Supramolecular metal–organic frameworks (SMOFs) are emerging as a new family of porous materials. In this work, a SMOF, [Cu 2 (ade) 4 (H 2 O) 2 ](SiF 6 ) 2 (SMOF-SIFSIX-1, ade = adenine) was successfully synthesized from the cationic complex of copper and adenine and hexafluorosilicate anions by a slow diffusion method and was demonstrated for trapping carbon dioxide in preference to methane and nitrogen. With one-dimensional pores of about 3.6 × 3.6 Å to induce their distinguishing interactions with the three components, SMOF-SIFSIX-1 exhibited excellent selective gas sorption behaviors for CO2/CH4 (50:50) and CO2/N2 (15:85) gas mixtures with ideal adsorbed solution theory selectivities of 21.1 and 131.7 at 273 K and 100 kPa pressure, respectively, outperforming most of reported hydrogen-bonded organic frameworks so far. Neutron powder diffraction and DFT-D calculations were also carried out to investigate the CO2 adsorption configuration on SMOF-SIFSIX-1a, which suggested that this framework catch CO2 due to “C···F” and “O···H” supramolecular interactions between CO2 molecules and SMOF-SIFSIX-1a. This study demonstrates that the rarely studied SMOF material shows promising potential in gas adsorption separation.
It is challenging to obtain high-purity xenon (Xe) and krypton (Kr) from the by-products of the air separation process due to their similar atom size and physical properties. Adsorption using porous materials such as metalorganic frameworks has been considered a promising technology to separate Xe/Kr. Herein, we reported two novel isostructural ionic supramolecular metal-organic frameworks (SMOFs, SMOF-PFSIX-1, and SMOF-AsFSIX-1), in which inorganic anions (PF 6or AsF 6-) and cationic metal-organic entities self-assembled through hydrogen bonds to give three-dimension pore channels. The two kinds of SMOFs can separate Xe/Kr efficiently with IAST selectivity of 6.9 and 6.7 under 298 K and 1.0 bar respectively. The breakthrough experiments further confirmed their industrial application potential. The Grand Canonical Monte Carlo (GCMC) and the Density Functional Theory (DFT) calculations revealed that there were multiple adsorptive sites to catch the Xe atom, and the affinity between Xe and frameworks can be attributed to the inorganic anions and amino groups on the ligands. To the best of our knowledge, it was the first time to report the SMOFs for Xe/Kr separation, and we proposed a new strategy for Xe/Kr separation based on the synergistic effect of amino and inorganic anions.
Hydrogen-bonded organic frameworks (HOFs) have emerged as rapidly growing porous materials while established permanent porosities are very fragile and difficult to stabilize due to weak hydrogen-bonding interactions among building units. Herein, we report a stable hydrogen-bonded metallotecton framework (termed as HOF-ZJU-102) that was constructed through hydrogen-bonding networks between cationic metal-organic complexes [Cu 2 (Hade) 4 (H 2 O) 2 ] 4 + (Hade = adenine) and GeF 6 2À anions. The framework not only shows permanent porosity, but also exhibits efficient separa-tion performance of C 2 H 2 /C 2 H 4 at room temperature. More interestingly, its crystal structure could be irreversibly transformed into isostructural counterpart HOF-ZJU-101 by ion exchange in the SiF 6 2À containing solution, evidenced by multiple characterization techniques including gas sorption measurements, 19 F NMR spectra, FTIR and EDS. Utilizing such an ion exchange mechanism, the collapsed HOF-ZJU-102 could be restored into HOF-ZJU-101 by simply soaking in the salt solution.
Seasonal cycle and interannual variability in coastal circulations in the northern South China Sea (NSCS) are investigated using satellite altimeter data from March 1993 to September 2016. Altimeter-derived velocity anomalies are in good agreement with acoustic Doppler current profilers (ADCP) observations at an adjacent location. Along-shelf volume transport anomalies in the NSCS indicate northeastward transports from mid-spring to summer and southwestward transports from mid-autumn to winter, which are consistent with previous studies in this region. According to convergence and divergence in the target control volumes, cross-shelf volume transports are estimated as the differences between two neighboring along-shelf volume transport anomalies, with the assumption that long-term mean along-shelf volume transports at each cross-sections are identical. The results show onshore transports in mid-autumn and offshore transports in early summer. The comparison between altimeter-derived and ADCP-estimated cross-shelf volume transports is encouraging, especially when the region has relatively low mesoscale activities and a low freshwater input. Reconstructed cross-shelf volume transports through multiple linear regression reveal that seasonal harmonics is the primary force in driving cross-shelf volume transports in the NSCS, while wind and El Niño have secondary effects on controlling cross-shelf volume transports in different regions. The present study helps to quantify the long-term coastal circulations, especially cross-shelf volume transports, based on altimeter data, which has important implications on the dynamics in coastal regions where observational data is limited.
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