Application of β-Cyclodextrin Adsorbents in the Removal of Mixed Per- and Polyfluoroalkyl Substances

The extensive use of per- and polyfluoroalkyl substances (PFASs) in industrial consumer products has led to groundwater contamination, raising concerns for human health and the environment. These persistent chemicals exist in different forms with varying properties, which makes their removal challenging. In this study, we assessed the effectiveness of three different β-cyclodextrin (β-CD) adsorbents at removing a mixture of PFASs, including anionic, neutral, and zwitterionic compounds, at neutral pH. We calculated linear partition coefficient (Kd) values to quantify the adsorption affinity of each PFAS. β-CD polymers crosslinked with hexamethylene diisocyanate (β-CD-HDI) and epichlorohydrin (β-CD-EPI) displayed some adsorption of PFASs. Benzyl chloride β-CD (β-CD-Cl), an adsorbent that had not been previously reported, was also synthesized and tested for PFAS adsorption. β-CD-Cl exhibited higher PFAS adsorption than β-CD-HDI and β-CD-EPI, with log Kd values ranging from 1.9 L·g-1 to 3.3 L·g-1. β-CD-Cl displayed no affinity for zwitterionic compounds, as opposed to β-CD-HDI and β-CD-EPI, which removed N-dimethyl ammonio propyl perfluorohexane sulfonamide (AmPr-FHxSA). A comparison between Kd values and the log Kow of PFAS confirmed the significant role of hydrophobic interactions in thee adsorption mechanism. This effect was stronger in β-CD-Cl, compared to β-CD-HDI and β-CD-EPI. While no effect of PFAS charge was observed in β-CD-Cl, some influence of charge was observed in β-CD-HDI and β-CD-EPI, with less negative compounds being more adsorbed. The adsorption of PFASs by β-CD-Cl was similar in magnitude to that of other adsorbents proposed in literature. However, it offers the advantage of not containing fluorine, unlike many commonly proposed adsorbents.

Evaluation of the Swelling Properties and Sorption Capacity of Maltodextrin-Based Cross-Linked Polymers

The development of polymers obtained from renewable sources such as polysaccharides has gained scientific and industrial attention. Cross-linked bio-derived cationic polymers were synthesized via a sustainable approach exploiting a commercial maltodextrin product, namely, Glucidex 2®, as the building block, while diglycidyl ethers and triglycidyl ethers were used as the cross-linking agents. The polymer products were characterized via FTIR-ATR, TGA, DSC, XRD, SEM, elemental analysis, and zeta-potential measurements, to investigate their composition, structure, and properties. Polydispersed amorphous granules displaying thermal stabilities higher than 250 °C, nitrogen contents ranging from 0.8 wt % and 1.1 wt %, and zeta potential values between 10 mV and 15 mV were observed. Subsequently, water absorption capacity measurements ranging from 800% to 1500%, cross-linking density determination, and rheological evaluations demonstrated the promising gel-forming properties of the studied systems. Finally, nitrate, sulfate, and phosphate removal tests were performed to assess the possibility of employing the studied polymer products as suitable sorbents for water remediation. The results obtained from the ion chromatography technique showed high sorption rates, with 80% of nitrates, over 90% of sulfates, and total phosphates removal.

Structural diversity, functional versatility and applications in industrial, environmental and biomedical sciences of polysaccharides and its derivatives - A review

Recent efforts on the expansion of sustainable and commercial primal matters are essential to enhance the knowledge of their hazards and noxiousness to humans and their environments. For example, polysaccharide materials are widely utilized in food, wound dressing, tissue engineering, industry, targeted drug delivery, environmental, and bioremediation due to their attractive degradability, nontoxicity and biocompatibility. There are numerous easy, quick, and efficient ways to manufacture these materials that include cellulose, starch, chitosan, chitin, dextran, pectin, gums, and pullulan. Further, they exhibit distinctive properties when combined favourably with raw materials from other sources. This review discusses the synthesis and novel applications of these carbohydrate polymers in industrial, environmental and biomedical sciences.

The influence of magnetic particle incorporation on bisphenol A removal by β-cyclodextrin-derived sorbent

A novel, biomass-derived hybrid sorbent Ban-CD-EPI-Fe was successfully synthesized in a coprecipitation method, in which β-cyclodextrin copolymerized with banana peel extract and epichlorohydrin was grafted onto an iron oxide surface. The composition, presence of functional groups, morphology, thermal stability, and magnetic properties of the obtained material were characterized by Powder X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Thermogravimetric Analysis (TGA), and Physical Properties Measurement System (PPMS). The material bearing around 28% of β-cyclodextrin units has mesoporous structure with plate-like morphology and active surface area determined by BET and Langmuir models equal to 38.35 and 53.59 m2 g-1, respectively. The sorption studies aimed to remove an endocrine disruptor - bisphenol A (BPA), from water. The results showed that the time evolution could be fitted with pseudo-second kinetic order with a rate constant k equal to 0.05 g mg-1 min-1. According to the Langmuir isotherm, a monolayer is created during BPA sorption, and the maximum sorption capacity was estimated as 93.5 mg g-1. After BPA sorption, the hybrid material could be easily separated by an external magnet and regenerated under mild conditions keeping its recyclability in at least eight cycles.

Rechargeable films for protection of dry foods: A sustainable method for covalent grafting of β-cyclodextrin-thymol complex on PET/viscose platform

Rechargeable materials for the effective protection of dry food products were developed. β-cyclodextrin-thymol inclusion complex was covalently grafted on a solid platform of polyethylene terephthalate-viscose using either traditional cross-linker of epichlorohydrin, or natural cross-linker of citric acid. A correlation between the grafting method and physicochemical properties, loading capacity and release capabilities of the resulted materials was studied. The developed materials demonstrated antimicrobial properties preventing mold propagation in wheat grains. The treated grains showed normal germination abilities verifying that the prepared materials can protect dry food products without using harmful chemicals. The suggested approach can be extended to other applications and active agents. A combination of rechargeable films with natural volatiles can serve as an effective platform for sustainable active materials for food protection and in other fields such as agriculture, cosmetics, and medicine.

Fabrication and Applications of Potentiometric Membrane Sensors Based on γ-Cyclodextrin and Calixarene as Ionophores for the Determination of a Histamine H1-Receptor Antagonist: Fexofenadine

Supramolecular fexofenadine sensors have been constructed. Although noncovalent intermolecular and intramolecular interactions, which are far weaker than covalent contacts, are the main focus of supramolecular chemistry, they can be used to create sensors with an exceptional affinity for a target analyte. The objective of the current research study is to adapt two PVC membrane sensors into an electrochemical approach for the dosage form determination of histamine H1-receptor antagonists: fexofenadine. The general performance characteristics of two new modified potentiometric membrane sensors responsive to fexofenadine hydrochloride were established. The technique was based on the employment of γ-cyclodextrin (CD) (sensor 1), 4-tert-butylcalix[8]arene (calixarene) (sensor 2) as an ionophore, potassium tetrakis (4-chlorophenyl) borate (KTpClPB) as an ion additive, and (o-NPOE) as a plasticizer for sensors 1 and 2. The sensors showed fast responses over a wide fexofenadine concentration range (1 × 10^-2 to 4.5 (4.7) × 10^-6 M), with detection limits of 1.3 × 10^-6 M and 1.4 × 10^-6 M for sensors 1 and 2, respectively, in the pH range of 2-8. The tested sensors exhibit the fexofenadine near-Nernstian cationic response at 56 and 58 mV/decade for sensors 1 and 2, respectively. The sensors exhibit good stability, fast response times, accuracy, precision, and longer life for fexofenadine. Throughout the day and between days, the sensors exhibit good recovery and low relative standard deviations. Fexofenadine in its pure, dose form has been identified with success using the modified sensors. The sensors were employed as end-point indications for the titration of fexofenadine with NaTPB.

Cyclodextrin-enabled green environmental biotechnologies

Most of the organic compounds contaminating the environment can form inclusion complexes with cyclodextrins resulting in enhanced solubility (a benefit in soil remediation) or just the opposite: reduced mobility by sorption (a benefit in wastewater treatment). Combining biotechnologies with cyclodextrin, a renewable and biodegradable material, green environmental technologies of high efficiency were developed. For instance, the cyclodextrin-enabled soil washing/flushing technologies combined with bioremediation have been demonstrated in full-scale field experiments. The efficiency of tertiary wastewater treatment by sorption of non-biodegradable xenobiotics, such as residual pharmaceutics, was proved. The biofilm formation in fouling processes can be prevented or reduced either by applying cyclodextrin-based coatings or by manipulation of quorum sensing (bacterial communication) via capturing signal molecules.

Synthesis of reusable cyclodextrin polymers for removal of naphthol and naphthylamine from water

As one group of important naphthalene derivatives, naphthol and naphthylamine are diffusely employed as dye intermediates. The presence of naphthol and naphthylamine in water systems may pose risks to the environment and public health due to their carcinogenicity. In this study, four mesoporous polymers prepared by β-cyclodextrin derivatives and tetrafluoroterephthalonitrile were obtained and applied to adsorbing 1-naphthylamine, 2-naphthylamine, 1-naphthol, and 2-naphthol from water. The impact of adsorption time, initial concentration of naphthol and naphthylamine, and temperature on the adsorption efficiency of the four polymers were explored separately. The four polymers present fast adsorption kinetics toward naphthol and naphthylamine, attaining 93 ~ 100% of adsorption equilibrium uptake for 1-naphthol, 1-naphthylamine, 2-naphthylamine in 15 min, and 87 ~ 90% of equilibrium uptake for 2-naphthol in 15 min. The kinetics could be depicted well by the pseudo-second-order kinetic model. The adsorption isotherms of the four polymers toward naphthol and naphthylamine accord with the Redlich-Peterson or Sips model. The maximum adsorption capacities of 1-naphthylamine, 2-naphthylamine, 1-naphthol, and 2-naphthol are 189.9 mg/g, 82.8 mg/g, 137.7 mg/g, and 88.7 mg/g, respectively. The adsorption ratio increases fast with reducing the initial concentration of naphthol and naphthylamine, and the adsorption ratio of naphthol and naphthylamine in 5 mg/L can achieve over 95% in 25 °C. In addition, the four polymers can be effortlessly regenerated by a gentle and simple washing procedure with little reduction in performance. The adsorption performance of the four polymers toward the four naphthalene derivatives can be improved by increasing the adsorption temperature. In conclusion, the prepared β-cyclodextrin polymers exhibit rapid water treatment in removing the four low-concentration naphthalene derivatives with convenient regeneration and good reusability.

Complexation of Lignin Dimers with β-Cyclodextrin and Binding Stability Analysis by ESI-MS, Isothermal Titration Calorimetry, and Molecular Dynamics Simulations

Lignin derived from lignocellulosic biomass is the largest source of renewable bioaromatics present on earth and requires environmentally sustainable separation strategies to selectively obtain high-value degradation products. Applications of supramolecular interactions have the potential to isolate lignin compounds from biomass degradation fractions by the formation of variable inclusion complexes with cyclodextrins (CDs). CDs are commonly used as selective adsorbents for many applications and can capture guest molecules in their internal hydrophobic cavity. The strength of supramolecular interactions between CDs and lignin model compounds that represent potential lignocellulosic biomass degradation products can be characterized by assessing the thermodynamics of binding stability. Consequently, the inclusion interactions of β-CD and lignin model compounds G-(β-O-4')-G, G-(β-O-4')-truncG (guaiacylglycerol-β-guaiacyl ether), and G-(β-β')-G (pinoresinol) were investigated empirically by electrospray ionization mass spectrometry and isothermal titration calorimetry, complemented by molecular dynamics (MD) simulations. Empirical results indicate that there are substantial differences in binding stability dependent on the linkage type. The lignin model β-β' dimer showed more potential bound states including 1:1, 2:1, and 1:2 (guest:host) complexation and, based on binding stability determinations, was consistently the most energetically favorable guest. Empirical results are supported by MD simulations that reveal that the capture of G-(β-β')-G by β-CD is promising with a 66% probability of being bound for G-(β-O-4')-truncG compared to 88% for G-(β-β')-G (unbiased distance trajectory and explicit counting of bound states). These outcomes indicate CDs as a promising material to assist in separations of lignin oligomers from heterogeneous mixtures for the development of environmentally sustainable isolations of lignin compounds from biomass fractions.

Modification of cyclodextrin and use in environmental applications

Water pollution, which has become a global problem in parallel with environmental pollution, is a problem that needs to be solved urgently, considering the gradual depletion of water resources. The inadequacy of the water treatment methods and the materials used somehow directed the researchers to look for dual character structures such as biocompatible and biodegradable β-cyclodextrin (β-CD). β-CD, which is normally insoluble in water, is used in demanding wastewater applications by being modified with the help of different agents to be water soluble or transformed into polymeric adsorbents as a result of co-polymerization via cross-linkers. In this way, in addition to the host-guest interactions offered by β-CD, secondary forces arising from these interactions provide advantages in terms of regeneration and reusability. However, the adsorption efficiency and synthesis steps need to be improved. Based on the current studies presented in this review, in which cross-linkers and modification methods are also mentioned, suggestions for novel synthesis methods of new-generation β-CD-based materials, criticisms, and recent methods of removal of micropollutants such as heavy metals, industrial dyes, harmful biomolecules, and pharmaceutics wastes are mentioned.

Recent progress, synthesis, and applications of chitosan-decorated magnetic nanocomposites in remediation of dye-laden wastewaters

Over the past several decades, the disposal of dyes from the industrial manufacturing sector has had an inadvertent impact on water ecology as polluted water bodies with these hazardous dyes...

Structural Adaptive, Self-Separating Material for Removing Ibuprofen from Waters and Sewage

β-Cyclodextrin nanosponge (β-CD-M) was used for the adsorption of ibuprofen (IBU) from water and sewage. The obtained material was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), Harkins and Jura t-Plot, zeta potential, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and elementary analysis (EA). Batch adsorption experiments were employed to investigate the effects of the adsorbent dose, initial IBU concentration, contact time, electrolyte ions and humic acids, and sewage over adsorption efficiency. The experimental isotherms were show off using Langmuir, Freundlich, Hill, Halsey and Sips isotherm models and thermodynamic analysis. The fits of the results were estimated according to the Sips isotherm, with a maximum adsorption capacity of 86.21 mg g-1. The experimental kinetics were studied by pseudo-first-order, pseudo-second-order, Elovich, modified Freundlich, Weber Morris, Bangham's pore diffusion, and liquid film diffusion models. The performed experiments revealed that the adsorption process fits perfectly to the pseudo-second-order model. The Elovich and Freundlich models indicate chemisorption, and the kinetic adsorption model itself is complex. The data obtained throughout the study prove that this nanosponge (NS) is extremely stable, self-separating, and adjusting to the guest structure. It also represents a potential biodegradable adsorbent for the removal IBU from wastewaters.

Recent Advances of Porous Materials Based on Cyclodextrin

Porous materials have attracted significant attention because of their rising applications in many fields. Cyclodextrins (CDs) are suitable building units in the fabrication of porous materials owing to their intrinsic nanoporous structure, easy modification, and biocompatibility, which may result in the formation of CD-based organic frameworks (including cyclodextrin metal-organic frameworks (CD-MOFs) and cyclodextrin covalent organic frameworks (CD-COFs)), and CD-based polymer hybrid porous materials. This review focuses on the recent progress in the fabrication and applications of CD-based porous materials with novel structures and functionalities.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

Simple and efficient method for the quantification of antiepileptic drugs in human plasma by using magnetic graphene oxide-β-cyclodextrin composite as a sorbent

Background

In recent days, solid-phase extraction methods are widely utilized for the extraction of drug molecules from plasma samples due to their easy operating procedures and low matrix effect. The trace-level solid-phase extraction of three structurally related antiepileptic drugs brivaracetam (BVC), eslicarbazepine acetate (ESL), and carbamazepine (CBZ) was investigated by using a magnetic porous material graphene oxide-β-cyclodextrin (MGO-CD). Morphology, magnetic properties, and structure of the synthesized MGO-CD were characterized by using FT-IR, SEM, XRD, and VSM.

Results

Solid-phase extraction (SPE) methods were used to extract the analytes from human plasma. Different extraction solvents such as acetonitrile (ACN), methanol (MeOH), acetone, chloroform (CHCl3), tertiary butyl diethyl ether (TBDE), and ethyl acetate (EtOAc) with variable polarities were used to extract drug molecules from MGO-CD. The linearity analysis showed good correlation coefficient values (R2) of 0.9989, 0.9995, and 0.9982 for BVC, ESL, and CBZ respectively. The LOD and LOQ ranges were found to be 6.14–28.32 ng mL−1 and 20.45–94.31 ng mL−1 respectively.

Conclusion

The high accuracy and precision made the developed HPLC method with MGO-CD a suitable alternative for the bioequivalence study of BVC, ESL, and CBZ in human plasma. This developed HPLC-UV method has good efficiency for recoveries and good linearity and is simple to handle. And also, it gave low retention time for the three antiepileptic drugs within 8 min. It provides high efficiency for the extraction of trace-level substances from human plasma.

History of cyclodextrin-based polymers in food and pharmacy: a review

Cyclodextrins are glucose macrocycles whose inclusional capabilities towards non-polar solutes can be modulated with the help of other macrostructures. The incorporation of cyclodextrin moieties into larger structures produces five types of new materials: crosslinked networks, functionalized chains, amphiphilic cyclodextrins, polyrotaxanes and nanocomposites. This review presents crosslinking and grafting to prepare covalently-attached cyclodextrins, and applications in the food and pharmaceutical sectors, from an historical point of view. In food science, applications include debittering of juices, retention of aromas and release of preservatives from packaging. In biomedical science, cyclodextrin polymers are applied classically to drug release, and more recently to gene delivery and regenerative medicine. The remarkable points are: 1) epichlorohydrin and diisocyanates have been extensively used as crosslinkers since the 1960s, but during the last two decades more complex cyclodextrin polymeric structures have been designed. 2) The evolution of cyclodextrin polymers matches that of macromolecular materials with regard to complexity, functionality and capabilities. 3) The use of cyclodextrin polymers as sorbents in the food sector came first, but smart packaging is now an active challenge. Cyclodextrins have also been recently used to design treatments against the coronavirus disease 2019 (COVID-19).

da Silva Alves D, Okeke C, Breslin CB. Cyclodextrins as Supramolecular Recognition Systems: Applications in the Fabrication of Electrochemical Sensors

Supramolecular chemistry, although focused mainly on noncovalent intermolecular and intramolecular interactions, which are considerably weaker than covalent interactions, can be employed to fabricate sensors with a remarkable affinity for a target analyte. In this review the development of cyclodextrin-based electrochemical sensors is described and discussed. Following a short introduction to the general properties of cyclodextrins and their ability to form inclusion complexes, the cyclodextrin-based sensors are introduced. This includes the combination of cyclodextrins with reduced graphene oxide, carbon nanotubes, conducting polymers, enzymes and aptamers, and electropolymerized cyclodextrin films. The applications of these materials as chiral recognition agents and biosensors and in the electrochemical detection of environmental contaminants, biomolecules and amino acids, drugs and flavonoids are reviewed and compared. Based on the papers reviewed, it is clear that cyclodextrins are promising molecular recognition agents in the creation of electrochemical sensors, chiral sensors, and biosensors. Moreover, they have been combined with a host of materials to enhance the detection of the target analytes. Nevertheless, challenges remain, including the development of more robust methods for the integration of cyclodextrins into the sensing unit.

One-step sustainable synthesis of cationic high-swelling polymers obtained from starch-derived maltodextrins

The good water solubility displayed by most starch-derived maltodextrins has limited their use when specific mechanical properties are required, particularly when working in aqueous media. As a result, numerous attempts to cross-link such polysaccharides to obtain cross-linked polymers have been reported; in this context, non-toxic and biocompatible water-soluble diglycidyl ethers have performed well. Besides, amines are commonly used as curing agents in combination with diglycidyl ethers for the production of epoxy resins. For this reason, amine-mediated epoxy ring-opening reactions of 1,4-butanediol diglycidyl ether have been studied as approaches to obtain sustainable cross-linked polymers suitable for eco-friendly scaling-up, based upon commercial starch-derived maltodextrins, using water as a unique solvent.

Main Applications of Cyclodextrins in the Food Industry as the Compounds of Choice to Form Host-Guest Complexes

Cyclodextrins (CDs) are cyclic oligomers broadly used in food manufacturing as food additives for different purposes, e.g., to improve sensorial qualities, shelf life, and sequestration of components. In this review, the latest advancements of their applications along with the characteristics of the uses of the different CDs (α, β, γ and their derivatives) were reviewed. Their beneficial effects can be achieved by mixing small amounts of CDs with the target material to be stabilized. Essentially, they have the capacity to form stable inclusion complexes with sensitive lipophilic nutrients and constituents of flavor and taste. Their toxicity has been also studied, showing that CDs are innocuous in oral administration. A review of the current legislation was also carried out, showing a general trend towards a wider acceptance of CDs as food additives. Suitable and cost-effective procedures for the manufacture of CDs have progressed, and nowadays it is possible to obtain realistic prices and used them in foods. Therefore, CDs have a promising future due to consumer demand for healthy and functional products.

Cyclodextrin-based adsorbents for the removal of pollutants from wastewater: a review

Water is a vital substance that constitutes biological structures and sustains life. However, water pollution is currently among the major environmental challenges and has attracted increasing study attention. How to handle contaminated water now mainly focuses on removing or reducing the pollutants from the wastewater. Cyclodextrin derivatives, possessing external hydrophilic and internal hydrophobic properties, have been recognized as new-generation adsorbents to exert positive effects on water pollution treatment. This article outlines recent contributions of cyclodextrin-based adsorbents on wastewater treatment, highlighting different adsorption mechanisms of cyclodextrin-based adsorbents under different influencing factors. The crosslinked and immobilized cyclodextrin-based adsorbents all displayed outstanding adsorption capacities. Particularly, according to specific pollutants including metal ions, organic chemicals, pesticides, and drugs in wastewater, this article has classified and organized various cyclodextrin-based adsorbents into tables, which could pave an intuitive shortcut for designing and developing efficient cyclodextrin-based adsorbents for targeted wastewater pollutants. Besides, this article specially discusses cost-effectiveness and regeneration performance of current cyclodextrin-based adsorbents. Finally, the challenges and future directions of cyclodextrin-based adsorbents are prospected in this article, which may shed substantial light on practical industrial applications of cyclodextrin-based adsorbents.

Insight into β-cyclodextrin polymer microsphere as a potential filtration reducer in water-based drilling fluids for high temperature application

Controlling the filtration of water-based drilling fluid effectively in high temperature environment is a great challenge in drilling engineering. In this study, β-cyclodextrin polymer microspheres (β-CDPMs) were synthesized by crosslinking between β-cyclodextrin and epichlorohydrin via inverse emulsion polymerization and employed as filtration reducers. The standard American Petroleum Institute filtration test showed that the β-CDPMs can only perform the enhanced filtration control ability at temperatures above 160 °C, and can tolerate the temperature resistance up to 240 °C without significant influence of rheology. As the thermal aging temperature is above 160 °C, numerous nano carbon spheres and nanostructured composites generated due to the occurrence of hydrothermal reaction. These high temperature stable nanoparticles bridged across the nano sized gaps and participated into forming dense filter cake, contributing to excellent filtration control. The filtration control mechanism proposed in this study opened a novel avenue for high temperature filtration control in water-based drilling fluids.

Molecular View into the Cyclodextrin Cavity: Structure and Hydration

We find, through atomistic molecular dynamics simulation of native cyclodextrins (CDs) in water, that although the outer surface of a CD appears like a truncated cone, the inner cavity resembles a conical hourglass because of the inward protrusion of the glycosidic oxygens. Furthermore, the conformations of the constituent α-glucose molecules are found to differ significantly from a free monomeric α-glucose molecule. This is the first computational study that maps the conformational change to the preferential hydrogen bond donating capacity of one of the secondary hydroxyl groups of CD, in consensus with an NMR experiment. We have developed a simple and novel geometry-based technique to identify water molecules occupying the nonspherical CD cavity, and the computed water occupancies are in close agreement with the experimental and density functional theory studies. Our analysis reveals that a water molecule in CD cavity loses out about two hydrogen bonds and remains energetically frustrated but possesses higher orientational degree of freedom compared to bulk water. In the context of CD-drug complexation, these imply a nonclassical, that is, enthalpically driven hydrophobic association of a drug in CD cavity.

Synthesis of New Cyclodextrin-Based Adsorbents to Remove Direct Red 83:1

Two cyclodextrins (CDs), γ– and hydroxypropyl (HP)–γ–CDs were used to synthesize new adsorbents by using epichlorohydrin (EPI) as cross-linking agent in order to remove Direct Red 83:1 (DR) from water. Both polymers were characterized in terms of Fourier spectroscopy, nuclear magnetic resonance, particle size distribution and thermogravimetric analysis. Experimental data for both polymers were well fitted to the pseudo-second order and intraparticle diffusion model, indicating that in the adsorption both chemical and physical interactions are essential in the removal of DR. Three different isotherm models were analyzed, concluding that γ–CDs–EPI followed the Temkin isotherm and HP–γ–CDs-EPI the Freundlich isotherm, these results suggested that the adsorption was happening onto heterogeneous surfaces. The results of the Gibbs free energy showed that the adsorption was spontaneous at room temperature. In order to eliminate the remaining dye after the polymer treatment, and advanced oxidation process (AOP) was considered, achieving more than 90% of removal combining both mechanisms.

Evaluation of Polyethylene Glycol Crosslinked β-CD Polymers for the Removal of Methylene Blue

The environment is at the heart of global worldwide discussion. This study describes the synthesis of ecofriendly polymers by a crosslinking reaction between β-cyclodextrin as the monomer and polyethylene glycol diglycidyl ether (PEDGE) as well as ethylene diglycidyl ether (EDGE) as the crosslinking agents. The studied polymers were characterized by several techniques, such as SEM, FTIR, TGA-TDA and XRD. Their adsorption properties for methylene blue under various conditions of pH, contact time and initial concentration of dye were assessed in order to find the optimal conditions. The results indicate that the polymers are good nominates for methylene blue adsorption with adsorption capacities up to 15 mg/g. The adsorption mechanism was demonstrated to follow the Langmuir model. Finally, the regeneration of the polymers was investigated using Soxhlet extraction with ethanol. The absorption capacities of the adsorbent were stable after three cycles.

Chemically crosslinked xylan-β-Cyclodextrin hydrogel for the in vitro delivery of curcumin and 5-Fluorouracil

Novel hydrogels were synthesized from xylan and β-Cyclodextrin using Ethylene Glycol Diglycidyl Ether as a crosslinker in alkaline medium at different molar ratio. The physical characterization of hydrogels was carried out by the swelling study whereas the chemical characterization was performed in Fourier Transform Infrared Spectroscopy. The morphological analysis revealed the porous structure of hydrogel and the rheological study summarised the flow behavior and gelation characteristics of the hydrogels. Curcumin and 5-Fluorouracil (5-FU) were used as the model drugs to be loaded in hydrogel and subsequent studies involving the in vitro release in phosphate buffer saline (PBS, pH = 7.4). The hydrogels showed drug loading of 98% of 5-FU and 26% of curcumin. Furthermore, the gels showed the highest cumulative release of 56% 5-FU and 37% curcumin after 24 h. The kinetics of drug release was then analyzed by various kinetic models.

Covalent Immobilization of Candida rugosa Lipase on Epichlorohydrin-Coated Magnetite Nanoparticles: Enantioselective Hydrolysis Studies of Some Racemic Esters and HPLC Analysis

In this study, a new biocatalyst was prepared by immobilizing Candida rugosa lipase epichlorohydrin-functionalized onto the surface of the nanoparticles. Magnetite nanoparticles were obtained by chemical co-precipitation method of Fe²⁺ and Fe³⁺, and then the prepared uncoated and coated nanoparticles were characterized by XRD, FT-IR and TGA. Lipase was covalently attached to activated nanoparticles. The catalytic properties of free and immobilized lipases were determined. It was found that the optimum temperature for free and immobilized lipases was 30 °C and 35 °C, respectively. The optimum pH values were found to be 7.0 and 8 for free and immobilized lipases, respectively. Immobilized lipase was found to retain significant activity even after the seventh use. In the final section of the study, optically pure compounds were obtained by carrying out the enantioselective hydrolysis studies of racemic esters by using immobilized lipase. Enantiomeric excesses of the products in the enantioselective hydrolysis of racemic ibuprofen and naproxen methyl ester and racemic butyl mandelate were determined to be 94.93, 77.30 and 68.15, respectively.

Interfacially crosslinked β-cyclodextrin polymer composite porous membranes for fast removal of organic micropollutants from water by flow-through adsorption

Persistent organic micropollutants have seriously damaged aquatic ecological equilibrium and affected human health. Conventional adsorbents are limited due to slow adsorption rate. Therefore, it's significant to integrate adsorbent into porous membrane to develop a highly efficient continuous filtration method for water purification. Herein, β-cyclodextrin polymer (β-CDP) composite porous membranes were prepared via convenient interfacial cross-linking. The membranes combined the adsorption ability of β-CDP and the convective mass transport process of filtration membrane to quickly remove contaminants from water by flow-through adsorption. In optimized preparation conditions, the composite membrane exhibited a 100% of removal efficiency towards bisphenol A and a high treating capacity up to 440 mg m^-2. The treating capacity kept nearly unchanged in acidic and neutral pH condition, while increased greatly with the addition of salts due to the salting-out effect. Also, the membrane could completely remove pollutants with ultrahigh flux up to 2500 L·m^-2 h^-1. In addition, the used membranes were fully regenerated by mild ethanol cleaning.

Adsorption of Direct Blue 78 Using Chitosan and Cyclodextrins as Adsorbents

The dyeing industry is one of the most polluting in the world. The adsorption of dyes by polymeric matrixes can be used to minimize the discharge of dyes into the environment. In the present study, chitosan-NaOH and β-cyclodextrin-epichlorohydrin polymers were used to remove the dye Direct Blue 78 from a wastewater model. To understand the adsorption behavior of Direct Blue 78 onto the polymers, adsorption rate and maximum adsorption capacity were calculated using kinetic tests and isotherm curves respectively. The kinetic data and mechanism of the adsorption process were analyzed by three models and the equilibrium data by three adsorption isotherms; also the different thermodynamic parameters were calculated. Results showed that the adsorption process follows pseudo-second-order kinetics in both polymers and the Langmuir isotherm best-fitted data for chitosan-NaOH polymer and the Freundlich isotherm for the β-CDs-EPI polymer. The adsorption process is exothermic in both cases and spontaneous for the β-CDs-EPI polymer to a certain temperature and not spontaneous for the chitosan-NaOH polymer and β-CDs-EPI polymer at higher temperatures. The complementary action of an advanced oxidation process eliminated >99% of the dye from water. The coupled process seems to be suitable for reducing the environmental impact of the dyeing industry.

Pineapple Bark Performance in Dyes Adsorption: Optimization by the Central Composite Design

This work is concerned with the study of the adsorption in aqueous medium of a three-dye mixture which contains Methylene Blue, Brilliant Green, and Congo Red on the pineapple bark. This adsorbent material has been characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The experimental design methodology, based on the response surface methodology (RSM) by the central composite design (CCD), has been applied for the optimization of the parameters, namely, the temperature, dose of the adsorbent, and pH. The yield reached 98.91% under optimal conditions (T = 30°C; adsorbent dose = 2.5 g·L−1; pH = 9.8) at an initial concentration of 20 mg·L−1.

A porous β-cyclodextrin-based terpolymer fluorescence sensor for in situ trinitrophenol detection

Permanent porosity plays a key role in fluorescent-based polymers with “on–off” emissive properties due to the role of guest adsorption at accessible fluorophore sites of the polymer framework. In particular, we report on the design of a porous fluorescent polymer (FL-PFP) composed of a covalently cross-linked ternary combination of β-cyclodextrin (β-CD), 4,4′-diisocyanato-3,3′-dimethyl biphenyl (DL) and tetrakis(4-hydoxyphenyl)ethene (TPE). The textural properties of FL-PFP were evaluated by the gas uptake properties using N₂ and CO₂ isotherms. The BET surface area estimates according to N₂ uptake ranged from 100–150 m² g⁻¹, while a lower range of values (20–30 m² g⁻¹) was estimated for CO₂ uptake. Model nitroarenes such as trinitrophenol (TNP) and nitrobenzene (NB) were shown to induce turn-off of the fluorescence emission of the polymer framework at concentrations near 50 nM with ca. 50% fluorescence quenching upon TNP adsorption and detection. The strong donor–acceptor interaction between the nitroarenes and the TPE reporter unit led to fluorescence quenching of FL-PFP upon nitroarene adsorption. The fluorescence lifetime (τ) for FL-PFP (τ = 3.82 ns) was obtained along with a quantum yield estimate of 0.399 relative to quinine sulphate. The β-CD terpolymer reported herein has significant potential for monitoring the rapid and controlled detection of nitroarenes (TNP and NB) in aquatic environments and other complex media.

Permanent porosity plays a key role in fluorescent-based polymers with “on–off” emissive properties due to the role of guest adsorption at accessible fluorophore sites of the polymer framework.