Achieving a molecular-level understanding of how the structures and compositions of metal-organic frameworks (MOFs) influence their charge carrier concentration and charge transport mechanism-the two key parameters of electrical conductivity-is essential for the successful development of electrically conducting MOFs, which have recently emerged as one of the most coveted functional materials due to their diverse potential applications in advanced electronics and energy technologies. Herein, we have constructed four new alkali metal (Na, K, Rb, and Cs) frameworks based on an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand, which formed continuous π-stacks, albeit with different π-π-stacking and S⋯S distances (dπ-π and dS⋯S). These MOFs also contained different amounts of aerobically oxidized TTFTC˙+ radical cations that were quantified by electron spin resonance (ESR) spectroscopy. Density functional theory calculations and diffuse reflectance spectroscopy demonstrated that depending on the π-π-interaction and TTFTC˙+ population, these MOFs enjoyed varying degrees of TTFTC/TTFTC˙+ intervalence charge transfer (IVCT) interactions, which commensurately affected their electronic and optical band gaps and electrical conductivity. Having the shortest dπ-π (3.39 Å) and the largest initial TTFTC˙+ population (∼23%), the oxidized Na-MOF 1-ox displayed the narrowest band gap (1.33 eV) and the highest room temperature electrical conductivity (3.6 × 10-5 S cm-1), whereas owing to its longest dπ-π (3.68 Å) and a negligible TTFTC˙+ population, neutral Cs-MOF 4 exhibited the widest band gap (2.15 eV) and the lowest electrical conductivity (1.8 × 10-7 S cm-1). The freshly prepared but not optimally oxidized K-MOF 2 and Rb-MOF 3 initially displayed intermediate band gaps and conductivity, however, upon prolonged aerobic oxidation, which raised the TTFTC˙+ population to saturation levels (∼25 and 10%, respectively), the resulting 2-ox and 3-ox displayed much narrower band gaps (∼1.35 eV) and higher electrical conductivity (6.6 × 10-5 and 4.7 × 10-5 S cm-1, respectively). The computational studies indicated that charge movement in these MOFs occurred predominantly through the π-stacked ligands, while the experimental results displayed the combined effects of π-π-interactions, TTFTC˙+ population, and TTFTC/TTFTC˙+ IVCT interaction on their electronic and optical properties, demonstrating that IVCT interactions between the mixed-valent ligands could be exploited as an effective design strategy to develop electrically conducting MOFs.
Recently, the Ministry of Environmental Protection of China started the development of emission inventories in fifteen Chinese cities. It includes the esmission of PM10 and PM2.5 from stationary sources. However, there is no national standard method in China for stationary source PM10 and PM2.5 sampling. In this study, a two-stage virtual impactor was developed for sampling PM10 and PM2.5 from stationary sources. Its performance was evaluated for four types of sataionary sources, i.e., coal-fired power plant, waste incineration, circulating fluid bed, and converter steelmaking. These four tested emission sources were equipped with high efficiency PM control devices. PM2.5 mass concentrations measured in the chimneys of these emission sources were (0.93±0.03), (3.3±0.65), (0.59±0.04), and (0.15±0.04) mg·m-3, respectively, while the PM10 mass concentrations were (1.13±0.11), (6.9±0.86), (1.12±0.16), and (0.43±0.15) mg·m-3, respectively.
Abstract SSZ‐13, small‐pore zeolite with chabazite (CHA) topology, exhibits outstanding performance in gas adsorption‐separation and catalysis. However, most of the studies on SSZ‐13 zeolite are limited to the powder form. In practical application, the SSZ‐13 zeolite should be shaped with a certain amount of inert binder into technical form resulting in reduced performance. Herein, shaped binder‐free SSZ‐13 zeolite was prepared by treating the extruded SSZ‐13/SiO 2 sample with amantadine solution under hydrothermal conditions, to crystallize the SiO 2 binder into the zeolite phase. The characterization and DFT calculation results point out that the recrystallization of SiO 2 binder in shaped SSZ‐13 into zeolite crystal could improve the physical and chemical properties. Enhanced CO 2 adsorption capacity and catalysis performance in CO 2 ‐assisted oxidative dehydrogenation of ethane and propane were also found on the shaped binder‐free SSZ‐13 zeolite.
Abstract Developing hydrogen‐bonded organic frameworks (HOFs) that combine functional sites, size control, and storage capability for targeting gas molecule capture is a novel and challenging venture. However, there is a lack of effective strategies to tune the hydrogen‐bonded network to achieve high‐performance HOFs. Here, a series of HOFs termed as HOF‐ZSTU‐M (M=1, 2, and 3) with different pore structures are obtained by introducing structure‐directing agents (SDAs) into the hydrogen‐bonding network of tetrakis (4‐carboxyphenyl) porphyrin (TCPP). These HOFs have distinct space configurations with pore channels ranging from discrete to continuous multi‐dimensional. Single‐crystal X‐ray diffraction (SCXRD) analysis reveals a rare diversity of hydrogen‐bonding models dominated by SDAs. HOF‐ZSTU‐2 , which forms a strong layered hydrogen‐bonding network with ammonium (NH 4 + ) through multiple carboxyl groups, has a suitable 1D “pearl‐chain” channel for the selective capture of propylene (C 3 H 6 ). At 298 K and 1 bar, the C 3 H 6 storage density of HOF‐ZSTU‐2 reaches 0.6 kg L −1 , representing one of the best C 3 H 6 storage materials, while offering a propylene/propane (C 3 H 6 /C 3 H 8 ) selectivity of 12.2. Theoretical calculations and in situ SCXRD provide a detailed analysis of the binding strength of C 3 H 6 at different locations in the pearl‐chain channel. Dynamic breakthrough tests confirm that HOF‐ZSTU‐2 can effectively separate C 3 H 6 from multi‐mixtures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Self‐assembly of a trigonal building subunit with diaminotriazines (DAT) functional groups leads to a unique rod‐packing 3D microporous hydrogen‐bonded organic framework (HOF‐3). This material shows permanent porosity and demonstrates highly selective separation of C 2 H 2 /CO 2 at ambient temperature and pressure.
The separation of ethane from its analogous ethylene is of great importance in the petrochemical industry, but very challenging and energy intensive. Adsorptive separation using C2H6-selective porous materials can directly produce high-purity C2H4 in a single operation but suffers from poor selectivity. Here, we report an approach to boost the separation of C2H6 over C2H4, involving the control of pore structures in two isoreticular ultramicroporous metal–organic framework (MOF) materials with weakly polar pore surface for strengthened binding affinity toward C2H6 over C2H4. Under ambient conditions, the prototypical compound shows a very small uptake difference and selectivity for C2H6/C2H4, whereas its smaller-pore isoreticular analogue exhibits a quite large uptake ratio of 237% (60.0/25.3 cm3 cm–3), remarkably increasing the C2H6/C2H4 selectivity. Neutron powder diffraction studies clearly reveal that the latter material shows self-adaptive sorption behavior for C2H6, which enables it to continuously maintain close van der Waals contacts with C2H6 molecules in its optimized pore structure, thus preferentially binds C2H6 over C2H4. Gas sorption isotherms, crystallographic analyses, molecular modeling, selectivity calculation, and breakthrough experiment comprehensively demonstrate this unique MOF material as an efficient C2H6-selective adsorbent for C2H4 purification.
Rechargeable aluminum batteries (RABs) have been considered as a potential candidate for next-generation energy storage systems because of their high security, abundant resources, and high specific capacity. However, the poor cycling performance and sluggish reaction kinetics hinder the practical application of RABs. In this paper, an electrode material of NiCo bimetallic selenide nanospheres embedded in fluorine-doped carbon (NiCoSe2@F-C) has been designed for enhancing electrochemical performance. NiCoSe2@F-C doping with heterogeneous elements presented a stable core–shell structure and large surface area, playing a significant role in improving the cycling ability, specific capacity, and electrochemical reaction kinetics for RABs. The RABs based on NiCoSe2@F-C cathode exhibit high reversible capacity (294 mAh g–1 at 0.5 A g–1) and excellent cycle performance (115 mAh g–1 at 1 A g–1 over 400 cycles). It is confirmed that the charge storage mechanism of the NiCoSe2@F-C electrode is the intercalation/deintercalation of AlCl4– with the charge/discharge processes jointly controlled by capacitance and diffusion. This work provides an effective approach for further developing advanced cathodes of RABs with excellent electrochemical performance.
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