A "turn-off" photoluminescent sensor for HO detection based on a zinc oxide-graphene quantum dot (ZnO-GQD) nanocomposite and the role of amine in the development of GQD.

In this work, graphene quantum dots (GQD) were prepared through a hydrothermal process. The photoluminescence (PL) emission spectrum for GQD prepared with high NHOH concentration (sample D1-t) was attained at lower wavelength (406 nm), compared to GQD synthesized with low NHOH concentration (sample D2-t attained at 418 nm). From these results, a smaller particle size for D1-t was deduced; according to TEM images the GQD particles are around 5 nm. The Raman / ratio which is related to C-O groups at the edges of GQD and the full width at half maximum was lower for D1-t than D2-t. This was ascribed to the amine group incorporation at the edges and at the basal planes in D1-t, whilst in D2-t they prefer principally the edges of the GQD structure. The ZnO nanoparticles bonded to GQD (ZnO-GQD, nanocomposites) enhance the PL emission intensity. The HO detection tested by photoluminescence spectroscopy, was found to occur thanks to the ZnO from the nanocomposite and its interaction with HO, producing a quenching effect. This quenching was accentuated by the increase of the HO concentration. Such properties suggest the ZnO-GQD nanocomposite as a candidate to be used as a sensor material.