Green Co-solvent Research Articles

Green co-solvent-assisted one-pot synthesis of high-performance flexible lignin polyurethane foam

Although lignin is a promising candidate as a source of polyol for producing eco-friendly polyurethane foam (PUF), its direct application has limitations, primarily stemming from the brittleness of the resulting products and poor processibility at high lignin loadings. To address these technical challenges, we introduced an effective co-solvent for the lignin-based polyurethane foams (LPUFs) with up to 80 wt% of lignin substitution for petroleum polyols. As a green co-solvent that involves carbon dioxide fixation during its production, propylene carbonate (PC), was blended with lignin and improved the distribution of lignin by decreasing the viscosity, providing a room-temperature reaction. The LPUFs demonstrated a comparable thermal insulation performance (R-values greater than 5 in−1) with commercially available PUF with a uniform size of closed-cell structure induced by the reduced viscosity of lignin-based polyol. LPUFs also showed enhanced fire retardancy and moisture resistance compared to the control PUFs, benefiting from lignin’s intrinsic fire-resistant and hydrophobic properties. To mitigate the brittleness issue at high lignin loadings, flexible polyethylene glycols (PEGs) with a high molecular weight (i.e., PEG-1000) were dissolved in PC at room temperature to further improve the mechanical strength of LPUFs. The compressive strength of LPUFs with 80 wt% lignin substitution content was remarkably improved to 226 kPa by the employment of co-solvent and PEG-1000 compared to the control PUF (<140 kPa). Moreover, the flexibility of the LPUFs was successfully controlled by simply adjusting the PEG-400/PEG-1000 ratio. The results of this study provide valuable insights for accelerating and broadening the utilization of lignin in sustainable materials and manufacturing areas.

Effect of green co-solvents on properties and synthesis of cellulose esters in superbase ionic liquid

Effect of green co-solvents on properties and synthesis of cellulose esters in superbase ionic liquid

Rheology and dissolution capacity of cellulose in novel [mTBNH][OAc] ionic liquid mixed with green co-solvents

Rheology and dissolution capacity of cellulose in novel [mTBNH][OAc] ionic liquid mixed with green co-solvents

Exploring solvation behaviour of biocompatible ionic liquid 2-hydroxyethylammonium formate + polyethylene glycols mixtures: Role of oxyethylene and hydroxyl units of PEGs

The favourable modification of the physicochemical properties of the ionic liquid with green co-solvent and their molecular level characterization with spectroscopic techniques is the area of current research. Further, the co-solvent modified ionic liquid mixtures furnishes interesting properties which render the utility of these solvents in several important applications. In the current work, the effects of addition of two polyethylene glycols (PEGs) with average molecular weights of 200, and 600 on solvent properties of IL 2-hydroxyethyl ammonium formate (HEF) has been explored with the help of solvatochromic absorbance probes. The physicochemical characteristics of the ionic liquid mixtures are altered in an unexpectedly positive way when PEGs are added to IL HEF. The absorbance behaviour of the solvatochromic probes Reichardt dye 33 shows interestingly positive non-ideal behaviour, which may be attributed to the high dipolarity/polarizability (π*) and hydrogen bond donor ability (HBD) (α) of the HEF + PEG mixtures. Further, the Kamlet-Taft parameters, including hydrogen bond acceptor ability (HBA) (β), and hydrogen bond donor ability (HBD) (α), and dipolarity/polarizability (π*) of the HEF + PEG binary mixtures display nonideality, which may be because of the strong Hydrogen bond networking of HEF-PEG molecules along with solute-HEF/PEG interaction present in the mixtures. Moreover, the preferential solvation approach has been invoked to explore the solute–solvent/solvent–solvent interactions present in the HEF + PEGs binary mixtures. The Redlich–Kister (CNIBS/R–K) theoretical model predicts the experimental results obtained by solvatochromic probe studies in satisfactory manner. The results of the DFT and FTIR study also predict the possibility of the H-bonding interactions in HEF + PEGs mixtures.

Photochromic performance of hydrogel based on deep eutectic solvent induced water soluble Cu-doped WO3 hybrids with antibacterial property

A novel fast photoresponse and self-fading photochromic hydrogel system was fabricated based on Cu-doped WO 3 , which prepared by employing DESs as co-solvent. The photochromic hydrogel displayed remarkable antibacterial ability and non-cytotoxicity, great potential in the applications of stimuli-responsive materials such as smart windows, repeatable erasing paper and photochromic sensors. • Deep eutectic solvents (DESs) as a green co-solvent was employed to prepare Cu-doped WO 3 photochromic materials with excellent water solubility. • The fabricated P(AM-HEA)-Cu-WO 3 -X photochromic hydrogels exhibit rapid photoresponse and enhanced self-fading rate. • The deep-blue colored P(AM-HEA)-Cu-WO 3 -25% hydrogel could come back to its original colorless state within 40 min. • The mechanism of photochromic and self-fading behaviors for P(AM-HEA)-Cu-WO 3 -X photochromic hydrogels was detailed analyzed. • The remarkable antibacterial performance and cell viability possessed in hydrogels also confirmed. A novel photochromic and self-bleaching hydrogel was prepared based on the Cu-doped tungsten oxide (WO 3 ) hybrid encapsulated in the co-polymer matrix polymerized using acrylamide (AM) and hydroxyethyl acrylate (HEA) as monomers. The Cu-WO 3 -25% hybrid was generated by introducing Cu species into the lattice of WO 3 with hexagonal-like prismatic structure and acted as light absorber. Given that WO 3 and Cu-doped WO 3 hybrids possess superior water solubility by using water and deep eutectic solvents (DESs, ChCl:EG) containing sufficient hydrogen bond as co-solvent, the high transparency of 90% of the hydrogels was achieved. As compared with P(AM-HEA)-WO 3 -based hydrogel, the P(AM-HEA)-Cu-WO 3 -X hydrogel exhibited the enhanced coloration degree under UV irradiation. The P(AM-HEA)-Cu-WO 3 -25% photochromic hydrogel changed from colorless to blue immediately once illuminated by UV light, and turns into dark-blue with the irradiation time going on. The self-bleaching process indicates it only takes 40 min for the P(AM-HEA)-Cu-WO 3 -25% hydrogel to return to the original colorless transparent state. Furthermore, the hydrogel systems exhibit efficient antibacterial activities against bacteria of both E. coli and S. aureus , accompanying with outstanding biocompatibility. As such, the fabricated hydrogel demonstrates rapid photoresponse, self-bleaching process, superior antibacterial performance, and cell viability, showing a great potential application as stimuli-responsive materials.

Ultrasound-Assisted Water Extraction of Gentiopicroside, Isogentisin, and Polyphenols from Willow Gentian "Dust" Supported by Hydroxypropyl-β-Cyclodextrin as Cage Molecules.

The residue after sieving ("dust") from the willow gentian underground parts is an unexploited herbal tea by-product, although it contains valuable bioactive compounds. Cyclodextrins as efficient green co-solvents, cage molecules, and multifunctional excipients could improve the extraction and contribute to the added value of the resulting extracts. The objective of this study was to determine the optimal conditions for the extraction of gentiopicroside, isogentisin, and total phenolics (TPC) from willow gentian "dust" using ultrasound-assisted water extraction coupled with hydroxypropyl-β-cyclodextrin (HPβCD). The influence of extraction temperature (X1: 20-80 °C), time (X2: 20-50 min), and HPβCD concentration (X3: 2-4% w/v) was analyzed employing the response surface methodology (RSM). The optimal extraction conditions for simultaneously maximizing the extraction yield of all monitored responses were X1: 74.89 °C, X2: 32.57 min, and X3: 3.01% w/v. The experimentally obtained response values under these conditions (46.96 mg/g DW for gentiopicroside, 0.51 mg/g DW for isogentisin, and 12.99 mg GAE/g DW for TPC) were in close agreement with those predicted, thus confirming the suitability and good predictive accuracy of the developed RSM models. Overall, the developed extraction system could be an applicable alternative strategy to improve the extraction of bioactive compounds from the underutilized "dust" of willow gentian underground parts.

Effect of deep eutectic solvents on the biocatalytic properties of β-glucosidase@ZnOFe nano-biocatalyst

In this work, we investigate the use of aqueous deep eutectic solvents (DESs) consisting of different hydrogen bond acceptors (choline chloride, ammonium salts or betaine) and hydrogen bond donors (amines, sugars and alcohols), as co-solvents in biocatalytic reactions catalyzed by a nano-biocatalyst with β-glucosidase (BGL) activity. For this purpose, β-glucosidase from Thermotoga maritima was immobilized on the surface of green zinc oxide-iron oxide nanoparticles (BGL@ZnOFe) derived from an aqueous olive leaf extract. The covalent bonding of β-glucosidase on the surface of nanoparticles was demonstrated by X-ray photoelectron spectroscopy. The effect of a wide range of DES solutions on the biocatalytic features of BGL@ZnOFe was thoroughly investigated. The concentration of DES as well as the specific combination of hydrogen bond acceptors and hydrogen bond donors had a significant impact on the hydrolytic activity of immobilized β-glucosidase. Most choline chloride and betaine-based DESs enhanced the enzymatic activity and thermal stability of BGL@ZnOFe up to 50%. The enzymatic activity of the nano-biocatalyst towards the hydrolysis of bioactive phenolic compounds depends on the nature of the DES used. Choline chloride:butylene glycol-based medium had beneficial effect on a transglycosylation reaction, such as the synthesis of salidroside, increasing the total turnover number of the biocatalytic process by 55%. This work indicates that the use of several choline chloride and betaine-based DESs can be successfully employed as green co-solvents in various hydrolytic and synthetic biocatalytic processes.

Functional properties of coatings based on novel waterborne polyurethane dispersions with green cosolvents

Three green sustainable cosolvents were used to produce polyurethane waterborne coatings. The effect of dihydrolevoglucosenone, gamma valerolactone and propylene carbonate on the performance of different coatings from a range of polyurethane structures with different hard segment content and different chain extender (a diol and a diamine) was studied. Properties of both synthesised polymers and water dispersions, like particle size distribution, stability, and pH, were carefully examined. The key properties of obtained coatings, including Koning hardness, specular gloss, hydrophobicity, abrasion resistance, adhesion or chemical resistance were detailly investigated to validate the use of these alternative green solvents in industrial coatings. The results indicated that the performance of materials based on sustainable cosolvents were equivalent to that of PUD coatings from commonly used cosolvent, N-methyl-2-pyrrolidone (NMP) maintaining a high gloss finished, as the properties of the dispersions keep optimal. Monomodal water dispersions with particle's diameter below 180 nm and stable for at least one month were achieved.

Enhancement of clozapine solubility in three aqueous choline chloride-based deep eutectic solvents: Experimental and COSMO-RS prediction

• Solubility behaviors of clozapine in aqueous DESs solutions were revealed by COSMO-RS. • Solubility of clozapine in aqueous DESs solutions was measured. • Solubility of clozapine was enhanced by increasing weight fraction of DES and temperature. • Dissolution thermodynamics of clozapine was calculated via van't Hoff equation. The clozapine (CLZ) solubility (molar fraction) in three aqueous choline chloride (ChCl) based deep eutectic solvents (DESs) with urea (U), glycerol (G) and ethylene glycol (EG) was determined at T = (293.15 to 313.15) K under an atmospheric pressure. As neoteric green co-solvents, DESs can apparently enhance the CLZ solubility more than 550-fold than that in pure water at T = 293.15 K, especially in ChCl/G. At the same DESs proportion (weight fraction) and same temperature, the CLZ solubility in aqueous DESs solutions is ranked as ChCl/G > ChCl/EG > ChCl/U. Furthermore, the experimental solubility of CLZ in aqueous DES solutions has been correlated by NRTL, three-Suffix Margules, UNIQUAC and Wilson models, suggesting NRTL model to be the best correlation. In addition, the SLE CLZ solubility data was also predicted by reference solubility method using COSMO-RS model, and the predicted results are consistent with the experiment data. The basic mechanism of the solubility behavior of CLZ and solvent molecules was analyzed by studying σ profiles of DESs as well as the molecular interaction energies, implying that the CLZ dissolution is a complex process affected by the synergy of molecular interactions. Based on van’t Hoff equation, the solution thermodynamic properties (Δ G dis o , Δ H dis o and Δ S dis o ) have been estimated, indicating the dissolution process of CLZ in aqueous DES solutions is endothermic and entropy-driven. The improved solubility of CLZ in aqueous DES solutions provides reference for its application in novel crystallization development for the CLZ manufacture.

Thermodynamic Properties of Ternary Systems Containing (LiCl and LiBr) + Propylene Carbonate + Ionic Liquid (1-Alkyl-3-methylimidazolium Thiocyanate).

The development of the Li-ion battery Industry in a green way is crucial for human beings’ future. Ionic liquids (ILs) are green cosolvents that could be applied in Li-ion battery electrolytes. A thermodynamic study has been carried out for a Li-ion electrolyte (propylene carbonate (PC) + LiCl and LiBr) in the presence of IL 1-alkyl-3-methylimidazolium thiocyanate [RMIM][SCN] (R = butyl, hexyl, and octyl). The studied thermodynamic properties were density, speed of sound, apparent molar volume, and compressibility. The effect of ILs in propylene carbonate (PC) has been investigated under atmospheric pressure at T = (288.15–318.15) K. Also, a microscopic approach using scaled particle theory has been implemented. The solvation effect of lithium halides, LiX (X = Cl–, Br–), on the volumetric and compressibility properties of the ILs has been studied at 298.15 K. The results show that [OMIM][SCN] has the strongest interactions with PC in the studied ILs and these interactions are more weakened with the addition of LiBr than LiCl. According to the partial molar compressibility results, the systems containing [OMIM][SCN] could be used under pressure more beneficially than other systems from the thermodynamic aspect of view.

Fractionation of Lignin with Decreased Heterogeneity: Based on a Detailed Characteristics Study of Sequentially Extracted Softwood Kraft Lignin

Industrial lignin fractionation is attracting increasing interest due to its enormous potential in the development of high value-added materials. However, the widely reported fractionation approaches are primarily focused on the separation of fractions with a low polydispersity index (PDI). In this study, based on the detailed characteristic examination of carefully sequential-extracted softwood Kraft lignin fractions, a novel method to isolate lignin fraction with decreased heterogeneity (LGF-dh), was established in consideration of impurities, elemental composition, molar mass distribution, carbohydrate content, functional hydroxyl content, and the content of lignin-relevant aromatic units. To characterize the mentioned properties, an elemental analyzer, SEC-MALS, GC–MS, GC-FID, Py/GC–MS, 31P-NMR, and HSQC-NMR were used to compare the differences of the sequential lignin fractions that were obtained by methyl tert-butyl ether (MTBE), ethyl acetate (EtOAc), ethanol (EtOH), methanol (MeOH), acetone, and dioxane. Moreover, a practical and feasible three-step extraction process was proposed to separate the low heterogeneity lignin fraction from industrial lignin according to the different solubilities of each fraction in the green cosolvent system of EtOH/water, MeOH/water, and acetone/water. Overall, this work presented a comprehensive study on the properties of softwood lignin as well as proposed a feasible and convenient method to reduce the heterogeneity of lignin, which would promote its valorization.

Impact of Green Cosolvents on the Catalytic Dehydrogenation of Formic Acid: The Case of Iridium Catalysts Bearing NHC-phosphane Ligands.

The catalysts [Ir(COD)(κ3-P,C,P′-PCNHCP)]BF4 and [Ir(COD)(κ2-P,C-PCNHCO)]BF4 proved to be active in the solventless dehydrogenation of formic acid. The impact of various cosolvents on the activity was evaluated, showing an outstanding improvement of the catalytic performance of [Ir(COD)(κ2-P,C-PCNHCO)]BF4] in “green” organic carbonates: namely, dimethyl carbonate (DMC) and propylene carbonate (PC). The TOF1h value for [Ir(COD)(κ2-P,C-PCNHCO)]BF4 increases from 61 to 988 h–1 upon changing from solventless conditions to a 1/1 (v/v) DMC/HCOOH mixture. However, in the case of [Ir(COD)(PCNHCP)]BF4, only a marginal improvement from 156 to 172 h–1 was observed under analogous conditions. Stoichiometric experiments allowed the identification of various key reaction intermediates, providing valuable information on their reactivity. Experimental data and DFT calculations point to the formation of dinuclear species as the catalyst deactivation pathway, which is prevented in the presence of DMC and PC.

Cyclodextrins as high-performance green co-solvents in the aqueous extraction of polyphenols and anthocyanin pigments from solid onion waste

Cyclodextrins as high-performance green co-solvents in the aqueous extraction of polyphenols and anthocyanin pigments from solid onion waste

A selective cellulose/hemicellulose green solvents extraction from buckwheat chaff

A two-phase extraction process was adopted to obtain cellulose and hemicellulose from buckwheat chaff by using green solvents. We are proposing a combination of propylene carbonate (PC) and ionic liquids (ILs) in a 1:5 ratio. We compared the first-generation ILs 1-butyl-2,3-dimethylimidazolium chloride (BdmimCl), and 1-butyl-3-methyl imidazolium acetate (BmimAc) with respect to the tetrabutyl ammonium acetate (TBAAc). The cellulose and hemicellulose were, firstly, extracted into the PC/IL mixture and subsequently precipitated by water addition. All precipitate materials were analysed by FTIR-ATR and TGA, while the organic phase and the supernatant after water addition were analysed by using self-diffusion NMR. The PC green co-solvent was proven to be an exceptional candidate to replace dimethyl sulfoxide. The highest amount of precipitate material after water addition was obtained with PC-BmimAc, while PC-TBAAc was showing the highest cellulose/hemicellulose selectivity. Furthermore, a preferential interaction of the supernatant cellulose residue with PC or acetate was observed by self-diffusion NMR.

Hydroxypropyl-β-Cyclodextrin as a Green Co-Solvent in the Aqueous Extraction of Polyphenols from Waste Orange Peels

There is, to-date, an expanding interest concerning the use of cyclodextrins as green food-grade co-solvents in the aqueous extraction of polyphenols, however, data regarding polyphenol extraction from waste orange peels (WOP) are lacking. On this ground, hydroxypropyl β-cyclodextrin (HP-β-CD), a highly water-soluble cyclodextrin, was used to develop a simple and straightforward methodology for the effective recovery of WOP polyphenols. Process optimization by response surface showed that maximum total polyphenol recovery (26.30 ± 1.49 mg gallic acid equivalents g−1 dry mass) could be accomplished with 15 mM HP-β-CD at 40 °C. On the other hand, integration of ultrasonication pretreatment was found unsuitable, as it resulted in reduced polyphenol yield. Examination of solvent acidity indicated that polyphenol extraction may be enhanced at pH 4, but the difference was non-significant (p &gt; 0.05) compared to yields attained at pH 2, 3, and 5. Extraction of WOP polyphenols with HP-β-CD was shown to provide significantly higher hesperidin yield compared to 60% (v/v) aqueous ethanol, which suggested selectivity of HP-β-CD toward this polyphenolic metabolite.

Solubility of cefixime in aqueous mixtures of deep eutectic solvents from experimental study and modeling

Deep eutectic solvents (DESs) as green cosolvents can be added to water for increasing the solubility of poorly water-soluble drugs. In this study, the solubility of cefixime is studied in three aqueous solutions of DES, including choline chloride+malonic acid, choline chloride+urea, and choline chloride+glucose. The experiments are conducted in the temperature range of 293.15 K to 333.15 K, pressure of 0.1 MPa and different compositions of the DESs. The results show that adding DES to water increases the solubility of cefixime significantly. For instance, adding 6% (mol/mol) of choline chloride+malonic acid to water increases the cefixime solubility by more than 17 times. The DESs of choline chloride+malonic acid and choline chloride+urea are more effective cosolvents compared with the DES of choline chloride+glucose in increasing the mole fraction of cefixime. In addition, the solubility data are successfully correlated with the activity models of NRTL, Wilson and van Laar. The overall AARD% of the NRTL, Wilson and van Laar models in estimating the mole fraction of cefixime in aqueous solutions of the DESs are 3.88, 3.62 and 10.14, respectively.

Influence of green solvent on levulinic acid production from lignocellulosic paper waste

Lignocellulosic wastes constitute a significant portion of the municipal solid waste, which should be valorised for the synthesis of value-added chemicals to achieve circular bioeconomy. This study evaluates the use of γ-valerolactone (GVL) and acetone as green co-solvents to produce levulinic acid (LA) from lignocellulosic paper towel waste at different temperatures using dilute H2SO4. At the highest reaction temperature (200 °C), H2O-only system achieved ~15 Cmol% of LA at maximum. while GVL/H2O and acetone/H2O co-solvent systems enhanced the depolymerisation of paper towel waste and the subsequent conversion to LA, with the highest yield amounted to ~32 Cmol%. Acetone/H2O solvent system generated ~17 Cmol% LA at a lower temperature (180 °C), while higher temperature induced polymerisation of soluble sugars and intermediates, hindering further conversion to LA. In contrast, the availability of soluble sugars was higher in the GVL/H2O system, which favoured the production of LA at higher temperatures.

Combining tannic acid-modified support and a green co-solvent for high performance reverse osmosis membranes

In this work, a support modified by tannic acid (TA) and a green co-solvent (dimethyl carbonate (DMC)) were used jointly to prepare high performance polyamide (PA) reverse osmosis (RO) membranes. The membrane characterization results showed that (1) the leaf-like structure became more pronounced on the membrane surface owing to the addition of DMC and (2) TA made the PA active layer thinner and denser. Because of these improvements of skin layer structure, the RO membranes prepared using TA and DMC (i.e., polysulfone (PSf)/TA-RO@DMC) had a better performance than the membranes prepared without using TA and DMC (i.e., PSf-RO) and those prepared using only TA (i.e., PSf/TA-RO) or only DMC (i.e., PSf-RO@DMC). By joining hands, TA and DMC endowed the RO membranes with a high flux of 64.2 ± 1.8 L m−1 h−2 and a high salt rejection of 99.03 ± 0.02% (the testing condition: 15.5 bar pressure, 2000 ppm NaCl feed and 25 °C). Besides, chlorination was used to improve the membrane performance further. The chlorination results showed that chlorinated PSf/TA-RO@DMC had a higher performance than chlorinated PSf-RO@DMC. This is because TA increased the compactness of PA active layer, which weakened the effect of chlorine attack on PA. After chlorination, the flux and salt rejection of PSf/TA-RO@DMC can be improved further to 90.5 ± 6.3 L m−1 h−2 and 99.25 ± 0.02%, respectively (the testing condition: 15.5 bar pressure, 2000 ppm NaCl feed and 25 °C).

Green preparation process using methyl lactate for cellulose-acetate-based nanofiltration membranes

Cellulose acetate (CA) membranes were prepared via phase inversion using methyl lactate as a green solvent and 2-methyltetrahydrofuran as a green co-solvent with or without evaporation period prior to immersion of the cast polymer solution in the coagulation bath. The membrane morphologies were characterized using scanning electron microscopy and the membrane performance was screened using aqueous rose bengal (RB) or MgSO4 feed solutions. With CA-concentration in the casting solution increasing from 8 to 20 wt%, RB-rejection increased from 31.1% to 99.5%, while permeance decreased from 32.0 to 2.4 L/m2·h·bar. CA-membranes cast from a 10 wt% polymer solution had a RB-rejection higher than 92.0% with good permeance around 3.5 L/m2·h·bar at low co-solvent concentration (10 wt%). However, with increased co-solvent concentration (i.e. 30–50 wt%), both rejection and permeance surprisingly decreased, regardless evaporation time. For membranes cast from a 20 wt% polymer solution, RB-rejection remained around 99% and permeance decreased with increasing co-solvent concentration in the casting solution. MgSO4 rejection was around 93.0% for membranes cast from a 20 wt% polymer solution with 10 wt% co-solvent without evaporation (at a flux of 1.0 L/m2·h·bar) and 96.5% with evaporation at a flux of 1.3 L/m2·h·bar.

Cellulose and chitin composite materials from an ionic liquid and a green co-solvent

We report on a method for the preparation of cellulose/chitin composite materials from the ionic liquid 1-butyl-3-methylimidazolium acetate and γ-valerolactone as a biosourced sustainable co-solvent. Element analysis and attentuated total reflectance Fourier transform infrared spectroscopy show that the average degree of acetylation of chitin in the composite materials was around 82.5%. This indicates that chitin is not deacetylated to chitosan during the dissolution process. The X-ray diffraction results show that the degree of crystallinity of the composite materials increases from amorphous to 59% with increasing chitin concentration accompanied by a developing crystallite size up to 3 nm. Mechanical testing yielded a maximum tensile stress of 4.7 MPa, an elastic modulus of 27.4 MPa and a breaking elongation of 78.7% for the composites with 80 wt% chitin. In addition, water contact angle measurements indicated that the presence of chitin rendered the materials more hydrophobic.