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A novel dual-emission ratiometric fluorescent sensor (CDs@Eu-MOFs) has been synthesized successfully by encapsulating water-soluble fluorescent CDs into the chambers of Eu-MOFs via a simple one-pot hydrothermal method, which can be used for the detection of Hg 2+ in environmental water samples. The synthesized CDs@Eu-MOFs inherited simultaneously the excellent luminescence performance of Eu 3+ and CDs and exhibited good structural and fluorescence stability in aqueous solution. The presence of Hg 2+ changed the fluorescence intensity of CDs, while the fluorescence intensity of Eu-MOFs hardly changed, which could be used as the recognition part and the reference part respectively to construct the ratiometric fluorescence sensor. The obtained Hg 2+ fluorescent probe showed a wide linear range (0-300 μM) and a low detection limit (0.12 nM). The developed method can be used as a multi-functional fluorescent sensor with high sensitivity and good selectivity for the determination of Hg 2+ in actual water samples., Competing Interests: Declaration of competing interest About this paper, no any interest conflict exists., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A novel composite (CDs@ZIF-8) based on carbon dots (CDs) and zeolitic imidazolate framework (ZIF-8) was successfully synthesized by encapsulating CDs into the pores of ZIF-8 through a simple one-pot solvothermal method. The as-synthesized CDs@ZIF-8 inherited simultaneously the strong adsorption capacity of ZIF-8 and the excellent optical properties of CDs. The composite exhibited excellent dispersibility and high structural and fluorescence stability in aqueous solution, which could be employed as an excellent turn-off mode fluorescent probe to detect Cu 2+ . The large specific surface area and strong adsorption properties of ZIF-8 enabled the resultant composite to effectively enrich Cu 2+ for further improving the analytical sensitivity. The possible fluorescence quenching mechanism has also been discussed in detail and it was found that the effective fluorescence quenching of Cu 2+ to CDs@ZIF-8 could be attributed to the strong ability of Cu 2+ to combine with the carboxyl group or amino group on the CD surface and the strong adsorption capacity of ZIF-8; their synergistic effect resulted in effective fluorescence quenching.

A new COF (NWNU-COF-4) linked by an aryl ether bond (Ar-O-Ar) was synthesized by the condensation reaction of 2,4,6-trihydroxypyrimidine and trinitrophenol under simple and easy reaction conditions. Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N 2 adsorption-desorption, thermogravimetric analysis (TGA), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the product. The BET specific surface area of NWNU-COF-4 was 21.33 m 2 g -1 , and its pore size was about 1.351 nm. Additionally, this method of preparation was simple and cheap. The electrochemical measurements showed that the synthesized NWNU-COF-4 had excellent pseudocapacitive performance with maximum specific capacitance of 133.44 F g -1 at 0.3 A g -1 in 6 mol L -1 KOH electrolyte. When the current density increased by 10 times (3.0 A g -1 ), the specific capacitance was 114.12 F g -1 , and the retention rate was 82%. After 10 000 GCD cycles, the capacitance still kept 94% of its initial capacitance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)