Photoelectrochemical Phenomena at Nano-V2O5 Films Impregnated with Bi3+

In the last two decades, the development of nanoscience and technology developed several nanostructures at different forms, such as nanoparticles, nanowires, nanotubes and nanoribbons. These materials offer a high potential for improving properties and can be used in many fields such as microelectronics, batteries, photovoltaic and photocatalytic devices. Vanadium oxides belong to the important class of 3d transition metals, with various electric, magnetic and structural properties, making these materials attractive for many industrial applications. This study aimed to obtain and characterize vanadium oxide films on titanium from ammonium metavanadate and then modify it by impregnation with Bi (III). The vanadium pentoxide was synthesized on Ti substrates by painting the surface with a suspension of 250 mg ammonium metavanadate in 5 ml of polyethylene glycol (PEG-300). The coated Ti plate was then heated at 400, 500 or 600 °C for one hour. Subsequently, the film obtained was impregnated with Bi (III) for 120 minutes under constant stirring, using 50 mL of a solution 10 mmol L^-1 of bismuth nitrate at nitric acid. Then the samples were again annealed for one hour at the same temperature. The films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Visible spectroscopy and photoelectrochemical. From SEM analysis was possible to observe, after impregnation of Bi(III), the growing of long crystals on V₂O₅ films at 400 and 500 °C, while for the sample to 600 °C a globular structure was preferentially deposited on the tip of V₂O₅ crystals. Through EDS analysis it was observed that the sample obtained at 500 °C is that has the highest amount of Bi in the composition. The mapping by EDS showed that the elements were distributed over all surface. From XRD analysis the presence of V₂O₅ orthorhombic phase and monoclinic BiVO₄ was detected. Band-gap calculated for the samples before and after impregnation also proved that V₂O₅ was converted to BiVO₄, since the value before impregnation was 2.20 eV and after impregnation showed a value of 2.42 eV. The photocurrent value obtained for nano-V₂O₅ films impregnated with Bi³⁺ at 500 °C was 5 times higher than pure BiVO₄ films. The results showed that it has been possible obtain a nanostructured V₂O₅ / BiVO₄film on Ti substrate which is photoactive and could be used both in photoelectrocatalytic water as oxidation of organic molecules.

Acknowledgements: FAPESP 2012/23422-5 and CAPES.