Outstanding visible light photocatalysis by nano-TiO2 hybrids with nitrogen-doped carbon quantum dots and/or reduced graphene oxide

Historically, titanium dioxide (TiO2) has been one of the most extensively studied metal oxide photocatalyst, however, it suffers from a large bandgap and fast charge recombination. We report for the first time the use of green, rapid, single-step continuous hydrothermal flow synthesis for the preparation of TiO2, and TiO2 hybrids with reduced graphene oxide (rGO) and/or N-doped carbon quantum dots (NCQD) with leap step enhancement in photocatalytic activity. Using a solar light generator under ambient conditions with no extra oxygen gas added, we observed the evolution reaction of the model pollutant (methylene blue) in real time. Tailoring of the light adsorption to match of that solar spectrum, was achieved by a combination of materials of nano-TiO2 hybrids of nitrogen-doped carbon quantum dots and graphene in its reduced form with a photocatalytic rate constant of ca. 25 x 10-5 s-1. Using a diversity of state-of-the-art techniques including high-resolution transmission electron microscopy, transient photoluminescence, X-ray photoelectron spectroscopy and high accuracy, sophisticated hybrid density functional theory calculations we have gained substantial insight into the charge transfer and modulation of the energy band edges of anatase due to the presence of graphene or carbon dots, parameters which play a key role in improving drastically the photocatalytic efficiencies when compared to pristine titania. More importantly, we prove that a combination of features and materials display the best photocatalytic behaviour. This performance is delivered in a greener synthetic process, that not only produces photocatalytic materials with optimised properties and tailored visible light adsorption and efficiency, but also provides a path to industrialization.