Effects of silver substrates on the visible light photocatalytic activities of copper-doped titanium dioxide thin films

Novel copper-doped titanium dioxide (Cu-doped TiO2) thin films on silver (Ag) substrates with different thicknesses were prepared by sol–gel and magnetron sputtering methods. The influences of the Ag substrate thickness on the morphology and performance of the films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV–visible spectroscopy, and photocatalytic degradation testing with methylene blue aqueous solution under visible light irradiation. The results indicated that Ag substrates with an optimal thickness of 30 nm not only maintained the tiny nanocrystals but also greatly improved dispersion of the nanoparticles on the surface of the nanofilms. Furthermore, during the calcination process, part of the Ag atoms diffused from the substrates into the Cu–TiO2 films and substituted for the Cu ions to form Ag–TiO2. A proper Ag substrate thickness (30 nm) greatly improved the photocatalytic properties of TiO2 with photocatalytic efficiency, reaching approximately 86% in 300 minutes under visible light irradiation. However, an excess of Ag substrate not only led to the Cu ion separating out in the form of CuO but also resulted in the agglomeration of TiO2 particles on the surface, which were detrimental to photocatalytic activities.