Tunable Pore Structure Research Articles

Potential and design of imine-linked two-dimensional covalent organic framework membranes for Ethane/Methane separation

Membrane separation of CH4 and C2H6 is challenging due to the similar kinetic diameter and chemical affinity. In comparison with other crystalline porous materials, covalent organic frameworks (COFs) possess the advantages of low density, large surface area, tunable pore structure, versatile functionality, and so on, providing the COFs with great potential as separation membranes. Herein, we studied the membrane-based C2H6/CH4 separation performance of 80 two-dimensional imine-linked COFs. Monte Carlo and molecular dynamics simulations were employed to investigate the adsorption and diffusion of gas molecules in the COF membranes. 7 promising COF structures are screened by evaluating the membrane’s selectivity and permeability, and they are found to have small pore size (<20 Å), void fraction (<0.7), and surface area (<8000 m2·g−1) as well as high framework density (>200 kg·m−3). Pore size and framework density are demonstrated to be dominating factors in determining the selectivity and permeability. Based on two typical COFs, COF-LZU1 and NUS-15, grafting hydrocarbons onto the linker and introducing high-carbon additives into the pore can effectively improve the separation performance. Especially, with an appropriate additive concentration, the fullerenes can increase the C2H6/CH4 selectivity by>10 times. This work aims to explore the potential of COFs as membranes for C2H6/CH4 separation, and provides design strategies to optimize the separation performance, which are also applicable to other porous materials.

Recent Advances in Carbon-Based Adsorbents for Adsorptive Separation of Light Hydrocarbons.

Light hydrocarbons (LHs) separation is an important process in petrochemical industry. The current separation technology predominantly relies on cryogenic distillation, which results in considerable energy consumption. Adsorptive separation using porous solids has received widespread attention due to its lower energy footprint and higher efficiency. Thus, tremendous efforts have been devoted to the design and synthesis of high-performance porous solids. Among them, porous carbons display exceptional stability, tunable pore structure, and surface chemistry and thus represent a class of novel adsorbents upon achieving the matched pore structures for LHs separations. In this review, the modulation strategies toward advanced carbon-based adsorbents for LHs separation are firstly reviewed. Then, the relationships between separation performances and key structural parameters of carbon adsorbents are discussed by exemplifying specific separation cases. The research findings on the control of the pore structures as well as the quantification of the adsorption sites are highlighted. Finally, the challenges of carbonaceous adsorbents facing for LHs separation are given, which would motivate us to rationally design more efficient absorbents and separation processes in future.

Multifunctional nanoarchitectured porous carbon for solar steam generation and supercapacitor applications

Multifunctional nanoporous carbon with high specific surface areas, tunable pore structures, good conductivity, and high optical absorption is a promising material for solar steam generation and supercapacitor applications.

A self-regenerating 3D sponge evaporator with a tunable porous structure for efficient solar desalination

Bottom-up design of 3D evaporator with high water evaporation rate shows excellent salt-rejection ability for effective and perpetual solar desalination system.

Transport tuning strategies in MOF film synthesis – a perspective

Metal–organic frameworks (MOFs), sometimes also known as coordination polymers, are a very versatile group of materials consisting of metal nodes and organic linkers forming a tunable porous structure that can exist in different structural phases.

Advances in antitumor nanomedicine based on functional metal-organic frameworks beyond drug carriers.

Nanoscale metal-organic frameworks (MOFs) have attracted widespread interest due to their unique properties including a tunable porous structure, high drug loading capacity, structural diversity, and outstanding biocompatibility. MOFs have been extensively explored as drug nanocarriers in biotherapeutics. However, by harnessing the functionality of ligands and metal ions or clusters in MOFs, the applications of MOFs can be extended beyond drug delivery vehicles. Based on the intrinsic properties of the components of MOFs (e.g. magnetic moments of metal ions and fluorescence of ligands), different imaging modes can be achieved with varied MOFs. With careful design of the composition of MOFs (e.g. modification of organic linkers), they can respond to tumor microenvironments to realize on-demand treatment. By incorporating porphyrin-based ligands (photosensitizers for photodynamic therapy) or high-Z metal ions (radiosensitizers for radiotherapy) into the scaffold of MOFs, MOFs themselves can act as anticancer therapeutic agents. In this review, we highlight the application of MOFs from the above-mentioned aspects and discuss the prospects and challenges for using MOFs in stimuli-responsive imaging-guided antitumor therapy.

Inducing Microscale Structural Order in Phage Nanofilament Hydrogels with Globular Proteins.

Biological hydrogels play important physiological roles in the body. These hydrogels often contain ordered subdomains that provide mechanical toughness and other tissue-specific functionality. Filamentous bacteriophages are nanofilaments with a high aspect ratio that can self-assemble into liquid crystalline domains that could be designed to mimic ordered biological hydrogels and can thus find applications in biomedical engineering. We have previously reported hydrogels of pure cross-linked liquid crystalline filamentous phage formed at very high concentrations exhibiting a tightly packed microstructure and high stiffness. In this work, we report a method for inducing self-assembly of filamentous phage into liquid crystalline hydrogels at concentrations that are several orders of magnitude below that of lyotropic liquid crystal formation, thus creating structural order but a less densely packed microstructure. Hybrid hydrogels of M13 phage and bovine serum albumin (0.25 w/v%) were formed and shown to adsorb up to 16× their weight in water. Neither component gelled on its own at the low concentrations used, suggesting synergistic action between the two components in the formation of the hydrogel. The hybrid hydrogels exhibited repetitive self-healing under physiological conditions and at room temperature, autofluorescence in three channels, and antibacterial activity toward Escherichia coli host cells. Furthermore, the hybrid hydrogels exhibited a more than 2× higher ability to pack water compared to BSA-only hydrogels and 2× lower compression modulus compared to tightly packed M13-only hydrogels, suggesting that our method could be used to create hydrogels with tunable mechanical properties and pore structure through the addition of globular proteins, while maintaining bioactivity and microscale structural order.

Coarsening-induced hierarchically interconnected porous carbon polyhedrons for stretchable ionogel-based supercapacitors

Carbonaceous materials have received extensive attention as electrode materials for electrochemical energy storage systems owing to their superior features, including light weight, high electrical conductivity and specific surface area (SSA), tunable pore structures, and desirable surface properties. For ultrahigh-energy-density supercapacitors (SCs), hierarchically interconnected micro-/meso‑/macroporous carbons (HICs) are desirable for both effective ion polarization and transport, especially when electrochemically stable but dynamically sluggish ionic liquids are employed as the electrolytes. Herein, we demonstrate coarsening-induced HIC polyhedrons with an ultrahigh SSA (3064 m2g−1) from polymer-infiltrated metal-organic frameworks (MOFs). The HIC-based SCs exhibit an outstanding capacitance of 268.4 F g−1 with an ultrahigh energy density of 149 Wh kg−1, which are comparable to the best values reported to date, indicating that expedited ion-transport via hierarchically interconnected large meso‑/macropores affords maximum utilization of the micropores of the carbon electrodes. Furthermore, stretchable all-solid-state SCs operating at 120% strain with a very high areal capacitance of 33 mF cm−2 and an energy density of 0.041 mWh cm−2 are also demonstrated. These results provide a ubiquitous strategy for developing MOF-based hierarchically interconnected carbonaceous materials with ultrahigh SSA for high-performance SCs compatible with stretchable and wearable electronic devices.

Dual Modification of Carbon Support Enables Robust Anchoring of Ruthenium Nanoclusters for Efficient Hydrogen Evolution and Aromatic Nitroreduction

AbstractGraphite carbons have been widely used as catalyst support due to their low‐cost, tunable porous structure, high electrical conductivity, and good resistance to harsh conditions. To date, various defect engineerings have been adopted to enhance the cohesion between graphite carbons and metallic nanocatalysts. Nevertheless, the modification of carbon basal plane has been less explored. In this work, a dual modification strategy is developed to achieve novel carbon support (denoted as NCf) incorporating both C60 units and trace N‐defects. Benefiting from the dual anchoring modes (Ru–C and Ru–N–C), ultrafine ruthenium (Ru) nanoclusters (average size: 2.26 ± 0.38 nm) can be well‐dispersed and robustly anchored on the NCf support. The optimal Ru0.013@NCf catalyst exhibits decent catalytic activities and long‐term stabilities toward both alkaline hydrogen evolution reaction (HER) and aromatic nitroreduction (ANR), outperforming the individually modified counterparts. Computational studies suggest that introducing both C60 and N‐defects into carbon support leads to electron‐deficient Ru nanocluster, which is critical for not only HER but also ANR. This work thus provides a new guideline for rational design of advanced carbon supported nanocatalysts for multipurpose applications.

Phase engineering of metal‐organic frameworks

AbstractAs an important category of porous crystalline materials, metal‐organic frameworks (MOFs) have attracted extensive research interests owing to their unique structural features such as tunable pore structure and enormous surface area. Besides controlling the size, dimensionality, and composition of MOFs, further exploring the crystal‐phase‐dependent physicochemical properties is essential to improve their performances in various applications. Recently, great progress has been achieved in the phase engineering of nanomaterials (PEN), which provides an effective strategy to tune the functional properties of nanomaterials by modulating the arrangement of atoms. In this review, we adopt “phase” instead of “topology” to describe the crystal structure of MOFs and summarize the recent advances in phase engineering of MOFs. The two main strategies used to control the phase of MOFs, that is, phase‐controlled synthesis and phase transformation of MOFs, will be highlighted. The roles of various reaction parameters in controlling the crystal phase of MOFs are discussed. Then, the phase dependence of MOFs in various applications including luminescence, adsorption, and catalysis are introduced. Finally, some personal perspectives about the challenges and opportunities in this emerging field are presented.

Resistive Memory Devices Based on Reticular Materials for Electrical Information Storage.

Recently, reticular materials, such as metal-organic frameworks and covalent organic frameworks, have been proposed as an active insulating layer in resistive switching memory systems through their chemically tunable porous structure. A resistive random access memory (RRAM) cell, a digital memristor, is one of the most outstanding emergent memory devices that achieves high-density electrical information storage with variable electrical resistance states between two terminals. The overall design of the RRAM devices comprises an insulating layer sandwiched between two metal electrodes (metal/insulator/metal). RRAM devices with fast switching speeds and enhanced storage density have the potential to be manufactured with excellent scalability owing to their relatively simple device architecture. In this review, recent progress on the development of reticular material-based RRAM devices and the study of their operational mechanisms are reviewed, and new challenges and future perspectives related to reticular material-based RRAM are discussed.

Agarose-Based Hierarchical Porous Carbons Prepared with Gas-Generating Activators and Used in High-Power Density Supercapacitors

Due to their high surface areas and large pore volumes, porous carbons (PCs) are valuable materials for use as electrodes in energy storage and conversion devices. Biomass is an ideal precursor for the preparation of PCs in part because it is sustainable and eco-friendly. Herein, new methodology for converting agarose, a naturally occurring type of biomass that forms robust hydrogels, into PCs with tunable pore structures and high electrochemical performance is described. The synthetic process is straightforward and entails heating a gel that is composed of agarose and potassium oxalate (K2C2O4). Since the salt transforms into gaseous byproducts at elevated temperatures, the decomposition process was harnessed to create activated, open pores as the hydrogel underwent carbonization. For example, a PC with a surface area of 1754.9 m2 g–1 and a pore volume of 2.643 cm3 g–1 was obtained by heating a mixture of agarose and K2C2O4 in a 1:3 weight ratio at 700 °C. The material was subsequently used as the electrode material in a supercapacitor and found to display a specific capacitance of 166.0 F g–1 at 0.125 A g–1. Varying the quantity of added K2C2O4 resulted in predictable changes in porosity and thus offered a means to tune the textural properties and the electrochemical performance of the PCs. For example, changing the feed ratio of agarose to K2C2O4 to 1:6 afforded a PC that exhibited a high persistent specific capacitance (64.1 F g–1 at 5 A g–1 after 10,000 cycles) and a high-power density (20 kW kg–1 at 10 A g–1).

Development of porous material via chitosan-based Pickering medium internal phase emulsion for efficient adsorption of Rb+, Cs+ and Sr2+

The radioactive Rb+, Cs+ and Sr2+ have serious threat for the aquatic life and human health, its removal has been granted increasing concern. Hence the adsorbent with excellent adsorption performance and favourable reusability is strongly demanded. This work prepared a novel porous polymer of chitosan-g-polyacrylamide (CTS-g-PAM) by grafting the acrylamide (AM) onto the chitosan (CTS) with sufficient pore structure via an eco-friendly surfactant-free (corn oil)-in-water Pickering medium internal phase emulsion (O/W Pickering MIPE), solely stabilized by CTS. Interestingly, its pore structure could be tuned by varying the emulsion character via changing the molecular weight and concentration of CTS, as well as the pH values. Due to the abundant –COO− and −NH2 functional groups in the porous material of CTS-g-PAM, the high adsorption capacities of 195.43, 237.44 and 185.63 mg/g for Rb+, Cs+ and Sr2+ could be reached within 40, 30 and 20 min, respectively. Moreover, the CTS-g-PAM had excellent regeneration ability and reusability. Herein, we provided a feasible and low-cost pathway for preparation of the porous adsorbent with tunable porous structure for adsorption and separation application.

Enhanced CO2 adsorption performance on amino-defective UiO-66 with 4-amino benzoic acid as the defective linker

UiO-66(Zr), one of the Zr-based metal–organic frameworks (MOFs), is a potential adsorbent for gas separation owing to its large surface area, easily tunable pore structure, and high chemical/thermal stability. Nevertheless, its CO2 adsorption amount is somewhat modest in comparison to that of various MOFs. In this study, 4-aminobenzoic acid (PABA) as amino-defective linker was mixed to terephthalic acid at various compositions in a one-step synthesis of UiO-66(Zr) framework. This new restructuring strategy produced defective UiO-66(Zr) with enhanced porosity owing to the missing-linker defects, simultaneously formed –NH2 groups in the framework, leading to the improvement of the CO2 capture capacity. At 298 K and 100 kPa, the defective UiO-66 modified with 10% PABA exhibited the highest CO2 uptake capacity of ~ 2.47 mmol g−1 and ideal adsorbed solution theory (IAST)-based CO2/N2 selectivity of ~ 46, which surpass many other CO2 benchmark adsorbents. This opens a new perspective for developing defective UiO-66(Zr) adsorbent contained amine functional groups, which can improve CO2 separation performance.

Applications of Metal–Organic Frameworks‐Based Membranes in Separation

Metal–organic frameworks (MOFs) are a new class of organic–inorganic hybrid microporous crystalline materials formed by the self‐assembly of inorganic metal ions and organic ligands. Due to their high specific surface area, tunable pore structures, good thermal stability, and exceptional porosity, MOFs are introduced as novel fillers for incorporation in the polymeric matrix to form composite membranes for different applications. In this review, the synthesis methods of MOFs and the preparation methods of MOFs‐based membranes are summarized, focusing on the application of MOFs‐based membranes in water purification. In addition, the perspectives of MOFs‐based membranes in the separation field are proposed.

Nanoscale Covalent Organic Frameworks with Donor-Acceptor Structures as Highly Efficient Light-Responsive Oxidase-like Mimics for Colorimetric Detection of Glutathione.

Although organic artificial enzymes have been reported as biomimetic oxidation catalysts and are widely used for colorimetric biosensors, developing organic artificial enzymes with high enzymatic activity is still a challenge. Two-dimensional (2D) covalent organic frameworks (COFs) have shown superior potential in biocatalysts because of their periodic π-π arrays, tunable pore size and structure, large surface area, and thermal stability. The interconnection of electron acceptor and donor building blocks in the 2D conjugated COF skeleton can lead to narrower band gaps and efficient charge separation and transportation and thus is helpful to improve catalytic activity. Herein, a donor-acceptor 2D COF was synthesized using tetrakis(4-aminophenyl)pyrene (Py) as an electron donor and thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT) as an electron acceptor. Under visible light irradiation, the donor-acceptor 2D COF exhibited superior enzymatic catalytic activity, which could catalyze the oxidation of chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) by the formation of superoxide radicals and holes. Based on the above property, the photoactivated donor-acceptor 2D COF with enzyme-like catalytic properties was designed as a robust colorimetric probe for cheap, highly sensitive, and rapid colorimetric detection of glutathione (GSH); the corresponding linear range of GSH was 0.4-60 μM, and the limit of detection was 0.225 μM. This study not only presents the construction of COF-based light-activated nanozymes for environmentally friendly colorimetric detection of GSH but also provides a smart strategy for improving nanozyme activity.

Hierarchical Porous Carbon Nanofibers with Tunable Geometries and Porous Structures Fabricated by a Scalable Electrospinning Technique.

Porous carbon nanofibers (PCNFs) have rich channels for transporting ions, molecules, and nanoparticles, but the control over their porous structures is a challenge. Here, we report a scalable electrospinning technique by using poly(tetrafluoroethylene) as a pore template, boric acid as a cross-linking agent, and polyvinyl alcohol and polyurethane as dual carbon precursors to fabricate flexible PCNFs with tunable geometries and macro/meso/microporous structures. In the water solvent, the negatively charged template cross-links with the positively charged carbon precursors to form a stable sol for electrospinning. By varying the mass ratios of these precursors, the electrospun hybrid nanofibers are directly transformed into B-F-N-O doped PCNFs with tunable macro-, meso-, and micropores after carbonization. The porosity of an individual PCNF is as high as ∼85%, and the pore volume can be tuned from 0.23 to 0.58 cm3·g-1. When constructing high-sulfur-content (86 wt %) electrodes with the freestanding PCNF films, the porous structures with rich electroactive sites provide rapid pathways for poly-anions and have strong chemisorption of poly-sulfides, leading to a great electrochemical performance. The reported strategy offers a new perspective for synthesizing hierarchical PCNFs with appealing applications.

Conjugated Porous Polydiaminophenylsulfone-Triazine Polymer-A High-Performance Anode for Li-Ion Batteries.

Organic compounds are promising electrode materials because of their resource sustainability, environmental friendliness, and highly tailorable properties. The porous conjugated polymer shows great potential as an electrode material for its tunable redox nature, conjugated skeleton, and porous structure. Herein, a novel conjugated porous polymer, polydiaminophenylsulfone-triazine, was synthesized by a simple nucleophilic substitution reaction. The conjugated structure and triazine ring can improve the conductivity, charge-transfer efficiency, and physicochemical stability. Also, the porous polymeric framework shows a large specific surface area and high porosity, providing a large contact area with electrolytes and reducing diffusion distance. The polymer demonstrates highly stable cycling performance and good rate capability as an anode for lithium-ion batteries, suggesting a promising strategy to design a competitive electrode material.

FeNi co-doped electrocatalyst synthesized via binary ligand strategy as a bifunctional catalyst for Zn-air flow battery

Developing low-cost and excellent performance bifunctional catalysts for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in rechargeable Zn-air batteries is of great significance. Recently, metal organic frameworks (MOFs)-derived electrocatalysts have been widely studied in ORR and OER due to their large specific surface area and tunable pore structure. However, it is still a challenge to prepare hierarchical porous structure catalysts via facile approach, which is desired in the device manner. Herein, we synthesized a MOF-derived FeNi co-doped catalyst (termed as B-FeNi-N/C-1000) using the binary ligand strategy with a large specific area and suitable hierarchical pore structures which efficiently improves mass transfer to boost the high device performance. As a result, the B-FeNi-N/C-1000 exhibits an outstanding ORR performance with a half potential of 0.9 V vs. RHE and a low potential of 1.62 V vs. RHE at 10 mA cm−2 in alkaline media, which exceeds FeNi catalyst (i.e., FeNi-N/C-1000) via single ligand method and commercial Pt/C + IrO2. Additionally, the B-FeNi-N/C-1000 presents a higher power density of 102 mW cm−2 and a long-term stability that only losses 2% after 95 h in the self-assembly Zn-air battery. Accordingly, this work can provide a facile method to synthesize efficient bifunctional catalyst for, but not limit to Zn-air flow batteries.

MOF-derived Co2+-doped TiO2 nanoparticles as photoanodes for dye-sensitized solar cells

Facile synthesis and application of nano-sized semiconductor metal oxides for optoelectronic devices have always affected fabrication challenges since it involves multi-step synthesis processes. In this regard, semiconductor oxides derived directly from metal–organic frameworks (MOFs) routes have gained a great deal of scientific interest owing to their high specific surface area, regular and tunable pore structures. Exploring the application potential of these MOF-derived semiconductor oxides systems for clean energy conversion and storage devices is currently a hot topic of research. In this study, titanium-based MIL-125(Ti) MOFs were used as a precursor to synthesize cobalt-doped TiO2-based dye-sensitized solar cells (DSSCs) for the first time. The thermal decomposition of the MOF precursor under an air atmosphere at 400 °C resulted in mesoporous anatase-type TiO2 nanoparticles (NPs) of uniform morphology, large surface area with narrow pore distribution. The Co2+ doping in TiO2 leads to enhanced light absorption in the visible region. When used as photoanode in DSSCs, a good power conversion efficiency (PCE) of 6.86% with good photocurrent density (Jsc) of 13.96 mA cm−2 was obtained with the lowest recombination resistance and the longest electron lifetime, which is better than the performance of the pristine TiO2-based photoanode.