Effects of calcining temperature on formation of hierarchical TiO2/g-C3N4 hybrids as an effective Z-scheme heterojunction photocatalyst

Hierarchical TiO 2 /g-C 3 N 4 heterojunction photocatalysts with well-defined multiscale porous TiO 2 framework are synthesized by simply calcinating tetrabutyl titanate and melamine precursors. The samples have been characterized by XRD, XPS, SEM, TEM, FTIR, nitrogen absorption-desorption equipment and TGA. The photocatalytic activity of these samples has been investigated in photo-degradation of Rhodamine B (RhB). The results show that calcining temperature critically affects the microstructure, surface area, interface structure and catalytic properties of the prepared samples. At the optimal calcining temperature of 550 °C, the apparent reaction rate constant of the catalyst is 55.0 × 10 −3  min −1 , which is 16.2 fold of pure TiO 2 (3.4 × 10 −3  min −1 ) and 3.4 fold of pure g-C 3 N 4 (16.4 × 10 −3  min −1 ), respectively. The strengthened visible-light-driven photocatalytic activity is attributed to the formation of a unique Z-scheme TiO 2 /g-C 3 N 4 heterojunction due to C- or N-doping at the surface of the porous TiO 2 framework. This mechanism explains the observation in a series of radical trapping experiments that superoxide ions and photo-generated holes play major roles in the photo-decolorizing process while hydroxyl radicals are also involved with a minor role.