Enhanced Uptake and Selectivity of CO₂ Adsorption in a Hydrostable Metal–Organic Frameworks via Incorporating Methylol and Methyl Groups

A new methylol and methyl functionalized metal–organic frameworks (MOFs) QI-Cu has been designed and synthesized. As a variant of NOTT-101, this material exhibits excellent CO₂ uptake capacities at ambient temperature and pressure, as well as high CH₄ uptake capacities. The CO₂ uptake for QI-Cu is high, up to 4.56 mmol g^–1 at 1 bar and 293 K, which is top-ranked among MOFs for CO₂ adsorption and significantly larger than the nonfunctionalized NOTT-101 of 3.93 mmol g^–1. The enhanced isosteric heat values of CO₂ and CH₄ adsorption were also obtained for this linker functionalized MOFs. From the single-component adsorption isotherms, multicomponent adsorption was predicted using the ideal adsorbed solution theory (IAST). QI-Cu shows an improvement in adsorptive selectivity of CO₂ over CH₄ and N₂ below 1 bar. The incorporation of methylol and methyl groups also greatly improves the hydrostability of the whole framework

Land Cover Classification with Multispectral LiDAR Based on Multi-Scale Spatial and Spectral Feature Selection

The distribution of land cover has an important impact on climate, environment, and public policy planning. The Optech Titan multispectral LiDAR system provides new opportunities and challenges for land cover classification, but the better application of spectral and spatial information of multispectral LiDAR data is a problem to be solved. Therefore, we propose a land cover classification method based on multi-scale spatial and spectral feature selection. The public data set of Tobermory Port collected by the Optech Titan multispectral airborne laser scanner was used as research data, and the data was manually divided into eight categories. The method flow is divided into four steps: neighborhood point selection, spatial–spectral feature extraction, feature selection, and classification. First, the K-nearest neighborhood is used to select the neighborhood points for the multispectral LiDAR point cloud data. Additionally, the spatial and spectral features under the multi-scale neighborhood (K = 20, 50, 100, 150) are extracted. The Equalizer Optimization algorithm is used to perform feature selection on multi-scale neighborhood spatial–spectral features, and a feature subset is obtained. Finally, the feature subset is input into the support vector machine (SVM) classifier for training. Using only small training samples (about 0.5% of the total data) to train the SVM classifier, 91.99% overall accuracy (OA), 93.41% average accuracy (AA) and 0.89 kappa coefficient were obtained in study area. Compared with the original information’s classification result, the OA, AA and kappa coefficient increased by 15.66%, 8.7% and 0.19, respectively. The results show that the constructed spatial–spectral features and the application of the Equalizer Optimization algorithm for feature selection are effective in land cover classification with Titan multispectral LiDAR point data

Gas sorption studies on a microporous coordination polymer assembled from 2D grid layers by strong π-π interactions

The microporous coordination polymer [Co(H2L)(bipy)0.5]⋅2 H2O (1, bipy=4,4′‐bipyridine) was synthesized on the basis of the V‐shaped flexible diphosphonate ligand (2,4,6‐trimethyl‐1,3‐phenylene)bis(methylene)diphosphonic acid (H4L) and the auxiliary bipy ligand under hydrothermal conditions. The structure of this compound was characterized by single‐crystal X‐ray diffraction. By joining the diphosphonate ligands and bipy through tetrahedral [CoO3N] clusters, a 2D square grid layered network was formed. Further stacking of these layers on the basis of π–π interactions resulted in a pseudo‐3D microporous network with 1D channels running through the a axis. Gas sorption studies for CO2, H2, CH4, N2, and O2 on this coordination polymer were performed, and the results revealed interesting dynamic and hysteresis sorption behavior toward H2 at low temperature

Hysteretic Gas and Vapor Sorption in Flexible Interpenetrated Lanthanide-Based Metal–Organic Frameworks with Coordinated Molecular Gating via Reversible Single-Crystal-to-Single-Crystal Transformation for Enhanced Selectivity

A series of flexible 3-fold interpenetrated lanthanide-based metal organic frameworks (MOFs) with the formula [Ln­(HL)­(DMA)₂]·DMA·2H₂O, where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Er, DMA = dimethylacetamide, and H₄L = 5,5′-(2,3,5,6-tetramethyl-1,4-phenylene)­bis­(methylene)­bis­(azanediyl)­diisophthalic acid, have been prepared. [Sm­(HL)­(DMA)₂]·DMA·2H₂O was studied as an exemplar of the series. The activated Sm­(HL)­(DMA)₂ framework exhibited reversible single-crystal-to-single-crystal (SCSC) structural transformations in response to adsorption and desorption of guest molecules. X-ray single crystal structural analysis showed that activation of [Sm­(HL)­(DMA)₂]·DMA·2H₂O by heat treatment to form Sm­(HL)­(DMA)₂ involves closing of 13.8 × 14.8 Å channels with coordinated DMA molecules rotating into the interior of the channels with a change from <i>trans</i> to <i>cis</i> Sm coordination and unit cell volume shrinkage of ∼20%, to a void volume of 3.5%. Solvent exchange studies with CH₂Cl₂ gave [Sm­(HL)­(DMA)₂]·2.8CH₂Cl₂ which, at 173 K, had a structure similar to that of <i>trans</i>-[Sm­(HL)­(DMA)₂]·DMA·2H₂O. CH₂Cl₂ vapor sorption on activated <i>cis</i>-[Sm­(HL)­(DMA)₂] results in gate opening, and the fully loaded structure has a similar pore volume to that of <i>trans</i>-[Sm­(HL)­(DMA)₂]·2.8CH₂Cl₂ structure at 173 K. Solvent exchange and heat treatment studies also provided evidence for intermediate framework structural phases. Structural, thermodynamic, and kinetic aspects of the molecular gating mechanism were studied. The dynamic and structural response of the endothermic gate opening process is driven by the enthalpy of adsorption, entropic effects, and Fickian diffusion along the pores produced during framework structure development thus relating the structure and function of the material. Exceptionally high CO₂ selectivity was observed at elevated pressure compared with CH₄, H₂, O₂, and N₂ due to molecular gate opening of <i>cis</i>-[Sm­(HL)­(DMA)₂] for CO₂ but not for the other gases. The CO₂ adsorption induced the structural transformation of <i>cis</i>-[Sm­(HL)­(DMA)₂] to <i>trans</i>-[Sm­(HL)­(DMA)₂], and hysteretic desorption behavior allows capture at high pressure, with storage at lower pressure

Gas Storage and Diffusion through Nanocages and Windows in Porous Metal–Organic Framework Cu₂(2,3,5,6-tetramethylbenzene-1,4-diisophthalate)(H₂O)₂

A novel nanoporous metal–organic framework NPC-4 with excellent thermal stability was assembled from 2,3,5,6-tetramethylbenzene-1,4-diisophthalate (TMBDI) and the paddle-wheel secondary building unit (Cu₂(COO)₄). The porous structure comprises a single type of nanoscale cage (16 Å diameter) interconnected by windows (5.2 × 6.3 Å), which give a high pore volume. CH₄ (195–290 K), CO₂ (198–303 K), N₂ (77 K), and H₂ (77 K) adsorption isotherms were studied for pressures up to 20 bar. NPC-4 exhibits excellent methane and carbon dioxide storage capacities on a volume basis with very high adsorbate densities, under ambient conditions. Isobars were investigated to establish the relationship for adsorption capacities over a range of storage temperatures. The isosteric enthalpies of adsorption for both CH₄ and CO₂ adsorption did not vary significantly with amount adsorbed and were ∼15 and ∼25 kJ mol^–1, respectively. The adsorption/desorption kinetics for CH₄ and CO₂ were investigated and activation energies, enthalpies of activation, and diffusion parameters determined using various kinetic models. The activation energies for adsorption obtained over a range of uptakes from the stretched exponential kinetic model were 5.1–6.3 kJ mol^–1 (2–13.5 mmol g^–1) for CO₂ and 2.7–5.6 kJ mol^–1 (2–9 mmol g^–1) for CH₄. The activation energies for surface barriers and diffusion along pores for both CH₄ and CO₂ adsorption obtained from a combined barrier resistance diffusion model did not vary markedly with amount adsorbed and were <9 kJ mol^–1. Comparison of kinetic and thermodynamic parameters for CH₄ and CO₂ indicates that a surface barrier is rate determining at high uptakes, while intraparticle diffusion involving diffusion through pores, consisting of narrow windows interconnecting with nanocages, being rate determining at very low uptakes. The faster CH₄ intraparticle adsorption kinetics compared with CO₂ for NPC-4 was attributed to faster surface diffusion due to the lower isosteric enthalpy of adsorption for CH₄