Synthesis of graphene quantum dots via one step hydrothermal cutting: The synergistic effect of graphene oxide and sodium hydroxide

Abstract

This study reports a one-step hydrothermal cutting method of synthesizing graphene quantum dots (GQDs) using commercially available, 4–10% edge oxidized precursor graphene oxide (GO). The controlled properties of synthesized GQDs formation on the treatment solely with alkali additives, sodium hydroxide (NaOH), act as alkaline-induced fragmentation and surface modifier to perform a surface functionalization. No additional hazardous chemicals were used during the synthesis process, contributing to the cost-effectiveness and simplicity of the GQDs formation and eco-friendly nature processes. Additionally, non-doped GQDs were synthesized at quantitative parameters: NaOH concentration (0.1 M), temperature (200 °C), and reaction time (24 h), that can achieve effective performance characteristics for sensing platforms. The synergistic mechanism between GO and NaOH in synthesizing GQDs involves three key processes: i) pre-treatment with NaOH, ii) hydrothermal cutting, and iii) reduction by NaOH. The GQDs were through the characterization process to trace the transformation using different analytical techniques such as ultra-high resolution scanning electron microscope (UHR-SEM), energy-dispersive x-ray spectroscopy (EDX), transmission electron microscope (TEM), photoluminescence spectroscopy (PL), x-ray diffraction (XRD),  ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and zeta potential to confirm their structural, optical, and surface characteristics. The finding demonstrated that NaOH-mediated hydrothermal cleavage without hazardous reagents, offering an eco-friendly approach, and successfully synthesized non-doped GQDs at average size of ~1.3 nm which led to an impressive enhancement in optical performance. The high oxygen content and surface functionality in synthesized GQDs were believed to provide active sites for molecule binding potentially used in sensing applications particularly in heavy metal ion detection, as evidenced by comprehensive analytical characterization.