The applications of SBA-15 mesoporous silica thin films containing photoactive semiconductors and the development of ordered crystalline mesoporous titania thin films

SBA-15 mesoporous silica thin films encapsulating Degussa P-25 TiO2 particles were synthesized using a block copolymer templating method. The thin films were characterized using small angle X-ray diffraction (XRD), variable angle spectroscopic ellipsometry (VASE), polarized light microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The SBA-15/TiO2 thin films were examined for applications in advanced oxidation processes (AOP) and photovoltaics. A study of the photodegradation of 2,4-dichlorophenol (2,4-DCP) was used to assess the photoactivity of the thin films using UV-visible spectroscopy and high performance liquid chromatography (HPLC). It was shown that the thin films were 88.8% as photoactive as dispersions of P-25 TiO2 on a per photon basis. The SBA-15/TiO2 thin films were also dip-coated onto indium tin oxide (ITO) conducting glass substrates. These electrodes were placed in photoelectrochemical cells in order to determine the photovoltaic efficiency of the thin films. The thin films were shown to have photovoltaic efficiencies between 8.0 x 10 -4 to 0.26% depending on the amount of TiO2 present in the sample. It was also shown that there was an increase in photovoltaic efficiency of approximately 44% for SBA-15/TiO2 thin film electrodes when compared with nonporous silica electrodes containing P-25 TiO2 particles. The development of ordered crystalline mesoporous TiO2 thin films was also examined. Different methods of mesostructure stabilization were explored such as the addition of phosphates and the electrodeposition of nickel within the mesopores. The thin films were calcined to various temperatures, and the thermal effects were examined. The mesoporous TiO2 samples were characterized using small angle XRD, TEM, and SEM.