Thioether-Crown-Rich Calix[4]arene Porous Polymer for Highly Efficient Removal of Mercury from Water

Adsorption and separation technologies based on supramolecular macrocycles for water treatment

The escalating challenges in water treatment, exacerbated by climate change, have catalyzed the emergence of innovative solutions. Novel adsorption separation and membrane filtration methodologies, achieved through molecular structure manipulation, are gaining traction in the environmental and energy sectors. Separation technologies, integral to both the chemical industry and everyday life, encompass concentration and purification processes. Macrocycles, recognized as porous materials, have been prevalent in water treatment due to their inherent benefits: stability, adaptability, and facile modification. These structures typically exhibit high selectivity and reversibility for specific ions or molecules, enhancing their efficacy in water purification processes. The progression of purification methods utilizing macrocyclic frameworks holds promise for improved adsorption separations, membrane filtrations, resource utilization, and broader water treatment applications. This review encapsulates the latest breakthroughs in macrocyclic host-guest chemistry, with a focus on adsorptive and membrane separations. The aim is to spotlight strategies for optimizing macrocycle designs and their subsequent implementation in environmental and energy endeavors, including desalination, elemental extraction, seawater energy harnessing, and sustainable extraction. Hopefully, this review can guide the design and functionality of macrocycles, offering a significantly promising pathway for pollutant removal and resource utilization.

Dual Brønsted acidic-basic function immobilized on the 3D mesoporous polycalix [4]resorcinarene: As a highly recyclable catalyst for the synthesis of spiro acenaphthylene/indene heterocycles

In this study, a novel dual Brønsted acidic-basic nano-scale porous organic polymer catalyst, PC4RA@SiPr-Pip-BuSO3H, was synthesized through various steps: preparation of a 3D network of polycalix, modification with (3-chloropropyl)-trimethoxysilane, then functionalization of polymer with piperazine and n-butyl sulfonic acid under the provided conditions. The catalyst characterization was performed by FT-IR, TGA, EDS, elemental mapping, PXRD, TEM, and FE-SEM analyses, confirming high chemical stability, activity, recoverability, and excellent covalent anchoring of functional groups. So, the designed catalyst was utilized for preparing spiro-acenaphthylene and amino-spiroindene heterocycles, providing good performance with a high yield of the corresponding products. Accordingly, this catalyst can be used in different organic transformations. Necessary experiments were conducted for the recyclability test of the polymeric catalyst, and the results showed the PC4RA@SiPr-Pip-BuSO3H catalyst can be reused 10 times without any decrease in its activity or quality with excellent stability. The structure of resultant spiro heterocycles was confirmed using 1H NMR, 13C NMR, and FT-IR.

Efficient and selective capture of various mercury species from water using an exfoliated thiocellulose

The primary challenge in mercury (Hg) adsorbents for large-scale practical applications is to achieve the balance between performance and economy. This work attempts to address this issue by synthesizing an exfoliated thiocellulose (CU-SH) with high thiol density and hierarchical porosity using in-situ ligands grafting combined with chemical stripping. The prepared CU-SH shows remarkable physical stability and chemical resistance, and the micron sized fiber is conducive to separation from water. Hg(II) adsorption tests in water demonstrate that CU-SH has broad working pH range (1-12), fast kinetics (0.64 g/(mg‧min)), high adsorption capacity (652.9 mg/g), outstanding selectivity (Kd = 6.2 × 106 mg/L), and excellent reusability (R > 95 % after 20 cycles). Importantly, CU-SH exhibits good resistance to various coexisting ions and organic matter, and can efficiently remove Hg(II) from different real water. CU-SH can be made into a Point of Use (POU) device for continuous and efficient removal of Hg(II) from drinking water. 0.1 g CU-SH filled device can purify 3.2 L of Hg(II) (0.5 ppm) contaminated tap water before the breakthrough point of 2 ppb. Moreover, CU-SH also reveals good adsorption affinity for Hg-dissolved organic matter complexes (Hg(II)-DOM) in water, chloro(phenyl)mercury (PMC) in organic media and Hg0 vapor in air, suggesting the great practical potential of CU-SH.

Promises of anionic calix[n]arenes in life science: State of the art in 2023

Because they hold together molecules by means of non-covalent interactions - relatively weak and thus, potentially reversible - the anionic calixarenes have become an interesting tool for efficiently binding a large range of ligands - from gases to large organic molecules. Being highly water soluble and conveniently biocompatible, they showed growing interest for many interdisciplinary fields, particularly in biology and medicine. Thanks to their intrinsic conical shape, they provide suitable platforms, from vesicles to bilayers. This is a valuable characteristic, as so they mimic the biologically functional architectures. The anionic calixarenes propose efficient alternatives for overcoming the limitations linked to drug delivery and bioavailability, as well as drug resistance along with limiting the undesirable side effects. Moreover, the dynamic non-covalent binding with the drugs enables predictable and on demand drug release, controlled by the stimuli present in the targeted environment. This particular feature instigated the use of these versatile, stimuli-responsive compounds for sensing biomarkers of diverse pathologies. The present review describes the recent achievements of the anionic calixarenes in the field of life science, from drug carriers to biomedical engineering, with a particular outlook on their applications for the diagnosis and treatment of different pathologies.

Thiophene-based porphyrin polymers for Mercury (II) efficient removal in aqueous solution

Development of novel sulf-functionalized porous organic polymers (POPs) for Mercury (II) (Hg2+) removal is of great significant, but the adsorbents always suffered by the low adsorption capacity, stability, and efficiency for the reason that the common construction of functionalized POPs from the functionalized monomers or post-functionalization of the POPs always sacrifice the porosity. In this paper, porphyrin-based POPs with different heteroatoms were constructed through the aldehyde monomer (benzene, 2,5-thiophenedicarboxaldehyde and thieno[3,2-b]thiophene-2,5-dicarboxaldehyde) and pyrrole according to the Adler-Longo method. In this way, nitrogen (N) in pyrrole and sulfur (S) in thiophene structures were embed into the backbone structure of the polymers. The functional structures not only act as the linking building block into the stable cross-linking structure, but also offer abundant uncovered functional sites for Hg2+ adsorption, resulting the porphyrin-based POPs high Hg2+ capacity (1049 mg/g), removal efficiency (more than 99.9%), good reusability and selectivity for its highest heteroatoms contents. The adsorption mechanism confirmed the cooperative coordination of N in porphyrin and S in thiophene with Hg2+. This work confirmed the functional groups play more important role in heavy metal adsorption, and the embedded functional sites into backbone also promotes the stability and the adsorption performance.

Synthesis of two-dimensional triazine covalent organic frameworks at ambient conditions to detect and remove water pollutants

Synthesis of fully triazine frameworks (C3N3) by metal catalyzed reactions at high temperatures results in carbonized and less-defined structures. Moreover, metal impurities affect the physicochemical, optical and electrical properties of the synthesized frameworks, dramatically. In this work, two-dimensional C3N3 (2DC3N3) has been synthesized by in situ catalyst-free copolymerization of sodium cyanide and cyanuric chloride, as cheap and commercially available precursors, at ambient conditions on gram scale. Reaction between sodium cyanide and cyanuric chloride resulted in electron-poor polyfunctional intermediates, which converted to 2DC3N3 with several hundred micrometers lateral size at ambient conditions upon [2 + 2+2] cyclotrimerization. 2DC3N3 sheets, in bulk and individually, showed strong fluorescence with 63% quantum yield and sensitive to small objects such as dyes and metal ions. The sensitivity of 2DC3N3 emission to foreign objects was used to detect low concentration of water impurities. Due to the high negative surface charge (-37.7 mV) and dispersion in aqueous solutions, they demonstrated a high potential to remove positively charged dyes from water, exemplified by excellent removal efficiency (>99%) for methylene blue. Taking advantage of the straightforward production and strong interactions with dyes and metal ions, 2DC3N3 was integrated in filters and used for the fast detection and efficient removal of water impurities.

Azophenyl Calix[4]arene Porous Organic Polymer for Extraction and Analysis of Triphenylmethane Dyes from Seafood

Porous organic polymers (POPs) based on calix[4]arene with a hydrophobic π-rich cavity and host-guest recognition properties exhibit a wide application range of molecular extraction and separation. However, it is still a challenge to improve the extraction and separation selectivity by exploring and seeking appropriate building blocks for the functionalization and pore size adjustment of calix[4]arene. Herein, an azophenyl calix[4]arene porous organic polymer (AC-POP) was proposed. By introducing an electron-rich cavity and adjusting the pore sizes of calix[4]arene, the AC-POP showed high selectivity extraction performance in triphenylmethane (TPM) dyes. The extraction mechanism was explored by adsorption thermodynamics study, density functional theory (DFT) calculation, and reduced density gradient (RDG) and electrostatic potential (ESP) analyses, which suggested that the selectivity adsorption of TPM dyes based on AC-POP was mainly the result of entropy driven by the hydrophobic effect. In addition, the noncovalent interactions including π-π stacking, van der Waals force, and electrostatic interaction were also important factors affecting the adsorption capacity of TPM dyes. Under optimal extraction conditions, the AC-POP possessed a maximum extraction amount of 95.3 mg·g-1 for Rhodamine B (RB), high enrichment factor of about 100, and excellent reusability more than 10 times. Then, an analytical method of TPM dyes with AC-POP as a solid-phase extractant combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) was established, which displayed excellent sensitivity with the limits of detection (LODs) and limits of quantitation (LOQs) in the ranges of 0.004-0.35 and 0.016-1.16, respectively. The mean recoveries for TPM dyes ranged from 85.0 to 109.4% with an RSD of 0.48-9.45%. The proposed method was successfully applied to the analysis of the five TPM dyes in seafood matrix samples.

Porphyrin-based conjugated microporous adsorbent material for the efficient remediation of hexavalent chromium from the aquatic environment

The encapsulation and eradication of anions from water have received a lot of scrutinize and are extremely important for virtuous production and environmental treatment. To prepare extremely efficient adsorbents, a highly functionalized and conjugated microporous porphyrin-based adsorbent material (Co-4MPP) was synthesized using the Alder Longo method. Co-4MPP featured a hierarchical microporous and mesoporous layered structure containing nitrogen and oxygen-based functional groups with a specific surface area of 685.209 m2/g and a pore volume of 0.495 cm3/g. Co-4MPP demonstrated a greater Cr (VI) adsorption empathy than the pristine porphyrin-based material did. The effects of various parameters such as pH, dose, time, and temperature were explored on the Cr (VI) adsorption by Co-4MPP. The pseudo-second-order model and the Cr (VI) adsorption kinetics were in agreement (R2 = 0.999). The Langmuir isotherm model matched the Cr (VI) adsorption isotherm, demonstrating the optimum Cr (VI) adsorption capacities: 291.09, 307.42, and 339.17 mg/g at 298K, 312K, and 320K, correspondingly, with remediation effectiveness of 96.88%. The model evaluation further revealed that Cr (VI) adsorption mechanism on Co-4MPP was endothermic, spontaneous, and entropy-rising. The detailed discussion of the adsorption mechanism suggested that it could be a reduction, chelation, and electrostatic interaction, in which the protonated nitrogen and oxygen-containing functional groups on the porphyrin ring interacted with Cr (VI) anions to form a stable complex, thus remediating Cr (VI) anions efficiently. Moreover, Co-4MPP demonstrated strong reusability, maintaining 70% of its Cr (VI) elimination rate after four consecutive adsorptions.

Organo-macrocycle-containing hierarchical metal-organic frameworks and cages: design, structures, and applications

Developing hierarchical ordered systems is challenging. Using organo-macrocycles to construct metal-organic frameworks (MOFs) and porous coordination cages (PCCs) provides an efficient way to obtain hierarchical assemblies. Macrocycles, such as crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, can be incorporated within MOFs/PCCs and they also endow the resultant composites with enhanced properties and functionalities. This review summarizes recent developments of organo-macrocycle-containing hierarchical MOFs/PCCs, emphasizing applications and structure-property relationships of these hierarchically porous materials. This review provides insights for future research on hierarchical self-assembly using macrocycles as building blocks and functional ligands to extend the applications of the composites.

Squaramide-Immobilized Carbon Nanoparticles for Rapid and High-Efficiency Elimination of Anthropogenic Mercury Ions from Aquatic Systems

Water pollution due to environmental remediation and poor waste administration in certain areas of the globe signifies a serious problem in acquiring safe and clean drinking water. This problem is especially critical in rural areas, where advanced water purification techniques are deficient, and it remains a daunting task for ecosystem and public health protection. This critical task can be addressed herein by developing scalable poly squaramide-phenyl methacrylamide (PSQ)-functionalized carbon nanoparticles (CNPs) (PSQ-CNPs) with densely populated chelating sites with strong Hg²⁺-binding capacity. The PSQ-CNPs have shown high efficiency in removing Hg²⁺ from aqueous solution, providing a Hg²⁺ capacity of 2840 mg g^-1, surpassing all the amine and thiol-based adsorbents reported hitherto. More significantly, the adsorbent reveals the largest distribution coefficient value (K_d) of 9.09 × 10¹⁰ mL g^-1, which allows it to reduce Hg²⁺ content from 10 ppm to less than 0.011 ppb, well below the United States Environmental Protection Agency (EPA) limits for drinking water standards (2 ppb). The adsorption measurements of the adsorbent followed the Langmuir isotherm model and pseudo-second order. The practical applicability of PSQ-CNPs was verified with the real samples (the lake, river, and industrial wastewater) and has been proven to be excellent. The adsorbent could still retain its Hg²⁺ removal efficacy even after 12 sorption cycles. It is attributed that the remarkable performance of PSQ-CNPs arises from the high-density chelating sites and pores on the surface of CNPs. The present work shows a new benchmark for Hg²⁺-removal adsorbents and presents a novel practical approach for decontaminating Hg²⁺ and other heavy metal ions from wastewater.

Thioether-functionalized porphyrin-based polymers for Hg2+ efficient removal in aqueous solution

In this paper, thioether-functionalized porphyrin-based polymers (TPPs) were constructed according to two different "bottom-up" and "top-down" strategies and they were applied for Hg²⁺ capture in aqueous solution. TPP1, which was constructed by one-step polycondensation of 2,5-bis(methylthio) terephthalaldehyde (BMTA) with pyrrole according to the "bottom-up" strategy, owned high Brunauer-Emmett-Teller (BET) surface area (S_BET, 554 m²/g), pore volume (V_total, 0.32 cm³/g), and S content (16.8%), resulting in high Hg²⁺ capture (913 mg/g) with high removal efficiency (> 99%). The adsorption mechanism clarified that the strong coordination between the S species and Hg²⁺ was the main driving force. In comparison, TPP2 and TPP3 were fabricated by the thioether functionalization of the porphyrin-based polymers according to the "top-down" strategy. They showed much lower S_BET, V_total, and S content for the reason that the post-functionalization process greatly blocked the pores and the functional sites were hardly fully post-functionalized, resulting in much lower Hg²⁺ capture (555 mg/g and 609 mg/g, respectively). This work reveals the advantage of the "bottom-up" strategy for the construction of the thioether-functionalized polymers and it offers the guidance for the construction of some other thioether-functionalized polymers.

Mechanistic insight into the adsorption of mercury (II) on the surface of red mud supported nanoscale zero-valent iron composite

Recently, nanoscale zero-valent iron (nZVI) particles have been efficiently used in the remediation of many heavy metals, yet potential agglomeration and loss of nZVI remain a critical area of research. In this study, we used red mud as a stable supporting medium to develop red mud modified nZVI to form (RM-nZVI) composite. We assessed its sorptive/reductive removal of mercury (Hg²⁺) from aqueous solutions. The RM-nZVI was synthesized through the reduction of ferric iron by sodium borohydride (NaBH₄) in the presence of red mud. Morphological characterization of RM-nZVI confirmed its diffusion state with lesser aggregation. The RM-nZVI has the BET surface area, pore diameter, and pore volume as 111.59 m²g^-1, 3.82 nm, and 0.49 cm³g^-1, respectively. Adsorption of mercury (Hg²⁺) by RM-nZVI exhibits pH-dependent behavior with increased removal of Hg²⁺ with the increase in pH up to 5, and the removal rate decreased gradually as the pH increased from 5 to 10. Extensive characterization of RM-nZVI corroborated the evidence that the removal of Hg²⁺ was initially by rapid physical adsorption, followed by a reduction of Hg²⁺ to Hg⁰. The adsorption data were best fitted with Langmuir isotherm with R² (correlation coefficient) > 0.99 with high uptake capacity of 94.58 (mg g^-1). The novel RM-nZVI composite with enhanced sorptive and reductive capacity is an ideal alternative for removing Hg²⁺ from contaminated water.

Thiacalixarenes with Sulfur Functionalities at Lower Rim: Heavy Metal Ion Binding in Solution and 2D-Confined Space

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air-water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L², O₂S₂-thiacrown-ether L³, and O₂S₂-bridged thiacalixtube L⁴). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag⁺ and Hg²⁺ ions vs. other soft metal ions. In thioether L² and thiacalixtube L⁴, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag⁺ species) and the appearance of ligand-to-metal charge transfer bands at 330-340 nm (for Hg²⁺ species). Theoretical calculations for thioether L² and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag-thioether L² complexes and Hg-thiacalixtube L⁴ complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg²⁺) or sulfur atoms on the lower rim and bridging unit (Ag⁺). In thiacrown L³, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg²⁺ ion uptake by the Langmuir-Blodgett (LB) films of ligand L³ was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg²⁺ ions, which could be useful in the development of Hg²⁺-selective water purification systems or thin-film sensor devices.

Macrocycle-Based Porous Organic Polymers for Separation, Sensing, and Catalysis

With the rapid development of materials science, porous organic polymers (POPs) have received remarkable attentions because of their unique properties such as the exceptionally high surface area and flexible molecular design. The ability to incorporate specific functions in a precise manner makes POPs promising platforms for a myriad of applications in molecular adsorption, separation, and catalysis. Therefore, many different types of POPs have been rationally designed and synthesized to expand the scope of advanced materials, endowing them with distinct structures and properties. Recently, supramolecular macrocycles with excellent host-guest complexation abilities are emerging as powerful crosslinkers for developing novel POPs with hierarchical structures and improved performance, which can be well-organized at different spatial scales. Macrocycle-based POPs could have unusual porous, adsorptive, and optical properties when compared to their nonmacrocycle-incorporated counterparts. This cooperation provides valuable insights for the molecular-level understanding of skeletal complexity and diversity. Here, the research advances of macrocycle-based POPs are aptly summarized by showing their syntheses, properties, and applications in terms of separation, sensing, and catalysis. Finally, the current challenging issues in this exciting research field are delineated and a comprehensive outlook is offered for their future directions.

Macrocycle-derived hierarchical porous organic polymers: synthesis and applications

Porous organic polymers (POPs), as a new category of advanced porous materials, have received broad research interests owing to the advantages of light-weight, robust scaffolds, high specific surface areas and good functional tailorability. According to the long-range ordering of polymer skeletons, POPs can be either crystalline or amorphous. Macrocycles with inherent cavities can serve as receptors for recognizing or capturing specific guest molecules through host-guest interactions. Incorporating macrocycles in POP skeletons affords win-win merits, e.g. hierarchical porosity and novel physicochemical properties. In this review, we focus on the recent progress associated with new architectures of macrocycle-based POPs. Herein, these macrocycles are divided into two subclasses: non-planar (crown ether, calixarene, pillararene, cyclodextrin, cyclotricatechylene, etc.) and planar (arylene-ethynylene macrocycles). We summarize the synthetic methods of each macrocyclic POP in terms of the functions of versatile building blocks. Subsequently, we discuss the performance of macrocyclic POPs in environmental remediation, gas adsorption, heterogeneous catalysis, fluorescence sensing and ionic conduction. Although considerable examples are reported, the development of macrocyclic POPs is still in its infancy. Finally, we propose the underlying challenges and opportunities of macrocycle-based POPs.

Versatile Porous Poly(arylene ether)s via Pd-Catalyzed C-O Polycondensation

Porous organic polymers (POPs) with strong covalent linkages between various rigid aromatic structural units having different geometries and topologies are reported. With inherent porosity, predictable structure, and tunable functionality, POPs have found utility in gas separation, heterogeneous catalysis, sensing, and water treatment. Poly(arylene ether)s (PAEs) are a family of high-performance thermoplastic materials with high glass-transition temperatures, exceptional thermal stability, robust mechanical properties, and excellent chemical resistance. These properties are desirable for development of durable POPs. However, the synthetic methodology for the preparation of these polymers has been mainly limited in scope to monomers capable of undergoing nucleophilic aromatic substitution (S_NAr) reactions. Herein, we describe a new general method using Pd-catalyzed C-O polycondensation reactions for the synthesis of PAEs. A wide range of new compositions and PAE architectures are now readily available using monomers with unactivated aryl chlorides and bromides. Specifically, monomers with conformational rigidity and intrinsic internal free volume are now used to create porous organic polymers with high molecular weight, good thermal stability, and porosity. The reported porous PAEs are solution processable and can be used in environmentally relevant applications including heavy-metal-ion sensing and capture.

Covalent Organic Polymers and Frameworks for Fluorescence-Based Sensors

Following the advancements and diversification in synthetic strategies for porous covalent materials in the literature, the materials science community started to investigate the performance of covalent organic polymers (COPs) and covalent organic frameworks (COFs) in applications that require large surface areas for interaction with other molecules, chemical stability, and insolubility. Sensorics is an area where COPs and COFs have demonstrated immense potential and achieved high levels of sensitivity and selectivity on account of their tunable structures. In this review, we focus on those covalent polymeric systems that use fluorescence spectroscopy as a method of detection. After briefly reviewing the physical basis of fluorescence-based sensors, we delve into various kinds of analytes that have been explored with COPs and COFs, namely, heavy metal ions, explosives, biological molecules, amines, pH, volatile organic compounds and solvents, iodine, enantiomers, gases, and anions. Throughout this work, we discuss the mechanisms involved in each sensing application and aim to quantify the potency of the discussed sensors by providing limits of detection and quenching constants when available. This review concludes with a summary of the surveyed literature and raises a few concerns that should be addressed in the future development of COP and COF fluorescence-based sensors.

Porous Polycalix[n]arenes as Environmental Pollutant Removers

A new and innovative class of calixarene-based polymers emerged as adsorbents for a variety of compounds and ions in solution and vapor media. These materials take advantage of the modifiable rims and hydrophobic cavities of the calixarene monomers, in addition to the porous nature of the polymeric matrix. With main-chain calixarenes' function as supramolecular hosts and the polymers' high surface areas, polycalixarenes can effectively encapsulate target analytes. This feature is particularly useful for environmental remediation as dangerous and toxic molecules reversibly bind to the macrocyclic cavity, which facilitates their removal and enables repeated use of the polymeric sorbent. This Spotlight touches on the unique characteristics of the calixarene monomers and discusses the synthetic methods of our reported calixarene-based porous polymers, including Sonogashira-Hagihara coupling, and diazo and imine bond formation. It then discusses the promising applications of these materials in adsorbing dyes, micropollutants, iodine, mercury, paraquat, and perfluorooctanoic acid (PFOA) from water. In most cases, these reports cover materials that outperform others in terms of recyclability, rates of adsorption, or uptake capacities of specific pollutants. Finally, this Spotlight addresses the current challenges and future aspects of utilizing porous polymers in pollution treatment.

Mesoscopic engineering materials for visual detection and selective removal of copper ions from drinking and waste water sources

The monitoring and removal of abundant heavy metals such as Cu ions are considerable global concerns because of their severe impact on the health of humans and other living organisms. To meet this global challenge, we engineered a novel mesoscopic capture protocol for the highly selective removal and visual monitoring of copper (Cu²⁺) ions from wide-ranging water sources. The capture hierarchy carriers featured three-dimensional, microsized MgO mesoarchitecture rectangular sheet-like mosaics that were randomly built in horizontal and vertical directions, uniformly arranged sheet faces, corners, and edges, smoothly quadrilateral surface coverage for strong Cu²⁺-to-ligand binding exposure, and multidiffusible pathways. The Cu²⁺ ion-selectively active captor surface design was engineered through the simple incorporation/encapsulation of a synthetic molecular chelation agent into hierarchical mesoporous MgO rectangular sheet platforms to produce a selective, visual mesoscopic captor (VMC). The nanoscale VMC dressing of MgO rectangular mosaic hierarchy by molecularly electron-enriched chelates with actively double core bindings of azo- and sulfonamide- groups and hydrophobic dodecyl tail showed potential to selectively trap and efficiently remove ultratrace Cu²⁺-ions with an extreme removal capability of ~233 mg/g from watery solutions, such as drinking water, hospital effluent, and food-processing wastewater at specific pH values. In addition to the Cu²⁺ ion-selective removal, the VMC design enabled the continuous visual monitoring of ultratrace Cu²⁺ ions (~3.35 × 10^-8 M) as a consequence of strong chelate-to-Cu²⁺ binding events among all accumulated matrices in water sources. Our experimental recycle protocol provided evidence of reusability and recyclability of VMC (≥10 cycles). With our mesoscopic capture protocol, the VMC can be a promising candidate for the selective decontamination/removal and sensitive detection of hazardous inorganic pollutants from different water sources with indoor or outdoor applications.

Amphiphilic Thiol Polymer Nanogel Removes Environmentally Relevant Mercury Species from Both Produced Water and Hydrocarbons

Technologies for removal of mercury from produced water and hydrocarbon phases are desired by oil and gas production facilities, oil refineries, and petrochemical plants. Herein, we synthesize and demonstrate the efficacy of an amphiphilic, thiol-abundant (11.8 wt % S, as thiol) polymer nanogel that can remove environmentally relevant mercury species from both produced water and the liquid hydrocarbon. The nanogel disperses in both aqueous and hydrocarbon phases. It has a high sorption affinity for dissolved Hg(II) complexes and Hg-dissolved organic matter complexes found in produced water and elemental (Hg⁰) and soluble Hg-alkyl thiol species found in hydrocarbons. X-ray absorption spectroscopy analysis indicates that the sorbed mercury is transformed to a surface-bound Hg(SR)₂ species in both water and hydrocarbon regardless of its initial speciation. The nanogel had high affinity to native mercury species present in real produced water (>99.5% removal) and in natural gas condensate (>85% removal) samples, removing majority of the mercury species using only a 50 mg L^-1 applied dose. This thiolated amphiphilic polymeric nanogel has significant potential to remove environmentally relevant mercury species from both water and hydrocarbon at low applied doses, outperforming reported sorbents like sulfur-impregnated activated carbons because of the mass of accessible thiol groups in the nanogel.

Cavitand and Molecular Cage-Based Porous Organic Polymers

Supramolecular cavitands and organic cages having a well-defined cavity and excellent host-guest complexing ability have been explored for a myriad of applications ranging from catalysis to molecular separation to drug delivery. On the other hand, porous organic polymers (POPs) having tunable porosity and a robust network structure have emerged as advanced materials for molecular storage, heterogeneous catalysis, water purification, light harvesting, and energy storage. A fruitful marriage between guest-responsive discrete porous supramolecular hosts and highly porous organic polymers has created a new interface in supramolecular chemistry and materials science, confronting the challenges related to energy and the environment. In this mini-review, we have addressed the recent advances (from 2015 to the middle of 2020) of cavitand and organic cage-based porous organic polymers for sustainable development, including applications in heterogeneous catalysis, CO2 conversion, micropollutant separation, and heavy metal sequestration from water. We have highlighted the "cavitand/cage-to-framework" design strategy and delineated the future scope of the emerging new class of porous organic networks from "preporous" building blocks.

Polymerized Molecular Receptors as Adsorbents to Remove Micropollutants from Water

Organic micropollutants (MPs) are increasing in number and concentration in water systems as a result of human activities. Often from human origin, these micropollutants build up in the environment because organisms lack the mechanisms to metabolize these substances, which cause negative health, ecological, and economic effects. Adsorption-based remediation processes for these compounds often rely on activated carbon materials. However, activated carbons are ineffective against certain MPs, exhibit low removal efficiencies in the presence of common aqueous matrix constituents, and require energy-intensive activation and regeneration processes. To overcome the deficiencies of traditional technologies, novel adsorbents based on molecular receptors offer promising alternative solutions. This Account describes the recent development of polymer adsorbents based on molecular receptors for removing trace organic chemicals from water. Polymer networks based on molecular receptors have high binding affinities for many MPs but, unlike activated carbons, have a specific molecule-binding mechanism that prevents these polymers from being fouled by matrix constituents such as natural organic matter. The size and hydrophobic pocket of the β-cyclodextrin receptor preferentially adsorbs target molecules such as organic micropollutants in the presence of matrix constituents, and the nature of the cross-linker tunes the binding affinity and selectivity of the adsorbent for specific classes of MPs, including those of varying charge and hydrophobicity. β-cyclodextrin polymers also exhibit rapid adsorption kinetics and are easily regenerated. This Account details β-cyclodextrin polymers made with three different cross-linkers, including a polymer that is postsynthetically transformed from a negatively charged polymer to a positively charged polymer to invert the polymer's micropollutant adsorption profile. Morphological constraints have so far limited these cross-linked polymers' ability to be used in commercial applications, but two methods to create larger and more uniformly sized particles for use in flow-through applications are described here. β-Cyclodextrin polymers are useful for trapping organic micropollutants such as bisphenol A, perfluorooctanoic acid, and many kinds of pharmaceuticals and pesticides, but their binding pockets are too large to capture micropollutants that are small or of high polarity. Other molecular receptors such as resorcinarene cavitands can target lower-molecular-weight MPs, including halomethane disinfection byproducts and industrial solvents, that are not bound strongly by β-cyclodextrins. These materials demonstrate the potential of expanding the library of polymers based on molecular receptors. Overall, these emerging adsorbents show promise for the removal of legacy and emerging MPs from water, as well as the ability to rationally tune the adsorbent's structure to target the most persistent and toxic MPs.

Melamine-based functionalized graphene oxide and zirconium phosphate for high performance removal of mercury and lead ions from water

Heavy metal ions are highly toxic and widely spread as environmental pollutants. This work reports the development of two novel chelating adsorbents, based on the chemical modifications of graphene oxide and zirconium phosphate by functionalization with melamine-based chelating ligands for the effective and selective extraction of Hg(ii) and Pb(ii) from contaminated water sources. The first adsorbent melamine, thiourea-partially reduced graphene oxide (MT-PRGO) combines the heavier donor atom sulfur with the amine and triazine nitrogen's functional groups attached to the partially reduced GO nanosheets to effectively capture Hg(ii) ions from water. The MT-PRGO adsorbent shows high efficiency for the extraction of Hg(ii) with a capacity of 651 mg g-1 and very fast kinetics resulting in a 100% removal of Hg(ii) from 500 ppb and 50 ppm concentrations in 15 second and 30 min, respectively. The second adsorbent, melamine zirconium phosphate (M-ZrP), is designed to combine the amine and triazine nitrogen's functional groups of melamine with the hydroxyl active sites of zirconium phosphate to effectively capture Pb(ii) ions from water. The M-ZrP adsorbent shows exceptionally high adsorption affinity for Pb(ii) with a capacity of 681 mg g-1 and 1000 mg g-1 using an adsorbent dose of 1 g L-1 and 2 g L-1, respectively. The high adsorption capacity is also coupled with fast kinetics where the equilibrium time required for the 100% removal of Pb(ii) from 1 ppm, 100 ppm and 1000 ppm concentrations is 40 seconds, 5 min and 30 min, respectively using an adsorbent dose of 1 g L-1. In a mixture of six heavy metal ions at a concentration of 10 ppm, the removal efficiency is 100% for Pb(ii), 99% for Hg(ii), Cd(ii) and Zn(ii), 94% for Cu(ii), and 90% for Ni(ii) while at a higher concentration of 250 ppm the removal efficiency for Pb(ii) is 95% compared to 23% for Hg(ii) and less than 10% for the other ions. Because of the fast adsorption kinetics, high removal capacity, excellent regeneration, stability and reusability, the MT-PRGO and M-ZrP are proposed as top performing remediation adsorbents for the solid phase extraction of Hg(ii) and Pb(ii), respectively from contaminated water.

Removal of mercury(II) from wastewater using a new and effective composite: sulfur-coated magnetic carbon nanotubes

A sulfur-coated magnetic multi-walled carbon nanotube (S-M-MWCNT) composite was synthesized via coating a thin S layer on M-MWCNTs via a facile heating process. The prepared superparamagnetic adsorbent was employed for the uptake of mercury(II) (Hg(II)) from aqueous solutions and then magnetically separated without filtration or centrifugation steps. The adsorption of Hg(II) increased with increasing pH and reached a plateau value in the pH range 4.5-8.0. The adsorption kinetics followed the pseudo-second-order (PSO) model and equilibrium was reached within 3 h. The isotherm data obeyed the Langmuir isotherm model, and the maximum adsorption capacity of S-M-MWCNT adsorbent was acquired as 62.11 mg g^-1. The adsorption of Hg(II) by the prepared composite is possibly controlled by the interaction between Hg(II) as a soft acid and elemental coated sulfur as a soft base. In addition, the coexist metal ions including copper(II) (Cu(II)), cadmium(II) (Cd(II)), cobalt(II) (Co(II)), lead(II) (Pb(II)), manganese(II) (Mn(II)), zinc(II) (Zn(II)), and chromium(III) (Cr(III)) had no significant effects on Hg(II) removal performance. It was found that the S-M-MWCNT composite could be reused after successive Hg(II) removal without any loss of adsorption capacity. Furthermore, the magnetic adsorbent holds high potential in the treatment of Hg-contaminated wastewater samples.

Two sulfur and nitrogen-rich cobalt–thiacalix[4]arene compounds for the selective mercury removal from aqueous solutions

Two thiacalix[4]arene-based coordination compounds, a {Co₂₄} octahedral coordination cage and a {Co₈} cluster, are effective adsorbents towards Hg(ii) and the adsorption capacity of the {Co₂₄} cage compound reaches 330 mg g⁻¹.

Thiadiazole containing N- and S-rich highly ordered periodic mesoporous organosilica for efficient removal of Hg(ii) from polluted water

We report a new N- and S-rich highly ordered periodic mesoporous organosilica material DMTZ-PMO bearing thiadiazole and thiol moieties inside the pore-wall for very efficient and fast removal of Hg²⁺ from polluted water (uptake = 2081 mg g⁻¹).