Carbonization of single polyacrylonitrile chains in coordination nanospaces

Facile Aqueous Route to Large-Scale Superhydrophilic TiO2-Incorporated Graphitic Carbon Nitride-Coated Ni(OH)2 and Ni2P Nano-Architecture Arrays as Efficient Electrocatalysts for Enhanced Hydrogen Production

Water splitting by an electrochemical method to generate hydrogen gas is an economic and green approach to resolve the looming energy and environmental crisis. Designing a composite electrocatalyst having integrated multichannel charge separation, robust stability, and low-cost facile scalability could be considered to address the issue of electrochemical hydrogen evolution. Herein, we report a superhydrophilic, noble-metal-free bimetallic nanostructure TiO2/Ni2P coated on graphitic polyacrylonitrile carbon fibers (g-C/TiO2/Ni2P) using a facile hydrothermal method followed by phosphorylation. In an aqueous-based route, PAN is dissolved in water in the presence of ZnCl2, followed by wet-spinning to prepare scalable PAN/ZnCl2 fibers. The nitrogen-contained porous graphitic carbon fibers are prepared via the pyrolysis of PAN/ZnCl2 fibers; now ZnCl2 acts as a volatile porogen to form porous matrix structures. Finally, the as-prepared graphitic carbon fibers are electrochemically activated by incorporating TiO2/Ni2P active sites. The materials formed in this work show excellent electrocatalytic activity for the hydrogen evolution reaction. The as-synthesized g-C/TiO2/Ni2P catalyst shows a low overpotential, its electrocatalytic activity is improved, and its efficiency is better than that of the commercial Pt/C catalyst. At a current density of -10 mA/cm2, the g-C/TiO2/Ni2P catalyst shows an overpotential of 55 mV, while the commercial Pt/C catalyst shows an overpotential of 77 mV. Our work provides a facile aqueous scalable route with no need for noble metals that can be considered as a potential alternative for the commercial Pt/C catalyst.

Regioselectivity in Pyrene-Templated Polymerization Using MOFs as 1D Porous Scaffolds

Physicochemical properties of polymers strongly depend on the arrangement and distribution of attached monomers. Templated polymerization using porous crystalline materials appears as a promising route to gain control on the process. Thus, we demonstrate here the potential of metal-organic frameworks as scaffolds with a versatile and very regular porosity, well adapted for the regioselective oxidative polymerization of pyrene. This photoresponsive monomer was first encapsulated within the one-dimensional (1D) microporosity of the robust zirconium(IV) carboxylate metal-organic framework (MOF) (MIL-140D) to, later, undergo in situ oxidative polymerization, enabling the growth of a highly selective polypyrene (PPyr) regioisomer over other potential polymer configurations. To confirm the polymerization and the geometry control of pyrene, the resulting composites were exhaustively characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), N2 sorption measurements, scanning transmission electron microscopy coupled with energy-dispersive X-ray (STEM-EDX) spectroscopy, and fluorescence spectroscopy. Among others, photoluminescence quenching and emission shift in the solid state demonstrated the presence of PPyr inside the MOF porosity. Furthermore, an in-depth joint analysis combining solid-state, magic-angle spinning (MAS) 1H and 13C NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), and molecular simulations (grand canonical Monte Carlo (GCMC) and density functional theory (DFT)) allowed the elucidation of the spatial, host-guest interactions driving the polymerization reaction.

Revealing the Indispensable Role of In Situ Electrochemically Reconstructed Mn(II)/Mn(III) in Improving the Performance of Lithium-Carbon Dioxide Batteries

Li-CO2 batteries are regarded as promising high-energy-density energy conversion and storage devices, but their practicability is severely hindered by the sluggish CO2 reduction/evolution reaction (CORR/COER) kinetics. Due to the various crystal structures and unique electronic configuration, Mn-based cathode catalysts have shown considerable competition to facilitate CORR/COER. However, the specific active sites and regulation principle of Mn-based catalysts remain ambiguous and limited. Herein, this work designs novel Mn dual-active sites (MOC) supported on N-doped carbon nanofibers and conduct a comprehensive investigation into the underlying relationship between different Mn active sites and their electrochemical performance in Li-CO2 batteries. Impressively, this work finds that owing to the in situ generation and stable existence of Mn(III), MOC undergoes obvious electrochemical reconstruction during battery cycling. Moreover, a series of characterizations and theoretical calculations demonstrate that the different electronic configurations and coordination environments of Mn(II) and Mn(III) are conducive to promoting CORR and COER, respectively. Benefiting from such a modulating behavior, the Li-CO2 batteries deliver a high full discharge capacity of 10.31 mAh cm-2, and ultra-long cycle life (327 cycles/1308 h). This fundamental understanding of MOC reconstruction and the electrocatalytic mechanisms provides a new perspective for designing high-performance multivalent Mn-integrated hybrid catalysts for Li-CO2 batteries.

Thermally activated structural phase transitions and processes in metal-organic frameworks

The structural knowledge of metal-organic frameworks is crucial to the understanding and development of new efficient materials for industrial implementation. This review classifies and discusses recent advanced literature reports on phase transitions that occur during thermal treatments on metal-organic frameworks and their characterisation. Thermally activated phase transitions and procceses are classified according to the temperaturatures at which they occur: high temperature (reversible and non-reversible) and low temperature. In addition, theoretical calculations and modelling approaches employed to better understand these structural phase transitions are also reviewed.

Dynamic behavior of metal nanoparticles in MOF materials: analysis with electron microscopy and deep learning

Electron microscopy is a key characterization technique for nanoscale systems, and electron microscopy images are typically recorded and analyzed in terms of the morphology of the objects under study in static mode. The emerging current trend is to analyze the dynamic behavior at the nanoscale observed during electron microscopy measurements. In this work, the study of the stability of MOF structures with different compositions and topologies under conditions of an electron microscope experiment revealed an unusual dynamic behavior of M NPs formed due to the electron-beam-induced transformation of specific frameworks. The transition to the liquid phase led to spatial movement, rapid sintering, and an increase in the M NPs size within seconds. In the case of copper nanoparticles, instantaneous sublimation was observed. The dynamic behavior of Co NPs was analyzed with a computational framework combining deep learning and classic computer vision techniques. The present study for the first time revealed unique information about the stability of a variety of MOFs under an electron beam and the dynamic behavior of the formed M NPs. The formation of Fe, Ni, Cu, and Co NPs was observed from a molecular framework with a specific subsequent behavior - a stable form for Fe, excessive dynamics for Co, and sublimation/condensation for Cu. Two important outcomes of the present study should be mentioned: (i) electron microscopy investigations of MOF samples should be made with care, as decomposition under an electron beam may lead to incorrect results and the appearance of "phantom" nanoparticles; and (ii) MOFs represent an excellent model for fundamental studies of molecular-to-nano transitions in situ in video mode, including a number of dynamic transformations.

A convenient catalytic method for preparation of new tetrahydropyrido[2,3-d]pyrimidines via a cooperative vinylogous anomeric based oxidation

In this study, a novel functionalized metal-organic frameworks MIL-125(Ti)-N(CH₂PO₃H₂)₂ was designed and synthesized via post-modification methodology. Then, MIL-125(Ti)-N(CH₂PO₃H₂)₂ as a mesoporous catalyst was applied for the synthesis of a wide range of novel tetrahydropyrido[2,3-d]pyrimidines as bioactive candidate compounds by one-pot condensation reaction of 3-(1-methyl-1H-pyrrol-2-yl)-3-oxopropanenitrile, 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and aromatic aldehydes at 100 °C under solvent-free condition. Interestingly, the preparation of tetrahydropyrido[2,3-d]pyrimidine was achieved via vinylogous anomeric based oxidation mechanism with a high yield and short reaction time.

Size-Selective Suzuki-Miyaura Coupling Reaction over Ultrafine Pd Nanocatalysts in a Water-Stable Indium-Organic Framework

Metal nanoparticles stabilized by crystalline metal-organic frameworks (MOFs) are highly promising for green heterogeneous catalysis. In this work, in situ formed ultrafine Pd nanocatalysts with an average size of 3.14 nm have been successfully immobilized into the mesopores or defects of a water-stable indium-based MOF by the double-solvent method and subsequent reduction. Significantly, the obtained Pd@InOF-1 displays an obvious and satisfactory size-selective effect in the Suzuki-Miyaura coupling reaction between arylboronic acids and aryl bromides. On the basis of the synergistic effect, microporous InOF-1 nanorods afford a confined space for improving the selectivity of target products while Pd nanoparticles endow abundant active sites for catalysis. Herein, choosing the smallest size reactant with only one benzene ring gives the highest isolated yield of 90%, and if the size is larger, the yield is obviously reduced or even the target product could not be collected. Looking forward, this demonstrated study not only assembles a well-designed Pd@MOF composite with unique micro-nanostructures but also delivers an impressive option for cross-coupling reaction, which has implications for the further development of MOF hybrids for sustainable applications.

Material Evolution with Nanotechnology, Nanoarchitectonics, and Materials Informatics: What will be the Next Paradigm Shift in Nanoporous Materials?

Materials science and chemistry have played a central and significant role in advancing society. With the shift toward sustainable living, it is anticipated that the development of functional materials will continue to be vital for sustaining life on our planet. In the recent decades, rapid progress has been made in materials science and chemistry owing to the advances in experimental, analytical, and computational methods, thereby producing several novel and useful materials. However, most problems in material development are highly complex. Here, the best strategy for the development of functional materials via the implementation of three key concepts is discussed: nanotechnology as a game changer, nanoarchitectonics as an integrator, and materials informatics as a super-accelerator. Discussions from conceptual viewpoints and example recent developments, chiefly focused on nanoporous materials, are presented. It is anticipated that coupling these three strategies together will open advanced routes for the swift design and exploratory search of functional materials truly useful for solving real-world problems. These novel strategies will result in the evolution of nanoporous functional materials.

Nanoconfined synthesis of conjugated ladder polymers

This review highlights recent advances in controlled synthesis of conjugated ladder polymers using templates.

Tetragonal CoMn2O4 nanocrystals on electrospun carbon fibers as high-performance battery-type supercapacitor electrode materials

We herein report a simple two-step procedure for fabricating tetragonal CoMn₂O₄ spinel nanocrystals on carbon fibers. The battery-type behavior of these composite fibers arises from the redox activity of CoMn₂O₄ in an alkaline aqueous solution, which, in combination with the carbon fibers, endows good electrochemical performance and long-term stability. The C@CoMn₂O₄ electrode exhibited high specific capacity, up to 62 mA h g^-1 at 1 A g^-1 with a capacity retention of around 90% after 4000 cycles. A symmetrical coin-cell device assembled with the composite electrodes delivered a high energy density of 7.3 W h kg^-1 at a power density of 0.1 kW kg^-1, which is around 13 times higher than that of bare carbon electrodes. The coin cell was cycled for 5000 cycles with 96.3% capacitance retention, at a voltage of up to 0.8 V, demonstrating excellent cycling stability.

Needle-Trap Device Containing a Filter: A Novel Device for Aerosol Studies

Particles in an aerosol sample contain a portion of the total available analytes. Therefore, particle trapping is required to fully characterize a gaseous sample. Needle-trap devices (NTDs) are highly useful to this end, as they allow sampling and preconcentration of free analytes, as well as the trapping of particles. Packing sorbents into the needle creates a filter that traps solid particles or liquid droplets. However, the particle-trapping efficiency of sorbent-packed NTDs is limited, especially for nanoparticles. To address this issue, an aerogel based on electrospun polyacrylonitrile (PAN) was prepared for trapping small particles to analyze particle-bound analytes. The PAN aerogel filter was fabricated by cutting electrospun PAN fibers and removing the remaining solvent via freeze-drying to obtain a light porous fibrous structure. The PAN aerogel was heated (H-PAN) prior to packing to ensure stability during thermal desorption. The trapping efficiency of the H-PAN-packed NTD was measured using a range of conditions, with high filtration efficiencies (>99%) being obtained in all cases. The mechanical stability of the H-PAN aerogel was tested using multiple extraction/desorption cycles with and without solid sorbent particles, with results indicating high repeatability (n = 94, relative standard deviation (RSD) <6%). The developed NTD was compared to thin-film microextraction with respect to their ability to characterize breath samples obtained with or without face masks; the NTD was able to trap both free and droplet-bound analytes, while thin-film microextraction was only able to extract free analytes, which is fully reflected in concentrations obtained with these two methods.

Anodic electrosynthesis of MIL-53(Al)-N(CH2PO3H2)2 as a mesoporous catalyst for synthesis of novel (N-methyl-pyrrol)-pyrazolo[3,4-b]pyridines via a cooperative vinylogous anomeric based oxidation

In this paper, the MIL-53(Al)-NH2 metal-organic frameworks (MOFs) was prepared based on the anodic electrosynthesis under green conditions. The anodic electrosynthesis as an environmentally friendly procedure was performed in the aqueous solution, room temperature, atmospheric pressure, and in the short reaction time (30 min). Also, the employed procedure was accomplished without the need for the ex-situ salt and base/probase additives as cation source and ligand activating agent at the constant current mode (10.0 mA cm-2). The electrosynthesized MOFs was functionalized with phosphorus acid tags as a novel mesoporous catalyst. This mesoporous catalyst was successfully employed for synthesis of new series (N-methyl-pyrrol)-pyrazolo[3,4-b]pyridines by one-pot condensation reaction of 3-methyl-1-phenyl-1H-pyrazol-5-amine, 3-(1-methyl-1H-pyrrol-2-yl)-3-oxopropanenitrile and various aromatic aldehydes (mono, bis and tripodal). This catalyst proceeded the organic synthetic reaction via a cooperative vinylogous anomeric based oxidation mechanism with a marginal decreasing its catalytic activity after recycling and reusability.

Solution-processable porous graphitic carbon from bottom-up synthesis and low-temperature graphitization

It is urgently desired yet challenging to synthesize porous graphitic carbon (PGC) in a bottom-up manner while circumventing the need for high-temperature pyrolysis. Here we present an effective and scalable strategy to synthesize PGC through acid-mediated aldol triple condensation followed by low-temperature graphitization. The deliberate structural design enables its graphitization in situ in solution and at low pyrolysis temperature. The resulting material features ultramicroporosity characterized by a sharp pore size distribution. In addition, the pristine homogeneous composition of the reaction mixture allows for solution-processability of the material for further characterization and applications. Thin films of this PGC exhibit several orders of magnitude higher electrical conductivity compared to analogous control materials that are carbonized at the same temperatures. The integration of low-temperature graphitization and solution-processability not only allows for an energy-efficient method for the production and fabrication of PGC, but also paves the way for its wider employment in applications such as electrocatalysis, sensing, and energy storage.

Introducing electrical conductivity to metal-organic framework thin films by templated polymerization of methyl propiolate

We herein present a case study on the templated, Pd-catalyzed polymerization reaction of methyl propiolate in the confined pore space of three different surface anchored metal-organic framework (SURMOF) systems in order to introduce electrical conductivity to MOF thin films and provide predictions for potential device integrations. To gain comprehensive insight into the influence of the template on polymerization, we chose Cu(bpdc), Cu2(bdc)2(dabco) and HKUST-1 because of their different types of pore channels, 1D, quasi-1D and 3D, and their free pore volumes. Well-defined MOF thin films were prepared using layer-by-layer deposition, which allows for the application of several characterization techniques not applicable for conventional powder MOFs. With SEM, AFM, XRD, MALDI-ToF/MS, ToF-SIMS and QCM, we were able to investigate the behaviour of the polymer formation. For lower dimensional pore channels, we find a depot-like release of monomeric units leading to top-layer formation determined by desorption kinetics, whereas for the 3D channels, quick release of an excess amount of monomers was observed and polymerization proceeds perfectly. Despite polymerization issues, control over the maximum chain lengths and the molecular weight distribution was achieved depending on the dimensionality of the pore systems. For the HKUST-1 system, polymerization was optimized and we were able to measure the electrical conductivity introduced by the conjugated polymer inside the channels.

Polymerization in MOF-Confined Nanospaces: Tailored Architectures, Functions, and Applications

This feature article describes recent trends and advances in structuring network polymers using a coordination-driven metal-organic framework (MOF)-based template approach to demonstrate the concept of crystal-controlled polymerization in confined nanospaces, forming tailored architectures ranging from simple linear one-dimensional macromolecules to tunable three-dimensional cross-linked network polymers and interwoven molecular architectures. MOF-templated network polymers combine the characteristics and advantages of crystalline MOFs (high porosity, structural regularity, and designability) with the intrinsic behaviors of soft polymers (flexibility, processability, stability, or biocompatibility) with widespread application possibilities and tunable properties. The article ends with a summary of the remaining challenges to be addressed, and future research opportunities in this field are discussed.