A “turn-off” photoluminescent sensor for H(2)O(2) 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 NH(4)OH concentration (sample D1-t) was attained at lower wavelength (406 nm), compared to GQD synthesized with low NH(4)OH 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 I(D3)/I(G) 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 H(2)O(2) detection tested by photoluminescence spectroscopy, was found to occur thanks to the ZnO from the nanocomposite and its interaction with H(2)O(2), producing a quenching effect. This quenching was accentuated by the increase of the H(2)O(2) concentration. Such properties suggest the ZnO–GQD nanocomposite as a candidate to be used as a sensor material.