Adsorption characteristics of (-)-epigallocatechin gallate and caffeine in the extract of waste tea on macroporous adsorption resins functionalized with chloromethyl, amino, and phenylamino groups

Recovery and separation of glycyrrhizic acid from Natural Deep Eutectic Solvent (NADES) extract by macroporous resin: adsorption kinetics and isotherm studies

Natural Deep Eutectic Solvents (NADESs) have emerged as a green and sustainable alternative to conventional organic solvents to extract bioactive compounds. However, the recovery of bioactive compounds from the NADES extracts is challenging, restricting their large-scale applications. The present work investigated the recovery of glycyrrhizic acid (GA) from choline-chloride/lactic acid NADES extract using macroporous resins. GA possesses a wide spectrum of biological activities, and it is extracted from the well-known herb Glycyrrhiza glabra. During resin screening, DIAIONTM SP700 showed high adsorption and desorption capacities. The adsorption kinetics study demonstrated that the adsorption of GA on SP700 followed Pseudo First-order kinetic model. Moreover, the adsorption behaviors were elucidated by the Freundlich isotherm using a correlation coefficient based on a static adsorption study at different temperatures and pH. Furthermore, the thermodynamic parameters, for instance, the change of Gibbs free energy (ΔG*), entropy (ΔS*), and enthalpy (ΔH*), showed that the adsorption process was spontaneous, favorable and exothermic. In addition, the sample after macroporous resin treatment, which is enriched with GA exhibited good anticancer potential analyzed by SRB assay. The regenerated NADES solvent was recycled twice, keeping more than 90% extraction efficiency, indicating good reusability of NADES in the GA extraction process by using macroporous resin.

Enhanced adsorption of humic/fulvic acids onto urea-derived graphitic carbon nitride

Since humic substances (HSs) can cause environmental problems, their elimination has been attracting more and more concerns. In this study, we investigated HSs adsorption onto urea-derived graphitic carbon nitride (CNU) and elucidated adsorption mechanisms (i.e. heterogeneity, interface rearrangement, and multiple interactions). The adsorption capacity of CNUs was enhanced as increasing calcination temperature and time. Among CNUs, CNU-575-3 showed the highest adsorption capacity; the maximum adsorption capacities for humic acid (HA) and fulvic acid (FA) were 164.06 mg C/g, 14.61 L/cm·g, 91.12 mg C/g, and 5.34 L/cm·g, respectively. The adsorption affinity of CNUs mainly correlated with the amount of amino groups, and that of HSs components was dependent on aromaticity due to π-π interactions. More specifically, terrestrial humic-like and fulvic-like components within HA and FA showed the greatest adsorption affinity, respectively. HSs adsorption was remarkably affected by pH, alkali metals, and alkali earth metals via electrostatic interactions, H-bonding, cation bridge, and configurational effect. In addition, the adsorption of Elliott soil HA (ESHA) and the landfill leachate concentrate by CNUs was also highly efficient. This study shows the great promise of CNUs for HSs adsorption in waters and wastewaters.

Ultrasound-assisted adsorption/desorption of jujube peel flavonoids using macroporous resins

The work explored the process of ultrasound-assisted adsorption/desorption to efficiently purify jujube peel flavonoids (JPFs) using macroporous resins (MRs). The impact of ultrasound power and temperature on the adsorption/desorption features of JPFs on MRs were studied. The maximum adsorption (80.21 ± 2.11 mg/g) /desorption (76.22 ± 1.68 mg/g) capacity of total flavonoids content were obtained. The pseudo-second-order kinetic and Freundlich isotherm models better described the whole process of ultrasound-assisted adsorption. The adsorption process was spontaneous, physical, and dominated by multilinear intraparticle diffusion. Ultrasound mainly enhanced the adsorption capacity by strengthening the formation of hydrogen bonds and increasing the surface roughness of MRs. Besides, the principal individual flavonoid ((+)-Catechin, (-)-Epicatechin, Rutin, Quercetin-3-O-robinobioside) content of JPFs in ultrasound treatment was 2-3 times that of shaking treatment, and biological activities were significantly increased. Overall, as a low-cost green technology, ultrasound can improve the properties of MRs and better purify JPFs.

A Review of Caffeine Adsorption Studies onto Various Types of Adsorbents

A systematic literature review of publications from 2000 to 2020 was carried out to identify research trends on adsorbent materials for the removal of caffeine from aqueous solutions. Publications were retrieved from three databases (Scopus, Web of Science, and Google Scholar). Words "adsorption AND caffeine" were examined into titles, abstracts, and keywords. A brief bibliometric analysis was performed with emphasis on the type of publication and of most cited articles. Materials for the removal of caffeine were classified according to the type of material into three main groups: organic, inorganic, and composites, each of them subdivided into different subgroups consistent with their origin or production. Tables resume for each subgroup of adsorbents the key information: specific surface area, dose, pH, maximum adsorption capacity, and isotherm models for the removal of caffeine. The highest adsorption capacities were achieved by organic adsorbents, specifically those with granular activated carbon (1961.3 mg/g) and grape stalk activated carbon (916.7 mg/g). Phenyl-phosphate-based porous organic polymer (301 mg/g), natural sandy loam sediment (221.2 mg/g), composites of MCM-48 encapsulated graphene oxide (153.8 mg/g), and organically modified clay (143.7 mg/g) showed adsorption capacities lower than those of activated carbons. In some activated carbons, a relation between the specific surface area (SSA) and the maximum adsorption capacity (Q max) was found.

Adsorption/Desorption Characteristics and Simultaneous Enrichment of Orientin, Isoorientin, Vitexin and Isovitexin from Hydrolyzed Oil Palm Leaf Extract Using Macroporous Resins

Oil palm leaves (OPL) containing flavonoid C-glycosides are abundantly generated as oil palm byproducts. The performances of three macroporous resins with different physical and chemical properties for the enrichment of isoorientin, orientin, vitexin, and isovitexin from acid-hydrolyzed OPL (OPLAH) extract were screened. The XAD7HP resin exhibited the best sorption capacities for the targeted flavonoid C-glycosides and was thus selected for further evaluation. Static adsorption using the XAD7HP resin under optimal conditions (extract adjusted to pH 5, shaken at 298 K for 24 h) gave adsorption kinetics that fit well with a pseudo-second-order kinetic model. The adsorption of isoorientin and orientin was well described by Langmuir isotherms, while vitexin and isovitexin fit well with the Freundlich isotherms. Dynamic sorption trials using the column-packed XAD7HP resin produced 55–60-fold enrichment of isovitexin and between 11 and 25-fold enrichment of isoorientin, vitexin, and orientin using aqueous ethanol. The total flavonoid C-glycoside-enriched fractions (enriched OPLAH) with isoorientin (247.28–284.18 µg/mg), orientin (104.88–136.19 µg/mg), vitexin (1197.61–1726.11 µg/mg), and isovitexin (13.03–14.61 µg/mg) showed excellent antioxidant free radical scavenging activities compared with their crude extracts, with IC50 values of 6.90–70.63 µg/mL and 44.58–200.00 µg/mL, respectively. Hence, this rapid and efficient procedure for the preliminary enrichment of flavonoid C-glycosides by using macroporous resin may have practical value in OPL biomass waste utilization programs to produce high value-added products, particularly in the nutraceuticals, cosmeceuticals, pharmaceuticals, and fine chemicals industries.

Separation of Glycyrrhizic Acid and Its Derivants from Hydrolyzation in Subcritical Water by Macroporous Resin

Glycyrrhizic acid (GL) and its derivants, glycyrrhetinic acid 3-O-mono-β-d-glucuronide (GAMG) and glycyrrhetinic acid (GA) hydrolyzed in subcritical water, are bioactive substances and edulcorators. In this work, a separation strategy for these three substances was established. The effects of adsorbent and eluent were investigated by static/dynamic adsorption and multi-stage desorption with the mechanism analysis. The adsorption of them onto EXA50 resin was well fitted by the pseudo second-order kinetic model. The optimal dynamic adsorption flow rate was 6 bed volume (BV)/h, and water of pH = 12 was used to elute GL at 4 BV/h, then n-buthanol was used subsequently to elute GA at 1 BV/h, and finally 90% ethanol was applied to elute GAMG at 2 BV/h. As a result, purities of these compounds increased, which demonstrated that this adsorption-desorption technology was simple and efficient, and indicated the potential for large-scale purification and preparation of GL and its derivants in the future.

Preparative Separation of Flavonoids from Goji Berries by Mixed-Mode Macroporous Adsorption Resins and Effect on Aβ-Expressing and Anti-Aging Genes

Flavonoids are the main constituents of Goji berries and have good biological and pharmacological activities. The mixed-mode macroporous adsorption resins (MARs) for purification of flavonoids from Goji berries through computer-assisted calculation of the molecular size of flavonoids and the precise matching of MAR physical and chemical properties was firstly developed in the present study. Ten varieties of MARs with suitable molecular dimensions and polarities were used for investigating the adsorption/desorption behaviors of the flavonoids. Both AUKJ-1 and BWKX-1 showed higher separation efficiency than other MARs and then were mixed in different ratios to constitute a mixed-mode macroporous adsorption resin to obtain the optimal adsorption phase. Under optimal conditions, total flavonoid content of purified flavonoid (p-FLA) extract increased from 0.97% to 36.88% after one purification. The p-FLA extract from Goji berries significantly improved the expression of six genes with anti-aging effects and played an important role in aging-related Alzheimer's disease by down-regulating Aβ expression.

Use of Amberlite Macroporous Resins To Reduce Bitterness in Whole Olives for Improved Processing Sustainability

Olives are inedible because of high levels of bitter phenolics (e.g., oleuropein) which are removed during commercial olive processing. Current commercial processing methods are highly water-intensive, produce toxic wastewater, and are environmentally unsustainable. To address this, macroreticular polymeric resins were used to assist debittering and decrease water use. Amberlite resins XAD4, XAD16N, XAD7HP, and FPX66 were evaluated for the ability to adsorb bitter and/or high-value phenolic compounds (i.e., oleuropein, ligstroside, oleuropein aglycone, ligstroside aglycone, oleocanthal, oleacein, and hydroxytyrosol) from whole olives during typical brine storage. All resins effectively adsorbed oleuropein and ligstroside. FPX66 reduced oleuropein in whole olives suspended in a 1.0% acetic acid brine to 0.635 mg/kg wet weight in 2.5 months with no further processing. This concentration is below levels measured in commercial California-style black ripe olives (0.975 mg/kg wet weight). Resins in storage brines effectively decrease levels of bitter phenolic compounds without additional lye processing. Excellent recoveries of high-value phenolic compounds are obtained from resins (e.g., 80.2 ± 3.3% to 89.4 ± 8.9% hydroxytyrosol).

Design of an enhanced SAT using the graphene-MAR mixture for the removal of 17β-E2 at a demonstration site of Qianjin farm in China

An adsorption-enhanced soil aquifer treatment (SAT) system was designed to reduce the level of estrogens below the threshold stipulated by the standards. The 17β-E2 adsorption by graphene and MARs (H103) was investigated and an optimum amount of graphene and MARs in the mixture was determined using the linear programming. The kinetics and isotherm characteristics of both adsorbents were well described by the Lagergren pseudo-second order and the Freundlich model, respectively. The 17β-E2 adsorption on graphene and H103 was 88% and 70.37%, and the high temperature was beneficial to the 17β-E2 adsorption on graphene while the thermodynamic behaviors of H103 were in direct contrast to that of graphene. The study found that the maximum economic benefits could be achieved when the mass of graphene and H103 in the mixture is 2.79 g and 13.20 kg, respectively.

Facile preparation of microporous organic polymers functionalized macroporous hydrophilic resin for selective enrichment of glycopeptides

A macroporous adsorption resin (MAR) with ∼10 μm diameter was synthesized by seed-swelling polymerization and further modified with a layer of microporous organic polymers (MOP) by "one-pot" solvothermal reaction. The resulting MAR@MOP exhibited high specific surface area of 131.3 m²/g, which was higher than that of pristine MAR (57.8 m²/g). The contact angle also decreased from 58.8° (MAR) to 24° (MAR@MOP), indicating that the MOP was successfully grafted onto the surface of MAR. The chemical composition of MAR@MOP was confirmed by Fourier-transform infrared spectroscopy, ¹³C NMR and element analysis. The enrichment efficiency of MAR@MOP to glycopeptides was demonstrated by trapping N-linked glycopeptides from tryptic digests of human immunoglobulin G (IgG), horseradish peroxidase (HRP) and bovine fetuin. Furthermore, 879 unique N-glycosylation sites in 811 unique glycopeptides sequence mapped to 516 N-glycosylated proteins were identified in three replicate analyses of proteins extracted from mouse liver. Therefore, this hydrophilic MOP-coated adsorbent would be applied in the enrichment and identification of low-abundance N-linked glycopeptides in complicated biological samples.

Preparation of Starch-Hard Carbon Spherules from Ginkgo Seeds and Their Phenol-Adsorption Characteristics

Carbon spherules from ginkgo seed starch were prepared through stabilization and carbonization processes. The ginkgo seed starch was first stabilized at 195 °C for 18 h, then carbonized at 500 °C for 2 h under an N₂ atmosphere. The characterization results confirmed that carbon spherules were in the size range of 10–20 μm. Experimental data were also evaluated to find out the kinetic characteristics of phenols on the carbon spherules during the adsorption process. Adsorption processes for phenol, p-nitrophenol and p-chlorophenol were found to follow the pseudo-first order kinetic model with R² values of 0.995, 0.997 and 0.998, while the rate constants k₁ = 0.014, 0.009 and 0.011 min⁻¹ showed that the adsorption is mainly controlled by adsorbate diffusion. The equilibrium data were analyzed with the Langmuir, Freundlich and Temkin–Pyzhev models and the best fit was observed with the Freundlich isotherm, suggesting the physical adsorption of phenols. From the thermodynamic functions, ∆G, ∆H, and ∆S were calculated, which showed that adsorption is more favorable at low temperature and is an exothermic process, and the adsorption of p-nitrophenol and p-chlorophenol were more advantageous than that of phenol.

Enrichment of chelidonine from Chelidonium majus L. using macroporous resin and its antifungal activity

Chelidonium majus L. (greater celandine) has been used as an herbal medicine for several centuries. This study investigated an efficient method to purify chelidonine from the extract of C. majus L. using macroporous adsorption resins and evaluated the antifungal activity of chelidonine against Botryosphaeria dothidea as a model strain. Static adsorption and desorption tests revealed that D101 was the optimal resin for chelidonine purification. Pseudo-second-order kinetics model and Freundlich equation model were the most suitable for evaluating the endothermic and spontaneous adsorption processes of chelidonine on D101. Dynamic adsorption and desorption tests on D101 columns showed that the concentration of chelidonine increased 14.16-fold, from 2.67% to 37.81%, with the recovery yield of 80.77%. The antifungal activity of enriched chelidonine products was studied with B. dothidea. The results showed that the EC₅₀ of crude extracts, enriched chelidonine products, and chelidonine standard against B. dothidea were 3.24mg/mL, 0.43mg/mL, and 0.77mg/mL, respectively. The result of antifungal activity test showed that chelidonine had the potential to be a useful antifungal agent. Moreover, the enrichment method of chelidonine was highly efficient, low cost, and harmless to the environment for industrial applications.

Enrichment of antioxidants from soy sauce using macroporous resin and identification of 4-ethylguaiacol, catechol, daidzein, and 4-ethylphenol as key small molecule antioxidants in soy sauce

The adsorption and desorption characteristics of seven macroporous resins on the antioxidants in soy sauce were investigated. SP-207 and SP-825 resins possessing good adsorption and desorption capacities were studied further. The pseudo-second-order kinetics and Langmuir isotherm models were demonstrated to be appropriate to describe the whole exothermic and physical adsorption processes of antioxidants onto resins. The 60% ethanol eluted fraction from soy sauce purified by SP-825 resin column possessed the strongest antioxidant activity. The antioxidant activities and contents of typical soy isoflavones, furanones, pyranones, and phenolic acids in soy sauce were determined. These compounds contributed to 50.02% of the total antioxidant activity of the SP-60% fraction. The key small molecule antioxidant compounds in soy sauce were identified as 4-ethylguaiacol, catechol, daidzein, and 4-ethylphenol by the antioxidants omission experiments. Additionally, the purified active fraction with high contents of antioxidants from soy sauce could be applied as bioactive ingredient in food industry.

Extraction and preparation of high-aroma and low-caffeine instant green teas by the novel column chromatographic extraction method with gradient elution

The lack of aroma and natural taste is a critical problem in production and consumption of instant green teas. A method to prepare instant green teas high in-natural-aroma and low-caffeine by the novel column chromatographic extraction with gradient elution is reported. This method simultaneously extracted aroma (or volatile) and non-aroma compounds from green tea. Green tea was loaded into columns with 2.0-fold of petroleum ether (PE): ethanol (8:2). After standing for 3 h until the aroma compounds dissolved, the column was sequentially eluted with 3.0-fold 40% ethanol and 3.5-fold water. The eluant was collected together and automatically separated into PE and ethanol aqueous phases. The aroma extracts was obtained by vacuum-evaporation of PE phase at 45 °C. The ethanol aqueous phase was vacuum-concentrated to aqueous and partially or fully decaffeinated with 4% or 9% charcoal at 70 °C. A regular instant green tea with epigallocatechin-3-gallate: caffeine of 3.5:1 and a low-caffeine instant green tea (less than 1% caffeine) with excellent aroma and taste were prepared, by combining the aroma and non-aroma extracts at a 1:10 ratio. This work provides a practical approach to solve the low-aroma and low-taste problems in the production of high quality instant green teas.

The effective and selective separation of (-)-epigallocatechin gallate by molecularly imprinted chitosan beads

The (-)-epigallocatechin gallate (EGCG) imprinted chitosan beads (EICBs) were fabricated for the effective and selective separation of EGCG. The EGCG molecules interacted with the amino groups of chitosan in the imprinting process, resulting in a highly porous structure of EICBs and more adsorption sites. Consequently, EICBs exhibited better adsorption performance than non-imprinted chitosan beads. The maximum adsorption capacity of EGCG onto EICBs reached 135.50 mg/g at 313 K. The imprinting factor of EICBs was 4.22, indicating that EICBs possess good recognition ability and selectivity for EGCG. After five cycles of reuse, only a slight decrease (7.77%) in the adsorption capacity was observed, demonstrating the satisfactory reusability of EICBs. Furthermore, the adsorption of EGCG onto EICBs is deduced to be the monolayer adsorption on an energetically homogeneous surface; the hydrogen bonding between EGCG and EICBs is the main driving force for the adsorption. Our studies suggest that EICBs have a great potential for the effective and selective separation of EGCG.

Adsorption characteristics of adsorbent resins and antioxidant capacity for enrichment of phenolics from two-phase olive waste

In this study, the adsorption properties of nine resins including polyamide resin (30-60), polyamide resin (60-100) AB-8, S-8, D-101, NKA-9, NKA-II, XDA-1 and XDA-4 for enrichment phenolics of the olive waste were investigated. XDA-1 and NKA-II were chosen for further study due to their outstanding adsorption and desorption capacity. XDA-1 and NKA-II had similar adsorption and desorption behaviors for phenolics of olive waste. The adsorption mechanism could be better explained by pseudo second-order kinetics model and Freundlich isotherm model, and the adsorption processes were spontaneously and exothermic. The experiment of gradient elution were carried out through treated XDA-1 resins column, the result indicated the total phenolics were mainly obtained from the 40% and 60% ethanol fraction. The order of antioxidant capacity by DPPH  , ABTS⁺ radical and FRAP assay was similar with the content of phenolics from fraction elution. The compositions of phenolics from different elution fractions were determined by reversed phase-HPLC-DAD method. Gallic acid, hydroxytyrosol, tyrosol and ferulic acid were the major constituent in the fraction elute, and the content of hydroxytyrosol reached to the 41.69mg/g. The above results revealed the synergistic effects of the different phenolics contribute to the antioxidant capacity.

A physical entrapment method for the preparation of carbon nanotube reinforced macroporous adsorption resin with enhanced selective extraction performance

In this paper, we demonstrate a novel carbon nanotube (CNT) reinforced macroporous adsorption resin (MAR) for the first time. The CNTs were dispersed in water via sonication, and then in situ physically entrapped in the pores of MAR by capillary forces and sonication. The resulting CNT reinforced MAR (CNT-MAR) was proved by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM), and subsequently applied to extract a mixture of 8 types, 14 natural products. For comparison, the extraction efficiency of original MAR without CNTs was also evaluated. After extraction, the supernatants were detected via high-performance liquid chromatography (HPLC). The results indicated that the introduction of carbon nanotubes (CNTs) into the pores of MAR can significantly improve the adsorptive selectivity of MAR for natural products. The original MAR without CNTs has almost the same adsorption capacity for selectively extracting 3 types of natural products (phenols, alkaloids and anthraquinones). However, the CNT-MAR only could selectively extract anthraquinones and the adsorption capacity for three anthraquinone natural products is 1.46-1.83 times higher than that of unmodified MAR. In order to achieve the highest extraction efficiency of CNT-MAR for anthraquinone natural products, the main extraction parameters such as the extraction time and the pH value were also optimized. The CNT-MAR demonstrated an excellent ability to extract anthraquinone natural products with high selectivity and adsorption capacity. Due to its low cost, easy preparation and use, and operational characteristics, it shows great potential for selective extraction of natural products.

Efficient extraction strategies of tea (Camellia sinensis) biomolecules

Tea is a popular daily beverage worldwide. Modulation and modifications of its basic components like catechins, alkaloids, proteins and carbohydrate during fermentation or extraction process changes organoleptic, gustatory and medicinal properties of tea. Through these processes increase or decrease in yield of desired components are evident. Considering the varied impacts of parameters in tea production, storage and processes that affect the yield, extraction of tea biomolecules at optimized condition is thought to be challenging. Implementation of technological advancements in green chemistry approaches can minimize the deviation retaining maximum qualitative properties in environment friendly way. Existed extraction processes with optimization parameters of tea have been discussed in this paper including its prospects and limitations. This exhaustive review of various extraction parameters, decaffeination process of tea and large scale cost effective isolation of tea components with aid of modern technology can assist people to choose extraction condition of tea according to necessity.

Evaluation of an efficient and selective adsorbent based on multi-walled carbon nanotubes coated silica microspheres for detecting nucleobases and nucleosides in human urine

Nucleobases and nucleosides in human urine could be detected by a new efficient and selective adsorbent of MWCNTs/SiO₂.

Synthesis and characterization of amino acid-modified adsorption resins and their adsorption properties in the purification of tabersonine from Voacanga africana seeds

The modified MARs had good adsorption of impurities but poor adsorption of tabersonine from extracts of Voacanga africana seeds.