Multivariate SAXS profiles analysis applied to synthesis of heterogeneous titania photocatalysts by Sol-Gel Method

Full text: The Persistent Organic Pollutants (POPs) that result from some industrial processes are a major source of water pollution, and they may create health problems for humans. In recent years, Advanced Oxidation Processes (AOPs) have been presented as an alternative to conventional methods. Among all of the AOPs, the degradation of organic pollutants by heterogeneous photocatalysis based on titania is one of the most successful applications that uses this technology for recalcitrant pollutant degradation in waste water at ambient conditions. In parallel, silica-based catalyst supports can be produced by sol-gel technology and have been widely used for catalysis applications. Nevertheless, to our knowledge, silica nanoparticles have not been employed as supports to remove POPs in water. In the present investigation, microporous nanoparticles and mixed-structured silicas were employed as supports for photocatalysts. TiCl4 was used as the titanium precursor in the preparation of the nano- and mixed heterogeneous supported titania photocatalysts. For comparative reasons, photocatalytic tests were carried out with commercial titania (P25). The systems were evaluated in the photodegradation of Rhodamine B (RhB). The solids were characterized by nitrogen porosimetry, small-angle X-ray scattering (SAXS), zeta potential (ZP), dynamic light scattering (DLS) and diffuse reflectance spectroscopy in the ultraviolet (DRS-UV). All intensity profiles of X-ray scattering were treated by multivariate analysis tools [4], using the Hierarchical Cluster Analysis (HCA) and the Principal Components Analysis (PCA) in the modulus of scattering vector (q) region from 0.04 to 4.0 nm-1. The supported nanometric photocatalyst prepared with silica nanoparticles achieved the highest percentage of RhB degradation under the ultraviolet (68.0%) and visible (45.1%) radiation. The photocatalyst activity of nanometric catalyst was better than the commercial P25 (12.3% under visible radiation. (author)