Ultrahigh surface area in porous solids

Utilizing Nanostructured Materials for Hydrogen Generation, Storage, and Diverse Applications

The rapid advancement of refined nanostructures and nanotechnologies offers significant potential to boost research activities in hydrogen storage. Recent innovations in hydrogen storage have centered on nanostructured materials, highlighting their effectiveness in molecular hydrogen storage, chemical storage, and as nanoconfined hydride supports. Emphasizing the importance of exploring ultra-high-surface-area nanoporous materials and metals, we advocate for their mechanical stability, rigidity, and high hydride loading capacities to enhance hydrogen storage efficiency. Despite the evident benefits of nanostructured materials in hydrogen storage, we also address the existing challenges and future research directions in this domain. Recent progress in creating intricate nanostructures has had a notable positive impact on the field of hydrogen storage, particularly in the realm of storing molecular hydrogen, where these nanostructured materials are primarily utilized.

Numerical Study on Fluid Flow Behavior and Heat Transfer Performance of Porous Media Manufactured by a Space Holder Method

The velocity field and temperature field are crucial for metal foams to be used as a heat exchanger, but they are difficult to obtain through physical experiments. In this work, the fluid flow behavior and heat transfer performance in open-cell metal foam were numerically studied. Porous 3D models with different porosities (55-75%) and pore sizes (250 μm, 550 μm, and 1000 μm) were created based on the porous structure manufactured by the Lost Carbonate Sintering method. A wide flow velocity range from 0.0001 m/s to 0.3 m/s, covering both laminar and turbulent flow regimes, is fully studied for the first time. Pressure drop, heat transfer coefficient, permeability, form drag coefficient, temperature and velocity distributions were calculated. The calculated results agree well with our previous experimental results, indicating that the model works well. The results showed that pressure drop increased with decreasing porosity and increasing pore size. Permeability increased and the form drag coefficient decreased with increasing porosity, and both increased with increasing pore size. The heat transfer coefficient increased with increasing velocity and porosity, whereas it slightly decreased with increasing pore size. The results also showed that at high velocity, only the metal foam close to the heat source contributes to heat dissipation.

Superlative Porous Organic Polymers for Photochemical and Electrochemical CO2 Reduction Applications: From Synthesis to Functionality

To mimic the carbon cycle at a kinetically rapid pace, the sustainable conversion of omnipresent CO2 to value-added chemical feedstock and hydrocarbon fuels implies a remarkable prototype for utilizing released CO2. Porous organic polymers (POPs) have been recognized as remarkable catalytic systems for achieving large-scale applicability in energy-driven processes. POPs offer mesoporous characteristics, higher surface area, and superior optoelectronic properties that lead to their relatively advanced activity and selectivity for CO2 conversion. In comparison to the metal organic frameworks, POPs exhibit an enhanced tendency toward membrane formation, which governs their excellent stability with regard to remarkable ultrathinness and tailored pore channels. The structural ascendancy of POPs can be effectively utilized to develop cost-effective catalytic supports for energy conversion processes to leapfrog over conventional noble metal catalysts that have nonlinear techno-economic equilibrium. Herein, we precisely surveyed the functionality of POPs from scratch, classified it, and provided a critical commentary of its current methodological advancements and photo/electrochemical achievements in the CO2 reduction reaction.

A Versatile Shaping Method of Very-High Loading Porous Solids Paper Adsorbent Composites

Owing to their high porosity and tunability, porous solids such as metal-organic frameworks (MOFs), zeolites, or activated carbons (ACs) are of great interest in the fields of air purification, gas separation, and catalysis, among others. Nonetheless, these materials are usually synthetized as powders and need to be shaped in a more practical way that does not modify their intrinsic property (i.e., porosity). Elaborating porous, freestanding and flexible sheets is a relevant shaping strategy. However, when high loadings (>70 wt.%) are achieved the mechanical properties are challenged. A new straightforward and green method involving the combination softwood bleached kraft pulp fibers (S) and nano-fibrillated cellulose (NFC) is reported, where S provides flexibility while NFC acts as a micro-structuring and mechanical reinforcement agent to form high loadings porous solids paper sheets (>70 wt.%). The composite has unobstructed porosity and good mechanical strength. The sheets prepared with various fillers (MOFs, ACs, and zeolites) can be rolled, handled, and adapted to different uses, such as air purification. As an example of potential application, a MOF paper composite has been considered for the capture of polar volatile organic compounds exhibiting better performance than beads and granules.

Machine-learning-assisted material discovery of oxygen-rich highly porous carbon active materials for aqueous supercapacitors

Porous carbons are the active materials of choice for supercapacitor applications because of their power capability, long-term cycle stability, and wide operating temperatures. However, the development of carbon active materials with improved physicochemical and electrochemical properties is generally carried out via time-consuming and cost-ineffective experimental processes. In this regard, machine-learning technology provides a data-driven approach to examine previously reported research works to find the critical features for developing ideal carbon materials for supercapacitors. Here, we report the design of a machine-learning-derived activation strategy that uses sodium amide and cross-linked polymer precursors to synthesize highly porous carbons (i.e., with specific surface areas > 4000 m²/g). Tuning the pore size and oxygen content of the carbonaceous materials, we report a highly porous carbon-base electrode with 0.7 mg/cm² of electrode mass loading that exhibits a high specific capacitance of 610 F/g in 1 M H₂SO₄. This result approaches the specific capacitance of a porous carbon electrode predicted by the machine learning approach. We also investigate the charge storage mechanism and electrolyte transport properties via step potential electrochemical spectroscopy and quasielastic neutron scattering measurements.

Photocurable 3D-Printable Systems with Controlled Porosity towards CO2 Air Filtering Applications

Porous organic polymers are versatile platforms, easily adaptable to a wide range of applications, from air filtering to energy devices. Their fabrication via vat photopolymerization enables them to control the geometry on a multiscale level, obtaining hierarchical porosity with enhanced surface-to-volume ratio. In this work, a photocurable ink based on 1,6 Hexanediol diacrylate and containing a high internal phase emulsion (HIPE) is presented, employing PLURONIC F-127 as a surfactant to generate stable micelles. Different parameters were studied to assess the effects on the morphology of the pores, the printability and the mechanical properties. The tests performed demonstrates that only water-in-oil emulsions were suitable for 3D printing. Afterwards, 3D complex porous objects were printed with a Digital Light Processing (DLP) system. Structures with large, interconnected, homogeneous porosity were fabricated with high printing precision (300 µm) and shape fidelity, due to the addition of a Radical Scavenger and a UV Absorber that improved the 3D printing process. The formulations were then used to build scaffolds with complex architecture to test its application as a filter for CO₂ absorption and trapping from environmental air. This was obtained by surface decoration with NaOH nanoparticles. Depending on the surface coverage, tested specimens demonstrated long-lasting absorption efficiency.

Biological Application of Porous Aromatic Frameworks: State of the Art and Opportunities

Porous aromatic frameworks (PAFs) were first reported in 2009 and have quickly attracted much attention because of their exceptionally ultrahigh specific surface area (5800 m²·g^-1). Uniquely, PAFs are constructed from carbon-carbon-bond-linked aromatic-based building units, which render PAFs extremely stable in various environments. At present, PAFs have been applied in many fields, such as adsorption, catalysis, ion exchange, electrochemistry, and so on. However, for such a unique material, its application in the biological fields is still rarely explored. Therefore, this Perspective introduces the reported application of PAFs in biological fields, for instance, diagnosis and treatment of diseases, artificial enzymes, drug delivery, and extraction of bioactive substances. Major challenges and opportunities for future research on PAFs in biology and biomedicine are identified in diagnostic platforms, novel drug carriers/antidotes, and novel artificial enzymes.

Controlled individual and partial polyethylene nanofibers with high Tm2 prepared by PPM-supported Cp2TiCl2 catalysts

Controlled individual and partial nanofibrous polyethylenes with high second melting point (T_m2) were obtained through ethylene-confined polymerization using a porous polymer microsphere (PPM)-supported Cp₂TiCl₂ catalyst.

High Melting Point of Linear, Spiral Polyethylene Nanofibers and Polyethylene Microspheres Obtained Through Confined Polymerization by a PPM-Supported Ziegler-Natta Catalyst

In this work, different types of polyethylene (linear, spiral nanofibers and microspheres) were obtained via confined polymerization by a PPM-supported Ziegler-Natta catalyst. Firstly, the Ziegler-Natta catalyst was chemical bonded inside the porous polymer microspheres (PPMs) supports with different pore diameter and supports size through chemical reaction. Then slightly and highly confined polymerization occurred in the PPM-supported Ziegler-Natta catalysts. SEM results illustrated that the slightly confined polymerization was easy to obtain linear and spiral nanofibers, and the nanofibers were observed in polyethylene catalyzed by PPMs-1#/cat and PPMs-2#/cat with low pore diameter (about 23 nm). Furthermore, the highly confined polymerization produced polyethylene microspheres, which obtained through other PPM-supported Ziegler-Natta catalysts with high pore diameter. In addition, high second melting point (Tm2: up to 143.3 °C) is a unique property of the polyethylene obtained by the PPM-supported Ziegler-Natta catalyst after removing the residue through physical treatment. The high Tm2 was ascribed to low surface free energy (σe), which was owing to the entanglement of polyethylene polymerized in the PPMs supports with interconnected multi-modal pore structure.

Porous Aromatic Frameworks (PAFs)

Porous aromatic frameworks (PAFs) represent an important category of porous solids. PAFs possess rigid frameworks and exceptionally high surface areas, and, uniquely, they are constructed from carbon-carbon-bond-linked aromatic-based building units. Various functionalities can either originate from the intrinsic chemistry of their building units or are achieved by postmodification of the aromatic motifs using established reactions. Specially, the strong carbon-carbon bonding renders PAFs stable under harsh chemical treatments. Therefore, PAFs exhibit specificity in their chemistry and functionalities compared with conventional porous materials such as zeolites and metal organic frameworks. The unique features of PAFs render them being tolerant of severe environments and readily functionalized by harsh chemical treatments. The research field of PAFs has experienced rapid expansion over the past decade, and it is necessary to provide a comprehensive guide to the essential development of the field at this stage. Regarding research into PAFs, the synthesis, functionalization, and applications are the three most important topics. In this thematic review, the three topics are comprehensively explained and aptly exemplified to shed light on developments in the field. Current questions and a perspective outlook will be summarized.

Conjugated porous polymers: incredibly versatile materials with far-reaching applications

This review discusses conjugated porous polymers and focuses on relating design principles and synthetic methods to key properties and applications such as (photo)catalysis, gas storage, chemical sensing, energy storage and environmental remediation.

Recent Innovation of Metal-Organic Frameworks for Carbon Dioxide Photocatalytic Reduction

The accumulation of carbon dioxide (CO2) pollutants in the atmosphere begets global warming, forcing us to face tangible catastrophes worldwide. Environmental affability, affordability, and efficient CO2 metamorphotic capacity are critical factors for photocatalysts; metal-organic frameworks (MOFs) are one of the best candidates. MOFs, as hybrid organic ligand and inorganic nodal metal with tailorable morphological texture and adaptable electronic structure, are contemporary artificial photocatalysts. The semiconducting nature and porous topology of MOFs, respectively, assists with photogenerated multi-exciton injection and adsorption of substrate proximate to void cavities, thereby converting CO2. The vitality of the employment of MOFs in CO2 photolytic reaction has emerged from the fact that they are not only an inherently eco-friendly weapon for pollutant extermination, but also a potential tool for alleviating foreseeable fuel crises. The excellent synergistic interaction between the central metal and organic linker allows decisive implementation for the design, integration, and application of the catalytic bundle. In this review, we presented recent MOF headway focusing on reports of the last three years, exhaustively categorized based on central metal-type, and novel discussion, from material preparation to photocatalytic, simulated performance recordings of respective as-synthesized materials. The selective CO2 reduction capacities into syngas or formate of standalone or composite MOFs with definite photocatalytic reaction conditions was considered and compared.

Construction of Porous Aromatic Frameworks with Exceptional Porosity via Building Unit Engineering

The construction of excellent porous organic frameworks (POFs) with high surface areas and stability is always a tremendous challenge in synthetic chemistry. The geometric configuration and reactive group of building unit are crucial factors to influence the structure and porosity of the resulting product. Herein, the design, synthesis, and characterization of two porous aromatic framework (PAF) materials, named PAF-100 and PAF-101, are reported via a strategy of building unit engineering. PAF-100 and PAF-101 present high Brunauer-Emmett-Teller surface areas exceeding 5000 m² g^-1 and uniform pore size distributions. Furthermore, PAF-100 and PAF-101 show high methane uptake with value of 742 and 622 cm³ g^-1 , respectively, at 298 K and 70 bar. The successful synthesis of PAFs with exceptional porosity from engineered building unit is powerful for constructing highly porous POFs.

Mesoporous Hexanuclear Copper Cluster-Based Metal-Organic Framework with Highly Selective Adsorption of Gas and Organic Dye Molecules

Despite many advances in the design and assembly of mesoporous metal-organic frameworks (meso-MOFs), it is still a challenge to obtain the desired structure. Here, we utilized an effective cluster cooperative assembly strategy by introducing SO₄^2- ions as chelating binding sites to construct a novel mesoporous MOF, [Cu₈(SO₄)(TBA)₆(OH)₂( N,N-dimethylacetamide (DMA))₄]·12DMA·12CH₃OH [JLU-MOF51, H₂TBA = 4-(1 H-tetrazol-5-yl)-benzoic acid]. Remarkably, the cooperative assembly of the infrequent hexanuclear [Cu₆SO₄(OH)₂] cluster and the classical paddlewheel [Cu₂(CO₂)₄] via linear hetero-N, O donor ligand results in an open three-dimensional framework, which possesses one-dimensional nanometer tube channels with the diameter of 24 and 28 Å. Fascinatingly, JLU-MOF51 displays an exceptionally large Langmuir surface area (5443 m² g^-1) and exhibits a high capacity for selective adsorption of C₃H₈ (C₃H₈: 348 cm³ g^-1 at 273 K; C₃H₈/CH₄ = 220 at 298 K). In addition, JLU-MOF51 can selectively adsorb fluorescein disodium salt dye among numerous organic dyes. An extremely high surface area and unique structural characteristics make JLU-MOF51 a promising meso-MOF material for the adsorption and separation of hydrocarbon gases and organic dyes. Moreover, this strategy will provide an effective means for constructing meso-MOFs via one-step synthesis.

Efficient Mercury Capture Using Functionalized Porous Organic Polymer

The primary challenge in materials design and synthesis is achieving the balance between performance and economy for real-world application. This issue is addressed by creating a thiol functionalized porous organic polymer (POP) using simple free radical polymerization techniques to prepare a cost-effective material with a high density of chelating sites designed for mercury capture and therefore environmental remediation. The resulting POP is able to remove aqueous and airborne mercury with uptake capacities of 1216 and 630 mg g^-1 , respectively. The material demonstrates rapid kinetics, capable of dropping the mercury concentration from 5 ppm to 1 ppb, lower than the US Environmental Protection Agency's drinking water limit (2 ppb), within 10 min. Furthermore, the material has the added benefits of recyclability, stability in a broad pH range, and selectivity for toxic metals. These results are attributed to the material's physical properties, which include hierarchical porosity, a high density of chelating sites, and the material's robustness, which improve the thiol availability to bind with mercury as determined by X-ray photoelectron spectroscopy and X-ray absorption fine structure studies. The work provides promising results for POPs as an economical material for multiple environmental remediation applications.

Porous Molecular Solids and Liquids

Until recently, porous molecular solids were isolated curiosities with properties that were eclipsed by porous frameworks, such as metal-organic frameworks. Now molecules have emerged as a functional materials platform that can have high levels of porosity, good chemical stability, and, uniquely, solution processability. The lack of intermolecular bonding in these materials has also led to new, counterintuitive states of matter, such as porous liquids. Our ability to design these materials has improved significantly due to advances in computational prediction methods.

Adamantane-based Bidendate Metal Complexes in Crystalline and Solution State

Bidentate organic molecules with imidazole or benzimidazole moieties connected to a rigid 1,3-diphenyladamantane spacer are simple and unique building blocks that facilitate the assembly of supramolecular architectures in the solid state via metal-coordination. Single-crystal X-ray analysis revealed that the complexation of bidentate ligand-bearing imidazole moieties with cobalt(II) or cadmium(II) ions in methanol/chloroform produced complexes that showed doubly-interpenetrated two-dimensional (2D) sheets through the formation of coordination bonds between the cobalt or cadmium metal centers and the nitrogen atoms of the imidazole groups. In the complexation of another ligand bearing a bulky benzimidazole group with cobalt(II) ion generated in methanol/chloroform, extended zigzag one-dimensional (1D) chains were formed, indicating that the molecular shape and bulkiness of the ligand design are crucial in the control of coordination polymers. The crystallization solutions were subjected to cold-spray ionization mass spectrometry (CSI-MS), and ion peaks derived from complexes with metal-ligand 1:2 and 1:1 were observed in complexation with ligands bearing the imidazole and benzimidazole moieties, respectively. The metal-ligand ratio in the CSI-MS analysis was identical to that found in the single-crystal X-ray analysis of an independent molecule. In addition, coordination oligomers with large molecular weight were detected as part of the obtained coordination polymers observed by CSI-MS/MS.

Assessing the Surface Area of Porous Solids: Limitations, Probe Molecules, and Methods

In this modeling study, the uses of nitrogen (77.3 K), probe molecule of choice for decades, and argon, opted as alternative in the 2015 IUPAC report on adsorptive characterization, as probe molecules for geometric surface area determination are compared. Graphene sheets possessing slit-shaped pores with varying size (width) are chosen as model porous solids, and different methods for the determination of specific surface areas are investigated. The BET method, which is the most commonly applied analysis, is compared to the Langmuir and relatively recently proposed ESW (excess sorption work) method. We show that either using argon or nitrogen as adsorptive, the physical meaningfulness of adsorption-derived surface areas highly depends on the pore size. When less than two full layers of adsorbate molecules can be formed within slitlike pores of a graphitic material (D_pore < 5.8 Å for Ar/N₂), adsorption-derived surface areas are about half that of the geometric surface area. Between two and four layers (6.8 < D_pore < 12.8 Å), adsorption surface areas can be significantly larger (up to 75%) than the geometric surface area because monolayer-multilayer formation and pore filling cannot be distinguished. For four or more layers of adsorbate molecules (D_pore > 12.8 Å), adsorption-derived surface areas are comparable to their geometrically accessible counterparts. Note that for the Langmuir method this only holds if pore-filling effects are excluded during determination. This occurs in activated carbon materials as well. In the literature, this indistinguishability issue has been largely overlooked, and erroneous claims of materials with extremely large surface areas have been made. Both the BET and Langmuir areas, for D_pore > 12.8 Å, correspond to geometric surface areas, whereas the ESW method yields significantly lower values. For the 6.8 Å < D_pore < 12.8 Å range, all methods erroneously overestimate the specific surface area. For the energetically homogeneous graphene sheets, differences between argon and nitrogen for the assessment of surface areas are minor.

Supramolecular organic network assembled from quadruple hydrogen-bonding motifs

A rigid triptycene derivative with three 2-ureido-4[1H]-pyrimidinone (UPy) terminals was employed to construct a supramolecular hydrogen-bonded organic polymer (HOP-1).

Tuning of ZIF-Derived Carbon with High Activity, Nitrogen Functionality, and Yield - A Case for Superior CO2 Capture

A highly effective and facile synthesis route is developed to create and tailor metal-decorated and nitrogen-functionalized active microporous carbon materials from ZIF-8. Clear metal- and pyrrolic-N-induced enhancements of the cyclic CO2 uptake capacities and binding energies are achieved, particularly at a much lower carbonization temperature of 700 °C than those often reported (1000 °C). The high-temperature carbonization can enhance the porosity but only at the expense of considerable losses of sample yield and metal and N functional sites. The findings are comparatively discussed with carbons derived from metal-organic frameworks (MOFs) reported previously. Furthermore, the porosity of the MOF-derived carbon is critically dependent on the structure of the precursor MOF and the crystal growth. The current strategy offers a new and effective route for the creation and tuning of highly active and functionalized carbon structures in high yields and with low energy consumption.

Crystallization-modulated nanoporous polymeric materials with hierarchical patterned surfaces and 3D interpenetrated internal channels

Poly(oxymethylene)/poly(L-lactic acid) (POM/PLLA) blends are typical melt-miscible binary systems. During isothermal crystallization at various temperatures, in the presence of amorphous PLLA chains, POM crystallizes into banded spherulites with different band spaces, which forms a continuous crystalline phase and serves as a sturdy frame in the final porous materials. On the other hand, the amorphous PLLA chains are simultaneously expelled out from POM crystal lamellae to generate the other continuous phase during the crystallization of POM. Consequently, the interpenetration of the POM lamellae and the amorphous PLLA phase construct a cocontinuous phase structure. All the PLLA constituents are fully included in the interlamellar or interfibrillar of POM crystals. Thus, nanoporous POM materials with hierarchical patterned surface and 3D interpenetrated internal channels have been successfully obtained by extracting the amorphous PLLA phase. It is further found that the POM crystal morphologies in the blends are much dependent on the crystallization conditions. Therefore, the hierarchical patterned structure and the size of internal channels (pore size) can be modulated by adjusting the crystallization conditions.

High surface area and Z′ in a thermally stable 8-fold polycatenated hydrogen-bonded framework

Permanent porosity, a large surface area, and unprecedented Z′ was exhibited in an 8-fold polycatenated hydrogen-bonded organic framework.

Porosity control in mesoporous polymers using CO2-swollen block copolymer micelles as templates and their use as catalyst supports

Mesoporous polymers with tunable large mesopores (14–22 nm) were synthesized through a CO₂-swollen micelle templating route.

Template-free synthesis of mesoporous polymers

Mesoporous polyacrylamides with tunable porosities were synthesized in 1-alkyl-3-methylimidazolium tetrafluoroborates ([C_nmim][BF₄], n = 4, 6, 8, 10).