Synthesis and post-heat treatment of complex compositions in Cu-Ti-O system: Phase investigation and optical properties

Thin layers of CuxTiOy and CuO/TiO2 compositions were successfully synthesized and coated on an alumina foam separately through a facile solution combustion synthesis method. The chemical composition, morphology, and microstructure of the synthesized powders and coated samples were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) methods, respectively. Depending on the initial temperature of the combustion process and/or the duration of the further heat treatment process, XRD results confirmed the crystallization of the CuO, TiO2, CuTiO3, and Cu3TiO4 phases. Results of UV–vis diffuse reflectance spectroscopy (DRS) illustrated a broad absorption bandwidth covering from 350 nm to 800 nm in the synthesized samples. Prolonging the duration of the heat treatment process at 1000 °C from 20 to 240 min diminished the bandgap values of the prepared samples from 2.9 to 2.07 eV and increased the visible absorption efficiency. The photoluminescence (PL) results revealed that the coated layers could generate UV, blue, and red light emissions. X-ray photoelectron spectroscopy (XPS) analysis was carried out to highlight the change in the surface composition during the local melting and solidification process in the simultaneously synthesized and coated samples. XPS results showed that the surface composition of the coated layer is mostly composed of Cu2+. The photocatalytic performance of the coated foam against methylene blue was about 70 % as a result of the presence of copper oxide on the surface layer. Methanol, ethanol, and acetic acid were used as the electron, hole, and radical scavengers, respectively. Acetic acid as a scavenger was more effective than methanol and ethanol in declining the photocatalyst performance. The photocatalytic activity of the sample containing complex oxides such as CuTiO3 and Cu3TiO4 stayed approximately unchanged in the presence of methanol and ethanol.