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

Removal of contaminants present in water and wastewater by cyclodextrin-based adsorbents: A bibliometric review from 1993 to 2022

Cyclodextrin (CD), a cyclic oligosaccharide from enzymatic starch breakdown, plays a crucial role in pharmaceuticals, food, agriculture, textiles, biotechnology, chemicals, and environmental applications, including water and wastewater treatment. In this study, a statistical analysis was performed using VOSviewer and Citespace to scrutinize 2038 articles published from 1993 to 2022. The investigation unveiled a notable upsurge in pertinent articles and citation counts, with China and USA contributing the highest publication volumes. The prevailing research focus predominantly revolves around the application of CD-based materials used as adsorbents to remove conventional contaminants such as dyes and metals. The CD chemistry allows the construction of materials with various architectures, including cross-linked, grafted, hybrid or supported systems. The main adsorbents are cross-linked CD polymers, including nanosponges, fibres and hybrid composites. Additionally, research efforts are actually concentrated on the synthesis of CD-based membranes, CD@graphene oxide, and CD@TiO2. These materials are proposed as adsorbents to remove emerging pollutants. By employing bibliometric analysis, this study delivers a comprehensive retrospective review and synthesis of research concerning CD-based adsorbents for the removal of contaminants from wastewater, thereby offering valuable insights for future large-scale application of CD-based adsorption materials.

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.

Characterization of New Polymer Material of Amino-β-Cyclodextrin and Sodium Alginate for Environmental Purposes

The β-cyclodextrin polymer (PβCD) cross-linked with pyromellitic dianhydride (PD) and functionalized with an amino group (PAβCD) was introduced into a matrix made of sodium alginate (SA). Scanning electron microscopy (SEM) images showed a homogeneous surface of the composite material. Infrared spectroscopy (FTIR) testing of the PAβCD confirmed polymer formation. The tested polymer increased its solubility relative to the polymer without the amino group. Thermogravimetric analysis (TGA) confirmed the stability of the system. Differential scanning calorimetry (DSC) showed the chemical binding of PAβCD and SA. Gel permeation chromatography (GPC-SEC) showed high cross-linking of PAβCD and allowed for accurate determination of its weight. The formation of the composite material such as PAβCD introduced into a matrix made of sodium alginate (SA) has several potential environmental implications, including the use of sustainable materials, reduced waste generation, reduced toxicity, and improved solubility.

Amphiphilically Modified Porous Polymeric Nanosandwich-Based Membranes for Rapid and Efficient Water Treatment

Low removal efficiency, long treatment time, and high energy consumption hinder advanced and eco-friendly use of traditional adsorbents and separation membranes. Here, a class of amphiphilically modified 2D porous polymeric nanosandwich is designed and is subsequently assembled into adsorptive membranes. The 2D nanosandwich is gifted with high porosity and excellent pore accessibility, demonstrating rapid adsorption kinetics. The as-assembled membrane integrates unimpeded interlayer channels and well-developed, amphiphilic, and highly accessible intralayer nanopores, leading to ultrafast water permeation (1.2 × 10⁴  L m^-2  h^-1  bar^-1 ), high removal efficiency, and easy regeneration. The family of the membrane can be expanded by changing amphiphilic functional groups, further providing treatment of a wide-spectrum of pollutants, including aromatic compounds, pesticide, and pharmaceuticals. It is believed that the novel amphiphilically modified adsorptive membrane offers a distinct water treatment strategy with ultrahigh water permeation and efficient pollutants removal performances, and provides a multiple-in-one solution to the detection and elimination of pollutants.

Coatings of Cyclodextrin/Citric-Acid Biopolymer as Drug Delivery Systems: A Review

In the early 2000s, a method for cross-linking cyclodextrins (CDs) with citric acid (CTR) was developed. This method was nontoxic, environmentally friendly, and inexpensive compared to the others previously proposed in the literature. Since then, the CD/CTR biopolymers have been widely used as a coating on implants and other materials for biomedical applications. The present review aims to cover the chemical properties of CDs, the synthesis routes of CD/CTR, and their applications as drug-delivery systems when coated on different substrates. Likewise, the molecules released and other pharmaceutical aspects involved are addressed. Moreover, the different methods of pretreatment applied on the substrates before the in situ polymerization of CD/CTR are also reviewed as a key element in the final functionality. This process is not trivial because it depends on the surface chemistry, geometry, and physical properties of the material to be coated. The biocompatibility of the polymer was also highlighted. Finally, the mechanisms of release generated in the CD/CTR coatings were analyzed, including the mathematical model of Korsmeyer-Peppas, which has been dominantly used to explain the release kinetics of drug-delivery systems based on these biopolymers. The flexibility of CD/CTR to host a wide variety of drugs, of the in situ polymerization to integrate with diverse implantable materials, and the controllable release kinetics provide a set of advantages, thereby ensuring a wide range of future uses.

Efficient capture of endocrine-disrupting compounds by a high-performance nanofiltration membrane for wastewater treatment

Conventional polyamide (PA) nanofiltration (NF) membranes can readily adsorb aromatic compounds, such as endocrine disrupting compounds (EDCs). Therefore, these substances can easily be transported across the membrane by solution-diffusion, resulting in a poor EDC-rejection. In this work, a novel thin film nanocomposite (TFN) membrane was fabricated by incorporating covalent organic frameworks (COFs) into the PA layer via an interfacial polymerization reaction. COFs with functional groups can provide abundant active binding sites for highly efficient EDC-capture. The rejection of the optimal TFN-COF membrane for bisphenol A, bisphenol AF, and sodium 2-biphenylate was 98.3%, 99.1%, and 99.3%, respectively, which was much higher than of the rejection of the pristine NF-membrane (82.4%, 95.5%, and 96.4%, respectively). Additionally, the TFN-COF membrane could be regenerated fast and efficiently by washing with ethanol for some minutes. COF nanofillers with porous structures provide additional water channels, making it possible to overcome the permeability-selectivity trade-off of NF membranes. The water permeance (17.1 L m^-2 h^-1 bar^-1) of the optimal membrane was about two times higher than for the pristine NF-membrane (8.7 L m^-2 h^-1 bar^-1). In addition, the TFN-COF membrane with a COF-loading of 0.05% w/v had an excellent Na₂SO₄ rejection (95.2%) due to size exclusion and strong Donnan effect. This work combines traditional NF membranes and adsorption materials to achieve efficient capture and rapid release of EDCs without sacrificing salt rejections, which opens the door to develop fit-for-purpose adsorptive NF membranes.

Microfiltration Membranes for the Removal of Bisphenol A from Aqueous Solution: Adsorption Behavior and Mechanism

This study mainly investigated the adsorption behavior and mechanism of microfiltration membranes (MFMs) with different physiochemical properties (polyamide (PA), polyvinylidene fluoride (PVDF), nitrocellulose (NC), and polytetrafluoroethylene (PTFE)) for bisphenol A (BPA). According to the adsorption isotherm and kinetic, the maximum adsorption capacity of these MFMs was PA (161.29 mg/g) > PVDF (80.00 mg/g) > NC (18.02 mg/g) > PTFE (1.56 mg/g), and the adsorption rate was PVDF (K1 = 2.373 h−1) > PA (K1 = 1.739 h−1) > NC (K1 = 1.086 h−1). The site energy distribution analysis showed that PA MFMs had the greatest adsorption sites, followed by PVDF and NC MFMs. The study of the adsorption mechanism suggested that the hydrophilic microdomain and hydrophobic microdomain had a micro-separation for PA and PVDF, which resulted in a higher adsorption capacity of PA and PVDF MFMs. The hydrophilic microdomain providing hydrogen bonding sites and the hydrophobic microdomain providing hydrophobic interaction, play a synergetic role in improving the BPA adsorption. Due to the hydrogen bonding force being greater than the hydrophobic force, more hydrogen bonding sites on the hydrophobic surface resulted in a higher adsorption capacity, but the hydrophobic interaction contributed to improving the adsorption rate. Therefore, the distribution of the hydrophilic microdomain and hydrophobic microdomain on MFMs can influence the adsorption capacity and the adsorption rate for BPA or its analogues. These consequences provide a novel insight for better understanding the adsorption behavior and mechanism on MFMs.

Microporous polymer adsorptive membranes with high processing capacity for molecular separation

Trade-off between permeability and nanometer-level selectivity is an inherent shortcoming of membrane-based separation of molecules, while most highly porous materials with high adsorption capacity lack solution processability and stability for achieving adsorption-based molecule separation. We hereby report a hydrophilic amidoxime modified polymer of intrinsic microporosity (AOPIM-1) as a membrane adsorption material to selectively adsorb and separate small organic molecules from water with ultrahigh processing capacity. The membrane adsorption capacity for Rhodamine B reaches 26.114 g m⁻², 10–1000 times higher than previously reported adsorptive membranes. Meanwhile, the membrane achieves >99.9% removal of various nano-sized organic molecules with water flux 2 orders of magnitude higher than typical pressure-driven membranes of similar rejections. This work confirms the feasibility of microporous polymers for membrane adsorption with high capacity, and provides the possibility of adsorptive membranes for molecular separation.

Trade-off between permeability and nanometer-level selectivity is an inherent shortcoming of membrane-based separation of molecules. Here, the authors report a membrane adsorption material based on hydrophilic amidoxime modified polymer of intrinsic microporosity to selectively adsorb and separate small organic molecules from water with ultrahigh processing capacity

Phosphate-crosslinked β-cyclodextrin polymer for highly efficient removal of Pb(ii) from acidic wastewater

Novel phosphate-crosslinked β-cyclodextrin polymer was synthesized for highly efficient Pb(ii) removal from acidic wastewater.

Facile metal-free synthesis of pyrrolo[3,2-b]pyrrolyl-based conjugated microporous polymers for high-performance photocatalytic degradation of organic pollutants

An efficient and metal-free approach to the synthesis of new kinds of CMPs (pyrrolo[3,2-b]pyrrolyl-based CMPs) on a gram scale within a short time has been developed for remarkable adsorbent and photocatalytic degradation of organic pollutants.

Novel Chemical Architectures Based on Beta-Cyclodextrin Derivatives Covalently Attached on Polymer Spheres

This study presents the synthesis and characterization of polymer derivatives of beta-cyclodextrin (BCD), obtained by chemical grafting onto spherical polymer particles (200 nm) presenting oxirane functional groups at their surface. The polymer spheres were synthesized by emulsion polymerization of styrene (ST) and hydroxyethyl methacrylate (HEMA), followed by the grafting on the surface of glycidyl methacrylate (GMA) by seeded emulsion polymerization. The BCD-polymer derivatives were obtained using two BCD derivatives with hydroxylic (BCD-OH) and amino groups (BCD-NH2). The degree of polymer covalent functionalization using the BCD-OH and BCD-NH2 derivatives were determined to be 4.27 and 19.19 weight %, respectively. The adsorption properties of the materials were evaluated using bisphenol A as a target molecule. The best fit for the adsorption kinetics was Lagergren's model (both for Qe value and for R2) together with Weber's intraparticle diffusion model in the case of ST-HEMA-GMA-BCD-NH2. The isothermal adsorption evaluation indicated that both systems follow a Langmuir type behavior and afforded a Qmax value of 148.37 mg g-1 and 37.09 mg g-1 for ST-HEMA-GMA-BCD-NH2 and ST-HEMA-GMA-BCD-OH, respectively. The BCD-modified polymers display a degradation temperature of over 400 °C which can be attributed to the existence of hydrogen bonds and BCD thermal degradation pathway in the presence of the polymers.

Fabrication of Antiswelling Loose Nanofiltration Membranes via a "Selective-Etching-Induced Reinforcing" Strategy for Bioseparation

With diverse selectivity, higher permeance, and good antifouling property, loose polyamide nanofiltration (NF) membranes can be potentially deployed in various bioseparation applications. However, the loose NF membrane with a low crosslinking degree generally suffers from the alkali-induced pore swelling during chemical cleaning, resulting in degradation of separation performance with time. In this work, we conceive a novel strategy to tailor the separating layer through alkaline post-etching following the interfacial polymerization process, where piperazine and tannic acid (TA) were used as water-phase monomers, and trimesoyl chloride (TMC) and ferric acetylacetonate were employed as organic monomers in n-hexane. Thereinto, the polyester network formed by TA and TMC was selectively etched by alkaline treatment, thus obtaining a loose NF membrane, whose structure and performance could be facilely tailored by controlling the TA ratio and the etching pH. As a result, the well-designed loose NF membrane exhibited higher flux, better selectivity, and more stable separation performance in a long-term filtration of diluted cane molasses. Interestingly, the obtained loose NF membrane showed excellent antiswelling ability during alkaline cleaning because of network locking induced by Fe³⁺ chelation, decrease in the carboxyl proportion (more hydroxyl generation due to the ester bond hydrolysis), and enhanced interface interaction between the separation layer and the sublayer attributed to catechol adhesion effect. Therefore, such a "selective-etching-induced reinforcing" strategy could endow the polyamide NF membrane with both loose and antiswelling separation layer in a reliable and scalable way, which provides a new perspective for preparing highly selective and stable NF membrane for resource recovery.

Ecotoxicological assessment of micropollutant Diclofenac biosorption on magnetic sawdust: Phyto, Microbial and Fish toxicity studies

Diclofenac (DCF), a persistent pharmaceutical micropollutant which occurs in the ecosystems causing adverse effects on aquatic as well as terrestrial organisms. In this study, magnetic sawdust (MSD) was prepared using co-precipitation method for biosorptive removal of DCF from water. The MSD was characterized using various analytical techniques like microscopic and spectroscopic analysis. Magnetometer study confirms the ferromagnetic behavior of the biosorbent which is a key advantage in the separation of MSD after biosorption. The effect of experimental parameters was optimized in batch mode with evaluated maximum efficiency of 86.12 % at pH 6, biosorbent dosage 25 mg for 50 mg/L of DCF. Ecotoxicological assessment has been performed for the treated and untreated sample using plant seeds, microbes and zebra fish to check the adverse effects of DCF on these organisms. Evaluation of toxicity studies revealed that inhibition concentration of DCF for various seeds (60.91 mg/L to 43.11 mg/L), E. coli (48.82 μg/mL) and B. subtilis (31.55 μg/mL). The lethal concentration of DCF on the Danio rerio was found to be 156.99 mg/L. In contrast, significant increase in both the concentration measures of DCF after biosorption was observed making this biosorbent a potent alternative to other available treatment measures.

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.

(E)-1,2-Diphenylethene-based conjugated nanoporous polymers for a superior adsorptive removal of dyes from water

A series of (E)-1,2-diphenylethene-based conjugated nanoporous polymers having extraordinary thermal stabilities, high surface areas, and superior adsorptive removal of dyes from water have been developed.

Palladium nanoparticle loaded β-cyclodextrin monolith as a flow reactor for concentration enrichment and conversion of pollutants based on molecular recognition

This study reports pollutant remediation by a catalyst-loaded, β-cyclodextrin cross-linked polymer monolith. The monolith enabled removal of the pollutant to a residual concentration with no environmental effect and conversion of the adsorbed pollutant into useful compounds with enriched concentration, allowing for the adsorption capacity regeneration.

Nonthermal Plasma Treatment Improves Uniformity and Adherence of Cyclodextrin-Based Coatings on Hydrophobic Polymer Substrates

Low surface energy substrates, which include many plastics and polymers, present challenges toward achieving uniform, adherent coatings, thus limiting intended coating function. These inert materials are common in various applications due to favorable bulk, despite suboptimal surface, properties. The ability to functionally coat low surface energy substrates holds broad value for uses across medicine and industry. Cyclodextrin-based materials represent an emerging, widely useful class of coatings, which have previously been explored for numerous purposes involving sustained release, enhanced sorption, and reversible reuse thereof. In this study, substrate exposure to nonthermal plasma was explored as a novel means to improve uniformity and adherence of cyclodextrin-based polyurethane coatings upon unreceptive polypropylene substrates. Plasma effects on substrates were investigated using contact angle goniometry and X-ray photoelectron spectroscopy (XPS). Plasma impact on coating uniformity was assessed through visualization directly and microscopically. Plasma effects on coating adhesion and bonding were studied with mechanical lap-shear testing and XPS, respectively. Substrate surface wettability and oxygen content increased with plasma exposure, and these modifications were associated with improved coating uniformity, adhesion, and interfacial covalent bonding. Findings demonstrate utility of, and elucidate mechanisms behind, plasma-based surface activation for improving coating uniformity, adherence, and performance on inert polymeric substrates.

Supramolecular adsorption of cyclodextrin/polyvinyl alcohol film for purification of organic wastewater

Into purified organic wastewater, α-, β-, and γ-cyclodextrin (α-, β-, and γ-CD) were added to polyvinyl alcohol (PVA) with ammonium persulfate as the crosslinker. The CD/PVA composite film with low water solubility and supramolecular adsorption was prepared by solvent evaporation. Fourier transform infrared spectroscopy showed that when CD was successfully added to PVA, the crosslinking process had no effect on -OH, and the structure was stable after soaking in water for 120 h. Solubility experiments showed that the stability of PVA in water was significantly improved. The results of phenolphthalein adsorption showed that the composite film followed the Langmuir isothermal adsorption and the pseudo-second-order kinetics. According to the Langmuir equation, the theoretical maximum adsorption capacities of α-, β- and γ-CD/PVA composite films were 0.41, 2.05, and 2.00 mg/g, respectively. The parameters of the Freundlich equation indicate that the adsorption of the composite film is physical adsorption. The time for α-CD/PVA composite film to reach equilibrium was the shortest, while the longest was for β-CD/PVA composite film. The intraparticle diffusion model showed that the adsorption was mainly affected by the diffusion of the boundary layer, and the diffusion rate limitation of the boundary layer of the high-concentration phenolphthalein solution was more obvious.