Deep Eutectic Solvent Treatment Research Articles

Ability of Deep Eutectic Solvent Modified Oat Straw for Cu(II), Zn(II), and Se(IV) Ions Removal

In the proposed study, agro-waste biomass oat straw (OS) was considered a potential adsorbent for Cu(II), Zn(II), and Se(IV) removal from aqueous solutions. In order to obtain material with better adsorption abilities, the OS was modified by a deep eutectic solvent (DES). Structural changes caused by the applied modification route were considered by pHpzc, SEM, FTIR, and DSC/TG analysis. These methods discovered that lignocellulosic biomass degradation and material functionalization were achieved by DES treatment. Preliminary adsorption tests showed an over fourfold increase in capacity upon modification. The kinetic parameters implied that adsorption on modified material followed the pseudo-second-order kinetic model. Different isotherm models were applied to experimental data, while the Sips isotherm model best describes the equilibrium of the adsorption process on the tested modified material. According to this isotherm model, the maximum achieved adsorption capacities of Cu(II), Zn(II), and Se(IV) were 48.21, 55.06, and 87.85 mg/g, respectively. The summarized experimental results revealed that the adsorption process of selected cations on modified OS was predominantly caused by chemisorption, while, in addition to chemisorption, electrostatic forces were also responsible for Se(IV) removal. Desorption test showed that the prepared material could be reused for at least 3 cycles, with minimal efficiency loss. Briefly, this study reinforces that DES-modified agro-waste biomass could be used as a promising adsorbent for cations and oxyanions from wastewater.

Fascinating polyphenol lignin extracted from sawdust via a green and recyclable solvent route

Due to the complexity, heterogeneity and recalcitrant structure of lignin, the extraction of multifunctional lignin directly from lignocellulose is still a challenge. Here, a green and recyclable route was proposed to separate high-quality lignin and tailor its functionalities. Through tuning the components of deep eutectic solvent (DES) and separation procedures, DES extracted lignin (DESL) exhibited high purity of 99.6 %, yield of 83.2 % and phenolic hydroxyl content of 8.33 wt%. The results of FTIR and 13C NMR demonstrated that DESL possessed more oxygen-containing reactive groups compared with commercial lignin (CL), enabling DESL with more superior functional activities. DESL exhibited higher antioxidant activity with the DPPH capture rate of 73.2 %. Meanwhile, DESL showed strong bactericidal effects against E. coli (100 %) and S. aureus (100 %) due to higher phenolic hydroxyl content, which could destroy bacterial cell membranes and inhibit bacterial metabolism by interacting with phospholipid layer and protein. Additionally, DESL displayed strong UV absorption and could be blended with polyurethane to enhance UV shielding property of polyurethane composite film with >50 of UPF value. In summary, DES treatment is a suitable strategy for high-quality lignin separation, which opens a broad spectrum of possibilities for lignin valorization.

Efficient Fractionation of Green Bamboo Using an Integrated Hydrothermal–Deep Eutectic Solvent Pretreatment for Its Valorization

Adopting an integrated strategy to realize efficient fractionation of lignocellulose into well-defined components for its valorization is challenging. Combinatorial pretreatments in this study decomposed hemicellulose of green bamboo during hydrothermal pretreatment (HP), and the hydrothermally pretreated bamboo was subsequently subjected to delignification using deep eutectic solvent (DES) consisting of choline chloride and lactic acid, finally facilitating enzymatic hydrolysis of cellulose residue. Upon hydrothermal treatment at 180 °C for 35 min, hemicellulose removal of 88.6% was achieved with xylo-oligosaccharide yield and purity of 50.9% and 81.6%, respectively. After DES treatment at 140 °C for 2 h, lignin removal was determined to be 79.1%. Notably, the regenerated lignin with high purity of 96.8% displayed superior antioxidant activity, and the decrease in the ratio of syringyl units to guaiacyl units led to a slight decrease in radical scavenging activity of lignin after five recycling runs of DES. Moreover, the two-step treated residue had much higher enzymatic digestibility than that of single HP residue and untreated green bamboo. Results show that synergistic pretreatment is a promising strategy to tackle the recalcitrance of lignocellulose towards high value-added utilization.

Acidic deep eutectic solvent treatment for viscosity control and reactivity enhancement of bamboo dissolving pulp

Acidic deep eutectic solvent treatment for viscosity control and reactivity enhancement of bamboo dissolving pulp

In-situ microstructure regulation towards feasible production of self-reinforced lignocellulose nanopaper with multifunctionality

Lignocellulose is an all-natural structural material with huge potential for a wide range of applications. Extensive studies have designed high-strength LNP via tuning the size/surface chemistry of lignocellulose fibrils for generating sufficient interfacial hydrogen bonds during their self-assembly process. Herein, we demonstrate the fabrication of highly strong LNP via in-situ fibrillation and subsequent self-densification of constituent fibrils induced by a continuous processing of deep eutectic solvent treatment and air-drying. This in-situ microstructure regulation strategy allows the formation of reinforced interfacial hydrogen bonds within LNP, which reveals a combination of high dry and wet strength (188 and 45 MPa, respectively). Moreover, the self-reinforced LNP exhibits intriguing light-management capacity including high visible-light transmittance (92%), considerable transmittance haze (71%) and excellent UV-shielding performance. Outstanding flame retardancy (LOI: 38%) is noted for self-reinforced LNPs arising from its favorable microstructural characteristics such as abundant sulfate groups, high lignin content and densified structure. Intriguingly, the estimated production cost for self-reinforced LNP was approximately one in ten of that for conventional cellulose nanopaper, ascribing from its significantly lower input of resources including materials, water, and energy. Overall, this work innovatively develops an in-situ engineering strategy for economically preparing mechanically strong and multifunctional LNP, which is extremely promising for structural applications.

Degradation of Alkaline Lignin in the Lactic Acid-Choline Chloride System under Mild Conditions

Lignin is a natural polymer, second only to cellulose in natural reserves. Degradation is one of the ways to achieve the high-value transformation of lignin. Deep eutectic solvent (DES) thermal degradation of lignin can be used as an excellent green degradation method. This paper introduces the degradation mechanism and effect of the lactic acid-choline chloride DES system in dissolving and degrading alkaline lignin, and the final solvent recovery. It can also be found from the scanning electron microscope (SEM) images that the surface of the degraded solid product is transformed from smooth to disordered. Fourier transform infrared (FTIR) spectroscopy and 1 H-NMR spectroscopy were used to characterize the changes in lignin functional groups during DES treatment. The results showed that the content of phenolic hydroxyl groups increased after degradation, indicating that the β-O-4 ether bond was broken. The molecular weight of the degraded lignin was observed by gel permeation chromatography (GPC), and the lignin residue with low molecular weight and narrow polydispersity index was obtained. The lowest average molecular weight (Mw) reached 2512 g/mol. The ratio of oxygen to carbon atoms in lignin increased substantially during degradation as measured by X-ray photoelectron spectroscopy (XPS), probably because DES treatment was accompanied by many oxidation reactions, which led to significant structural changes in lignin and a large number of ether bond breakage reactions during the reaction. The main final degradation products are aromatic monomers, vanillin, butyrovanillone, etc.

Preparation of Anti-Bacterial Cellulose Nanofibrils (CNFs) from Bamboo Pulp in a Reactable Citric Acid-Choline Chloride Deep Eutectic Solvent.

In this study, bamboo pulp was simultaneously fibrillated and esterified in one-pot citric acid-choline chloride deep eutectic solvent treatment. The results indicated that increasing the temperature and time promoted esterification, yielding 0.19 to 0.35 mmol/g of the carboxyl group in CNFs. However, increasing the temperature and time resulted in decreases in yields and the diameter of CNFs from 84.5 to 66.6% and 12 to 4 nm, respectively. Analysis of the anti-bacterial activities of CNFs suggested that the high carboxyl group content corresponded to the effective inhibition of Escherichia coli and Staphylococcus aureus Taking yield, size, carboxyl group content, and anti-bacterial activate into consideration, treatment at 120 °C for 24 h was the optimal condition, yielding 76.0% CNF with 0.31 mmol/g carboxyl groups with a diameter of 8 nm and the inhibition fof E. coli (81.7%) and S. aureus (63.1%). In addition, effect of different CNFs on characteristics of polyvinyl alcohol (PVA) films were investigated. The results indicated that CNF obtained from the optimal condition was a favorable additive for the composite film, which enhanced (74%) the tensile strength of composite film compared with the pure PVA film due to its considerable size and carboxyl group content. However, the composite films did not show an anti-bacterial activate as CNF.

Recovery and regeneration of anode graphite from spent lithium-ion batteries through deep eutectic solvent treatment: Structural characteristics, electrochemical performance and regeneration mechanism

Recovery of graphite from spent lithium-ion batteries (LIBs) as new anode materials in the LIBs after regeneration can not only promote the recycling of spent LIBs, but also help to alleviate its environmental risks. However, the removal of the impurities in spent graphite is unsatisfying and its electrochemical performance need to be further improved when using conventional regeneration methods (such as acid treatment). Herein, we proposed a novel deep eutectic solvent (DES) leaching method to recover and regenerate waste graphite from spent LIBs under mild condition. The result showed that DES leaching could not only effectively remove the impurities in spent graphite, but also restore its crystal structure and morphology. The regenerated graphite obtained by DES treatment (DRG) exhibited a high specific capacity of 449.4 mAh/g for the first cycle at 0.1C and 285.4 mA h/g even after 500 cycles at 1C. In addition, the retention rate and coulombic efficiency of DRG were as high as 96.0 % and 100 %, respectively. These results demonstrated the excellent electrochemical performance of DRG, which was even comparable to that of commercial graphite. The regeneration mechanism of the proposed method was also elucidated. The organic binder was dissolved in DES by forming hydrogen bonds (OH…F and CH…Cl−). The Li coordination complex formed between SEI film and DES contributed to the dissolution of SEI film, and the residual electrolytes were removed based on the similarity-intermiscibility theory. This study provides a facile and green method to accomplish the closed-loop utilization of spent graphite in spent LIBs.

Comparison of the Degradation Performance of Seven Different Choline Chloride-Based DES Systems on Alkaline Lignin.

Lignin is a natural polymer second only to cellulose in natural reserves, whose structure is an aromatic macromolecule composed of benzene propane monomers connected by chemical bonds such as carbon-carbon bonds and ether bonds. Degradation is one of the ways to achieve the high-value conversion of lignin, among which the heating degradation of lignin by deep eutectic solvent (DES) can be an excellent green degradation method. In this study, choline chloride (CC) was used as the hydrogen bond acceptor, and urea (UR), ethylene glycol (GC), glycerol (GE), acetic acid (AA), formic and acetic mixed acid (MA), oxalic acid (OX), and p-toluenesulfonic acid (TA) were used as hydrogen bond donors to degrade lignin. NMR hydrogen spectroscopy was used for the simple and rapid determination of phenolic hydroxyl groups in lignin. FT-IR spectroscopy was used to characterize the changes of functional groups of lignin during DES treatment. GPC observed the molecular weight of lignin after degradation and found a significant increase in the homogeneity (1.6-2.0) and a significant decrease in the molecular weight Mw (2478-4330) of the regenerated lignin. It was found that acidic DES was more effective in depolymerizing alkaline lignin, especially for the toluene-choline chloride. Seven DES solutions were recovered, and it was found that the recovery of DES still reached more than 80% at the first recovery.

Insights into cellulose deconstruction and pseudo-lignin formation during deep eutectic solvent treatment

Insights into cellulose deconstruction and pseudo-lignin formation during deep eutectic solvent treatment

Integrated biorefinery of bamboo for fermentable sugars, native-like lignin, and furfural production by novel deep eutectic solvents treatment

Herein, a novel class of DESs comprising tetramethylammonium chloride/lactic acid (TMAC/LA) and tetramethylammonium bromide/lactic acid (TMAB/LA) was proposed to refine bamboo for cascaded production of cellulose residue, native-like lignin, and hemicellulose-derived sugars under a relatively mild condition (120 °C for 2 h). The cellulose residue showed an outstanding digestibility with approximately 90 % glucose yield, which was ten-fold higher than that of raw bamboo. The efficient conversion was attributed to the open structure and increased porosity caused by the hemicellulose removal (71.24–86.57 %) and delignification (53.27–73.62 %). Lignin recovered from the treatment liquor exhibited the β-O -4′ linkages (86.3–89.3 %) characteristic of native milled wood lignin (MWL). The recovered lignin could be well-suited for phenolic compounds production (yield > 50 %). After lignin extraction, the residual liquor is a suitable reaction substrate and medium for furfural production, reaching a furfural yield of 86.9 %. The novel DESs treatment could offer a cascaded biorefinery for sustainable development. • A novel DESs system was proposed to cascade refine bamboo. • Enzymatic digestibility was significantly increased from 10.0 % to 91.0 %. • DESs lignin exhibited the β-O -4′ linkages (86.3–89.3 %) characteristic of MWL. • More than 50 % of phenolic compounds and 20 % of aromatic hydrocarbons was achieved. • 86.9 % of furfural yield was obtained from the treatment liquor.

Ammonia fiber expansion-assisted deep eutectic solvent treatment for wheat straw fraction separation and bioconversion

In this study, an ammonia fiber expansion (AFEX)-assisted deep eutectic solvent (DES) pretreatment method was developed for the rapid separation of wheat straw fractions, which reduced the pretreatment time for DES and improved the pretreatment efficiency. This study describes the feasibility of the AFEX-assisted DES pretreatment in terms of both progressive and parallel relationships and analyzes the subsequent enzymatic effect in generating glucose from cellulose. Ammonia fiber expansion-assisted DES one-pot pretreatment at 120 °C, for 1.5 h resulted in an enzymatic efficiency of 98.0 ± 3.1 %. Moreover, the enzyme efficiency remained greater than 85 % after three recovery cycle experiments. The comparison between regenerated-lignin (d-lignin) and alkaline-lignin showed that regenerated lignin has a lower molecular weight and belongs to para-hydroxy-phenyl-guaiacyl-syringyl (H-G-S) type lignin. This study developed is a green and efficient pretreatment process with great potential in the separation and utilization of biomass fractions.

Facile nanofibrillation of strong bamboo holocellulose via mild acid-assisted DES treatment

A facile and sustainable strategy for preparing bamboo holocellulose nanofibrils (HCNFs) via zinc acetate/ choline chloride deep eutectic solvents treatment assisted with mild acetic acid (HAc) was developed in the present work. The treatment was performed under fast microwave irradiation and followed by mechanical homogenization , resulting in HCNFs with considerable amounts of xylan hemicellulose (15 %−19 %) remained. Less HAc consumption was achieved, which is beneficial for fabricating nanofibrils with higher aspect ratios (>800). More xylan contents and higher degrees of acetylation on cellulose were investigated, resulting in greater charge repulsion and steric hindrance between HCNFs and favoring the fibrils dissociation. Moreover, the HCNFs maintained high crystallinity of 70 %− 80 % and good thermal stability, confirming the intact hydrogen bonding linkages between cellulose and xylan hemicellulose. Transparent films prepared from the HCNFs suspensions by vacuum drying approach displayed better mechanical strength (>40 MPa) and well-mimicked the complex of polysaccharides interactions in plant cell walls. • Bamboo HCNFs were prepared by ZnAc/ChCl DES with mild HAc and microwave assistance. • Acetylation and charge repulsion favored the holocellulose nanofibrillated. • Higher DES ratios fabricated HCNFs with greater aspect ratios and xylan content. • HCNFs films present high transparency and improved mechanical strength.

Lignin-containing cellulose nanomaterials produced by microwave-assisted deep eutectic solvent treatment as rheology modifiers for fracturing fluids

Fracturing fluids used hydraulic fracturing in energy industry are formulated to have superior rheological properties for suspending and transporting rigid proppants into the fractures. Herein, we report the utilization of lignin-containing cellulose nanomaterials (LCNMs) to enhance the rheological properties of viscoelastic fracturing fluids (VFFs) based on borax-crosslinked guar gum (GG) gels. Two types of LCNMs, i.e., lignin-containing cellulose nanofibers (LCNFs) from energy cane bagasse and nanocrystals (LCNCs) from bleached wood pulp were manufactured using microwave-assisted deep eutectic solvent (MV-DES, choline chloride and lactic acid) pretreatment combined with high-pressure homogenization (HPH). The resultant LCNFs and LCNCs showed fibril- and rod-like morphology with lignin content of 13.7 % and 5.9 %, respectively; and their suspensions exhibited the typical shear-thinning behaviors and gel-like viscoelastic properties. Benefited from the superior rheology of LCNMs and hydrogen bonding formed between LCNMs and GG, the presence of LCNMs significantly increased the zero-shear viscosity, yield stress, shear-thinning capacity as well as thermal stability of GG-VFFs. LCNM/GG-VFFs exhibited outstanding proppant-suspending capacity as demonstrated by sand particles being uniformly dispersed in the fluids without settling after standing for 24 h at 25 and 80 ℃. • The morphologies of lignin-containing cellulose nanomaterials (LCNMs) are affected by the lignin content in origins. • LCNMs are utilized as rheology modifiers in the guar gum-viscoelastic fracturing fluids (GG-VFFs). • GG-VFFs with the addition of LCNMs exhibited outstanding proppant-suspending capacity.

The Effect of Acidic Ternary Deep Eutectic Solvent Treatment on Native Lignin

Ternary deep eutectic solvents (DESs) are gaining increased attention to serve as a cheap green alternative medium for the processing of lignocellulosic biomass. For example, mixtures of choline chloride (ChCl), ethylene glycol (EG), and oxalic acid (OA) were recently explored for the fractionation of lignocellulosic biomass into its main components. Interestingly, during this processing, the recovered lignin was structurally modified by incorporation of EG, which altered its solubility properties and led to the need for different lignin recovery strategies. This offers an excellent starting point for a deeper investigation of the effect of acidic DES systems on the structure of lignin. In particular, native-like residual enzyme lignins (RELs) that are hard to completely dissolve in organic solvents are specifically suitable for this task. Here, a ternary DES is used consisting of ChCl/EG with OA or trifluoromethanesulfonic acid (HOTf) as a third component. The results showed that both solvent systems led to high EG incorporation into REL. The HOTf system showed a lesser extent of lignin depolymerization at similar modification levels as it already induced modification at lower temperature (25–30 °C). Low recovery yields from typical acidic precipitation were observed for treatment with both acidic DES systems. Analysis of THF and DCM extracts showed that the products in the water phase included small EG modified lignin fragments and aromatic monomers released from lignin aryl ether linkage cleavage. This analysis details the types of other products that can be expected and where these will end up during fractionation. These results show that the treatment of lignin with acidic DES in the presence of alcohols leads to low- and high-molecular-weight products that are not effectively recovered by typical precipitation procedures.

Life cycle assessment instructed preparation of wood-based filtration device with efficient water purification and oil reclamation by deep eutectic solvent

Organic oils and dyes are universal contaminants in the water environment that is exceptionally hazardous to health. However, low flux and degradation efficiency hinder those contaminants remove. Herein, the wood-based filtration device handles oily-dyed water by deep eutectic solvent (DES) treatment, exhibiting high specificity surface area and porosity. Life cycle assessment (LCA) provides evidence that the DES one-step treatment introduces fewer environmental impacts (EI) than the traditional two-step method of wood pretreatment. Moreover, DES-treated wood substrate (DTWS) decorated with palladium nanoparticles (PdNPs) shows high oil/water separation efficiency (98.9%) and excellent catalytic activity to convert MB (99.8%). Compared with numerous existing filtration membrane materials, the enhancement factors for outstanding oil/water separation and excellent catalytic performances are related to the high porosity and PdNPs content by adjusting DES treatment time. This wood-based filtration device with environmental-friendly, high flux, and excellent degradation efficiency gains optimistic expectations for practical sewage treatment application.

Low-energy nanoemulsified systems containing antioxidant eutectic extract from Rhodotorula mucilaginosa yeast cells

The addition of extracts, rich in bioactive compounds from alternative sources, in final product formulations is a recurrent trend in cosmetic and food industries. This study investigates the applicability of an antioxidant extract from Rhodotorula mucilaginosa CCT3892 yeast cells, obtained after the use of a deep eutectic solvent treatment, in the formulation of nanoemulsified systems. After the determination of inhibitory concentration for oxidative species (IC50), the extract was added into a fatty acid mixture. This oil phase was then emulsified with distilled water (aqueous phases) and polysorbate 20 (surfactant). The formation of two promising nanoemulsions was noticed. Both systems were characterized in relation to their droplet size, pH, zeta potential and polydispersity index. After stability tests, the systems showed to be stable in relation to centrifugal force action and unsteady in kinetic terms, at the evaluated storage temperatures (4.0, 25.0 and 45.0 ± 0.1 °C), for 30 days. The rheology of obtained nanoemulsions was also investigated and showed that the fluid dynamic behavior is conditioned to system oil content and ranging from newtonian to non-newtonian.

Lightweight, High-Strength Wood Prepared by Deep Eutectic Solvent Treatment as a Green Structural Material

Lightweight, High-Strength Wood Prepared by Deep Eutectic Solvent Treatment as a Green Structural Material

Energy pellets from whole-wheat straw processed with a deep eutectic solvent: A comprehensive thermal, molecular and environmental evaluation

Storage and transportation are main considerations for seasonal crop residues to become competitive alternatives to non-sustainable fossil fuels and chemicals. Hence, pelletization and briquetting are highly relevant to mass and energy densification and associated supply chains. Here, we propose a green treatment based on recyclable, deep eutectic solvent (DES) to achieve partial swelling and dissolution of residual agricultural biomass (wheat straw), leading to improved structuring and cohesion of energy pellets. The mild DES-based process enhances access to lignin, which migrates and regenerates at interphases for effective binding, enabling improved pellet durability (increased by 90–97% compared to pellets produced from the untreated biomass). The role of lignin was studied by molecular dynamics simulation, which revealed non-bonding interactions with cellulose, impacting the strength of the pellet structure. The DES treatment enhanced the heating value of the pellets (from 16.1 to 19.5 MJ/kg), partially a result of a higher acidy ratio, and simultaneously led to better devolatilization, lignin accessibility and release of volatile matter during pyrolysis. The potential environmental benefit of DES-treated pellets over wood-based counterparts is revealed by a life cycle assessment. Our study further indicates the reduced environmental impact of DES-treated pellets, which can be furthered by recycling of the solvent.

Degumming of hemp fibers using combined microwave energy and deep eutectic solvent treatment

Hemp bast fibers were degummed using combined microwave energy (MWE) and deep eutectic solvent (DES) to generate pure hemp cellulose fibers for potential textile applications. The properties of the degummed fibers were investigated and compared with those of the alkali-treated fibers using several analytical techniques. Results revealed that hemp fiber surface underwent dramatic structural disruption during the pretreatment, due to the removal of “gummy” compounds (i.e., pectin, oil, wax, etc.), lignin, and amorphous cellulose. The treated fibers had much enhanced thermal stability due to the removal of the gummy materials. The reduced enthalpy (171.34 J/g) of MWE-DES treated fibers at 1:20 fiber-DES ratio as compared to that of raw hemp fibers (272.09 J/g) also confirmed the higher thermal stability of MWE-DES treated fibers. Chemical composition analysis showed that the holocellulose content in the treated fiber samples at 1:20 fiber-DES ratio increased to 98.63% which was comparable with the holocellulose content (98.87%) of the alkali-treated fibers. The Ultraviolet (UV) protection factor (UPF) of MWE-DES treated fibers at 1:10 and 1:20 fiber-DES ratio was, respectively, 118.11 and 114.19, meeting the requirement of UV resistant textile fibers. The study demonstrates a potentially effective, less time-consuming, and environmentally sustainable protocol for manufacturing purified hemp cellulose fibers using combined MWE-DES treatment.