Deep Eutectic Solvent Extraction Research Articles

Efficient extraction of pectic polysaccharides from thinned unripe kiwifruits by deep eutectic solvent-based methods: Chemical structures and bioactivities

To promote the potentially industrial applications of thinned unripe kiwifruits, two deep eutectic solvent-based methods, including deep eutectic solvent-assisted extraction (DAE) and microwave-assisted deep eutectic solvent extraction (MDE), were optimized for the extraction of polysaccharides from thinned unripe kiwifruits (YKP). Results showed that the yields of YKP-D prepared by DAE and YKP-DM prepared by MDE were extremely higher than YKP-H prepared by hot water extraction. Furthermore, YKP-H, YKP-D, and YKP-DM were mainly composed of pectic polysaccharides, including homogalacturonan (HG) and rhamnogalacturonan I (RG I) domains. Besides, both YKP-D and YKP-DM exhibited stronger antioxidant, anti-glycosylation, and immunomodulatory effects than those of YKP-H, and their higher contents of uronic acids and bound polyphenols as well as lower molecular weights could partially contribute to their bioactivities. Overall, these results revealed that the developed MDE method could be utilized as a promising method for highly efficient extraction of YKP with superior beneficial effects.

Optimization of ultrasound-assisted deep eutectic solvent extraction of polyphenols from Rhamnus alaternus for their antioxidant activity

Optimization of ultrasound-assisted deep eutectic solvent extraction of polyphenols from Rhamnus alaternus for their antioxidant activity

Gastrointestinal delivery of codfish Skin-Derived collagen Hydrolysates: Deep eutectic solvent extraction and bioactivity analysis

The fishing industry produces substantial by-products, such as heads, skins, bones, and scales, rich in collagen—a prevalent protein in these materials. However, further application of deep eutectic solvent-based extraction remains unexplored. In this study, we extracted collagen with urea: propanoic acid mixture (U:PA; 1:2) with a 2.2 % yield, followed by enzymatic hydrolysis with alcalase for 120 min. The resulting bioactive peptides demonstrated notable antioxidant activity (961 µmol TE) and antihypertensive properties (39.3 % ACE inhibition). Subsequently, we encapsulated 39.3 % of these hydrolysates in chitosan-TPP capsules, which released about 58 % of their content, primarily in the intestine, as mimicked in the in vitro model of the gastrointestinal tract. Although the digestion process did not significantly alter the size of the non-encapsulated collagen peptides, it did influence their health benefits. The promising results suggest that further research could optimize the use of collagen from fish by-products, potentially offering a sustainable source for health products.

Ultrasound-assisted deep eutectic solvent extraction of bioactive compounds from persimmon calyx.

This study aimed to investigate the ultrasound-assisted extraction of bioactive compounds from persimmon (Diospyros kaki) calyx by deep eutectic solvents (DES) with different molar ratios. For this reason, the prepared DES extracts' total phenolic-flavonoid compounds and antioxidant activities (1,1-diphenyl-2-picrilhydrazyl radical scavenging activity [DPPH•], Cupric Reducing Antioxidant Capacity (CUPRAC), and ferric reducing antioxidant power [FRAP]) were investigated as a result of the experimental design and optimization study conducted for this purpose. A sonication time of 20min was determined as the optimal condition. Under these conditions, a molar ratio of 1.9:1 (lactic acid:choline chloride) and a water ratio of 70% provided the highest phenolic/flavonoid compounds and antioxidative activity. Correlations among water ratio, molar ratio, and sonication time were determined using principal component analysis (PCA). In conditions where total flavonoid compound, FRAP, and DPPH• are high due to PCA, it can be concluded that the sonication time is at high level; on the contrary, the water and molar ratios are at low level. In conclusion, ultrasound-assisted extraction using DES proved effective in persimmon calyx. Therefore, it can be recommended to use these environmentally friendly green solvents as an alternative to organic solvents in preparing extracts in various fields. PRACTICAL APPLICATION: This study shows the effectiveness of the ultrasound-assisted green extraction method using persimmon calyx specified as waste. These findings are compelling in the food industry in terms of consumers being now aware of green technology and the discovery that calyx is a good source of bioactive compounds.

Molecularly imprinted solid-phase extraction combined with non-ionic hydrophobic deep eutectic solvents dispersed liquid-liquid microextraction for efficient enrichment and determination of the estrogens in serum samples

Hormonal drugs in biological samples are usually in low concentration and highly intrusive. It is of great significance to enhance the sensitivity and specificity of the detection process of hormone drugs in biological samples by utilizing appropriate sample pretreatment methods for the detection of hormone drugs. In this study, a sample pretreatment method was developed to effectively enrich estrogens in serum samples by combining molecularly imprinted solid-phase extraction, which has high specificity, and non-ionic hydrophobic deep eutectic solvent-dispersive liquid-liquid microextraction, which has a high enrichment ability. The theoretical basis for the effective enrichment of estrogens by non-ionic hydrophobic deep eutectic solvent was also computed by simulation. The results showed that the combination of molecularly imprinted solid-phase extraction and deep eutectic solvent-dispersive liquid-liquid microextraction could improve the sensitivity of HPLC by 33∼125 folds, and at the same time effectively reduce the interference. In addition, the non-ionic hydrophobic deep eutectic solvent has a relatively low solvation energy for estrogen and possesses a surface charge similar to that of estrogen, and thus can effectively enrich estrogen. The study provides ideas and methods for the extraction and determination of low-concentration drugs in biological samples and also provides a theoretical basis for the application of non-ionic hydrophobic deep eutectic solvent extraction.

A novel deep eutectic solvent as an extractant for the determination of bisphenol compounds in edible oils by high-performance liquid-phase fluorescence detection

In this study, an efficient, low-cost and environmentally friendly deep eutectic solvent (DES) was prepared using methanol and betaine, which was then employed as an extractant to detect BPA and BPF in several edible oils by high performance liquid chromatography-fluorescence detection (HPLC-FLD) with good results. The electrostatic potentials of methanol, betaine, water and BPs were analyzed by quantum chemical computational techniques to explain the mechanism of DES extraction. Several important parameters affecting the extraction efficiency, composition, volume and extraction time of DES were optimized. The optimum conditions for the use of DES were the molar ratio of 1:30 (betaine: methanol), the volume of DES of 200 μL and the extraction time of 1.5 min. The results of the method evaluation showed a wide linear range (0.01–0.8 μg g−1) and a high linear correlation coefficient (R2 ≥0.994). The limit of detection (LOD) and limit of quantification (LOQ) values ranged from 1.65 to 2.92 ng g−1 and 5.45–9.64 ng g−1, respectively. The greenness of the assay was evaluated by applying the green analytical procedure index method, and the results showed that the experimental method has the advantages of simple sample pre-treatment and low amount of waste generated during the assay. The experimental method has potential applications in the field of the detection of bisphenol compounds in edible oils.

Novel reusable and switchable deep eutectic solvent for extraction and determination of curcumin in water and food samples

For the first time, a fast and easy extraction method based on a unique reusable and switchable deep eutectic solvent (made of octylamine, succinic acid, and water as precursors) was presented and utilized for the microextraction and determination of curcumin as a model analyte. The main factors used to induce a phase transition in the as-prepared deep eutectic solvent were solutions of NaOH and HCl. Among the standout characteristics of the suggested deep eutectic solvent are the removal of toxic organic solvents like THF, the lack of a need for centrifugation, and the ability to be reused in subsequent extractions. The influence of effective parameters (i.e., proportions of deep eutectic solvent structure components, volume of prepared deep eutectic solvent, volume and concertation of NaOH, volume of HCl, and salt effect) on the extraction procedure were investigated. The calibration curve also was linear in the range of 35–500 μg L−1 with coefficients of determination (R2) of 0.9976. Limit of detection (S/N = 3) 10.0 μg L−1, the limit of quantification (LOQ) of 35.0 μg L−1, the relative standard deviations (RSDs %) composed of intra-day RSD (4.7) and inter-day RSD (6.4), preconcentration factor of 40.0, enrichment factor of 38.68, and relative recovery of 92.6%–100.3 % were achieved. The reusable and switchable deep eutectic solvent based-dispersive liquid-liquid microextraction technique was proficiently employed to expedite easy and fast extraction of curcumin from water and food samples.

A green method to extract rutin from Sophora japonica L.

Sophora japonica L. contains high levels of rutin, which has great potential for use in pharmaceutical products for the treatment of diseases related to the cardiovascular and circulatory systems. We proposed a method of extracting rutin from S. japonica by using a green solvent.•Green deep eutectic solvents (DESs) of choline chloride and ethylene glycol (ChCl-Eth) showed the highest extraction efficiency of rutin from S. japonica.•Under optimal conditions, the extraction yield of ChCl-Eth was 1.34 times higher than that of methanol as solvent.•Rutin was recovered from the DES extracts using water as the antisolvent with a high recovery yield, and the DESs of ChCl-Eth could be productively recovered and reused at least 3 times.

Extraction optimization of tea saponins from Camellia oleifera seed meal with deep eutectic solvents: Composition identification and properties evaluation.

Traditional organic solvent extractions of tea saponins have many drawbacks. This study aimed to establish an environment-friendly and efficient technology based on deep eutectic solvents (DESs) to extract tea saponins from Camellia oleifera seed meal. The solvent consisting of choline chloride and methylurea was screened as optimal DES. Under the optimal extraction conditions obtained by response surface methodology, the extraction yield of tea saponins reached 94.36mg/g, which increased by 27% compared with ethanol extraction, while the extraction time was reduced by 50%. Analysis of UV, FT-IR, and UPLC-Q/TOF-MS indicated tea saponins did not alter during DES extraction. Surface activity and emulsification evaluation showed that extracted tea saponins could reduce interfacial tension at the oil-water interface with excellent foamability and foam stability, and they could form nanoemulsions (d32<200nm) with excellent stability. This study provides a suitable approach for the efficient extraction of tea saponins.

Efficient Plutonium Extraction and Electrochemical Insights in a Hydrophobic Deep Eutectic Solvent for Radioactive Waste Management

In this study, we explore the extraction and electrochemical characteristics of Plutonium using a hydrophobic deep eutectic solvent (DES) consisting of tetra-Butyl Ammonium Bromide(TBABr) as the hydrogen bond acceptor and Decanoic acid (DA) as the hydrogen bond donor in a 1:2 ratio composition. Hydrophobic DES possesses unique attributes, such as low volatility and a high affinity for metal ions, making it a promising choice for Plutonium extraction. We systematically investigate the influence of various parameters, including DES composition, acid concentration, and extraction duration. Our extraction experiments reveal that the hydrophobic DES exhibits its maximum Plutonium extraction efficiency (95%) at a 4 M HNO3 concentration, with a distribution coefficient (D) reaching nearly 71. To gain insights into the electrochemical behavior of Plutonium within the hydrophobic DES, we conduct cyclic voltammetry experiments. The resulting voltammograms offer valuable insights into the redox properties and stability of Plutonium species within the DES. Furthermore, we analyze the impact of potential scan rate on the electrochemical response, shedding light on the kinetics and mechanisms underlying Plutonium electrochemistry within the hydrophobic DES. These findings underscore the considerable potential of hydrophobic DES for efficient Plutonium extraction and electrochemical separation. This research contributes to the development of sustainable and environmentally friendly approaches for managing Plutonium, particularly in the context of nuclear waste disposal

Natural deep eutectic solvent extraction of xanthorrhizol and curcuminoids from Curcuma xanthorrhiza Roxb and simultaneous determination by high-performance liquid chromatography

Context: Curcuma xanthorrhiza, a native to Indonesia, has been recognized as a potential medicinal plant. Xanthorrhizol (XTZ), curcumin (Cur), bisdemethoxycurcumin (BDMC), and demethoxycurcumin (DMC) are the main major metabolites with different bioactivities. Thus, the selective extraction of these markers is required. Aims: To characterize and use natural deep eutectic solvents (NADES) for the extraction of XTZ and curcuminoids (CURS) from C. xanthorrhiza. Methods: Four NADES, comprising of glucose:lactic acid (Glu:LA, 1:3), choline chloride: malic acid (ChCl:MA, 1:1), choline chloride: glycerol (ChCl:Gly, 1:1), and choline chloride: sucrose (ChCl:Suc, 3:1) were synthesized and subjected to FTIR. The physicochemical properties of NADES were characterized, including polarity, viscosity, and density. Their antioxidant profiles were evaluated. The toxicity of NADES was assessed towards Escherichia coli by real-time growth monitoring. Tested NADES were employed to extract marker compounds from the rhizome of C. xanthorrhiza. A validated high-performance liquid chromatography (HPLC) method was applied to simultaneously quantify XTZ and CURS in NADES extracts. Results: FTIR spectra confirmed the formation of hydrogen bonds between components. Using the DPPH and FRAP methods, all NADES and NADES extracts displayed antioxidative activity, suggesting the contribution of NADES to the activity. Of the tested NADES, Glu:LA (1:3) obtained the highest content of XTZ over Cur, BDMC, and DMC, comparable to that of ethanol maceration. All tested NADES were harmless to E. coli, except for ChCl:MA (1:1). However, NADES extracts of Glu:LA (1:3) and ChCl:MA (1:1) suppressed the growth of the bacterium. Scanning electron micrographs demonstrated the destruction of the surface structure of the rhizome powder by NADES-ultrasonication. Conclusions: The study recommended the use of Glu:LA (1:3) to selectively extract XTZ to promote environmentally friendly and sustainable extraction.

The Bioactivity Potential of Acmella Paniculata Plant Extract in Antioxidant Activity by Two Different Extraction Methods

Widely used synthetic chemicals like heavy metals act as active compounds in personal care products such as shampoo, soap and cosmetics. These hazardous chemicals cause harmful threats to the environment and unintentionally lead to dangerous exposure towards human health. Thus, demands on natural organic compounds have increased nowadays. Bioactive compounds from plant extracts are well known to have intrinsic biological values that are relevant in promoting human health. There are numerous ways to extract these unique and important compounds involving techniques that are simple, environmentally friendly and efficient. The aim of this study is to highlight the biological potential of compounds from the local plant, Acmella paniculata in antioxidant activity. This small flowering shrub species is also known locally as Subang nenek. The first phase of this study involved the leaf extraction of A. paniculata performed by a common method known as Soxhlet extraction using methanol solvent and a simple centrifuged method using deep eutectic solvent (DES) which is a green solvent. Soxhlet method is a conventional procedure that takes longer time and involves specific equipments. However, this method has been used for many years as standard method due to its consistent results. Meanwhile, DES based centrifugation method is a new, innovative method for plant extraction with a fast procedure and minimal used of equipment. The second phase involved phytochemical screening and antioxidant activity testing. The phytochemical screening for A. paniculata leaf extract showed noticeable secondary metabolites such as alkaloids, tannins, terpenoids and steroids. This plant showed good pharmacological values in antioxidant activity using DPPH free radical scavenging assay. The antioxidant percentage of DES extract showed higher potential results (56.11±3.54) compared to the Soxhlet extract (39.15±23.99) in leaf. Overall, the DES extraction is promising method in increasing the yield of antioxidant compounds as well as provided a simple and rapid technique in plant extraction.

Extraction of triterpene acids from loquat leaves via a novel hydrophobic deep eutectic solvent screened by COSMO-SAC model

Triterpene acids (TTAs) have promising applications in functional food, medicine and other fields. Here, ultrasonic-assisted hydrophobic deep eutectic solvent (HDES) extraction was employed to gain TTAs from loquat leaves. Combining COSMO-SAC model prediction with experimental verification，the HDES, composed of thymol and benzyl alcohol (molar ratio 2:1), was proved to have the highest extraction ability for TTAs. The preliminarily optimized extraction conditions were solid to solvent ratio 1:10 (g/g), temperature 60 °C and extraction time 60 min. Under these conditions, the extraction yield of ursolic acid (the main component of loquat leaf TTAs) was 17.769 ± 0.799 mg/g dry loquat leaf. HDES and TTAs were recovered from HDES extracting solution via gradient elution (60% and 80% ethanol aqueous solution, respectively) based on C18 reverse-phase silica gel column chromatography under low pressure (0.5 MPa). Recovered HDES could be reused for extracting TTAs from loquat leaves directly and had a similar extraction performance compared to fresh HDES. The purity of the obtained crude TTAs sample was 81.18% based on the total contents of maslinic acid (MA), corosolic acid (CA), oleanolic acid (OA) and ursolic acid (UA), with a mass ratio of 11:26:10:53. Crude TTAs sample was further separated by C18 reverse-phase silica gel column chromatography using 80% ethanol aqueous solution as mobile phase under high pressure (15 Mpa). By this mean, CA sample with 69.30% purity (MA to CA mass ratio 7:18) and UA sample with 93.94% purity (OA to UA mass ratio 4:21) were obtained. The in vitro antioxidant ability order of the attained TTAs samples was CA sample > crude TTAs sample > UA sample. This study laid a good scientific basis for applying HDES and C18 reverse-phase silica gel column chromatography in the bioactive component extraction and separation fields. It also provided theoretical basis and technical support for obtainment and utilization of high-purity loquat leaf TTAs in the fields of medicine, functional food, cosmetics and so on.

A green hydrophobic deep eutectic solvent for extraction of phenol from aqueous phase

Deep eutectic solvents (DESs), have been recognized as effective materials for the extraction of different compounds. In this study, the performance of a novel hydrophobic DES was evaluated for the extraction of phenol from aqueous solutions. Octanoic and dodecanoic fatty acid precursors with a definite molar ratio of 3:1, respectively, were used for the DES having a low melting point of 8.3 °C. The purity and stability of the product were confirmed via characterizing by FTIR, 1H and 13C NMR methods. The liquid–liquid equilibrium of the water + phenol + DES ternary system at different temperatures of 293.2, 298.2 and 308.2 K was accordingly studied through cloud point titration method and refractive index measurement. Interestingly, the important parameters of the solute distribution coefficient and the separation factor were, respectively, within the high levels of (6.8321–9.7787) and (895.76–2770.17), indicating the amazing capability of the DES. Reasonably, both of these parameters decreased with temperature. The NRTL and UNIQUAC thermodynamic models were employed to reproduce the obtained tie-lines and to determine the interaction parameters at each temperature. The low level root mean square deviations for the mentioned models were, respectively, within (0.0014–0.0027) and (0.0045–0.0063); confirming satisfactorily agreement with the experimental data.

Green ultrasound-assisted natural deep eutectic solvent extraction of phenolic compounds from waste broccoli leaves: Optimization, identification, biological activity, and structural characterization

In this study, an efficient natural deep eutectic solvent (NADES, 30 mL/100 mL water content) was identified and coupled with ultrasonication to extract phenolic compounds from broccoli leaves (BLs). A NADES prepared using choline chloride and 1,2-propylene glycol (ChCl-PG) at a molar ratio of 1:2 provided the highest extraction rate. Phenolic extraction conditions were optimized using single-factor experiments coupled with response surface methodology. The optimal parameters were as follows: solvent-to-solid ratio, 36.35 mL/g; extraction temperature, 49.5 °C; extraction time, 31.4 min; and ultrasonic power, 383 W. Under these parameters, the phenolic yield was 4.91 mg/g. Quantitative analysis revealed that neochlorogenic acid was the most abundant phenolic compound, followed by ferulic acid, erucic acid, quinic acid, chlorogenic acid, and caffeic acid. Furthermore, the isolation of broccoli leaf phenolics (BLPs) using ultrasonication-assisted extraction coupled with ChCl-PG (UAE + ChCl-PG) yielded a higher total phenolic content than other extraction methods. These BLPs also had greater antioxidant activity (DPPH, ABTS assay) and inhibitory effects against S. aureus, E. coli, and Salmonella. DSC, FT-IR, and SEM results further validated the synergistic efficiency of the new phenolic extraction process. Accordingly, this study offers an efficient and green alternative strategy for extracting phenolic compounds from plant by-products.

Research on the Impact of Deep Eutectic Solvent and Hot-Water Extraction Methods on the Structure of Polygonatum sibiricum Polysaccharides.

Deep eutectic solvent (DES) and hot-water extraction (HWE) methods were utilized to extract polysaccharides from Polygonatum sibiricum, referred to as DPsP and WPsP, respectively. The extracted polysaccharides were purified using the Superdex-200 dextran gel purification system, resulting in three components for each type of polysaccharide. The structures of these components were characterized. The molecular weight analysis revealed that DPsP components had slightly larger molecular weights compared with WPsP, with DPsP-A showing a slightly higher dispersity index and broader molecular weight distribution. The main monosaccharide components of both DPsP and WPsP were mannose and glucose, while DPsP exhibited a slightly greater variety of sugar components compared with WPsP. FTIR analysis demonstrated characteristic polysaccharide absorption peaks in all six PSP components, with a predominance of acidic pyranose sugars. NMR analysis revealed the presence of pyranose sugars, including rhamnose and sugar aldehyde acids, in both DPsP-B and WPsP-A. DPsP-B primarily exhibited β-type glycosidic linkages, while WPsP-A predominantly displayed α-type glycosidic linkages, with a smaller fraction being β-type. These findings indicated differences in monosaccharide composition and structure between PSPs extracted using different methods. Overall, this study provided experimental evidence for future research on the structure-function relationship of PSPs.

Preparation and characterization of bio-inspired full-biomass-derived aerogel with vertically aligned structure

Using renewable biomass resources to prepare porous materials can reduce the dependence on petroleum-based energy, promote green, low-carbon, and high-quality development, and achieve carbon neutrality. Here, we report a bio-inspired full-biomass-derived aerogel with an ultra-light (10.33–27.77 mg/cm3), highly porous (98.66–99.19 %), and vertically aligned structure. The fabrication involves an ultrasonic-assisted deep eutectic solvent (DES) extraction of cellulose nanofibrils (CNFs)-blending-directional freeze-drying-hydrophobic modification. Initially, CNFs were extracted from corncobs using DES pretreatment. Then, the aerogels were prepared by co-mixing CNFs with alkali lignin and freeze-drying the precursor suspension using the ice-templated method. Finally, the aerogels were modified using trimethoxymethylsilane chemical vapor deposition to render them hydrophobic. The silanization-modified aerogels exhibited superior static and dynamic hydrophobic properties, with a water contact angle of up to 153.4°, and demonstrated self-cleaning properties. These aerogels exhibited adsorption capabilities for various oils and organic solvents (9.6–29.8 g/g) and the ability to separate oil–water mixtures and adsorb methylene blue. Moreover, the aerogels with vertically aligned structures exhibited exceptional axial compression properties (up to 959 kPa), more than four times greater than the radial compression properties. Furthermore, the aerogels exhibited rapid liquid transport properties, with an axial transport rate of soybean oil that was more than 10 times higher than the radial transport rate. This study provides a green, eco-friendly, and sustainable strategy for preparing 3D porous aerogels, paving the way for developing full-biomass-derived aerogels as a promising alternative to petroleum-based adsorbent materials.

Recovery of rare earth metal oxides from NdFeB magnet leachate by hydrophobic deep eutectic solvent extraction, oxalate stripping and calcination

With the scarcity of resources and the growing consumer demand for rare earth elements (RE), it is imperative to develop clean and sustainable methods to recover these valuable elements. This research proposes a novel green process for the selective recovery of RE from spent NdFeB permanent magnet using hydrophobic deep eutectic solvent (HDES). A total of 13 HDES systems composed of trioctylphosphine oxide (TOPO) as hydrogen bond acceptor (HBA) and alcohols as hydrogen bond donor (HBD) were prepared and characterized. Through a simple screening process, it was determined that ternary HDES (DA:MA:TOPO = 5:5:4) exhibited the best extraction and separation performance for REs and Fe. The extraction conditions such as aqueous phase acidity, organic/aqueous phase ratio, the concentration of Fe3+ and equilibration time were further studied and optimized. Under the most suitable conditions, HDES (DA:MA:TOPO = 5:5:4) was used for batch countercurrent extraction, where the concentration of REs in the raffinate was lowered from 4390 mg/L to 34 mg/L, and the recovery reached 99%. The HDES could be stripped by 0.2 mol/L Na2C2O4, which could further separate a small amount of loaded Fe (133 mg/L) and RE, so that the purity of the final product reached >99%. The stripped HDES could be recovered after washing with deionized water. Even after five cycles, HDES still maintained good stability. This innovative process does not require the use of salting-out agents or toxic volatile solvents, providing new possibilities for efficient and clean separation.

Process optimization and characterization of nanocellulose from chestnut shell

Nanocellulose, a unique and promising natural substance extracted from cellulose-based materials, has gained tremendous attention for its use in various applications. Latest studies hypothesized that green extraction techniques reveal high-yield cellulose nanoparticles with lower environmental hazard and also highlighted that selectivity and characteristics of final products are highly dependent upon process parameters. This study aimed to produce nanocellulose powders from the chestnut shell –an agroindustrial waste without pertinent reuse– by acid hydrolysis (conventional), microwave-assisted acid hydrolysis, hydrotropic solvent, and deep eutectic solvent extraction techniques. The effectiveness of process parameters was investigated, and optimum conditions were determined by targeting the highest yields for each method. Additionally, the physico-chemical and microstructural properties of nanocellulose powders produced by each method were analyzed to investigate the product characteristics. The highest yield was obtained by deep eutectic solvent extraction (99.2%) followed by hydrotropic solvent (89.6%), conventional (64.5%), and microwave-assisted (34.1%) extractions. The methods bearing strong acid solvents resulted in a higher crystallinity index (up to 81%). The highest viscosity and absolute zeta potential values were obtained in deep eutectic solvent extraction as 843.6 cp and −23.7 mV, respectively. For all nanocellulose suspensions, the storage modulus (G′) was greater than the loss modulus (G″), indicating a more gel-like behavior. Nanocellulose powders produced by different methods had characteristic Fourier transform Infrared (FTIR) spectrum. The results of X-ray diffractometer (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) evidenced that nanofibrils could be produced via hydrotropic and deep eutectic solvent extraction systems while acid hydrolysis, i.e., conventional and microwave-assisted extraction generate nanocrystals. Obtained results indicated that green solvent systems could be utilized in the production of nanocellulose with many advantages, including efficiency, sustainability, reduced environmental harm, and low cost.

Selective leaching and recovery of neodymium from NdFeB carbonyl residues

Neodymium iron boron (NdFeB) is a widely-used magnetic material; however, the production process generates significant amounts of rare earth element-rich waste. Refining the Fe via carbonylation leads to carbonylated slag containing 0.2–2.0 % rare earth elements. The extraction of trace rare earth elements from waste materials has not been reported, although the Nd recovery would be economically and environmentally beneficial. In this work, we calcinated NdFeB carbonylation slag (with less than 0.3 % rare earth content) and identified a green deep eutectic solvent (DES) that can selectively recover Nd. The best performing DES comprised a 2:1 M ratio of ethylene glycol to maleic acid and was highly selective for Nd and inert toward Fe, thus enabling effective separation. Specifically, the Nd/Fe selectivity factor exceeded 3000, i.e., under optimal conditions, 28.07 % of the Nd was extracted, while the Fe leaching rate was less than 0.01 %. The Nd in the DES was subsequently extracted and then enriched by reverse extraction using a di-(2-ethylhexyl)phosphoric acid (P204)-sulfonated kerosene system and hydrochloric acid. DES still had recyclability after extraction. Finally, the Nd was precipitated by adding oxalic acid to form the rare earth oxalate, which was calcined to obtain a high-purity Nd2O3. The strategy applied in this work based on DES and conventional organic extraction represents a promising and sustainable approach for the selective recovery of trace rare earth elements.