Photocatalytic properties of TiO2 and TiO2/Pt: A sol-precipitation, sonochemical and hydrothermal approach

•Sol-precipitation, sonochemical and hydrothermal synthesis of TiO2 and TiO2/Pt.•The synthesis method influences the final properties the materials.•The presence of the Pt-phase improves the photocatalytic activity of the TiO2.•The free OH groups improve the photocatalytic activity of the TiO2 and TiO2/Pt.•Methods that enable the formation of a biphasic TiO2 have a significant benefit on the photocatalytic activity. In this work we prepared TiO2 nano-powders and TiO2/Pt nano-composites via three synthesis methods (sol-precipitation, sonochemical method, hydrothermal method) starting with the same precursors and media. To evaluate and compare the physical properties of the prepared materials, X-ray diffraction analysis, BET measurements, FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron microscopy (TEM, HRTEM, SAED) were applied. The results showed changes to the TiO2 phase composition and crystallinity, the specific surface area as well as the platinum’s particle shape and size, depending on the method of synthesis. To determine the photocatalytic efficiency of the prepared materials, the photocatalytic discoloration of the methylene blue solution was evaluated using UV–Vis spectroscopy. The important properties required for a high photocatalytic activity, related to the surface characteristics and the phase composition, were determined in terms of the synthesis method. It was concluded that the optimum characteristics were obtained when using the hydrothermal approach, where the TiO2 had two phases, i.e., – anatase and rutile, a Pt-phase in the form of nanoparticles and adsorbed Pt-molecular species, as well as the presence of available free surface hydroxyl groups. Such characteristics had a critical influence on the photocatalytic activity of the final material.