Photocatalytic reduction of CO2 over K2Ti6O13 films

Abstract Ti metallic sheets were treated in a basic medium using the hydrothermal technique and then calcined at different temperatures to obtain K2Ti6O13 films. The X-ray diffraction characterization showed a preferential orientation in the plane (020) in the sample thermally treated at 600 °C. The structural results were used to elucidate the crystal shape by using the VESTA software. This simulation agreed with the morphological characterization that shows the growth of narrow and well-defined nanowires in film at 600 °C. In contrast, the as-prepared and the samples calcined at 700 °C and 800 °C samples exhibited significant wire agglomeration. PL lifetime decay analysis exhibited a larger lifetime in the film calcined at 600 °C. This parameter involves a prolonged time of available charges in the surface of the photocatalyst and improves the possibility to take place the CO2 reduction reaction. In a comparison between the prepared samples, the one calcined at 600 °C presented higher production of fuels (8 μmol cm−2 HCOOH, 0.5 μmol cm−2 HCHO, 1.5 μmol cm−2 H2), being this result attributed to the well-defined wire nanostructure which promotes a better charges transport. Even though formic acid presents more negative reduction potential than the other products, the K2Ti6O13 material shows higher selectivity for this fuel, which can be attributed to the more negative flat band potential calculated for all the films. Besides, trunked bonds formed due to rectangular shape (rectangular wire) could act as active sites for this interesting reaction.