Pore Engineering Research Articles

Molecular secondary recombination for pitch-derived carbon microsphere toward ultra-high sodium storage

Because the direct carbonization of low-cost pitch will form a highly graphitized soft carbon, and the soft carbon lacks a low-voltage platform to store sodium, so the sodium storage performance is poor. Therefore, in this research, by combining defect and pore engineering, the porous carbon microspheres with primary oxygen crosslinking were reorganized through secondary sulfur crosslinking to achieve the oxygen/sulfur complex crosslinked defect structure. At the same time, small molecular sulfur fragments filled the pores of the porous carbon microspheres to form the ultramicropores structure. It is worth noting that this pitch-derived carbon microsphere exhibits a new sodium storage mechanism of a new 'high-voltage platform'. Therefore, it shows stable cycle performance (220 mAh g−1 at 1 A g−1 after 2000 cycles) and excellent rate performance (101 mAh g−1 at 10 A g−1) in half cells; In addition, the structure of the ultramicropores can improve the initial coulomb efficiency of carbon microspheres. The sodium storage mechanism dominated by surface adsorption was determined by kinetic analysis and in-situ characterization techniques. This study provides a new idea for precise molecular regulation of anode materials for sodium ion batteries.

Hierarchically Ordered Pore Engineering of Metal-Organic Framework-Based Materials for Electrocatalysis.

Ordered pore engineering that embeds uniform pores with periodic alignment in electrocatalysts opens up a new avenue for achieving further performance promotion. Hierarchically ordered porous metal-organic frameworks (HOP-MOFs) possessing multilevel pores with ordered distribution are the promising precursors for the exploration of ordered porous electrocatalysts, while the scalable acquisition of HOP-MOFs with editable components and adjustable pore size regimes is critical. This review presents recent progress on hierarchically ordered pore engineering of MOF-based materials for enhanced electrocatalysis. The synthetic strategies of HOP-MOFs with different pore size regimes, including the self-assembly guided by reticular chemistry, surfactant, nanoemulsion, and nanocasting, are first introduced. Then the applications of HOP-MOFs as the precursors for exploring hierarchically ordered porous electrocatalysts are summarized, selecting representatives to highlight the boosted performance. Especially, the intensification of molecule and ion transport integrated with optimized electron transfer and site exposure over the hierarchically ordered porous derivatives are emphasized to clarify the directional transfer and integration effect endowed by ordered pore engineering. Finally, the remaining scientific challenges and an outlook of this field are proposed. It is hoped that this review will guide the hierarchically ordered pore engineering of nanocatalysts for boosting the catalytic performance and promoting the practical applications.

Pore engineering of MOF-808 for effective adsorption of roxarsone

The development of high-efficiency adsorbents for the removal of roxarsone from wastewater is necessary but remains difficult. Herein, a strategy of pore engineering was applied by using trifluoroacetic acid (TFA), formic acid (FA), and acetic acid (AA) as modulators to construct defective MOF-808. Physicochemical characterizations show that the type of acid modulators as well as their dosages has an impact on the material’s structure defect. Benefiting from these defective units, the diffusion and mass transfer of roxarsone in the material can be promoted. Particularly, MOF-808-AA-b with the most defects exhibits the highest adsorption capacity (860.8 mg g−1) and rapid adsorption equilibrium (360 minutes). The adsorption isotherm and adsorption kinetics conform to Langmuir isotherm model and pseudo-second-order kinetic model, respectively. Adsorption thermodynamics indicates that the adsorption process was spontaneous and endothermic. Experimental characterization and density functional theory calculation jointly demonstrate electrostatic attraction, hydrogen bonding, π-π interactions, coordination interaction and pore-filling promote the roxarsone adsorption on MOF-808-AA-b. Additionally, this adsorbent possesses excellent chemical stability, outstanding anti-interference ability and regeneration-recycling performance. Thus, our work provides a powerful guidance in the optimization of modulators for constructing a high-efficiency adsorbent.

"Cave Effect" Induces Self-Assembled Bimetallic Hollow Structure for Three-in-One Lateral Flow Immunoassay.

Bimetallic hollow structures have attracted much attention due to their unique properties, but they still face the problems of nonuniform alloys and excessive etching leading to structural collapse. Here, uniform bimetallic hollow nanospheres are constructed by pore engineering and then highly loaded with hemin (Hemin@MOF). Interestingly, in the presence of polydopamine (PDA), the competitive coordination between anionic polymer (γ-PGA) and dimethylimidazole does not lead to the collapse of the external framework but self-assembly into a hollow structure. By constructing the Hemin@MOF immune platform and using E. coli O157:H7 as the detection object, we find that the visual detection limits can reach 10, 3, and 3 CFU/mL in colorimetric, photothermal, and catalytic modes, which is 4 orders of magnitude lower than the traditional gold standard. This study provides a new idea for the morphological modification of the metal-organic skeleton and multifunctional immunochromatography detection.

Monoliths for gas storage manufactured with precision pore engineering using 3D-printed templates

A fast, customizable, and systematic route for producing activated carbon monoliths for gas storage with low interparticle porosity (9 % to 24 %) containing tailored macro channels is disclosed. The production uses a three-dimensional (3D)-printed polymeric lattice, rich in oxygen, as a sacrificial template. Its interstitial voids are filled with a phenolic resin that is carbonized and activated at 1173 K under carbon dioxide (CO2). Sequential pyrolysis occurs via thermal treatment with the 3D-printed lattice removed first, rendering macro channels with the same shape as the template in accurately placed positions. Resulting in adsorbents with interparticle porosities ranging from 10 % to 23 %, calculated from X-ray micro-computed tomography (micro-CT) images. The axial resolution of these macro channels was similar to the SLA printing layer thickness used of 100 µm. Making it the best resolution attained to date in fabricating monoliths via a 3D-printed sacrificial templating method. Breakthrough experiments indicated healthy macro channel connectivity due to the reduced mass transfer zone. Moreover, excellent mechanical integrity was displayed, with a monolith withstanding 900 N before excessive fracturing occurred despite the presence of macro channels. Therefore, this method emphasizes its use for gas storage applications by enabling the adsorbent material to efficiently utilize the volumetric space while allowing a fast rate of adsorption over the entire structure.

Vertical-Channel Cathode Host Enables Rapid Deposition Kinetics toward High-Areal-Capacity Sodium-Chlorine Batteries.

Rechargeable sodium chloride (Na-Cl2) batteries have emerged as promising alternatives for next-generation energy storage due to their superior energy density and sodium abundance. However, their practical applications are hindered by the sluggish chlorine cathode kinetics related to the aggregation of NaCl and its difficult transformation into Cl2. Herein, the study, for the first time from the perspective of electrode level in Na-Cl2 batteries, proposes a free-standing carbon cathode host with customized vertical channels to facilitate the SOCl2 transport and regulate the NaCl deposition. Accordingly, electrode kinetics are significantly enhanced, and the deposited NaCl is distributed evenly across the whole electrode, avoiding the blockage of pores in the carbon host, and facilitating its oxidation to Cl2. With this low-polarization cathode, the Na-Cl2 batteries can deliver a practically high areal capacity approaching 4 mAh cm-2 and a long cycle life of over 170 cycles. This work demonstrates the significance of pore engineering in electrodes for mediating chlorine conversion kinetics in rechargeable alkali-metal-Cl2 batteries.

Single-Atom Catalysts on Covalent Organic Frameworks for Energy Applications.

Single-atom catalysts (SACs) have been investigated and applied to energy conversion devices. However, issues of metal agglomeration, low metal loading, and substrate stability have hindered realization of the SACs' full potential. Recently, covalent organic framework (COF)-based SACs have emerged as promising materials to enable highly efficient catalytic reactions. Here, we summarize the representative COF-based SACs and their wide application in clean energy devices and conversion reactions, such as hydrogen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, and oxygen evolution reaction. Based on their catalysis conditions, these reactions are categorized into photocatalyzed and electrocatalyzed reactions. We also summarize their design strategies, including heteroatom inclusion, donor-acceptor pairs, pore engineering, interface engineering, etc. Although COF-based SACs are promising, more efforts, such as linkage engineering, functional groups, ionization, multifunctional sites for cocatalyzed systems, etc., could improve them to be the ideal SAC materials. At the end, we provide our perspectives on where the field will proceed in the next 5 years.

Maximizing Electrostatic Interaction in Ultramicroporous Metal-Organic Frameworks for the One-Step Purification of Acetylene from Ternary Mixture.

Developing efficient adsorbents for acetylene purification from multicomponent mixtures is of critical significance in the chemical industry, but the trade-off between regenerability and selectivity significantly restricts practical industrial applications. Here, we report ultramicroporous metal-organic frameworks with acetylene-affinity channels to enhance electrostatic interaction between C2H2 and frameworks for the efficient one-step purification of C2H2 from C2H2/CO2/C2H4 mixtures, in which the electrostatic interaction led to high regenerability. The obtained SNNU-277 exhibits significantly higher adsorption capacity for C2H2 than that for both C2H4 and CO2 at 298 K and 0.1 bar, while an ultrahigh selectivity of C2H2/C2H4 (100.6 at 298 K) and C2H2/CO2 (32.8 at 298 K) were achieved at 1 bar. Breakthrough experiments validated that SNNU-277 can efficiently separate C2H2 from C2H2/C2H4/CO2 mixtures. CO2 and C2H4 broke through the adsorption column at 4 and 14.8 min g-1, whereas C2H2 was detected until 177.6 min g-1 at 298 K. Theoretical calculations suggest that the framework is electrostatically compatible with C2H2 and electrostatically repels C2H4 and CO2 in the mixed components. This work highlights the importance of rational pore engineering for maximizing the electrostatic effect with the preferentially absorbed guest molecule for efficient multicomponent separation.

Microporous Fluorinated MOF with Multiple Adsorption Sites for Efficient Recovery of C2H6 and C3H8 from Natural Gas.

Purifying C2H6/C3H8 from a ternary natural gas mixture through adsorption separation is an important but challenging process in the petrochemical industry. To address this challenge, the industry is exploring effective strategies for designing high-performance adsorbents. In this study, we present two metal-organic frameworks (MOFs), DMOF-TF and DMOF-(CF3)2, which have fluorinated pores obtained by substituting linker ligands in the host material. This pore engineering strategy not only provides suitable pore confinement but also enhances the adsorption capacities for C2H6/C3H8 by providing additional binding sites. Theoretical calculations and transient breakthrough experiments show that the introduction of F atoms not only improves the efficiency of natural gas separation but also provides multiple adsorption sites for C2H6/C3H8-framework interactions.

Nanoengineering of Porous 2D Structures with Tunable Fluid Transport Behavior for Exceptional H2O2 Electrosynthesis.

Precision nanoengineering of porous two-dimensional structures has emerged as a promising avenue for finely tuning catalytic reactions. However, understanding the pore-structure-dependent catalytic performance remains challenging, given the lack of comprehensive guidelines, appropriate material models, and precise synthesis strategies. Here, we propose the optimization of two-dimensional carbon materials through the utilization of mesopores with 5-10 nm diameter to facilitate fluid acceleration, guided by finite element simulations. As proof of concept, the optimized mesoporous carbon nanosheet sample exhibited exceptional electrocatalytic performance, demonstrating high selectivity (>95%) and a notable diffusion-limiting disk current density of -3.1 mA cm-2 for H2O2 production. Impressively, the electrolysis process in the flow cell achieved a production rate of 14.39 mol gcatalyst-1 h-1 to yield a medical-grade disinfectant-worthy H2O2 solution. Our pore engineering research focuses on modulating oxygen reduction reaction activity and selectivity by affecting local fluid transport behavior, providing insights into the mesoscale catalytic mechanism.

Closed pore engineering of activated carbon enabled by waste mask for superior sodium storage

Carbonaceous materials with closed pore structure have emerged as intriguing anode materials for sodium-ion batteries (SIBs). However, it remains a significant challenge to precisely regulate the structure of closed pores to achieve superior electrochemical Na-storage performance. Herein, a simple but practical strategy is proposed to convert the open pores in activated carbon (AC) into closed pores with the assistance of polypropylene (PP) waste masks. This transition occurs via the carbonization of light aromatic compounds from PP, which deposit on the entrance of the AC's open pore and generate PP-based carbon layer thus regulating the pore configuration of AC. When configured as an anode for SIBs, the hard carbon with optimal closed pores (CMAC-2) delivered a high reversible capacity of 335.5 mAh g−1 with satisfactory initial coulombic efficiency of 88.7 % as well as remarkable cycle and rate capability. Additionally, the assembled O3-NaNi1/3Fe1/3Mn1/3O2//CMAC-2 full cell achieves a high energy density of 277.5 Wh kg−1 (based on the total mass of anode and cathode) with an outstanding rate capability. This work not only offers an ingenious method to fabricate closed pore structure with boosted Na+ storage performance, but also provides a sustainable practice by repurposing polyolefin waste into value-added energy storage products.

2D arrays of hollow carbon nanoboxes: outward contraction-induced hollowing mechanism in Fe-N-C catalysts.

Maximizing the utilization efficiency of monatomic Fe sites in Fe-N-C catalysts poses a significant challenge for their commercial applications. Herein, a structural and electronic dual-modulation is achieved on a Fe-N-C catalyst to substantially enhance its catalytic performance. We develop a facile multi-component ice-templating co-assembly (MIC) strategy to construct two-dimensional (2D) arrays of monatomic Fe-anchored hollow carbon nanoboxes (Fe-HCBA) via a novel dual-outward interfacial contraction hollowing mechanism. The pore engineering not only enlarges the physical surface area and pore volume but also doubles the electrochemically active specific surface area. Additionally, the unique 2D carbon array structure reduces interfacial resistance and promotes electron/mass transfer. Consequently, the Fe-HCBA catalysts exhibit superior oxygen reduction performance with a six-fold enhancement in both mass activity (1.84 A cm-2) and turnover frequency (0.048 e- site-1 s-1), compared to microporous Fe-N-C catalysts. Moreover, the incorporation of phosphorus further enhances the total electrocatalytic performance by three times by regulating the electron structure of Fe-N4 sites. Benefitting from these outstanding characteristics, the optimal 2D P/Fe-HCBA catalyst exhibits great applicability in rechargeable liquid- and solid-state zinc-air batteries with peak power densities of 186 and 44.5 mW cm-2, respectively.

Quasi-Discrete Pore Engineering via Ligand Racemization in Metal-Organic Frameworks for Thermodynamic-Kinetic Synergistic Separation of Propylene and Propane.

The adsorptive separation of propylene and propane offers an energy-efficient alternative to the conventional cryogenic distillation technology. However, developing porous adsorbents with both high equilibrium and kinetic selectivity remains extremely challenging due to the similar size and physical properties of these gases. Herein, this work reports a ligand racemization strategy to construct quasi-discrete pores in MOFs for a synergistically enhanced thermodynamic and kinetic separation performance. The use of enantiopure l-malic acid versus racemic dl-malic acid as ligands afforded isoreticular Ni-based MOFs with contrasting one-dimensional channels (l-mal-MOF) and quasi-discrete cavities connected by small windows (dl-mal-MOF). The periodic pore constrictions in dl-mal-MOF significantly increased the differentiation in diffusion rates and binding energies between propylene and propane. dl-mal-MOF exhibited an exceptional propylene uptake of 1.82 mmol/g at 0.05 bar and 298 K along with an ultrahigh equilibrium-kinetic combined selectivity of 62.6. DFT calculations and MD simulations provided insights into the synergistic mechanism of preferential propylene adsorption and diffusion. Breakthrough column experiments demonstrated the excellent separation and high-purity recovery of propylene over propane on dl-mal-MOF. The robust stability and facile regeneration highlight its potential for propylene purification applications.

Pore engineering of a Quasi-MOF-801 with unsaturated metal site and modulate porosity for selective and effective phosphate uptake

MOF-801, a highly water-stable metal-organic framework, underwent carefully monitored thermal treatment at temperatures between 240 and 300 °C for the development of defective quasi-MOF. The treatment leads to the formation of structural defects, more porosity, and the elimination of ligands. The resulting quasi-MOF-801, which structurally connects crystalline materials and the associated metal oxides, serves as a unique and very effective phosphate adsorbent thanks to its many free adsorption sites. The findings showed that the free open metals site was crucial in forming the binding with phosphate. Q-M801-280 (quasi MOF-801 heated to 280 °C) exhibited the highest adsorption capacity (415 mg. g−1) with a broad pH range of 3–11 and high phosphate selectivity when there are competing anions present. The created Q801-280 is an effective adsorbent that may be utilized to reduce the growing eutrophication of water through phosphate uptake.

Covalent Organic Frameworks (COFs): Characteristics and Applications for Lithium-Ion Batteries (LIBs) and Sodium Ion Batteries (SIBs)

Covalent organic frameworks (COFs) belong to a family of porous organic materials that form 2D or 3D tuned structures via a covalent bond formation between organic blocks. COFs exhibit a remarkable array of characteristics that make them highly promising materials for various applications. COFs are characterized by their chemical and physical stability, their highly porous structure, and their easy structural tunability. They emerged as promising candidates for electrode materials in advanced energy storage devices such as sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). COFs can be precisely customized for each application via pore engineering and framework functionalization as well as the pre- and post-synthesis. Research has been conducted to examine the effect of various functional groups, active redox sites, pore size, and interlayer distances on the performance of COFs as electrode materials. Herein, this review reports the most recent advances in using COFs as electrode materials in both LIBs and SIBs. It also discusses the synthesis of COFs, structural engineering, and pore engineering. The main advantages and challenges that arise with the application of COFs in rechargeable batteries are presented. This review concluded that COFs do have the potential as anode materials in both LIBs and SIBs by virtue of their crystalline structure and high porosity that enable efficient ion diffusion and storage. COFs provided enhanced battery electrochemical performance, improved energy density, and prolonged cycle life.

Pore engineering in robust carbon nanofibers for highly efficient capacitive deionization

Capacitive deionization (CDI) is considered as a revolutionary desalination method to alleviate the global water crisis. However, the current carbon-based CDI cells are constrained by the inferior desalination efficiency, resulting from the undesirable pore structure and sluggish electron/ion transport. Herein, a new porogen of silicalite-1 is proposed for the tailorable fabrication of flexible porous carbon nanofibers (PCNFs) by electrospinning, carbonization and alkali etching, where the surface area, total pore volume, mechanical robustness, specific capacitance, and electrosorption performance of the developed PCNFs are associated with the silicalite-1 dosage. The symmetric CDI unit assembled by the freestanding PCNF membrane electrodes shows a state-of-the-art desalination capacity (38.64 mg g−1), a remarkable salt removal rate (12.1 mg g−1 min−1), a desirable charge efficiency (82.36 %), an acceptable energy consumption (0.668 Wh g−1), and a satisfactory cyclic durability, and such excellent deionization performance can be explained by that the abundant hierarchical pores, the large accessible surface area, and the interconnected conductive carbon network effectively expedite the electron/ion transport. Additionally, the home-made CDI device has a favorable desalination capability toward the high-ion concentration seawater from the Yellow Sea (Xiaomai Island). This work not only validates the feasibility of silicalite-1 as the pore-forming agent for the targeted preparation of flexible PCNFs, but also it highlights the potential of pore engineering in freestanding PCNFs for advanced CDI.

Lewis acidic Fe3+-driven catalytic active Ni3+ formation in Fe-free metal–organic framework for enhanced electrochemical glucose sensing

Manipulating metal valence states and porosity in the metal–organic framework (MOF) by alloying has been a unique tool for creating high-valent metal sites and pore environments in a structure that are inaccessible by other methods, favorable for accelerating the catalytic activity towards sensing applications. Herein, we report Fe3+-driven formation of catalytic active Ni3+ species in the amine-crafted benzene-dicarboxylate (BDC-NH2)-based MOF as a high-performance electrocatalyst for glucose sensing. This work took the benefit of different bonding stability between BDC-NH2 ligand, and Fe3+ and Ni2+ metal precursor ions in the heterometallic NixFe(1-x)-BDC-NH2 MOF. The FeCl3 that interacts weakly with ligand, oxidizes the Ni2+ precursor to Ni3+-based MOF owing to its Lewis acidic behavior and was subsequently removed from the structure supported by Ni atoms, during solvothermal synthesis. This enables to create mesopores within a highly stable Ni-MOF structure with optimal feed composition of Ni0.7Fe0.3-BDC-NH2. The Ni3+-based Ni0.7Fe0.3-BDC-NH2 demonstrates superior catalytic properties towards glucose sensing with a high sensitivity of 13,435 µA mM−1 cm−2 compared to the parent Ni2+-based Ni-BDC-NH2 (10897 μA mM−1cm−2), along with low detection limit (0.9 μM), short response time (≤5 s), excellent selectivity, and higher stability. This presented approach for fabricating high-valent nickel species, with a controlled quantity of Fe3+ integrated into the structure allowing pore engineering of MOFs, opens new avenues for designing high-performing MOF catalysts with porous framework for sensing applications.

Highly Flexible Dielectric Films from Solution Processable Covalent Organic Frameworks.

Covalent organic frameworks (COFs) are known to be a promising class of materials for a wide range of applications, yet their poor solution processability limits their utility in many areas. Here we report a pore engineering method using hydrophilic side chains to improve the processability of hydrazone and β-ketoenamine-linked COFs and the production of flexible, crystalline films. Mechanical measurements of the free-standing COF films of COF-PEO-3 (hydrazone-linked) and TFP-PEO-3 (β-ketoenamine-linked), revealed a Young's modulus of 391.7 MPa and 1034.7 MPa, respectively. The solubility and excellent mechanical properties enabled the use of these COFs in dielectric devices. Specifically, the TFP-PEO-3 film-based dielectric capacitors display simultaneously high dielectric constant and breakdown strength, resulting in a discharged energy density of 11.22 J cm-3 . This work offers a general approach for producing solution processable COFs and mechanically flexible COF-based films, which hold great potential for use in energy storage and flexible electronics applications.

Highly Flexible Dielectric Films from Solution Processable Covalent Organic Frameworks**

AbstractCovalent organic frameworks (COFs) are known to be a promising class of materials for a wide range of applications, yet their poor solution processability limits their utility in many areas. Here we report a pore engineering method using hydrophilic side chains to improve the processability of hydrazone and β‐ketoenamine‐linked COFs and the production of flexible, crystalline films. Mechanical measurements of the free‐standing COF films of COF‐PEO‐3 (hydrazone‐linked) and TFP‐PEO‐3 (β‐ketoenamine‐linked), revealed a Young's modulus of 391.7 MPa and 1034.7 MPa, respectively. The solubility and excellent mechanical properties enabled the use of these COFs in dielectric devices. Specifically, the TFP‐PEO‐3 film‐based dielectric capacitors display simultaneously high dielectric constant and breakdown strength, resulting in a discharged energy density of 11.22 J cm−3. This work offers a general approach for producing solution processable COFs and mechanically flexible COF‐based films, which hold great potential for use in energy storage and flexible electronics applications.

Coupled Surface-Confinement Effect and Pore Engineering in a Single-Fe-Atom Catalyst for Ultrafast Fenton-like Reaction with High-Valent Iron-Oxo Complex Oxidation.

The nanoconfinement effect in Fenton-like reactions shows great potential in environmental remediation, but the construction of confinement structure and the corresponding mechanism are rarely elucidated systematically. Herein, we proposed a novel peroxymonosulfate (PMS) activation system employing the single Fe atom supported on mesoporous N-doped carbon (FeSA-MNC, specific surface area = 1520.9 m2/g), which could accelerate the catalytic oxidation process via the surface-confinement effect. The degradation activity of the confined system was remarkably increased by 34.6 times compared to its analogue unconfined system. The generation of almost 100% high-valent iron-oxo species was identified via 18O isotope-labeled experiments, quenching tests, and probe methods. The density functional theory illustrated that the surface-confinement effect narrows the gap between the d-band center and Fermi level of the single Fe atom, which strengthens the charge transfer rate at the reaction interface and reduces the free energy barrier for PMS activation. The surface-confinement system exhibited excellent pollutant degradation efficiency, robust resistance to coexisting matter, and adaptation of a wide pH range (3.0-11.0) and various temperature environments (5-40 °C). Finally, the FeSA-MNC/PMS system could achieve 100% sulfamethoxazole removal without significant performance decline after 10,000-bed volumes. This work provides novel and significant insights into the surface-confinement effect in Fenton-like chemistry and guides the design of superior oxidation systems for environmental remediation.