Heterogeneous photocatalysis continues to be an active area of research with focus on developing catalytic systems that can degrade toxic pollutants in the gas and aqueous phase, and split water to generate hydrogen and oxygen. In this review, the incorporation of silica phases in titanium dioxide based photocatalysts is reviewed.

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Platinized TiO2 photocatalysts of different compositions of Pt0 and PtO2 were prepared by modifying the synthesis procedures. The physicochemical properties of the composite materials were characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Energy dispersive X-ray spectroscopy measurements confirmed the presence of Pt species existing as PtO2 and/or mixtures of Pt0 and PtO2. The composite material, Pt–TiO2–2%H, contained a high amount of metallic Pt0 and PtO2 in close proximity with TiO2 that promoted an enhanced photocatalytic hydrogen evolution activity under simulated solar light irradiation. Although Pt–TiO2–2%C and Pt–TiO2–2%T consisted of similar compositions of PtO2, these oxidized platinum species seem to appear further apart from TiO2 in Pt–TiO2–2%C than Pt–TiO2–2%T. This caused dramatic variation in their optical behaviors such as strong fluorescence quenching and lower photocatalytic hydrogen evolution activity in the former photocatalyst. A photocatalyst prepared by the conventional photodeposition method was also prepared, characterized, and its photocatalytic activity assessed. This work provides an opportunity to understand the role of PtO2 for photocatalytic production of hydrogen from platinized TiO2 composites and the importance of heterojunctions in such photocatalysts for solar energy conversion.

The photocatalytic activity of hydrothermally synthesized TiO2−SiO2 mixed oxides was examined in this study. Powder X-ray diffractometry, nitrogen adsorption, diffuse reflectance spectrometry, Raman, and UV−vis spectrometry demonstrated that the pore geometries and the nature of the crystal phase can be tailored by cosolvent-induced gelation (CIG) in the synthesis of mixed oxide materials. This body of work attempts to support the role of crystallinity enhanced by the hydrothermal synthesis (HTS) in establishing active sites pertinent to the advanced oxidation process (AOP) in TiO2−SiO2 mixed oxide materials.