Photoelectrochemical activity of graphene quantum dots/hierarchical porous TiO₂ photoanode

In this study, initially graphene quantum dots (GQDs) were synthesized by an electrochemical technique and hierarchical porous TiO₂ were made by a sol – gel method. Subsequently, GQDs/hierarchical porous TiO₂ nanocomposites were prepared by two different methods for the purpose of comparison: spin coating (SC) and electrophoretic (EP) deposition. The GQDs/hierarchical porous TiO₂ nanocomposites were characterized by various analytical methods including field emission scanning electron microscopy, atomic force microscopy, transmission electron microscopy, high resolution transmission electron microscopy, Fourier transform infra-red spectroscopy, photoluminescence spectroscopy and ultraviolet–visible spectroscopy. Under visible light irradiation, photoanodes made of the hierarchical porous TiO₂, EP- GQDs/hierarchical porous TiO₂ and SC- GQDs/hierarchical porous TiO₂ nanocomposite produced the photocurrent densities of about 1.86, 3.29 and 6.35 A/m², respectively. The results showed that the nanocomposites prepared by the SC technique exhibit a higher photoelectrochemical (PEC) activity as compared to both the EP deposited composite and the pure hierarchical porous TiO₂. Finally, the photoenhancement was described based on a charge transfer mechanism. - Highlights: • Comparison of two deposition methods including spin coating and electrophoretic methods. • Deposition of graphene quantum dots (GQDs) on the porous TiO₂ as a promising photocatalyst for water splitting. • Two models to describe possible charge transfer mechanism at the interface of GQDs/TiO₂ porous in both systems.