Influence of synthesis conditions on the properties of photocatalytic titania-silica composites

Titania-silica composites are a promising alternative to titania for photocatalysis, because of their lower material costs, longer lifetimes and higher activities. Different synthesis routes for titania-silica composites were thoroughly investigated in this study to gain more fundamental insight on their impact on the resulting samples and their photocatalytic oxidation efficiency. The investigated routes were based on precipitation, slow addition of an alkoxide precursor and sol-gel method. The silica for the composites was synthesized by dissolving the silicate mineral olivine in sulfuric acid. This method is cheaper, environmentally friendly and produces silica with favorable properties (i.e. large surface area with a high hydroxyl density) to support the titania. The resulting samples were tested by measuring their efficiency to oxidize nitric oxide under UV-light irradiation, XRD, nitrogen physisorption, FTIR and XPS. The results show that the most active photocatalysts were prepared by precipitation by slow addition of water or slow addition of precursor to a low water content dispersion. In addition, an optimal pH of 3 was observed for these synthesis methods. Compared to pure titania, the prepared titania-silica composites with only 15% titania showed slightly higher photocatalytic activities (82.3% vs. 78.9%), showing the composites to be a promising cost-effective alternative to the current photocatalysts.