Photocatalytic elimination of water pollutants using innovative titania thin film heterostructures embedding carbon quantum dots

Titanium dioxide based photocatalysis is a well-established advanced oxidation process (AOP) that recently has expanded its borders comprising advanced reduction processes (ARPs) as well. To enhance the photocatalytic activity, titania heterostructures embedding semiconductors, or clays, or plasmonic metals can be proposed as very promising solutions. In this study, carbon quantum dots (C-QDs) prepared hydrothermally, were successfully combined with titania (TiO2). The photocatalytic activity of the C-QDs/TiO2 heterostructures was successfully tested in the photocatalytic reduction of 4-nitrophenol (PNP) and hexavalent chromium (Cr+6) pollutants. Moreover, the composite thin films were also effectively used in photocatalytic degradation of characteristic dye contaminants, thus confirming their high potential for photoinduced oxidation reactions. The mechanisms of the photocatalytic reactions were studied using appropriate scavengers and it was demonstrated that electrons (e-) are at the origin of the photocatalytic reduction of Cr+6 and 4-NP, while holes (h+) are the main active species for the photocatalytic oxidation reactions.