Structure and stability of p-cresol – xenon clathrate:Raman spectroscopy study

Abstract Interaction between p-cresol and xenon was studied by Raman spectroscopy. The main questions are crystal structure of resulting clathrate and its stability. The most informative regions of our spectra are those related to the O-H stretching vibrations, the aromatic ring vibrations between 900 and 800 cm⁻¹ and the lattice vibrations of the host. From obtained data and their analysis we confirmed formation of hexagonal rings of [···O-H⋯O-]₆ hydrogen bonds as the main structural motif of the clathrate cages and we estimated length of the O⋯O bridges of these bonds. We found evidence that the last factor is responsible for low stability of studied complex and for higher stability of similar clathrates formed by hydroquinone

¹²⁹Xe NMR analysis of pore structures and adsorption phenomena in rare-earth element phosphates

Abstract Rare-earth elements (REEs) are indispensable in various applications ranging from catalysis to batteries and they are commonly found from phosphate minerals. Xenon is an excellent exogenous NMR probe for materials because it is inert and its ¹²⁹Xe chemical shift is very sensitive to its local physical or chemical environment. Here, we exploit, for the first time, ¹²⁹Xe NMR for the characterization of porous structures and adsorption properties of REE phosphates (REEPO₄). We study four different REEPO₄ samples (REE = La, Lu, Sm and Yb), including both light (La and Sm) and heavy (Lu and Yb) as well as diamagnetic (La and Lu) and paramagnetic (Sm and Yb) REEs. ¹²⁹Xe resonances are very sensitive to the porous structures and moisture content of the REEPO₄ samples. In the samples treated at a lower temperature (80 °C), free water hinders the access of hydrophobic xenon into small mesopores, but the treatment at a higher temperature (200 °C) removes the free water and allows xenon to explore the mesopores. Based on a standard two-site exchange model analysis of the variable-temperature ¹²⁹Xe chemical shifts, as well as its proposed, novel modification for paramagnetic materials, the average mesopore sizes were determined. The size was the largest (79 nm) for the La sample with mixed monazite (70%) and rhabdophane (30%) phases and the smallest (6 nm) for the Yb sample with pure xenotime phase. The mesopore sizes of the Lu and Yb samples (12 and 6 nm) differed by a factor of two regardless of their similar xenotime phase. The ¹²⁹Xe NMR analysis revealed that the heats of adsorption of the samples are similar, varying between 8.7 and 10.1 kJ/mol. For diamagnetic samples, computational modelling confirmed the order of magnitude of the chemical shifts of Xe adsorbed on surfaces and therefore the validity of the two-site exchange model analysis. Overall, ¹²⁹Xe NMR provides exceptionally versatile information about the pore structures and adsorption properties of REEPO₄ materials, which may be very useful for developing the extraction processes and applications of REEs

Correlation of aluminum doping and lithiation temperature with electrochemical performance of LiNi₁-ₓAlₓO₂ cathode material

Abstract This article presents a process for producing LiNi₁-ₓAlₓO₂ (0 < × < 0.05) cathode material with high capacity and enhanced cycle properties of 145 mAh/g after 600 cycles. The LiNi₁-ₓAlₓO₂ (0 < × < 0.05) cathode material is prepared by mixing coprecipitated Ni(OH)₂ with LiOH and Al(OH)₃, followed by lithiation at temperature range of 650–710 °C, after which any residual lithium from lithiation is washed from the particle surfaces. Electrochemical performance was studied within full-cell and half-cell application; in addition, different material characterization methods were carried out to explain structure changes when certain amount of aluminum is introduced in the LiNi₁-ₓAlₓO₂ structure. Surface analyses were carried out to demonstrate how washing process changes the chemical environment of the LiNi₁-ₓAlₓO₂ secondary particle surface. The results demonstrate how Al doping, lithiation temperature, and the washing process affect the performance of the LiNi₁-ₓAlₓO₂ cathode material

Development and characterization of composite carbon adsorbents with photocatalytic regeneration ability:application to diclofenac removal from water

Abstract This paper presents results related to the development of a carbon composite intended for water purification. The aim was to develop an adsorbent that could be regenerated using light leading to complete degradation of pollutants and avoiding the secondary pollution caused by regeneration. The composites were prepared by hydrothermal carbonization of palm kernel shells, TiO₂, and W followed by activation at 400 °C under N₂ flow. To evaluate the regeneration using light, photocatalytic experiments were carried out under UV-A, UV-B, and visible lights. The materials were thoroughly characterized, and their performance was evaluated for diclofenac removal. A maximum of 74% removal was observed with the composite containing TiO₂, carbon, and W (HCP25W) under UV-B irradiation and non-adjusted pH (~5). Almost similar results were observed for the material that did not contain tungsten. The best results using visible light were achieved with HCP25W providing 24% removal of diclofenac, demonstrating the effect of W in the composite. Both the composites had significant amounts of oxygen-containing functional groups. The specific surface area of HCP25W was about 3 m²g⁻¹, while for HCP25, it was 160 m²g⁻¹. Increasing the specific surface area using a higher activation temperature (600 °C) adversely affected diclofenac removal due to the loss of the surface functional groups. Regeneration of the composite under UV-B light led to a complete recovery of the adsorption capacity. These results show that TiO₂- and W-containing carbon composites are interesting materials for water treatment and they could be regenerated using photocatalysis

Clathrate structure determination by combining crystal structure prediction with computational and experimental ¹²⁹Xe NMR spectroscopy

Abstract We present an approach for the structure determination of clathrates using NMR spectroscopy of enclathrated xenon to select froma set of predicted crystal structures. Crystal structure prediction methods have been used to generate an ensemble of putative structures of o- and m-fluorophenol, whose previously unknown clathrate structures have been studied by ¹²⁹Xe NMR spectroscopy. The high sensitivity of the ¹²⁹Xe chemical shift tensor to the chemical environment and shape of the crystalline cavity makes it ideal as a probe for porous materials. The experimental powder NMR spectra can be used to directly confirm or reject hypothetical crystal structures generated by computational prediction, whose chemical shift tensors have been simulated using density functional theory. For each fluorophenol isomer we find one predicted crystal structure whose measured and computed chemical shift tensors agree within experimental and computational error margins and these are thus proposed as the true fluorophenol xenon clathrate structures