Porous Organic Materials Research Articles

Construction of Highly Porous and Robust Hydrogen-Bonded Organic Framework for High-Capacity Clean Energy Gas Storage.

Development of highly porous and robust hydrogen-bonded organic frameworks (HOFs) for high-pressure methane and hydrogen storage remains a grand challenge due to the fragile nature of hydrogen bonds. Herein, we report a strategy of constructing the double-walled framework to target highly porous and robust HOF (ZJU-HOF-5a) for extraordinary CH4 and H2 storage. ZJU-HOF-5a features a minimized twofold interpenetration with double-walled structure, in which multiple supramolecular interactions are existed between the interpenetrated walls. This structural configuration can notably enhance the framework robustness while maintaining its high porosity, affording one of the highest gravimetric and volumetric surface areas of 3102 m2 g-1 and 1976 m2 cm-3 among the reported HOFs so far. ZJU-HOF-5a thus exhibits an extremely high volumetric H2 uptake of 43.6 g L-1 at 77 K/100 bar and working capacity of 41.3 g L-1 under combined swing conditions (77 K/100 bar→160 K/5 bar), and also impressive methane storage performance with a 5-100 bar working capacity of 187 (or 159) cm3 (STP) cm-3 at 270 K (or 296 K), outperforming most of the reported porous organic materials. Single-crystal X-ray diffraction studies on CH4-loaded ZJU-HOF-5a reveal that abundant supramolecular binding sites combined with ultrahigh porosities account for its high CH4 storage capacities. Combined with high stability, super-hydrophobicity, and easy recovery, ZJU-HOF-5a is placed among the most promising materials for H2 and CH4 storage applications.

Bidirectional enhancement of output performance of nanogenerators by M-COFs materials

The emergence of nanogenerators, which have the ability to capture mechanical energy from the environment and to collect and transmit tiny energy, is rapidly becoming a hot research topic. The performance of electrode materials is the key to the efficiency of nanogenerators. Covalent organic skeletons (COFs), a class of crystalline organic porous materials with the advantages of large specific surface area, high porosity, tunable structure, and flexible tailorability, have very significant advantages in being used as nanogenerator materials. In this paper, we synthesised two COF materials to investigate the effect of the introduction of active metals on the friction power generation performance of COFs without changing their topology, COF-2 containing zinc ions is capable of generating a short-circuit current of 107.5 µA during friction. The porous structure increases the effective contact area to form a larger charge density, and the introduction of metal ions can accelerate the charge separation and transport. The two bidirectional synergistic effects of the materials significantly improve the output performance of the nanogenerator, and a simple and efficient method is explored for the enhancement of the output performance of COF-based triboelectric nanogenerators.

Ionic Liquid‐Functionalized Porous Materials for Catalyzing CO2 Cycloaddition Reaction

AbstractIonic liquids (ILs) are incorporated into traditional porous materials to create ILs‐functionalized porous materials, which exhibit excellent absorption capacity and good catalytic activity for CO2. As a result, they are extensively utilized in the chemical conversion of CO2. This paper specifically focuses on the utilization of ILs‐functionalized organic porous materials, ILs‐functionalized inorganic porous materials, and ILs‐functionalized organic‐inorganic hybrid porous materials in the conversion of CO2. The synergistic effects of combining ILs with porous materials in CO2 conversion are thoroughly discussed. Furthermore, an in‐depth analysis is provided regarding the potential prospects and future applications of utilizing ILs‐functionalized porous materials within the broader realm of catalytic CO2 conversion technologies.

Porous Organic Frame Materials for Adsorption and Removal of Pesticide Contaminants: A Review

Porous Organic Frame Materials for Adsorption and Removal of Pesticide Contaminants: A Review

Efficient photocatalytic hydrogen production via single-atom Pt anchored hydrogen-bonded organic frameworks

Constructing single-atom catalysts (SACs) using organic porous framework materials as supports presents a promising approach for developing highly efficient photocatalysts for hydrogen evolution. However, the fabrication of SACs that are both highly stable and active poses a significant challenge, particularly in the precise anchoring of metal single atoms. In this study, we utilized 1,3,6,8-tetra (p-methyl benzoate) pyrene as a ligand to synthesize pyrene-based hydrogen-bonded organic frameworks (denoted as PFC-1) through a self-assembly approach. Subsequently, a liquid-phase photoreduction process was employed to deposit noble metal platinum (Pt) onto PFC-1, resulting in the fabrication of SACs (PFC-1@Pt). Characterization results confirmed that Pt existed in a monatomic state, anchored through PtC and PtO coordination bonds with PFC-1. Serving as electron capture and separation centers, the Pt single atoms effectively suppressed electron-hole recombination, thereby prolonging carrier lifetimes. Consequently, the PFC-1@Pt SAC exhibited efficient hydrogen evolution performance with a rate of 2202.5 μmol g−1 h−1 and maintained photocatalytic activity for over 40 h. Our findings provide a systematic approach for developing efficient and stable SACs based on HOFs, expanding the potential applications of HOF materials in photocatalysis.

In Situ Growth of Well-Aligned MOF Nanoneedle Arrays into Composite Photothermal Membranes for Solar Desalination.

The solar-driven interfacial evaporation (SDIE) technology serves as a clean and facile approach combining seawater desalination to address water shortage and energy crisis. Recently, porous organic framework materials have aroused great attention, and the development of MOF-based composites with significant performance in photothermal conversion and water activation has become one of the important focuses in this field. In this work, an MOF-based composite photothermal membrane (PON@MOF) was prepared via the in situ growth of metal-organic framework (MOF) nanoneedle arrays induced by a pyridine-based organic polymer nanowire network (PON). The PON@MOF membrane possessed an MOF array layer, a PON-induced layer, and a porous support layer. The PON is rich in coordinated nitrogen atoms for anchoring the metal-ion source, and the main role of the PON layer is to provide favorable nucleation sites and orient in situ growth of well-aligned MOF nanoneedle arrays. With the highly conjugated framework of PON@MOF and the light trapping of the nanoarrays strengthening the photothermal conversion as well as the hydrophilic chemical structure facilitating the decrease of the water evaporation enthalpy, the PON@MOF membrane realizes highly efficient thermal vapor conversion. Under solar irradiation (1.0 kW m-2), PON@MOF demonstrated an evaporation rate of 2.14 kg m-2 h-1 and a solar-to-vapor conversion efficiency of 98.5%. Meanwhile, the PON@MOF membrane has excellent salt resistance and stability, highlighting its potential application in desalination. Overall, this work provides a special idea for the structural design of photothermal composites for solar desalination and freshwater production.

HNTs Improve Flame Retardant and Thermal Insulation of the PVA/CA Composite Aerogel.

Porous materials are widely used in construction, batteries, electrical appliances, and other fields. In order to meet the demand for flame-retardant and thermal insulation properties of organic porous materials, in this work, poly(vinyl alcohol)/calcium alginate/halloysite nanotube (PVA/CA/HNTs) aerogels with a hierarchical pore structure at micrometer-nanometer scales were prepared through freeze-drying using PVA as the substrate. The cross-linking reactions of PVA with H3BO3 and sodium alginate (SA) with CaCl2 constructed a double cross-linking network structure within the aerogel. And the HNTs were incorporated as reinforcing agents. The experimental results showed that the PVA/CA/HNTs aerogels had excellent flame-retardant and thermal insulation properties, and the heat release rate (HRR) and total heat release (THR) were effectively reduced compared to the PVA/CA aerogel. In addition, PVA/CA/HNTs aerogels had a high limiting oxygen index (LOI 60%) and low thermal conductivity (0.040 W/m·K). While their surface was subjected to a flame (800-1000 °C) for 25 min, the temperatures of the back surface were still lower than 80 °C. The low thermal conductivity of HNTs with hollow nanotube-like structures and the excellent flame-retardant properties of CA contributed to this phenomenon. The presence of HNTs and CA facilitated the formation of a dense carbon layer during combustion, enhancing the flame retardancy for PVA. In addition, the interpenetrating cross-linking network and the unique nanopores of HNTs collectively established a hierarchical pore structure within the gel, effectively impeding substance and heat exchange between the substrate and external environment. As the flame-retardant and thermal insulating material, PVA/CA/HNTs aerogels have a promising development prospect and potential in the fields of construction, transportation, electronics, and electrical appliances.

3D Covalent Organic Framework Membranes for Molecular Separations.

Membrane separation has become an indispensable separation technology in social production, playing an important role in drug production, water purification, etc. The key core of membranes lies in achieving efficient and precise sieving between substances. As a result, a typical trade-off arises: highly permeable membranes usually sacrifice selectivity and vice versa. To address this dilemma, long-term research has focused on comprehensive understanding and modelling of synthetic membranes at various scales. A significant advancement in this arena is the advent of three-dimensional covalent organic framework (3D COF) membranes, a novel category of long-range ordered porous organic polymer materials. Characterized by an abundance of interconnected channels, diverse pore wall properties, tunable structures, and robust thermal and chemical resilience, 3D COF membranes offer a promising approach for efficient substance separation. This review undertakes a meticulous investigation of the synthesis and physicochemical properties of 3D COF membranes, accentuating the underlying design principles, fabrication methods, and application attempts. A comprehensive assessment of their research trajectory and current standing in the field of membrane processes is provided. The review culminates in a forward-looking outlook, summarizing future research directions and highlighting the substantial potential of this innovative work to shape the future of efficient membrane separation processes.

Ionic covalent organic framework-MXene heterojunction constructed by electrostatic interaction for stable electrocatalytic hydrogen generation

Constructing stable electrocatalysts by pyrolysis-free technique is an important topic in hydrogen-evolution reaction (HER) for water splitting reactions. Covalent organic frameworks (COFs), an emerging class of porous materials, offer ideal candidates owing to their abundant active sites and unique structures. Herein, a novel pyrolysis-free heterostructure was constructed using electrostatic interactions between an ionic COF (JUC-628) and Ti3C2Tx (MXene) nanosheets, which exhibits an impressively low overpotential of 137 mV at 10 mA cm−2 and excellent catalytic activity and stability for five days operation under alkaline conditions. Theoretical calculations depict that the formation of a stable heterostructure between MXene nanosheets and JUC-628 is the critical factor underlying the outstanding catalytic performance. Moreover, the optimized catalyst showed superior hydrogen-evolution capability in alkaline seawater electrolysis, highlighting the first successful application of a COF-based catalyst for hydrogen production from seawater electrolysis. As a leading covalent organic porous material–based catalyst for HER, as a proof of concept, this study represents a novel strategy to construct efficient electrocatalysts by COFs directly without the pyrolysis technique.

Imine‐linked covalent organic frameworks: Recent advances in design, synthesis, and application

AbstractCovalent organic frameworks (COFs) are new porous organic materials made of organic building blocks precisely constructed by strong covalent bonds. These new materials feature tunable structure, permanent porosity, high crystallinity, high specific surface area, and excellent stability, which enable COFs to be used in many applications. Linkage chemistry is a key factor in the synthesis of COFs and the control of their physicochemical properties. The boroxine, boronate‐ester, imine, hydrazone, imide, and C=C linkages have been widely used in the construction of COFs. Among the various linkages, imine has become the most important linkage for the COFs due to the easy formation of imine linkage with structural and functional diversity. Over the past decade, imine‐linked COFs have made significant progress and become an indispensable part of various applications of COFs. Here, we aim to provide a comprehensive review of the research progress in the field of imine‐linked COFs, especially the advances in topology design and COF powder and film preparation, and their important advances in gas adsorption, catalysis, and optoelectronic devices. Finally, we discuss the challenges in the design, synthesis, and application of imine‐linked COFs, and present our views on the further development of imine‐linked COFs.

Potential building blocks for porous organic materials

2,4-Difluoronitrobenzene has been reacted with a linker diamine (ethylenediamine or propylenediamine) and butylamine, in either order, to give new molecular building blocks for porous supramolecular networks. Two structures were established by X-ray single crystal structure determinations. The propylenediamine structure displays small pores, which may be due to the longer and more flexible linker in the structure.

A Simple and Sequential Strategy for the Introduction of Complexity and Hierarchy in Hydrogen-Bonded Organic Framework (HOF) Crystals for Environmental Applications.

Hydrogen-bonded organic frameworks (HOFs) are a new class of crystalline porous organic molecular materials (POMMs) with great potential for a diverse range of applications. HOFs face common challenges to POMMs, and in general to purely organic crystals, that is, the difficulty of integrating complexity in crystals. Herein, we propose a simple and sequential strategy for the formation of HOFs with hierarchical superstructures. The strategy is based on controlling the assembly conditions, avoiding the use of any surface functionalization or template, which allows to obtain hierarchical crystalline porous superstructures in an easy manner. As proof of concept, we obtained the first example of core-shell (HOF-on-HOF) crystals and HOFs with hierarchical superstructures having superhydrophobicity and trapping abilities for the capture of persistent water contaminants such as oils and microplastics. We expect that this strategy could serve as inspiration for the construction of more intricate multiscale structures that could greatly expand the library of HOF materials.

A Simple and Sequential Strategy for the Introduction of Complexity and Hierarchy in Hydrogen‐Bonded Organic Framework (HOF) Crystals for Environmental Applications

AbstractHydrogen‐bonded organic frameworks (HOFs) are a new class of crystalline porous organic molecular materials (POMMs) with great potential for a diverse range of applications. HOFs face common challenges to POMMs, and in general to purely organic crystals, that is, the difficulty of integrating complexity in crystals. Herein, we propose a simple and sequential strategy for the formation of HOFs with hierarchical superstructures. The strategy is based on controlling the assembly conditions, avoiding the use of any surface functionalization or template, which allows to obtain hierarchical crystalline porous superstructures in an easy manner. As proof of concept, we obtained the first example of core–shell (HOF‐on‐HOF) crystals and HOFs with hierarchical superstructures having superhydrophobicity and trapping abilities for the capture of persistent water contaminants such as oils and microplastics. We expect that this strategy could serve as inspiration for the construction of more intricate multiscale structures that could greatly expand the library of HOF materials.

A high-temperature-triggered crosslinking reaction to achieve excellent intrinsic flame retardancy of organic phase change composites.

The host-guest composite that integrates a porous scaffold and organic phase change materials (PCMs) features high energy density and customizable function, promising for advanced thermal storage/utilization. However, highly flammable organic PCMs are prone to severe combustion in porous structures, making it challenging for traditional flame-retardant methods to balance fire safety and latent heat. Herein, a high-temperature-triggered crosslinking reaction between the host and guest is designed using a polybenzoxazine-based aerogel (PB-1) and benzoxazine-based PCMs (C-dad). At high temperatures, the ring-opening polymerization (ROP) of C-dad can be initiated by and reacted with the phenolic groups of PB-1 to form a polybenzoxazine copolymer monolith with an improved char yield and intrinsic low flammability and without using the typical flame-retardant components. This enables the obtained composite (PB-1/C-dad) to well balance latent heat (145.3 J g-1), char yield (a char residue of 13.1% at 600 °C), and flame retardancy (a peak heat release rate of 231 W g-1), outperforming the representative flame-retardant modified polymer/organic PCM complexes reported in the literature. This thermal-triggered mechanism allows PB-1/C-dad to be repeatedly and stably used within the working temperature and activates its flame retardancy when exposed to open flames. The proposed host-guest crosslinking strategy is believed to inspire the development of inherently nonflammable phase change composites for safer thermal management.

Heavy Metal-Based Toxic Oxo-Pollutants Sequestration by Advanced Functional Porous Materials for Safe Drinking Water.

ConspectusWater scarcity as a consequence of either environmental or economic actions is the most compelling global concern of the 21st century, as ∼2 billion people (26% of the total population) struggle to access safe drinking water and ∼3.6 billion (46% of the total population) lack access to clean water sanitation. In this context, groundwater pollution by toxic heavy metals and/or their oxo-pollutants, such as CrO42-, Cr2O72-, AsO43-, SeO32-, SeO42-, TcO4-, UO22+, etc., have been becoming rapidly growing global concerns. The severe toxicity upon bioaccumulation of these oxo-anions has prompted the US Environment Protection Agency (EPA) to mark these persistent and hazardous substances as priority pollutants. Additionally, the heavy-metal-based pollutants are difficult to transform into eco-friendly substances, thus presenting serious challenges toward human health and environmental preservation. To this end, the emergence of advanced functional porous materials (AFPMs), including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), metal-organic polyhedrons (MOPs), porous organic polymers (POPs), etc., have presented extraordinary opportunities in material research and water treatment applications. The liberty in designing and structural tunability of AFPMs, facilitated by utilization of structure-encoded molecular building blocks, enables precise control over target-specificity and structure-property correlations. Bridging the gap between strategic material design and on-demand real-world application can facilitate the development of next-generation sorbents/ion-exchangers for efficient water treatment.In this Account, we summarize the recent advancements from our group toward the development of cutting-edge multifunctional ionic-porous sorbents, offering viable solutions toward providing clean and safe drinking water. Our vision allows us to comprehend this challenge through two strategic factors: efficient oxo-anion capture via ion-exchange and specific host-guest interactions via installation of modular functional groups. To provide an overview, we first highlight the different structural variants and coexistance of various toxic oxo-anions depending on the pH of the medium and their adverse effects. Next, we highlight the promising potential of water stable cationic MOFs toward selective remediation of toxic Cr(VI), Mn(VII), Tc(VI), Se(IV), Se(VI), U (VI), As(III), and As(V)-based toxic oxo-pollutants from water. In the subsequent sections, we summarize the target-specific design strategies and oxo-anion remediation performances of ionic porous organic polymers and hybrid functional porous materials. The key role of target-specific designability and/or structural fine-tuning of AFPMs toward preferential sorption of oxo-pollutants is systematically demonstrate. Particularly, the role of ion-exchange (anion-exchange) processes toward targeted oxo-pollutant capture by ionic AFPMs has been discussed in details. In several examples, the AFPMs were successful in reducing the toxic oxo-anion concentration levels lower than the permitted values for drinking water by the World Health Organizing Committee (WHO), showcasing their real-world applicability potency.Our contemporaneous endeavors in exploring ionic AFPMs for selective toxic oxo-anion sequestration may serve as a blueprint to researchers for future development of the next generation sorbent materials for energy-economically feasible water treatment methods.

Flux synthesis of two-dimensional covalent organic frameworks.

Covalent organic frameworks (COFs) are crystalline porous polymers constructed from organic building blocks into ordered two- or three-dimensional networks through dynamic covalent bonds. Attributed to their high porosity, well-defined structure, tailored functionality and excellent chemical stability, COFs have been considered ideal sorbents for various separation applications. The synthesis of COFs mainly employs the solvothermal method, which usually requires organic solvents in sealed Pyrex tubes, resulting in unscalable powdery products and environmental pollution that seriously limits their practical applications. Herein, our protocol focuses on an emerging synthesis method for COFs based on organic flux synthesis without adding solvents. The generality of this synthesis protocol has been applied in preparing various types of COFs, including olefin-linked, imide-linked, Schiff-based COFs on both gram and kilogram scales. Furthermore, organic flux synthesis avoids the disadvantages of solvothermal synthesis and enhances the crystallization and porosity of COFs. Typically, COF synthesis takes 3-5 d to complete, and subsequent washing procedures leading to pure COFs need 1 d. The procedure for kilogram-scale production of COFs with commercially available monomers is also provided. The resulting COFs are suitable for separation applications, particularly as adsorbent materials for industrial gas separation and water treatment applications. The protocol is suited for users with prior expertise in the synthesis of inorganic materials and porous organic materials.

Crystalline Porous Organic Cage Membranes Constructed Using Fortified Intermolecular Interactions for Molecular Sieving.

Among the various types of materials with intrinsic porosity, porous organic cages (POCs) are distinctive as discrete molecules that possess intrinsic cavities and extrinsic channels capable of facilitating molecular sieving. However, the fabrication of POC membranes remains highly challenging due to the weak noncovalent intermolecular interactions and most reported POCs are powders. In this study, we constructed crystalline free-standing porous organic cage membranes by fortifying intermolecular interactions through the induction of intramolecular hydrogen bonds, which was confirmed by single-crystal X-ray analysis. To elucidate the driving forces behind, a series of terephthaldehyde building blocks containing different substitutions were reacted with flexible triamine under different conditions via interfacial polymerization (IP). Furthermore, density functional theory (DFT) calculations suggest that intramolecular hydrogen bonding can significantly boost the intermolecular interactions. The resulting membranes exhibited fast solvent permeance and high rejection of dyes not only in water, but also in organic solvents. In addition, the membrane demonstrated excellent performance in precise molecular sieving in organic solvents. This work opens an avenue to designing and fabricating free-standing membranes composed of porous organic materials for efficient molecular sieving.

Crystalline Porous Organic Cage Membranes Constructed Using Fortified Intermolecular Interactions for Molecular Sieving

AbstractAmong the various types of materials with intrinsic porosity, porous organic cages (POCs) are distinctive as discrete molecules that possess intrinsic cavities and extrinsic channels capable of facilitating molecular sieving. However, the fabrication of POC membranes remains highly challenging due to the weak noncovalent intermolecular interactions and most reported POCs are powders. In this study, we constructed crystalline free‐standing porous organic cage membranes by fortifying intermolecular interactions through the induction of intramolecular hydrogen bonds, which was confirmed by single‐crystal X‐ray analysis. To elucidate the driving forces behind, a series of terephthaldehyde building blocks containing different substitutions were reacted with flexible triamine under different conditions via interfacial polymerization (IP). Furthermore, density functional theory (DFT) calculations suggest that intramolecular hydrogen bonding can significantly boost the intermolecular interactions. The resulting membranes exhibited fast solvent permeance and high rejection of dyes not only in water, but also in organic solvents. In addition, the membrane demonstrated excellent performance in precise molecular sieving in organic solvents. This work opens an avenue to designing and fabricating free‐standing membranes composed of porous organic materials for efficient molecular sieving.

Monolithic conjugated microporous polymers with antibacterial activity for air filtration

The air pollution caused by particulate matters (PMs) poses a severe threat to the human health. In particular, the fine particles with diameter smaller than 2.5 μm (PM2.5) can be carriers of various bacteria and viruses, accelerating spread of epidemic. In this work, we synthesized two robust and flexible conjugated microporous polymer (CMP) aerogels for PMs removal, via one-step coupling polymerization of arylethynylenes and aryl halides with different molecular configuration. The resulting CMP aerogels comprise of hollow nanotubes with 3D porous network and high surface areas up to 660 m2/g. The efficiency of CMP aerogels for PM2.5 and PM10 was 99.5 ± 0.3 % and 99.8 ± 0.1 % with a long-term durability. In combination with their physicochemical stability and inherent surface hydrophobicity, a high efficiency for PM2.5 filtration more than 99.6 ± 0.1 % also can be obtained at a high humidity at room temperature both for the two CMP aerogels. In addition, benefiting from the rich alkynyl groups in skeletons, post-modification of the resulting CMP aerogels with thiol-yne chemistry followed by silver ion uptake gives rise to antibacterial materials with outstanding activity for gram-positive strains far superior to other porous organic polymer materials. This work provides a new avenue to fabricate bifunctional CMPs derived porous aerogels for air filtration with high performance and antibacterial activity, and is expected to expand the application of CMPs in environmental purification.

Challenging POPular opinion: Porous organic polymers for atmospheric water harvesting

As humanity faces growing water scarcity in many parts of the world, innovative solutions are imperative to achieve equitable access to safe drinking water for all. Atmospheric water harvesting (AWH) is a highly promising solution to water scarcity, comprising water adsorption directly from air using hydrophilic adsorbents, followed by collection upon desorption. Porous organic polymers exhibit distinct advantages for AWH, including broad tailorability, desirable porous properties, and outstanding chemical and thermal stability. This perspective outlines the current state-of-the-art in porous organic materials for AWH, distinguishing between reticular and amorphous materials, to discern key properties and outline future design principles. We also outline key performance metrics and provide a guide for the characterisation of such porous organic materials for those seeking to enter the field of AWH.