Stable Covalent Organic Frameworks for Exceptional Mercury Removal from Aqueous Solutions

Sulfhydryl-functionalized anisotropic photonic crystal hydrogels for visual Hg2+ detection and adsorption in cinnabar mine water area

Emissions of mercury ions from human activities during mining and smelting processes cannot be overlooked due to their potential for environmental pollution. Consequently, developing a material that offers both visual detection capability and efficient adsorption for Hg2+ is crucial. Inspired by cephalopod skin, we have prepared a sulfhydryl-functionalized anisotropic photonic crystal hydrogel (PDGI/PAAm-SH). The bilayer structure of polydodecyl glyceryl itaconate (PDGI) is immobilized and stabilized within the sulfhydryl-functionalized polyacrylamide network after polymerization. The porous structure of hydrogel facilitates the adsorption of Hg2+ in solution, resulting in a blue shift in structural color, which allows for visual detection. The PDGI/PAAm-SH effectively adsorbs and removes Hg2+ from water, with an impressive uptake capacity of 129.06 mmol kg-1. Additionally, this hydrogel exhibits good reproducibility, excellent mechanical properties, and remarkable selectivity for Hg2+. It can shield interference from other ions during detection and shows promising applications in environmental monitoring and purification.

Semiconducting Polyaromatic Covalent Organic Frameworks Constructed through Self-Aldol Condensation

The construction of semiconducting covalent organic frameworks (COFs) via single-component self-polymerization is of broad interest in reticular chemistry. Herein, two semiconducting polyaromatic COFs with all-fused-ring conjugation structures were synthesized through the self-aldol condensation of indanone-based building blocks. The resulting COFs exhibit n-type semiconducting properties and exceptional stability under harsh acidic and alkaline conditions. The electrical conductivity and charge carrier mobility of the polyaromatic COFs reached up to 5.5 × 10-3 S cm-1 and 0.62 cm2 V-1 s-1, which ranked as the highest values among n-type semiconducting COFs. The high crystallinity, intrinsic porosity, excellent conductivity, and abundant five-membered rings as active sites render these COFs as effective metal-free electrocatalysts toward oxygen reduction reaction (ORR). Notably, one of these COFs shows a half-wave potential of up to 0.77 V under alkaline conditions, which constitutes one of the highest values among the reported metal-free ORR electrocatalysts. In addition, owing to the strong robustness of the polyaromatic COFs, they also exhibit long-term catalytic durability. This study not only expands the diversity of semiconducting COFs but also establishes new paradigms for the development of high-performance metal-free electrocatalysts toward the ORR process.

Enhanced Separation of Palladium from Nuclear Wastewater by the Sulfur-Rich Functionalized Covalent Organic Framework

The separation of palladium from radioactive waste streams represents a critical aspect of the secure handling and disposal of such hazardous materials. Palladium, in addition to its radioactive nature, holds intrinsic value as a resource. Despite the urgency, prevailing adsorbents fall short in their ability to effectively separate palladium under highly acidic environments. To surmount this challenge, our research has pioneered the development of 1,3,5-tris(4-aminophenyl)benzene-2,5-Bis(methylthio)terephthalaldehyde COF (TAPB-BMTTPA-COF), a novel material distinguished by its remarkable stability and an abundance of sulfur-containing functional groups. Leveraging the pronounced affinity of the soft ligands' nitrogen and sulfur within its molecular architecture, TAPB-BMTTPA-COF demonstrates an exceptional capability for the selective adsorption of palladium. Empirical evidence underscores the material's swift adsorption kinetics, with equilibrium achieved in as little as ten minutes, and its broad tolerance to varying acidity levels ranging from 0.1 to 3 M HNO3. Furthermore, TAPB-BMTTPA-COF boasts an impressive adsorption capacity, peaking at 343.6 mg/g, coupled with high selectivity in 13 interfering ions' environment and the ability to be regenerated, making it a sustainable solution. Comprehensive analyses, including Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), alongside Density Functional Theory (DFT) calculations, have corroborated the pivotal role played by densely packed nitrogen and sulfur active sites within the framework. These sites exhibit a robust affinity for Pd(II), which is the cornerstone of the material's outstanding adsorption efficacy. The outcomes of this research underscore the immense potential of COFs endowed with resilient linkers and precisely engineered functional groups. Such COFs can adeptly capture metal ions with high selectivity, even in the face of severe environmental conditions, thereby paving the way for the more effective and environmentally responsible management of radioactive waste.

Insight into the mechanism of semi-hydrogenation of phenylacetylene over Pd embedded in thioether functionalized Schiff-base linked covalent organic frameworks

We report a novel catalyst comprising palladium supported on thioether functionalized Schiff-base conjugated covalent organic frameworks, which significantly enhances the semi-hydrogenation conversion and selectivity of phenylacetylene. Theoretical calculations substantiate that the imide and thioether groups modify the electron density around Pd, reducing the energy barriers for phenylacetylene adsorption and styrene desorption, thereby improving the conversion and selectivity of the catalyst.

Synthesis of ZIF-8/chitosan composites for Cu2+ removal from water

In this work, a kind of novel Chitosan (Cs)-doped zeolite imidazole framework (ZIF-8@Cs) with a larger surface area and a smaller pore size was synthesised via a facial solvothermal approach and applied to remove Cu2+ from mine wastewater. Compared to nondoped ZIF-8, ZIF-8@Cs exhibited a stronger adsorption performance and removal efficiency. The reason was that ZIF-8@Cs doped by the Cs could suppress the aggregation and increase the monodispersity of ZIF-8. Using the high-performance ZIF-8@Cs, as a novel adsorbent, was successfully developed for the efficient removal of Cu2+ from mine wastewater. Various parameters, such as contact time, initial Cu2+ concentration, adsorbent dosage, and pH, were investigated. The results showed that a removal efficiency of 85% was obtained at 4 h contact time for a Cu2+ concentration of 30 mg/L at the optimum pH of 6.0. Equilibrium data were analysed using different isothermal models and kinetic models, analytic results indicated that the capture of Cu2+ by ZIF-8@Cs could favourably comply with the pseudo-first-order kinetic model and Langmuir isotherm model. The single-layer adsorption of Cu2+ on ZIF-8@Cs was dominated by diffusional mass transfer. Additionally, the results of the thermodynamic analysis indicated that the adsorption of Cu2+ by ZIF-8/Cs was a spontaneous, exothermic, and ordered process. Overall, the results reported herein indicated that ZIF-8/Cs with high adsorption efficiency are very attractive and imply a potential practical application for the removal of potentially toxic elements in wastewater.

Unlocking Enhanced Detection of Perfluoroalkanesulfonic Acids via Fluorinated Nonpolar 3D Covalent Organic Frameworks-Based Ambient Probe Nanoelectrospray Ionization Mass Spectrometry

The trace levels and severe matrix interferences greatly limited the determination of stable, persistent, and long-range-transported perfluoroalkanesulfonic acids (PFSAs) in complex environments. Here, we design and prepare the first fluorinated nonpolar 3D COF (TFPM-Pa-CF3) as an adsorbent, consisting of tetrakis(4-formylphenyl)methane (TFPM) and 2,5-diaminobenzo-trifluoride (Pa-CF3) for adsorption and extraction of PFSAs. The proposed TFPM-Pa-CF3 demonstrates excellent adsorption capacity (509.1 mg g-1) and rapid adsorption kinetics (5 min) for PFSAs attributed to the synergistic effects of F-F, hydrophobic, and electrostatic interactions. Furthermore, TFPM-Pa-CF3 is grown in situ on a stainless needle and coupled with ambient probe nanoelectrospray ionization mass spectrometry (PESI-MS) to develop a rapid and direct determination method with a low limit of detection (0.05-0.86 ng L-1) and wide linear range (1-10,000 ng L-1) for trace perfluorooctanesulfonate and its alternatives in environmental soil, algae and water. This work unlocks the efficient determination or removal of PFSAs in a complex environment, facilitating the solution of critical environmental PFSAs problems.

Electrospun Polyvinyl Chloride/UiO-66(COOH)2 Nanocomposite Membranes for Efficient and Rapid Heavy Metal Removal

This study explores the effectiveness of a new composite membrane fabricated from poly(vinyl chloride) (PVC) and the UiO-66(COOH)2 metal-organic framework (MOF) for the removal of heavy metals from water. The electrospinning technique was successfully employed to homogeneously incorporate UiO-66(COOH)2 nanocrystals into PVC, producing fibrous composite membranes. The membranes were fully characterized using several techniques such as scanning electron microscopy (SEM), capillary flow porometry, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and tensile strength analysis. The metal removal performance of the membranes was evaluated against lead, cadmium, and mercury in both single and mixed metal solutions at different concentrations. Results indicated a high removal efficiency (>90%) and selectivity for lead in both single and mixed solutions, especially at concentrations less than 50 ppm, along with a high adsorption capacity (Qmax = 203 mg/g). While cadmium demonstrated a lower % removal efficiency of 40% in mixed solutions compared to 80% in single solutions, it exhibited the highest adsorption capacity (Qmax = 1312 mg/g) among the three metals. For mercury, however, the decrease in removal efficiency was more pronounced, with only 10% removal in mixed systems and the lowest adsorption capacity (Qmax = 40.5 mg/g). Further experiments showed that the presence of salts, such as chlorides, nitrates, and sulfates, did not significantly affect lead and cadmium removal. Conversely, mercury removal was consistently low, regardless of these conditions. Additionally, temperature-dependent studies revealed that increasing temperature enhanced both removal efficiency and adsorption capacity, confirming that the process was spontaneous and endothermic. Interestingly, the reusability of the membranes showed a consistent removal efficiency of over 90% for lead after four cycles of use, particularly at 15 ppm, although the other metals exhibited a decrease in efficiency. Almost all pollutants showed a better fit for Langmuir and second-order kinetic models, suggesting that adsorption is a single-layered chemical adsorption process. Furthermore, a membrane holder design was fabricated using three-dimensional (3D) printing and tested to underscore the potential of PVC/MOFs composite membranes as effective materials for efficient and rapid heavy metal remediation (5 mins) in contaminated water sources. The holder significantly improved lead removal efficiency while maintaining mechanical stability, addressing the issue of handling MOFs powder alone by providing a robust matrix and support for both the MOFs and the membrane. This approach facilitates easier handling while maintaining a high efficiency, paving the way for potential industrial applications.

Thiolated non-conjugated nano polymer network for advanced mercury removal from water

Developing advanced adsorbents for selectively deducing mercury (Hg) in water to one billionth level is of great significance for public health and ecological security, but achieving the balance among efficiency, cost and environmental friendliness of adsorbents still faces enormous challenges. Herein, we present a high thiol content non-conjugated nano polymer network (PVB-SH) through simple microemulsion polymerization for efficient Hg ion (Hg(II)) removal. The PVB-SH is prepared by conventional commercial reagents and does not consume toxic organic solutions. This nano network reveals uniformly distributed nano sizes, leading to good accessibility of adsorption sites. The long and flexible polymer chains in the network allow two thiol sites to coordinate with one Hg(II), displaying significantly stronger binding than 1:1 coordination. Therefore, PVB-SH shows high affinity toward Hg(II) (Kd = 3.04 × 107 mL/g) and can selectively reduce Hg(II) in water to extremely low level of 0.14 μg/L, well below the safe limit of 2 μg/L. PVB-SH possesses excellent renewability (removal efficiency = 99.58 % after 10 regenerations), good resistance to various environmental factors (pH, ions and organic matter) and long-term stability in acid, alkali, and salt solutions. Impressively, PVB-SH is further made into a membrane by simple phase-inversion and can effectively purify 1592.4 L/m2 Hg(II) polluted drinking water before the breakthrough point of 2 μg/L. These results demonstrate the good practical potential of PVB-SH for decontamination of Hg from aqueous media.

Thiophene-Based Porous Triazine Polyamide (Tb-PTPa) as the Next Promising and Cost-Effective Eliminator of Hg2+ in Aqueous Media

Research suggests that wastewater is highly polluted by Hg2+, threatening the sustainability of our environment and the health conditions of human beings. However, most of the existing adsorbents have a poor adsorption performance and require expensive raw materials. A low-cost adsorbent material with a very high adsorption performance is therefore an urgent need. In this work, we have successfully prepared thiophene-based porous triazine polyamide (Tb-PTPa) for the first time, using two inexpensive raw materials and a simple amidation reaction. Tb-PTPa was then used for the efficient adsorption of Hg2+ in the aqueous media. The adsorption capacity of Tb-PTPa for Hg2+ was up to 2562 mg g-1 and the adsorption rate was 12.9 mg g-1 min-1. In addition, Tb-PTPa shows good selectivity for the adsorption of Hg2+. The removal rate is still higher than 91% after five adsorption cycles. The interfering substances present in water only slightly affect the capture of Hg2+ by Tb-PTPa. The combination of our experimental results and density functional theory calculations clearly shows that the introduction of amide bonds can greatly enhance the chelating ability of the N atoms of triazine and the S atoms of thiophene for Hg2+. Based on our extensive investigation, we have demonstrated that Tb-PTPa is a low-cost adsorbent with excellent adsorption properties. Therefore, Tb-PTPa is expected to be a new adsorbent material for the treatment of Hg2+ in the wastewater.

Emerging MOFs, COFs, and their derivatives for energy and environmental applications

Traditional fossil fuels significantly contribute to energy supply, economic development, and advancements in science and technology. However, prolonged and extensive use of fossil fuels has resulted in increasingly severe environmental pollution. Consequently, it is imperative to develop new, clean, and pollution-free energy sources with high energy density and versatility as substitutes for conventional fossil fuels, although this remains a considerable challenge. Simultaneously, addressing water pollution is a critical concern. The development, design, and optimization of functional nanomaterials are pivotal to advancing new energy solutions and pollutant remediation. Emerging porous framework materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), recognized as exemplary crystalline porous materials, exhibit potential in energy and environmental applications due to their high specific surface area, adjustable pore sizes and structures, permanent porosity, and customizable functionalities. This work provides a comprehensive and systematic review of the applications of MOFs, COFs, and their derivatives in emerging energy technologies, including the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, lithium-ion batteries, and environmental pollution remediation such as the carbon dioxide reduction reaction and environmental pollution management. In addition, strategies for performance adjustment and the structure-effect relationships of MOFs, COFs, and their derivatives for these applications are explored. Interaction mechanisms are summarized based on experimental discussions, theoretical calculations, and advanced spectroscopy analyses. The challenges, future prospects, and opportunities for tailoring these materials for energy and environmental applications are presented.

Carbazole-Phosphazene Based Polymer for Efficient Extraction of Gold and Precious Elements from Electronic Waste

The continuous advancement of industry and technology has significantly increased electronic waste, which contributes to the depletion of valuable metal reserves. Therefore, it is crucial to recycle precious metals in electronic waste effectively and sustainably. This study introduces a novel approach by applying a carbazole-phosphazene-based polymer, EBE-06, in a two-stage leaching method for efficient metal extraction. In the first leaching stage, tin is selectively separated using an acid solution at a controlled pH. In the second stage, valuable metals such as gold are recovered through adsorption onto EBE-06. The polymer exhibited a 99% gold adsorption rate within 1 h, independent of pH, and a maximum adsorption capacity of 1.787 g of gold per gram of polymer. The desorption process yielded 95% efficiency, with the polymer maintaining 94% efficiency over three cycles of use.

Sulfonated Covalent Organic Frameworks Anchoring Cobalt as High-Efficient and Stable Catalysts for Peroxymonosulfate Activation

Heterogeneous cobalt-based catalysts are highly effective in activing peroxymonosulfate (PMS) and produce free radicals to deal with recalcitrant organic pollutants in water. However, unfeasible recyclability and gradual performance degradation remain challenging due to the easy agglomeration and leaching of active cobalt species. Herein, a strategy is proposed to construct stably anchored and highly dispersed Co2+ sites on dual functional sulfonated covalent organic frameworks (COF-Co). The sulfonic acid groups are able to realize the targeted binding with cobalt ions through a two-step cation-exchange method, leading to strong combination with active Co2+ sites and utmost utilization efficiencies. Moreover, the super-hydrophility of sulfonic acid groups favors the rapid accessibility of organic molecules to the catalyst and accelerates the degradation. Remarkably, COF-Co exhibits high activity in PMS activation, effective oxidation for tetracycline degradation (92% within 30 min at 30 mg L-1) and other coloring contaminants, and excellent recycle stability. This work can guide the rational design of efficient and environmentally friendly PMS-activated catalyst with great potential for application in wastewater treatment.

Deposition of Imidazole into Mesoporous Zirconium Metal-Organic Framework for Iodine Capture

Efficient capture of radioiodine is essential for the protection of the ecological environment and the sustainable development of nuclear energy generation. Metal-organic frameworks (MOFs) and their derivatives provide alternative potential for overcoming the limitations of traditional iodine adsorbents. Herein this work, imidazole (Im) is dispersed into a robust mesoporous zirconium MOF PCN-222 by the heat deposition method, forming a high-uniformity composite Im@PCN-222. The large pore size and marked chemical resistance skeleton of PCN-222 allow the incorporation of Im to reach 43 wt % while surviving the chemical corrosion of activated Im. The nearly saturated loading of Im significantly benefits the sorption capability toward iodine and gives rise to an exceptional adsorption capacity of 10.04 g g-1 and excellent recyclability. This value is higher than that of most of the MOFs and their derivatives. Further, Im was also successfully deposited onto the PCN-222 functionalized porous Al2O3 ceramic filtration membrane, which endowed the hybrid membrane with efficient iodine sorption and separation properties. This work highlights a new strategy for the fabrication of the MOF-based radioiodine adsorption composite as well as MOF composite-based filters.

Wiring Covalent Organic Frameworks with Conducting Polymers

Covalent organic frameworks are a class of crystalline porous polymers formed by linking organic units into periodically aligned skeletons and pores. Here we report a strategy for wiring these frameworks with conducting polymers via wall engineering and polymerization. We anchored each edge site with one pyrrole unit, which is densely packed along the z direction yet protruded from pore walls. This assembly enables the polymerization of pyrrole units to form polypyrrole and creates a new polypyrrole chain conformation. The resultant framework constitutes six single file polypyrrole chains in each pore and develop spatially segregated yet built-in single molecular wires with exceptional stable polarons. Hall effect measurements revealed that the materials are p-type semiconductors, increase conductivity by eight orders of magnitude compared to the pristine frameworks, and achieve a carrier mobility as large as 13.2 cm2 V-1 s-1. Our results open an avenue to π electronic frameworks by interlayer molecular wiring with conducting polymers.

Synergistic Linker and Linkage of Covalent Organic Frameworks for Enhancing Gold Capture

The tunable pore walls and skeletons render covalent organic frameworks (COFs) as promising absorbents for gold (Au) ion. However, most of these COFs suffered from low surface areas hindering binding sites exposed and weak binding interaction resulting in sluggish kinetic performance. In this study, COFs have been constructed with synergistic linker and linkage for high-efficiency Au capture. The designed COFs (PYTA-PZDH-COF and PYTA-BPDH-COF) with pyrazine or bipyridine as linkers showed high surface areas of 1692 and 2076 m2 g‒1, providing high exposed surface areas for Au capture. In addition, the Lewis basic nitrogen atoms from the linkers and linkages are easily hydronium, which enabled to fast trap Au via coulomb force. The PYTA-PZDH-COF and PYTA-BPDH-COF showed maximum Au capture capacities of 2314 and 1810 mg g-1, higher than other reported COFs. More importantly, PYTA-PZDH-COF are capable of rapid adsorption kinetics with achieving 95% of maximum binding capacity in 10 min. The theoretical calculation revealed that the nitrogen atoms in linkers and linkages from both COFs are simultaneously hydronium, and then the protonated PYTA-PZDH-COF are more easily binding the AuCl4 ‒, further accelerating the binding process. This study gives the a new insight to design COFs for ion capture.

Heavy-Metal Ions Removal and Iodine Capture by Terpyridine Covalent Organic Frameworks

Porous materials are excellent candidates for water remediation in environmental issues. However, it is still a key challenge to design efficient adsorbents for rapid water purification from various heavy metal ions-contaminated wastewater in one step. Here, two robust nitrogen-rich covalent organic frameworks (COFs) bearing terpyridine units on the pore walls by a "bottom-up" strategy are reported. Benefitting from the strong chelation interaction between the terpyridine units and various heavy metal ions, these two terpyridine COFs show excellent removal efficiency and capability for Pb2+, Hg2+, Cu2+, Ag+, Cd2+, Ni2+, and Cr3+ from water. These COFs are shown to remove such heavy metal ions with >90% of contents at one time after the aqueous metal ions mixture is passed through the COF filter. The nitrogen-rich features of the COFs also endow them with the capability of capturing iodine vapors, offering the terpyridine COFs the potential for environmental remediation applications.

Green and Mild Fabrication of Magnetic Poly(trithiocyanuric acid) Polymers for Rapid and Selective Separation of Mercury(II) Ions in Aqueous Samples

The removal and detection of highly toxic mercury(II) ions (Hg2+) in water used daily is essential for human health and monitoring environmental pollution. Efficient porous organic polymers (POPs) can provide a strong adsorption capacity toward heavy metal ions, although the complex synthetic process and inconvenient phase separation steps limit their application. Hence, a combination of POPs and magnetic nanomaterials was proposed and a new magnetic porous organic polymer adsorbent was fabricated by a green and mild redox reaction in the aqueous phase with trithiocyanuric acid (TA) and its sodium salts acting as reductive monomers and iodine acting as an oxidant. In the preparation steps, no additional harmful organic solvent is required and the byproducts of sodium iodine are generally considered to be non-toxic. The resulting magnetic poly(trithiocyanuric acid) polymers (MPTAPs) are highly porous, have large surface areas, are rich in sulfhydryl groups and show easy magnetic separation ability. The experimental results show that MPTAPs exhibit good adsorption affinity toward Hg2+ with high selectivity, rapid adsorption kinetics (10 min), a large adsorption capacity (211 mg g-1) and wide adsorption applicability under various pH environments (pH 2~8). Additionally, MPTAPs can be reused for up to 10 cycles, and the magnetic separation step of MPTAPs is fast and convenient, reducing energy consumption compared to centrifugation and filtration steps required for non-magnetic adsorbents. These results demonstrate the promising capability of MPTAPs as superior adsorbents for effective adsorption and separation of Hg2+. Based on this, the prepared MPTAPs were adopted as magnetic solid-phase extraction (MSPE) materials for isolation of trace Hg2+ from aqueous samples. Under optimized conditions, the extraction and quantification of trace Hg2+ in water samples were accomplished using inductively coupled plasma mass spectrometry (ICP-MS) detection after MSPE procedures. The proposed MPTAPs-based MSPE-ICP-MS method is efficient, rapid, sensitive and selective for the determination of trace Hg2+, and was successfully employed for the accurate analysis of trace Hg2+ in tap water, wastewater, lake water and river water samples.

Rational Design of Regenerable Amino-Functionalized Fluorescent Covalent Organic Framework for the Exclusive Detection of Mercury(II)

Goal-oriented development of novel covalent organic frameworks (COFs) to construct a sensing platform for highly toxic mercury (II, Hg2+) is of tremendous significance. Recently, numerous COFs with sulfur-based ligands were developed for Hg2+ monitoring; however, strong binding of Hg2+ by sulfur makes their regeneration very tough. Herein, we designed and developed an amino-functionalized fluorescent COF (COF-NH2) through facile postmodification for Hg2+ detection in which the π-conjugation skeleton is the signal reader and the nitrogen-based side is the highly selective Hg2+ receptor. More importantly, this nitrogen-based receptor permits the reversible binding of Hg2+. As a sensing platform, the outstanding performance of COF-NH2 for Hg2+ detection was reached with respect to high sensitivity with an ultralow detection of 15.3 nM, real-time response with rapid signal change of 10 s, and facile visualization with significant fluorescence color change. Expectedly, COF-NH2 obtained facile recycling which still shows excellent response performance toward Hg2+ after six cycles based on the reversible interaction between amino groups and Hg2+. Our work not only shows an attractive foreground of fluorescent COF for Hg2+ detection but also emphasizes the easy construction of novel COF materials via the rational introduction of metal ligands for the recognition of other metal ions.

Covalent organic framework membranes with vertically aligned nanorods for efficient separation of rare metal ions

Covalent organic frameworks (COFs) have emerged as promising platforms for membrane separations, while remaining challenging for separating ions in a fast and selective way. Here, we propose a concept of COF membranes with vertically aligned nanorods for efficient separation of rare metal ions. A quaternary ammonium-functionalized monomer is rationally designed to synthesize COF layers on porous substrates via interfacial synthesis. The COF layers possess an asymmetric structure, in which the upper part displays vertically aligned nanorods, while the lower part exhibits an ultrathin dense layer. The vertically aligned nanorods enlarge contact areas to harvest water and monovalent ions, and the ultrathin dense layer enables both high permeability and selectivity. The resulting membranes exhibit exceptional separation performances, for instance, a Cs+ permeation rate of 0.33 mol m-2 h-1, close to the value in porous substrates, and selectivities with Cs+/La3+ up to 75.9 and 69.8 in single and binary systems, highlighting the great potentials in the separation of rare metal ions.

Recent Progress on Covalent Organic Frameworks Supporting Metal Nanoparticles as Promising Materials for Nitrophenol Reduction

With the utilization of nitrophenols in manufacturing various materials and the expansion of industry, nitrophenols have emerged as water pollutants that pose significant risks to both humans and the environment. Therefore, it is imperative to convert nitrophenols into aminophenols, which are less toxic. This conversion process is achieved through the use of noble metal nanoparticles, such as gold, silver, copper, and palladium. The primary challenge with noble metal nanoparticles lies in their accumulation and deactivation, leading to a decrease in catalyst activity. Covalent organic frameworks (COFs) are materials characterized by a crystalline structure, good stability, and high porosity with active sites. These properties make them ideal substrates for noble metal nanoparticles, enhancing catalytic activity. This overview explores various articles that focus on the synthesis of catalysts containing noble metal nanoparticles attached to COFs as substrates to reduce nitrophenols to aminophenols.

Removal of mercury and lead ions from water using bioinspired N3Se3 type small sized moieties

Mercury and lead toxicity in water has serious repercussions on human health. There is an urgent need to develop effective and efficient small moieties for their removal. The convenient one-pot synthesis of a few N3Se3 type small sized moieties is reported herein. The highest metal ion uptake capacity of Hg(II) and Pb(II) ions was found to be 314.3 mg g-1 and 93.5 mg g-1, respectively, by ICP-MS analysis. These ion uptake values are the highest for small sized moieties known in the literature to date.

An Alkyne-Bridged Covalent Organic Framework Featuring Interactive Pockets for Bromine Capture

The high degree of corrosivity and reactivity of bromine, which is released from various sources, poses a serious threat to the environment. Moreover, its coexistence with iodine forming an equilibrium compound, iodine monobromide (IBr) necessitates the selective capture of bromine from halogen mixtures. The electrophilicity of halogens to π-electron rich structures enabled us to strategically design a covalent organic framework for halogen capture, featuring a defined pore environment with localized sorption sites. The higher capture capacity of bromine (4.6 g g-1) over iodine by ~41 % shows its potential in selective capture. Spectroscopic results uncovering the preferential interaction sites are supported by theoretical investigations. The alkyne bridge is a core functionality promoting the selectivity in capture by synergistic physisorption, rationalized by the higher orbital overlap of bromine due to its smaller atomic size as well as reversible chemical interactions. The slip stacking in the structure has further promoted this phenomenon by creating clusters of molecular interaction sites with bromine intercalated between the layers. The inclusion of unsaturated moieties, i.e. triple bonds and the complementary pore geometry offer a promising design strategy for the construction of porous materials for halogen capture.

Hg2+-enhanced oxidase-like activity of platinum nanoparticles immobilized on porphyrin-based porous organic polymer for the colorimetric detection and removal of Hg2

Porphyrin-based porous organic polymer (POP) with uniformly immobilized platinum nanoparticles (Pt NPs) were designed and synthesized, and it was demonstrated that such nanocomposites (Pt/POP) have oxidase-like activity. Surprisingly, Hg2+ significantly enhanced the oxidase-like activity of Pt/POP. The enhancement was attributed to the capture of Hg2+ by the thioether group in Pt/POP and the subsequent redox reaction of Hg2+ with Pt NPs, accelerating the electron transfer. In the presence of Hg2+, Pt/POP catalyzed the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to turn blue rapidly and changed its absorbance at 652 nm. Based on this, a fast-response colorimetric sensor was constructed for the sensitive detection of Hg2+ with a linear range of 0.2-50 μM and a detection limit of 36.5 nM. Importantly, Pt/POP can be used as an adsorbent for the efficient removal of Hg2+ with a removal efficiency as high as 99.4%. This work provides a valuable strategy for colorimetric detection and efficient removal of Hg2+.

Photo-Induced Geometry and Polarity Gradients in Covalent Organic Frameworks Enabling Fast and Durable Molecular Separations

Azobenzene, which activates its geometric and chemical structure under light stimulation enables noninvasive control of mass transport in many processes including membrane separations. However, producing azobenzene-decorated channels that have precise size tunability and favorable pore wall chemistry allowing fast and durable permeation to solvent molecules, remains a great challenge. Herein, an advanced membrane that comprises geometry and polarity gradients within covalent organic framework (COF) nanochannels utilizing photoisomerization of azobenzene groups is reported. Such functional variations afford reduced interfacial transfer resistance and enhanced solvent-philic pore channels, thus creating a fast solvent transport pathway without compromising selectivity. Moreover, the membrane sets up a densely covered defense layer to prevent foulant adhesion and the accumulation of cake layer, contributing to enhanced antifouling resistance to organic foulants, and a high recovery rate of solvent permeance. More importantly, the solvent permeance displays a negligible decline throughout the long-term filtration for over 40 days. This work reports the geometry and polarity gradients in COF channels induced by the conformation change of branched azobenzene groups and demonstrates the strong capability of this conformation change in realizing fast and durable molecular separations.

Highly efficient capture of mercury from complex water matrices by AlZn alloy reduction-amalgamation and in situ layered double hydroxide

Mercury pollution is a critical, worldwide problem and the efficient, cost-effective removal of mercury from complex, contaminated water matrices in a wide pH range from strongly acidic to alkaline has been a challenge. Here, AlZn and AlFe alloys are investigated and a new process of synergistic reduction-amalgamation and in situ layered double hydroxide (SRA-iLDH) for highly efficient capture of aqueous Hg(II) is developed using AlZn alloys. The parameters include the pH values of 1-12, the Hg(II) concentrations of 10-1000 mg L-1, and the alloy's Zn concentrations of 20%, 50% and 70% and Fe concentrations of 10%, 20% and 50%. The initial rate of Hg(II) uptake by AlZn alloys decreases with increasing Zn concentration while the overall rate is not affected. Specifically, AlZn50 alloy removes >99.5% Hg(II) from 10 mg L-1 solutions at pH 1-12 in 5 min at a rate constant of 0.055 g mg-1 min-1 and achieves a capacity of 5000 mg g-1, being the highest value reported so far. The super-performance of AlZn alloy is attributed to multiple functions of chemical reduction, dual amalgamation, in situ LDH's surface complexation and adsorption, isomorphous substitution and intercalation. This study provides a simple and highly efficient approach for removing Hg(II) from complex water matrices.

Highly Conductive Imidazolate Covalent Organic Frameworks with Ether Chains as Solid Electrolytes for Lithium Metal Batteries

Poly(ethylene oxide) (PEO)-based electrolytes are often used for Li+ conduction as they can dissociate the Li salts efficiently. However, high entanglement of the chains and lack of pathways for rapid ion diffusion limit their applications in advanced batteries. Recent developments in ionic covalent organic frameworks (iCOFs) showed that their highly ordered structures provide efficient pathways for Li+ transport, solving the limitations of traditional PEO-based electrolytes. Here, we present imidazolate COFs, PI-TMEFB-COFs, having methoxyethoxy chains, synthesized by Debus-Radziszewski multicomponent reactions and their ionized form, Li+@PI-TMEFB-COFs, showing a high Li+ conductivity of 8.81 mS cm-1 and a transference number of 0.974. The mechanism for such excellent electrochemical properties is that methoxyethoxy chains dissociate LiClO4, making free Li+, then those Li+ are transported through the imidazolate COFs' pores. The synthesized Li+@PI-TMEFB-COFs formed a stable interface with Li metal. Thus, employing Li+@PI-TMEFB-COFs as the solid electrolyte to assemble LiFePO4 batteries showed an initial discharge capacity of 119.2 mAh g-1 at 0.5 C, and 82.0 % capacity and 99.9 % Coulombic efficiency were maintained after 400 cycles. These results show that iCOFs with ether chains synthesized via multicomponent reactions can create a new chapter for making solid electrolytes for advanced rechargeable batteries.

Effect of interlayer slipping on the geometric, thermal and adsorption properties of 2D covalent organic frameworks: a comprehensive review based on computational modelling studies

Two-dimensional covalent organic frameworks (2D-COFs) are a class of crystalline porous organic polymers, consisting of 2D-planar sheets stacked together perpendicularly via noncovalent forces. Since their discovery, 2D-COFs have attracted extensive attention for optoelectronic and adsorption applications. Owing to the layer stacking nature of 2D COFs, various new slipped structures that are energetically favourable can be designed. These interlayer slipped structures are actively responsible for tuning (mostly enhancing) the optoelectronic properties, thermal properties, and mechanical strength of 2D COFs. This review summarizes the effect of interlayer slipping on the energetic stability, electronic behaviour and gas adsorption properties of 2D layered COFs, which is explained through computational modelling simulations. Since computational modelling offers a deep insight into electronic behaviour at the atomic scale, which is potentially impossible through experimental techniques, the introduction and role of computational techniques in such studies have also been described.

Highly crystalline polyimide covalent organic framework as electrochemical sensing platform for the ultrasensitive detection of purine bases in DNA

It is of great significance to propose simple methods to detect DNA bases sensitively for biological analysis and medical diagnosis. Herein, a highly crystalline polyimide covalent organic framework (TAPM-COF) has been successfully synthesized via a solvothermal route using pyromellitic dianhydride (PMDA) and tris(4-aminophenyl) amine (TAPA), which possessed large specific surface area (2286 m2 g-1) and excellent thermal stability. Intriguingly, the crystallinity of the TAPM-COF improved significantly with the increase of water content in the reaction medium. To verify this phenomenon, we synthesized TPPM-COF with two pores by pyromellitic dianhydride (PMDA) and N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA), which bonding was similar to TAPM-COF. Furthermore, the prepared TAPM-COF-0.3 was used to construct a novel and independent electrochemical biosensor on glassy carbon electrode for simultaneously determination of adenine (A) and guanine (G) without other additives. However, to further improve signal of TAPM-COF in electrochemical sensing, the crystalline TAPM-COF-0.3 can be readily integrated with amino-functionalized multiwalled carbon nanotubes (NH2-MWCNT) to form core-shell TAPM-COF-0.3@NH2-MWCNT driven by a π-π stacking interaction for more sensitive electrochemical sensing toward purine bases. In comparison to TAPM-COF/GCE, the TAPM-COF@NH2-MWCNT/GCE exhibited more favorable linear range and lower limit of detection. The work provided a new strategy for amplifying signal of COF in the field of electrochemical sensors.

Rapid, easy and catalyst-free preparation of magnetic thiourea-based covalent organic frameworks at room temperature for enrichment and speciation of mercury with HPLC-ICP-MS

The complex and cumbersome preparation of magnetic covalent organic frameworks (COFs) nanocomposites on a small scale limits their application. Herein, a rapid and easy route was employed for the preparation of magnetic thiourea-based COFs nanocomposites. COFs were coated on Fe3O4 nanoparticles at room temperature without a catalyst within approximately 30 min. This method is suitable for the large-scale preparation of magnetic adsorbent. Using the as-prepared magnetic adsorbent (Fe3O4@COF-TpTU), we developed a simple, efficient, and sensitive magnetic solid-phase extraction-high performance liquid chromatography-inductively coupled plasma-mass spectrometry (MSPE-HPLC-ICP-MS) for the enrichment and determination of mercury species, including Hg2+, methylmercury (MeHg), and ethylmercury (EtHg). The effects of the experimental parameters on the extraction efficiency, including solution pH, adsorption and desorption time, composition and volume of the elution solvent, salinity, coexisting ions, and dissolved organic matter, were comprehensively investigated. Under optimised conditions, the limits of detection in the developed method were 0.56, 0.34, and 0.47 ng L-1 with enrichment factors of 190, 195, and 180-fold for Hg2+, MeHg, and EtHg, respectively. The satisfactory spiked recoveries (97.0-103%) in real water samples and high consistency between the certified and determined values in a certified reference material demonstrate the high accuracy and reproducibility of the developed method. The as-proposed method with simple operation, high sensitivity, and excellent anti-matrix interference performance was successfully applied to the enrichment and determination of trace levels of mercury species in the natural samples with complicated matrices, such as underground water, surface water, seawater and biological samples.

Thiol-Ene Click Reaction Modified Triazinyl-Based Covalent Organic Framework for Pb(II) Ion Effective Removal

As a common water pollutant, Pb2+ has harmful effects on the nervous, hematopoietic, digestive, renal, cardiovascular, and endocrine systems. Due to the drawbacks of traditional adsorbents such as structural disorder, poor stability, and difficulty in introducing adsorption active sites, the adsorption capacity is low, and it is difficult to accurately study the adsorption mechanism. Herein, vinyl-functionalized covalent organic frameworks (COFs) were synthesized at room temperature, and sulfur-containing active groups were introduced by the click reaction. By precisely tuning the chemical structure of the sulfur-containing reactive groups through the click reaction, we found that the adsorption activity of the sulfhydryl group was higher than that of the sulfur atom in the thioether. Moreover, the incorporation of flexible linking groups was observed to enhance the adsorption activity at the active site. The maximum adsorption capacity of the postmodified COF TAVA-S-Et-SH for Pb(II) reached 303.0 mg/g, which is 2.9 times higher than that of the unmodified COF. This work not only demonstrates the remarkable potential of the "thiol-ene" click reaction for the customization of active adsorption sites but also demonstrates the remarkable potential of the "thiol-alkene" click reaction to explore the structure-effect relationship between the active adsorption sites and the metal ion adsorption capacity.

Multimedia Mercury Recovery from Coal-Fired Power Plants Utilizing N-Containing Conjugated Polymer Functionalized Fly Ash

To recover multimedia mercury from coal-fired power plants, a novel N-containing conjugated polymer (polyaniline and polypyrrole) functionalized fly ash was prepared, which could continuously adsorb 99.2% of gaseous Hg0 at a high space velocity of 368,500 h-1 and nearly 100% of aqueous Hg2+ in the solution pH range of 2-12. The adsorption capacities of Hg0 and Hg2+ reach 1.62 and 101.36 mg/g, respectively. Such a kind of adsorbent has good environmental applicability, i.e. good resistance to coexisting O2/NO/SO2 and coexisting Na+/K+/Ca2+/Mg2+/SO42-. This adsorbent has very low specific resistances (6 × 106-5 × 109 Ω·cm) and thus can be easily collected by an electrostatic precipitator under low-voltage (0.1-0.8 kV). The Hg-saturated adsorbent can desorb almost 100% Hg under relatively low temperature (<250 °C). Characterization and theoretical calculations reveal that conjugated-N is the critical site for adsorbing both Hg0 and Hg2+ as well as activating chlorine. Gaseous Hg0 is oxidized and adsorbed in the form of HgXClX(ad), while aqueous Hg2+ is adsorbed to form a complex with conjugated-N, and parts of Hg2+ are reduced to Hg+ by conjugated-N. This adsorbent can be easily large-scale manufactured; thus, this novel solid waste functionalization method is promising to be applied in coal-fired power plants and other Hg-involving industrial scenes.

Thioether-functionalized porous β-cyclodextrin polymer for efficient removal of heavy metal ions and organic micropollutants from water

Herein, a thioether-functionalized porous β-cyclodextrin polymer (P(Bn-S-CD)) was prepared for efficient removal of heavy metal ions and organic micropollutants (OMPs) from water. P(Bn-S-CD) showed a surface area of 763 m2/g and a sulfur content 5.83 wt%. Based on screening studies, Hg2+ and diclofenac sodium (DS) were selected as model pollutants. P(Bn-S-CD) could adsorb Hg2+ and DS simultaneously, while the adsorbed Hg2+ afforded positive charges to the primary rims of CDs, greatly enhancing the adsorption rate and adsorption capacity of DS. Although the adsorbed DS showed no obvious effect on Hg2+ adsorption, it improved the affinity of Hg2+ upon P(Bn-S-CD). Adsorption mechanism studies confirmed the essential role of electrostatic interactions for these results. P(Bn-S-CD) also showed good selectivity towards heavy metal ions, excellent adsorption performance in real water at environmental levels and good reusability, implying great promise for water treatment.

Modulating Skeletons of Covalent Organic Framework for High-Efficiency Gold Recovery

Covalent organic frameworks (COFs) have attracted considerable attention as adsorbents for capturing and separating gold from electronic wastes. To enhance the binding capture efficiency, constructing hydrogen-bond nanotraps along the pore walls was one of the most widely adopted approaches. However, the development of absorbing skeletons was ignored due to the weak binding ability of the gold salts (Au). Herein, we demonstrated skeleton engineering to construct highly efficiently absorbs for Au capture. The strong electronic donating feature of diarylamine units enhanced the electronic density of binding sites (imine-linkage) and thus resulted in high capacities over 1750 mg g-1 for all three COFs. Moreover, the absorbing performance was further improved via the ionization of diarylamine units. The ionic COF achieved 90 % of the maximal adsorption capacity, 1.63 times of that from the charge-neutral COF within ten minutes, and showed remarkable uptakes of 1834 mg g-1 , exceptional selectivity (97.45 %) and cycling stability. The theoretical calculation revealed the binding sites altering from imine bonds to ionic amine sites after ionization of the frameworks, which enabled to bind the AuCl4 - via coulomb force and contributed to enhanced absorbing kinetics. This work inspires us to design molecular/ionic capture based on COFs.

Revolutionizing the structural design and determination of covalent-organic frameworks: principles, methods, and techniques

Covalent organic frameworks (COFs) represent an important class of crystalline porous materials with designable structures and functions. The interconnected organic monomers, featuring pre-designed symmetries and connectivities, dictate the structures of COFs, endowing them with high thermal and chemical stability, large surface area, and tunable micropores. Furthermore, by utilizing pre-functionalization or post-synthetic functionalization strategies, COFs can acquire multifunctionalities, leading to their versatile applications in gas separation/storage, catalysis, and optoelectronic devices. Our review provides a comprehensive account of the latest advancements in the principles, methods, and techniques for structural design and determination of COFs. These cutting-edge approaches enable the rational design and precise elucidation of COF structures, addressing fundamental physicochemical challenges associated with host-guest interactions, topological transformations, network interpenetration, and defect-mediated catalysis.

Covalent organic frameworks: Pioneering remediation solutions for organic pollutants

Covalent Organic Frameworks (COFs) have emerged as a promising class of crystalline porous materials with customizable structures, high surface areas, and tunable functionalities. Their unique properties make them attractive candidates for addressing environmental contamination caused by pharmaceuticals, pesticides, industrial chemicals, persistent organic pollutants (POPs), and endocrine disruptors (EDCs). This review article provides a comprehensive overview of recent advancements and applications of COFs in removing and remedying various environmental contaminants. We delve into the synthesis, properties, and performance of COFs and their potential limitations and future prospects.

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.

Development of p-n Heterostructures Using Phosphorene and SnO2: Its Efficacy toward the Adsorption Study of CO2 and Rose Bengal Dye

Adsorption-mediated methods for environmental pollution control are suitable as they are cost-effective and easy to use. Porous materials can play an important role in adsorption studies. Herein, we synthesized a p-n heterostructure of phosphorene and metal oxide using a simple hydrothermal approach. The synthesized material is porous in nature, with a surface area of 127.44 m2/g and pore volume of about 1.73 nm with appreciable thermal stability. As the material is microporous, we used it for the adsorption of CO2 gas and dye. For CO2 adsorption, we determined the CO2 gas uptake according to the mass balance principle of the ideal gas equation, and it was found to be about 21.478 mol/kg. We have also studied different isotherm models to check the adsorption phenomena. Moreover, for dye adsorption, we have chosen the xanthene-derived rose bengal (RB) dye, which shows a removal percentage of about 92.02%. In the case of dye adsorption, the material shows good reusability and significant adsorption up to five cycles.

Quantitative Construction of Boronic-Ester Linkages in Covalent Organic Frameworks for the Carbon Dioxide Reduction

Covalent organic frameworks (COFs) have been utilized for catalyzing the reduction of carbon dioxide (CO2RR) due to their atomic metal centers and controllable pore channels, which are facilitated by different covalent bonds. However, the exploration of boron-based linkages in these catalytic COFs has been limited owing to potential instability. Herein, we present the construction of boronic ester-linked COFs through nucleophilic substitution reactions in order to catalyze the CO2 RR. The inclusion of abundant fluorine atoms within the frameworks enhances their hydrophobicity and subsequently improves water tolerance and chemical stability of COFs. The content of boron atoms in the COF linkages was carefully controlled, with COFs featuring a higher density of boron atoms exhibiting increased electronic conductivity, enhanced reductive ability, and stronger binding affinity towards CO2 . Consequently, these COFs demonstrate improved activity and selectivity. The optimized COFs achieve the highest activity, achieving a turnover frequency of 1695.3 h-1 and a CO selectivity of 95.0 % at -0.9 V. Operando synchrotron radiation measurements confirm the stability of Co (II) atoms as catalytically active sites. By successfully constructing boronic ester-linked COFs, we not only address potential instability concerns but also achieve exceptional catalytic performance for CO2 RR.

Selective scandium ion capture through coordination templating in a covalent organic framework

The use of coordination complexes within covalent organic frameworks can significantly diversify the structures and properties of this class of materials. Here we combined coordination chemistry and reticular chemistry by preparing frameworks that consist of a ditopic (p-phenylenediamine) and mixed tritopic moieties-an organic ligand and a scandium coordination complex of similar sizes and geometries, both bearing terminal phenylamine groups. Changing the ratio of organic ligand to scandium complex enabled the preparation of a series of crystalline covalent organic frameworks with tunable levels of scandium incorporation. Removal of scandium from the material with the highest metal content subsequently resulted in a 'metal-imprinted' covalent organic framework that exhibits a high affinity and capacity for Sc3+ ions in acidic environments and in the presence of competing metal ions. In particular, the selectivity of this framework for Sc3+ over common impurity ions such as La3+ and Fe3+ surpasses that of existing scandium adsorbents.

Covalent organic frameworks as highly versatile materials for the removal and electrochemical sensing of organic pollutants

The presence of persistent organic compounds in water has become a worldwide issue due to its resistance to natural degradation, inducing its environmental resilience. Therefore, the accumulation in water bodies, soils, and humans produces toxic effects. Also, low levels of organic pollutants can lead to serious human health issues, such as cancer, chronic diseases, thyroid complications, immune system suppression, etc. Therefore, developing efficient and economically viable remediation strategies motivates researchers to delve into novel domains within material science. Moreover, finding approaches to detect pollutants in drinking water systems is vital for safeguarding water safety and security. Covalent organic frameworks (COFs) are valuable materials constructed through strong covalent interactions between blocked monomers. These materials have tremendous potential in removing and detecting persistent organic pollutants due to their high adsorption capacity, large surface area, tunable porosity, porous structure, and recyclability. This review discusses various synthesis routes for constructing non-functionalized and functionalized COFs and their application in the remediation and electrochemical sensing of persistent organic compounds from contaminated water sources. The development of COF-based materials has some major challenges that need to be addressed for their suitability in the industrial configuration. This review also aims to highlight the importance of COFs in the environmental remediation application with detailed scrutiny of their challenges and outcomes in the current research scenario.

Olefin-linked covalent organic frameworks: synthesis and applications

Covalent organic frameworks (COFs) with high specific porosity, easy functionalization, and tailored structure are an emerging class of crystalline porous polymers that have been extensively exploited as ideal materials in various fields. Among them, sp2-carbon linked COFs with high chemical stability, porous backbone, and unique π-electron conjugated architectures structure have raised widespread attention. Specifically, the porous channels of olefin-linked COFs could be packed with active sites for catalysis and guest molecules, while π-π stacking interactions and conjugation systems pave the way for electron transfer. In recent years, many efforts have been devoted to the development of sp2-carbon linked COFs for applications in catalysis, energy storage, gas adsorption, and separation. In this review, we highlight the design principles, synthesis strategies, and impactful applications of olefin-linked COFs. We are looking forward to this review to deepen the understanding of the synthesis of olefin-linked COFs and motivate the further development of these novel conjugated organic materials with distinctive physicochemical properties, as well as their applications in a variety of fields.

Combination of covalent organic frameworks (COFs) and polyoxometalates (POMs): the preparation strategy and potential application of COF-POM hybrids

Both covalent organic frameworks (COFs) and polyoxometalates (POMs) show excellent properties and application potential in many fields, thus receiving widespread attention. In recent years, COF-POM hybrid materials were prepared by combining COFs and POMs through physical or chemical methods. COF-POM hybrids have shown high performance in many fields, such as catalysis, sensing, energy storage, and biomedicine. In this review, we introduced the preparation strategy and application of COF-POM hybrids in detail. We believe that the combination of COFs and POMs will provide more abundant functions and broad application prospects.

State-of-the-art adsorption and adsorptive filtration based technologies for the removal of trace elements: A critical review

Water and wastewater are contaminated with various types of trace elements that are released from industrial activities. Their presence, at concentrations above the permissible limit, will cause severe negative impacts on human health and the environment. Due to their cost-effectiveness, simple design, high efficiency, and selectivity, adsorption, and adsorptive filtration are techniques that have received lots of attention as compared to other water treatment techniques. Adsorption isotherms and kinetic studies help to understand the mechanisms of adsorption and adsorption rates, which can be used to develop and optimize different adsorbents. This state-of-the-art review provides and combines the advancements in different conventional and advanced adsorbents, biosorbents, and adsorptive membranes for the removal of trace elements from water streams. Herein, this review discusses the sources of different trace elements and their impact on human health. The review also covers the adsorption technique with a focus on various advanced adsorbents, their adsorption capacities, and adsorption isotherm modeling in detail. In addition, biosorption is critically discussed together with its mechanisms and biosorption isotherms. In the end, the application of various advanced adsorptive membranes is discussed and their comparison with adsorbents and biosorbents is systematically presented.

Removal of typical PFAS from water by covalent organic frameworks with different pore sizes

Adsorption is highly effective and desirable for the removal of per- and polyfluoroalkyl substances (PFAS) from water, and suitable pore size of porous adsorbents is important for efficient removal of PFAS, but the relationship between adsorbent pore size and PFAS adsorption remains unclear. In this study, five regular covalent organic frameworks (COFs) with distinct pore sizes were successfully synthesized, and the correlation between the pore size of COFs and PFAS length for efficient PFAS adsorption was investigated. Both excessively small and large pore sizes of COFs are not conducive to the efficient adsorption of PFAS due to the diffusion hindrance and weak binding forces. The COFs with a pore size ranging from 2.5 to 4.0 times of the PFAS molecular size demonstrated the most suitable for PFAS adsorption. This study also investigated the potential impact of nanobubbles on PFAS adsorption on orderly porous COFs through aeration and degassing treatment of the adsorption system. The bubbles on hydrophobic COFs were verified to be responsible for PFAS adsorption, another important adsorption mechanism of PFAS on COFs. The long-chain PFAS have stronger enrichment at the gas-liquid interface than the short-chain PFAS, resulting in higher adsorption capacity for long-chain PFAS.

Assessing CO2 Adsorption Behavior onto Free-Standing, Flexible Organic Framework-PVDF Composite Membrane: An Empirical Modeling and Validation of an Experimental Data Set

Covalent organic framework (COF) materials have greatly expanded their range in a variety of applications since the cognitive goal of a highly organized and durable adsorbent is quite rational. The characteristics of a conjugated organic framework are combined with an industrially relevant polymer to produce a composite membrane optimized for selectively adsorbing carbon dioxide (CO2) gas across a wide temperature range. Additionally, treatment of the composite membrane with cold atmospheric plasma (CAP) that specifically enhanced the parent membrane's surface area by 36% is established. Following CAP treatment, the membrane accelerates the CO2 uptake by as much as 66%. This is primarily due to a Lewis acid-base interaction between the electron-deficient carbon atom of CO2 and the newly acquired functionalities on the COFs@PVDF membrane's surface. In particular, the C-N bonds, which appear to be a higher electron density site, play a key role in this interaction. Moreover, the empirical model proposed here has confirmed CO2 adsorption phenomena in the COF@PVDF composite membrane, which closely matches the findings from the experimental data set under designated operating conditions. As a result, the current study may pave the way for future design work as well as refine the covalent framework polymer composite membrane's features, revealing a more sophisticated approach to addressing CO2 capture problems.

One-step synthesis of a benzothiadiazole-based nonbranching functionalized covalent organic framework and its application in efficient removal of Hg2

In recent years, a variety of adsorbents have been developed for Hg2+ removal. However, these adsorbents are unsatisfactory for adsorption due to narrow and irregular pore channels or poor adsorption capacity and low stability. Therefore, it is worth exploring a porous Hg2+ adsorbent material with high adsorption performance and stability. In this study, a benzothiadiazole-based nonbranching functionalized covalent organic framework (COF) material (TPS-COF) by one-step synthesis was reported, which exhibited a high specific surface area of 1564 m2 g-1, high crystallinity and stability attributed to its high conjugated linkage structure of benzothiadiazole. In addition, due to the rich S and N elements of the benzothiadiazole unit, it exhibited excellent adsorption performance on Hg2+, including excellent adsorption amount (1040 mg g-1), high initial adsorption rate (448 mg g-1 min-1) and very short adsorption equilibrium time (10 min), with an efficient removal rate of Hg2+ in the pH range of 2-8. After desorption, the TPS-COF still retained good pore stability, adsorption capacity, and reusability. Such a one-step synthetic unbranched functionalization strategy provides further insights to achieve a good balance between the high crystallinity, functionality and stability of COFs.

A novel cationic covalent organic framework as adsorbent for simultaneous removal of methyl orange and hexavalent chromium

The simultaneous removal of toxic, carcinogenic organic dyes and metal ions from water by one material offers significant advantages when fast, facile, and robust water purification is required. Ionic covalent organic frameworks (ICOFs) have the combined properties of COFs and ion exchange resins and are expected to achieve simultaneous capture of heavy metal ions and organic dyes from water. Herein, a novel guanidinium-based ICOF was synthesized using a solvothermal method. Benefitting from the cationic character, porosity and nanoscale pore size of ICOFs, the adsorbent exhibited high simultaneous adsorption capacities of 290 mg g-1 and 158 mg g-1 for methyl orange (MO) and Cr(vi), respectively, and retained more than 90% adsorption capacity after six adsorption-desorption cycles. In addition, based on dual control of size-exclusion and charge-selection, precisely selective adsorption is achieved towards diverse mixed anionic and cationic pollutants. This strategy offers a practical solution for COFs to confront environmental pollution issues.

Synthesis of a pyridine-based covalent organic framework as an efficient adsorbent for rhodamine B removal

Covalent organic frameworks (COFs), featured with crystalline structures, permanent porosity, and designable organic skeletons, are good candidates for serving as adsorbents. Herein, a new pyridine-based two-dimensional COF (TAPP-DBTA-COF) was constructed via the condensation of 2,4,6-tris(4-aminophenyl)pyridine and 2,5-dibromobenzene-1,4-dicarbaldehyde. TAPP-DBTA-COF displayed high-performance for the removal of rhodamine B (Rh B) from water with high capacity, good adaptability and reusability. The maximum adsorption capacity for Rh B can reach up to 1254 mg g-1, and the kinetic constant was determined as k2 = 0.00244 g mg-1 min-1. Moreover, the corresponding amorphous polymer of TAPP-DBTA-COF, termed as TAPP-DBTA-COP, was synthesized from the same starting materials. The lower efficiency of TAPP-DBTA-COP in capture of Rh B revealed that the ordered pore structure, large specific surface area and rich adsorption sites play an important role in adsorption.

Recent Developments in Two-Dimensional Materials-Based Membranes for Oil-Water Separation

The industrialization witnessed in the last century has resulted in an unprecedented increase in water pollution. In particular, the water pollution induced by oil contaminants from oil spill accidents, as well as discharges from pharmaceutical, oil/gas, and metal processing industries, have raised concerns due to their potential to pose irreversible threats to the ecosystems. Therefore, the effective treating of these large volumes of oily wastewater is an inevitable challenge to address. Separating oil-water mixtures by membranes has been an attractive technology due to the high oil removal efficiency and low energy consumption. However, conventional oil-water separation membranes may not meet the complex requirements for the sustainable treatment of wastewater due to their relatively shorter life cycle, lower chemical and thermal stability, and permeability/selectivity trade-off. Recent advancements in two-dimensional (2D) materials have provided opportunities to address these challenges. In this article, we provide a brief review of the most recent advancements in oil-water separation membranes modified with 2D materials, with a focus on MXenes, graphenes, metal-organic frameworks, and covalent organic frameworks. The review briefly covers the backgrounds, concepts, fabrication methods, and the most recent representative studies. Finally, the review concludes by describing the challenges and future research directions.