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.
Highlights
Water pollution by heavy metal ions due to the emission of industrial waste presents a major environmental problem [1,2,3]
Comparing the Fourier Transform infrared spectroscopy (FTIR) spectra of these nitrogen-doped carbon dots (N-CDs), we found that the center of the absorption peak of the bonds transfers from 3250 to 3300 cm−1 as the porosities of the copper fibers ranged from 98% to
The N-CDs with a high PL quantum yield (QY) and stability were synthesized by applying a microreactor with different porosities of copper fibers
Summary
Water pollution by heavy metal ions due to the emission of industrial waste presents a major environmental problem [1,2,3]. Several methods, such as anodic stripping voltammetry [11], Auger-electron spectroscopy [12], inductively coupled plasma mass spectrometry (IC-PMS) [13], atomic absorption spectrometry (AAS) [14], atomic fluorescence spectroscopy (AFS) [15], and X-ray absorption spectroscopy (XBS) [16] have been applied for the detection of Hg2+ ions These techniques need large-scale instruments, complex sample preparation, time-consuming procedures, and trained personnel, which restrict their practical applications in the routine detecting of Hg2+ [17,18]. Many fluorescent probes based on quantum dots, organic fluorescent materials, and noble-metal nanoclusters have been developed [22,23,24] Their practical applications have been limited due to their disadvantages, including the toxic materials involved, low photostability, low selectivity, and complex preparation process. In order to improve the detection performance for practical use, new fluorescent probes need to be developed
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