A simple and green method for the production of nanostructured materials from poly(vinyl alcohol)/graphene quantum dots

Abstract

Herein, a simple, low-cost and fast approach was proposed to produce fluorescent fibers from the electrospinning of poly (vinyl alcohol)/water-soluble graphene quantum dots (GQDs). Initially, the preparation of GQDs was explored via an easy bottom-up method based on the incomplete carbonization of citric acid under different times (30, 45 and 60 min). Next, fluorescent fibrous mats were prepared from the electrospinning of PVA solutions with different contents of GQDs. These materials were further characterized via several techniques, including High-Resolution Transmission Electronic Microscopy (HRTEM), UV–vis and fluorescence spectroscopies, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The GQDs presented a strong blue photoluminescence under UV light exposure. Among the investigated carbonization times, 45 min led to GQDs with the highest fluorescence intensity (regardless the pH) and fluorescence quantum yield (10.5%). HRTEM analysis showed that this carbonization time led to GQDs with uniform and homogeneous dimensions, with an average diameter of 2.5 ± 0.2 nm. After electrospinning, HRTEM revealed a homogeneous distribution of GQDs into the polymeric ultrathin fibers, while increasing the GQDs content in the PVA matrix led to a clear increase in the fluorescence intensity. Interestingly, as the GQDs content increased, a slight red-shift was observed for the maximum of emission, which may be related to light re-adsorption or even as result of Föster Resonance Energy Transfer. This set of results widens the perspectives of application of this low-cost substrate in many fields, via a simple approach using a water-soluble polymer and a naturally occurring component from citrus fruits.