Study Of Photo-catalysis Of Anatase TiO₂?001? Surface

The photo-catalysis of titanium dioxide (TiO2) has attracted enormous attention in recent years. While most of researches on TiO2 surfaces are based on rutile phase,especially on rutile (110) surfaces. few work was done on anatase TiO2(001) surface,which was theoretically expected to be more reactive. In this thesis, using home-made temperature programmed desorption (TPD) system, we studied the thermochemistry and photochemistry of small molecules, like formaldehyde (CH2O) and methanol(CH3OH),on anatase TiO2(001)-(1×4) single crystal surface,which was obtained by pulsed laser deposition (PLD).In chapter 1, the basic rules for desorption were summarized, together with research methods and the way to analyze TPD spectra. The composition of quadrupole mass spectrometer (QMS) used in this thesis was introduced and some improvements for the apparatus according to different experimental requirements were described. We also gave an overview on TiO2 photocatalysis mechanism and research progress, for instance, structure of TiO2 and process for production of photo-generated carriers.Finally the method for sample preparation is described.In chapter 2, we studied the thermal and photo-catalytic decomposition of CH2O on anatase TiO2(001) surface. We found that CH2O desorbed from the surface at 200 K and produce ethylene (C2H4) on defect sites, which was desorbed at 560 K. During UV light irradiation, the products such as C2H4, formic acid (HCOOH) and CH3OH were identified for photo-catalytic decomposition of CH2O on anatase TiO2(001) surface.HCOOH finally decomposed to CO at high temperature. We proposed that the activation and breaking of C-H during UV light irradiation were key processes, which further initiated the production of C2H4, HCOOH and CH3OH.Chapter 3 is focused on the coupling reaction of CH3OH on anatase TiO2(001)-(1×4) as-grown surface. Multi-carbon products were formed and detected at 340 K as a result of coupling reactions of CH3OH on anatase TiO2(001) as-grown surface once the surface was dosed by a lot of CH3OH at room temperature or 260 K. The signal of m/z=27 and 39 indicate the C-C bond in the products. The products contains at least 4 kinds of species, two of which have been confirmed as C3H8O2 and C4H10O. It is also found that the yield and selectivity of the coupling reaction can be controlled by the thickness of the sample film, coverage of defects and (1×4) reconstruction.