Preparation of sputter-deposited Cu-doped BiVO4 nanoporous thin films comprised of amorphous/crystalline heterostructure as enhanced visible-light photocatalyst

The synthesis of Cu-doped BiVO4 nanoporous thin films with various Cu contents was performed using reactive magnetron sputtering to prepare a stable and inexpensive photocatalyst with high photoactivity under visible light for wastewater treatment applications. The X-ray diffraction (XRD) analysis showed exclusively the for-mation of the photoactive monoclinic BiVO4 phase up to 17 at.% Cu. Beyond, a Cu-based compound crystallizes in addition to the BiVO4 monoclinic phase. The field-emission scanning electron microscopy (FESEM) and elemental mappings results revealed the formation of shard-like nodules composed of V, O and Cu in the films having less than 6 at. % Cu. From 6 at. % Cu, the morphology appears more homogeneous. X-ray photoelectron spectroscopy (XPS) showed the presence of Cu2+ and Cu+, as well as the rise of V4+/V5+ ions. Transmission electron microscopy (TEM) verified the amorphous structure of the Cu-O-V phase, as well as demonstrated the crystallographic interplanar spacings of BiVO4. The thin film with a 2 at. % Cu exhibited superior photoactivity (100, 99 and 63 %) over pristine BiVO4 in photocatalytic dye degradation (Rhodamine-B, Methylene Blue and Methyl Orange). The thin films' stability, recyclability and reusability were demonstrated in the recycling experiment, and the crucial role of photogenerated charge carriers and hydroxyl radicals was identified in the experiment involving scavengers. The photocatalytic performance towards various dye pollutions at acidic, basic and neutral pH conditions is also discussed in detail.