of the alkyne chain that provides sufficient adsorption space and site for CH₄.The positive electroconductivity of the CH₄ surface after adsorption decreases,reducing the influence of repulsion between the CH₄ molecules and producing strong electrostatic interactions with the negatively charged GDY,all beneficial for increasing the amount of adsorption.In order to improve the adsorption property of GDY on CH₄ molecules,doping and metal modification of functional modification were used to improve its electronic structure.Based on the GDY system,a nitrogen-doped graphdiyne(N-graphdiyne)model was successfully prepared experimentally,which has enlarged pores and enhanced electrochemical performance.The study found that the adsorption property of N-graphdiyne on CH₄ was significantly improved by the Mn-modified.Two Mn can adsorb 36 CH₄ upon double-sided modification,with average adsorption energy and storage capacities of-0.158 eV,and 0.585 g g-1,respectively.The adsorption of the first CH₄ molecule,which is mainly affected by the Mn atoms,involves a strong Coulomb interaction with Mn accompanied by the highest adsorption energy.Subsequently,an increase in the distance between CH₄ and Mn atoms increases leads to weakened Coulomb interaction.The adsorption of CH₄ molecules is then mainly affected by the van der Waals force between the substrate and the adsorption energy decreases.The N-graphdiyne system increases its adsorption space and sites owing to the doping of N atoms,the adsorption capacity is increased compared with GDY,but adsorption energy is reduced.In order to study the relationship between the adsorption performance and the pore size of the material,and to improve the adsorption energy of CH₄ molecules,this paper finally studied the adsorption property of metal modified graphyne(GY)system of CH₄ molecules,GY is an allotrope composed of sp and sp2 hybridized carbon atoms,its pores are smaller than GDY and N-graphdiyne.The study found that the most stable adsorption site for Ti atoms is the benzene ring.Ti-modified GY adsorbs up to 14 CH₄ molecules on double-sided,and the adsorption structure is stratified,with average adsorption energy is-0.300 eV,and adsorption capacity reaches 0.484 g g-1.The first layer of CH₄ was adsorbed,which is mainly affected by the Ti atoms.There is a strong Coulomb interaction between it and Ti.While the second layer of CH₄ molecules is due to the distance Ti atoms are far away,the interaction is mainly the electrostatic interaction between the positively charged CH₄ and the negatively charged GY and the van der Waals interaction between the CH₄ molecules.Intrinsic graphyne materials have weak adsorption energy for CH₄ molecules,and metal modified can improve the adsorption property of graphyne materials for CH₄.The study found that Ti and Mn atoms improved the electronic structure of graphyne materials,enhanced the interaction with CH₄ molecules,and stabilized the structure.The doping of N atoms makes the C atoms in the GDY positively charged and the N atoms negatively charged(-0.37e),which is conducive to the adsorption of the positively charged CH₄ on the surface,thereby increasing the adsorption sites of the CH₄ molecules.The adsorption property of CH₄ is closely related to the pore size of the two-dimensional adsorbent.When the pore size is small,the interaction between molecules is enhanced and the average adsorption energy is larger.On the contrary,the larger the pore size,the higher the adsorption capacity.