Issue 18, 2024

Open system massive synthesis of narrow-band blue and green fluorescent graphene quantum dots and their application in water sensing

Abstract

Graphene quantum dots (GQDs) are environmentally friendly fluorescent carbon-based nanomaterials. However, there is no report on the massive synthesis of GQDs with narrow-band fluorescence and a high photoluminescence quantum yield (PLQY) using a simple liquid-phase method under atmospheric conditions. In this study, GQDs were successfully synthesized in ∼100% product yield by heating phloroglucinol (PG) with Na3PO4·12H2O in 1,2-pentanediol at 180 °C for 6 h in an open system with air flow, followed by dialysis purification. The high product yield was attributed to the addition of Na3PO4·12H2O as a base catalyst, which promoted the dehydration–condensation reaction between PG molecules. The dispersion of PG derived GQDs (PG-GQDs) in ethanol resulted in blue fluorescence with a full width at half maximum of 32 nm and a PLQY of 54%. Further purification of PG-GQDs by silica gel column chromatography improved the PLQY to 75%. Fourier-transform infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy confirmed that dehydration–condensation reactions occurred not only between PGs but also between GQDs and 1,2-pentanediol. The binding of 1,2-pentanediol to the edges of GQDs suppressed the stacking of GQDs and prevented concentration quenching, resulting in a high PLQY. PG-GQDs exhibited negative fluorescence solvatochromism, i.e., the fluorescence wavelength blue-shifted with increasing solvent polarity. Dispersion of PG-GQDs in N-methyl-2-pyrrolidone (MP) resulted in green fluorescence with a PLQY of 96%. Dispersion of PG-GQDs in water resulted in blue fluorescence and a low PLQY of 6% at pH 7, while the PLQY was more than 50% at pH ≥ 11. Using these properties, the sensing of water (pH 13) in MP was investigated. The results showed that as the water content was increased from 0% to 100%, the fluorescence color gradually changed from green to blue and the fluorescence wavelength continuously shifted from 514 nm to 466 nm, indicating their applicability in water sensing.

Graphical abstract: Open system massive synthesis of narrow-band blue and green fluorescent graphene quantum dots and their application in water sensing

Supplementary files

Article information

Article type
Paper
Submitted
12 Mar 2024
Accepted
04 Apr 2024
First published
05 Apr 2024
This article is Open Access
Creative Commons BY license

J. Mater. Chem. C, 2024,12, 6548-6558

Open system massive synthesis of narrow-band blue and green fluorescent graphene quantum dots and their application in water sensing

Y. Ochi, A. Otani, R. Katakami, A. Ogura, K. Takao, Y. Iso and T. Isobe, J. Mater. Chem. C, 2024, 12, 6548 DOI: 10.1039/D4TC00983E

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