Temperature-dependent work function, thermionic emission and bulk modulus of TiC: a study on the identification of free valence electrons and localized valence electrons and their roles played in carbides.

By analyzing the projected states of valence electrons (fatband structures), the localized valence electrons and the free valence electrons of TiC were identified, respectively. After defining the volumes and the magnitudes of localized valence electrons and free valence electrons, the influences of the temperature, including the thermal expansion and the atomic thermal vibration, on the localized valence electron density and the free valence electron density were investigated, respectively. Based on the metallic plasma model (MPM), the temperature-dependent work functions and the thermionic emission current densities of TiC were calculated in terms of temperature-dependent free valence electron densities. The results were in good agreement with experimental results. Furthermore, as it was observed, the linear dependence of the bulk modulus on the localized valence electron density demonstrated that the bulk modulus of TiC was determined by the localized valence electron density. The different roles played by the free valence electrons and the localized valence electrons in the work function and the bulk modulus of TiC could be attributed to their different contributions to the kinetic energy density of valence electrons. The influences of the temperature on the work function, thermionic emission and bulk modulus of TiC indicated that the transition metal carbides with lower free valence electron density, higher localized valence electron density and heavier atomic mass were desired to achieve lower work function, higher current density and higher stability.

Correction: Facile preparation of a Ni-imidazole compound with high activity for ethylene dimerization.

Correction for 'Facile preparation of a Ni-imidazole compound with high activity for ethylene dimerization' by Zhaohui Liu et al., Chem. Commun., 2024, 60, 188-191, https://doi.org/10.1039/D3CC04794F.

Planar Core and Macrocyclic Shell Stabilized Atomically Precise Copper Nanocluster Catalyst for Efficient Hydroboration of C-C Multiple Bond.

Atomically precise metal nanoclusters (NCs) have become an important class of catalysts due to their catalytic activity, high surface area, and tailored active sites. However, the design and development of bond-forming reaction catalysts based on copper NCs are still in their early stages. Herein, we report the synthesis of an atomically precise copper nanocluster with a planar core and unique shell, [Cu45(TBBT)29(TPP)4(C4H11N)2H14]2+ (Cu45) (TBBT: 4-tert-butylbenzenethiol; TPP: triphenylphosphine), in high yield via a one-pot reduction method. The resulting structurally well-defined Cu45 is a highly efficient catalyst for the hydroboration reaction of alkynes and alkenes. Mechanistic studies show that a single-electron oxidation of the in situ-formed ate complex enables the hydroboration via the formation of boryl-centered radicals under mild conditions. This work demonstrates the promise of tailored copper nanoclusters as catalysts for C-B heteroatom bond-forming reactions. The catalysts are compatible with a wide range of alkynes and alkenes and functional groups for producing hydroborated products.

Strategies for high-temperature methyl iodide capture in azolate-based metal-organic frameworks.

Efficiently capturing radioactive methyl iodide (CH3I), present at low concentrations in the high-temperature off-gas of nuclear facilities, poses a significant challenge. Here we present two strategies for CH3I adsorption at elevated temperatures using a unified azolate-based metal-organic framework, MFU-4l. The primary strategy leverages counter anions in MFU-4l as nucleophiles, engaging in metathesis reactions with CH3I. The results uncover a direct positive correlation between CH3I breakthrough uptakes and the nucleophilicity of the counter anions. Notably, the optimal variant featuring SCN- as the counter anion achieves a CH3I capacity of 0.41 g g-1 at 150 °C under 0.01 bar, surpassing all previously reported adsorbents evaluated under identical conditions. Moreover, this capacity can be easily restored through ion exchange. The secondary strategy incorporates coordinatively unsaturated Cu(I) sites into MFU-4l, enabling non-dissociative chemisorption for CH3I at 150 °C. This modified adsorbent outperforms traditional materials and can be regenerated with polar organic solvents. Beyond achieving a high CH3I adsorption capacity, our study offers profound insights into CH3I capture strategies viable for practically relevant high-temperature scenarios.

Facile preparation of a Ni-imidazole compound with high activity for ethylene dimerization.

A compound consisting of Ni and imidazole (Ni-imidazole) was synthesized in large quantities by a one-step co-precipitation method. The structure and stability of this Ni-imidazole were well studied by a series of characterization methods. The Ni-imidazole compound exhibited excellent catalytic properties for the dimerization of ethylene to 1-butene.

A study on feature selection using multi-domain feature extraction for automated k-complex detection.

Background: K-complex detection plays a significant role in the field of sleep research. However, manual annotation for electroencephalography (EEG) recordings by visual inspection from experts is time-consuming and subjective. Therefore, there is a necessity to implement automatic detection methods based on classical machine learning algorithms. However, due to the complexity of EEG signal, current feature extraction methods always produce low relevance to k-complex detection, which leads to a great performance loss for the detection. Hence, finding compact yet effective integrated feature vectors becomes a crucially core task in k-complex detection. Method: In this paper, we first extract multi-domain features based on time, spectral analysis, and chaotic theory. Those features are extracted from a 0.5-s EEG segment, which is obtained using the sliding window technique. As a result, a vector containing twenty-two features is obtained to represent each segment. Next, we explore several feature selection methods and compare their performance in detecting k-complex. Based on the analysis of the selected features, we identify compact features which are fewer than twenty-two features and deemed as relevant and proceeded to the next step. Additionally, three classical classifiers are employed to evaluate the performance of the feature selection models. Results: The results demonstrate that combining different features significantly improved the k-complex detection performance. The best performance is achieved by applying the feature selection method, which results in an accuracy of 93.03%±7.34, sensitivity of 93.81%±5.62%, and specificity 94.13±5.81, respectively, using a smaller number of the combined feature sets. Conclusion: The proposed method in this study can serve as an efficient tool for the automatic detection of k-complex, which is useful for neurologists or doctors in the diagnosis of sleep research.

Linker Vacancy Engineering of a Robust ftw-type Zr-MOF for Hexane Isomers Separation.

Discrimination of physically similar molecules by porous solids represents an important yet challenging task in industrially relevant chemical separations. Precisely controlled pore dimension and/or tailored pore surface functionality are crucial to achieve high-efficiency separation. Metal-organic frameworks (MOFs) are promising candidates for these challenging separations in light of their structural diversity as well as highly adjustable pore dimension/functionality. We report here a microporous, ftw-type Zr-based MOF structure, HIAM-410 (HIAM=Hoffmann Institute of Advanced Materials), built on hexanuclear Zr6 cluster and pyrene-1,3,6,8-tetracarboxylate (ptc4- ). Its crystallographic structure has been determined using continuous rotation electron diffraction (cRED) technique combined with Rietveld refinement against powder X-ray diffraction data, aided by low-dose high-resolution transmission electron microscopy (HRTEM) imaging. The compound features exceptional framework stability that is comparable to the prototype MOF UiO-66. Interestingly, the linker vacancies in the pristine MOF structure could be partially restored by post-synthetic linker insertion. Its separation capability of hexane isomers is enhanced substantially upon the linker vacancy engineering. The restored structure exhibits efficient splitting of monobranched and dibranched hexane isomers at both room temperature and industrially relevant temperature.

Ultra-Highly Active Ni-Doped MOF-5 Heterogeneous Catalysts for Ethylene Dimerization.

Here, an ultra-highly active Ni-MOF-5 catalyst with high Ni loading for ethylene dimerization is reported. The Ni-MOF-5 catalysts are synthesized by a facile one-pot co-precipitation method at room temperature, where Ni2+ replaces Zn2+ in MOF-5. Unlike Zn2+ with tetrahedral coordination in MOF-5, Ni2+ is coordinated with extra solvent molecules except for four-oxygen from the framework. After removing coordinated solvent molecules, Ni-MOF-5 achieves an ethylene turnover frequency of 352 000 h-1 , corresponding to 9040 g of product per gram of catalyst per hour, at 35 °C and 50 bar, far exceeding the activities of all reported heterogeneous catalysts. The high Ni loading and full exposure structure account for the excellent catalytic performance. Isotope labeling experiments reveal that the catalytic process follows the Cossee-Arlman mechanism, rationalizing the high activity and selectivity of the catalyst. These results demonstrate that Ni-MOF-5 catalysts are very promising for industrial catalytic ethylene dimerization.

A RUSBoosted tree method for k-complex detection using tunable Q-factor wavelet transform and multi-domain feature extraction.

Background: K-complex detection traditionally relied on expert clinicians, which is time-consuming and onerous. Various automatic k-complex detection-based machine learning methods are presented. However, these methods always suffered from imbalanced datasets, which impede the subsequent processing steps. New method: In this study, an efficient method for k-complex detection using electroencephalogram (EEG)-based multi-domain features extraction and selection method coupled with a RUSBoosted tree model is presented. EEG signals are first decomposed using a tunable Q-factor wavelet transform (TQWT). Then, multi-domain features based on TQWT are pulled out from TQWT sub-bands, and a self-adaptive feature set is obtained from a feature selection based on the consistency-based filter for the detection of k-complexes. Finally, the RUSBoosted tree model is used to perform k-complex detection. Results: Experimental outcomes manifest the efficacy of our proposed scheme in terms of the average performance of recall measure, AUC, and F10-score. The proposed method yields 92.41 ± 7.47%, 95.4 ± 4.32%, and 83.13 ± 8.59% for k-complex detection in Scenario 1 and also achieves similar results in Scenario 2. Comparison to state-of-the-art methods: The RUSBoosted tree model was compared with three other machine learning classifiers [i.e., linear discriminant analysis (LDA), logistic regression, and linear support vector machine (SVM)]. The performance based on the kappa coefficient, recall measure, and F10-score provided evidence that the proposed model surpassed other algorithms in the detection of the k-complexes, especially for the recall measure. Conclusion: In summary, the RUSBoosted tree model presents a promising performance in dealing with highly imbalanced data. It can be an effective tool for doctors and neurologists to diagnose and treat sleep disorders.

Transparent and Flexible Electromagnetic Interference Shielding Materials by Constructing Sandwich AgNW@MXene/Wood Composites.

Electromagnetic interference (EMI) shielding materials have attracted intensive attention with the increased electromagnetic pollution, which are required to possess high transparency and flexibility for applications in visualization windows, aerospace equipment, and wearable devices. However, it remains a challenge to achieve high-performance EMI shielding while maintaining excellent light transmittance. Herein, a sandwich composite is constructed by coating the core material of transparent wood (TW) with silver nanowire (AgNW)@MXene, exhibiting a maximum transmittance of 28.8% in the visible range and a longitudinal tensile strength of 47.8 MPa. The average EMI shielding effectiveness can reach up to 44.0 dB under X-band (8-12.4 GHz), ascribed to the increased absorption shielding induced by the multireflection of electromagnetic waves within microchannels of the TW layer and the interfacial polarization between AgNW and MXene. Simultaneously, large-scale EMI shielding films can be conveniently produced by our proposed method, which provides inspiration for the development of advanced EMI shielding materials for wide applications.

Structural evolution and strain generation of derived-Cu catalysts during CO2 electroreduction.

Copper (Cu)-based catalysts generally exhibit high C2+ selectivity during the electrochemical CO2 reduction reaction (CO2RR). However, the origin of this selectivity and the influence of catalyst precursors on it are not fully understood. We combine operando X-ray diffraction and operando Raman spectroscopy to monitor the structural and compositional evolution of three Cu precursors during the CO2RR. The results indicate that despite different kinetics, all three precursors are completely reduced to Cu(0) with similar grain sizes (~11 nm), and that oxidized Cu species are not involved in the CO2RR. Furthermore, Cu(OH)2- and Cu2(OH)2CO3-derived Cu exhibit considerable tensile strain (0.43%~0.55%), whereas CuO-derived Cu does not. Theoretical calculations suggest that the tensile strain in Cu lattice is conducive to promoting CO2RR, which is consistent with experimental observations. The high CO2RR performance of some derived Cu catalysts is attributed to the combined effect of the small grain size and lattice strain, both originating from the in situ electroreduction of precursors. These findings establish correlations between Cu precursors, lattice strains, and catalytic behaviors, demonstrating the unique ability of operando characterization in studying electrochemical processes.

Fast water transport and molecular sieving through ultrathin ordered conjugated-polymer-framework membranes.

The development of membranes that block solutes while allowing rapid water transport is of great importance. The microstructure of the membrane needs to be rationally designed at the molecular level to achieve precise molecular sieving and high water flux simultaneously. We report the design and fabrication of ultrathin, ordered conjugated-polymer-framework (CPF) films with thicknesses down to 1 nm via chemical vapour deposition and their performance as separation membranes. Our CPF membranes inherently have regular rhombic sub-nanometre (10.3 × 3.7 Å) channels, unlike membranes made of carbon nanotubes or graphene, whose separation performance depends on the alignment or stacking of materials. The optimized membrane exhibited a high water/NaCl selectivity of ∼6,900 and water permeance of ∼112 mol m-2 h-1 bar-1, and salt rejection >99.5% in high-salinity mixed-ion separations driven by osmotic pressure. Molecular dynamics simulations revealed that water molecules quickly and collectively pass through the membrane by forming a continuous three-dimensional network within the hydrophobic channels. The advent of ordered CPF provides a route towards developing carbon-based membranes for precise molecular separation.

Efficient and simultaneous capture of iodine and methyl iodide achieved by a covalent organic framework.

Radioactive molecular iodine (I2) and organic iodides, mainly methyl iodide (CH3I), coexist in the off-gas stream of nuclear power plants at low concentrations, whereas few adsorbents can effectively adsorb low-concentration I2 and CH3I simultaneously. Here we demonstrate that the I2 adsorption can occur on various adsorptive sites and be promoted through intermolecular interactions. The CH3I adsorption capacity is positively correlated with the content of strong binding sites but is unrelated to the textural properties of the adsorbent. These insights allow us to design a covalent organic framework to simultaneously capture I2 and CH3I at low concentrations. The developed material, COF-TAPT, combines high crystallinity, a large surface area, and abundant nucleophilic groups and exhibits a record-high static CH3I adsorption capacity (1.53 g·g-1 at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I2 and 50 ppm of CH3I, COF-TAPT presents an excellent total iodine capture capacity (1.51 g·g-1), surpassing various benchmark adsorbents. This work deepens the understanding of I2/CH3I adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.

Laser-sintering fabrication of integrated Al/Ni anodes for lithium-ion batteries.

Integrated Al/Ni electrodes of lithium-ion batteries (LIBs) with variant atomic ratios were successfully fabricated by a one-step laser-sintering process. The microstructure, phase composition, and pore structure were controlled by the raw material composition and laser parameters. The electrodes showed working merits without any conductive agent and binder, or even the collector used in a traditional battery. It was shown that the electrode consisted of multi-phases, i.e., Al, Al3Ni2, Al3Ni, and Ni, when the Al/Ni atomic ratio was higher than 5 : 5. A lower Al/Ni atomic ratio less than 5 : 5 favored the formation of a dual-phase electrode consisting of Al3Ni2 and Ni. As the Al content increased, the specific surface area of the as-sintered electrodes increased in the initial stage and then decreased. The formation of pores was closely related to the content of the residual Al phase after the laser sintering. The residual Al phase filled the pores when the Al content was high, leading to a lower pore size. In contrast, the liquid Al phase completely reacted with the Ni component, leaving a large number of pores at its original sites. The linked pores can serve as transport channels for Li+ ions, provide mass sites for electrochemical reactions, and also buffer huge volume changes of the active material. Among the electrodes, the one with an Al/Ni ratio of 3 : 7 showed the best cycling/rate performance, i.e., a capacity of 522.8 mA h g-1 by a current of 0.1 A g-1 after 200 cycles, even holding to 338.4 mA h g-1 by a big current impact at 2 A g-1. It formed a metallurgical combination between the conductive network and the active material with multiple porous structures, which is helpful for the electrodes to provide high capacity and maintain structural stability during cycling. In addition, the average laser-sintering time of a single electrode was within 10 s, which is suitable for industrial mass production.

Chemically Stable Guanidinium Covalent Organic Framework for the Efficient Capture of Low-Concentration Iodine at High Temperatures.

The capture of radioactive I2 vapor from nuclear waste under industrial operating conditions remains a challenging task, as the practical industrial conditions of high temperature (≥150 °C) and low I2 concentration (∼150 ppmv) are unfavorable for I2 adsorption. We report a novel guanidinium-based covalent organic framework (COF), termed TGDM, which can efficiently capture I2 under industrial operating conditions. At 150 °C and 150 ppmv I2, TGDM exhibits an I2 uptake of ∼30 wt %, which is significantly higher than that of the industrial silver-based adsorbents such as Ag@MOR (17 wt %) currently used in the nuclear fuel reprocessing industry. Characterization and theoretical calculations indicate that among the multiple types of adsorption sites in TGDM, only ionic sites can bond to I2 through strong Coulomb interactions under harsh conditions. The abundant ionic groups of TGDM account for its superior I2 capture performance compared to various benchmark adsorbents. In addition, TGDM exhibits exceptionally high chemical and thermal stabilities that fully meet the requirements of practical radioactive I2 capture (high-temperature, humid, and acidic environment) and differentiate it from other ionic COFs. Furthermore, TGDM has excellent recyclability and low cost, which are unavailable for the current industrial silver-based adsorbents. These advantages make TGDM a promising candidate for capturing I2 vapor during nuclear fuel reprocessing. This strategy of incorporating chemically stable ionic guanidine moieties in COF would stimulate the development of new adsorbents for I2 capture and related applications.

Carbon nanotube supported oriented metal organic framework membrane for effective ethylene/ethane separation.

Zeolitic imidazolate framework 8 (ZIF-8) is effective for C3H6/C3H8 separation because of the "sieving effect" of a six-membered (6-M) window. Here, we demonstrate that ZIF-8 is a versatile material that could effectively separate C2H4 from C2H6 via its 4-M window along the <100> direction. We established a facile and environmentally friendly carbon nanotube (CNT)-induced oriented membrane (CNT-OM) approach to fabricate a {100}-oriented ZIF-8 membrane (100-M). In this approach, 2-methyimidazole was anchored onto the CNT surface followed by 3-hour in situ growth in aqueous solution at room temperature. The obtained 100-M, whose 4-M window is aligned along the transport pathway, showed ~3 times higher C2H4/C2H6 selectivity than a randomly oriented membrane. Thus, this work demonstrates that the membrane orientation plays an important role in tuning selectivity toward different gas pairs. Furthermore, 100-M exhibited excellent mechanical stability that could sustain the separation performance after bending at a curvature of ~109 m-1.

The Complex Crystal Structure and Abundant Local Defects of Zeolite EMM-17 Unraveled by Combined Electron Crystallography and Microscopy.

In this study, we successfully solve polymorphs A and B of zeolite EMM-17, which can only crystallize in sub-micrometer-sized crystals while containing complex stacking disorders, from the three-dimensional (3D) electron diffraction (ED) data. This is the first time that the atomic structure of this polymorph has been ab initio solved, and the result reveals a unique 10(12)×10(12)×11-ring channel system. Moreover, we acquire the first atomic-resolution images of EMM-17 using integrated differential phase-contrast scanning transmission electron microscopy. The images allow us to directly observe polymorphs B and C and discover a large number of local structural defects. Based on structural features unraveled from the reciprocal-space 3D ED data and real-space images, we propose a series of energetically feasible local structures in EMM-17. We also demonstrate that the unique porous structure of EMM-17 enables efficient kinetic separation of C6 alkane isomers.

Ionic Functionalization of Multivariate Covalent Organic Frameworks to Achieve an Exceptionally High Iodine-Capture Capacity.

Adsorption-based iodine (I2 ) capture has great potential for the treatment of radioactive nuclear waste. In this study, we apply a "multivariate" synthetic strategy to construct ionic covalent organic frameworks (iCOFs) with a large surface area, high pore volume, and abundant binding sites for I2 capture. The optimized material iCOF-AB-50 exhibits a static I2 uptake capacity of 10.21 g g-1 at 75 °C and a dynamic uptake capacity of 2.79 g g-1 at ≈400 ppm I2 and 25 °C, far exceeding the performances of previously reported adsorbents under similar conditions. iCOF-AB-50 also exhibits fast adsorption kinetics, good moisture tolerance, and full reusability. The promoting effect of ionic groups on I2 adsorption has been elucidated by experimentally identifying the iodine species adsorbed at different sites and calculating their binding energies. This work demonstrates the essential role of balancing the textural properties and binding sites of the adsorbent in achieving a high I2 capture performance.

Upgrading Octane Number of Naphtha by a Robust and Easily Attainable Metal-Organic Framework through Selective Molecular Sieving of Alkane Isomers.

The separation of alkanes, particularly monobranched and dibranched isomers, is of paramount importance in the petrochemical industry for optimizing the feedstock of ethylene production as well as for upgrading the octane number of gasoline. Here, we report the full separation of linear/monobranched alkanes from their dibranched isomers by a robust and easily scalable metal-organic framework material, Co3 (HCOO)6 . The compound completely excludes dibranched alkanes but adsorbs their linear and monobranched isomers, as evidenced by single-component and multicomponent adsorption measurements. More importantly, the material exhibits excellent performance in separating naphtha and is capable of providing high quality feedstock for the production of ethylene and gasoline components with high octane number, making it a promising candidate for naphtha separation in petrochemical industry.

A Roadmap to Sorption-Based Atmospheric Water Harvesting: From Molecular Sorption Mechanism to Sorbent Design and System Optimization.

Sorption-based atmospheric water harvesting (SAWH), which uses sorbents to capture water vapor from the air and low-grade energy to produce fresh liquid water, has been recognized as a promising strategy for decentralized water supply in arid areas. This review aims to summarize the latest progress in this field and provide perspectives for the further development of SAWH, focusing on the design of sorbent materials and the optimization of the entire system. We first introduce the water sorption mechanisms on different sorbent materials. Next, we discuss the properties and performances of various sorbents developed for SAWH by categorizing them into specific groups: nanoporous solids, hygroscopic polymers, salt-based composites, and liquid sorbents; for each type of sorbent materials, we have analyzed its advantages and limitations, as well as design strategies. In addition, we discuss the influences of the mass and heat transport of the SAWH system on its overall performance in actual operations, and introduce different types of water harvesters developed for SAWH. In the last section, we outline the challenges in this field from fundamental research and practical application aspects, and describe roadmaps for the future development of this technology.