First - Principles Study Of Porous Germanium For Gas Separation And Purification

In recent years, carbon nano materials have been concerned widely. Carbon is one of the most important elements in the nature, which has sp、sp2、sp3 and other kinds of orbital hybrid forms. In addition to the three-dimensional layered structure of graphite and the diamond with regular tetrahedral structure, carbon atoms can exist in the form of a zero dimensional fullerene, one-dimensional carbon nanotube and two-dimensional graphene. Among them, graphene as a two-dimensional structure with single atomic thickness, due to its simple symmetrical honeycomb atomic configuration, unique electronic band structure and excellent physical and chemical properties, since its birth, it attracts a lot of attention in the worldwide. When the optical, thermal, electrical, mechanical and other properties of graphene are thoroughly researched,scientists began turning their interest to the other two-dimensional structure composed of siliconand germanium. Silicene and germanene have been successfully synthesizedcurrently, and it has been proved experimentally and theoretically that they are also the two-dimensional honeycomb structure.However, it is difficult to prepare a perfect two-dimensional materialin the experiment, since a variety of defects cannot be removed completely.Therefore, the research of the defects in two-dimensionalmaterialsis necessary and the utilization of defects becomes an important wayfor functionalizationof two-dimensional nanomaterials.Vacancy point defects is the main form of two-dimensionalcrystal defect. These defects are likely to affect the structure and the function of materials critically, and make the two-dimensional nanomaterials exhibit many special properties.In this paper, the first-principles method is used to study the geometric and electronic structure of germenene with various defects.At the same time, the permeability and selectivity for common gases and inert gases through the porous of germanene with different defects are also calculated.Based on these, the way to use thegermanene with defects in the selective separation technology is discussed and the possibility to usegermaneneas a molecular filter material is also analyzed.Our results show that there are four kinds of structural defects in germanene: single vacancy defect (SV), Stone-Wales defect(SW),585 vacancydefect and 555777 double vacancy defect.The 555777 defect is the most stable structure after the optimization, secondlystable structure is the 585 defect.SV is more stable than SW, while SW is the most unstable structure.SV aperture defects as "V" shaped, SW,585 and 555777 is approximately circular aperture. The pore size is about 4.4A,4.9A and 4.9A,respectively. Simulation of the reaction process of gas and the porous germanium with defects was found. The 555777 displays anexcellentpermeability for hydrogen with low energy barrier, and for other common gases (H2O, N2, CO CO2, CH4) to maintain a large energy barrier. Furthermore,the selectivityof porous germanene for hydrogen to methane is high up to1031,which is considerable potential for germanenewith 555777 defect to be used as hydrogen separation material.In another way, the germanenewith 585 defect have high hydrogen and water permeability,which can be used as anappropriatewater purified film material.For the rare gases(He、Ne、 Ar), both germanenewith 555777 and 585 defectshave good selectivity,indicating that they arefavorablecandidates for the rare gas separation membrane.