Photocatalytic activity of SnO-TiO composite nanoparticles modified with PVP.

Interface modified SnO-TiO composite nanoparticles were produced in two stages: first SnO nanoparticles were prepared by chemical precipitation in the presence of polyvinylpyrrolidone (PVP) and thermally treated at 500 °C then TiO was deposited on top of modified SnO and followed by a final annealing. As a consequence SnO-TiO composite nanoparticles get crystallized while PVP is decomposed into monomer units and other attached smaller molecular fragments. TGA coupled with FT-IR spectroscopy confirmed the presence of monomers and other moieties as a result of PVP thermal fragmentation. The crystalline phases and composition of the two oxides were evidenced by X-ray diffraction, HRTEM and XPS. It was found that specific surface area of the composites increases with the increase in the initial amount of PVP. Also, the oxidation potential of the TiO shell, as determined by UV photoelectron spectroscopy (UPS), significantly decreases as the PVP quantity increase and further modifies the band alignment between SnO and TiO components. Additionally, both XPS and UPS spectra as well as EPR investigations indicate the presence of many localized states inside the band gap of TiO. With a moderate PVP content the combined effects of band alignment, gap localized states and porosity make possible an increased number of reactive oxygen species (ROS) generation thus increasing photocatalytic activity against RhB dye solution under visible irradiation. The photocatalytic mechanism was elucidated based on the identification of radical species involved and in accordance with energy bands alignment, gap states, and porosity. Besides water purification by photocatalysis, SnO-TiO as ROS generating heterostructures may be used in applications like antibacterial and antitumoral, deodorizing, air purifying, self-cleaning, gas sensing, as well as in hydrogen production.