Abstract
Carbon quantum dots (CQDs) are nanomaterials with a particle size range of 2 to 10 nm. CQDs have a wide range of applications such as medical diagnostics, bio-imaging, biosensors, coatings, solar cells, and photocatalysis. Although the effect of various experimental parameters, such as the synthesis method, reaction time, etc., have been investigated, the effect of different feedstocks on CQDs has not been studied yet. In this study, CQDs were synthesized from hydroxymethylfurfural, furfural, and microcrystalline cellulose via hydrothermal carbonization at 220 °C for 30 min of residence time. The produced CQDs showed green luminescence behavior under the short-wavelength UV light. Furthermore, the optical properties of CQDs were investigated using ultraviolet-visible spectroscopy and emission spectrophotometer, while the morphology and chemical bonds of CQDs were investigated using transmission electron microscopy and Fourier-transform infrared spectroscopy, respectively. Results showed that all CQDs produced from various precursors have absorption and emission properties but these optical properties are highly dependent on the type of precursor. For instance, the mean particle sizes were 6.36 ± 0.54, 5.35 ± 0.56, and 3.94 ± 0.60 nm for the synthesized CQDs from microcrystalline cellulose, hydroxymethylfurfural, and furfural, respectively, which appeared to have similar trends in emission intensities. In addition, the synthesized CQDs experienced different functionality (e.g., C=O, O-H, C-O) resulting in different absorption behavior.
Highlights
Carbon quantum dots (CQDs) are a new class of carbon nanomaterials sized below10 nm [1,2]
The top-down approach refers to the breakdown of larger carbon particles by laser ablation, electrochemical oxidation, chemical oxidation, and ultrasonic synthesis [14,15,16,17], while the bottom-up approach synthesizes the CQDs from molecular precursors through microwave synthesis, thermal decomposition, and hydrothermal treatment [4,18,19,20]
From the UV-vis spectra shown in Figure 2, it was observed that all CQDs exhibit a broad range of absorption in the UV region, with the tails of the spectra in the near-visible region
Summary
Carbon quantum dots (CQDs) are a new class of carbon nanomaterials sized below10 nm [1,2]. CQDs have attracted tremendous attention in the research community due to their unique photoluminescence (PL) properties, biocompatibility, electrochemical luminescence properties, and low toxicity [3,4,5]. These properties enable them to be used in bio-imaging, biosensor, drug delivery, and photo-catalysis applications [6,7,8,9,10,11,12,13]. Hydrothermal carbonization (HTC) has been considered as the most promising method due to high quantum efficiency, lower cost, environmentally friendly nature, and non-toxicity [4,5,20,21,22]
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