Vertically aligned rutile TiO2 nanorods sensitized with sulfur and nitrogen co-doped graphene quantum dots for water splitting: An energy level study

Abstract

Highly S and N co-doped graphene quantum dots (SNGQDs) with an average width of ∼4 nm and a broad absorption band in the visible region of light were investigated as an effective light absorber, and their LUMO and HOMO energy states against the vacuum were determined using cyclic voltammetry for the first time. Vertically deposited TiO2 nanorods films were decorated with various amounts of the SNGQD solution (x = 5, 10, 20 and 30 μL) by a spin coater and their photovoltaic properties were comprehensively investigated for water splitting applications. Optical characterizations reveal that the SNGQDs are highly photoluminescent and absorb UV and visible photons with wavelengths up to 700 nm. The prepared SNGQDs–x/TiO2 electrode shows a photocurrent enhancement of ∼4.5× as compared to the bare TiO2 electrode for the optimum sample (x = 20 μL) at an applied voltage of P = 0.5 V using 1 M Na2SO4 solution as the electrolyte.