Facile Synthesis of Fluorescent Nitrogen‐Doped Carbon Quantum Dots Using Scindapsus as a Carbon Source

Abstract

A green method is used to synthesize nitrogen-doped carbon quantum dots (N-CQDs) using dried scindapsus leaves as the carbon source. The average diameter of the N-CQDs varies from 2 to 6 nm. The N-CQDs emit blue light, and the emission wavelength exhibits excitation wavelength dependence. The characteristic peak is found to originate from a N-related state. The surface defects and quantum effects of the CQDs play a strong role in the luminescence process and resulted in the excitation wavelength dependence of the photoluminescence, which is confirmed by changing the solvent to ethanol. This work can encourage the exploration of new carbon sources to synthesize doped CQDs and stimulate investigation of the photoluminescence mechanism of CQDs.

Synthesis and Properties of Nitrogen-Doped Carbon Quantum Dots Using Lactic Acid as Carbon Source

“…We synthesized N-CQDs through one-step hydrothermal method employing L-lactic acid as carbon source and ethylenediamine as nitrogen source [26,33] (Scheme 1). 30.0 g L-lactic acid and 2 mL ethylenediamine were mixed with 30 mL deionized water in a 100 mL three-necked flask, then the solution was heated up to 150 • C and reacted for 12 h. The reaction solution was then allowed to cool naturally before even being centrifuged for 10 min at 10,000 rpm, The supernatant was collected and transferred to a dialysis bag with a molecular weight cut-off of 1000 Da, then dialyzed for 72 h with deionized water in the glass flume.…”

“…The surface chemical composition and element status of N-CQDs were investigated further utilizing X-ray photoelectron spectroscopy (XPS). The XPS spectrum of N-CQD in Figure 2a shows three peaks at 532.3 eV, 286 eV and 400.4 eV, corresponding to O1s, C1s and N1s, respectively [26,44,45], indicating that N-CQDs are mostly constituted of carbon, nitrogen, and oxygen. The high resolution XPS spectrum of C1s in Figure 2b shows five peaks at 284.6 eV, 285.5 eV, 286.4 eV, 287.1 eV and 288.3 eV that may be traced to C=C, C-C, C-N, C-O and C=O bonding on the surface of N-CQDs [26,46].…”

“…The XPS spectrum of N-CQD in Figure 2a shows three peaks at 532.3 eV, 286 eV and 400.4 eV, corresponding to O1s, C1s and N1s, respectively [26,44,45], indicating that N-CQDs are mostly constituted of carbon, nitrogen, and oxygen. The high resolution XPS spectrum of C1s in Figure 2b shows five peaks at 284.6 eV, 285.5 eV, 286.4 eV, 287.1 eV and 288.3 eV that may be traced to C=C, C-C, C-N, C-O and C=O bonding on the surface of N-CQDs [26,46]. In Figure 2c, the high resolution XPS spectrum of N1s displays two peaks at 401.3eV and 399.8 eV caused by C-N and N-H, respectively [32,47].…”

“…The complexation of Fe 3+ with the carboxyl group, amino group and hydroxyl group on the surface of N-CQDs may be responsible for the fluorescence quenching caused by Fe 3+ [26,60]. Meanwhile, the N atom has a large electronegativity, which is conducive to enhancing the electron density distribution on N-CQDs surface and promoting the complexation of Fe 3+ with N-CQDs surface functional groups [61].…”

“…These synthetic methods have two main purposes: one purpose is to crack different carbon source materials, and the other is the carbonization of small molecules or polymers [20]. Meanwhile, a variety of carbon-sources materials, including graphite [21], citric acid [22,23], watermelon peel [24], saccharum officinarum juice [25], scindapsus leaves [26], and others, have been developed for the preparation of CQDs. Therefore, various synthesis methods and carbon sources may obtain CQDs with various sizes, structures and excitation wavelengths, which will have an obvious impact on the fluorescence emission intensity of CQDs.…”