Improved Texturing and Photocatalytic Efficiency in TiO sub(2) Films Grown Using Aerosol-Assisted CVD and Atmospheric Pressure CVD

Four different TiO sub(2) films are formed on glass at 500 degree C by aerosol-assisted (AA)CVD, atmospheric pressure (AP)CVD, AACVD followed by APCVD, and APCVD followed by AACVD. The APCVD films are formed from reaction of TiCl sub(4)(g) whilst the AACVD films are made by decomposing Ti[OCH(CH sub(3)) sub(2)] sub(4) contained in an aerosol. The film composition is studied using X-ray photoelectron spectroscopy (XPS) to ascertain the purity of the films, and no Cl traces can be found on any of the surfaces. The use of different combinations of CVD gives rise to significant changes in microstructure and preferred orientations. X-ray diffraction (XRD) patterns and Raman spectroscopy (RS) confirm that TiO sub(2) in the anatase form is the dominant phase on all samples. All films show superhydrophilicity after 50min of black-light irradiation. The photocatalytic efficiencies of the films are assessed qualitatively by an ink test based on Resazurin, and quantitatively studied by measuring formaldehyde formation from tris(hydroxymethyl)aminomethane (Tris). Both methods show that the AACVD film and the film seeded by APCVD are the most photocatalytically efficient ones, both having an apparent quantum yield (AQY) of around 4.2%, while the APCVD film and the film seeded by AACVD have an AQY of 0.8% and 1.5%, respectively. The changes in photocatalytic activity are explained in part by changes in film microstructure and the accessible surface area. Films are synthesized using AACVD, APCVD, and combined AACVD and APCVD, and then characterized by XRD, SEM, XPS, Raman, and water contact angle measurements. The photocatalytic efficiencies of the films are assessed qualitatively by the well-established ink test based on Resazurin, and quantitatively studied by a new method based on tris(hydroxymethyl)aminomethane. It is shown that both methods are in agreement.