Microwave-Assisted Dual Fabrication of Graphene Quantum Dots and Turbostratic Carbon: Implications for Biomedical and Photocatalytic Applications

Abstract

Carbon-based nanomaterials have attracted tremendous interest as metal-free fluorophores and photocatalysts due to their unique optoelectronic properties and (photo)stability. Herein, we report the ultrarapid (75 s) microwave-assisted synthesis of two distinct carbon-based materials using benzoic acid (BA) as the sole precursor. Comprehensive structural and spectroscopic characterization allowed the identification of graphene quantum dots (GQDs) and turbostratic carbon (TC) formed simultaneously. The GQDs (average size of 6.5 nm) exhibit excitation-independent green emission with a photoluminescence quantum yield of 11%, show excellent cytocompatibility toward HaCaT cells at concentrations up to 10 μg·mL⁻¹, and potential selective toxicity toward skin cancer cells. In contrast, the TC demonstrates efficient visible-light photocatalytic activity for the photoreduction of methyl viologen (MV²⁺) to MV^•+, maintaining activity over at least four consecutive cycles, thus evidencing its performance as a robust carbon-based photocatalyst for electron−transfer reactions. Overall, this work presents an eco-friendly and fast synthetic strategy to obtain two structurally and functionally distinct carbon nanomaterials with potential for biological and visible-light photocatalytic applications, respectively.