First-principles Study On The Adsorption Of CO 2 And SO 2 Gas Molecules By Doped Boron Nitride Nanotubes

Nowadays,carbon dioxide(CO2)and sulfur dioxide(SO2)have become one of the major causes of global warming and haze,which have serious effects on human and ecosystems.At present,the detection and monitoring for CO2 and SO2 has more urgent needs and broad application prospects in the atmospheric environment safety and industrial applications.Effective improvement of the physical and chemical properties for the nanotube due to the surface of the nanotube doping adsorption modification,which can expand the nanotube application in the CO2 and SO2 sensor area.In this paper,using the first-principles calculation,the structure,electronic and optical properties of the boron nitride nanotube(pristine(8,0)BNNT)and its doping and adsorption are studied,respectively.This research can offer theoretical properties analysis for development of gas detection sensor in the industrial application.The main research and conclusions are summarized as follows.(1)The structures of the pristine BNNT and modified BNNTs(which are a single B atom(B site)or a single N atom(N site)in the middle of the supercell is substituted by an impurity Al and Si atom,respectively)are optimized,and which verified the rationality of the structures and the appropriateness of the used calculation method.Also,the adsorption energies of doped BNNTs where CO2 and SO2 molecules adsorbed on Al atom or Si atom are calculated,respectively.The results show that that the adsorption processes are exothermically adsorbed with negative adsorption energies,and CO2 and SO2 gas molecules adsorbed on BNNT structure which is replaced by the B site is more stable.(2)The band structure,band gap and density of states are studied for the electronic properties of pristine BNNT and modified BNNTs.Also,the variation trend of band structure and total density of states(TDOS),and the change of band gap and the origin of the impurity are analyzed.It can be found that the TDOS shifts to the lower energy region and a few new asymmetry impurity states are emerged in the proximity of the Fermi level for modified BNNTs which are compared with the pristine BNNT.Additionally,the energy shift eventually resulted in a large reduction of the band gapand the BNNT doped with N site is more obvious than the BNNT doped with B site.The asymmetry impurity states of CO2 molecule adsorption on Al-doped BNNT are mainly composed by the C-2p states hybridized with a bit O-2p and Al-3p states.And the asymmetry impurity states of SO2 molecule adsorption on Si-doped BNNT are mainly contributed by the S-3p states hybridized with a little O-2p and Si-3p states.(3)In the calculations of optical properties of pristine BNNT and modified BNNTs,the dielectric function,refractive index and extinction coefficient as well as absorption coefficient are discussed.Compared with the pristine BNNT,the results indicate that the static dielectric constants and static refractive indexes of Al-doped BNNT and CO2 molecule adsorption on Al-doped BNNT are increased;the slight red-shifts are shown in the main peaks of the real parts(?1)of dielectric functions of AlN-BNNTT and CO2-AlN-BNNT,while CO2-AlB-BNNT and AlB-BNNT are shown in a slight blue-shift.The slight blue-shifts are displayed on the main peaks of the imaginary part(?2)of dielectric functions of AlN-BNNTT,CO2-AlN-BNNT,AlB-BNNT and C02-AlB-BNNT compared with the pristine BNNT.Additionally,their main peak value and secondary peak value of the extinction coefficient k are reduced,and the main peak of the CO2-AlN-BNNT and the secondary peak of the AlN-BNNT are shown the largest reduction,respectively.What's more,the slight blue-shifts are demonstrated on the main peak of the extinction coefficient k of AlN-BNNTT,CO2-AlN-BNNT and AlN-BNNT,while CO2-AlB-BNNT has a slight red-shift;the slight red-shifts are observed on the secondary peak of the extinction coefficient k for modified BNNTs.In the low energy region 0.300eV-7.674eV,the slight blue-shifts are shown in absorption peak of the absorption coefficient of AlN-BNNTT,CO2-AlN-BNNT and AlB-BNNT,while CO2-AlB-BNNT has no significant changes;while the slight red-shifts are shown in absorption peak of the absorption coefficient of the modified BNNTs in the energy region 7.674eV-35eV.For the Si-doped BNNT and SO2 molecule adsorption on Si--doped BNNT,compared with the pristine BNNT,the results indicate that the static dielectric constants and static refractive indexes are increased;the slight blue-shifts are shown in the main peaks of the real parts(?1)of dielectric functions of SiB-BNNT and SO2-SiB-BNNT,while SiN-BNNT and SO2-SiN-BNNT are shown in a slight red-shift.The slight blue-shifts are displayed on the main peaks of the imaginary part(?2)of dielectric functions of SiB-BNNT,SO2-SiB-BNNT and SO2-SiN-BNNT compared with the pristine BNNT,while SiN-BNNT is shown in a slight red-shift.Additionally,their main peak value and secondary peak value of the extinction coefficient k are reduced,and the slight blue-shifts are demonstrated on the main peak of the extinction coefficient k of SiB-BNNT and SO2-SiB-BNNT,while SiN-BNNT and SO2-SiN-BNNT have a slight red-shift;the slight red-shifts are observed on the secondary peak of the extinction coefficient k for modified BNNTs.In the low energy region 3.500eV-8.500eV,the slight red-shifts are shown in absorption peak of the absorption coefficient of SiB-BNNT,SiN-BNNT and SO2-SiN-BNNT,while S02-SiB-BNNT has a slight blue-shift.