Mingxi Guo

Coal derived porous carbon fibers with tunable internal channels for flexible electrodes and organic matter absorption

Coal-derived porous carbon fibers (CPCFs) were prepared by single-nozzle electrospinning the aqueous solution of acid treated coal and polyvinyl alcohol followed by thermal treatment in an inert atmosphere. The production yield of CPCFs was about 92% from coal. The structural, textural, and surface properties of CPCFs were investigated by means of spectroscopy, microscopy, and Brunauer–Emmett–Teller (BET) techniques. The results showed that the flexible CPCFs had an abundant pore structure and large specific surface area. The electrochemical performance of supercapacitor electrodes with these fiber mats was studied. The binder free electrodes showed a capacitance of 170 F g−1 at a current density of 1 A g−1 in 6 M aqueous KOH electrolyte. The electrodes also showed stable cycling performance without any decrease in the specific capacitance after 20000 charge/discharge cycles at a current density of 2 A g−1. Besides, the CPCFs were superhydrophobic and showed outstanding performance in oil-absorption and good circulation for the removal of dyes from water. These outstanding properties potentially make the flexible CPCFs a promising candidate for energy storage and environmental protection.

Photochromism and mechanism of pyrazolones in crystals: structural variations directly observed by X-ray diffraction

Structural changes of photochromic pyrazolones were first verified by an X-ray crystallographic method directly. A tautomeric transformation between enol and keto form isomers occurs, accompanied by proton transfer during the photochromic processes.

Photochromism and fluorescence modulation of pyrazolone derivatives in the solid state

Two novel photochromic compounds derived from pyrazolones, which undergo a photochromic reaction in the solid state, have been synthesized and their photochromic and fluorescence properties were investigated. Their fluorescence emission can be efficiently modulated by photoisomerization of pyrazolones almost up to 90% upon UV light irradiation. Importantly, the fluorescence emission of 1 can be reversibly switched “on” and “off” upon alternative UV light irradiation and heating. These compounds exhibited photochromic coloration from white E-form to yellow brown K-form. On the basis of the molecular structure determined by X-ray single crystal analysis, there are intermolecular hydrogen bonds which provide suitable proton transfer channels for the enol–keto transformation. The colored K-form isomers, which are very stable at ambient temperature, may be due to the reverse reaction occurring at a high temperature.

Hierarchical porous carbon spheres constructed from coal as electrode materials for high performance supercapacitors

Hierarchical porous carbon spheres (PCS) are prepared by a simple one-pot spray pyrolysis of coal oxide solution without any further activation process. The specific surface area and total pore volume of the resultant carbon spheres are increased significantly with the increase of spray pyrolysis temperature. When evaluated as electrode materials for supercapacitors in 6 M KOH electrolyte, the PCS exhibits a high specific capacitance 227 F g−1 at a current density of 1 A g−1 and outstanding cycling stability after 10 000 charge/discharge cycles at a current density of 2 A g−1. In symmetric supercapacitor, the specific capacitance of the sample PCS-8 is 180 F g−1 at a current density of 0.2 A g−1 and has excellent rate capability. The proposed strategy offers a facile and green method to produce porous carbon spheres from coal, and has potential application in energy storage.

Fluorescence modulation of a pyrazolone dye in the solid state based on energy transfer

A new pyrazolone dye was synthesized and its fluorescence modulation was achieved based on energy transfer. The prepared pyrazolone dye was combined with a photochromic pyrazolone to obtain a fluorescence photoswitching material (FPM), which exhibits stable and reversible fluorescence photoswitching properties in the solid state. Upon characterization of the samples through 1H NMR, XRD, FT-IR, UV and fluorescence spectra, it was found that the photochromic pyrazolone and the pyrazolone dye integrally retained their inherent properties in the FPM. An investigation of the FPM revealed that the photoswitching response depended on the fluorescence dye species, the content of the fluorescence dye and the synthetic route of the FPM. The photoswitching mechanism of the FPM was studied in detail using FT-IR, UV and fluorescence spectroscopy. The results show that the photochromism of the photochromic pyrazolone plays an important role in the efficient energy transfer from the pyrazolone dye to the keto-form of the photochromic pyrazolone. The emission wavelength of the pyrazolone dye hardly induces a photochemical reaction of the photochromic pyrazolone in the FPM, which has the potential to be used as a non-destructive fluorescence readout of optical information. This study presents a simple and efficient alternative to covalent systems to obtain FPMs, and it may be applied in photoelectronic devices.

Synthesis and improved photochromic properties of pyrazolones in the solid state by incorporation of halogen.

Four novel photochromic pyrazolones have been prepared by introducing halogen atoms as substituents on the benzene ring. All as-synthesized compounds exhibited excellent reversible photochromic performances in the solid state. Upon UV light irradiation, the as-synthesized compounds can change their structures from E-form to K-form with yellow coloration. Further processed by heating, they rapidly reverted to their initial states at 120°С. Their photo-response and thermal bleaching kinetics were detailed investigated by UV absorption spectra. The results showed that the time constants were higher than that of our previously reported compounds at least one order of magnitude and the rate constants of the as-synthesized compounds were significantly influenced by the size and electronegativity of different halogen atoms. The fluorescence emission were modulated in a high degree via photoisomerization of pyrazolones, which might be due to the efficient energy transfer from E-form to K-form isomers for their partly overlaps between their E-form absorption spectra and K-form fluorescence spectra.