| Nowadays, energy shortage and environmental pollution are increasing, which attractted the worldwide highly attention. Ti O2 is widely used in environmental pollution control and photocatalytic application, because it has some properties such as chemical stability, non-toxic harmless, features of easy preparation and photocatalytic ability strong, and played an important role in environment problem and energy utilization. However, photocatalytic activity of Ti O2 is relatively low. Through the doping of impurity ions, to prevent photogenerated holes and the recombination of photogenerated electrons, then to improve the photocatalytic activity of Ti O2. At the same time, the study on microstructure characteristics and optical properties of Ti O2 surface adsorption of gas molecules, which can provide the theoretical basis for experimental study of Ti O2 optical gas sensors.Frist of all in this paper, under the first-principles plane-wave ultrasoft pseudopotential method based on density functional theory(DFT) system, simulate computation geometric structure, band structure, density of states, optical properties and defect formation energy of N and Ru,Rh,Pd doped rutile Ti O2. The calculation results show that the N and Ru, Rh, Pd Co doped rutile Ti O2, 4D electron of Ru, Rh, Pd will be formed the donor level and acceptor level, the synergistic effect of shallow acceptor level formed with N doping, provided an intermediate step to electronic transition, improved the probability of electronic transition in a certain extent, thus to improve the photocatalytic activity of Ti O2 to visible light. Among them, The N-Rh doped rutile Ti O2 was best to improve the absorption of visible light and easy to be realized.Secondly, this paper studied rutile titanium dioxide(110) surface adsorption sp3 hybrid gas molecules H2 O, NH3 and CH4. The results showed that: comparing to the surface without oxygen vacancy, the surface containing oxygen vacancy more easily adsorbed gas molecules. The main factor affecting the adsorption stability and adsorption energy is polarizability of molecular. The polarizability of molecular is greater; the adsorption will be more stable. But the stability level of the same molecular adsorption on the surface is relevant to the mutual position of molecule and surface after adsorption, the sums of distance from molecular positive and negative charge center to surface of oxygen vacancies are more close, the adsorption energy will be greater. The main reason for the adsorption is the adsorption of surface oxygen vacancies to the negative charge center of molecular. From analysis of electron density difference and charge population, the number of charge distribution of atoms O,N,C of gas molecules′ center are reduced, but the whole molecule are oxidized by the material surface. The strength order of of redox of surface to molecular is NH3> H2 O > CH4, the adsorption process is chemical adsorption. After adsorption, in bottom of conduction band, the electrons of O,N,C atoms resulted in a peak appeared in density of states, which would improve the resistance characteristics and optical properties. this paper provides the theoretical basis for the further study of material gas sensing properties.Lastly, hydrogen halide gas(HX, X=F, Cl, Br) adsorbed on Ti O2 surface were be studied. The calculation results show comparing to complete surface, the surface containing oxygen vacancy of Ti O2(110) is more easily adsorbed hydrogen halide molecules. Factor affecting the adsorption stability and adsorption energy is the molecular dipole moment, the molecular dipole moment is larger, the adsorption will be more stable. There is a charge transfer between the surface containing oxygen vacancy and HF, HCl, HBr, the adsorption was chemical adsorption. From the analysis of density of states and optical properties, after surface adsorption of HF, HCl and HBr molecules, the bottom of the conduction band appearred new impurity level, can different improve the surface optical properties of Ti O2(110), the improvement effect of adsorption of HF was the best. |
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