Facile encapsulation of P25 (TiO2) in spherical silica with hierarchical porosity with enhanced photocatalytic properties for gas-phase propene oxidation

Abstract

In this work, we have performed the encapsulation of a reference TiO2 material (P25) in spherical silica with hierarchical porosity using a sol-gel methodology. The same P25 material has been encapsulated within a “classical” MCM-41 mesoporous silica and a precipitated silica. The materials synthesized in this work were characterized by ICP-OES, SEM, TEM, EDX, XRD, UV–VIS, TG, and nitrogen adsorption. It has been observed that the P25 samples encapsulated in silica present improved CO2 production rates per mol of P25 in the photooxidation of propene, compared to P25 alone as well as the physical mixture of the two components. Moreover, the sample with a low content of P25 encapsulated in silica with hierarchical porosity presents the highest CO2 production rates per mol of P25 with respect to the other P25/silica samples, due to a better accessibility of the titania phase and improved illumination of the active phase. Furthermore, the hierarchical porosity of the silica shell material favours mass transport and an increased concentration of reagents by adsorption near the titania phase. This improvement in photocatalytic activity is obtained by following a simple and reproducible synthesis methodology that employs an established silica preparation protocol. Thus, the choice of a silica with an adequate porosity for this application is proven to be a promising advancement in the development of efficient photocatalysts.