Abstract
Fluorescent carbon quantum dots (CQDs) have held great promise in analytical and environmental fields thanks to their congenitally fascinating virtues. However, low quantum yield (QY) and modest fluorescent stability still restrict their practical applications. In this investigation, a green hydrothermal strategy has been devised to produce water-soluble nitrogen/phosphorus (N/P) co-doped CQDs from edible Eleocharis dulcis with multi-heteroatoms. Without any additives and further surface modifications, the resultant CQDs exhibited tunable photoluminescence just by changing hydrothermal temperatures. Appealingly, they showed remarkable excitation-dependent emission, high QY, superior fluorescence stability, and long lifetime. By extending the CQDs solutions as a “fluorescent ink”, we found their potential application in the anti-counterfeit field. When further evaluated as a fluorescence sensor, the N/P co-doped CQDs demonstrated a wide-range determination capability in inorganic cations, and especially the remarkable sensitivity and selectivity for elemental Fe3+. More significantly, the green methodology we developed here can be readily generalized for scalable production of high-quality CQDs with tunable emission for versatile applications.
Highlights
Carbon quantum dots (CQDs) with the size of 2–10 nm have emerged as the promising photoluminescent (PL) material due to their high stability, low toxicity, excellent biocompatibility, versatile surface chemistry, and cost-efficient nature along with easy availability [1,2]
The morphologies of the carbon quantum dots (CQDs) were determined by high-resolution transmission electron microscope (HRTEM) (JEOL JEM 2100 system operating at 200 kV, Akishima-shi, Tokyo, Japan)
Eleocharis dulcis connately contains carbohydrates, proteins, vitamins, minerals (Ca, P and Fe) as well as an assortment of phytochemicals, which endows it with abundance in the elemental C, N, O, and P
Summary
Carbon quantum dots (CQDs) with the size of 2–10 nm have emerged as the promising photoluminescent (PL) material due to their high stability, low toxicity, excellent biocompatibility, versatile surface chemistry, and cost-efficient nature along with easy availability [1,2]. We present a simple, low-cost and green synthetic strategy towards the water-soluble multi-colored nitrogen/phosphorus (N/P) co-doped CQDs via one-step hydrothermal treatment of the Eleocharis dulcis juice without any more additive. The as-synthesized N/P co-doped CQDs showed strong fluorescence, which is highly stable under a high ionic strength environment, and under UV light irradiation, treatment with constant temperatures, and various acidic/neutral/alkaline conditions. Owing to their fluorescent nature, the potential use as an invisible fluorescent ink was assessed. Fluorescence QY, integrated area of emission, the absorbance at the excited wavelength, and the refractive index for the reference, respectively
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