Theoretical Study On Adsorption Of Surface, Electronic, And Optical Properties For Several Solids

Nowadays, climate change and ecological deterioration are the concerned problemsrelated to the survival of mankind. In the field of chemistry, aerosol related to theatmospheric environment, also aroused widespread attention. At present, the academiathinks the effect of atmospheric environment of aerosols is related to its hygroscopicity;however, there should be further research on many important microscopic mechanisms ofphysical and chemical processes of aerosol surface. Due to the depletion of oil resourcescoming, people began to pay close attention to new energy sources, dye sensitized solar cellhas been a hotspot in scientific research. Moreover, titanium dioxide and zinc oxide areimportant photoanode semiconductor materials, the research on the photoelectric propertiesof bulk and surface of semiconductor materials can provide a theoretical basis for furtherdevelopment of high performance solar cell materials. In this thesis, density functionaltheory has been used to study the mechanism of water adsorbed on the aerosol NaNO3(001)and MgSO4(100) surfaces, doping effect of electronics and optical properties of catecholadsorbed on anatase TiO2(101) surface, as well as electronic structure and opticalproperties of (Zr-Al) co-doped ZnO.(1) The adsorption properties of water molecules on MgSO4(100) surface wasinvestigated. Optimized stable geometries of one and more than one water moleculesadsorbed on MgSO4(100) ideal surface was obtained. The configurations with watermolecules adsorbed on atoms of the second and third atomic layers of MgSO4(100) surfaceare quite stable. After adsorption, both the distances of the adjacent Mg atoms (RMg-Mg) andthe adjacent O atoms of the surface (RO-O) increase which means that the water adsorptionon MgSO4(100) surface is helpful for understanding the molecular mechanism ofdeliquescence process. In addition, one water molecule is more likely to adsorb ondefective surface, not on ideal surface. Mulliken population analysis suggests that fewercharges transfer from Mg atom of defective substrate to water molecule. One monolayer(ML) is defined as a water molecule corresponding to a unit of MgSO4. Finally, Ramanspectra were calculated for0.5ML,1ML and2ML water adsorption on MgSO4(100)surface, which is helpful for further related experiments. (2) Single water molecule is more likely to locate on the bridge site with its H atomattracted by the O atom of nitrate ion and its O atom adjacent to Na+. Mulliken populationanalysis shows that fewer electrons transfer from the Na atom of substrate to watermolecule.1ML is defined as a water molecule corresponding to a unit of NaNO3. Asystematic study of water clusters adsorption at high coverages ranging from0.5monolayer(ML),0.75ML,1ML,1.25ML, and1.5ML on NaNO3(001) surface was also investigatedand the results indicate that for1ML water adsorption on NaNO3(001) surface, a waterchain is formed among four water molecules through hydrogen bonds. Interestingly, thewater molecules are linked through hydrogen bonds to form a14-membered macrocyclicwater ring for1.5ML adsorption on NaNO3(001) surface. Our estimated O-H symmetricstretching frequency (νO-H) will have blue-shift with decrease of water coverage, which isconsistent with the tendency given by experiments.(3) The doping effects of several metal atoms (Al, Mg and Cr) on the electronic andoptical properties of catechol absorbed on anatase (101) surface have been investigated bydensity-functional theory. Our results show that the adsorption of catechol on pure anddoped TiO2(101) surfaces is quite stable, and shifts the Fermi energy positively. Moreover,the obtained defect formation energy indicates Al-doped TiO2(101) surface is the mostenergetically favorable structure. Furthermore, in catechol adsorbed Cr-doped TiO2(101)surface, the band gap is evidently reduced and some impurity states appear in between,which implies an improved light harvesting ability in the near infrared region. This point isconfirmed by the simulated absorption spectra, where the absorbance is the strongest andthe spectrum is greatly red-shifted for catechol adsorbed Cr-doped TiO2(101) surface.More importantly, the Fermi energy is positively shifted due to Cr-doping, which favors theincrease of the circuit voltage. Therefore, the obtained electronic and optical propertiesreveal that Cr-doped TiO2is a promising photoanode material for high efficientdye-sensitized solar cells.(4) The hybrid density functional was used to investigate the electronic structure andoptical properties of (Zr-Al)-codoped ZnO. The calculated results show that the formationenergy of (Zr-Al)-codoped ZnO is low, indicating that it is the energetically favorable structure and the first absorption peak of optical absorption spectra for (Zr-Al)-codopedZnO has a red-shift compared with pure ZnO, which may lead to the improvement on thevisible-light photocatalytic ability. The zinc and oxygen vacancies introduced by(Zr-Al)-codoped ZnO have also been investigated. Through analysis the main absorptionpeaks of the imaginary part of the dielectric function on polarization vectors perpendicularor parallel to the Z axis, we think that oxygen vacancy introduced by (Zr-Al) codoping canalso improve the visible-light photocatalytic ability and zinc vacancy has weak effect toenhance the optical photocatalytic ability compared with (Zr-Al)-codoped ZnO.