Heteroatom-doped carbon dots (CDs) with a high photoluminescent quantum yield (PLQY) have recently attracted attention due to their applications in chemical sensors, photocatalysis, bioimaging, and drug delivery. Nitrogen and phosphorus are in close proximity to carbon in the periodic table and are key tracking elements in the field of biomedical imaging. These two elements alter the optical and electronic properties of CDs and help improve the fundamental understanding of their PLQY. This can also lead to multifunctional usage in photoimaging and photothermal therapy. However, most PLQYs resulting from the synthesis of P-doped CDs are currently below 50%. These CDs have limited usefulness in the fields of bioimaging and drug delivery. In this study, a single-step, high-efficiency hydrothermal method was applied to synthesize nitrogen and phosphorous-doped carbon dots ((N,P)-CDs) with a PLQY of up to 53.8% with independent emission behavior. Moreover, the CDs presented high monodispersity, robust excitation-independent luminescence, and stability over a large pH range. Spectroscopic investigations indicated that the PLQY of the (N,P)-CDs was primarily due to the addition of P and the passivation effect of the oxidized surface. The excellent fluorescence properties of (N,P)-CDs can be effectively and selectively quenched by Hg 2+ ions. Such systems show a linear response in the 0–900 nM concentration range with a short response time, indicating their potential for applications in the fields of chemistry and biology.
Dendritic fiber nanosilica (DFNS) possesses a unique porous structure, and its potential application for adsorption and separation, particularly of heavy metals, should be explored. This study, to our knowledge, is the first time to introduce fluorescence recognition ability to DFNS and to combine it with polymer materials. Firstly, the fluorescent DFNS (FL-DFNS) was prepared by a Schiff base formation reaction between the naphthalamide fluorophore and the modified DFNS. Then, a two-step approach was employed to fabricate FL-DFNS/polyurethane (FL-DFNS/CSPU-02) nanocomposite materials. FL-DFNS functions as a “turn off” sensor for Hg 2+ /Hg + ions, exhibiting fluorescence quenching of up to 81.1 %/75.9 %. It also has an excellent adsorption capacity to mercury. Specifically, FL-DFNS/CSPU-02 membrane enabled portable detection of Hg 2+ /Hg + ions. Importantly, it exhibited superior performance in the adsorption and separation of Hg 2+ /Hg + ions, achieving a removal efficiency of 97.7 % and 98.0 %, with an absorption capacity of 382.4/373.5 µg/cm 2 . And it can be recycled for at least nine times. Overall, this study confirms the practical application value of FL-DFNS and FL-DFNS/CSPU-02 membrane in the recognition and removal of Hg 2+ /Hg + ions, it will achieve the real application in environmental science and engineering.
Fluorescent silica nanoparticles (SiNPs) have application prospects in cell imaging, optoelectronic devices, and ion detection due to their excellent optical properties, low cytotoxicity, and diverse array of surface modification methods. However, their low product yield using current preparation processes limits their further development. In this study, a high-yield one-step microwave hydrothermal synthesis method of fluorescent silica nanoparticles (SiNPs) was developed using 3-thiocyanopropyl triethoxysilane (3-TCPTES) as the silicon source and sodium citrate as the reductant. The product yield was 91.1 %, and the quantum yield (QY) was 49.1 %. In addition, the mechanism of SiNPs fluorescence quenching by different ions was analyzed, and the quenching contribution ratio of different mechanisms was estimated. The results showed that this method greatly improved the yield of SiNPs while maintaining their excellent luminescent properties and low cytotoxicity, which provides a new method for the large-scale production of high-quality SiNPs. The unique functional group structure on the surface of SiNPs realized fluorescence quenching by changing the proportion of Fe 3+ and Hg 2+ ions via static quenching, fluorescence resonance energy transfer, and aggregation-caused quenching, giving them potential applications as fluorescent probes.
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