Study Of Electro-magnetic And Kinetic Properties For Carbon-based Two-dimensional Materials

In this thesis,graphene and MXenes（Ti₂C）are the mianly carbon-based two-dimensional materials.With the method of metal/non-metal atom doping and defect designing,a series of single atomic catalysts,seawater desalination membranes and molecular detector models were established.By using first-principles calculation and molecular dynamics simulation,the following properties were investigated theoretically,including the electro-magnetic,optical and dynamic properties.Meanwhile,the"structure-property"correspondence was built.The main research results are divided into the three parts as follow:（1）We take graphene as the major carbon-based two-dimensional materials in this part.Using the first-principles calculation,the effect of some factors（metal types,defect sizes,nitrogen atoms number and arrangement）on the electro-magnetic properties of graphene derivative materials with transition metal and nitrogen atoms co-doped（TM@N_xC_y-GR）are systematically investigated.Firstly,TM@N₃-GR（the minimum defect size）and TM@N₇-GR（the maximum defect size）materials always possess metallic property regardless the metal type.However,doping different TM can regulate the medium defects（TM@N₂C₂-GR-I and TM@N₂C₂-GR-II）among metallicity,half-metallicity and semiconductivity.Secondly,the different TM and defect types largely affects the magnetic moment between 0-5μB.Thirdly,the spin density and projected density of state calculations show that the net charges of the defect structure are mainly located near the hole,and the magnetic regulation comes from the coupling of TM-d orbital with carbon（nitrogen）-s（p）orbitals.The present study provides abundant valuable information for the TM@Nx Cy-GR materials designs and applicants in the future.（2）The functional application for graphene is the focus of the present charpter.Firstly,based on the last reseach results:with the effect of metal types,most of TM@N₄-GR-Ⅰand TM@N₄-GR-Ⅱmaterials are metallicity and semiconductivity,respectively.Combining the high catalytic performance of single Fe atom,we compare the oxygen reduction ability of Fe@N₄-GR-Ⅰand Fe@N₄-GR-Ⅱusing the first-principle calculation.The basic reaction path of various intermediates is determined as follow:*O₂→*OOH→*O→*OH→*H₂O.Secondly,we design four kinds of seawater desalination membranes with different defect size and different founctional groups.The filtration effects of sodium ions and chloride ions as well as water flux are evaluated by applying different pressures.We found that the big-size defected graphene with-NH under 200MPa is suitable as seawater desalination membrane.Theses two works have promoted the connection between theoretical simulation and practical production.（3）Employing first principles calculations,we systematically investigate the geometrical and electronic structures of pure,titanium defected and carbon defected Ti₂C materials.Firstly,the defected Ti₂C exhibits stronger metallic property than pure Ti₂C due to the enhanced density of Ti-d orbital state near the fermi level.Secondly,we study the adsorption as well as the infrared spectrum response of the four kinds of gas molecules（CH₄,NH₃,CO and NO）on different Ti₂C surfaces.Simulations show that CO and NO molecules are chemically adsorbed on all Ti₂C surface with similar adsorption sites.With stronger peak intensity,CO and NO are selected as ideal probe molecules to identify Ti₂C materials.However,CH₄ and NH₃ molecules will be dissociated on Ti₂C surface.Thirdly,the projected density of state as well as the crystal orbital Hamilton population calculations show that the redshift in infrared spectrum of CO and NO molecules originates from the decreasing bonding strength of probe molecules.Finally,we investigate the dynamic property for CO and NO adsorbed on different Ti₂C to determine the stability of adsorption structures.The present work provides a novel method to identify the Ti₂C materials as well as defected types.