Novel C-dots/titanate nanotubular hybrid materials with enhanced optical and photocatalytic properties

Abstract

Advanced nanomaterials with enhanced optical and photocatalytic properties for the photodegradation of organic pollutants, in particular pharmaceuticals and personal care products (PPCPs), were successfully prepared by a swift one-pot synthesis. Nanostructured materials were synthesized through an integrated hydrothermal procedure which generates titanate nanotubes (TNTs) with different carbon dots (C-dots) contents, from an amorphous titanium oxide-based source and cork industry wastewaters (CIWWs) as carbon source. Their structural, microstructural, morphological, and optical properties were studied by XRD, TEM, UV-Vis diffuse reflectance and photoluminescence spectroscopies. As aimed, the hybrid C-dots/TNT nanomaterials extend their light absorption towards the red, in comparison to pristine TNTs, prompting them for a more efficient use of light in photocatalysis by widening the TNTs energy uptake range. The decrease of bandgap energy with increasing sample's C-dots content seems to be originated from energy intermediate states formed within the TNTs forbidden band resulting from Ti-O-C bonds established between the TNTs and the C-dots that form tails of states. The as-synthesized C-dots/TNT samples were tested in the photodegradation of caffeine as a pollutant model. Rewarding results were obtained, with the hybrid C-dots/TNT nanomaterials showing significant enhanced photocatalytic ability toward caffeine degradation in comparison to pristine TNTs. Photocatalysis assays in the presence of scavengers and/or in the absence of oxygen were also performed aiming to characterize the most reactive species formed during the semiconductor photo-activation process and thus assessing to possible reactive pathways underpinning the photocatalytic activity of the hybrid C-dots/TNT nanomaterials.