Ionic liquids (ILs) have proven effective solvents for pretreating lignocellulose, leading to the fast saccharification of cellulose and hemicellulose. However, the high current cost of most ILs remains a major barrier to commercializing this recent approach at a practical scale. As a strategic detour, aqueous solutions of ILs are also being explored as less costly alternatives to neat ILs for cellulose pretreatment. However, limited studies on a few select IL systems are known and there remains no systematic survey of various ILs, eluding an in-depth understanding of pretreatment mechanisms afforded by aqueous IL systems. As a step toward filling this gap, this study presents results for Avicel cellulose pretreatment by neat and aqueous solutions (1.0 and 2.0 M) of 20 different ILs and three deep eutectic solvents, correlating enzymatic hydrolysis rates of pretreated cellulose with various IL properties such as hydrogen-bond basicity, polarity, Hofmeister ranking, and hydrophobicity. The pretreatment efficiencies of neat ILs may be loosely correlated to the hydrogen-bond basicity of the constituent anion and IL polarity; however, the pretreatment efficacies for aqueous ILs are more complicated and cannot be simply related to any single IL property. Several aqueous IL systems have been identified as effective alternatives to neat ILs in lignocellulose pretreatment. In particular, this study reveals that aqueous solutions of 1-butyl-3-methylimidazolium methanesulfonate ([BMIM][MeSO3]) are effective for pretreating switchgrass (Panicum virgatum), resulting in fast saccharification of both cellulose and hemicellulose. An integrated analysis afforded by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and cellulase adsorption isotherm of lignocellulose samples is further used to deliver a more complete view of the structural changes attending aqueous IL pretreatment.

Task-specific ternary deep eutectic solvent (DES) systems comprising choline chloride, glycerol, and one of three different superbases were investigated for their ability to capture and release carbon dioxide on demand. The highest-performing systems were found to capture CO2 at a capacity of ∼10% by weight, equivalent to 2.3–2.4 mmol of CO2 captured per gram of DES sorbent. Of the superbases studied, 1,5-diazabicyclo[4.3.0]-non-5-ene (DBN) gave the best overall performance in terms of CO2 capture capacity, facility of release, and low sorbent cost. Interestingly, we found that only a fraction of the theoretical CO2 capture potential of the system was utilized, offering potential pathways forward for further design and optimization of superbase-derived DES systems for further improved reversible CO2 sequestration. Finally, the shear rate-dependent viscosities indicate non-Newtonian behavior which, when coupled to the competitive CO2 capture performance of these task-specific DESs despite a 1 to 2 orders of magnitude higher viscosity, suggest that the Stokes–Einstein–Debye relation may not be a valid predictor of performance for these structurally and dynamically complex fluids.

We have demonstrated an easy, economic, one-step synthetic route to water-soluble fluorescent carbon dots derived from the thermal upcycling of urine.

One of the hallmarks of ionic liquids (ILs) and a critical part of their sustainable implementation is their low volatility, although statements in this regard are frequently made in the absence of a critical evaluation. Although it is generally accepted that conventional ILs exhibit significantly reduced vapor pressures relative to common organic solvents, glib statements about ILs having zero volatility can no longer be abided, even if a concrete temperature-dependent vapor pressure, Pvap(T), framework for placement of IL performance has not yet been established. In this communication, Pvap(T) values of 30 illustrative low-volatility fluids—including representative imidazolium-, ammonium-, and pyrrolidinium-based aprotic ILs; examples of protic, polymeric, and di-cationic ILs; as well as deep eutectic solvents (DESs) and glycols—were determined using a simple, convenient, and reproducible isothermal thermogravimetric method. Guided by this “vapor pressure map”, observed trends can be discussed in terms of anion basicity, cation geometry, alkane chain length, hydrogen bonding strength, and van der Waals forces, providing a context for the placement of theoretical and experimental vapor pressures gleaned in future IL and DES studies.