Theoretical Study On The Electronic Structure Of Chalcogenides And Corresponding Adsorption For Small Molecule

Owing to the unique electronic and optical properties,the graphene-like Transition metal dichalcogenides has drawn a great deal of attention.Especially for the over high surface-to-volume ratio and mechanical stability make it great potential in chemical sensors and catalysts.Based on the density functional theory,we employ the substitutional doping and design the vacancy defect on surface of a series of metal chalcogenides including MoS2,MoSe2 and WS2.Then we investigate the effect of adsorption for small gas molecule.Moreover,we also further discuss for the reaction mechanism about geometrical configuration and charge transfer,as well as the electronic structure.The main contents are listed as follows:1.Comparing for the theorectical adsorption of NO on pure and B-,P-and Cl-doped monolayer MoS2.The study shows that pure MoS2 is only physisorption toward NO,while the doped system all express improvement in adsorption.Especially for the B-doped MoS2 has the strongest adsorption,and the change of band gap is obvious.But it is too sturdy to chemical bind with NO,making the gas difficult for desorption.And Cl-doped is possibly not reactive enough to NO,only slightly stronger than the pure system.P-doped MoS2 has moderate chemical adsorption toward NO,meanwhile the band gap has outstanding variation,greatly improve the conductivity.So we think P may be relative proper doping material than B-and Cl-doped MoS2 in detecting NO gas.2.The theoretical adsorption of NH3 on pure and Si-doped,Fe-doped monolayer MoSe2 has been explored.The results indicate that NH3 is physisorbed on pure MoSe2.Fe atom doped in interbedded Mo site,which would make little direct influence on NH3 adsorption,the adsorption energy is partial small.While Fe doped in external Se site can adsorb NH3 molecule directly.The adsorption energy is largly improved.However the variation of band gap is still difficult to define;The Si-doped MoSe2 is chemically bind with NO and the adsorption energy is proper.NH3 molecule donate charge to substrate,make evident change on the band gap,and improve the conductivity.So the Si-doped MoSe2 would be better than Fe-doped in strengthening the sensitivity of NH3 adsorption.3.By theoretical simulation for the behavior of N02 adsorption on pure,W and S vacancy on WS2 system.The results indicate that interbedded W vacancy on WS2 is adverse to NO2 adsorption.Pure WS2 has extremely weak adsorption toward NO2,almost shows no catalytic ability.Owing to exposure to more surfacial active site,the S vacancy shows better decomposition effects.The single S vacancy is strongly attractive for O atom in NO2,make NO2 breaking the bond,the remained NO is free above.The two S vacancy similarly catalyse NO2 decomposing as O and NO,meanwhile the NO(with N end)is also adsorbed on S vacancy site,the NO bond is stretched,which is in favor of further desorption.The electrons are transferred from substrate to adsorbate,and make different effect on the energy band of S vacancy system.Moreover,as the number of S vacancy grows,the adsorption energy keeps increasing,however the band gap keep narrowed.Different concentration of S vacancy would lead to different catalytic effect for NO2 decomposition.