Functionalized Imidazalium Carboxylates for Enhancing Practical Applicability in Cellulose Processing

Developing cellulose-based products is highly important because of their low-cost, reproducibility, and biodegradability. However, extensive application for cellulose has been actually hindered due to its well-known insolubility. Herein, some 22 novel functionalized imidazalium carboxylates exhibit tremendously enhanced dissolution capacity for cellulose even without extra energy consumption and are much superior to the previously reported solvents so far. Systematic investigations reveal that the powerful dissolution capacity for cellulose mainly results from the contribution of the imidazolium skeleton cation, not replacing acidic H atoms in imidazolium skeleton by alkyl, binding more allyl in N atoms of imidazolium cation, and binding an electron-donating group in carboxylate anion. Of particular importance, porous cellulose materials with varying micromorphology, for the first time, are reported by tuning the anionic and/or cationic structures of an IL. Moreover, the regenerated cellulose material retains sufficient thermostability and chemical structure. Therefore, this investigation provides a viable strategy for practical application in cellulose conversion into valuable products even without extra heating

Insight into the Cosolvent Effect of Cellulose Dissolution in Imidazolium-Based Ionic Liquid Systems

Recently, it has been reported that addition of a cosolvent significantly influences solubility of cellulose in ionic liquids (ILs), but little is known about the influence mechanism of the cosolvent on the molecular level. In this work, four kinds of typical molecular solvents (dimethyl sulfoxide (DMSO), <i>N</i>,<i>N</i>-dimethylformamide (DMF), CH₃OH, and H₂O) were used to investigate the effect of cosolvents on cellulose dissolution in [C₄mim]­[CH₃COO] by molecular dynamics simulations and quantum chemistry calculations. It was found that dissolution of cellulose in IL/cosolvent systems is mainly determined by the hydrogen bond interactions between [CH₃COO]⁻ anions and the hydroxyl protons of cellulose. The effect of cosolvents on the solubility of cellulose is indirectly achieved by influencing such hydrogen bond interactions. The strong preferential solvation of [CH₃COO]⁻ by the protic solvents (CH₃OH and H₂O) can compete with the cellulose–[CH₃COO]⁻ interaction in the dissolution process, resulting in decreased cellulose solubility. On the other hand, the aprotic solvents (DMSO and DMF) can partially break down the ionic association of [C₄mim]­[CH₃COO] by solvation of the cation and anion, but no preferential solvation was observed. The dissociated [CH₃COO]⁻ would readily interact with cellulose to improve the dissolution of cellulose. Furthermore, the effect of the aprotic solvent-to-IL molar ratio on the dissolution of cellulose in [C₄mim]­[CH₃COO]/DMSO systems was investigated, and a possible mechanism is proposed. These simulation results provide insight into how a cosolvent affects the dissolution of cellulose in ILs and may motivate further experimental studies in related fields

Enhanced Electrocatalytic Activity of Ethanol Oxidation Reaction on Palladium–Silver Nanoparticles via Removable Surface Ligands

This work developed a facile colloidal route to synthesize BH₄^–-capped Pd_<i>x</i>Ag_<i>y</i> nanoparticles (NPs) in water using the reducing ionic liquids of [C_<i>n</i>mim]­BH₄, and the resulting NPs were prone to form the nanocomposites with [amim]⁺-modified reduced graphene (RG). The removal of the metal-free inorganic ions of BH₄^– can create the profoundly exposed interfaces on the Pd_<i>x</i>Ag_<i>y</i> NPs during the electrooxidation, and favor the ethanol oxidation reaction (EOR) in lowering energy barrier. The counterions of [C_<i>n</i>mim]⁺ can gather ethanol, OH^– ions, and the reaction intermediates on catalysts, and synergistically interact with RG to facilitate the charge transfer in nanocomposites. The interface-modified RG nanosheets can effectively segregate the Pd_<i>x</i>Ag_<i>y</i> NPs from aggregation during the EOR. Along with the small size of 4.7 nm, the high alloying degree of 60.2%, the large electrochemical active surface area of 64.1 m² g^–1, and the great peak current density of 1501 mA cm^–2 mg^–1, Pd₁Ag₂@[C₂mim]­BH₄-amimRG nanocomposite exhibits the low oxidation potentials, strong poison resistance, and stable catalytic activity for EOR in alkaline media, and hence can be employed as a promising anodic catalyst in ethanol fuel cells

Synthesis of Ketones through Microwave Irradiation Promoted Metal-Free Alkylation of Aldehydes by Activation of C(sp³)–H Bond

In this paper, a novel methodology for the synthesis of ketones via microwave irradiation promoted direct alkylation of aldehydes by activation of the inert C­(sp³)–H bond has been developed. Notably, the reactions were accomplished under metal-free conditions and used commercially available aldehydes and cycloalkanes as substrates without prefunctionalization. By using this novel method, an alternative synthetic approach toward the key intermediates for the preparation of the pharmaceutically valuable oxaspiroketone derivatives was successfully established

Effect of Alkyl Chain Length in Anions on Thermodynamic and Surface Properties of 1-Butyl-3-methylimidazolium Carboxylate Ionic Liquids

Carboxylate-anion-based imidazolium ionic liquids (ILs) are powerful solvents for cellulose and lignin. However, little is known about their fundamental physicochemical properties. In this work, 1-butyl-3-methylimidazolium carboxylate ILs 1-butyl-3-methylimidazolium formate ([C₄mim]­[HCOO]), acetate ([C₄mim]­[CH₃COO]), propionate ([C₄mim]­[CH₃CH₂COO]), and butyrate ([C₄mim]­[CH₃(CH₂)₂COO]), in which the alkyl chain length in the anions is being varied in contrast to the more usual studies where alkyl chain length in the cations is varied, have been synthesized and their densities and surface tensions have been determined experimentally at different temperatures. By using these data, the molar volume, isobaric expansivity, standard entropy, lattice energy, surface excess entropy, vaporization enthalpy, and Hildebrand solubility parameter have been estimated for these ILs. From the analysis of structure–property relationship, the effect of alkyl chain length in the anions on these physicochemical properties of the ILs has been assessed and the dissolution of cellulose and lignin in these ILs has been discussed. Such knowledge is expected to be useful for understanding the nature of this class of solvent for the dissolution of biomacromolecules

Effect of Substituent Groups in Anions on Some Physicochemical Properties of 1‑Butyl-3-methylimidazolium Carboxylate Ionic Liquids

In this work, four 1-butyl-3-methylimidazolium carboxylate ionic liquids (ILs) with different substituent groups in anions, including 1-butyl-3-methylimidazolium glycollate [C₄mim]­[HOCH₂COO], 1-butyl-3-methylimidazolium lactate [C₄mim]­[CH₃CHOHCOO], 1-butyl-3-methylimidazolium benzoate [C₄mim]­[C₆H₅COO], and 1-butyl-3-methylimidazolium glycinate [C₄mim]­[H₂NCH₂COO], have been synthesized and characterized. Their densities (ρ) and surface tensions (γ) have been determined experimentally in the temperature range of (298.15 to 343.15) K. By using thermodynamic and empirical equations, molar volume (<i>V</i>_m), isobaric expansivity (α_<i>p</i>), standard entropy (<i>S</i>°), lattice energy (<i>U</i>_POT), surface excess entropy (<i>S</i>_s), vaporization enthalpy (Δ_l^g<i>H</i>_m⁰) and Hildebrand solubility parameter (δ_H) of these ILs have been derived from density and surface tension data. The effects of substituent groups in carboxylate anions on densities and surface tensions of these ILs have been assessed from the analysis of the structure–property relationship

Structural Transition of Cinnamate-Based Light-Responsive Ionic Liquids in Aqueous Solutions and Their Light-Tunable Rheological Properties

Light-responsive wormlike micelles have important applications in fields such as microfluids, photoswichable fluids, and rheology control. However, single-component light-responsive wormlike micelles formed only from a single tail surfactant have not been reported in literature. In this work, self-assembly behavior of 1-alkyl-3-methylimidazolium <i>trans</i>-ortho-methoxycinnamate [C_<i>n</i>mim]­[OMCA] (n = 8, 10, 12, 14, 16) ionic liquids in aqueous solutions is studied by UV–vis spectroscopy, viscosity, rheology, conductivity, and cryo-TEM measurements. It is found for the first time that, among the single tail ionic liquid surfactants studied, [C₁₆mim]­[OMCA] can form wormlike micelles in aqueous solutions without any additives and light irradiation. Then these wormlike micelles are able to transform into cylindrical micelles under UV light irradiation, resulting in significantly tunable rheological properties of the solutions. The photoisomerization of anion of [C₁₆mim]­[OMCA] from trans- to cis-isomer as well as the relative hydrophilicity and structural feature of the cis-isomer are suggested to be responsible for such transition

Nanoplasmonically Engineered Interfaces on Amorphous TiO₂ for Highly Efficient Photocatalysis in Hydrogen Evolution

The nanoplasmonic metal-driven photocatalytic activity depends heavily on the spacing between metal nanoparticles (NPs) and semiconductors, and this work shows that ethylene glycol (EG) is an ideal candidate for interface spacer. Controlling the synthetic systems at pH 3, the composite of Ag NPs with EG-stabilized amorphous TiO₂ (Ag/TiO₂-3) was synthesized by the facile light-induced reduction. It is verified that EG spacers can set up suitable geometric arrangement in the composite: the twin hydroxyls act as stabilizers to bind Ag NPs and TiO₂ together and the nonconductive alkyl chains consisting only of two CH₂ are able to separate the two building blocks completely and also provide the shortest channels for an efficient transfer of radiation energies to reach TiO₂. Employed as photocatalysts in hydrogen evolution under visible light, amorphous TiO₂ hardly exhibits the catalytic activity due to high defect density, whereas Ag/TiO₂-3 represents a remarkably high catalytic efficiency. The enhancement mechanism of the reaction rate is proposed by the analysis of the compositional, structural, and optical properties from a series of Ag/TiO₂ composites

Anion-Based pH Responsive Ionic Liquids: Design, Synthesis, and Reversible Self-Assembling Structural Changes in Aqueous Solution

The creation of pH responsive materials that undergo morphological transitions between micelle and vesicle induced by solution pH change is of great importance for their potential application in drug delivery and biochemical engineering. Here, we have developed a series of 18 pH responsive ionic liquids composed of 1-alkyl-3-methylimidazolium cation, [C_<i>n</i>mim]⁺ (<i>n</i> = 4, 6, 8, 10, 12, 14), and different pH responsive anions such as potassium phthalic acid ([C₆H₄COOKCOO]⁻), sodium sulfosalicylic acid ([C₆H₃OHCOOSO₃Na]⁻), and sodium <i>m</i>-carboxylbenzenesulfonate ([C₆H₄COOSO₃Na]⁻). The aggregation behavior and self-assembly structures of the ILs in aqueous solution have been investigated by surface tension, dynamic light scattering, transmission electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance spectroscopy. It was found for the first time that single tail ionic liquids, [C_<i>n</i>mim]­X (<i>n</i> = 12 and 14, X = [C₆H₄COOKCOO], [C₆H₃OHCOOSO₃Na], and [C₆H₄COOSO₃Na]) could form vesicles without any additives, and reversible transition was observed between spherical micelles and vesicles with the change of solution pH value. The transition in self-assembly structures is suggested to be driven by the variation in molecular structure and hydrophilicity/hydrophobicity of anions of the ILs

Molecular Origin for the Difficulty in Separation of 5‑Hydroxymethyl­furfural from Imidazolium Based Ionic Liquids

Ionic liquids (ILs) have shown superior performance in the conversion of biomass to 5-hydroxymethyl­furfural (5-HMF) as reaction medium and/or catalyst, which is a green platform compound with a wide range of applications in manufacturing fine chemicals and biofuels. Nevertheless, the separation of 5-HMF from ILs is very difficult and becomes a technical bottleneck for IL application in the preparation of 5-HMF. To resolve this problem, understanding the interactions between ILs and 5-HMF is essential. In this work, attenuated total reflectance Fourier transform infrared, ¹H nuclear magnetic resonance, and quantum chemistry calculations were combined to investigate the interaction between 5-HMF and each of the eight ILs over the whole composition range. The studied ILs have the same 1-butyl-3-methylimidazolium cation [C₄mim]⁺ but different anions. It was found that interactions between the ILs and 5-HMF were mainly ascribed to the strong hydrogen bonds of 5-HMF with anions of the ILs, and the formation abilities of hydrogen bonds of the anions with O–H group of 5-HMF were found to decrease in the order [CH₃COO]⁻, [C₂H₅COO]⁻ > [HSO₄]⁻ > [CF₃COO]⁻ > [N­(CN)₂]⁻ > [NO₃]⁻ > [CH₃OSO₃]⁻ > [BF₄]⁻. These results suggest that the anions with stronger hydrogen bond accepting ability have stronger interaction with 5-HMF and the separation of 5-HMF from the ILs is mainly governed by the hydrogen bonding interactions between anion of the ILs and 5-HMF. In addition, partition coefficients of 5-HMF between 1,4-dioxane and the ILs phases were determined experimentally to support the conclusion