Effect of Ag Co-catalyst on TiO₂-Cu₂O nanocomposites structure and apparent visible photocatalytic activity

Although Cu₂O is a commonly used narrow band gap semiconductor to fabricate visible response photocatalysts, up to date there are only a few reports on Ag co-catalysed TiO₂-Cu₂O nanocomposites. Herein we report a facile wet chemical synthesis approach to prepare TiO₂-Ag-Cu₂O ternary hybrid nanomaterials. Uniquely, both the effect of Ag content and the synthesis sequence of Ag deposition step was investigated on the visible decoloration rate. The crystal structure, morphology, optical and dark adsorption properties of the nanostructures were characterized by XRD, SEM, TEM and diffuse reflectance, respectively. Due to the mixed indirect and direct nature of the nanocomposites, the band gap estimation was performed by using both Tauc plot and differential reflectance model. The dark adsorption properties of catalysts could be typically well-approximated by pseudo-second order kinetics, while TiO₂-Ag(5%)-Cu₂O catalyst cannot be described by standard models due to a delayed adsorption behaviour observed in the first 50 min. The apparent visible activities followed pseudo-zero order kinetics. It was found that TiO₂-Ag(3%)-Cu₂O catalyst exhibited the highest rate constant which was ca. two times as high as that of the binary TiO₂-Cu₂O catalyst. The synthesis sequence of the Ag deposition step significantly altered the material properties which resulted in different dark adsorption and apparent visible activities.