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theses

Binary TiO2-SiO2 oxides are materials that have attracted attention due to their usefulness as heterogeneous catalysts and catalytic supports. Due to the large difference between their optical properties, in particular, band gap and refractive index, and their compatibility with respect to the deposition conditions, SiO2 and TiO2 appear well suited for these purposes. These materials have been synthesized by several techniques including chemical vapor deposition, sputtering and sol-gel. The sol-gel process is a versatile method to control the thickness, uniformity and thermal stability of high surface area materials. The sol-gel method presents many advantages such as utilization of simple equipment, high homogeneity and the possibility of using a variety of substrates of different sizes.
This thesis investigates the preparation of glass coatings from TiO2-SiO2 and Fe-doped TiO2-SiO2 by using the low-temperature sol-gel process. The TiO2-SiO2 sol was prepared from titanium (IV) butoxide Ti(OCH2CH2CH2CH3)4, and tetraethylorthosilicate (TEOS), (Si (OC2H5)4). The steps involved in the fabrication of sol-gel derived thin films, such as sol preparation and substrate preparation are discussed. Physical and chemical characterization of the thin films are discussed in detail. UV-Visible spectroscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to measure transmittance, thickness of films, the identification of phases, and chemical structure.
Eleven different compositions, 3, 5, 7.9, 10, and 15% TiO2, and iron (Fe) doped TiO2- SiO2 were investigated. Films with five compositions of SiO2-TiO2 were coated onto glass microscope slides using dip-coating method. Thin films in this study were subjected to heat treatment in a furnace at 100ºC for 24 hours. The samples with 1 and 3 dip-coatings of 10% TiO2-90% SiO2 and 15% TiO2-85% SiO2 with solution age 0, 5, 15, and 25 days exhibit higher transmittance than any of the other compositions, especially in the spectral region 400-600nm. Since the peak of the solar radiation spectrum lies in this important spectral region, the optical performance of these samples is promising, and these samples were studied further. Transmission spectra for different amounts of Fe(NO3)3 doped TiO2-SiO2 thin films show that the films with smaller amounts of Fe(NO3)3 0.0001 % exhibited higher transmittance in the spectral region 450nm - 550nm. This dopant amount has negligible absorption. Also, the transmittance of the as-deposited films at 0 days for all layers 1 and 3 is higher than the transmittance of the films for the solution aged 25 days. The solution should not be aged, if practical. The thickness of films with 1 and 3 coatings on the glass substrate were measured in fresh and aged solutions. The results of thickness measurements are in agreement with the transmittance measurement results.
Based on XRD analysis, the synthesized powders are amorphous. No characteristic crystalline peaks are observed. Higher photocatalytic activity is predicted for samples which are amorphous. Also, the amount of Fe ions had little effect on the crystal structure of the TiO2-SiO2.
The FT-IR spectra of all samples look similar. Hydroxyl groups were observed in all samples at around 3300 cm-1 and at about 1630 cm-1. Siloxane bonds were detected at 1051, 1130, and 795 cm-1. The linkage between TiO2-SiO2 was confirmed by the band at 935 cm-1 which is attributed to the Si-O-Ti stretching mode. The spectral features of TiO2 can be discerned at around 553 and 446 cm-1, attributed to Ti-O and Ti-O-Ti bonds. The addition of iron is evidenced by the peak of the ν Fe-O vibration band at ~420 cm-1.

ETD_9099

Ph.D.

Includes bibliographical references

by Adeal Sobhe Matuk

doi:10.7282/t3-45az-3b79

ETD doctoral

The author owns the copyright to this work.