Construction of magnetic bifunctional β-cyclodextrin nanocomposites for adsorption and degradation of persistent organic pollutants

An eco-friendly self-assembled catalyst preparation and study of tetracycline degradation: Performance, mechanism to application

Chloromethyl styrene resin can undergo specific chemical modifications and is an excellent adsorbent material for treating difficult-to-degrade substances in wastewater. In this study, chloromethyl styrene resin will be used as a carrier, and polystyrene chloromethyl resin (PS-Cl) was converted into PS-NH2 by amino modification. The self-assembly of cobalt-based metal-organic framework (CoMOF) was induced on the surface of PS-NH2 by using a novel preparation technique. The performance of the prepared PS-NH2@CoMOF self-assembled catalysts with core-shell-like structures in degrading the target pollutant, tetracycline (TC), was evaluated. The catalysts effectively induced rapid OH radical production from H2O2, had a degradation rate of as high as 88.3 % for 20 mg/L TC solution, and were highly stable and adaptable to aqueous environments. Free radicals and intermediates in the catalytic degradation process were detected by electron paramagnetic resonance and high-performance liquid chromatography mass spectrometry, and possible catalytic degradation pathways were analyzed. The catalytic dissociation behavior of H2O2 in the presence of different catalysts was studied in depth and compared with that of similar metal-organic framework materials through density-functional theory calculations. Results demonstrated the excellent performance of the PS-NH2@CoMOF catalysts. Finally, the catalysts' potential for use in practical engineering applications was evaluated with a flow column experimental model, and the results were more than satisfactory. Therefore, the use of the catalysts to degrade TC has great potential.

Molecular level investigation of interactions between pharmaceuticals and β-cyclodextrin (β-CD) functionalized adsorption sites for removal of pharmaceutical contaminants from water

This study describes a novel application of the use of molecular modeling tools for investigating the adsorption of organic micropollutants (OMPs) from water by nanocomposites. The partitioning of pharmaceuticals onto β-Cyclodextrin (β-CD) functionalized adsorbents was investigated at the molecular level to explore the atomistic interactions of pharmaceutical contaminants in water systems with β-CD and to provide insight into possible approaches for removal of pharmaceuticals from water. Molecular electrostatic surface potential mapping of β-CD derivatives was employed to examine the impact of substitution degree of β-CD and type of grafting agent on host-guest complexation. The stability of the complexes of selected pharmaceuticals and β-CD derivatives were assessed via molecular dynamics simulations to evaluate competitive adsorption between organic micropollutants (OMPs) and between OMPs and fulvic acid, a representative natural organic material (NOM) component found in water systems. Molecular electrostatic surface potential maps showed that grafting agents with aromatic and amine functional groups were found to provide attractive interactions for negatively charged OMPs. In addition, optimization of substitution degree of β-CD is necessary to enhance adsorption of target OMPs. Furthermore, it was found that aromatic ring bearing grafting agents can provide additional electrostatic attractions by π-π interactions with the aromatic ring of the OMPs. The impact of common water quality characteristics on adsorption was assessed and it was revealed that the effect of pH and calcium on adsorption depends on the ionizable functional groups present on the grafting agent. Molecular dynamics simulations showed that adsorption of target OMPs does not solely depend on hydrophobicity but is affected by electrostatic interactions. The simulations revealed that fulvic acid which is commonly present in environmental waters can be a competitor with ibuprofen for the β-CD cavity. Ultimately, this study showed that molecular level simulation can be effectively employed to investigate adsorption of OMPs by β-CD functionalized adsorbents and could be employed to enhance their design and subsequent environmental applications.

β-Cyclodextrin functionalized adsorbents for removal of organic micropollutants from water

The presence of organic micropollutants in water is an ongoing concern due to the potential risks to living organisms. β-Cyclodextrin-based adsorbents have been developed to remove organic micropollutants from water as they are deemed to be efficient, selective and reusable. This literature review establishes the current state of the knowledge on the application of β-Cyclodextrin adsorbents for the removal of organic micropollutants from water and determines knowledge gaps and recommendations for future studies. An inventory of organic micropollutants that have been studied was developed and it revealed that bisphenol-A has been the most commonly studied. Adsorbent configurations were reviewed and modifications to the adsorbent structures that have provided enhanced adsorption properties were identified. The size and shape of the organic micropollutants was found to affect the adsorption behavior. The surface charge of β-Cyclodextrin adsorbents influence adsorption when repulsive forces are present and the extent of repulsion can depend on the pH of the solution. Common competitors such as natural organic matter and inorganic ions do not significantly impact the adsorption of organic micropollutants however relatively small fulvic acids may compete for the β-Cyclodextrin cavity depending on the adsorbent type. Desorption of organic micropollutants from these adsorbents has been accomplished with alcohols and most adsorbents have been recovered and reused in adsorption/desorption cycles. The need for enhanced recovery processes that maintain water quality and adsorbent integrity was identified. The use of quantitative structure-activity relationships and molecular computational tools could potentially guide future environmental applications of β-Cyclodextrin adsorbents.

Development of a TiO2/Sepiolite Photocatalyst for the Degradation of a Persistent Organic Pollutant in Aqueous Solution

A clay-based TiO₂ nanocomposite material was synthesized by a facile method, to investigate its structure and photocatalytic efficiency. The supported TiO₂ nanoparticles were generated using a sol-gel method, and subsequently, mixed with a suspension of sepiolite. The material was recovered in powder form (Mc-80) and then calcined to properly arrange the crystal lattice of the TiO₂ particles for use in heterogeneous photocatalysis (Mc-80-500). A powder X-ray diffractogram of Mc-80-500 revealed a dispersion of anatase and rutile phase TiO₂ particles on the clay surface, exhibiting a size in the order of 4-8 nm. TEM images of Mc-80-500 confirmed the presence of isolated TiO₂ beads on the surface of the fibrous sepiolite. The specific surface area of Mc-80-500 was larger than that of raw sepiolite and that of free TiO₂ nanoparticles. Mc-80-500 was found to be more efficient in heterogeneous photocatalysis compared to other TiO₂ materials based on sepiolite. Total depollution of a reactive dye (Orange G) was achieved after 1 h irradiation time, which is relatively quick compared to previous reports. The photocatalyst material can be washed with distilled water without chemical additives or calcination, and can be reused several times for photocatalysis, without loss of efficiency.

Fabrication of Polyaniline@β-cyclodextrin Nanocomposite for Adsorption of Carcinogenic Phenol from Wastewater

We synthesized a stable, eco-friendly, and low-cost polyaniline@β-cyclodextrin (PANI@β-CD) nanocomposite via oxidative polymerization for phenol adsorption from water waste since phenol pollution is a global danger to human and animal health and the environment. The production of the composite and synergistic alteration of PANI with β-CD resulted in 66% reduction in particle size from 59 nm (PANI) to 20 nm (PANI@β-CD) as well as better phenol adsorption. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA) were used to analyze the produced PANI@β-CD nanocomposite. Our results show the optimum conditions for phenol adsorption: time (50 min), pH (8.0), nanosorbent dose (0.5 g), and the sorption isotherm fitted with Langmuir model; the monolayer adsorption capacity of the prepared PANI@β-CD for phenol was determined to be 8.56 mg g-1. The average pore size, total pore volume, and surface area of PANI/βCD nanocomposite are 15.62 nm, 0.1586 cm3/g, and 90.901 m2/g, respectively, for the pseudo second order model. Finally, modifying PANI nanoparticles with βCD allowed reusability up to four cycles with superior adsorption performance of ∼95% using (0.01 N) HNO3.

Solar light photocatalytic transformation of heptachlorobiphenyl (PCB 180) using g-C3N4 based magnetic porous photocatalyst

A novel porous core-shell magnetic β-cyclodextrin/graphitic carbon nitride photocatalyst (Mβ-CD/GCN) was synthesized and employed in a solar light driven catalytic system for the degradation of polychlorinated biphenyls (PCBs). The Mβ-CD/GCN display superior photocatalytic performance on account of porous structure and ultrathin GCN nanosheets design, the former improves the utilization of visible light by multiple scattering and reflection of incident light, and the latter accelerates electron transfer. The ultrahigh specific surface area (1255 m² g^-1) of Mβ-CD/GCN provided a large number of active sites for adsorption and degradation of the target pollution. The pseudo-first order reaction rate constant (k_obs) for the degradation of PCB180 by Mβ-CD/GCN was 0.021 min^-1, which improved 3.23 times than the bulk GCN. Additionally, the effects of various reaction parameters and water matrices were studied on the degradation of PCB180. Three possible degradation pathways and mechanism of PCB180 were speculated according to the identification of reaction intermediates and detection of reactive species. The solar light driven Mβ-CD/GCN catalytic technology is a promising method not only for the control of persistent organic pollutants (POPs), but also the catalyst could be recovered and reused through simple magnetic separation.

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.

Green Preparation of Robust Hydrophobic β-Cyclodextrin/Chitosan Sponges for Efficient Removal of Oil from Water

A relatively straightforward green method to fabricate robust hydrophobic sponges for effective removal of oil pollutants and other organic contaminants was developed. These sponges were constructed from bio-sources: citronellal and palmitic acid-modified aminoethyl cyclodextrin-sodium phytate-chitosan (ACCTCS). The modified sponge exhibited desirable mechanical properties and strong hydrophobicity with a water contact angle (WCA) of 147.8°. Scanning electron microscopy showed that the ACCTCS sponge had a highly porous structure that was particularly suitable for organic component absorption. The sponge exhibited excellent absorption capacities for n-hexane, trichloromethane, vacuum pump oil, and peanut oil (47.9, 32.3, 32.6, and 32.2 g/g, respectively). The removal rate of oil was more than 80% (>26.2 g/g) after 10 absorption-desorption cycles. The ACCTCS sponge also showed good oil/water and organic components/water separation performance. The bio-source materials, green preparation method, and new absorbed-oil recovery strategy provided a novel pathway to construct multifunctional absorbents for oil/water separation in industrial wastewater.

Overview of Sample Preparation and Chromatographic Methods to Analysis Pharmaceutical Active Compounds in Waters Matrices

In the environment, pharmaceutical residues are a field of particular interest due to the adverse effects to either human health or aquatic and soil environment. Because of the diversity of these compounds, at least 3000 substances were identified and categorized into 49 different therapeutic classes, and several actions are urgently required at multiple steps, the main ones: (i) occurrence studies of pharmaceutical active compounds (PhACs) in the water cycle; (ii) the analysis of the potential impact of their introduction into the aquatic environment; (iii) the removal/degradation of the pharmaceutical compounds; and, (iv) the development of more sensible and selective analytical methods to their monitorization. This review aims to present the current state-of-the-art sample preparation methods and chromatographic analysis applied to the study of PhACs in water matrices by pinpointing their advantages and drawbacks. Because it is almost impossible to be comprehensive in all PhACs, instruments, extraction techniques, and applications, this overview focuses on works that were published in the last ten years, mainly those applicable to water matrices.

Immobilization techniques of a photocatalyst into and onto a polymer membrane for photocatalytic activity

This article reviews the various techniques of immobilizing a photocatalyst into and onto the polymer membrane for pollutant removal and as a problem solver in handling suspended photocatalyst issues from the previous literature. A particular focus is given to the preparation of mixed matrix membranes and deposition techniques for photocatalytic degradation in applications for wastewater treatment. Advantages and disadvantages in this application are evaluated. Various operating conditions during the process are presented. About 90 recently published studies (2008–2020) are reviewed. From the literature, it was found that TiO₂ is the most favoured photocatalyst that is frequently used in photocatalytic water treatment. Dry–wet co-spinning and sputtering techniques emerged as the promising technique for immobilizing a uniformly distributed photocatalyst within the polymeric membrane, and exhibited excellence pollutant removal. In general, the technical applicability is the key factor in selecting the best photocatalyst immobilizing technique for water treatment. Finally, the scope of various techniques that have been reviewed may provide potential for future photocatalytic study.

This article reviews the various techniques of immobilizing a photocatalyst into and onto the polymer membrane for pollutant removal and as a problem solver in handling suspended photocatalyst issues from the previous literature.

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.

Modification of epoxy groups of poly(hydroxylmethyl methacrylate-co-glycidyl methacrylate) cryogel with H3PO4 as adsorbent for removal of hazardous pollutants

Poly(hydroxylmethyl methacrylate-co-glycidyl methacrylate) (p(HEMA-GMA)) macroporous cryogel with high density of epoxy groups was synthesized, and the epoxy groups of the cryogel were modified into phosphonate groups. The effects of dye concentrations, adsorption time, pH, salt concentration, and adsorption temperature on the adsorption of Direct Blue-53 (DB-53) and Reactive Blue-160 (RB-160) dyes were studied. The maximum adsorption capacity was found to be 245.3 and 155.8 mg/g (0.255 or 0.119 mmol/g) for the DB-53 and RB-160 dyes, respectively. The higher adsorption capacity achieved for the DB-53 compared with the RB-160 dye can result from the pendant primary amino groups of the DB-53 dye as well as the smaller size of the dye molecule. The Langmuir isotherm model and the pseudo-second-order kinetic model well described the experimental data. The p(HEMA-GMA)-PO₄^2- adsorbent has many operational advantages for the removal of pollutants. It could be a promising adsorbent to be used in industrial wastewater treatment.

Iron-Montmorillonite-Cyclodextrin Composites as Recyclable Sorbent Catalysts for the Adsorption and Surface Oxidation of Organic Pollutants

Iron-clay-cyclodextrin composites were designed as sorbent catalysts to adsorb and oxidize pollutants from water. The clay-iron backbone served as a mechanical support and as a heterogeneous Fenton catalyst, and the cyclodextrin monomers or polymers cross-linked with polyfluorinated aromatic molecules were used to accommodate adsorption of the pollutants. The composite based on iron-clay-cyclodextrin-polymers (Fe-MMT-βCD-DFB) exhibited superior adsorption and degradation of the model pollutants, bisphenol A (BPA), carbamazepine (CBZ), and perfluorooctanoic acid (PFOA), compared to the monomer-based composite and the native iron clay. The variety of adsorption sites, such as the polyfluorinated aromatic cross-linker, cyclodextrin toroid, and iron-clay surface, resulted in high adsorption affinity toward all pollutants; BPA was primarily adsorbed to the cyclodextrin functional groups, CBZ showed high affinity toward the Fe-MMT surface and the Fe-MMT-βCD-DFB composite, whereas PFOA was adsorbed mainly to the βCD-DFB polymer. Degradation, using H₂O₂, was highly efficient, reaching over 90% degradation in 1 h for BPA and CBZ and ∼80% for PFOA. The composite also showed excellent degradation efficiency in a multicomponent system with all three model pollutants. Furthermore, the composite's activity remained steady for five consecutive cycles of adsorption and degradation. The ability to remediate a broad range of pollutants, and the high overall removal exhibited by this novel material, demonstrates the potential for future application in water remediation technologies.

Adsorption isotherm models: Classification, physical meaning, application and solving method

Adsorption is widely applied separation process, especially in environmental remediation, due to its low cost and high efficiency. Adsorption isotherm models can provide mechanism information of the adsorption process, which is important for the design of adsorption system. However, the classification, physical meaning, application and solving method of the isotherms have not been systematical analyzed and summarized. In this paper, the adsorption isotherms were classified into adsorption empirical isotherms, isotherms based on Polanyi's theory, chemical adsorption isotherms, physical adsorption isotherms, and the ion exchange model. The derivation and physical meaning of the isotherm models were discussed in detail. In addition, the application of the isotherm models were analyzed and summarized based on over 200 adsorption equilibrium data in literature. The statistical parameters for evaluating the fitness of the models were also discussed. Finally, a user interface (UI) was developed based on Excel software for solving the isotherm models, which was provided in supplemental material and can be easily used to model the adsorption equilibrium data. This paper will provide theoretical basis and guiding methodology for the selection and use of the adsorption isotherms.

Simultaneous extraction of permethrin diastereomers and deltamethrin in environmental water samples based on aperture regulated magnetic mesoporous silica

The aperture of KIT-6 can influence the recoveries of magnetic solid phase extraction.