Effect of microwave irradiation on the synthesis of mesoporous titania

Combining photocatalytic properties with a high specific surface area, mesoporous titania can be used in a wide range of applications such as water treatment, air purification and water splitting. Conventionally, soft template synthesis routes comparable to silica syntheses (EISA, hydrothermal syntheses, etc.) are used. These syntheses are time consuming processes, including long aging times and inefficient heating procedures while still only moderate degrees of crystallinity are obtained. [1] Obtaining a material with both a high porosity and a high crystallinity poses a challenge as crystal growth leads to collapsing of the pores. Microwave irradiation can be the solution for these problems. Microwaves directly couple to the solvent molecules used during synthesis, making it possible to create very fast heating, avoiding slow heat transfer through different materials (air-metal-solution) typical for hydrothermal routes. In TiO2 nanoparticle synthesis, replacing a hydrothermal synthesis by microwave irradiation not only reduced the synthesis time but also an increase in crystallinity was observed [2], therefore it is also possible that microwave irradiation improves the degree of crystallinity in mesoporous titania, solving both problems of conventional solution syntheses. We found that the use of microwave irradiation makes it indeed possible to enhance the degree of crystallinity of mesoporous titania, while avoiding the loss of specific surface area. Other properties like particle size, band gap energy and isoelectric point also remained unaffected by the microwave treatment. Against expectations the photocatalytic activity of the microwave irradiated samples, exhibiting an increased crystallinity, was lower compared to the non treated samples. We are investigating this reduction using EPR and other techniques to understand the underlying effects of microwave irradiation. REFERENCES [1] Ismail, A. A. and Bahnemann, D. W., J. Mater.Chem. 32 (2011) 11686. [2] Dufour, F., Cassaignon, S., Durupthy, O., Colbeau-Justin, C. and Chaneac, C., Eur. J. Inorg. Chem. 16 (2012) 2707