Photocatalytic reduction of Cr(VI) by WO@PVP with elevated conduction band level and improved charge carrier separation property.

Photocatalytic reduction of heavy metal ions is a green and promising technology which requires electrons with enough negative energy levels as well as efficient separation property from photo-generated holes of photocatalysts. For WO, the low conduction band edge and the severe photo-generated charge carrier recombination limited its application in photocatalytic reduction of pollutants. In this work, we prepared WO@PVP with PVP capped WO by a simple one-step hydrothermal method, which showed an elevated energy band structure and improved charge carrier separation property. XRD, SEM, TEM, XPS, DRS, and the photocurrent density test were carried out to study the properties of the composite. Results demonstrated monoclinic WO with a size of ∼100-250 nm capped by PVP was obtained, which possessed fewer lattice defects inside but more defects (W) on the surface. Moreover, the results of the photocatalytic experiment showed the kinetic constant of Cr(VI) reduction process on WO@PVP was 0.532 h, which was 3.1 times higher than that on WO (0.174 h), demonstrating WO@PVP with good photocatalytic capability for Cr(VI) reduction. This can be attributed to the improved charge carrier separation performance, the improved adsorption capacity and the elevated conduction band edge of WO@PVP. More importantly, the energy band structure of WO@PVP was proved elevated with a value as high as 1.14 eV than that of WO nanoparticles, which enables WO@PVP a promising material in the photocatalytic reduction reaction of heavy metal ions from wastewater.