Compression and pressure-induced amorphization of Co(OH)2 characterized by infrared vibrational spectroscopy

Interlayer Modulation of Layered Transition Metal Compounds for Energy Storage

Layered transition metal compounds are one of the most important electrode materials for high-performance electrochemical energy storage devices, such as batteries and supercapacitors. Charge storage in these materials can be achieved via intercalation of ions into the interlayer channels between the layer slabs. With the development of lithium-beyond batteries, larger carrier ions require optimized interlayer space for the unrestricted diffusion in the two-dimensional channels and effectively shielded electrostatic interaction between the slabs and interlayer ions. Therefore, interlayer modulation has become an efficient and promising approach to overcome the problems of sluggish kinetics, structural distortion, irreversible phase transition, dissolution of some transition metal elements, and air instability faced by these materials and thus enhance the overall electrochemical performance. In this review, we focus on the interlayer modulation of layered transition metal compounds for various batteries and supercapacitors. Merits of interlayer modulation on the charge storage procedures of charge transfer, ion diffusion, and structural transformation are first discussed, with emphasis on the state-of-art strategies of intercalation and doping with foreign species. Following the obtained insights, applications of modified layered electrode materials in various batteries and supercapacitors are summarized, which may guide the future development of high-performance and low-cost electrode materials for energy storage.

Pressure-dependent distinct luminescent evolutions of pyrene and TPA-Py single crystals

The effects of the high pressure on two single crystals, pyrene and N,N-diphenyl-4-(pyren-1-yl)aniline (TPA-Py), were studied by in situ fluorescent and Raman spectroscopies. During the compression, the pyrene with one structureless excimer emission band showed a continuous bathochromic-shift. In contrast, with the pressure increasing to 10.36 GPa, TPA-Py previously dominated with the hybridized local and charge transfer (HLCT) excited state gradually exhibited a new band at longer wavelengths, which is assigned to a new excited state species with the intramolecular charge transfer (ICT) state, caused by the pressure-induced changes on its molecular configuration. Accompanied by the spectral changes, a sequential color variation from blue to cyan was observed, giving a change to yellow and then red. The significant broadening of the full-width half-maximum (FWHM) of the TPA-Py is observed due to the enhanced dipole-dipole interaction and the existence of pressure gradient. Both pyrene and TPA-Py showed the delayed recovery of the luminescence in the compression-decompression cycle, which results from the poor reversibility of electronic structure caused by the compression-induced piezochromic effect. Furthermore, the evolutions of the Raman spectra of pyrene and TPA-Py indicated that the pressure-induced reversible transformation is caused by the molecular conformational change. This study is a deeper understanding of the structure-property relation of the HLCT species and will be a helpful reference for the regulation of photoluminescence in these intramolecular electron donor-acceptor crystal materials.

On-line monitoring of vacuum drying of theophylline using NIR spectroscopy: solid-state transitions, water content and semi-empirical modeling

The aim of this work was to monitor in-line and at a real time, the solid-state forms during pharmaceuticals manufacturing. It concerns the dehydration behavior and the solid-state transitions of theophylline in an agitated vacuum contact dryer. First, a near infrared spectroscopy (NIRS) method was performed using a reflectance diffuse probe to measure the in-line and in-situ exact composition of the mixture of different forms of theophylline and water content during drying. A multivariate modeling has been investigated to build a robust model which can predict four components at the same time during drying process. The XRPD analysis was used as a reference method in the process of calibration of NIRS. The indicators of the accuracy in quantitative spectral analysis confirm the robustness of the model and the efficiency of the method of calibration. Second, the kinetics of solid state transformations were investigated. It was shown that the dehydration advanced first by the formation of the metastable anhydrate and after a lag time of the stable one. Once the stable form appeared, formation of the metastable form came to an end. The temperature was found out to be the main factor controlling the overall process rate but also the final contents of the stable and metastable anhydrates for the considered dryer and operating conditions range. Finally, a semi-empirical drying model was proposed and significant quantitative differences were found, particularly at the product temperature which was probably caused by the excessive simplicity of the model.