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Flexible supercapacitors (SCs) using gel polymer electrolytes (GPEs) have attracted increasing attention given the popularity of portable and wearable electronics. However, the facile preparation of GPEs with not only outstanding mechanical and electrochemical properties but also recyclability, flame-resistance and sustainability is still a challenge. Herein, a dual cross-linking strategy was developed using levulinic acid (LA) and sodium borate to engineer chitosan into flame-resistant and recyclable GPEs with satisfactory mechanical properties and high ionic conductivity for application in flexible SCs. In this strategy, LA functioned as a protonation reagent to make chitosan soluble in water and a crosslinker via imine formation between its ketone groups and the amino groups of chitosan to form a crosslinked polymer network. Sodium borate functioned as not only a cross linker but also an ionic conductor and flame retardant in the GPEs. The engineered GPEs exhibited high flame-resistant ability (self-extinguishing time <1 s), desirable mechanical performance (0.87 MPa), and high ionic conductivity (24.02 mS cm−1). The assembled flexible SC exhibited a high energy density of 14.58 W h kg−1 and cycling stability over 35 000 cycles. Furthermore, benefiting from the pH sensitivity of the formed imine bonds, the GPEs could be easily degraded in acidic conditions, and then recycled for the fabrication of other GPEs. Overall, it is believed that the as-prepared eco-friendly and safe electrolyte shows great promise for applications in consumable electronics. [ABSTRACT FROM AUTHOR]

It is difficult to study the nucleation process of crystals intuitively due to the limitations of the current methods. In this study, based on the aggregation-induced emission enhancement mechanism, phase transition and nucleation of different polymorphs of dimethyl 5-aminoisophthalate (DM5AIP) were investigated by using fluorescence changes. The relationship between fluorescence variation and solution concentration was studied, which proved that when the concentration increased, DM5AIP molecules would prefer H-aggregates in acetonitrile. The evaporation crystallization of dimethyl 5-aminoisophthalate was successfully monitored in real time by fluorescence changes. And the evolution of DM5AIP aggregation during evaporation crystallization was systemically studied by means of Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectrometry. The results showed that the solute molecules tend to form aggregates via π–π interactions in a face-to-face manner in acetonitrile, while they tend to form aggregates by staggered accumulation and C–H⋯π weak interactions in methanol. Finally, because of the obvious difference in the fluorescence color of the two polymorphs of DM5AIP, the phase transition process was successfully observed in real time. [ABSTRACT FROM AUTHOR]

The introduction of unexpected solvent is inevitable in the crystallization process of rifampicin in industry, which could lead to products with different morphologies. Therefore, the study of crystal habit is needed for preparing rifampicin with better performance. In this work, an unreported solvate of rifampicin was prepared in n-butanol/acetone solvent. The interactions among solutes were analyzed through Hirshfeld surfaces and population fingerprints. The crystal morphology of the solvate in a vacuum was predicted by employing the attachment energy (AE) model, acquiring six habit faces. Surface structures of the faces were studied. Molecular electrostatic potentials (ESPs), concentration distribution and mean squared distribution (MSD) were then used to analyze the crystal face–solvent interface. By using the modified attachment energy (MAE) model, the morphology of rifampicin in n-butanol/acetone was finally obtained through calculations. The results show that the intermolecular interactions of solvate molecules were dominantly H⋯H and H⋯O/O⋯H contacts. Six morphologically important faces were found in the solvate crystal simulated in a vacuum, and among them, the (0 −2 0), (0 2 0), (0 0 1) and (1 0 0) faces were morphologically more important. It was found that the diffusion ability, surface structure and ESP were all important to the inhibitory effect. The morphology of the solvate was largely altered in the presence of n-butanol/acetone solvent and was consistent with the experiment result. [ABSTRACT FROM AUTHOR]

Flexible crystals have attracted extensive attention for their potential as smart materials, such as flexible field-effect transistors, wearable devices and flexible displayers. Developing flexible materials with specific properties still remains challenging because the design standards for flexible organic crystals are still not well established. Herein, we reported two Schiff-based molecules, together with their polymorphs, which exhibit different photophysical behaviors and mechanical properties. It was found that, due to the distinguished molecular stacking arrangements, they exhibit diverse fluorescence properties. MN-I exhibits orange emission at 590 nm, while MN-II shows yellow emission at 579 nm. MO-I shows bright yellow-green fluorescence at 538 nm, while the emission spectrum of MO-II cannot be measured due to the presence of photochromism caused by its distorted molecular conformation. Furthermore, MN-I exhibits better elasticity than MN-II, while MO-I and MO-II are plastic and brittle, respectively. Detailed crystallographic analyses and energy framework calculations were performed to reveal the mechanisms, which suggest that the differences in the strength of intermolecular interactions and the diverse types of intermolecular interactions caused by the differences in molecular conformation lead to flexible properties. [ABSTRACT FROM AUTHOR]

In this study, the complicated solvation behaviors of arbutin were studied from both experiment investigations and theoretical calculations. Six solid forms of arbutin, namely the anhydrous form I and five solvates, were successfully obtained. The structures of form I, solvate S1, solvate S4, and solvate S5 are reported for the first time. The obtained forms of arbutin were thoroughly characterized and distinguished by PXRD, PLM, DSC, TGA, Raman, and FTIR spectroscopy techniques. It was found that solvate S4 and solvate S5 were isostructural solvates. Further, the packing arrangements and pore structures were analyzed to illustrate the formation of the isostructural solvates. Moreover, analyses of the crystal structures showed that arbutin exhibited flexible conformations in various solid forms, and there were strong correlations between the crystal lattice energy and the thermal stability of various solvates. Finally, the formation mechanism of arbutin solvates was proposed and rationalized and the conversion relationship between different solid forms was also established. [ABSTRACT FROM AUTHOR]

Organic crystals, possessing both flexibility and stimuli-responsive properties, are attractive candidates as smart materials, namely sensors, actuators, optoelectronic devices, information storage, medical applications, etc. They are emerging as a new research direction in materials science, namely, crystal adaptronics. For a long time, it has been generally considered that crystals are inclined to crack upon external force, which limits their application as elements. Recently, however, more and more crystals that display excellent deformation have been reported, which sparks interest in their potential applications as stimuli-responsive flexible smart materials. This comprehensive review summarizes these remarkably flexible crystals with stimuli-responsive (light, thermal, electrical and multiple) properties reported to date, delves into their response mechanisms and structure–property relationships, and discusses the design strategies for endowing flexible organic crystals with stimuli-responsive properties. Finally, the challenges and future outlook in this field are discussed. [ABSTRACT FROM AUTHOR]

Stimuli-responsive crystals have aroused tremendous interest due to their potential as smart materials. However, endowing mono-component crystals with multiple stimuli-responsive and multifunction properties is still a great challenge. Here, we report an anthracene derivative, 9-anthraldehyde, which can respond to mechanical force and light. It possesses two-dimensional (2D) elastic bending, plastic twisting and photoinduced bending properties. Unusual elastic bending of the plastic twisted crystal was achieved in one crystal. The crystal obtained in this work is a multi-dimensional elastic crystal, which is different from reported twistable materials. To reveal the mechanisms of the properties of 2D elastic bending, plastic twisting and photoinduced bending, nanoindentation tests, energy framework analysis and Hirshfeld surface analysis were used to study the property–structure relationship at the molecular level. It was found that these properties can be ascribed to the unique intermolecular interactions and types of molecular arrangement. [ABSTRACT FROM AUTHOR]

Exploiting cost-effective, highly efficient and stable alkaline electrocatalysts is a great challenge for the hydrogen evolution reaction (HER). Herein, NiMoO4 and CoFe layered double hydroxide (CoFe LDH) with poor crystallinity were successively deposited on Cu nanowire (Cu NW) grown on Cu foam by a two-step electrodeposition process, which was verified by XRD, Raman, ATR-FTIR, XPS, SEM, TEM and HRTEM characterizations. The HER performance measurement in 1.0 M KOH solution showed the optimal CoFe LDH-60 s/NiMoO4/Cu NW/Cu foam sample demonstrated prominent alkaline HER activity and long-term durability with an ultralow overpotential of 45 mV at −10 mA cm−2 and a Tafel slope of 94.0 mV dec−1, superior to the recently reported transition metal-based electrocatalysts. Further study clarified that the remarkable alkaline HER performance could be attributed to the strong synergistic effect between CoFe LDH-60 s and NiMoO4 in favor of water adsorption/activation and optimizing hydrogen adsorption, and providing plentiful exposed active sites as well as an enhanced electron transfer process offered by the unique 1D nanostructure with Cu nanowire as the core. This work can provide a guidance for designing a highly active and stable electrocatalyst for hydrogen production. [ABSTRACT FROM AUTHOR]

Stumbled by the diversity and similarity of rction products, the artistic design of CO2 photocatalysts is complex. Herein, the well-designed CoO single-unit-cell layers collaborating O-vacancies-rich and Fe-dopants (Vo–Fe–CoO) are proposed as a prototype for exploring the relationship between O-vacancies/Fe-dopants and the photocatalytic performance. The Fe dopants and enough O vacancies contribute to the efficiency and product selectivity in the photoreduction of CO2, respectively. Through combined density functional theory (DFT) calculations and experiment, it was testified that introducing Fe-dopants in CoO single-unit-cell layers can convert the absorption of CO2 from an endoergic step to exoergic process and lower the energy barrier of the rate-determining step for forming CH4 to increase the catalytic efficiency. Moreover, designing O-vacancies can increase the desorption energy of CO and reduce the desorption energy of CH4, mainly facilitating the selectivity to form CH4. As expected, Vo–Fe–CoO guarantees high CO2 photoreduction efficiency (52.5 μmol g−1 h−1) and excellent CH4 selectivity (91.4%). This work uncovers the influence of multiple collaborating active sites in single-unit-cell layers for CO2 photoreduction performances, providing a new perspective for photocatalyst design. [ABSTRACT FROM AUTHOR]

A molten salt method has been used to prepare porous La0.8Sr0.2Mn1−xCuxO3 (0 ≤x≤ 0.4) (LSMC-X) microspheres and La0.8Sr0.2MnO3 (LSM) nanocubes using spherical and cubic MnCO3 as templates, respectively. XRD patterns showed a single perovskite phase when the Cu content was less than x = 0.3. SEM and TEM images indicated that the porous microspheres comprised many aggregated nanoparticles, while the nanocubes were solid with a smooth surface. LSM and LSMC-0 samples both possessed high surface areas (63.5045 and 49.6504 m2 g−1, respectively). Furthermore, the CO conversions showed that LSMC-0.2 had the best catalytic activity (T50 = 83.63 °C, T90 = 97.40 °C) and good stability. XPS analysis confirmed that Cu2+ doping induced Mn4+ formation and slight changes in the oxygen species, leading to different catalytic activity. Owing to their facile synthesis and high catalytic performance, we propose that these porous spherical La0.8Sr0.2Mn1−xCuxO3 (0 ≤x≤ 0.4) and nanocubic La0.8Sr0.2MnO3 catalysts are promising candidates for CO oxidation. [ABSTRACT FROM AUTHOR]

We have investigated the gravity-driven transport of spherical colloids suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) within microfluidic arrays of cylindrical obstacles arranged in a square lattice. Homeotropic anchoring at the surfaces of the obstacles created periodic director-field patterns that strongly influenced the motion of the colloids, whose surfaces had planar anchoring. When the gravitational force was oriented parallel to a principal axis of the lattice, the particles moved along channels between columns of obstacles and displayed pronounced modulations in their velocity. Quantitative analysis indicates that this modulation resulted from a combination of a spatially varying effective drag viscosity and elastic interactions engendered by the periodic director field. The interactions differed qualitatively from a sum of pair-wise interactions between the colloids and isolated obstacles, reflecting the distinct nematic environment created by confinement within the array. As the angle α between the gravitational force and principal axis of the lattice was varied, the velocity did not follow the force but instead locked into a discrete set of directions commensurate with the lattice. The transitions between these directions occurred at values of α that were different from those observed when the spheres were in an isotropic liquid, indicating the ability of the liquid crystal forces to tune the lateral displacement behavior in such devices.

Efficient and highly stereoselective oxidation of olefins to cis-diols as the major product is obtained by using biomimetic non-heme FeII catalysts in combination with H2O2.