Low-frequency ultrasound (LFUS) irradiation induces morphological, optical and surface changes in a commercial nano-TiO2-based photocatalyst. Low-temperature electron spin resonance (ESR) measurements performed on this material provided the first experimental evidence for the formation of oxygen vacancies (Vo), which were also found responsible for the visible-light absorption. The Vo surface defects might result from high-speed inter-particle collisions and shock waves generated by LFUS sonication impacting the TiO2 particles. This was in contrast to a number of well-established technologies, where the formation of oxygen vacancies on the TiO2 surface often requires harsh technological conditions and complicated procedures, such as annealing at high temperatures, radio-frequency-induced plasma or ion sputtering. Thus, this study reports for the first time the preparation of visible-light responsive TiO2-based photocatalysts by using a simple LFUS-based approach to induce oxygen vacancies at the nano-TiO2 surface. These findings might open new avenues for synthesis of novel nano-TiO2-based photocatalysts capable of destroying water or airborne pollutants and microorganisms under visible light illumination.

Low-Frequency Ultrasound Induces Oxygen Vacancies Formation and Visible Light Absorption in TiO2 P-25 Nanoparticles. P.A.Osorio-Vargas, C.Pulgarin, A.Sienkiewicz, L.R.Pizzio, M.N.Blanco, R.A.Torres-Palma, C.Pétrier, J.A.Rengifo-Herrera: Ultrasonics Sonochemistry, 2012, 19[3], 383–6