Environmentally Benign Synthesis of Blue Fluorescent Graphene Quantum Dots for Nitroaromatic Sensing (p-Nitroaniline and 2,4,6-Trinitrophenol) and Nanophytotoxicity Analysis

Abstract

This work introduces an environmentally benign route for producing strongly blue-emissive graphene quantum dots (GQDs) from graphene oxide synthesized via a modified Tour method. GQDs are nanoscale (<10 nm) fragments of graphene known for their excellent biocompatibility, photostability, and tunable fluorescence properties. The resulting graphene oxide and GQDs were meticulously examined using UV-Vis spectroscopy, FTIR, PXRD, FESEM and TEM. Leveraging their exceptional optical properties, the GQDs were employed to construct a highly sensitive and selective fluorometric platform for the detection of two eco-hazardous nitroaromatic pollutants, para-nitroaniline (PNA) and 2,4,6-trinitrophenol (TNP). The sensing system exhibited impressive analytical performance, achieving low optical detection limits of 0.217 µM for PNA and 0.108 µM for TNP. The fluorescence quenching of GQDs by TNP and PNA is governed by the inner filter effect, accompanied by a static quenching component arising from ground-state complex formation. Beyond their sensing capability, the GQDs were evaluated for ecological safety through a nanophytotoxicity assay using mung bean (Vigna radiata L.) seeds. Although quantum dots are generally considered non-toxic within the research community, no comprehensive studies have examined their effects on seed germination. Addressing this major research gap, our investigation reveals that at sufficiently high concentrations, quantum dots can in fact inhibit seed germination. In contrast, the GQDs used in this study exhibited negligible nanophytotoxicity across a broad concentration range, confirming their strong environmental compatibility. Moreover, when applied as nanoprobes, the working concentrations required are extremely low, rendering them effectively non-toxic. Overall, this work not only introduces GQDs as green, efficient nanosensors but also establishes their value as a platform for assessing the broader environmental implications of quantum-dot-based technologies.