Highly effective ammonia removal in a series of Brønsted acidic porous polymers: investigation of chemical and structural variations

Recent advances on metal-organic framework-based electrochemical sensors for determination of organic small molecules

Metal-organic frameworks (MOFs) are an extraordinarily versatile class of porous materials renowned for their intricate three-dimensional skeletal architectures and exceptional chemical properties. These extraordinary attributes have pushed MOFs into the vanguard of diverse disciplines such as microporous conduction, catalysis, separation, biomedical engineering, and electrochemical sensing. The focus of this review is to offer a comprehensive summary of recent advancements in designing MOF-based electrochemical sensors for detecting organic small molecules. offer a comprehensive survey of the recent progress in the methodologies adopted for the construction of MOF composites, covering template-assisted synthesis, Modification in synthesis, and post-synthesis modification. In addition, we discuss the practical application of MOF-based electrochemical sensors in the detection of organic small molecules. Our findings highlight the superior electrochemical sensing capabilities of these novel composites compared to those of their pristine counterparts. In conclusion, we provide a condensed perspective on the potential future trajectories in this domain, underscoring the impetus for continued enquiry and enhancement of MOF composite assemblies. With sustained investigation, the horizon appears bright for electrochemical sensing of small organic molecules and their myriad applications.

Reversible Adsorption of Ammonia in the Crystalline Solid of a CO2H-Functionalized Cyclic Oligophenylene

Ammonia (NH3) is a viable candidate for the storage and distribution of hydrogen (H2) due to its exceptional volumetric and gravimetric hydrogen energy density. Therefore, it is desirable to develop NH3 storage materials that exhibit robust stability across numerous adsorption-desorption cycles. While porous materials with polymeric frameworks are often used for NH3 capture, achieving reversible NH3 uptake remains a formidable challenge, primarily due to the high reactivity of NH3. Here, we advocate the use of CO2H-functionalized cyclic oligophenylene 1a with high chemical stability as a novel single-molecule-based adsorbent for NH3. Simple reprecipitation of 1a selectively yielded microporous crystalline solid 1a (N). Crystalline 1a (N) adsorbs up to 8.27 mmol/g of NH3 at 100 kPa and 293 K. Adsorbed NH3 in the pore of 1a (N) has a packing density of 0.533 g/cm3 at 293 K, which is close to the density of liquid NH3 (0.681 g/cm3 at 240 K). Crystalline 1a (N) also exhibits reversible NH3 adsorption over at least nine cycles, sustaining its storage capacity (1st cycle: 8.27 mmol/g; 9th cycle: 8.25 mmol/g at 100 kPa and 293 K) and crystallinity. During each desorption cycle, NH3 was removed from 1a (N) under reduced pressure (∼65 Pa), leaving <3% of the total uptake, and 1a (N) was fully purged under dynamic vacuum conditions (∼5 × 10-4 Pa at 293 K for 1 h) before the subsequent adsorption cycles. Thus, microporous crystalline 1a (N) can reliably adsorb and desorb NH3 repeatedly, which avoids the need for heat-based activation between cycles.

Helical polyisocyanide-based macroporous organic catalysts for asymmetric Michael addition with high efficiency and stereoselectivity

Porous materials have attracted interest due to their high specific surface area and rich functionality. Immobilizing organocatalysts onto porous polymers not only boosts enantioselectivity but also improves the reaction rates. In this work, a series of porous polymers C-poly-3ms with rigid polyisocyanide-carrying secondary amine pendants as building blocks were successfully prepared. And the pore size and optical activity of C-poly-3ms can be controlled by the length of the polyisocyanide blocks due to their rigid and helical backbone. C-poly-3150 demonstrated a preferred left-handed helix with a θ 364 value of -8.21 × 103. The pore size and S BET of C-poly-3150 were 17.52 nm and 7.98 m2 g-1, respectively. The porous C-poly-3150 catalyzes the asymmetric Michael addition reaction efficiently and generates the target products in satisfactory yield and excellent enantioselectivity. For 6ab, an enantiomeric excess (ee) and a diastereomeric ratio (dr) up to 99% and 99/1 could be achieved, respectively. The recovered catalyst can be recycled at least 6 times in the asymmetric Michael addition reaction while maintaining activity and stereoselectivity.

Crystalline Porous Organic Frameworks Based on Multiple Dynamic Linkages

A novel class of crystalline porous materials has been developed utilizing multilevel dynamic linkages, including covalent B-O, dative B←N and hydrogen bonds. Typically, boronic acids undergo in situ condensation to afford B3O3-based units, which further extend to molecular complexes or chains via B←N bonds. The obtained superstructures are subsequently interconnected via hydrogen bonds and π-π interactions, producing crystalline porous organic frameworks (CPOFs). The CPOFs display excellent solution processability, allowing dissolution and subsequent crystallization to their original structures, independent of recrystallization conditions, possibly due to the diverse bond energies of the involved interactions. Significantly, the CPOFs can be synthesized on a gram-scale using cost-effective monomers. In addition, the numerous acidic sites endow the CPOFs with high NH3 capacity, surpassing most porous organic materials and commercial materials.

A comprehensive review of the application of Zr-based metal-organic frameworks for electrochemical sensors and biosensors

A family of inorganic-organic hybrid crystalline materials made up of organic ligands and metal cations or clusters is known as metal-organic frameworks (MOFs). Because of their unique stability, intriguing characteristics, and structural diversity, zirconium-based MOFs (Zr-MOFs) are regarded as one of the most interesting families of MOF materials for real-world applications. Zr-MOFs that have the ligands, metal nodes, and guest molecules enclosed show distinct electrochemical reactions. They can successfully and sensitively identify a wide range of substances, which is important for both environmental preservation and human health. The rational design and synthesis of Zr-MOF electrochemical sensors and biosensors, as well as their applications in the detection of drugs, biomarkers, pesticides, food additives, hydrogen peroxide, and other materials, are the main topics of this comprehensive review. We also touch on the current issues and potential future paths for Zr-MOF electrochemical sensor research.

Advanced Materials for NH3 Capture: Interaction Sites and Transport Pathways

Ammonia (NH3) is a carbon-free, hydrogen-rich chemical related to global food safety, clean energy, and environmental protection. As an essential technology for meeting the requirements raised by such issues, NH3 capture has been intensively explored by researchers in both fundamental and applied fields. The four typical methods used are (1) solvent absorption by ionic liquids and their derivatives, (2) adsorption by porous solids, (3) ab-adsorption by porous liquids, and (4) membrane separation. Rooted in the development of advanced materials for NH3 capture, we conducted a coherent review of the design of different materials, mainly in the past 5 years, their interactions with NH3 molecules and construction of transport pathways, as well as the structure-property relationship, with specific examples discussed. Finally, the challenges in current research and future worthwhile directions for NH3 capture materials are proposed.

Application and Challenge of Metal/Covalent Organic Frameworks in Ammonia Sorption and Separation

As both a critical chemical feedstock and an environmental pollutant, the production and utilization of ammonia (NH3) are accompanied by the progress of social civilization. In recent years, research on metal/covalent organic framework materials as NH3 adsorbents has attracted increasing attention due to their high porosity, versatile architecture and tunable functionality. This review was organized to highlight the recent advancement of MOF/COF materials for NH3 sorption, which successively presented the key properties of solid adsorbents and summarized the strategies along with their mechanisms for enhancing NH3 adsorption. In addition, perspectives and outlook regarding the future development of MOF/COF-based NH3 adsorbents were outlined to meet the requirements of practical applications under various condition.

Improved NH3 Uptake of a Macromolecule-Metal Complex Constructed with Dual Polymeric Ligands and M(II)

MOFs are considered as efficient NH3 adsorbents for their high capacity but are accompanied by the collapse of MOFs. In this work, macromolecule-metal complexes (MMCs), which could provide metal sites like MOFs, were developed for reversible NH3 uptake with high capacity with the assistance of the polymeric ligands. Based on the tunable structure of MMCs, the role of the polymeric ligands and metallic center was investigated. Thereinto, MMCs-3 with dual polymeric ligands presented higher NH3 adsorption capacity and reversibility of adsorbents compared with MMCs containing a single polymeric ligand (MMCs-1 and MMCs-2). Combined with the NH3 adsorption test, characterization of FT-IR, UV-vis, EPR spectroscopy, NH3-TPD measurement, and the DFT calculations, it was found that the neutral polymeric ligands PVIm contributed to improve the stability of MMCs-3 under a NH3 atmosphere for the tough networks of PVIm-M(II), while the polymeric ligands with a carboxylate anion together with M(II) enhanced the NH3 capacity for the feasible coordination of a carboxylate anion with M(II). The mechanism of NH3 uptake by PVIm-Co-PVBA was proposed that the NH3 was fixed through the coordination with Co(II) along with the departure of PVBA and the following hydrogen bonding interaction with PVBA, while the coordination between PVIm and Co(II) was not destroyed. Thus, MMCs-3 with dual polymeric ligands presented a higher NH3 uptake capacity and stability. Optimally, PVIm-M-PVBA with the metal center of Co(II), Cu(II), and Ni(II) were obtained with a high capacity of 20.8-23.7 NH3 mmol/g at 25 °C and 1 bar and a high selectivity of NH3 over CO2 (54.9-99.9) and N2 (73.0-187.6) through the breakthrough measurement with a gas mixture of 0.2% NH3, 2% CO2, and 99.6% N2 at 25 °C.

Dispersing LiCl in Zwitterionic COF for Highly Efficient Ammonia Storage and Separation

Efficient and inherently safe NH3 storage and separation are of significant importance for the chemical industry. Herein, we proposed zwitterionic COF as a porous host to disperse LiCl for highly efficient NH3 storage and separation with record adsorption capacity. The equivalently cationic and anionic groups in the channels of zwitterionic COF could act as two separated sites to facilitate the dispersion of LiCl, hence the optimal composite exhibits a high capture capacity of 44.98 mmol/g at 25 °C and 1 bar, far exceeding other existing porous materials. Notably, the adsorption capacity is completely reversible and the efficient separation of NH3 from NH3 /CO2 /N2 mixture is achieved through breakthrough experiments. DFT calculation combined with XPS and 7 Li NMR experimental results give insight into the interaction between zwitterionic COF and LiCl. This work extends possibilities for the development of efficient adsorbents for NH3 storage and separation.

Porous acid-base hybrid polymers for enhanced NH3 uptake with assistance from cooperative hydrogen bonds

Carboxylic acid-modified materials are a common means of achieving efficient NH3 adsorption. In this study, we report that improved NH3 adsorption capacity and easier desorption can be achieved through the introduction of substances containing Lewis basic groups into carboxylic acid-modified materials. Easily synthesized mesoporous acid-base hybrid polymers were constructed with polymers rich in carboxylic acid and Lewis base moieties through cooperative hydrogen bonding interactions (CHBs). The hybrid polymer PAA-P4VP presented higher NH3 capacity (18.2 mmol g-1 at 298 K and 1 bar NH3 pressure) than PAA (6.0 mmol g-1) through the acid-base reaction and the assistance from CHBs with NH3, while the NH3 desorption from PAA-P4VP was easier for the reformation of CHBs. Based on the introduction of CHBs, a series of mesoporous acid-base hybrid polymers was synthesized with NH3 adsorption capacity of 15.8-19.3 mmol g-1 and high selectivity of NH3 over CO2 (SNH3/CO2 = 25.4-56.3) and N2 (SNH3/N2 = 254-1068), and the possible co-existing gases, such as SO2, had a lower effect on NH3 uptake by hybrid polymers. Overall, the hybrid polymers present efficient NH3 adsorption owing to the abundant acidic moieties and CHBs, while the concomitant Lewis bases promote NH3 desorption.

Chitosan-Based Hydrogel-Incorporated Trp-CDs with Antibacterial Properties and pH-Mediated Fluorescence Response as a Smart Food Preservation Material

The great problem of food spoilage is causing food waste worldwide. However, prolonging the shelf life of food and responding to spoilage are good strategies for dealing with this problem. Herein, we present the design of multifunctional chitosan-based hydrogel-incorporated tryptophan carbon quantum dots (Trp-CDs) with antibacterial properties and pH-mediated fluorescence response (pH = 1-13). This chitosan (CS)/tannic acid (TA)/Trp-CDs hydrogel (CTTC hydrogel) was rapidly formed by a high density of hydrogen bonds and has the advantages of good mechanical properties (1628.55 kPa, 280%), washability (5-10 min), antioxidant activity (95.83%), and antibacterial properties. In practical application with fruits, the hydrogel significantly prolonged the shelf life of strawberries by at least 5 days and oranges by 20 days under ambient conditions. In particular, the hydrogel has good pH-mediated fluorescence responsiveness and reversibility due to doping with Trp-CDs, laying a foundation for its application in response to food spoilage.

A novel micro-sphere activated carbon synthesized from waste cigarette butts for ammonia adsorption

Waste cigarette filters mainly contain hardly degradable cellulose acetate, toxic nicotine, and traces of heavy metals, and therefore cause environmental pollution hazards when discarded. In order to convert cigarette butt waste into a valuable product, this article investigates the preparation of activated carbon from cigarette butts via a two-step process of hydrothermal reaction and a subsequent chemical activation with phosphoric acid as an activator. During hydrothermal reaction, it was found that a process of decarboxylation and dehydration cleavage of acetate occurs, leading to micron fragments and subsequent agglomeration into carbonaceous micro-spheres. The cigarette-butts-derived activated carbon micro-spheres have a high BET surface area of ∼ 1406 m2/g and NH3 adsorption capacity of ∼ 35.9 mg/g. It was revealed that the ammonia adsorption capacity tends to be positively and linearly correlated with the acidic functional group content of the activated carbon surface while negatively with BET surface area.

Application of Hydrogen-Bonded Organic Frameworks in Environmental Remediation: Recent Advances and Future Trends

The hydrogen-bonded organic frameworks (HOFs) are a class of porous materials with crystalline frame structures, which are self-assembled from organic structures by hydrogen bonding in non-covalent bonds π-π packing and van der Waals force interaction. HOFs are widely used in environmental remediation due to their high specific surface area, ordered pore structure, pore modifiability, and post-synthesis adjustability of various physical and chemical forms. This work summarizes some rules for constructing stable HOFs and the synthesis of HOF-based materials (synthesis of HOFs, metallized HOFs, and HOF-derived materials). In addition, the applications of HOF-based materials in the field of environmental remediation are introduced, including adsorption and separation (NH3, CO2/CH4 and CO2/N2, C2H2/C2He and CeH6, C2H2/CO2, Xe/Kr, etc.), heavy metal and radioactive metal adsorption, organic dye and pesticide adsorption, energy conversion (producing H2 and CO2 reduced to CO), organic dye degradation and pollutant sensing (metal ion, aniline, antibiotic, explosive steam, etc.). Finally, the current challenges and further studies of HOFs (such as functional modification, molecular simulation, application extension as remediation of contaminated soil, and cost assessment) are discussed. It is hoped that this work will help develop widespread applications for HOFs in removing a variety of pollutants from the environment.

Ammonia Capture in Rhodium(II)-Based Metal-Organic Polyhedra via Synergistic Coordinative and H-Bonding Interactions

Ammonia (NH₃) is among the world's most widely produced bulk chemicals, given its extensive use in diverse sectors such as agriculture; however, it poses environmental and health risks at low concentrations. Therefore, there is a need for developing new technologies and materials to capture and store ammonia safely. Herein, we report for the first time the use of metal-organic polyhedra (MOPs) as ammonia adsorbents. We evaluated three different rhodium-based MOPs: [Rh₂(bdc)₂]₁₂ (where bdc is 1,3-benzene dicarboxylate); one functionalized with hydroxyl groups at its outer surface [Rh₂(OH-bdc)₂]₁₂ (where OH-bdc is 5-hydroxy-1,3-benzene dicarboxylate); and one decorated with aliphatic alkoxide chains at its outer surface [Rh₂(C₁₂O-bdc)₂]₁₂ (where C₁₂O-bdc is 5-dodecoxybenzene-1,3-benzene dicarboxylate). Ammonia-adsorption experiments revealed that all three Rh-MOPs strongly interact with ammonia, with uptake capacities exceeding 10 mmol/g_MOP. Furthermore, computational and experimental data showed that the mechanism of the interaction between Rh-MOPs and ammonia proceeds through a first step of coordination of NH₃ to the axial site of the Rh(II) paddlewheel cluster, which triggers the adsorption of additional NH₃ molecules through H-bonding interaction. This unique mechanism creates H-bonded clusters of NH₃ on each Rh(II) axial site, which accounts for the high NH₃ uptake capacity of Rh-MOPs. Rh-MOPs can be regenerated through their immersion in acidic water, and upon activation, their ammonia uptake can be recovered for at least three cycles. Our findings demonstrate that MOPs can be used as porous hosts to capture corrosive molecules like ammonia, and that their surface functionalization can enhance the ammonia uptake performance.

Desorption of Ammonia Adsorbed on Prussian Blue Analogs by Washing with Saturated Ammonium Hydrogen Carbonate Solution

Prussian blue analogs (PBAs) have been reported as promising ammonia (NH₃) adsorbents with a high capacity compared to activated carbon, zeolite, and ion exchange resins. The adsorbed NH₃ was desorbed by heating and washing with water or acid. Recently, we demonstrated that desorption was also possible by washing with a saturated ammonium hydrogen carbonate solution (sat. NH₄HCO₃aq) and recovered NH₃ as an NH₄HCO₃ solid by introducing CO₂ into the washing liquid after desorption. However, this has only been proven for copper ferrocyanide and the relationship between the adsorption/desorption behavior and metal ions in PBAs has not been identified. In this study, we investigated the adsorption/desorption behavior of PBAs that are complexes of first row transition metals with hexacyanometalate anions. Six types of PBAs were tested in this study and copper ferricyanide exhibited the highest desorption/adsorption ratio. X-ray diffraction results revealed high structural stability for cobalt hexacyanocobaltate (CoHCC) and nickel ferricyanide (NiHCF). The Fourier transform infrared spectroscopy results showed that the NH₃ adsorbed on the vacancy sites tended to desorb compared to the NH₃ adsorbed on the interstitial sites as ammonium ions. Interestingly, the desorption/adsorption ratio exhibited the Irving-Williams order.

Heteroatom-Doped Porous Carbons as Effective Adsorbers for Toxic Industrial Gasses

Ammonia (NH3), often stored in large quantities before being used in the production of fertilizer, and sulfur dioxide (SO2), a byproduct of fossil fuel consumption, particularly the burning of coal, are highly toxic and corrosive gases that pose a significant danger to humans if accidentally released. Therefore, developing advanced materials to enable their effective capture and safe storage is highly desired. Herein, advanced benzimidazole-derived carbons (BIDCs) with an exceptional capacity for NH3 and SO2 have been designed and tested. These heteroatom-doped porous carbon adsorbents were synthesized by thermolysis of imidazolate-potassium salts affording high surface area and controlled heteroatom content to optimize for rapid NH3 and SO2 gas uptake and release under practical conditions. According to gas uptake measurements, these nitrogen-doped carbons exhibit exceptional gas adsorption capacity, with BIDC-3-800 adsorbing 21.42 mmol/g SO2 at 298 K and 1 bar, exceeding most reported porous materials and BIDC-2-700 adsorbing 14.26 mmol/g NH3 under the same conditions. The NH3 uptake of BIDC-2-700 surpassed reported activated carbons and is among the best adsorbents including metal organic frameworks (MOFs). Our synthetic method allows for control over both textural and chemical properties of the carbon and enables heteroatom functionality to be incorporated directly into the carbon framework without the need for postsynthetic modification. These materials were also tested for recyclability; all adsorbents showed almost complete retention of their initial gas uptake capacity during recyclability studies and maintained their structural integrity and their previous adsorption capacity of both NH3 and SO2, highlighting their potential for practical application.

High Gravimetric and Volumetric Ammonia Capacities in Robust Metal-Organic Frameworks Prepared via Double Postsynthetic Modification

Ammonia is a promising energy vector that can store the high energy density of hydrogen. For this reason, numerous adsorbents have been investigated as ammonia storage materials, but ammonia adsorbents with a high gravimetric/volumetric ammonia capacity that can be simultaneously regenerated in an energy-efficient manner remain underdeveloped, which hampers their practical implementation. Herein, we report Ni_acryl_TMA (TMA = thiomallic acid), an acidic group-functionalized metal-organic framework prepared via successive postsynthetic modifications of mesoporous Ni₂Cl₂BTDD (BTDD = bis(1H-1,2,3,-triazolo [4,5-b],-[4',5'-i]) dibenzo[1,4]dioxin). By virtue of the densely located acid groups, Ni_acryl_TMA exhibited a top-tier gravimetric ammonia capacity of 23.5 mmol g^-1 and the highest ammonia storage of 0.39 g cm^-3 at 1 bar and 298 K. The structural integrity and ammonia storage capacity of Ni_acryl_TMA were maintained after ammonia adsorption-desorption tests over five cycles. Temperature-programmed desorption analysis revealed that the moderate strength of the interaction between the functional groups and ammonia significantly reduced the desorption temperature compared to that of the pristine framework with open metal sites. The structures of the postsynthetic modified analogues were elucidated based on Pawley/Rietveld refinement of the synchrotron powder X-ray diffraction patterns and van der Waals (vdW)-corrected density functional theory (DFT) calculations. Furthermore, the ammonia adsorption mechanism was investigated via in situ infrared and vdW-corrected DFT calculations, revealing an atypical guest-induced binding mode transformation of the integrated carboxylate. Dynamic breakthrough tests showed that Ni_acryl_TMA can selectively capture traces of ammonia under both dry and wet conditions (80% relative humidity). These results demonstrate that Ni_acryl_TMA is a superior ammonia storage/capture material.

A record ammonia adsorption by calcium chloride confined in covalent organic frameworks

Ammonia is a vital chemical raw material, but it is also a highly toxic environmenal pollutant. However, its highly efficient uptake and reversible release is a challenge. Herein, we have designed and synthesized a series of hybrid materials for efficient NH₃ capture by confining calcium chloride (CaCl₂) in a porous covalent organic framework (COF). A high capture capacity of 26.5 mmol g^-1 is obtained at 25 °C and 1 bar, which is the highest value among existing porous materials, and NH₃ can be easily desorbed at 80 °C under vacuum for 2 h. Particularly, the hybrid COF is highly efficient for the absorption of low NH₃ content. Such excellent performance is ascribed to the highly dispersion of CaCl₂ in the pores of the COF, and coordinating interaction of NH₃ to Ca²⁺ together with hydrogen bond interaction between NH₃ and Cl^-.

Effects of Moisture on NH3&nbsp;Capture Using Activated Carbon and Acidic Porous Polymer Modified by Impregnation with H3PO4: Sorbent Material Characterized by Synchrotron XRPD and FT-IR

The performances of reactive adsorbents, H₃PO₄/C (activated carbon) and H₃PO₄/A (Amberlyst 35), in removing NH₃ from a waste-gas stream were investigated using a breakthrough column. Accelerated aging tests investigated the effects of the water content on the performance of the adsorbents. Results of breakthrough tests show that the adsorption capacity greatly decreased with the drying time of H₃PO₄/C preparation. Synchrotron XRPD indicated increased amorphous phosphorus species formation with drying time. Nitrogen adsorption-desorption isotherms results further suggested that the evaporation of water accommodated in macropores decreases adsorption capacity besides the formation of the amorphous species. Introducing water moisture to the NH₃ stream increases the adsorption capacity concomitant with the conversion of some NH₄H₂PO₄ to (NH₄)₂HPO₄. Due to the larger pore of cylindrical type and more hydrophilic for acidic porous polymer support, as opposed to slit-type for the activated carbon, the adsorption capacity of H₃PO₄/A is about 3.4 times that of H₃PO₄/C. XRPD results suggested that NH₃ reacts with aqueous H₃PO₄ to form NH₄H₂PO_4, and no significant macropore-water evaporation was observed when acidic porous polymer support was used, as evidenced by N₂ isotherms characterizing used H₃PO₄/A.

Identifying UiO-67 Metal-Organic Framework Defects and Binding Sites through Ammonia Adsorption

Ammonia is a widely used toxic industrial chemical that can cause severe respiratory ailments. Therefore, understanding and developing materials for its efficient capture and controlled release is necessary. One such class of materials is 3D porous metal-organic frameworks (MOFs) with exceptional surface areas and robust structures, ideal for gas storage/transport applications. Herein, interactions between ammonia and UiO-67-X (X: H, NH₂ , CH₃ ) zirconium MOFs were studied under cryogenic, ultrahigh vacuum (UHV) conditions using temperature-programmed desorption mass spectrometry (TPD-MS) and in-situ temperature-programmed infrared (TP-IR) spectroscopy. Ammonia was observed to interact with μ₃ -OH groups present on the secondary building unit of UiO-67-X MOFs via hydrogen bonding. TP-IR studies revealed that under cryogenic UHV conditions, UiO-67-X MOFs are stable towards ammonia sorption. Interestingly, an increase in the intensity of the C-H stretching mode of the MOF linkers was detected upon ammonia exposure, attributed to NH-π interactions with linkers. These same binding interactions were observed in grand canonical Monte Carlo simulations. Based on TPD-MS, binding strength of ammonia to three MOFs was determined to be approximately 60 kJ mol^-1 , suggesting physisorption of ammonia to UiO-67-X. In addition, missing linker defect sites, consisting of H₂ O coordinated to Zr⁴⁺ sites, were detected through the formation of nNH₃ ⋅H₂ O clusters, characterized through in-situ IR spectroscopy. Structures consistent with these assignments were identified through density functional theory calculations. Tracking these bands through adsorption on thermally activated MOFs gave insight into the dehydroxylation process of UiO-67 MOFs. This highlights an advantage of using NH₃ for the structural analysis of MOFs and developing an understanding of interactions between ammonia and UiO-67-X zirconium MOFs, while also providing directions for the development of stable materials for efficient toxic gas sorption.

Constructing Well-Defined and Robust Th-MOF-Supported Single-Site Copper for Production and Storage of Ammonia from Electroreduction of Nitrate

A combined technique of production and storage of ammonia (NH3) from electroreduction of nitrate (NO3 -) through one material is highly desirable but remains a huge challenge. Herein, we proposed a proof-of-concept strategy for combined NH3 production and storage from electroreduction of NO3 - through elaborately designing a single-site CuII-bipyridine-based thorium metal-organic framework (Cu@Th-BPYDC). Noticeably, the single CuII site, anchored by a solid-liquid postsynthetic metalation within Th-BPYDC, shows a novel square coordination structure, as determined by the single-crystal X-ray diffraction. This strongly implies its enormous potential as an open metal site and consequently enables excellent performance in electroreduction of NO3 - for NH3 production, giving 92.5% Faradaic efficiency and 225.3 μmol h-1 cm-2 yield. Impressively, we can further use Cu@Th-BPYDC material to effectively capture the previously produced NH3 from electroreduction of NO3 -, affording an uptake up to 20.55 mmol g-1 at 298 K at 1 bar. The results in this work will outline a new direction toward the combined technique for advanced electrocatalysis such as gas production plus storage/or separation.

Removal of hazardous dyes, toxic metal ions and organic pollutants from wastewater by using porous hyper-cross-linked polymeric materials: A review of recent advances

Water quality plays a central role in the well-being of all the living organisms on planet Earth. The ever-increasing human population and consequently increasing industrialization, urbanization, and chemically boosted cultivation are rapidly contaminating already stressed water resources. The availability of clean drinking water has become scarce for masses across the globe, and this situation is becoming alarming in developing countries. Therefore, the immediate need for cost-effective, easily accessible, eco-friendly, portable, thermally efficient, and chemically stable technologies and materials is desperately felt to meet the high global demand for clean water. To search for effective materials for wastewater treatment, the hyper-cross-linked porous polymers (HCPs) have emerged as an excellent class of porous materials for wastewater treatment due to their unique features of high surface area, tunability, biodegradability, and chemical versatility. This review describes the advances in fabrication strategies and the efficient utilization of hyper-cross-linked porous polymers for wastewater treatment. Moreover, this review specifically discusses the hyper-cross-linked porous polymers effectiveness for the separation of the dyes, nutrients, inorganic ions, organic contaminants, and toxic metals ions. Finally, the review provides insight into the challenges and prospects in the area of hyper-cross-linked porous polymers. Overall, the hyper-cross-linked porous polymers with empowering proper functionalization can provide an opportunity for the wastewater treatment not only to remove toxic contaminants but also to make contaminated water useful for various applications.

Exceptional Packing Density of Ammonia in a Dual-Functionalized Metal-Organic Framework

We report the reversible adsorption of ammonia (NH₃) up to 9.9 mmol g^-1 in a robust Al-based metal-organic framework, MFM-303(Al), which is functionalized with free carboxylic acid and hydroxyl groups. The unique pore environment decorated with these acidic sites results in an exceptional packing density of NH₃ at 293 K (0.801 g cm^-3) comparable to that of solid NH₃ at 193 K (0.817 g cm^-3). In situ synchrotron X-ray diffraction and inelastic neutron scattering reveal the critical role of free -COOH and -OH groups in immobilizing NH₃ molecules. Breakthrough experiments confirm the excellent performance of MFM-303(Al) for the capture of NH₃ at low concentrations under both dry and wet conditions.

Allomelanin: A Biopolymer of Intrinsic Microporosity

Melanin is a ubiquitous natural pigment found in a diverse array of organisms. Allomelanin is a class of nitrogen-free melanin often found in fungi. Herein, we find artificial allomelanin analogues exhibit high intrinsic microporosity and describe an approach for further increasing and tuning that porosity. Notably, the synthetic method involves an oxidative polymerization of 1,8-DHN in water, negating the need for multiple complex templating steps and avoiding expensive or complex chemical precursors. The well-defined morphologies of these nanomaterials were elucidated by a combination of electron microscopy and scattering methods, yielding to high-resolution 3D reconstruction based on small-angle X-ray scattering (SAXS) results. Synthetic allomelanin nanoparticles exhibit high BET areas, up to 860 m²/g, and are capable of ammonia capture up to 17.0 mmol/g at 1 bar. In addition, these nanomaterials can adsorb nerve agent simulants in solution and as a coating on fabrics with high breathability where they prevent breakthrough. We also confirmed that naturally derived fungal melanin can adsorb nerve gas simulants in solution efficiently despite lower porosity than synthetic analogues. Our approach inspires further analysis of yet to be discovered biological materials of this class where melanins with intrinsic microporosity may be linked to evolutionary advantages in relevant organisms and may in turn inspire the design of new high surface area materials.

Postsynthetically Modified Polymers of Intrinsic Microporosity (PIMs) for Capturing Toxic Gases

Polymers of intrinsic microporosity (PIMs) are promising materials for gas adsorption because of their high surface area, processability, and tailorable backbone. Specifically, nitrile groups on the backbone of PIM-1, an archetypal PIM, can be converted to other functional groups to selectively capture targeted gas molecules. Despite these appealing features of PIMs, their potential has mainly only been realized for the separation of nontoxic gases. Here, we prepared PIM-1 materials modified with carboxylic acid and amidoxime functional groups and investigated their performance as adsorbents for the capture of ammonia (NH₃) and sulfur dioxide (SO₂) gases. After determining the Brønsted acidity or basicity of the PIMs from potentiometric acid-base titrations, which can be correlated with affinity for acidic or basic toxic gases, we explored the uptake capacity toward NH₃ and SO₂, respectively. Gas sorption studies revealed that the carboxylated PIM showed higher affinity toward NH₃ through the incorporation of Brønsted acid sites, while the amidoxime functionalized PIM exhibited affinity toward SO₂ through the installed of slightly basic functional groups. Overall, this study highlights new insight into PIMs as solid sorbent materials for capturing toxic gases, which can be transferred to their potential use in practical applications, such as personal protective equipment or air filtration.

Spatial Engineering Direct Cooperativity between Binding Sites for Uranium Sequestration

Preorganization is a basic design principle used by nature that allows for synergistic pathways to be expressed. Herein, a full account of the conceptual and experimental development from randomly distributed functionalities to a convergent arrangement that facilitates cooperative binding is given, thus conferring exceptional affinity toward the analyte of interest. The resulting material with chelating groups populated adjacently in a spatially locked manner displays up to two orders of magnitude improvement compared to a random and isolated manner using uranium sequestration as a model application. This adsorbent shows exceptional extraction efficiencies, capable of reducing the uranium concentration from 5 ppm to less than 1 ppb within 10 min, even though the system is permeated with high concentrations of competing ions. The efficiency is further supported by its ability to extract uranium from seawater with an uptake capability of 5.01 mg g-1, placing it among the highest-capacity seawater uranium extraction materials described to date. The concept presented here uncovers a new paradigm in the design of efficient sorbent materials by manipulating the spatial distribution to amplify the cooperation of functions.

Ammonia Storage in Hydrogen Bond-Rich Microporous Polymers

The fascinating structural flexibility of porous polymers is highly attractive because it can result in optimized materials with specific host-guest interactions. Nevertheless, the fundamental mechanisms responsible for controlling the weak interactions of these hydrogen bond-rich networks-essential for developing smart task-specific materials used in recognition, capture, and sequestration processes-remain unexplored. Herein, by systematically comparing performance changes between poly(amic acid) (PAA)- and polycyclic imide (PI)-based porous polymers before and after NH₃ adsorption, the role of hydrogen bonds in conformational lability and responsiveness toward guest molecules is highlighted. By combining thermal gravimetric analysis with neutron spectroscopy supported by DFT calculations, we demonstrate that PAA's chemical and physical stability is enhanced by the presence of stronger host-guest interactions. This observation also emphasizes the idea that efficient adsorption relies on having a high number of sites, upon which gas molecules can adsorb with greater affinity via strong hydrogen bonding interactions.

Emerging Porous Materials and Their Composites for NH3 Gas Removal

NH3, essential for producing artificial fertilizers and several military and commercial products, is being produced at a large scale to satisfy increasing demands. The inevitable leakage of NH3 during its utilization, even in trace concentrations, poses significant environmental and health risks because of its highly toxic and reactive nature. Although numerous techniques have been developed for the removal of atmospheric NH3, conventional NH3 abatement systems possess the disadvantages of high maintenance cost, low selectivity, and emission of secondary wastes. In this context, highly tunable porous materials such as metal-organic frameworks, covalent organic frameworks, hydrogen organic frameworks, porous organic polymers, and their composite materials have emerged as next-generation NH3 adsorbents. Herein, recent progress in the development of porous NH3 adsorbents is summarized; furthermore, factors affecting NH3 capture are analyzed to provide a reasonable strategy for the design and synthesis of promising materials for NH3 abatement.

High Ammonia Uptake of a Metal-Organic Framework Adsorbent in a Wide Pressure Range

Although numerous porous adsorbents have been investigated for NH₃ capture applications, these materials often exhibit insufficient NH₃ uptake, low NH₃ affinity at the ppm level, and poor chemical stability against wet NH₃ conditions. The NH₃ capture properties of M₂ (dobpdc) complexes (M=Mg²⁺ , Mn²⁺ , Co²⁺ , Ni²⁺ , and Zn²⁺ ; dobpdc^4- =4,4-dioxidobiphenyl-3,3-dicarboxylate) that contain open metal sites is presented. The NH₃ uptake of Mg₂ (dobpdc) at 298 K was 23.9 mmol g^-1 at 1 bar and 8.25 mmol g^-1 at 570 ppm, which are record high capacities at both pressures among existing porous adsorbents. The structural stability of Mg₂ (dobpdc) upon exposure to wet NH₃ was superior to that of the other M₂ (dobpdc) and the frameworks tested. Overall, these results demonstrate that Mg₂ (dobpdc) is a recyclable compound that exhibits significant NH₃ affinity and capacity, making it a promising candidate for real-world NH₃ -capture applications.

Confining Polyoxometalate Clusters into Porous Aromatic Framework Materials for Catalytic Desulfurization of Dibenzothiophene

Removal of notorious sulfur compounds to produce low-sulfur-content (≤10 ppm) diesel is necessary and vital for modern industry and environmental protection. A new type of inorganic-organic hybrid material has been designed and synthesized via confining molybdenum-containing polyoxometalate (POM) clusters within porous aromatic framework-1 (PAF-1) cavities named POM-PAF-1. Deep oxidative desulfurization experiments reveal that POM-PAF-1 possesses excellent reactivity under mild conditions, exemplified by a sulfur removal degree of 98.5% dibenzothiophene within 30 min at 30 °C. The improvement in oxidative desulfurization reactivity from traditional porous POM-based catalysts is owing to uniform POMs and lipophilic and porous PAF-1. The high performance of POM-PAF-1 in terms of excellent reactivity and good stability means it has potential in new heterogeneous catalysis.

Sequential Ammonia and Carbon Dioxide Adsorption on Pyrolyzed Biomass to Recover Waste Stream Nutrients

The amine-rich surfaces of pyrolyzed human solid waste (py-HSW) can be "primed" or "regenerated" with carbon dioxide (CO₂) to enhance their adsorption of ammonia (NH₃) for use as a soil amendment. To better understand the mechanism by which CO₂ exposure facilitates NH₃ adsorption to py-HSW, we artificially enriched a model sorbent, pyrolyzed, oxidized wood (py-ox wood) with amine functional groups through exposure to NH₃. We then exposed these N-enriched materials to CO₂ and then resorbed NH₃. The high heat of CO₂ adsorption (Q _st) on py-HSW, 49 kJ mol^-1, at low surface coverage, 0.4 mmol CO₂ g^-1, showed that the naturally occurring N compounds in py-HSW have a high affinity for CO₂. The Q _st of CO₂ on py-ox wood also increased after exposure to NH₃, reaching 50 kJ mol^-1 at 0.7 mmol CO₂ g^-1, demonstrating that the incorporation of N-rich functional groups by NH₃ adsorption is favorable for CO₂ uptake. Adsorption kinetics of py-ox wood revealed continued, albeit diminishing NH₃ uptake after each CO₂ treatment, averaging 5.9 mmol NH₃ g^-1 for the first NH₃ exposure event and 3.5 and 2.9 mmol NH₃ g^-1 for the second and third; the electrophilic character of CO₂ serves as a Lewis acid, enhancing surface affinity for NH₃ uptake. Furthermore, penetration of ¹⁵NH₃ and ¹³CO₂ measured by NanoSIMS reached over 7 μm deep into both materials, explaining the large NH₃ capture. We expected similar NH₃ uptake in py-HSW sorbed with CO₂ and py-ox wood because both materials, py-HSW and py-ox wood sorbed with NH₃, had similar N contents and similarly high CO₂ uptake. Yet NH₃ sorption in py-HSW was unexpectedly low, apparently from potassium (K) bicarbonate precipitation, reducing interactions between NH₃ and sorbed CO₂; 2-fold greater surface K in py-HSW was detected after exposure to CO₂ and NH₃ than before gas exposure. We show that amine-rich pyrolyzed waste materials have high CO₂ affinity, which facilitates NH₃ uptake. However, high ash contents as found in py-HSW hinder this mechanism.

A Flexible Interpenetrated Zirconium-Based Metal-Organic Framework with High Affinity toward Ammonia

Flexible metal-organic frameworks (MOFs) are highly attractive porous crystalline materials presenting structural changes when exposed to external stimuli, the mechanism of which is often difficult to glean, owing to their complex and dynamic nature. Herein, a flexible interpenetrated Zr-MOF, NU-1401, composed of rare 4-connected Zr₆ nodes and tetratopic naphthalenediimide (NDI)-based carboxylate linkers, was designed. The intra-framework pore opening deformation and inter-framework motions, when subjected to different solvent molecules, were investigated by single-crystal XRD. The distance and overlap angle between the stacked NDI pairs in the entangled structure could be finely tuned, and the interactions between NDI and solvent molecules led to solvochromism. Furthermore, the presence of electron-deficient NDI units in the linker and acid sites on the node of the interpenetrated porous structure offered high density of adsorption sites for ammonia molecules, resulting in high uptake at low pressures.

A Single-Ion Conducting Borate Network Polymer as a Viable Quasi-Solid Electrolyte for Lithium Metal Batteries

Lithium-ion batteries have remained a state-of-the-art electrochemical energy storage technology for decades now, but their energy densities are limited by electrode materials and conventional liquid electrolytes can pose significant safety concerns. Lithium metal batteries featuring Li metal anodes, solid polymer electrolytes, and high-voltage cathodes represent promising candidates for next-generation devices exhibiting improved power and safety, but such solid polymer electrolytes generally do not exhibit the required excellent electrochemical properties and thermal stability in tandem. Here, an interpenetrating network polymer with weakly coordinating anion nodes that functions as a high-performing single-ion conducting electrolyte in the presence of minimal plasticizer, with a wide electrochemical stability window, a high room-temperature conductivity of 1.5 × 10^-4 S cm^-1 , and exceptional selectivity for Li-ion conduction (t_Li+ = 0.95) is reported. Importantly, this material is also flame retardant and highly stable in contact with lithium metal. Significantly, a lithium metal battery prototype containing this quasi-solid electrolyte is shown to outperform a conventional battery featuring a polymer electrolyte.

A recyclable metal–organic framework for ammonia vapour adsorption

The incorporation of sterically hindered boron centers into MOFs allows the recyclable adsorption of NH₃ vapour from aqueous solution.

A Hydrogen-Bonded Organic Framework (HOF) with Type IV NH3 Adsorption Behavior

An S-shaped gas isotherm pattern displays high working capacity in pressure-swing adsorption cycle, as established for CO₂ , CH₄ , acetylene, and CO. However, to our knowledge, this type of adsorption behavior has not been revealed for NH₃ gas. Herein, we design and characterize a hydrogen-bonded organic framework (HOF) that can adsorb NH₃ uniquely in an S-shape (type IV) fashion. While conventional porous materials, mostly with type I NH₃ adsorption behavior, require relatively high regeneration temperature, this platform which has significant working capacity is easily regenerated and recyclable at room temperature.

Iron detection and remediation with a functionalized porous polymer applied to environmental water samples

Iron is one of the most abundant elements in the environment and in the human body. As an essential nutrient, iron homeostasis is tightly regulated, and iron dysregulation is implicated in numerous pathologies, including neuro-degenerative diseases, atherosclerosis, and diabetes. Endogenous iron pool concentrations are directly linked to iron ion uptake from environmental sources such as drinking water, providing motivation for developing new technologies for assessing iron(ii) and iron(iii) levels in water. However, conventional methods for measuring aqueous iron pools remain laborious and costly and often require sophisticated equipment and/or additional processing steps to remove the iron ions from the original environmental source. We now report a simplified and accurate chemical platform for capturing and quantifying the iron present in aqueous samples through use of a post-synthetically modified porous aromatic framework (PAF). The ether/thioether-functionalized network polymer, PAF-1-ET, exhibits high selectivity for the uptake of iron(ii) and iron(iii) over other physiologically and environmentally relevant metal ions. Mössbauer spectroscopy, XANES, and EXAFS measurements provide evidence to support iron(iii) coordination to oxygen-based ligands within the material. The polymer is further successfully employed to adsorb and remove iron ions from groundwater, including field sources in West Bengal, India. Combined with an 8-hydroxyquinoline colorimetric indicator, PAF-1-ET enables the simple and direct determination of the iron(ii) and iron(iii) ion concentrations in these samples, providing a starting point for the design and use of molecularly-functionalized porous materials for potential dual detection and remediation applications.

Functionalized Porous Aromatic Frameworks as High-Performance Adsorbents for the Rapid Removal of Boric Acid from Water

This study demonstrates that functionalized, highly porous polymers are promising for the adsorptive capture of boric acid, a neutral contaminant that is difficult to remove from seawater using conventional reverse osmosis membranes. Appending N-methyl-d-glucamine (NMDG) to the pore walls of high-surface-area porous aromatic frameworks (PAFs) yields the adsorbents PAF-1-NMDG and P2-NMDG in a simple two-step synthesis. The boron-selective PAFs demonstrate adsorption capacities that are up to 70% higher than those of a commercial boron-selective resin, Amberlite IRA743, and markedly faster adsorption rates, owing to their higher NMDG loadings and greater porosities relative to the resin. Remarkably, PAF-1-NMDG is able to reduce the boron concentration in synthetic seawater from 2.91 to <0.5 ppm in less than 3 min at an adsorbent loading of only 0.3 mg mL^-1 . The boron adsorption rate constants of both frameworks, determined via a pseudo-second-order rate model, represent the highest values reported in the literature-in most cases orders of magnitude higher than those of other boron-selective adsorbents. The frameworks can also be readily regenerated via mild acid/base treatment and maintain constant boron adsorption capacities for at least 10 regeneration cycles. These results highlight the numerous advantages of PAFs over traditional porous polymers in water treatment applications.

Scalable, room temperature, and water-based synthesis of functionalized zirconium-based metal–organic frameworks for toxic chemical removal

An inexpensive, environmentally benign and scalable strategy was developed to synthesize UiO-66 derivatives in water at room temperature.