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Experimental studies on the metastable solubilities and the physicochemical properties including density, refractive index, conductivity, and pH values in the reciprocal quaternary system containing lithium, sodium, chloride, and sulfate at 273.15 K were determined with the method of isothermal evaporation. According to the experimental results, the dry-salt phase diagram, the water phase diagram, and the physicochemical properties versus composition were plotted. In the dry-salt phase diagram, there are three invariant points, seven solubility isotherm curves, and five crystallization fields corresponding to sodium chloride, mirabilite, lithium chloride dehydrate (LiCl·2H2O), lithium sulfate monohydrate, and a double salt (Li2SO4·3Na2SO4·12H2O). There were no solid solutions formed in the reciprocal quaternary system. The crystallizing region of mirabilite is the largest, while the region of LiCl·2H2O is the smallest with the highest concentration and a strong salting-out effect to NaCl and Li2SO4·H2O. When compared with the stable phase diagram at 273.15 K, the area of the phase region of mirabilite is enlarged significantly, while the areas of the phase regions of NaCl, Li2SO4·H2O, and Li2SO4·3Na2SO4·12H2O are decreased. The calculated values of densities and refractive index in the quaternary system with empirical equations are in good agreement with the experimental values. [ABSTRACT FROM AUTHOR]

By incorporating a cationic dye within a metal-organic framework (MOF) through an ion-exchange process, a responsive dye@bio-MOF-1 composite has been synthesized, serving as a dual-emitting platform for enhanced detection of different kinds of nitro-explosives, especially nitroalkanes, nitramines, and nitrate esters. The dye@bio-MOF-1 composite was constructed with free amines on their well-defined cavities, which is essential for the capture of explosives into their confined nanospace. It was observed that the encapsulation of explosives into the constructed dye@bio-MOF-1 composite could dramatically alter the luminescent properties of the dyes as well as the MOF skeletons owing to the size exclusivity and confinement-induced effect. For nitroaromatics, the dye@bio-MOF-1 composite exhibits turn-off responses via fluorescence quenching. Unexpectedly, the composite shows unique turn-on responses for aliphatic nitro-organics via confinement-induced enhancement, demonstrating enhanced ability to detecting different kinds of explosives selectively in aqueous solution. Furthermore, the dye@bio-MOF-1 film was facilely fabricated, making the chemical sensing more convenient and easier to realize the discrimination of the targeted explosives. The dual tunable responses indicate that dye@bio-MOF-1 composites are favorable materials for molecular sensing. On the basis of the host-guest properties of the constructed dye@bio-MOF-1 composite, our work can be further extended to sensing specific analytes with remarkable turn-on sensing properties, in particular those difficult to recognize with conventional methods.

In this article, the fabrication of an active organic-inorganic one-dimensional photonic crystal structure to offer electrothermal fluorescence switching is described. The film is obtained by spin-coating of liquid crystal elastomers (LCEs) and TiO 2 nanoparticles alternatively. By utilizing the property of LCEs that can change their size and shape reversibly under external thermal stimulations, the λ max of the photonic band gap of these films is tuned by voltage through electrothermal conversion. The shifted photonic band gap further changes the matching degree between the photonic band gap of the film and the emission spectrum of organic dye mounting on the film. With rhodamine B as an example, the enhancement factor of its fluorescence emission is controlled by varying the matching degree. Thus, the fluorescence intensity is actively switched by voltage applied on the system, in a fast, adjustable, and reversible manner. The control chain of using the electrothermal stimulus to adjust fluorescence intensity via controlling the photonic band gap is proved by a scanning electron microscope (SEM) and UV-vis reflectance. This mechanism also corresponded to the results from the finite-difference time-domain (FDTD) simulation. The comprehensive usage of photonic crystals and liquid crystal elastomers opened a new possibility for active optical devices.