Macroscopic Architecture of Charge Transfer-Induced Molecular Recognition from Electron-Rich Polymer Interpenetrated Porous Frameworks

Fluorescent and electron-rich polymer threaded into porous framework provides a scaffold for sensing acceptor molecules through noncovalent interactions. Herein, poly­(9-vinylcarbazole) (PVK) threaded MIL-101 with confined nanospace was synthesized by vinyl-monomer impregnation, in situ polymerization, and interpenetration. The pore size of the resulted hybrid could be controlled by varying the time of polymerization and interpenetration. The interaction of PVK-threaded MIL-101 with guest molecules showed a charge-transfer progress with an obvious red shift in the optical spectra. Depending on the degree of the interaction, the solution color changed from blue to green or to yellow. In particular, electron-rich PVK-threaded MIL-101 could effectively probe electron-poor nitro compounds, especially 1,3,5-trinitrobenzene (TNP), a highly explosive material. This sensing approach is a colorimetric methodology, which is very simple and convenient for practical analysis and operation

Kinetic and Thermodynamic Insights into Advanced Energy Storage Mechanisms of Battery-Type Bimetallic Metal–Organic Frameworks

The engineering of high-performance battery-type electrode materials highly depends on the guidance from the combination of experimental analysis and theoretical simulation. Herein, the joint experimental–theoretical investigation provides a mechanistic explanation for the electrochemical performance enhancement in bimetallic metal–organic frameworks (MOFs). The superior CoNi-MOF in our study exhibits advanced electrochemical energy storage performance, achieving a high specific capacity of 382 C g–1 (1 A g–1), 2.0 and 1.4 times that of Co-MOF and Ni-MOF, respectively. Such a significant enhancement results from the surface-controlled reaction kinetics and the low onset potential contributed by the well-tuned electronic structures of bimetallic MOFs. Our study opens up new perspectives for understanding the advantages of mixed metal sites in MOFs for electrochemical energy storage

Covalent Organic Frameworks Formed with Two Types of Covalent Bonds Based on Orthogonal Reactions

Covalent organic frameworks (COFs) are excellent candidates for various applications. So far, successful methods for the constructions of COFs have been limited to a few condensation reactions based on only one type of covalent bond formation. Thus, the exploration of a new judicious synthetic strategy is a crucial and emergent task for the development of this promising class of porous materials. Here, we report a new orthogonal reaction strategy to construct COFs by reversible formations of two types of covalent bonds. The obtained COFs consisting of multiple components show high surface area and high H₂ adsorption capacity. The strategy is a general protocol applicable to construct not only binary COFs but also more complicated systems in which employing regular synthetic methods did not work

A Triazole-Containing Metal–Organic Framework as a Highly Effective and Substrate Size-Dependent Catalyst for CO₂ Conversion

A highly porous metal–organic framework (MOF) incorporating both exposed metal sites and nitrogen-rich triazole groups was successfully constructed via solvothermal assembly of a clicked octcarboxylate ligand and Cu­(II) ions, which presents a high affinity toward CO₂ molecules clearly verified by gas adsorption and Raman spectral detection. The constructed MOF featuring CO₂-adsorbing property and exposed Lewis-acid metal sites could serve as an excellent catalyst for CO₂-based chemical fixation. Catalytic activity of the MOF was confirmed by remarkably high efficiency on CO₂ cycloaddition with small epoxides. When extending the substrates to larger ones, its activity showed a sharp decrease. These observations reveal that MOF-catalyzed CO₂ cycloaddition of small substrates was carried out within the framework, while large ones cannot easily enter into the porous framework for catalytic reactions. Thus, the synthesized MOF exhibits high catalytic selectivity to different substrates on account of the confinement of the pore diameter. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO₂ cycloaddition make this MOF a promising heterogeneous catalyst for carbon fixation

Atomically Dispersed Fe/N-Doped Hierarchical Carbon Architectures Derived from a Metal–Organic Framework Composite for Extremely Efficient Electrocatalysis

Hierarchical graphitic porous carbon architectures with atomically dispersed Fe and N doping have been fabricated from a metal–organic framework (MOF) composite by using a facile strategy, which show high specific surface areas, hierarchical pore structures with macro/meso/micro multimodal pore size distributions, abundant surface functionality with single-atom dispersed N and Fe doping, and improved hydrophilicity. Detailed analyses unambiguously disclosed the main active sites of doped N atoms and FeNx species in the catalyst. The resultant catalyst affords high catalytic performance for oxygen reduction, outperforming the benchmark Pt catalyst and many state-of-the-art noble-metal-free catalysts in alkaline media, particularly in terms of the onset and half-wave potentials and durability. Such catalytic performance demonstrates the significant advantages of the unique hierarchical porous structure with efficient atomic doping, which provides a high density of accessible active sites for much improved mass and charge transports

Nanostructured Electrode Materials Derived from Metal–Organic Framework Xerogels for High-Energy-Density Asymmetric Supercapacitor

This work successfully demonstrates metal–organic framework (MOF) derived strategy to prepare nanoporous carbon (NPC) with or without Fe₃O₄/Fe nanoparticles by the optimization of calcination temperature as highly active electrode materials for asymmetric supercapacitors (ASC). The nanostructured Fe₃O₄/Fe/C hybrid shows high specific capacitance of 600 F/g at a current density of 1 A/g and excellent capacitance retention up to 500 F/g at 8 A/g. Furthermore, hierarchically NPC with high surface area also obtained from MOF gels displays excellent electrochemical performance of 272 F/g at 2 mV/s. Considering practical applications, aqueous ASC (aASC) was also assembled, which shows high energy density of 17.496 Wh/kg at the power density of 388.8 W/kg. The high energy density and excellent capacity retention of the developed materials show great promise for the practical utilization of these energy storage devices

A Robust Aluminum Metal-Organic Framework with Temperature-Induced Breathing Effect

A robust, yet flexible, Al-based metal-organic framework (MOF), Al2(OH)2(bpydc)·0.5H2O (1np), is synthesized via a hydrothermal strategy utilizing 2,2′-bipyridine-5,5′-dicarboxylate (bpydc2–) as the organic ligand. The structure of 1np is built from infinite trans chains of corner-sharing AlO4(OH)2 octahedra interconnected by bpydc2– ligands, forming a three-dimensional framework. 1np is robust, because of its superior thermal, hydrothermal, and chemical stability. The flexibility of 1np is reflected in the activation by the removal of unreacted H2bpydc molecules and/or occluded solvent molecules, followed by degassing at 250 °C, leading to the large pore form (1lp) of the title compound. A reversible structural change from 1lp to 1np is achieved via the hydration in water at 200 °C. The unusual combination of rigidity and flexibility enables precise control and fixation of the swelling magnitude in this MOF material

A Triazole-Containing Metal–Organic Framework as a Highly Effective and Substrate Size-Dependent Catalyst for CO₂ Conversion

A highly porous metal–organic framework (MOF) incorporating both exposed metal sites and nitrogen-rich triazole groups was successfully constructed via solvothermal assembly of a clicked octcarboxylate ligand and Cu­(II) ions, which presents a high affinity toward CO₂ molecules clearly verified by gas adsorption and Raman spectral detection. The constructed MOF featuring CO₂-adsorbing property and exposed Lewis-acid metal sites could serve as an excellent catalyst for CO₂-based chemical fixation. Catalytic activity of the MOF was confirmed by remarkably high efficiency on CO₂ cycloaddition with small epoxides. When extending the substrates to larger ones, its activity showed a sharp decrease. These observations reveal that MOF-catalyzed CO₂ cycloaddition of small substrates was carried out within the framework, while large ones cannot easily enter into the porous framework for catalytic reactions. Thus, the synthesized MOF exhibits high catalytic selectivity to different substrates on account of the confinement of the pore diameter. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO₂ cycloaddition make this MOF a promising heterogeneous catalyst for carbon fixation

Tailoring Carbon Nanotube Density for Modulating Electro-to-Heat Conversion in Phase Change Composites

We report a carbon nanotube array-encapsulated phase change composite in which the nanotube distribution (or areal density) could be tailored by uniaxial compression. The <i>n</i>-eicosane (C20) was infiltrated into the porous array to make a highly conductive nanocomposite while maintaining the nanotube dispersion and connection among the matrix with controlled nanotube areal density determined by the compressive strains along the lateral direction. The resulting electrically conductive composites can store heat at driven voltages as low as 1 V at fast speed with high electro-to-heat conversion efficiencies. Increasing the nanotube density is shown to significantly improve the polymer crystallinity and reduce the voltage for inducing the phase change process. Our results indicate that well-organized nanostructures such as the nanotube array are promising candidates to build high-performance phase change composites with simplified manufacturing process and modulated structure and properties

Experimental and Theoretical Investigation of Mesoporous MnO₂ Nanosheets with Oxygen Vacancies for High-Efficiency Catalytic DeNO_<i>x</i>

A solvent-free synthetic method was employed for the construction of mesoporous α-MnO₂ nanosheets. Benefiting from a solid interface reaction, the obtained MnO₂ nanosheets with large oxygen vacancies exhibit a high surface area of up to 339 m²/g and a mesopore size of 4 nm. The MnO₂ nanosheets as a catalyst were applied in NH₃-assisted selective catalytic reduction (NH₃-SCR) of DeNO_<i>x</i> at a relatively low temperature range. The conversion efficiency could reach 100% under a gas hourly space velocity (GHSV) of 700000 h^–1 at 100 °C. To gain insight into the mechanism about NH₃-SCR of nitric oxide on the MnO₂ nanosheets, temperature-programmed desorption of NH₃, a density functional theory study, and in situ diffuse reflectance infrared Fourier transform spectra were carried out, revealing the cooperative effect of catalytic sites on the reduction of nitric oxide. This work provides a strategy for the facile preparation of porous catalysts in low-temperature DeNO_<i>x</i>