A “turn-off” photoluminescent sensor for H2O2 detection based on a zinc oxide–graphene quantum dot (ZnO–GQD) nanocomposite and the role of amine in the development of GQD

Abstract

In this work, graphene quantum dots (GQD) were prepared through a hydrothermal process. The photoluminescence (PL) emission spectrum for GQD prepared with high NH₄OH concentration (sample D1-t) was attained at lower wavelength (406 nm), compared to GQD synthesized with low NH₄OH 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 H₂O₂ detection tested by photoluminescence spectroscopy, was found to occur thanks to the ZnO from the nanocomposite and its interaction with H₂O₂, producing a quenching effect. This quenching was accentuated by the increase of the H₂O₂ concentration. Such properties suggest the ZnO–GQD nanocomposite as a candidate to be used as a sensor material.