Hollow Ni3S4@Co3S4 with core-satellite nanostructure derived from metal-organic framework (MOF)-on-MOF hybrids as an electrode material for supercapacitors.

Metal-organic frameworks (MOFs) have found wide applications in the field of supercapacitors due to their highly controllable porous structure, big specific surface area, and abundant chemical functional groups. MOF-on-MOF hybrids not only enhance the composition of MOFs (such as ligands and/or metal centers) but also provide greater structural diversity. By utilizing MOFs as precursors for preparing sulfides, the unique characteristics and inherent structure of MOFs are preserved but their conductivity and capacitance are enhanced. This study successfully synthesized hollow-structured Ni3S4@Co3S4 derived from an Ni-MOF@ZIF-67 hybrid structure, where the Ni-MOF serves as the core and ZIF-67 as the satellite. The Ni3S4@Co3S4 electrode demonstrated a specific capacity as high as 747.3 C g-1 at 1 A g-1, and it could still maintain 77% of its initial capacity at 10 A g-1. Furthermore, the assembled Ni3S4@Co3S4//AC hybrid supercapacitor (HSC) device achieved a maximum energy density of 30.8 W h kg-1 when the power density was 750 W kg-1. The device exhibited remarkable cycling durability, retaining 85.4% of its initial capacitance after 5000 cycles. Therefore, the derived functional materials based on MOF-on-MOF provide a more scalable and promising approach for the preparation of efficient electrode materials.

Fluorescent sensor based on bismuth metal-organic frameworks (Bi-MOFs) mimic enzyme for H2O2 detection in real samples and distinction of phenylenediamine isomers.

Although peroxidase-like nano-enzymes have been widely utilized in biosensors, nano-enzyme based biosensors are seldom used for both quantitative analysis of H2O2 and differentiation of isomers of organic compounds simultaneously. In this study, a dual-functional mimetic enzyme-based fluorescent sensor was constructed using metal-organic frameworks (Bi-MOFs) with exceptional oxidase activity and fluorescence properties. This mimetic enzyme sensor facilitated quantitative analysis of H2O2 and accurate discrimination of phenylenediamine isomers. The sensor exhibited a wide linear range (0.5-400 µM) and low detection limit (0.16 µM) for the detection of H2O2. Moreover, the sensor can also be used for the discrimination of phenylenediamine isomers, in which the presence of o-phenylenediamine (OPD) leads to the appearance of a new fluorescence emission peak at 555 nm, while the presence of p-phenylenediamine (PPD) significantly quenched its fluorescence due to the internal filtration effect. The proposed strategy exhibited a commendable capability in distinguishing phenylenediamine isomers, thereby paving the way for novel applications of MOFs in the field of environmental science.

A dual-functional fluorescence probe CDs@ZIF-90 for highly specific detection of Al3+ and Hg2+ in environmental water samples.

In recent years, the escalating water pollution has resulted in serious harm to human health and ecological environment due to the excessive discharge of toxic metal ions such as Al3+ and Hg2+. Therefore, it is crucial to develop a simple, efficient, and rapid detection method for monitoring the levels of the metal ions in water environment to ensure public health and ecological safety. In this study, carbon dots (CDs) containing heteroatom Si were successfully synthesized by the solvothermal method. Subsequently, a novel dual-functional fluorescent sensor (CDs@ZIF-90) was constructed by integrating CDs with zeolitic imidazolate framework-90 (ZIF-90). The fluorescent composite CDs@ZIF-90 showed outstanding optical properties and excellent structural and luminescence stability in aqueous medium. Particularly, its fluorescence at 453 nm can be remarkably enhanced by Al3+ and quenched upon exposure to Hg2+. As a result, the CDs@ZIF-90 was applied in sensitive and selective determination of Al3+ and Hg2+ ions with wide linear ranges (1-200 µM and 0.05-240 µM) and low detection limits (0.81 µM and 19.6 nM). Moreover, a convenient and rapid fluorescence test strip was also successfully prepared for visual detection of Al3+ and Hg2+ ions. This work is the first try to use the CDs@ZIF-90 fluorescence sensing material for highly sensitive and selective determination of Al3+ and Hg2+ based on "turn-on" and "turn-off" dual modes, respectively and it provides a new idea for monitoring quality of drinking water and environmental water. It is of great significance for human health and environmental protection.