Search

Deep eutectic solvents (DESs) offer a suitable alternative to conventional solvents in terms of both performance and cost-effectiveness. Some DESs also offer certain green features, the greenness of which is notoriously enhanced when combined with water. Aqueous DES dilutions are therefore attracting great attention as a novel green medium for biotechnological processes, with the aqueous dilutions of reline-a DES composed of urea and choline chloride-being one of the most studied systems. Despite their macroscopic homogeneous appearance, both H NMR spectroscopic studies and molecular dynamics simulations have revealed the occurrence of certain dynamic heterogeneity at a microscopic molecular level. Ultrasonic measurements were also used with the aim of getting further insights but nonconclusive results were obtained. Herein, we have studied aqueous reline dilutions by Brillouin spectroscopy given its proved suitability for detecting local structure rearrangements in liquid mixtures of H-bonded co-solvents. Brillouin spectroscopy revealed the formation of a co-continuous structure resulting from local structure rearrangements and micro-segregation into aqueous and DES phases. Interestingly, there is agreement between H NMR and Brillouin spectroscopy when pointing to the DES content where microphase segregation and formation of co-continuous structures occurred.

Porous carbons are really interesting materials for applications such as gas adsorption, electrocatalysts or energy harvesting and conversion.[1] Among others, spinodal decomposition (SD) processes have proved effective for the synthesis of macro- and mesoporous materials.[2] Despite the theoretical aspects of SD processes are well understood, finding the proper experimental conditions to obtain bicontinuous structures via SD processes is a non-predictable and quite tedious process, typically based on trial and error. The challenge is therefore finding a ¿tool¿ capable to predict the suitability of a particular starting solution to undergo a spinodal decomposition process. We have used aqueous solutions of different DESs containing common carbon precursors (i. e. resorcinol) for the preparation of bicontinuous porous carbons via polycondensation of resorcinol with formaldehyde. Scanning electron microscopy analysis of the different carbons allowed us to determine which solutions leads to bicontinuous structures via SD. Moreover, we studied the starting DES/H2O binary mixtures by Brillouin spectroscopy given the capability of this technique to observe local structure rearrangements resulting from non-ideal mixing of the components. In our case, we found that the representation of data obtained by Brillouin spectroscopy allows predicting the range of molar fractions of DES in H2O for which bicontinuous structures via SD are ultimately obtained.

Spinodal decomposition (SD) processes have proved effective for the synthesis of macro- and mesoporous materials. Despite the theoretical aspects of SD processes are well understood, finding the proper experimental conditions – both the components as well as the ratio in which they have to be combined – to attain co-continuous structures is a non-predictable and quite tedious process, typically based on trial and error. The challenge is finding a “tool” capable to predict the suitability of a particular starting solution to undergo SD processes. Here in, we used aqueous solutions of deep eutectic solvents (DESs) for the preparation via SD of co-continuous porous carbons, the morphologies of which ranged from spinodal to aggregates-of-particles-like just depending on dilution. Despite the starting DES/HO binary mixture was macroscopically homogeneous, Brillouin spectroscopy revealed the occurrence of certain nanostructural rearrangements within a dilution range that coincided with that used for preparation of carbons with morphologies transitioning from spinodal to aggregates-of-particles-like. Moreover, carbons exhibited a noticeable degree of heteroatom co-doping – e.g. N and P – and proved particularly effective for CO capture with adsorptions of up to 4.7 mmol/g at 0 °C and 760 mbar.