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Abstract: Nanoporous materials are of great interest in many applications, such as catalysis, separation, and energy storage. The performance of these materials is closely related to their pore sizes, which are inefficient to determine through the conventional measurement of gas adsorption isotherms. Nuclear magnetic resonance (NMR) relaxometry has emerged as a technique highly sensitive to porosity in such materials. Nonetheless, streamlined methods to estimate pore size from NMR relaxometry remain elusive. Previous attempts have been hindered by inverting a time domain signal to relaxation rate distribution, and dealing with resulting parameters that vary in number, location, and magnitude. Here we invoke well‐established machine learning techniques to directly correlate time domain signals to BET surface areas for a set of metal‐organic frameworks (MOFs) imbibed with solvent at varied concentrations. We employ this series of MOFs to establish a correlation between NMR signal and surface area via partial least squares (PLS), following screening with principal component analysis, and apply the PLS model to predict surface area of various nanoporous materials. This approach offers a high‐throughput, non‐destructive way to assess porosity in c.a. one minute. We anticipate this work will contribute to the development of new materials with optimized pore sizes for various applications.

Crystallographic defects play a crucial role in cement hydration, with initial dissolution being dominated by the formation of etch pits that rely on the intersection of defects on surfaces. However, the defects present in cement particles have remained a mystery due to the lack of detailed direct observation at the atomic scale. In this study, we used scanning transmission electron microscopy to unravel the defects in alite particles at the single-atom level. Our observations identified different types of defects, including vacancies, doping, dislocations, rough surfaces, and grain boundaries. Atomic ordering in the alite crystal was further examined based on our single-atom recognition method. Our findings indicate that defects in cement particles may serve as reactive sites during the early hydration stage, facilitating the initial dissolution and providing nucleation sites for hydration products. This work provides insights into cement defect formation at the single-atom level and offers new opportunities in tuning the hydration process through defect engineering of cement particles.

In nature, nonheme iron enzymes use dioxygen to generate high-spin iron(IV)=O species for a variety of oxygenation reactions. Although synthetic chemists have long sought to mimic this reactivity, the enzyme-like activation of O2 to form high-spin iron(IV) = O species remains an unrealized goal. Here, we report a metal-organic framework featuring iron(II) sites with a local structure similar to that in α-ketoglutarate-dependent dioxygenases. The framework reacts with O2 at low temperatures to form high-spin iron(IV) = O species that are characterized using in situ diffuse reflectance infrared Fourier transform, in situ and variable-field Mössbauer, Fe Kβ x-ray emission, and nuclear resonance vibrational spectroscopies. In the presence of O2, the framework is competent for catalytic oxygenation of cyclohexane and the stoichiometric conversion of ethane to ethanol.

Understanding nanodiamond structures is of great scientific and practical interest. It has been a long-standing challenge to unravel the complexity underlying nanodiamond structures and to resolve the controversies surrounding their polymorphic forms. Here, we use transmission electron microscopy with high-resolution imaging, electron diffraction, multislice simulations, and other supplementary techniques to study the impacts of small sizes and defects on cubic diamond nanostructures. The experimental results show that common cubic diamond nanoparticles display the (200) forbidden reflections in their electron diffraction patterns, which makes them indistinguishable from new diamond (n-diamond). The multislice simulations demonstrate that cubic nanodiamonds smaller than 5 nm can present the d-spacing at 1.78 Å corresponding to the (200) forbidden reflections, and the relative intensity of these reflections increases as the particle size decreases. Our simulation results also reveal that defects, such as surface distortions, internal dislocations, and grain boundaries can also make the (200) forbidden reflections visible. These findings provide valuable insights into the diamond structural complexity at nanoscale, the impact of defects on nanodiamond structures, and the discovery of novel diamond structures.

To compare the allergenicity of native arginine kinase (nAK) and recombinant AK (rAK) from Scylla paramamosain and to identify the predominant allergenic domain of AK, AK was divided into 4 fragments: AK-E1 (amino acid (AA) 1–92), AK-E2 (AA 87–187), AK-E3 (AA 172–265), and AK-E4 (AA 276–357) based on the distribution of epitopes and the spatial structure of the AK molecule. The four recombinant fragments were expressed in the prokaryotic system Escherichia coli, and then nAK, rAK, and the recombinant fragments were purified. The allergenicity of recombinant proteins were evaluated using BALB/c mice. The results showed that the levels of specific antibodies in the serum and the secretion of Th2 type cytokines by the splenocytes of mice sensitized with rAK significantly increased, but the immunogenicity of rAK was weaker than that of nAK. Among the 4 fragments of AK, AK-E2 had the strongest immunogenicity. Meanwhile, rAK could stimulate RBL-2H3 cells to release β-hexokinase, but it was less effective than nAK. Among the 4 expressed fragments, AK-E2 and AK-E4 had a stronger stimulating effect on effector cells. In conclusion, the rAK expressed in the prokaryotic system showed weaker immunogenicity than nAK, and among the 4 fragments of AK, AA 87–187 has the strongest immunogenicity while AA 276–357 has the strongest immunoreactivity.

Hydrogen evolution, corrosion, and dendrite formation in the Zn anodes limit their practical applications in aqueous Zn metal batteries. Herein, we propose an interfacial chemistry regulation strategy that uses hybrid electrolytes of water and a polar aprotic N,N-dimethylformamide to modify the Zn2+-solvation structure and in situ form a robust and Zn2+-conducting Zn5(CO3)2(OH)6 solid electrolyte interphase (SEI) on the Zn surface to achieve stable and dendrite-free Zn plating/stripping over a wide temperature range. As confirmed by 67Zn nuclear magnetic resonance relaxometry, electrochemical characterizations, and molecular dynamics simulation, the electrochemically and thermally stable Zn5(OH)6(CO3)2-contained SEI achieved a high ionic conductivity of 0.04 to 1.27 mS cm-1 from −30 to 70 °C and a thermally activated fast Zn2+ migration through the [010] plane. Consequently, extremely stable Zn-ion hybrid capacitors in hybrid electrolytes are demonstrated with high capacity retentions and Coulombic efficiencies over 14,000, 10,000, and 600 cycles at 25, −20, and 70 °C, respectively.

Achieving hierarchical nanomaterials from a bottom-up approach remains challenging. Here, we report a closed-cage, onion nanostructure of covalent organic framework (COF) obtained through a low-temperature solvothermal synthesis. Atomic resolution transmission electron microscopy revealed the atomic arrangement in this COF onion, in which rich nitrogen was uniformly embedded in the periodic porous graphitic framework. The COF onion structure displayed graphitic features at a 0.33 nm interlayer spacing with Van der Waals interactions predominated between the layers. The onion layers exhibited significant heterogeneity in layer stacking by adopting a combination of different stacking modes. Defects were also found, such as five- or seven-member rings deviating from the perfect hexagonal lattice. These geometrical defects resulted in curving the 2D layers, which may have promoted the formation of onion nanostructures through a layer-by-layer attachment. We constructed a corresponding model that predicts COF onion properties. This novel onion exhibited a bandgap value of 2.56 eV, resembling other carbon-based nanomaterials, suggesting potential applications in sensors, photocatalysts, and nanoelectronics.

Carbon capture and sequestration reduces carbon dioxide emissions and is critical in accomplishing carbon neutrality targets. Here, we demonstrate new sustainable, solid-state, polyamine-appended, cyanuric acid-stabilized melamine nanoporous networks (MNNs) via dynamic combinatorial chemistry (DCC) at the kilogram scale toward effective and high-capacity carbon dioxide capture. Polyamine-appended MNNs reaction mechanisms with carbon dioxide were elucidated with double-level DCC where two-dimensional heteronuclear chemical shift correlation nuclear magnetic resonance spectroscopy was performed to demonstrate the interatomic interactions. We distinguished ammonium carbamate pairs and a mix of ammonium carbamate and carbamic acid during carbon dioxide chemisorption. The coordination of polyamine and cyanuric acid modification endows MNNs with high adsorption capacity (1.82 millimoles per gram at 1 bar), fast adsorption time (less than 1 minute), low price, and extraordinary stability to cycling by flue gas. This work creates a general industrialization method toward carbon dioxide capture via DCC atomic-level design strategies.

Covalent organic frameworks (COFs) show great potential for many advanced applications on account of their structural uniqueness. To address the synthetic challenges, facile chemical routes to engineer the porosity, crystallinity, and functionality of COFs are highly sought after. Herein, we report a synthetic approach that employs the Cadogan reaction to introduce nitrogen-containing heterocycles as the linkages in the framework. Irreversible indazole and benzimidazolylidene (BIY) linkages are introduced into COFs for the first time via phosphine-induced reductive cyclization of the common imine linkages following either stepwise or one-pot reaction protocols. The successful linkage transformation introduces new functionalities, as demonstrated in the case of BIY-COF, which displays excellent intrinsic proton conductivity without the need of impregnation with external proton transfer reagents. Such a general strategy will open the window to a broader class of functional porous crystalline materials.

Covalent organic frameworks (COFs) with efficient charge transport and exceptional chemical stability are emerging as an import class of semiconducting materials for opto-/electronic devices and energy-related applications. However, the limited synthetic chemistry to access such materials and the lack of mechanistic understanding of carrier mobility greatly hinder their practical applications. Herein, we report the synthesis of three chemically stable polyarylether-based metallophthalocyanine COFs (PAE-PcM, M = Cu, Ni, and Co) and facile in situ growth of their thin films on various substrates (i.e., SiO2/Si, ITO, quartz) under solvothermal conditions. We show that PAE-PcM COFs thin films with van der Waals layered structures exhibit p-type semiconducting properties with the intrinsic mobility up to ∼19.4 cm2 V-1 s-1 and 4 orders of magnitude of increase in conductivity for PAE-PcCu film (0.2 S m-1) after iodine doping. Density functional theory calculations reveal that the carrier transport in the framework is anisotropic, with the out-of-plane hole transport along columnar stacked phthalocyanine more favorable. Furthermore, PAE-PcCo shows the redox behavior maximumly contributes ∼88.5% of its capacitance performance, giving rise to a high surface area normalized capacitance of ∼19 μF cm-2. Overall, this work not only offers fundamental understandings of electronic properties of polyarylether-based 2D COFs but also paves the way for their energy-related applications.

The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited, at present, by the sluggish water oxidation reaction. Single-atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms toward designing high-performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir5.3+) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environment of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir0.1/Ni9Fe SAC) via a unique in situ cryogenic-photochemical reduction method that delivers an overpotential of 183 mV at 10 mA ⋅ cm-2 and retains its performance following 100 h of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO2 catalysts. These findings open the avenue toward an atomic-level understanding of the oxygen evolution of catalytic centers under in operando conditions.

Hyperpolarization is one of the approaches to enhance Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) signal by increasing the population difference between the nuclear spin states. Imaging hyperpolarized solids opens up extensive possibilities, yet is challenging to perform. The highly populated state is normally not replenishable to the initial polarization level by spin-lattice relaxation, which regular MRI sequences rely on. This makes it necessary to carefully "budget" the polarization to optimize the image quality. In this paper, we present a theoretical framework to address such challenge under the assumption of either variable flip angles or a constant flip angle. In addition, we analyze the gradient arrangement to perform fast imaging to overcome intrinsic short decoherence in solids. Hyperpolarized diamonds imaging is demonstrated as a prototypical platform to test the theory.

Topochemical polymerization reactions hold the promise of producing ultra-high molecular weight crystalline polymers. However, the totality of topochemical polymerization reactions has failed to produce ultra-high molecular weight polymers that are both soluble and display variable functionality, which are restrained by the crystal-packing and reactivity requirements on their respective monomers in the solid state. Herein, we demonstrate the topochemical polymerization reaction of a family of para-azaquinodimethane compounds that undergo facile visible light and thermally initiated polymerization in the solid state, allowing for the first determination of a topochemical polymer crystal structure resolved via the cryoelectron microscopy technique of microcrystal electron diffraction. The topochemical polymerization reaction also displays excellent functional group tolerance, accommodating both solubilizing side chains and reactive groups that allow for post-polymerization functionalization. The thus-produced soluble ultra-high molecular weight polymers display superior capacitive energy storage properties. This study overcomes several synthetic and characterization challenges amongst topochemical polymerization reactions, representing a critical step toward their broader application.

Hyperpolarization is one of the approaches to enhance Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) signal by increasing the population difference between the nuclear spin states. Imaging hyperpolarized solids opens up extensive possibilities, yet is challenging to perform. The highly populated state is normally not replenishable to the initial polarization level by spin-lattice relaxation, which regular MRI sequences rely on. This makes it necessary to carefully "budget" the polarization to optimize the image quality. In this paper, we present a theoretical framework to address such challenge under the assumption of either variable flip angles or a constant flip angle. In addition, we analyze the gradient arrangement to perform fast imaging to overcome intrinsic short decoherence in solids. Hyperpolarized diamonds imaging is demonstrated as a prototypical platform to test the theory.

Hierarchical nanoporous carbons combining pore sizes of different length scales are highly important for separation processes. However, critical questions remain regarding the hierarchical structure regulation and the molecular mechanisms of gaseous adsorbate uptake and interactions within the hierarchical nanoporous carbons. These materials present characterization challenges in that there are no experimental techniques that can elucidate the molecular mechanisms of the organic compounds and CO2 within the materials. We deployed multidimensional solid-state nuclear magnetic resonance (NMR) to generate maps of guest-framework interactions as a function of adsorbate concentrations and adsorption times. The NMR spectra provide insight toward the design of effective hierarchical pore structures. Our materials show a high volatile organic compounds/CO2 physisorption capacity, which reveals promising application to carbon-capture strategies to mitigate global warming.

Nanoporous membranes with two-dimensional materials such as graphene oxide have attracted attention in volatile organic compounds (VOCs) and H2 adsorption because of their unique molecular sieving properties and operational simplicity. However, agglomeration of graphene sheets and low efficiency remain challenging. Therefore, we designed hierarchical nanoporous membranes (HNMs), a class of nanocomposites combined with a carbon sphere and graphene oxide. Hierarchical carbon spheres, prepared following Murray's law using chemical activation incorporating microwave heating, act as spacers and adsorbents. Hierarchical carbon spheres preclude the agglomeration of graphene oxide, while graphene oxide sheets physically disperse, ensuring structural stability. The obtained HNMs contain micropores that are dominated by a combination of ultramicropores and mesopores, resulting in high VOCs/H2 adsorption capacity, up to 235 and 352 mg/g at 200 ppmv and 3.3 weight % (77 K and 1.2 bar), respectively. Our work substantially expands the potential for HNMs applications in the environmental and energy fields.

Ordered interlayer stacking is intrinsic in two-dimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors.

Ternary organic solar cells (OSCs) provide a convenient and effective means to further improve the power conversion efficiency (PCE) of binary ones via composition control. However, the role of the third component remains to be explored in specific binary systems. Herein, we report ternary blend solar cells by adding the narrow-band-gap donor PCE10 as the mediator into the PBDB-T:IDTT-T binary blend system. The extended absorption, efficient fluorescence resonance energy transfer, enhanced charge dissociation, and induced tighter molecular packing of the ternary blend films enhance the photovoltaic properties of devices and deliver a champion PCE of 10.73% with an impressively high open-circuit voltage (VOC) of 1.03 V. Good miscibility and similar molecular packing behavior of the components guarantee the desired morphology in the ternary blend films, leading to solar cell devices with over 10% PCEs at a range of compositions. Our results suggest that ternary systems with properly aligned energy levels and overlapping absorption among the components hold great promises to further enhance the performance of corresponding binary ones.

Porous graphitic framework (PGF) is a two-dimensional (2D) material that has emerging energy applications. An archetype contains stacked 2D layers, the structure of which features a fully annulated aromatic skeleton with embedded heteroatoms and periodic pores. Due to the lack of a rational approach in establishing in-plane order under mild synthetic conditions, the structural integrity of PGF has remained elusive and ultimately limited its material performance. Here, we report the discovery of the unusual dynamic character of the C=N bonds in the aromatic pyrazine ring system under basic aqueous conditions, which enables the successful synthesis of a crystalline porous nitrogenous graphitic framework with remarkable in-plane order, as evidenced by powder X-ray diffraction studies and direct visualization using high-resolution transmission electron microscopy. The crystalline framework displays superior performance as a cathode material for lithium-ion batteries, outperforming the amorphous counterparts in terms of capacity and cycle stability. Insertion of well-defined, evenly spaced nanoscale pores into the two-dimensional (2D) layers of graphene invokes exciting properties due to the modulation of its electronic band gaps and surface functionalities. A bottom-up synthesis approach to such porous graphitic frameworks (PGFs) is appealing but also remains a great challenge. The current methods of building covalent organic frameworks rely on a small collection of thermodynamically reversible reactions. Such reactions are, however, inadequate in generating a fully annulated aromatic skeleton in PGFs. With the discovery of dynamic pyrazine formation, we succeeded in applying this linking chemistry to obtain a crystalline PGF material, which has displayed high electrical conductivity and remarkable performance as a cathode material for lithium-ion batteries. We envision that the demonstrated success will open the door to a wide array of fully annulated 2D porous frameworks, which hold immense potential for clean energy applications. We report the unusual dynamic characteristics of the C=N bonds in the pyrazine ring promoted under basic aqueous conditions, which enables the successful synthesis of two-dimensional porous graphitic frameworks (PGFs) featuring fully annulated aromatic skeletons and periodic pores. The PGF displayed high electrical conductivity and remarkable performance as a cathode material for lithium-ion batteries, far outperforming the amorphous counterparts in terms of capacity and cycle stability.

The effects of Co addition on the chemical and electronic structure of PbTiO3 were explored both by theory and through experiment. Cobalt was incorporated into PbTiO3 during the sol-gel process with the X-ray diffraction (XRD) data of the resulting compounds confirming a perovskite structure for the pure samples. The XRD lines broadened and showed emerging cubic structure features as the Co incorporation increased. The changes in the XRD pattern were interpreted as double perovskite structure formation. 207Pb NMR measurements revealed a growing isotropic component in the presence of Co. Consistent with the experiments, density functional theory (DFT)-calculated chemical-shift values corroborate isotropic coordination of Pb, suggesting the formation of cubic Pb2CoTiO6 domains in the prepared samples. Hybrid functional first-principles calculations indicate formation of Pb2CoTiO6 with cubic structure and confirm that Co addition can decrease oxygen binding energy significantly. Experimental UV-vis spectroscopy results indicate that upon addition of Co, the band gap is shifted toward visible wavelengths as confirmed by energy band and absorption spectrum calculations. The oxygen binding energies were determined by temperature-programmed reduction (TPR) measurements. Upon addition of Co, TPR lines shifted to lower temperatures and new features appeared in the TPR patterns. This shift was interpreted as weakening of the oxygen-cobalt bond strength. The change in the electronic structure by the alterations of oxygen vacancy formation energy and bond lengths upon Co insertion is determined by DFT calculations.

Hexagonal hexaminophenyl benzene, tetragonal tetrakis(4-aminophenyl) ethane, and trigonal 1,3,5-tris(p-formylphenyl)benzene were all joined together by imine linkages to yield a 2D porous covalent organic framework with unprecedented tth topology, termed COF-346. Unlike the 5 simple existing 2D topologies reported in COFs, COF-346 has 3 kinds of vertices and 2 kinds of edges and is constructed with linkers of 3 kinds of connectivity, and thus represents a higher degree of complexity in COF structures. The success in crystallizing COF-346 was based on precisely chosen geometry and metrics of the linkers and error correction offered by dynamic imine formation. We also report two additional related COFs: a crystalline, porous COF, termed COF-360 with a rare kgd topology, as well as the first crystalline, porous COF with defected tth topology, termed COF-340.

Triangular 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and linear tetrafluorophthalonitrile (TFPN) or 2,3,5,6-tetrafluoro-4-pyridinecarbonitrile (TFPC) were linked by 1,4-dioxin linkages to form crystalline 2D covalent organic frameworks, termed COF-316 and -318. Unlike the condensation reactions commonly used to crystallize the great majority of COFs, the reactions used in this report are based on nucleophilic aromatic substitution reactions (SNAr) that are considered irreversible. Our studies show that the reactivity of TFPN and TFPC with HHTP is enhanced by the nitrile substituents leading to facile reactions of planar building units to yield the present 1,4-dioxin linked COFs. Because these reactions are irreversible, the resultant frameworks have high chemical stability in both acid and base. This has led to postsynthetic modifications of COF-316 by reactions necessitating extreme conditions to covalently install functionalities not otherwise accessible. We also report the permanent porosity of these COFs.