The effect of Cu dopants on electron transfer to O2 and the connection with acetone photocatalytic oxidations over nano-TiO2

Abstract

Modifying TiO₂ with the Cu element has been shown to be useful for photocatalysis. Although it had been known that Cu species could trap electrons from TiO₂, whether they can affect the kinetics of electron transfer and how this can contribute to photocatalysis still remain unknown. In the current research, Cu–TiO₂ samples were firstly prepared with a hydrothermal reaction and characterized in detail. It was shown that Cu elements were doped in the TiO₂ lattice in +1/0 valence states and have a minor effect on the TiO₂ structure. By means of photoconductances, it is shown that the Cu dopants could catalyze the electron transfer from TiO₂ to O₂ by reducing the apparent activation energy (E_app) by about 2 times. The photocatalytic experiments conducted at different temperatures showed that the E_app of the acetone photocatalytic oxidations could be decreased by ∼2 times; this implies that the Cu dopants change the photocatalytic pathway. First-principles computation showed that the surface Cu dopants, along with the compensated oxygen vacancies, can mediate both of the electron and hole transfer. By combining other studies, we proposed that the Cu sites could act as Lewis acid and base pairs that could combine with acetone and O₂ molecules under UV light illumination; this allows electron transfer to O₂via the Cu sites that then react with acetone. As compared to pure TiO₂ surfaces, the different chemical environment of the Cu sites leads to the decrease in the E_app of photocatalysis.