Thermal stability of imidazolium-based ionic liquids

Effects of the Ionic Liquid Structure on Porosity of Lignin-Derived Carbon Materials

Converting lignin into advanced porous carbon materials, with desirable surface functionalities, can be challenging. While lignin-derived carbons produced by pyrolysis at >600 °C develop porosity, they also simultaneously lose nearly all their surface functional groups. By contrast, pyrolysis of lignin at lower temperatures (e.g., <400 °C) results in the formation of nonporous char that retains some surface functionalities. However, copyrolysis of lignin with some ionic liquids (ILs) at lower temperatures offers an opportunity to produce porous carbon materials with both large surface areas and an abundance of surface functional groups. This study investigates the effects of IL properties (solubility, thermal, and ionic size) on the specific surface areas of lignin-derived carbons produced by copyrolysis of lignin and ILs at 350-400 °C for 20 min. It was found that ILs that have bulky anions and small cation sizes can induce porosity in lignin-derived carbons with large surface areas. Among 16 ILs that were tested, [C2MIm][NTF2] demonstrated the best performance; the inclusion of it in the copyrolysis process resulted in lignin-derived carbons with ∼528 m2 g-1 and 0.48 cm3 g-1. Lignin-derived carbons produced using no IL, [C2MIm][NTF2], and [C4MIm][OTF] were further characterized for morphology, interfacial chemical, and elemental properties. The copyrolysis of lignin and [C2MIm][NTF2], and [C4MIm][OTF] resulted in doping of heteroatoms (N and S) on the porous carbon materials during pyrolysis reaction. The present findings contribute to a better understanding of the main property of ILs responsible for creating porosity in lignin carbon during pyrolysis.

Ruthenium Nanoparticles Stabilized with Methoxy-Functionalized Ionic Liquids: Synthesis and Structure-Performance Relations in Styrene Hydrogenation

A series of ruthenium nanoparticles (RuNPs) were synthesized by the organometallic approach in different functionalized imidazolium ionic liquids (FILs). Transmission electron microscopy (TEM) showed well-dispersed and narrow-sized RuNPs ranging from 1.3 to 2.2 nm, depending on the IL functionalization. Thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) allowed the interaction between the RuNPs and the ILs to be studied. The RuNPs stabilized by methoxy-based FILs (MEM and MME) displayed a good balance between catalytic activity and stability when evaluated in the hydrogenation of styrene (S) under mild reaction conditions. Moreover, the catalysts showed total selectivity towards ethylbenzene (EB) under milder reaction conditions (5 bar, 30 °C) than reported in the literature for other RuNP catalysts.

Thermal Decomposition, Low Temperature Phase Transitions and Vapor Pressure of Less Common Ionic Liquids Based on the Bis(trifuoromethanesulfonyl)imide Anion

Four ionic liquids (ILs) based on the bis(trifluoromethanesulfonyl)imide (NTf₂) anion were synthesized and characterized concerning their thermal stability, the occurrence of low temperature phase transitions and their volatility. All these physical quantities are highly important for possible applications. Both monocationic and dicationic ILs were considered. All ILs exhibit thermal stability exceeding 350 °C, an extremely high value, due to the presence of the NTf₂ anion. Monocationic ILs can undergo crystallization, and they melt at 1 and 38 °C. On the contrary, dicationic ILs containing large positively charged ions display only a glass transition around −40 °C, without any crystallization or melting process; this fact is particularly important in view of the possibly low temperature applications of the dication ILs. The vapor pressure, p_v, of the four ILs was measured by isothermal thermogravimetry in the temperature range between 250 and 325 °C; the lowest values of p_v were obtained for the two dicationic liquids, suggesting that they are particularly well suited for high temperature applications. The vaporization enthalpy was calculated through the Clausius–Clapeyron equation and was found in the range between ~140 and ~180 kJ/mol depending on the specific IL.

Effect of Graphene Oxide on the Properties of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate)

The main shortcomings of polyhydroxybutyrate (PHB), which is a biodegradable and biocompatible polymer used for biomedical and food packaging applications, are its low thermal stability, poor impact resistance and lack of antibacterial activity. This issue can be improved by blending with other biodegradable polymers such as polyhydroxyhexanoate to form poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), which is a copolymer with better impact strength and lower melting point. However, PHBHHx shows reduced stiffness than PHB and poorer barrier properties against moisture and gases, which is a drawback for use in the food industry. In this regard, novel biodegradable PHBHHx/graphene oxide (GO) nanocomposites have been prepared via a simple, cheap and environmentally friendly solvent casting method to enhance the mechanical properties and antimicrobial activity. The morphology, mechanical, thermal, barrier and antibacterial properties of the nanocomposites were assessed via several characterization methods to show the enhancement in the biopolymer properties. The stiffness and strength of the biopolymer were enhanced up to 40% and 28%, respectively, related to the strong matrix-nanofiller interfacial adhesion attained via hydrogen bonding interactions. Moreover, the nanocomposites showed superior thermal stability (as far as 40 °C), lower water uptake (up to 70%) and better gas and vapour barrier properties (about 45 and 35% reduction) than neat PHBHHx. They also displayed strong biocide action against Gram positive and Gram negative bacteria. These bio-based nanocomposites with antimicrobial activity offer new perspectives for the replacement of traditional petroleum-based synthetic polymers currently used for food packaging.

A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids

Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO2 capture, etc. As solvents, the unlimited combinations of cations and anions have given ionic liquids a remarkably wide range of solvation power covering a variety of organic and inorganic materials. Ionic liquids are also considered "green" solvents due to their negligible vapor pressure, which means no emission of volatile organic compounds. Due to these interesting properties, ionic liquids have been explored as promising solvents for the dissolution and fractionation of wood and cellulose for biofuel production, pulping, extraction of nanocellulose, and for processing all-wood and all-cellulose composites. This review describes, at first, the potential of ionic liquids and the impact of the cation/anion combination on their physiochemical properties and on their solvation power and selectivity to wood polymers. It also elaborates on how the dissolution conditions influence these parameters. It then discusses the different approaches, which are followed for the homogeneous and heterogeneous dissolution and fractionation of wood and cellulose using ionic liquids and categorize them based on the target application. It finally highlights the challenges of using ionic liquids for wood and cellulose dissolution and processing, including side reactions, viscosity, recyclability, and price.