Structural and photocatalytic properties of sol–gel-derived TiO 2 samples prepared by conventional and hydrothermal methods using a low amount of water

Titania is a versatile semiconductor widely used in many applications, including photocatalysis. Among the processing routes used to prepare titania, the sol–gel process deserves to be highlighted because it allows obtaining samples with tailored composition, particle size, and specific surface area. Such properties play a key role in the photocatalytic behavior of titania. In this study, we show that by adjusting the sol–gel parameters and drying/heat treatment conditions it is possible to control the co-existence of anatase and rutile in the synthesized sol–gel titania. The works found in the literature usually deal with the preparation of crystalline titania using water-rich solutions, which usually gives rise to anatase. However, we demonstrate that the lack of water in the starting solution favors the formation of both anatase and rutile; the co-existence of these two phases has been reported to improve the photocatalytic behavior of titania due to a band-gap alignment. Furthermore, we propose a sol–gel route based on a single-step hydrothermal procedure where nanoparticles with sizes of about 3 nm and surface areas up to 120 m 2 .g −1 are obtained. This study accounts for the knowledge regarding the preparation and use of sol–gel titania for photocatalysis applications. It is supported by a series of experimental techniques, including X-ray diffraction, N 2 sorption, thermogravimetry, differential thermal analysis, Raman spectroscopy, transmission electron microscopy, selected area electron diffraction, and UV–Vis diffuse reflectance spectroscopy. The photoactivity of the prepared samples was evaluated in terms of the photodegradation of methylene blue under near-ultraviolet (UV-A) light. Graphical abstract