Two-dimensional Framework Research Articles

Topology-Selective Manipulation of Two-Dimensional Covalent Organic Frameworks.

The manipulation of topological architectures in two-dimensional (2D) covalent organic framework (COF) materials for different applications is promising but remains a great challenge. Here, we first report the topology-selective synthesis of two distinct varieties of 2DCOFs, imine-based HT-COFs and benzimidazole-fused BI-HT-COFs, by simply altering acid catalysts. To HT-COFs, a superlattice of 1D channel with a persistent triangular shape is formed via Schiff base reaction, while to BI-HT-COFs, a hexagonal lattice structure with a highly conjugated structure and imidazole linkages is constructed due to an imine-based cyclization reaction. The two COFs exhibited marked differences in their bandgap, chemical stability, molecular adsorption, and catalytic activity, which make them have different fields of application. This work not only diversifies the hexaaminotriphenylene-based 2DCOF topologies but also provides vivid examples of structure-property relationships, which would facilitate fundamental research and potential applications of 2DCOFs.

Synergistic Induction of Solvent and Ligand-Substitution in Single-Crystal to Single-Crystal Transformations toward a MOF with Photocatalytic Dye Degradation.

External-stimuli responsiveness as found in natural organisms and smart materials is attractive for functional materials scientists who attempt to design and imitate fascinating behavior into their materials. Herein, we report a couple of new solvent-responsive isostructural two-dimensional cationic metal-organic frameworks (MOFs) of Mn(II) (1a) and Zn(II) (2a) that undergo unprecedented single-crystal to single-crystal (SCSC) transformation toward the corresponding isostructural three-dimensional MOFs of Mn(II) (1b) and Zn(II) (2b). The 2D MOFs 1a and 2a have been effortlessly and rapidly synthesized via the microwave-heating technique. The SCSC transformations are synergistically induced by solvent and ligand-substitution reactions and able to be triggered by water, methanol, ethanol, and n-propanol. Time-dependent SCSC transformations were studied by in situ X-ray diffraction. Investigations on photodegradation of methyl orange showed that Zn-MOF 2b has higher efficiency than Mn-MOF 1b under UV-C irradiation at 300 min, 94.27%, and 21.91%, respectively. The influence of charge on the dye molecules, heterogeneity of the catalysis, and •OH radical-scavenging test was studied. First-principles computations suggest that the high photocatalytic activity of 2b may be attributed to its suitable band-edge position for redox reactions.

Revealing bimetallic synergy in van der Waals AgInP2Se6 nanosheets for alkali metal ion battery electrodes

We report two-dimensional AgInP2Se6 (AIPSe) bimetallic phosphorus trichalcogenides nanosheets as anodes for advanced alkali metal ion batteries (AMIBs). The intrinsic layered architecture of this compound not only facilitates rapid charge propagation but also accentuates ion storage due to its expansive surface area. The integration of the bimetallic component results in a synergistic enhancement in electronic/ionic conductivity and optimizes the redox dynamics of multi-electronic materials, eventually attaining superior electrochemical characteristics. Moreover, the accompanying deposition of metallic silver during electrochemical processes reduces battery polarization, while the presence of metallic indium acts as an efficacious structural stabilizer, effectively inhibit dendrite proliferation. As an anode electrode coupled with graphite (G) in lithium-ion (LIBs) and potassium-ion batteries (PIBs), AIPSe@G anodes for LIBs achieve 707.8 mA h g−1 at 0.1 A g−1, retain over 900 cycles at 2.0 A g−1, and demonstrate 318.5 mA h g−1 at 3.0 A g−1 rate capability. For PIBs, they reach 480.3 mA h g−1 at 25.0 mA g−1, sustains for 550 cycles at 250 mAg−1, and offers 214.2 mA h g−1 at 3.0 A g−1 rate performance. Comprehensive full cell tests further endure 100 cycles in both LIBs and PIBs under diverse current regimes. Our study pioneers a new direction for AMIB anode materials, emphasizing the advantages of integrating bimetallic features into two-dimensional frameworks to boost electrode dynamics and achieve consistent conversion reactions.

Unveiling the catalytic potential of two-dimensional boron nitride in lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries, renowned for their potential high energy density, have attracted attention due to their use of earth-abundant elements. However, a significant challenge lies in developing suitable materials for both lithium-based anodes, which are less prone to lithium dendrite formation, and sulfur-based cathodes. This obstacle has hindered their widespread commercial viability. In this study, we present a novel sulfur host material in the form of a two-dimensional semiconductor boron nitride framework, specifically the 2D orthorhombic diboron dinitride (o-B2N2). The inherent conductivity of o-B2N2 mitigates the insulating nature often observed in sulfur-based electrodes. Notably, the o-B2N2 surface demonstrates a high binding affinity for long-chain Li-polysulfides, leading to a significant reduction in their dissolution into the DME/DOL electrolytes. Furthermore, the preferential deposition of Li2S on the o-B2N2 surface expedites the kinetics of the lithium polysulfide redox reactions. Additionally, our investigations have revealed a catalytic mechanism on the o-B2N2 surface, significantly reducing the free energy barriers for various sulfur reduction reactions. Consequently, the integration of o-B2N2 as a host cathode material for Li–S batteries holds great promise in suppressing the shuttle effect of lithium polysulfides and ultimately enhancing the overall battery performance. This represents a practical advancement for the application of Li–S batteries.

Synthesis of 2D bi-metallic Zn/Cu metal-organic framework integrated graphene nanocomposites for all-solid-state asymmetric supercapacitors

In this work, a novel two-dimensional (2D) bi-metallic metal-organic frameworks (MOFs) consisting of zinc and copper metal centers with 1,3,5-tricarboxylic acid as a chief and efficient organic linker (Zn/Cu-BTC) and its composite with exfoliated graphene nanosheets (EGNSs) have been investigated for supercapacitor applications. The composites were synthesized via facile in-situ solvothermal process. Different spectroscopic, microscopic, and surface analyses confirmed the successful formation of porous electroactive composites, where 2D MOF nanosheets were vertically grown on the EGNS surfaces. In the two-electrode symmetric system, the as-synthesized Zn/Cu-BTC MOF@EGNS electrode achieved an enhanced specific gravimetric capacitance and equivalent volumetric capacitance of 1284.9 F/g and 813.3 F/cm3 at 0.5 A/g. It exhibits high-rate performance and prolonged cycling stability with >90 % retention after 8000 cycles. All-solid-state asymmetric supercapacitor (ASC) device was constructed with Zn/Cu-BTC MOF@EGNS composite and EGNS electrodes, where PVA-KOH membrane served as a separator-cum-electrolyte. The ASC device delivered a satisfactory energy density of 60.55 Wh kg−1 and a maximum power density of 10 kW kg−1 with an admirable cycling stability of 92 % after 10,000 charge-discharge cycles. In the future, this work can encourage manufacturing innovation.

Chemically Asymmetric Polymers Manipulate the Crystallization of Two-Dimensional Covalent Organic Frameworks to Synthesize Processable Nanosheets.

Nanosheets derived from two-dimensional covalent organic frameworks (2D COFs) are increasingly desirable in various fields. While breakthroughs in the chemical and physical delamination of 2D COFs are rising, precisely regulating the growth of the COF nanosheets has not been realized yet. Herein, we report an effective strategy of polymer-manipulated crystallization to accurately control the growth of COF nanosheets. Chemically asymmetric polyvinylpyrrolidone (PVP) is developed as the manipulator that selectively interacts with the aldehydes and (100) facet to induce anisotropic growth of COFs. The number of PVP constitutional units determines this specific interaction, leading to molecularly thin but thickness-controllable nanosheets with excellent dispersity. We process these nanosheets into robust A4-sized membranes for ultraselective molecular separation. The membrane intercalated with long-chain PVP demonstrates largely improved performance, surpassing the reported COF membranes. This work reports a strategy for anisotropically crystallizing 2D COFs to yield processable nanosheets toward practical applications.

Isomeric Dual-Pore Two-Dimensional Covalent Organic Frameworks.

Two-dimensional (2D) covalent organic frameworks (COFs) with hierarchical porosity have been increasingly recognized as promising materials in various fields. Besides, the 2D COFs with kagome (kgm) topology can exhibit unique optoelectronic features and have extensive applications. However, rational synthesis of the COFs with kgm topology remains challenging because of competition with a square-lattice topology. Herein, we report two isomeric dual-pore 2D COFs with kgm topology using a novel geometric strategy to reduce the symmetry of their building blocks, which are four-armed naphthalene-based and azulene-based isomeric monomers. Owing to the large dipole moment of azulene, as-prepared azulene-based COF (COF-Az) possesses a considerably narrow band gap of down to 1.37 eV, which is much narrower than the naphthalene-based 2D COF (COF-Nap: 2.28 eV) and is the lowest band gap among reported imine-linked dual-pore 2D COFs. Moreover, COF-Az was used as electrode material in a gas sensor and exhibits high selectivity for NO2, including a high response rate (58.7%) to NO2 (10 ppm), fast recovery (72 s), up to 10 weeks of stability, and resistance to 80% relative humidity, which are superior to those of reported COF-based NO2 gas sensors. The calculation and in situ experimental results indicate that the large dipole moment of azulene boosts the sensitivity of the imine linkages. The usage of isomeric building blocks not only enables the synthesis of 2D COFs with isometric kgm topology but also provides an azulene-based 2D platform for studying the structure-property correlations of COFs.

A sandwich electrochemiluminescence immunoassay based on 1T-MoS2@dual MOFs for detecting CA153

A “signal-on” electrochemiluminescence (ECL) immunosensor has been proposed for detecting carbohydrate antigen 153 (CA153) based on the dual MOFs sandwich strategy. The conductive and porous substrate consisting of 1T-MoS2 and two-dimensional conductive metal-organic framework (MOF, Ni-HAB) was anchored onto the glassy carbon electrode (GCE) to label the capture antibody (Ab1), and the luminescence-functionalized MOF (Ru(bpy)32+@UiO-66-NH2) was utilized to immobilize the detection second antibody (Ab2) to construct a “signal-on” responsive sandwich-type electrochemiluminescence immunoassay. Meanwhile, tripropylamine (TPA) acts as the co-reactant and provides a luminescence system for Ru(bpy)32+@UiO-66-NH2. The luminescence-functionalized MOFs showed excellent ECL activity owing to the tunable structure of MOFs. The remarkable enhancement in ECL intensity was obtained by the immunoreaction of antigen and antibody. Under the optimized conditions, the biosensor exhibited a detection limit of 0.0001 U mL−1 (S/N = 3) with a wide range from 0.001 to 50 U mL−1. The proposed ECL immunosensor was applicable for detecting human serum samples with a recovery of 99.83 ∼ 101 % (RSD < 5 %). This work demonstrates that the advantage of multifunctional MOFs could be applied to construct highly selective ECL immunosensor, and it may facilitate the diagnosis of breast cancer in clinics.

God’s necessary existence: a thomistic perspective

AbstractThere are strong reasons for assuming that Thomas Aquinas conceived of God’s existence in terms of logical necessity in a broad sense. Yet this seems to stand in some tension with the fact that he excludes the possibility of a priori arguments for the existence of God. One apparently attractive way of handling this tension is to use a two-dimensional framework inspired by Saul Kripke. Against this, this article demonstrates that a Kripke-inspired framework is inapt in this context because it allows for the conceivability of God’s non-existence, thereby rendering his non-existence possible in some important, and for Aquinas inacceptable, sense. Drawing on David Chalmers, the article submits that the existence of God can only be necessary if God’s non-existence is ideally inconceivable. On the basis of Aquinas’ own understanding of God, however, the article argues further that God’s non-existence in fact is inconceivable. The alleged conceivability of God’s non-existence is ultimately due to our (human) inability to grasp the nature of being, whereas creatures who grasp the nature of being are unable to conceive of God’s non-existence. This removes God’s non-existence from the realm of relevant conceivability and, therefore, from the range of possible worlds.

Dominant Role of Hole Transport Pathway in Achieving Record High Photoconductivity in Two-Dimensional Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) with mobile charges have attracted significant attention due to their potential applications in photoelectric devices, chemical resistance sensors, and catalysis. However, fundamental understanding of the charge transport pathway within the framework and the key properties that determine the performance of conductive MOFs in photoelectric devices remain underexplored. Herein, we report the mechanisms of photoinduced charge transport and electron dynamics in the conductive 2D M-HHTP (M=Cu, Zn or Cu/Zn mixed; HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) MOFs and their correlation with photoconductivity using the combination of time-resolved terahertz spectroscopy, optical transient absorption spectroscopy, X-ray transient absorption spectroscopy, and density functional theory (DFT) calculations. We identify the through-space hole transport mechanism through the interlayer sheet π-π interaction, where photoinduced hole state resides in HHTP ligand and electronic state is localized at the metal center. Moreover, the photoconductivity of the Cu-HHTP MOF is found to be 65.5 S m-1 , which represents the record high photoconductivity for porous MOF materials based on catecholate ligands.

Identifying topological corner states in two-dimensional metal-organic frameworks

Due to the diversity of molecular building blocks, the two-dimensional (2D) metal-organic frameworks (MOFs) are ideal platforms to realize exotic lattice models in condensed matter theory. In this work, we demonstrate the universal existence of topological corner states in 2D MOFs with a star lattice configuration, and confirm the intriguing higher-order nontrivial topology in the energy window between two Kagome-bands, or between Dirac-band and four-band. Furthermore, combining first-principles calculations and scanning tunneling microscopy measurements, the unique topological corner state is directly identified in monolayer Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) grown on the Au(111) substrate. Our results not only illustrate the first organic topological state in the experiments, but also offer an exciting opportunity to study higher-order topology in 2D MOFs with the large insulating band gap.

Effects of hydrogen blending and exhaust gas recirculation on NO[formula omitted] emissions in laminar and turbulent [formula omitted] flames at 25 bar

In this work, the effect of Exhaust Gas Recirculation (EGR) on NOx emissions in a CH4/H2/air combustion at 25 bar, at an equivalence ratio Φ = 0.7, is analyzed in laminar and turbulent partially premixed flames. Numerical simulations of twenty premixed and partially premixed counterflow flames with H2 ranging from 0 to 100%, with and without EGR, are carried out. Analysis of NO formation mechanisms shows that the thermal path is the main responsible for the NOx production in each flame, with a contribution of nearly 80%. In laminar flames an increase of H2 leads to an increase in NOx emissions. The addition of the exhaust gas decreases the flame temperature and therefore NOx: each laminar flame shows a NOx reduction of about 60% with the presence of exhaust gas. Four turbulent slot jet flames with a CH4/H2/Air/EGR premixed central core and Air/EGR as coflow are studied in a two-dimensional framework using the Reynolds Averaged Navier–Stokes (RANS) approach and the Large Eddy Simulation (LES) methodology, to take into account some flame dynamics, despite the 2D context. Accurate molecular transport properties are considered and, a reduced specifically designed chemical mechanism for methane/hydrogen-air combustion at Φ=0.7, consisting of 48 transported species and 465 elementary reactions is adopted. The four turbulent flames were simulated with 0 and 50% hydrogen concentration, with and without EGR. The presence of hydrogen reduces CO2 emissions, but at the same time increases NO concentration, the thermal path being the main NO formation mechanism. The use of exhaust gas recirculation leads to NO reduction as in laminar flames. The results obtained in this work show that at high pressure, the hydrogen enrichment of natural gas in the EGR mode leads to lower NOx as well as CO2 emissions.

MOF-derived 2D Co@C nanosheet membrane with enhanced catalytic activity: Mechanism and stability insights

Two-dimensional (2D) metal-organic frameworks (MOFs) membranes have recently gained attention as novel material membranes for advanced oxidation processes (AOPs). Nonetheless, the susceptibility of 2D MOFs to reactive oxygen species (ROS) limits 2D MOF membranes’ effectiveness in AOPs. In this study, we introduce a novel approach, fabricating a 2D Co-MOF-derived nanosheet membrane (referred to as Co@C NS), assembled from pyrolyzed and exfoliated Co-MOF nanosheets, for the activation of peroxymonosulfate (PMS) in the removal of bisphenol A (BPA). Crucially, the synthesis process involves the pyrolysis of a carbon layer, serving as a protective barrier. This barrier effectively prevents the release of Co ions, ensuring the long-term structural and catalytic stability of the Co@C NS membrane. Notably, the membrane exhibits remarkable capabilities in discriminating between natural organic matter (NOM) and BPA through size exclusion, significantly mitigating the impact of NOM competition for ROS. Additionally, our study demonstrates an exceptional removal efficiency, achieving 100% BPA removal at an ultrahigh permeance of 1100 L m−2 h−1 bar−1, corresponding to an exceedingly short retention time of 0.14 s. Our mechanistic investigation reveals the involvement of singlet oxygen and sulfate radicals in the removal of BPA within the nanochannels, facilitated by the nanoconfinement effect. This study introduces valuable strategies for the development of 2D MOF-derived nanosheet membranes characterized by high catalytic activity and excellent stability, underlining their practical potential in AOP applications.

Two-Dimensional Cu-Porphyrin Metal-Organic Framework Nanosheet-Supported Flaky TiO2 as an Efficient Visible-Light-Driven Photocatalyst for Dye Degradation and Cr(VI) Reduction.

A series of 2D M(Cu, Zn, Co, and Mn)-TCPP MOFs/TiO2 binary nanocomposites (TCPP = tetrakis(4-carboxyphenyl)porphyrin) were constructed by solvothermal in situ loading of flaky TiO2 on the surface of 2D metal-organic frameworks (MOFs). The influence of different coordination metals on the catalytic activity was studied, and it was found that the 2D Cu-TCPP MOFs/TiO2 nanocomposite exhibited the best photo-Fenton performance. The superior property can be attributed to the high absorption coefficient and ultrathin two-dimensional structure of the 2D Cu-TCPP MOFs nanosheets. Meanwhile, the 2D Cu-TCPP MOFs/TiO2 II heterostructure can effectively promote the separation and transfer of photoformed carriers. Moreover, under visible irradiation, the optimized 2D Cu-TCPP MOFs/TiO2 composite can convert 99.9% of Cr(VI) to Cr(III) within 60 min with methanol as the hole scavenger at pH 3.14. Also, the photocatalytic performance of 2D Cu-TCPP MOFs/TiO2 was maintained after five reaction cycles. Furthermore, the proposed visible-light-driven photocatalysis mechanism of the 2D Cu-MOFs/TiO2 composite was reasonably derived according to experimental results. This study demonstrates the potential of building efficient TiO2-based visible light photocatalysts with 2D metal-porphyrin MOFs.

Two-Dimensional Covalent Organic Frameworks as Tailor-Made Scaffolds for Water Harvesting.

Developing materials to harvest water from the air is of great importance to alleviate the water shortage for people living in arid regions, where the annual average relative humidity (RH) is lower than 0.4. In this work, we report a general nitrogen atom incorporation strategy to prepare high-performance covalent organic frameworks (COFs) for water harvesting from the air in arid areas. A series of COFs, namely COF-W1, COF-W2, and COF-W3 were developed for this purpose. Different contents of nitrogen were embedded into COFs by incorporating pyridine units into the building blocks. With the increasing content of nitrogen from COF-W1 to COF-W3, the inflection points of their water isotherms shift distinctly from RH values from 0.65 to 0.25. Significantly, COF-W3 exhibits the lowest inflection point at a low RH value of 0.25 and reaches a high uptake capacity of 0.28 g g-1 at 25 °C with a low hysteresis loop. Moreover, the gram-scale COF-W3 retains its high performance, which renders it more attractive in water harvesting. This work demonstrates the feasibility of this nitrogen incorporation strategy to acquire high-performance COFs as water harvesters in the future.

Solutions Are the Problem: Ordered Two-Dimensional Covalent Organic Framework Films by Chemical Vapor Deposition.

Covalent organic frameworks (COFs) are a promising class of crystalline polymer networks that are useful due to their high porosity, versatile functionality, and tunable architecture. Conventional solution-based methods of producing COFs are marred by slow reactions that produce powders that are difficult to process into adaptable form factors for functional applications, and there is a need for facile and fast synthesis techniques for making crystalline and ordered covalent organic framework (COF) thin films. In this work, we report a chemical vapor deposition (CVD) approach utilizing co-evaporation of two monomers onto a heated substrate to produce highly crystalline, defect-free COF films and coatings with hydrazone, imine, and ketoenamine COF linkages. This all-in-one synthesis technique produces highly crystalline, 40 nm-1 μm-thick COF films on Si/SiO2 substrates in less than 30 min. Crystallinity and alignment were proven by using a combination of grazing-incidence wide-angle X-ray scattering (GIWAXS) and transmission electron microscopy (TEM), and successful conversion of the monomers to produce the target COF was supported by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV-vis measurements. Additionally, we used atomic force microscopy (AFM) to investigate the growth mechanisms of these films, showing the coalescence of triangular crystallites into a smooth film. To show the wide applicability and scope of the CVD process, we also prepared crystalline ordered COF films with imine and ketoenamine linkages. These films show potential as high-quality size exclusion membranes, catalytic platforms, and organic transistors.

Structural Modulation of Nitrogen-Rich Covalent Organic Frameworks for Iodine Capture.

Developing efficient adsorbent materials for iodine scavenging is essential to mitigate the threat of radioactive iodine causing adverse effects on human health and the environment. In this context, we explored N-rich two-dimensional covalent organic frameworks (COFs) with diverse functionalities for iodine capture. The pyridyl-hydroxyl-functionalized triazine-based novel 5,5',5″-(1,3,5-triazine-2,4,6-triyl)tris(pyridine-2-amine) (TTPA)-COF possesses high crystallinity (crystalline domain size: 24.4 ± 0.6 nm) and high porosity (specific BET surface area: 1000 ± 90 m2 g-1). TTPA-COF exhibits superior vapor-phase iodine adsorption (4.43 ± 0.01 g g-1) compared to analogous COF devoid of pyridinic moieties, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-COF. The high iodine capture by TTPA-COF is due to the enhanced binding affinity conferred by the extra pyridinic active sites. Furthermore, the crucial role of long-range order in porous adsorbents has been experimentally evidenced by comparing the performance of iodine vapor capture of TTPA-COF with an amorphous network polymer having identical functionalities. We have also demonstrated the high iodine scavenging ability of TTPA-COF from the organic and aqueous phases. The mechanism of iodine adsorption by the heteroatom-rich framework is elucidated through FTIR, XPS, and Raman spectral analyses. The present study highlights the need for structural tweaking of the building blocks toward the rational construction of advanced functional porous materials for a task-specific application.

Mesoporous dopamine-modified leaf-like zeolitic imidazolate frameworks derived carbon for efficient capacitive deionization

The onstruction of novel porous carbon materials for efficient desalination is crucial but remains challenging for capacitive deionization (CDI) development. Herein, a micelle-assisted strategy was raised to coat mesoporous polydopamine (mPDA) on the surface of two-dimensional (2D) leaf-like zeolitic imidazolate frameworks (ZIFL) followed by confinement pyrolysis. The introduction of the mPDA layer can not only mitigate the backbone collapse of ZIFL during pyrolysis to build a favorable porous environment for efficient ion transport and diffusion, but also induce explosive growth of carbon nanotubes (CNTs) to improve the electron conductivity. As expected, the derivative ZIFL@mPDA-C possessed a high desalination capacity of 41.9 mg g−1 in 500 mg L-1 NaCl solution at an operating voltage of 1.2 V. In particular, the retention ratio of the desalination capacity of ZIFL@mPDA-C was about 100 % after 50 consecutive adsorption-desorption cycles, while its leaf-like morphology and hierarchical pore structures were well preserved. This study highlights the importance of rationally designed structures and components for the performance breakthrough of carbon-based CDI electrode materials.

Ag Nanoparticles-Induced Metallic Conductivity in Thin Films of 2D Metal-Organic Framework Cu3(HHTP)2.

Two-dimensional (2D) metal-organic frameworks (MOFs) are usually associated with higher electrical conductivity and charge carrier mobility when compared with 3D MOFs. However, attaining metallic conduction in such systems through synthetic or postsynthetic modifications is extremely challenging. Herein, we present the fabrication of thin films of a 2D MOF, Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), decorated with silver nanoparticles (AgNPs) exhibiting significant conductivity enhancement at room temperature. Variable-temperature electrical transport measurements across the low-temperature (200 K) to high-temperature (373 K) regime evidenced metallic conduction. Interestingly, thin films of a 3D MOF, CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane), upon decoration with AgNPs, disclosed a converse trend. The origin of such distinctive observations on AgNPs@Cu3(HHTP)2 and AgNPs@CuTCNQ systems was comprehended by using first-principles density functional theory (DFT) calculations and attributed to an interfacial electronic effect. Our work sheds new light on rationally designing synthetic modifications in thin films of MOFs to tune the electrical transport property.

Boosting CO2 Photoreduction via Regulating Charge Transfer Ability in a One-Dimensional Covalent Organic Framework.

Two-dimensional (2D) imine-based covalent organic frameworks (COFs) hold potential for photocatalytic CO2 reduction. However, high energy barrier of imine linkage impede the in-plane photoelectron transfer process, resulting in inadequate efficiency of CO2 photoreduction. Herein, we present a dimensionality induced local electronic modulation strategy through the construction of one-dimensional (1D) pyrene-based covalent organic frameworks (PyTTA-COF). The dual-chain-like edge architectures of 1D PyTTA-COF enable the stabilization of aromatic backbones, thus reducing energy loss during exciton dissociation and thermal relaxation, which provides energetic photoelectron to traverse the energy barrier of imine linkages. As a result, the 1D PyTTA-COF exhibits significantly enhanced CO2 photoreduction activity under visible-light irradiation when coordinated with metal cobalt ion, yielding a remarkable CO evolution of 1003 μmol g-1 over an 8-hour period, which surpasses that of the corresponding 2D counterpart by a factor of 59. These findings present a valuable approach to address in-plane charge transfer limitations in imine-based COFs.