The Adsorption Of Thiophene And Hydrogen Sulfide Performance Of Transition Metal Doped Zinc Oxide Nanotube:a First-Principles Study

Using the first-principle methods, we investigate the structures of transition metal and rare earth metal doped (ZnO)15 nanotube, and influence on adsorption performances of thiophene and H2S. The main results are listed as follows:1. By comparing the optimized TM (Ni/Co/Mn)-doped (ZnO)is nanotube, it is noted that the S-C bond are stretched in all adsorption models except for Zn4c-η2 and Mn3c-η1 models compared with free thiophene, illustrating that the doping of TM (Ni/Co/Mn) atom promotes to weaken the S-C bond. The stability analysis is carried out by calculating the adsorption energy of thiophene adsorption on TM (Ni/Co/Mn)-doped (ZnO)is nanotubes. For same bonding mode, the adsorption energy of thiophene adsorption on TM (Ni/Co/Mn)-doped nanotube is larger than that on prisine (ZnO)is nanotube, indicating that there is a noticeable improve in the reactivity ability with an impurity TM atom in the nanotube. The thiophene adsorption on TM (Ni/Co/Mn)-doped (ZnO)15 nanotube exhibited relative smaller energy gaps (0.52-1.46 eV), compared with the HOMO-LUMO gaps (1.92-1.95 eV) in thiophene adsorption on pristine (ZnO)15 nanotube. It can be seen that the addition of Ni/Co/Mn atoms should be responsible for the reduction of the HOMO-LUMO gap. The HOMO-LUMO gap of η1 bonding mode is smaller than that in η2 bonding mode for thiophene adsorption on TM (Ni/Co/Mn)-doped (ZnO)15 nanotubes. The v(C=C)Sym bands in the η2 bonding mode of thiophene adsorption on TM (Ni/Co/Mn)-doped (ZnO)15 nanotubes are shifted to lower wavenumber.2. We have investigated the adsorption of thiophene on the Ni and La co-doped (ZnO)15 nanotubes with density functional theory. The calculation results show that the stability of the nanotube increases with the doping of the Ni and La atom. It is found that the impurity of Ni and La atom should be mainly responsible for the reduction of the energy gap Eg. However, the decrease of the energy gap depends on the doping site of Ni and La atoms. This characteristic is attributed to the different coordinated species. In all thiophene adsorption structrues, the Ni2-Lal-η5 structrue has the largest adsorption energy of-2.78 eV. The result indicates that thiophene favors adsorption on La atom with the thiophene π-binding to a La atom site through all five atoms in the ring. We also observed that an elongation of the S-C bond among all thiophene adsorption modes is confirmed that Ni and La co-doped (ZnO)15 nanotube promote the activity of catalyst. The analysis of charge transfer and Mayer bond order of different adsorption modes explains the interaction between thiophene and Ni/La doped sites. The characteristic is also found in the partial density of states.3. H2S adsorption on pure and TM (Ni/Mn/Cu)-doped (ZnO)15 nanotubes. Compared with pure (ZnO)15 nanotube, the stability of the TM (Ni/Mn/Cu)-doped (ZnO)is nanotube increases with the doping of Ni/Mn/Cu. In addition, the doped sites have a significant effect on the binding energies per atom (Eb). When H2S is adsorbed on pure (ZnO)15 nanotube,there is no apparent changes in Zn4c-H2S, however, there is severe deformation occurs after the adsorption of H2S on Zn3c-H2S. The S-H bond in H2S is activated to broken while the H atom bonds with O atom in (ZnO)15 nanotube. Similar deformation characteristics exist in Ni4c-H2S, Mn3c-H2S, Cu4c-H2S structrues. When H2S is adsorbed on other structures, S-H-S bond in H2S is parallel with 0-TM-O bond in the pure and TM (Ni/Mn/Cu)-doped (ZnO)15 nanotube.