Abstract

Background: In photocatalysis and surface chemistry, charge trapping extends the lifetime of photogenerated electrons and holes and decreases their recombination rate. The stable surface of crystals with lowest energy is (110) for rutile and (101), (010) or (100) for anatase. When these surfaces are exposed to simple molecules such as water, oxygen or methane, different reactions can occur. In this paper, the activity and mechanism of dye adsorption were studied and demonstrated significant increase in the resulting photo-catalysis with optimizing surface properties for the first time.

Methods: Degussa P25 (Aldrich) was used a based materials. The mixtures of ethanol (C2H5OH) and triethanolamine (TEA, C6H15NO3) and 1 M HNO3 solution were prepared and applied to chemical etching of anatase/rutile mixture. The nano composites with (0.5 % Pt) prepared by wet impregnation methods used as photo catalysts in water splitting reaction. The metallurgical and photo catalytical properties were characterized with standard methods.

Results: The X-ray diffraction (XRD) Results of the samples were shown that the chemical process affected the phases and molar ratios. The photo-catalytic properties of these powders were measured with phase ratios, crystalline size, and reaction time as parameters. TEM images of powders chemically etched at different conditions are shown that the average surface area increased. The TiO2powders consist of spherical particles, that modified to cubic like structure with etching but core of the powders seems to have similar microstructures and shapes. The photo reactivity clearly shows that with adjusting phase ratios, the microstructure, surface and photo-catalytic activity of powders are adjusted.

Conclusion: In this study, new method to preparation of core shell structure of anatase and rutile with using of etching developed and photo-catalytic activity of anatase and rutile hetro structure has been investigated using two systems. The reaction rate was related to the surface area, phase's ratio, particle and pore size, adsorption mechanism of reactants, concentration of dye and catalyst. The surface reaction sites and photo reactivity are higher in composite powders with similar particle size and band gap. The concentration of reactants (dye or water, H2, O2) is important because they react in suitable surface sites. The suitable sites are determined by size of compounds and surface charges. Additional to the surface properties, effectively charge separation was increasing the photo reactivity of composites.

Keywords: Etching, TiO2, nanocomposite, core-shell, surface properties, photocatalysis.