Calixarene-based extractants for heavy metal ions removal from aqueous solutions

The p-diethanolaminomethylcalix[4]arene-incorporated polyacrylonitrile-based facilitated-transport-nanofiber mat for O2/N2 separation

Separation of gases from air mixture is one of the most challenging and laborious separations due to the remarkably uniform molecular size of gas molecules. Therefore, the present study aimed to synthesize polyacrylonitrile-based nanofibers mat(NM) impregnated with p-diethanolaminomethylcalix[4]arene (PAN/p-DEAC4 NM) for the separation of two crucial gases O2 and N2. The affinity of the prepared PAN/p-DEAC4 NM for O2 was examined by optimizing the loading concentration of p-DEAC4 in the range from 5% to 20% (w/v). The results showed remarkable performance of the PAN/p-DEAC4 NM for O2/N2 separation with a superior O2/N2 selectivity of 12.75 and excellent permeance of 10.2 GPU for O2 and 0.8 GPU for N2 at 2 bar. The PAN/p-DEAC4 NM followed a facilitated transport mechanism for the separation of gases and it was revealed that the p-DEAC4 platform in the PAN NM is facilitating the transport of O2 due to its greater affinity towards O2. BET analysis revealed that the prepared NM possesses non-porous morphology with a surface area of 12.69 m2 g-1. SEM micrographs also confirmed the formation of defect-free NM. Thus, this study presents a unique perspective and direction for fabricating highly permeable nanofiber mats for O2/N2 separation.

Removal of Methylene Blue Dye from Aqueous Solutions Using Polymer Inclusion Membrane Containing Calix[4]pyrrole

The effective purification of aqueous solutions of methylene blue dye was tested using polymer inclusion membranes (PIMs) that contained cellulose triacetate (CTA) as a polymer base, o-nitrophenyl octyl ether (o-NPOE) as a plasticizer, and meso-tetra methyl tetrakis-[methyl-2-(4-acetlphenoxy)] calix[4]pyrrole (KP) as a carrier. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy were used to define the microstructure and surface of PIMs. Experimental results showed that, with an increased concentration of methylene blue in an aqueous solution, the removal percentage also increased. Further observation showed that the flux increased with the rise in the source phase pH values from 3 to 10. The carrier and plasticizer content in the membrane significantly influenced the membrane's transport properties. The optimal composition of the membrane in percent by weight for KP was 74% plasticizer; 18% support, and 8% carrier. The maximum MB removal (93.10%) was achieved at 0.10 M HCl solution as the receiving phase. It was shown that the membrane with optimal composition showed good reusability and enabled the easy and spontaneous separation of methylene blue from aqueous solutions.

Substantial and efficient adsorption of heavy metal ions based on protein and polyvinyl alcohol nanofibers by electrospinning

The adverse effects of heavy metal pollutants in wastewater have threatened human health in recent decades. Therefore, the development of absorbents for such pollutants is essential to overcome these problems. Electrospun nanofibers are often used for wastewater treatment owing to their high porosity and high specific surface area. Zein from plants and collagen from animals are vulnerable to moisture, which limits its broad application in practice. However fully biodegradable polyvinyl alcohol (PVA), which is soluble in water, can be mixed with protein individually to overcome the limitation. In this work, the two proteins described above and PVA were combined to prepare protein nanofibers by electrospinning technology, which could achieve adsorption of Cu2+. As the protein content increased, the adsorption properties of the obtained nanofibers for Cu2+ showed a rising and then decreasing trend, with the highest point at 50 % of protein content, especially the collagen nanofibers, which reached 24.62 mg/g. Both protein nanofibers reached adsorption equilibrium after 15 h, but overall, collagen nanofibers showed a superior adsorption performance for Cu2+ than that by zein nanofibers. In the process of Cu2+ adsorption by protein nanofibers, both physical and chemical effect existed, and the physical effect played the leading role.

Functionalized Calixarenes as Promising Antibacterial Drugs to Face Antimicrobial Resistance

Since the discovery of polyphenolic resins 150 years ago, the study of polymeric compounds named calix[n]arene has continued to progress, and those skilled in the art perfectly know now how to modulate this phenolic ring. Consequently, calix[n]arenes are now used in a large range of applications and notably in therapeutic fields. In particular, the calix[4]arene exhibits multiple possibilities for regioselective polyfunctionalization on both of its rims and offers researchers the possibility of precisely tuning the geometry of their structures. Thus, in the crucial research of new antibacterial active ingredients, the design of calixarenes finds its place perfectly. This review provides an overview of the work carried out in this aim towards the development of intrinsically active prodrogues or metallic calixarene complexes. Out of all the work of the community, there are some excellent activities emerging that could potentially place these original structures in a very good position for the development of new active ingredients.

Tuning phase compositions of MoS2 nanomaterials for enhanced heavy metal removal: performance and mechanism

Two-dimensional MoS₂ nanosheets have shown great potential in heavy metal remediation due to their unique properties. MoS₂ has two primary phases: 1T and 2H. Each has different physiochemical properties, but the impact of these differences on the overall material's heavy metal removal performance and associated mechanisms is rarely reported. In this study, we synthesized morphologically similar but phase-distinct MoS₂ samples via hydrothermal synthesis, which comprised dominantly either a metallic 1T phase or a semiconducting 2H phase. 1T-MoS₂ samples exhibited higher removal capacities for Ag⁺ and Pb²⁺ cations relative to 2H-MoS₂. In particular, an eight-fold increase in the Pb²⁺ adsorption capacity was observed in the 1T-MoS₂ samples (i.e. ∼632.9 mg g^-1) compared to the 2H-MoS₂ samples (∼81.6 mg g^-1). The mechanisms driving the enhanced performance of 1T-MoS₂ were investigated through detailed characterization of metal-laden MoS₂ samples and DFT modelling. We found that 1T-MoS₂ intrinsically had a larger interlayer spacing than 2H-MoS₂ because water molecules were retained between the hydrophilic 1T nanosheets during hydrothermal synthesis. The widened interlayer spacing in 1T-MoS₂ allowed the diffusion of heavy metal ions into the nanochannels, increasing the number of adsorption sites and total removal capacities. On the other hand, DFT modelling revealed the energy-favorable adsorption complex of Ag⁺ and Pb²⁺ for 1T-MoS₂, in which each metal atom was bonded with three S atoms leading to much higher adsorption energies relative to 2H-MoS₂ for Ag⁺ and Pb²⁺. This study unravels the underlying mechanisms of phase-dependent heavy metal remediation by MoS₂ nanosheets, providing an important guide for the use of 2D nanomaterials in environmental applications which include heavy metal removal, contaminant sensing, and membrane separation.

Calixresorcin[4]arene-Mediated Transport of Pb(II) Ions through Polymer Inclusion Membrane

A facilitated transport of Pb(II) through polymer inclusion membrane (PIM) containing 1,8,15,22-tetra(1-heptyl)-calixresorcin[4]arene and its tetra- and octasubstituted derivatives containing phosphoryl, thiophosphoryl or ester groups as an ion carrier was investigated. The efficiency of Pb(II) removal from aqueous nitrate solutions was considered as a function of the composition of membrane (effect of polymer, plasticizer, and carrier), feed (effect of initial metal concentration and presence of other metal ions) and stripping phases, and temperature of the process conducting. Two kinetic models were applied for the transport description. The highest Pb(II) ions removal efficiency was obtained for the membrane with tetrathiophosphorylated heptyl-calixresorcin[4]arene as an ion carrier. The activation energy value, found from Eyring plot to be equal 38.7 ± 1.3 kJ/mol, suggests that the transport process is controllable both by diffusion and chemical reaction. The competitive transport of Pb(II) over Zn(II), Cd(II), and Cr(III) ions across PIMs under the optimal conditions was also performed. It was found that the Cr(III) ions’ presence in the feed phase disturb effective re-extraction of Pb(II) ions from membrane to stripping phase. Better stability of PIM-type than SLM-type membrane was found.

1,3-Diketone Calix[4]arene Derivatives-A New Type of Versatile Ligands for Metal Complexes and Nanoparticles

The present review is aimed at highlighting outlooks for cyclophanic 1,3-diketones as a new type of versatile ligands and building blocks of the nanomaterial for sensing and bioimaging. Thus, the main synthetic routes for achieving the structural diversity of cyclophanic 1,3-diketones are discussed. The structural diversity is demonstrated by variation of both cyclophanic backbones (calix[4]arene, calix[4]resorcinarene and thiacalix[4]arene) and embedding of different substituents onto lower or upper macrocyclic rims. The structural features of the cyclophanic 1,3-diketones are correlated with their ability to form lanthanide complexes exhibiting both lanthanide-centered luminescence and magnetic relaxivity parameters convenient for contrast effect in magnetic resonance imaging (MRI). The revealed structure–property relationships and the applicability of facile one-pot transformation of the complexes to hydrophilic nanoparticles demonstrates the advantages of 1,3-diketone calix[4]arene ligands and their complexes in developing of nanomaterials for sensing and bioimaging.

Pillararenes as macrocyclic hosts: a rising star in metal ion separation

Pillararenes are macrocyclic oligomers of alkoxybenzene akin to calixarenes but tethered at the 2,5-positions via methylene bridges. Benefiting from their unique pillar-shaped architecture favorable for diverse functionalization and versatile host-guest properties, pillararenes decorated with chelating groups worked excellently as supporting platforms to construct extractants or adsorbents for metal ion separation. This feature article provides a detailed summary of pillararenes in Ln/An separation by liquid-liquid extraction and heavy metal separation by solid-liquid extraction. The preorganization effect of the rigid pillararene framework has a profound impact on the extraction of metal ions, and a unique extraction mechanism is observed when employing ionic liquids as solvents. The rich host-guest chemistry of pillararenes enables construction of a wide variety of supramolecular materials as metal ion adsorbents. We also discuss the differences between pillararenes and several well-known macrocycles, with a focus on the metal-ligand coordination and its influencing factors. We hope this review will provide useful information and unleash new opportunities in this field.

Single-crystal X-ray diffraction study, NMR and electrochemical analysis of a copper(i) 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-[(6-methyl-2,2′-bipyridyl-6-yl)methoxy]calix[4]arene complex: an original M4L2“hand-to-hand” system

An original M₄L₂“hand-to-hand” copper(i)/tetra-bipyridyl-calix[4]arene complex was obtained and characterized in the solid state by X-ray diffraction. It changes in MeCN solution to its M₂L analogue.

4-Sulfocalix[4]arene/Cucurbit[7]uril-Based Supramolecular Assemblies through the Outer Surface Interactions of Cucurbit[n]uril

Upon mixing of aqueous solutions of the freely soluble building blocks cucurbit[7]uril (Q[7]) and 4-sulfocalix[4]arene (SC[4]A), white microcrystals instantly separate in near-quantitative yield. The driving force for this assembly is suggested to be the outer-surface interaction of the Q[n]. Dynamic light scattering, scanning electron microscopy, and NMR (diffusion-ordered NMR spectroscopy) analyses have confirmed the supramolecular aggregation of Q[7] and SC[4]A. Titration ¹H NMR spectroscopy and isothermal titration calorimetry have shown that the interaction ratio of Q[7] and SC[4]A is close to 3:1. Moreover, the Q[7]/SC[4]A-based supramolecular assembly can accommodate molecules of some volatile compounds or luminescent dyes. Thus, this work offers a simple and highly efficient means of preparing adsorbent or solid fluorescent materials.

Luminescence Properties of Self-Aggregating TbIII-DOTA-Functionalized Calix[4]arenes

Self-aggregating calix[4]arenes carrying four DOTA ligands on the upper rim for stable complexation of paramagnetic GdIII-ions have already been proposed as MRI probes. In this work, we investigate the luminescence properties of TbIII-DOTA-calix[4]arene-4OPr containing four propyl-groups and compare them with those of the analog substituted with a phthalimide chromophore (TbIII-DOTA-calix[4]arene-3OPr-OPhth). We show that, given its four aromatic rings, the calix[4]arene core acts as an effective sensitizer of Tb-centered luminescence. Substituents on the lower rim can modulate the aggregation behavior, which in turn determines the luminescence properties of the compounds. In solid state, the quantum yield of the phthalimide derivative is almost three times as high as that of the propyl-functionalized analog demonstrating a beneficial role of the chromophore on Tb-luminescence. In solution, however, the effect of the phthalimide group vanishes, which we attribute to the large distance between the chromophore and the lanthanide, situated on the opposite rims of the calix[4]arene. Both quantum yields and luminescence lifetimes show clear concentration dependence in solution, related to the strong impact of aggregation on the luminescence behavior. We also evidence the variability in the values of the critical micelle concentration depending on the experimental technique. Such luminescent calix[4]arene platforms accommodating stable lanthanide complexes can be considered valuable building blocks for the design of dual MR/optical imaging probes.