Synthesis of high surface area TiO2 nanoparticles by mild acid treatment with HCl or HI for photocatalytic propene oxidation

• TiO2 nanoparticles can be obtained by sol–gel at low temperature.
• Ethanol treatment under reflux leads to amorphous TiO2.
• The acid–ethanol treatment under reflux leads to TiO2 with good crystallinity.
• The samples treated by acid–ethanol possess high photocatalytic activity with UVA.

Nanostructured TiO2 photocatalysts with small crystalline sizes have been synthesized by sol–gel using the amphiphilic triblock copolymer Pluronic P123 as template. A new synthesis route, based on the treatment of TiO2 xerogels with acid–ethanol mixtures in two different steps, synthesis and extraction–crystallization, has been investigated, analyzing two acids, hydrochloric and hydriodic acid. As reference, samples have also been prepared by extraction–crystallization in ethanol, being these TiO2 materials amorphous and presenting higher porosities. The prepared materials present different degrees of crystallinity depending on the experimental conditions used. In general, these materials exhibit high surface areas, with an important contribution of microporosity and mesoporosity, and with very small size anatase crystals, ranging from 5 to 7 nm.The activity of the obtained photocatalysts has been assessed in the oxidation of propene in gas phase at low concentration (100 ppmv) using a UVA lamp with a wavelength of 365 nm. Under the conditions studied, these photocatalysts show different activities in the oxidation of propene which do not depend on their surface areas, but on their crystallinity and band gap energies. Sample prepared with HCl both during synthesis and in extraction–crystallization steps is the most active one, with superior performance than Evonik P25.

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