From titania nanoparticles to decahedral anatase particles: Photocatalytic activity of TiO2 /zeolite hybrids for VOCs oxidation

Abstract

In this work, zeolite/TiO2 hybrid photocatalysts based on TiO2 particles of different nature for photooxidation of VOCs in air have been developed. TiO2 with different morphologies, namely, TiO2 nanoparticles (Ti-NP) and decahedral anatase particles (DAPs), have been synthetized and characterized. A commercial TiO2 (Ti-C) catalyst has been used as a reference. Titania has been incorporated on ZSM-5 by different techniques: incipient wetness impregnation, freeze-drying, or mechanical mixing from a TiO2 sol, DAPs, or commercial TiO2. The TiO2 and hybridized photocatalysts were characterized by SEM, TEM, XRD, UV–vis spectroscopy, N2 adsorption-desorption and electrophoretic migration. Moreover, the formaldehyde or trichloroethylene adsorption ability of the composites has been analysed. The photocatalytic performance for the HCHO or C2HCl3 photooxidation under UV-A irradiation and continuous air flow has been evaluated. TiO2 nanoparticles of 5 nm, DAPs of ca. 100 nm, and 1.0 μm clusters of TiO2 made of 15 nm mean particle size characterized the three types of TiO2. These characteristics are maintained in the zeolite/TiO2 composites. In spite of the lower BET area, DAPs presented the highest VOCs reaction rate comparing to the other TiO2. The incorporation of titanium oxide to the microporous material results in the improvement of the photocatalytic performance, regardless of the actual nature of the TiO2 particles. Nevertheless, a relationship between the particle size and the improvement of the photocatalytic performance can be established. Thus, the incorporation of TiO2-NP into the zeolitic material, lead to composites with around ten times more photoactivity that the single titania particles. This effect is less pronounced for larger TiO2 particles such as DAPs and less evident for TiO2 aggregates present in commercial material. TiO2 nanoparticles homogeneous distributed on the hierarchical material shows the highest VOCs photooxidation and CO2 formation rates of the series.