Removal of hexavalent chromium from water by Z-scheme photocatalysis using TiO2 (rutile) nanorods loaded with Au core-Cu2O shell particles.

All-solid-state Z-scheme photocatalysts, containing Cu2O, TiO2 (rutile), and Au as the electron mediator, were prepared and applied to the reduction of Cr(VI) in aqueous solutions. The Cu2O-Au-TiO2 composites were prepared by loading Au core-Cu2O shell hemisphere particles on TiO2 (rutile) nanorods using a two-step photocatalytic deposition process. Under ultraviolet-visible (UV-vis) light illumination, the Cu2O-Au-TiO2 composites exhibited higher photocatalytic Cr(VI) reduction activities than those exhibited by single TiO2 (rutile) and Cu2O. In this reaction, a precipitate containing Cr, which was considered to be Cr(OH)3, was deposited site-selectively on the Au core-Cu2O shell particles of the composites, indicating that the reduction site of the composite was Cu2O, and the reaction proceeded according to the Z-scheme. The Cu2O-Au-TiO2 composites also exhibited photocatalytic activity under visible light illumination. The oxidation state of Cu in the Cu2O-Au-TiO2 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 Cu2O-Au-TiO2 composite was examined by comparing the properties of the Cu2O-Au-TiO2 composite with those of the Cu2O-TiO2 composite prepared via direct Cu2O deposition on TiO2.