ABSTRACT
Deep Eutectic Solvents (DESs) are hygroscopic liquids composed of a hydrogen bond donor (HBD) and acceptor (HBA). Their physical, chemical and electrochemical properties can be tailored to use them as solvents for different applications, i.e. electrodeposition, catalysis, extraction, etc. This can be done by changing the HBD, as well by adding water. However, the interrelated influence of H2O and HBD on the structure of the electrolyte, and on the behavior of the active species is not fully understood. In this work, we select nickel electrodeposition as a case study and we combine electrochemical techniques (cyclic voltammetry, chronoamperometry) with UV-vis spectroscopy and molecular dynamics to understand the influence of water and HBD on the electrochemical behaviour of DESs. The unique combination of these different experimental and modelling techniques provides new insights into the field. The addition of H2O changes, not only the interactions between the constituents of the liquid, but also the coordination of metal cations, which is reflected in the electrochemical performance of different DESs. More importantly, we show that, in the presence of very little (between 0.1 wt% and 2.8 wt%) and high (>4.5 wt%) water contents, DESs behave differently, and the changes in their electrochemical behavior are caused by both the complexation of metal cations and the electrolyte transport properties.
ABSTRACT
Organofunctional silanes are applied as coupling agents between organic coatings and low carbon steel substrates to promote adhesion. Although the metal oxide-silane interface plays an important role in the performance of the entire overlying coating system, it remains challenging to obtain a clear understanding of the interfacial molecular bonding mechanism and its influence on adhesion. In this work, time-of-flight secondary ion mass spectrometry is used to study interfacial interactions between aminopropyl triethoxysilane (APS) and low carbon steel. APS is shown to bond to the steel substrate through silanol steel and amine-steel interactions, and coatings are cured at varying temperatures to evaluate the influence of curing on these different types of bonding interactions. Unambiguous evidence for hydrogen bond interactions between APS silanol groups and steel surface hydroxyl groups is provided for the first time in this work through deuteration of the steel substrate and allows to tackle long-lasting doubts about the most wide-spread bonding theory that has been postulated for silane adsorption on metals.
ABSTRACT
In the last decade, deep eutectic solvents (DES) have risen as promising and cheap alternatives for the often expensive and moisture-sensitive ionic liquids. For the application in metal processing industries such as hard chrome plating, still very little is known of the behavior of metal ions in these types of liquids. Therefore, we use the model-free Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) method to study Cr(iii) as sustainable alternative to the hazardous Cr(vi) and obtain reference UV/Vis spectra of chromium(iii)chlorides in several aqueous solutions and in water-DES mixtures. In addition, the results have been confirmed by EXAFS measurements. We observe that in the DES ethaline, ethylene glycol ligands are coordinating with the chromium(iii) metal ions and hence, different UV/Vis reference spectra are obtained, compared to those in aqueous solutions. Additionally, concentration profiles provide a tool for tuning the coordination chemistry, based on the choice of the appropriate DES mixture or aqueous solutions. Consequently, valuable UV/Vis reference spectra for some known and unknown chromium chloride complexes in several aqueous solutions and DES-water mixtures were obtained, which showed that the coordination chemistry in these liquids can be considerably different and comparison should be done with great care.
