ZSM-5/TiO2 Hybrid Photocatalysts: Influence of the Preparation Method and Synergistic Effect

In this work, the influence of the preparation method of ZSM-5/TiO2 hybrids on the photocatalytic performance for removal of formaldehyde (HCHO) or trichloroethylene (C2HCl3) in gas phase was analyzed. For this purpose, two methods for the synthesis of the hybrids, the incipient wetness impregnation (I) and the mechanical mixing method (M), were selected. The photocatalysts were characterized by N-2 adsorption-desorption, TEM, UV-Vis spectroscopy, XRD and electrophoretic migration. Also, the adsorption ability of the individual materials and hybrids was analyzed. ZSM-5/TiO2 hybrids showed higher photocatalytic activity than bare TiO2, independently of the preparation method selected. Mechanical mixing is a simple and easily scalable method to prepare highly active photocatalyst with high amounts of titania. The internal diffusion processes of the reactants to the active sites could be improved due to the micro-mesoporous structure developed on these hybrids. Incipient wetness impregnation method leads to photocatalysts with higher photodegradation rates per active site. The hybrids synthetized by this method show TiO2 nanoparticles homogeneously dispersed on the ZSM-5 phase. The fraction of TiO2 exposed on the surface ca. 75 mol% was similar for materials prepared by both methods, explaining the similar adsorption and photocatalytic properties, independently of the TiO2 content. The nature of the pollutant has an important role in the adsorption and photocatalytic properties of the composites. Finally, the effect of the incorporation of the zeolite in the photocatalytic system was analyzed. For this purpose, the influence of the zeolite and titania arrangement in the sample holder on the photodegradation rate was analyzed. Although the incorporation of the zeolite induces a positive effect on the photocatalytic performance, independently of the position on the sample holder, a clear synergistic effect when both phases were in intimate contact such as in the ZSM-5/TiO2 hybrid was observed.