Highly Photoluminescent and Stable N-Doped Carbon Dots as Nanoprobes for Hg2+ Detection

Abstract

We developed a microreactor with porous copper fibers for synthesizing nitrogen-doped carbon dots (N-CDs) with a high stability and photoluminescence (PL) quantum yield (QY). By optimizing synthesis conditions, including the reaction temperature, flow rate, ethylenediamine dosage, and porosity of copper fibers, the N-CDs with a high PL QY of 73% were achieved. The PL QY of N-CDs was two times higher with copper fibers than without. The interrelations between the copper fibers with different porosities and the N-CDs were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). The results demonstrate that the elemental contents and surface functional groups of N-CDs are significantly influenced by the porosity of copper fibers. The N-CDs can be used to effectively and selectively detect Hg2+ ions with a good linear response in the 0~50 μM Hg2+ ions concentration range, and the lowest limit of detection (LOD) is 2.54 nM, suggesting that the N-CDs have great potential for applications in the fields of environmental and hazard detection. Further studies reveal that the different d orbital energy levels of Hg2+ compared to those of other metal ions can affect the efficiency of electron transfer and thereby result in their different response in fluorescence quenching towards N-CDs.

Evaluation of the Environmental Impact and Efficiency of N-Doping Strategies in the Synthesis of Carbon Dots

“…More importantly, N-doping generally enhances the fluorescence quantum yield (QY FL ) of the CDs [27][28][29], which has made N-doping one of the main strategies for enhancing the photoluminescence of CDs [3,30,31]. N-doping is generally achieved by adding a nitrogen-rich small organic molecule as a nitrogen precursor to the carbon precursor in hydrothermal-based bottom-up synthetic routes, with typical nitrogen precursors being molecules such as urea [17,26] and EDA [32,33].…”

“…Herein, the aim of this work was to assess the efficiency and sustainability of different N-doping strategies employed during the synthesis. Namely, CDs prepared from CA (a typical carbon precursor [17,[23][24][25][26]) were N-doped via two different strategies: (1) Microwave-assisted hydrothermal synthesis with addition of N-containing small organic molecules (urea or EDA), which are typically used as nitrogen precursors [17,26,32,33]; (2) microwave-assisted solvothermal synthesis in an N-containing solvent (DMF, acetonitrile or pyridine). The first step of this study was the characterization of the obtained CDs by X-ray photoelectron spectroscopy (XPS), UV-Visible (UV-Vis) spectroscopy and fluorescence spectroscopy, and by dynamic light scattering (DLS), which allowed us to determine the efficiency of N-doping and its effects on the photoluminescence of the CDs.…”

Designing of Ultrafine PdNPs Immobilized Pyridinic‐NDoped Carbon and Evaluation of its Catalytic Potential for Konevenagel Condensation, Synthesis of 4H‐pyran Derivatives and Nitroreduction

“…The leaching of PdNPs was also prevented due to this MSI. The XRD pattern (Figure e) of the Pd@NC showed wide diffraction peak at 23.59°, which revealed a distorted graphitic structure corresponding to (002) diffraction pattern of amorphous carbon . Furthermore, the XRD spectrum of PdNPs was also depicted in Figure 3e which indicated the diffraction peaks at 39.69° which corresponds to the Pd (111) .…”

Transport of N-CD and Pre-Sorbed Pb in Saturated Porous Media

“…Therefore, a correction was applied to convert the measured absorbances to the corresponding CD and N-CD concentrations at different pH and IS conditions in the transport experiments. The absorbance of N-CDs decreased slightly with increases in NaCl/CaCl2 concentrations ( Figure 2D), likely due to alteration of surface plasmon resonance at higher ionic strengths due to Na + and Ca 2+ sorption or due to N-CD aggregation [25]. Therefore, a correction was applied to convert the measured absorbances to the corresponding CD and N-CD concentrations at different pH and IS conditions in the transport experiments.…”