Minimization of recombination losses in 3D nanostructured TiO2 coated with few layered g-C3N4 for extended photo-response

Abstract

We have successfully fabricated 3D (3-dimensional) nanostructures of TiO2 coated with a g-C3N4 layer via hydrothermal and sintering methods to enhance photoelectrochemical (PEC) performance. Due to the coupling of TiO2 and g-C3N4, the nanostructures exhibited good performance as the higher conduction band of g-C3N4, which can be combined with TiO2. To fabricate 3D nanostructures of g-C3N4/TiO2, TiO2 was first grown as a double layer structure on FTO (Fluorine-doped tin oxide) substrate at 150°C for 3 h. After this, the g-C3N4 layer was coated on the TiO2 film at 520°C for 4 h. As-prepared samples were varied according to loading of melamine powder, with values of loading of 0.25 g, 0.5 g, 0.75 g, and 1 g. From SEM and TEM analysis, it was possible to clearly observe the 3D sample morphologies. From the PEC measurement, 0.5 g of g-C3N4/TiO2 film was found to exhibit the highest current density of 0.12 mA/cm2, along with a long-term stability of 5 h. Compared to the pristine TiO2, and to the 0.25 g, 0.75 g, and 1 g g-C3N4/TiO2 films, the 0.5 g of g-C3N4/TiO2 sample was coated with a thin g-C3N4 layer that caused separation of the electrons and the holes; this led to a decreasing recombination. This unique structure can be used in photoelectrochemical applications.