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Methane has been successfully encapsulated within cages of C60 fullerene, which is an appropriate model system to study confinement effects. Its chemistry and physics are also relevant for theoretical model descriptions. Here we provide insights into intermolecular interactions and predicted spectroscopic responses of the CH4@C60 complex and compared them with results from other methods and with data from the literature. Local energy decomposition analysis (LED) within the domain-based local pair natural orbital coupled cluster singles, doubles, and perturbative triples (DLPNO-CCSD(T)) framework was used, and an efficient protocol for studies of endohedral complexes of fullerenes is proposed. This approach allowed us to assess energies in relation to electronic and geometric preparation, electrostatics, exchange, and London dispersion for the CH4@C60 endohedral complex. The calculated stabilization energy of CH4 inside the C60 fullerene was −13.5 kcal mol−1 and its magnitude was significantly larger than the latent heat of evaporation of CH4. Evaluation of vibrational frequencies and polarizabilities of the CH4@C60 complex revealed that the infrared (IR) and Raman bands of the endohedral CH4 were essentially “silent” due to the dielectric screening effect of C60, which acted as a molecular Faraday cage. Absorption spectra in the UV-vis domain and ionization potentials of C60 and CH4@C60 were predicted. They were almost identical. The calculated 1H/13C NMR shifts and spin–spin coupling constants were in very good agreement with experimental data. In addition, reference DLPNO-CCSD(T) interaction energies for complexes with noble gases (Ng@C60; Ng = He, Ne, Ar, Kr) were calculated. The values were compared with those derived from supramolecular MP2/SCS-MP2 calculations and estimates with London-type formulas by Pyykko and coworkers [Phys. Chem. Chem. Phys., 2010, 12, 6187–6203], and with values derived from DFT-based symmetry-adapted perturbation theory (DFT-SAPT) by Hesselmann & Korona [Phys. Chem. Chem. Phys., 2011, 13, 732–743]. Selected points at the potential energy surface of the endohedral He2@C60 trimer were considered. In contrast to previous theoretical attempts with the DFT/MP2/SCS-MP2/DFT-SAPT methods, our calculations at the DLPNO-CCSD(T) level of theory predicted the He2@C60 trimer to be thermodynamically stable, which is in agreement with experimental observations.

The chemisorption of CO2 on aminated silica has a rich chemistry, and its details are important to research in relation to CO2 capture and catalytic chemistry. In this study, such chemisorption was investigated on aminated and diaminated silica with 1H and 13C solid state nuclear magnetic resonance (NMR) spectroscopy under dry and wet conditions. Fast magic-angle spinning (MAS) allowed us to obtain high resolution spectra. Porous silica was modified into a monoaminated version using (3-aminopropyl)triethoxysilane (APTS) and a diaminated one by using 3-(2-aminoethylamino)propyltriethoxysilane (AEAPTS). From the corresponding NMR spectra we could conclude that, under dry conditions, CO2 chemisorbed as carbamic acid and carbamate ammonium ion pairs and gave similar spectra for both directly-excited 13C and under cross-polarization (CP) {1H}13C MAS NMR. Under wet conditions, direct excitation and {1H}13C CPMAS NMR showed that carbamate ammonium ion pairs formed along with bicarbonates (HCO3−). For the wet conditions, the 13C and 1H NMR spectra were especially well resolved, and we could detect two different types of carbamate ammonium ion pairs forming on the diaminated silica. We conclude that carbamate ammonium ion pairs and HCO3− moieties can be detected by {1H}13C MAS NMR, at least qualitatively, in addition to the more time consuming direct excitation.

Organosilica foams are commonly formed by a multistep process involving hydrolysis and condensation of organosilanes followed by solvent exchange and e.g. supercritical CO2 drying. Here, we propose a straightforward route to synthesize lightweight hybrid foams from aqueous dispersions of a surface-active aminosilane (AS) and TEMPO-oxidized cellulose nanofibrils (TCNFs). Air bubbles were introduced in the TCNF/AS dispersion by mechanical blending, and the foam was solidified by oven-drying. Evaporative drying at mild temperature (60 °C) resulted in dry foams with low densities (25–50 kg m−3), high porosities (96–99%) and macropores of 150–300 μm in diameter. The foaming and foam stabilization were successful for a pH range of 10.4–10.8 for foams containing 55–65 wt% of organosilica in the dry state. The protonation of AS increased the ionic strength of the dispersion and enhanced the interparticle interactions with TCNFs and, in turn, the foam viscosity and foam stability upon drying. The evaporation of water catalyzed the condensation of the AS to form low-molecular linear polymers, which resulted in an increased stiffness and strength of the foam lamella. The crosslinking of the AS polymeric network with the TCNF matrix allowed lightweight and homogeneous macroporous foams to be obtained with controlled densities and high amine content (amine content >4.5 mmol g−1) using an environmentally friendly technique.

The|Na10.2KCs0.8|8[Al12Si12O48]8(Fm3[combining macron]c)-LTA zeolite adsorbs CO2-over-CH4 with a high selectivity (over 1500). The uptake of carbon dioxide is also high (3.31 mmol g(-1), 293 K, 101 kPa). This form of zeolite A is a very promising adsorbent for applications such as biogas upgrading, where keeping the adsorption of methane to a minimum is crucial.

Amine-modified sorbents are relevant to the capturing of dilute carbon dioxide from gas mixtures, and micro-/mesoporous polymers are promising substrates due to their rich chemistry. Here, we prepared an aldehyde-rich polyimine with micro- and mesopores by a Schiff-base condensation of 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-benzenetricarboxaldehyde using an excess of aldehyde. The micropores were crucial to the physisorption of CO2, while the mesopores provided space for the post-modification with tris(2-aminoethyl)amine (tren) that induced the chemisorption of CO2. The amine modified polymer showed a high uptake of CO2 at low pressures (1.13 mmol g−1 at 0.05 bar and 273 K) and a high estimated CO2-over-N2 selectivity (1.04 × 103 at 273 K for 5 v%/95 v% CO2/N2 mixture). CO2 both physisorbed and chemisorbed on the amine-modified polyimine, which we confirmed by studying the CO2-amine chemistry using in situ FTIR spectroscopy and solid state 13C NMR spectroscopy. Carbamic acid formed during the chemisorption of CO2, as the CO2 reacted with the amine groups. Due to the formation of carbamic acid, the isosteric heat of adsorption was high, with values up to 80 kJ mol−1 at a low coverage of CO2. It appears that amine-modified porous polymers could be relevant to the removal of CO2 from gas streams with low concentrations.

Amorphous calcium carbonate (ACC) is known to play a prominent role in biomineralization. Different studies on the structure of biogenic ACCs have illustrated that they can have distinct short-range orders. However, the origin of so-called proto-structures in synthetic and additive-free ACCs is not well understood. In the current work, ACC has been synthesised in iso-propanolic media by direct precipitation from ionic precursors, and analysed utilising a range of different techniques. The data suggest that this additive-free type of ACC does not resemble clear proto-structural motifs relating to any crystalline polymorph. This can be explained by the undefined pH value in iso-propanolic media, and the virtually instantaneous precipitation. Altogether, this work suggests that aqueous systems and pathways involving pre-nucleation clusters are required for the generation of clear proto-structural features in ACC. Experiments on the ACC-to-crystalline transformation in solution with and without ethanol highlight that polymorph selection is under kinetic control, while the presence of ethanol can control dissolution re-crystallisation pathways.

The insight into the molecular aspects of ligand grafting and potential maximal capacity of hybrid organic–inorganic adsorbents bearing phosphonate ligand monolayers as active functions was obtained by single crystal X-ray studies of ligand-functionalized titanium alkoxide complexes. The attachment of molecules occurs generally in the tripodal vertical fashion with the minimal distance between them being about 8.7 A, resulting in 0.19 nm2 as the minimal surface area per function. In the present experimental work the theoretical loading capacity could almost be achieved for functionalization of mesoporous nanorods of anatase with imino-bis-methylphosphonic acid (IMPA, NH(CH2PO3H2)2) or aminoethylphosphonic acid (AEPA, H2NC2H4PO3H2). The products had the same morphology as the starting material, as was established by SEM and optical microscopy. The size and structure of the individual nanoparticles of the constituting inorganic component of the material were preserved and practically unchanged through the surface modification, as established by powder XRD and EXAFS studies. The surface area of the inorganic–organic hybrids decreased somewhat from the initial ∼250 m2 g−1, on adsorption of AEPA (0.21 mmol g−1) to ∼240 m2 g−1, and on adsorption of IMPA (0.17 mmol g−1) to ∼190 m2 g−1. The ligands were bound effectively to the surface according to TGA, EDS and FTIR analyses and remained in the mono-deprotonated form. The produced hybrid adsorbents had for the selected pH (3.5) high capacities towards adsorption of Rare Earth Element (REE) cations, but with equilibria achieved relatively slowly. The composition of the surface complexes was determined as M : L = 1 : 1 for IMPA, but varied for the AEPA from 1 : 3 to 1 : 1 dependent on the REE, which can be interpreted in terms of charge compensation as the major driving force behind binding. The cation desorption in strongly acidic media for recuperation of the adsorbed REE and the relative capacity of the re-used adsorbent have been quantified.

A series of microporous organic polymers (MOPs) were synthesized by Schiff base condensation of 1,3,5-tris(4-aminophenyl)benzene and a number of dialdehyde monomers. The polymers were structurally characterized by in situ infrared and ex situ solid state 13C{1H} nuclear magnetic resonance (NMR) spectroscopy. Synthesis conditions were optimized to enhance CO2 uptake by the MOPs. Synthesis at low temperatures results in the MOPs being linked by imine groups. Heating of the MOPs reduces the number of imine groups and after heating to >300 °C nitrile groups were found to be present in the MOPs. The MOPs have specific surface areas up to 614 m2 g−1 and narrow pore size distributions of ∼4 to 8 A. The selectivity of CO2-over-N2 at 273 K and 1 bar was 56–77, which requires either an influence of chemisorption on CO2 or a molecular sieving (or kinetic selection) of CO2-over-N2. The materials had also heats of adsorption typical for physisorption of CO2.

Adsorption-driven separation of CO2 from flue gas has the potential to cut the cost for carbon capture and storage. Among the porous physisorbents, metal–organic frameworks (MOFs) are a class of promising candidates for gas separation and storage owing to their extraordinarily high specific surface areas and pore volumes, and predesigned pore structures. Here, we report three interpenetrated MOFs composed of Zn4O clusters and rigid dicarboxylate anions, namely SUMOF-n (SU = Stockholm University; n = 2, 3, 4). All the interpenetrated MOFs possess small pores of two different types and high pore volumes. SUMOF-2 had a structure similar to interpenetrated MOF-5, but with an extra-framework cation present in one of the two types of pores. SUMOF-3 was an interpenetrated version of IRMOF-8 while SUMOF-4 crystallized with mixed linkers, biphenyl-4,4′-dicarboxylic acid and benzene-1,4-dicarboxylic acid. Among the three SUMOFs, SUMOF-4 had the largest specific surface area (1612 m2 g−1) and pore volume. Single component adsorption of CO2 and N2 was determined at 273 K. We showed that the interpenetrated SUMOF-2 adsorbed more CO2 than non-interpenetrated MOF-5 under 273 K and 1 bar. This may be explained by the increased electric field gradients due to the interpenetration in the MOF. The uptake of CO2 for SUMOF-2 and SUMOF-4 was significant at somewhat higher pressure. Their CO2 isotherms were close to linear, which could be beneficial for separation of CO2via pressure swing adsorption from biogas or natural gas. On the other hand, SUMOF-3 adsorbed most CO2 at pressures relevant for CO2 capture from flue gas.

Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N2 were determined and used to predict the co-adsorption of CO2 and N2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 °C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g−1) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.

The uptake of carbon dioxide and nitrogen gas by zeolite NaKA was studied. A very high ideal CO(2)-over-N(2) selectivity and a high CO(2) capacity were observed at an optimal K(+) content of 17 at.%. NaKA is a very promising adsorbent for CO(2) separation from water-free flue gases.