Control of Functionalities in GO: Effect of Bronsted Acids as Supported by Ab Initio Simulations and Experiments

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

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.

Functionalized graphene/polystyrene composite, green synthesis and characterization

A composite of sulfonated waste polystyrene (SWPS) and graphene oxide was synthetized by an inverse coprecipitation in-situ compound technology. Polystyrene (PS) has a wide range of applications due to its high mechanical property. the graphene were incorporated into sulfonated polystyrene (SPS) to improve the thermal stability and mechanical performance of the composites. Functionalized graphene were synthesized with tour method by using recovered anode (graphite) of dry batteries while sulfonated waste expanded polystyrene was obtained through sulfonation of the polymer. The SPS and GO + SPS composite were characterized using by Fourier Transform Infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). While the degree of sulfonation (DS) was determined through elemental analysis. The results show the degree of sulfonation of the composite is 23.5% and its ion exchange capacity is 1.2 meq g^-1. TEM analysis revealed that the GO particles were loaded on the surface of sulphonated polystyrene and that the SWPS was intercalated into the sub-layers of nanoG homogeneously, which result in an increase in electrical conduction.