Adsorption performance and mechanisms of Pb(II), Cd(II), and Mn(II) removal by a β-cyclodextrin derivative

Super capacity of ligand-engineered biochar for sorption of malachite green dye: key role of functional moieties and mesoporous structure

This study synthesized a new thiomalic acid-modified rice husk biochar (TMA-BC) as a versatile and eco-friendly sorbent. After undergoing chemical treatments, the mercerized rice husk biochar (NaOH-BC) and TMA-BC samples showed higher BET surface area values of 277.1 m2/g and 305.8 m2/g, respectively, compared to the pristine biochar (BC) sample, which had a surface area of 234.2 m2/g. In batch adsorption experiments, it was found that the highest removal efficiency for malachite green (MG) was achieved with TMA-BC, reaching 96.4%, while NaOH-BC and BC exhibited removal efficiencies of 38.6% and 27.9%, respectively, at pH 8. The engineered TMA-BC exhibited a super adsorption capacity of 104.17 mg/g for MG dye at pH 8.0 and 25 °C with a dosage of 2 g/L. The SEM, TEM, XPS, and FTIR spectroscopy analyses were performed to examine mesoporous features and successful TMA-BC carboxylic and thiol functional groups grafting on biochar. Electrostatic forces, such as π - π interactions, hydrogen bonding, and pore intrusion, were identified as key factors in the sorption of MG dye. As compared to single-solution adsorption experiments, the binary solution experiments performed at optimized dosages of undesired ions, such as humic acid, sodium dodecyl sulfate surfactant, NaCl, and NaSCN, reflected an increase in MG dye removal of 2.8%, 8.7%, 5.4%, and 12.7%, respectively, which was attributed to unique mesoporous features and grafted functional groups of TMA-BC. Furthermore, the TMA-BC showed promising reusability up to three cycles. Our study indicates that mediocre biochar modified with TMA can provide an eco-friendly and cost-effective alternative to commercially accessible adsorbents.

β-cyclodextrin polymer composites for the removal of pharmaceutical substances, endocrine disruptor chemicals, and dyes from aqueous solution- A review of recent trends

Cyclodextrin (CD) and its derivatives are receiving attention as a new-generation adsorbent for water pollution treatment due to their external hydrophilic and internal hydrophobic properties. Among types of CD, β-Cyclodextrin (βCD) has been a material of choice with a proven track record for a range of utilities in distinct domains, owing to its unique cage-like structural conformations and inclusion complex-forming ability, especially to mitigate emerging contaminants (ECs). This article outlines βCD composites in developing approaches of their melds and composites for purposes such as membranes for removal of the ECs in aqueous setups have been explored with emphasis on recent trends. Electrospinning has bestowed an entirely different viewpoint on polymeric materials, comprising βCD, in the framework of diverse functions across a multitude of niches. Besides, this article especially discusses βCD polymer composite membrane-based removal of contaminants such as pharmaceutical substances, endocrine disruptors chemicals, and dyes. Finally, in this article, the challenges and future directions of βCD-based adsorbents are discussed, which may shed light on pragmatic commercial applications of βCD polymer composite membranes.

Graphene oxide@Fe3O4-decorated iota-carrageenan composite for ultra-fast and highly efficient adsorption of lead (II) from water

The aggravated problem of lead pollution, especially in aquatic environments, necessitates the development of eminent adsorbents that could radically solve this environmental problem. Hence, a new composite was constructed based on iota carrageenan (i.Carr), graphene oxide (GO) and magnetite (Fe3O4) for removing noxious Pb2+ ions. The GO@Fe3O4-i.Carr composite was characterized by VSM, SEM, XPS, XRD, FTIR and Zeta potential. The removal of Pb2+ ions attained a quick equilibrium of almost 30 min with a removal efficiency reaching 93.68 %. The removal of Pb2+ was boosted significantly, in the order of GO@Fe3O4-i.Carr(1:1) > GO@Fe3O4-i.Carr(1:3) > GO@Fe3O4-i.Carr(3:1). Moreover, acquired experimental data fitted the pseudo 2nd order kinetic model and Freundlich isotherm model with a maximal monolayer adsorption capacity reached 440.05 mg/g. Notably, after five adsorption runs, the composite maintained its removal efficiency exceeding 74 %. The assumed adsorption mechanisms of Pb2+ onto GO@Fe3O4-i.Carr were complexation, precipitation, Lewis acid-base, and electrostatic attraction forces. Overall, the GO@Fe3O4-i.Carr composite elucidated the auspicious adsorbent criteria, comprising fast adsorption with high performance, ease-separation and tolerable recyclability, advising its feasible use to decontaminate water bodies from hazardous heavy metals.

Recent Advancements in Cyclodextrin-Based Adsorbents for the Removal of Hazardous Pollutants from Waters

Water is an essential substance for the survival on Earth of all living organisms. However, population growth has disturbed the natural phenomenon of living, due to industrial growth to meet ever expanding demands, and, hence, an exponential increase in environmental pollution has been reported in the last few decades. Moreover, water pollution has drawn major attention for its adverse effects on human health and the ecosystem. Various techniques have been used to treat wastewater, including biofiltration, activated sludge, membrane filtration, active oxidation process and adsorption. Among the mentioned, the last method is becoming very popular. Moreover, among the sorbents, those based on cyclodextrin have gained worldwide attention due to their excellent properties. This review article overviewed recent contributions related to the synthesis of Cyclodextrin (CD)-based adsorbents to treat wastewater, and their applications, especially for the removal of heavy metals, dyes, and organic pollutants (pharmaceuticals and endocrine disruptor chemicals). Furthermore, new adsorption trends and trials related to CD-based materials are also discussed regarding their regenerative potential. Finally, this review could be an inspiration for new research and could also anticipate future directions and challenges associated with CD-based adsorbents.

A review on remediation technologies using functionalized Cyclodextrin

Modern lifestyle and alleviated anthropogenic activities have increased the pollutant load, ultimately causing stress on the environment. In industrialization, many harmful compounds are released into the environment polluting air, water, and soil, triggering adverse impacts on the ecosystem and human beings. Therefore, the development of advanced remediation technologies turns out as a significant environmental priority. Less polar cyclic oligosaccharide Cyclodextrin (CD) with cavity binding organic compounds attracted attention by helping effectively as environmental application. The formation of inclusion complexes and modified Cyclodextrin by cross-linking or surface modification enhances their capacity to abate pollutant effectively from the environment. Modification results in the formation of several novel materials such as CD-based composites, nanocomposites, crosslinked polymer or hydrogels, potent cross-linkers, CD-based membranes, and CD immobilized supports. Several environmental remediation technologies based on Cyclodextrin and modified Cyclodextrin have been discussed in detail in this review. Various environmental applications of Cyclodextrin and its derivatives have been discussed, along with their formation, properties, and characterization. Effective removal of organic pollutants, inorganic pollutants, micropollutants, volatile compounds etc., has been explained using several remediation technologies. Based on CD innocuity, this is referred to as the green process. The reversible equilibrium corresponded by the inclusion phenomenon sets a significant trend in the field of CD environmental application to develop techniques by incorporating supramolecular chemistry as well as irreversible methods such as biodegradation and advanced oxidation. It helps in the complete removal of pollutants and ultimately recycling the CD.

A flexible self-healing Zn3V2O7(OH)2·2H2O-based Zn-ion battery under continuous folding and twisting

Engineering flexible and self-healing batteries is significant for wearable electronics. Here, we develop a flexible self-healing Zn-ion battery with a three-dimensional Zn3V2O7(OH)2·2H2O cathode working with polyvinyl alcohol and Zn2+/Mn2+ ions-based...

Preparation of hemicellulose-based hydrogels from biomass refining industrial effluent for effective removal of methylene blue dye

Cold caustic extraction (i.e. CCE) is an essential technique for removing hemicellulose from paper-grade pulp and thus obtaining high-purity dissolving pulp in pulp and paper industry. The generated wastewater from the CCE process contains large amounts of valuable hemicellulose which should be properly treated in a cost-effective way. Therefore, in this research, the hemicellulose has been used as a raw material for preparing hemicellulose-graft-polyacrylamide (hemi-g-pAAm) hydrogel particles for efficiently adsorbing methylene blue (MB) from aqueous solutions. The mass transfer kinetic behaviours of hemicellulose during a multiple CCE process were also studied. The MB adsorption kinetic test results showed that the removal efficiency can be higher than 90% for the simulated wastewater containing 500 mg/L of MB. Of note, the maximum removal capacities for the wastewater samples containing 500 and 1000 mg/L of MB could be reached up to ∼1800 and ∼2300 (mg/g) respectively with the equilibrium time of ∼40 min. Compared to other reported materials, the superior adsorption performance of the prepared hemicellulose-based hydrogel proved its great potential for application in the wastewater treatment of dye industry.

A manganese (II)-based coordinative dendrimer with robust efficiency in intracellular peptide delivery

Peptides have gained increasing interests as drug candidates in modern pharmaceutical industry, however, the development of peptide drugs acting on intracellular targets is limited due to their membrane impermeability. Here, we reported the use of metal-terpyridine based coordinative dendrimer for cytosolic peptide delivery. Among the investigated transition metal ions, Mn²⁺-coordinated polymer showed the highest delivery efficiency due to balanced peptide binding and release. It showed robust efficiency in the delivery of peptides with different charge property and hydrophobicity into various primary cells. The efficiency of Mn²⁺-terpyridine based polymer is superior to cell penetrating peptides such as oligoarginines. The material also delivered an autophagy-inducing peptide derived from Beclin-1 into cells and efficiently induced autophagy in the cells. This study provides a promising alternative to cell penetrating peptides for cytosolic peptide delivery.

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A Mn²⁺/terpyridine based polymer is rationally designed for cytosolic peptide delivery.

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The polymer shows robust efficiency in the delivery of 22 peptides with different properties into various primary cells.

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The polymer delivers an autophagy-inducing peptide derived from Beclin-1 into cells and efficiently induces autophagy.

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This study provides a promising alternative to cell penetrating peptides for cytosolic peptide delivery.

Facile separation of enantiomers via covalent organic framework bonded stationary phase

Covalent organic frameworks (COFs), a type of crystalline polymers, have attracted increasing interest because of their controllability of geometry and functionality. Featuring infinitely extended networks and tremendous interaction sites, COFs emerge as a potential platform for separation science. Here, a novel chiral COF (β-CD COF_BPDA) constructed by the imine condensation of 4,4'-biphenyldicarboxaldehyde and heptakis(6-amino-6-deoxy)-β-cyclodextrin was introduced into an electrochromatographic system via a photopolymerization method and applied to the separation of enantiomers. The structure and properties of as-synthesized β-CD COF_BPDA were investigated by powder X-ray diffraction (PXRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and N₂adsorption-desorption isotherms. It was proved that β-CD COF_BPDA was provided with larger pore size and BET surface area. The β-CD COF_BPDA coating endowed the chiral stationary phase with superior three-dimensional orientation, and realized satisfactory separation with improved selectivity and column efficiency for a dozen racemic drugs. Under the optimized conditions, homatropine, ondansetron, metoprolol, terbutaline, tulobuterol, and promethazine were all baseline separated with resolution values of 2.24, 2.03, 1.65, 1.62, 1.60, and 1.58, respectively. The results indicate the high perspective of COF modified stationary in enantioseparation.

[Recent developments of pesticide adsorbents based on cyclodextrins]

The invention and application of pesticides have greatly increased the yield of crops, greatly contributing to ensuring people's basic livelihoods and gradually improving their livelihoods to a well-off level. However, foods, water sources, and soil, containing high levels of pesticide residues, result in increasingly serious pollution. Pesticide residues usually have the characteristics of micro toxicity, difficult biodegradation, and bioaccumulation, and thus pose serious threat to living organisms and ecosystems. In recent years, pesticide pollution has earned worldwide focus. Thus, methods for the efficient detection of trace pesticides and reduction of the harm caused by pesticide pollution are urgently required. Researchers have used catalysis, electrochemistry, membrane separation, adsorption, and other methods to enrich pesticides from complex matrices. Among these, adsorbents have attracted much attention owing to their advantages of simple operation steps, rapid treatment process, and low amounts of organic solvents required. Research on adsorption materials has always been a very active field, and is also the key to the success of separation and enrichment of pesticides from complex matrices. Development of adsorbents with the advantages of simple synthesis, environment-friendliness, high stability, and strong reusability is of great significance. There has been some progress in the field of pesticide adsorption using supramolecular compounds. Cyclodextrin is a macrocyclic compound with a cavity after crown ether, which can form inclusion complexes via host guest interactions as the main body. Cyclodextrin can also be modified by etherification, esterification, oxidation, and other chemical reactions to improve its adsorption performance. Pesticides can be classified into organic and inorganic substances. One of the most widely used inorganic fungicides is the Bordeaux solution, whose main component is Cu²⁺. Organic fungicides, insecticides, herbicides, and plant growth regulators are basically organic molecules, whose hydroxyl and carboxyl groups can form complexes with Cu²⁺. As a matrix, cyclodextrin not only increases the surface area of the materials, but also provides the binding sites of hydroxyl and carboxyl groups, which guarantees efficient enrichment of Cu²⁺. Organic pesticides with high polarity, high electron density, and strong hydrophobicity could be better adsorbed. In this paper, the application of cyclodextrin-based adsorbents in pesticide adsorption was reviewed, and on this basis, reference to future development directions and application prospects were provided. The adsorption capacity of individual pesticide adsorbents based on cyclodextrin, as reviewed in this paper, is not high enough. Therefore, improving the adsorption capacity is currently a major research target. Some of the above-mentioned adsorbents have unclear degradation mechanisms and can easily cause secondary pollution. Therefore, the development of environment-friendly pesticide adsorbents that are easy to regenerate is a promising research direction for the future. After adsorption, some detection methods are used to determine whether the pesticide residues are up to the standard; however, the detection instruments are expensive. Therefore, the development of a combined detection mechanism that can reduce workload and cost is a promising research direction. Finally, the development of smart cyclodextrin-based adsorbents is also an efficient and rapid method to reduce the cost of detecting residual pesticide concentrations and the risk of pesticide pollution. For example, intelligent materials, whose color changes can be observed by the naked eye, not only adsorb pesticides, but also respond according to the concentration of residual pesticides.

Value-added utilization of paper sludge: Preparing activated carbon for efficient adsorption of Cr(VI) and further hydrogenation of furfural

After normal alkali treatment process, the industrial Cr(VI) containing wastewater still contains a ppm level of Cr(VI) ions which should be further purified before discharging. In this study, the Cr(VI)-containing wastewater has been efficiently treated by the porous paper sludge-based activated carbon (psAC) with an excellent specific surface area and rich oxygen functional groups. The batch experimental results showed that under acidic conditions, pH has little effect on the Cr(VI) removal. The kinetic and isotherms studies showed that the Elovich and Freundlich model could describe the adsorption process well and the maximum adsorption capacity of psAC was 54.04 mg/g. The thermodynamic studies indicated that the reaction process was endothermic and spontaneous. Adsorption enthalpy was 17.37 kJ/mol, showing that the chemisorption process was a hydrogen bonding-controlled that has been also verified by some analytical techniques. Lastly, this study also provided an idea for reutilization of waster Cr(VI)-contained psAC in furfural hydrogenation.

Enhanced Pb(II) adsorption onto functionalized ordered mesoporous carbon (OMC) from aqueous solutions: the important role of surface property and adsorption mechanism

Functionalized ordered mesoporous carbon (MOMC-NP) was synthesized by chemical modification using HNO₃ and H₃PO₄ to enhance Pb(II) adsorption. The phosphate functional group represented by P-O-C bonding onto the surface of OMC was verified by FT-IR and XPS. Batch adsorption experiments revealed the improvement of adsorption capacity by 39 times over the virgin OMC. Moreover, the Pb(II) adsorption results provided excellent fits to Langmuir model and pseudo-second-order kinetic model. The adsorption mechanism of Pb(II) onto MOMC-NP revealed the formation of metal complexes with carboxyl, hydroxyl, and phosphate groups through ion exchange reactions and hydrogen bondings. The calculated activation energy was 22.09 kJ/mol, suggesting that Pb(II) adsorption was a chemisorption. At pH>pH_pzc, the main Pb(II) existing species of Pb(II) and Pb(OH)⁺ combine with the carboxyl, hydroxyl, and phosphate functional groups via electrostatic interactions and hydrogen bonding. All these findings demonstrated that MOMC-NP could be a useful and potential adsorbent for adsorptive removal of Pb(II). Graphical abstract.

PDA-cross-linked beta-cyclodextrin: a novel adsorbent for the removal of BPA and cationic dyes

In this study, 4,4'-(hexafluoroisopropene) diphthalic acid (PDA)-CD polymers containing β-cyclodextrin (CD) were synthesized for the adsorption of endocrine disrupting chemicals (EDCs) and dyes. It features great adsorption of bisphenol A (BPA), methylene blue (MB) and neutral red (NR). The maximum adsorption capacities of MB, NR and BPA can reach 113.06, 106.8 and 51.74 mg/g, respectively. The tandem adsorption results revealed that adsorptions of dyes and BPA onto PDA-CD polymer were two independent processes: non-polar BPA entrapment by cyclodextrin cavities while dyes were captured by the carboxyl groups and π-π stacking interactions. The adsorption processes performed well in a wide range of pH (4.0-10.0) and were not affected by fulvic acid (FA) and inorganic ions.

Novel cyclodextrin-based adsorbents for removing pollutants from wastewater: A critical review

Over the past few decades, cyclodextrin-based adsorbents have drawn worldwide attention as new-generation adsorbents for wastewater treatment due to its extraordinary physicochemical properties. This review outlined the recent development in the synthesis of cyclodextrin-based adsorbents as well as highlighted their applications in the removal of heavy metals, dyes, endocrine disrupting chemicals (EDCs), and mixed pollutants from water. The cross-linked and immobilized cyclodextrin-based adsorbents exhibited excellent adsorption performances. The removal of dyes and heavy metals were effectively controlled by ion exchanging, mainly depending upon the pH; while the adsorptions of EDCs always occurred in cyclodextrin cavities and pH-independent. An easier separation process between aqueous and adsorbents could be achieved compared to native cyclodextrin, which promoted the application of cyclodextrin-based adsorbents in practical industry. This review could provide an inspiration for the advanced study in the development of cyclodextrin-based adsorbents for high efficiency wastewater treatment.

Construction of β-Cyclodextrin Covalent Organic Framework-Modified Chiral Stationary Phase for Chiral Separation

Chiral covalent organic frameworks (CCOFs), built by the condensation reactions of organic building blocks with enantiomeric purity and linking subunits, have emerged as a marvelous category of porous crystalline material. In addition to stability and good porosity, CCOFs possess remarkable enantioselectivity, which would be exploited for asymmetric catalysis and chiral separation. β-cyclodextrin (β-CD) and its derivatives, a group of supramolecules with a hydrophobic cavity, have been widely applied to molecular specific recognitions. In this work, the β-CD covalent organic framework (COF) was exploited to construct chiral stationary phase (CSP) for chiral drugs analysis for the first time. We fabricated β-CD COF via the condensation reaction of heptakis(6-amino-6-deoxy)-β-CD and terephthalaldehyde at room temperature. β-CD COF-modified capillary columns were subsequently prepared by a photopolymerization method with shortened time and applied for separation of chiral drugs on capillary electrochromatography with good resolution and repeatability. Baseline separation for six enantiomers was achieved and the precisions (relative standard deviations) for intraday, interday, and column-to-column were <2.1%, 4.5%, and 7.3%, respectively. The results reveal that CCOFs-coated capillary columns show great prospect for chromatographic separation of chiral drugs.

Three-dimensional porous graphene oxide-maize amylopectin composites with controllable pore-sizes and good adsorption-desorption properties: Facile fabrication and reutilization, and the adsorption mechanism

Three-dimensional (3D) porous graphene oxide-maize amylopectin (GO-MA) composites with controllable pore-sizes composites in the range of 6-40 nm were prepared by facile hydrothermal-assisted assembly approaches. The morphologies, pore sizes, specific surface area (SSA) and compositions of GO-MA_x:y composites with and different GO-to-MA mass ratios (x:y) were characterized by scanning electron microscopy (SEM), N₂ adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). To reveal the adsorption-desorption mechanism, effects of contact time, temperature, initial adsorbate concentration, pH value of the solution on the adsorption process were studied in detail. The adsorption capacities of 3D GO-MA_20:1 composite for organic contaminants including tert-butyl hydroquinone (TBHQ), p-aminophenol (PAP), p-nitrophenol (PNP), o-nitrophenol (MNP), hydroquinone (HQ), alizarin red S (ARS) and neutral red (NR) were 22.17, 116.4, 44.78, 36.96, 16.10, 39.92 and 24.23 mg g^-1, respectively. The adsorption capacities of GO-MA_30:1 composite for inorganic substances including Pb²⁺, Mn²⁺, Cr₂O₇^2-, Cd²⁺, Cu²⁺, Nd³⁺, La³⁺, Y³⁺, Yb³⁺ and Er³⁺ were 84.76, 7.92, 13.6, 17.64, 30.56, 25.52, 12.48, 16.96, 23.32 and 30.32 mg g^-1, respectively. In addition, GO-MA_x:y composites also exhibited high mechanical properties and good reusability. Consequently, GO-MA_x:y composites could be used as reusable adsorbents for removal/enrichment inorganic/organic substances in aqueous solutions.