Effect of Oxidation Level on the Interfacial Water at the Graphene Oxide-Water Interface: From Spectroscopic Signatures to Hydrogen-Bonding Environment

The interfacial region of the graphene oxide (GO)-water system is nonhomogenous due to the presence of two distinct domains: an oxygen-rich surface and a graphene-like region. The experimental vibrational sum-frequency generation (vSFG) spectra are distinctly different for the fully oxidized GO-water interface as compared to the reduced GO-water case. Computational investigations using ab initio molecular dynamics were performed to determine the molecular origins of the different spectroscopic features. The simulations were first validated by comparing the simulated vSFG spectra to those from the experiment, and the contributions to the spectra from different hydrogen bonding environments and interfacial water orientations were determined as a function of the oxidation level of the GO sheet. The ab initio simulations also revealed the reactive nature of the GO-water interface

VALIDATED RP HPLC METHOD DEVELOPMENT FOR EXEMESTANE IN TABLET DOSAGE FORM

The aim of this present work was to develop stability indicating LC method, which is selective, accurate, simple, precise, reliable, cost effective and rapid for the quantification of all possible degradants and determination of exemestane. In addition, to develop and validate Stability Indicating Method for the determination of impurities (degradation products) in exemestane API by RP-HPLC. Finally, validate the developed method as per ICH guidelines

Tribochemistry of TaN, TiAlN and TaAlN coatings under ambient atmosphere and high-vacuum sliding conditions

© 2019 Elsevier B.V.Tribochemical analysis of monolithic TaN, TiAlN, and TaAlN coatings deposited by reactive magnetron sputtering onto 316LN stainless steel (SS) substrates are described. Tribology experiments were carried out in ambient atmospheric and high-vacuum sliding conditions to investigate the tribo-atmospheric dependent friction and wear characteristics of these coatings. The lower friction coefficient and improved wear-resistant properties were observed for TaN and TiAlN coatings in the humid atmosphere than in high-vacuum testing condition. Interestingly, lower friction and wear resistance properties of TaAlN coated SS are significantly enhanced in atmospheric as well as high-vacuum sliding conditions because of their highly dense and fine-grained microstructure with stable cubic B1 TaAlN phase. Energy dispersive X-ray spectroscopy elemental mapping and micro-focused X-ray photoelectron spectroscopy were carried out on the wear tracks to explore the comprehensive tribo-environment dependent tribochemistry. Formations of alumina (Al2O3) rich tribolayer reduced the friction and enhanced the wear resistance of TaAlN/SS sample tested in atmospheric condition; whereas this coating is highly stable in the high-vacuum condition with higher wear resistance11sciescopu

Breaking the scales: Electrolyte modeling in metal-ion batteries

© The Electrochemical Society. All rights reserved. Computational modeling is an increasingly important tool for investigating electrolytes at length-scales that are difficult to achieve in the lab. A brief overview of computational studies of electrolytes for metal-ion batteries is presented and the theoretical framework behind these simulations is examined. Particular emphasis is placed on the need for multiscale models that can span orders of magnitude spatially to connect atomistic interactions to large scale properties. These studies range from investigations of the pure electrolyte to interfaces such as those formed by the electrode and electrolyte. Two specific examples are discussed in the context of model development for electrolytes, namely a prototypical carbonate-based electrolyte for lithium ion batteries and a glyme-based material for sodium energy storage

Reactive events at the graphene oxide-water interface

Graphene oxide exhibits interesting reactive events at its interface with water, with water as an active participant. The reactive events are influenced by the level of oxidation of the graphene oxide sheet. The fully oxidized sheet tends to make the interfacial water media acidic leaving the sheet negatively charged, whereas the reduced sheet can form comparatively long lived carbocations as well as split water forming two alcohol groups on the sheet

The polarizing forces of water

A brief review of popular polarizable potentials for water, including both those parameterized to fit experimental properties, typically of the liquid, or electronic structure calculations on small clusters, is presented. The recently developed POLIR potential, which was parameterized to reproduce both ab initio calculations on clusters and the experimental liquid IR spectrum, is discussed, and some new results for both clusters and the liquid phase are shown, indicating its transferable nature. © 2012 Springer-Verlag

The relation between the structure of the first solvation shell and the IR spectra of aqueous solutions

The spectroscopic signatures of solvated anions and cations, in the O-H stretch region of water, are studied using the POLIR potential. Shifts in the spectra are shown to correlate very well with the distribution of a particular hydrogen bond angle for the waters in the first solvation shell. The results indicate that the spectral shifts might be predicted from MD simulations in a computationally convenient fashion, avoiding an explicit calculation of the spectra, as first suggested by Sharp et al. (J Chem Phys 114(4):1791-1796, 2001). © 2011 Springer Science+Business Media B.V