Removal of hexavalent chromium from water by Z-scheme photocatalysis using TiO (rutile) nanorods loaded with Au core-CuO shell particles.

All-solid-state Z-scheme photocatalysts, containing CuO, TiO (rutile), and Au as the electron mediator, were prepared and applied to the reduction of Cr(VI) in aqueous solutions. The CuO-Au-TiO composites were prepared by loading Au core-CuO shell hemisphere particles on TiO (rutile) nanorods using a two-step photocatalytic deposition process. Under ultraviolet-visible (UV-vis) light illumination, the CuO-Au-TiO composites exhibited higher photocatalytic Cr(VI) reduction activities than those exhibited by single TiO (rutile) and CuO. In this reaction, a precipitate containing Cr, which was considered to be Cr(OH), was deposited site-selectively on the Au core-CuO shell particles of the composites, indicating that the reduction site of the composite was CuO, and the reaction proceeded according to the Z-scheme. The CuO-Au-TiO composites also exhibited photocatalytic activity under visible light illumination. The oxidation state of Cu in the CuO-Au-TiO composite gradually changed from Cu(I) to Cu(II) during the photocatalytic Cr(VI) reduction. However the composite maintained its high photocatalytic performance even after oxidation. The role of Au in the CuO-Au-TiO composite was examined by comparing the properties of the CuO-Au-TiO composite with those of the CuO-TiO composite prepared via direct CuO deposition on TiO.