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IMPROVING PHOTOCATALYTIC PROPERTIES OF TIO2 THROUGH THIN FILM COATING AND METAL DOPING VIA FLAME AEROSOL COATING METHOD
Citation:
SahleDemessie*, E AND Z. Wang. IMPROVING PHOTOCATALYTIC PROPERTIES OF TIO2 THROUGH THIN FILM COATING AND METAL DOPING VIA FLAME AEROSOL COATING METHOD. Presented at AIChE, Austin, TX, November 07 - 12, 2004.
Impact/Purpose:
To inform the public
Description:
There has been an increasing demand for efficient, economical and environmentally friendly methods for partial oxidation of hydrocarbons by molecular oxygen, to desirable industrial feedstock oxygenates. Current processes are energy intensive, have low conversion efficiencies and overoxidation products, and generate environmentally hazardous wastes and by-products. Titanium dioxide (TiO2) has been used as an effective photocatalyst with wide rang of applications including photooxychemical manufacturing processes as green alternative to the traditional technology. However, the large band gap of 3.2 eV energy, UV light of wavelength range 320~400 nm is required to generate electron-hole pairs and the visible portion of the natural sun light then could not be used.
In this study, flame aerosol deposition process was used to 1) synthesize iron or vanadium doped in TiO2, and 2) deposit nano-size layers of TiO2 on surfaces with no further calcinations. Solid-state characterization of the coatings was conducted by different techniques, such as X-Ray diffraction spectrum, and Scanning Electron Microscopy, and the effect of the dopants on the crystal phase and morphology of the resulted catalyst were studied. Catalyst activities were studied using partial oxidation of 1-phenlethanol to acetophenone. An optimal doping concentration existed for both V and Fe+ species in the applied photocatalytic reaction systems. Increasing doped vanadium or iron above 4 wt% decreased the crystallinity of TiO2 and the anatase-to-rutile ratio amorphous fine powders with detectable crystal patterns. The effect of solvents on the photocatalytic reaction was also studied by using both water and acetonitrile as the reaction solution. The possible reason for the optimal doping concentration is correlated with solid state properties of TiO2.
The effects of film thickness, anatase-to-rutile ratio and particle morphology on the reactivity of the catalyst were studied. There is an optimal film thickness (between 400 and 700 nm) for the photooxidation process that gives a maximum rate of photoactivity. The yield and selectivity of TiO2 increased with the increase of the film thickness up to 350 - 400nm. The activity decreased with further increase in thickness. The influence of crystallographic structure of TiO2 on partial oxidation of cyclohexane showed that the catalyst activity increased almost linearly with the increase of the anatase fraction between 20 to 95%. The study shows improving the photoactivity of TiO2 through doping metals and nano-size coatings would greatly expand its potential applications and reduce operating costs.