Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Coumarin-Based Small-Molecule Fluorescent Chemosensors.

Mixed metal sulfides (MMSs) have attracted increased attention as promising electrode materials for electrochemical energy storage and conversion systems including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), hybrid supercapacitors (HSCs), metal–air batteries (MABs), and water splitting. Compared with monometal sulfides, MMSs exhibit greatly enhanced electrochemical performance, which is largely originated from their higher electronic conductivity and richer redox reactions. In this review, recent progresses in the rational design and synthesis of diverse MMS-based micro/nanostructures with controlled morphologies, sizes, and compositions for LIBs, SIBs, HSCs, MABs, and water splitting are summarized. In particular, nanostructuring, synthesis of nanocomposites with carbonaceous materials and fabrication of 3D MMS-based electrodes are demonstrated to be three effective approaches for improving the electrochemical performance of MMS-based electrode materials. Furthermore, some potential challenges as well as prospects are discussed to further advance the development of MMS-based electrode materials for next-generation electrochemical energy storage and conversion systems.

Mixed Metal Sulfides for Electrochemical Energy Storage and Conversion

Metal cations and anions are essential for versatile physiological processes. Dysregulation of specific ion levels in living organisms is known to have an adverse effect on normal biological events. Owing to the pathophysiological significance of ions, sensitive and selective methods to detect these species in biological systems are in high demand. Because they can be used in methods for precise and quantitative analysis of ions, organic dye-based ratiometric fluorescent probes have been extensively explored in recent years. In this review, recent advances (2015-2019) made in the development and biological applications of synthetic ratiometric fluorescent probes are described. Particular emphasis is given to organic dye-based ratiometric fluorescent probes that are designed to detect biologically important and relevant ions in cells and living organisms. Also, the fundamental principles associated with the design of ratiometric fluorescent probes and perspectives about how to expand their biological applications are discussed.

Synthetic ratiometric fluorescent probes for detection of ions

Review of the use of transition-metal-oxide and conducting polymer-based fibres for high-performance supercapacitors

Metal–organic frameworks (MOFs) have obtained increasing attention as a kind of novel electrode material for energy storage devices. Yet low capacity in most MOFs largely thwarts their application. In this study, an effective strategy was developed to improve the conductivity of MOFs by partially substituting Ni2+ in the Ni-MOF with Co2+ or Zn2+. The mixed-metal organic frameworks (M-MOFs) showed excellent electrochemical performance, which is attributed not only to the favorable paths for charge transport due to the presence of free pores, but also to the raised electrochemical double-layer capacitance (EDLC) at the enlarged specific surface area of the material. Meanwhile, the cycling stability of the assembled hybrid supercapacitors (M-MOFs//CNTs–COOH) is enhanced due to the alleviation of phase transformation during electrochemical cycling tests. More interestingly, the Co/Ni-MOF//CNTs–COOH also exhibited an excellent energy density (49.5 W h kg−1) and power density (1450 W kg−1) simultaneously. These values demonstrated the better performance of all the MOF materials in supercapacitors at present. In addition to broadening the application of MOFs, our study may open a new avenue for bridging the performance gap between batteries and supercapacitors.

Mixed-metallic MOF based electrode materials for high performance hybrid supercapacitors

Self-assembling hierarchical NiCo2O4/MnO2 nanosheets and MoO3/PPy core-shell heterostructured nanobelts for supercapacitor

A highly selective and sensitive photoinduced electron transfer (PET) based HOCl fluorescent probe in water and its endogenous imaging in living cells

High energy and power lithium-ion capacitors based on Mn3O4/3D-graphene as anode and activated polyaniline-derived carbon nanorods as cathode

High-performance supercapacitors, as highly promising candidates for bridging the gap between conventional lithium-ion batteries and traditional electrostatic capacitors, are the key to progress in the field of energy storage. To improve the performance of supercapacitors, the exploration of novel functional electrode materials is always at the forefront of technology. Herein, the rational design of a novel deformable soft supercapacitor, which is based on a compressible capacitive polyvinyl alcohol/polypyrrole (PVA/PPy) composite hydrogel and a flexible carbon nanotubes (CNTs) film, is reported. Due to the unique layered wrinkle structure of the PVA/PPy composite hydrogel, whose internal structure contains a large amount of water, the fabricated supercapacitor exhibits fascinating mechanical properties, including elasticity, compressibility and softness. In addition, the CNTs self-supported film without any binder shows an excellent flexibility as well as a stable capacitance in long-term cycles, which results in an enhanced cycle performance of the (PVA/PPy)(−)//CNTs(+) supercapacitor. Furthermore, the (PVA/PPy)(−)//CNTs(+) supercapacitor exhibits a high working voltage (0–2 V) accompanied with an energy density of 33.3 W h kg−1 (a power density of 1600 W kg−1). The high-performance compressible soft supercapacitor with deformability heralds a new territory of hydrogel-based supercapacitor for energy storage applications.

Elastic soft hydrogel supercapacitor for energy storage

Metal oxides have attracted renewed interest in applications as energy storage and conversion devices. Here, a new design is reported to acquire an asymmetric supercapacitor assembled by all free-standing metal oxides. The positive electrode is made of 3D NiO open porous nanoribbons network on nickel foam and the negative electrode is composed of SnO2/MnO2 nanoflakes grown on carbon cloth (CC) substrate. The combination of two metal oxide electrodes which replaced the traditional group of carbon materials together with metal oxide has achieved a higher energy density. The self-supported 3D NiO nanoribbons network demonstrates a high specific capacitance and better cycle performance without obvious mechanical deformation despite of undergoing harsh bulk redox reactions. The SnO2/MnO2 nanoflakes as the pseudocapacitive electrode exhibit a wide range of voltage window (−1 to 1 V), which is conducive to electrochemical energy storage. The (CC/SnO2/MnO2)(−)//(NiO/Ni foam)(+) asymmetric supercapacitor device de...

Chang Liu

Papers

Self-assembling hierarchical NiCo2O4/MnO2 nanosheets and MoO3/PPy core-shell heterostructured nanobelts for supercapacitor

A highly selective and sensitive photoinduced electron transfer (PET) based HOCl fluorescent probe in water and its endogenous imaging in living cells

High energy and power lithium-ion capacitors based on Mn3O4/3D-graphene as anode and activated polyaniline-derived carbon nanorods as cathode

Elastic soft hydrogel supercapacitor for energy storage

In Situ Growth of Free-Standing All Metal Oxide Asymmetric Supercapacitor