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.