Amorphous derivates prepared by aqueous reaction of various aluminosilicate clay minerals with concentrated KF solution at 80–110°C were studied for their gas adsorption properties. The four clay minerals studied are halloysite, a well-crystallized kaolinite, a poorly crystallized kaolinite, and a montmorillonite. The gases tested are N2, O2, CH4, CO, CO2, and C2H2. The kaolin-group mineral derivatives are characterized by substantial reduction in particle size, high specific surface, and significant selectivity towards CO2 and C2H2 relative to the other gases. The montmorillonite derivative shows no increase in adsorption over the starting material, however, for all the materials high adsorption of CO2 and C2H2 was observed. Levels of gas adsorption and gas adsorption ratios are comparable to pillared clays.

Structure control and quantitative evaluation of porous materials are essential for many industrial and consumer applications of clay minerals, and nanotubular halloysite (HNT) has been used extensively for such purposes; performance enhancements are still needed, however. The objective of the present study was to improve the gas-adsorption capacity of HNT by controlling the particle size and porosity. This was accomplished through acid treatment and particle-size fractionation by centrifugation. Various particle sizes were obtained and porosities ranged from macropores to mesopores. Natural halloysite nanotubes were modified by sulfuric acid in various concentrations to selectively remove the alumina composition of the tubes. X-ray diffraction and energy dispersive X-ray spectroscopy were used to verify the mineralogical and compositional changes. Surface modification by the acid treatment increased the inner space volume of the tubes and decreased the mass of the nanotubes because of the elimination of alumina. The gas adsorption capacity of both natural and modified halloysite nanotubes was measured quantitatively using N2 adsorption and the Brunauer-Emmett-Teller (BET) method, and the morphology was determined from transmission electron microscopy (TEM) images. The results showed that the modified halloysite nanotube was 7.47 times more efficient at gas adsorption than pristine halloysite. Moreover, the dealumination of the surface increased the inner space. Greatly increased porosity characteristics, including gas adsorption and macroporosity, were obtained through modification by acid treatment.

Metal–organic frameworks (MOFs) possess tuneable properties and a variety of important applications in the areas of catalysis, adsorption, gas storage, and separation, among others. Herein, recent computational studies by density functional theory (DFT) applied for simulations of MOF structure and complex architecture determination, prediction of properties, and computational characterization, including large-scale screening and geometrical properties of hypothetical MOFs, diffusion and adsorption processes in MOFs, are reviewed. DFT calculations have been applied in the MOF area to study chemical stability; mechanical, photophysical, optical, and magnetic properties; photoluminescence; porosity; and semiconductor or metallic character. The prediction of MOF analogs with open-metal sites, studies of chemical bonding and the prediction of energies by quantum mechanics allows reducing experimental efforts in the creation of MOF/polymer membranes, adsorbents for CO2 uptake, separation of C2H2/CH4, C2H2/CO2, and inert gases, radionuclides sequestration, and water adsorption, as well as other promising advances. For the MOF-derived carbons, a lack of profound DFT investigations is currently observed, being mainly restricted to the electrocatalysis area (nitrogen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction), resulting applications in batteries and other storage devices, CO2 sequestration, and absorbance of organic substances.

The surface properties of various synthetic layered silicates, Na-kanemite, Nakenyaite and magadiite, exchanged with H, K and Ca, were examined using high-resolution nitrogen and argon adsorption and the data were treated using the Derivative Isotherm Summation method. Using argon as an adsorbate, the aspect ratio of platelets can be determined. In the case of magadiite exchanged with various cations, the stacking of particles is influenced by the nature of the exchangeable cations, thicker platelets being observed for ions with low polarizability. Highresolution argon adsorption data also confirm some structural information previously deduced from Raman spectroscopy experiments concerning the existence of rather open six-membered rings at the surfaces of both magadiite and kenyaite. Furthermore, in the low-energy domain of the isotherms, argon forms a very organized film on basal planes, suggesting a commensurate relationship between silica framework and argon atoms for both magadiite and kenyaite, contrary to what is observed for kanemite. Nitrogen adsorption results reveal the presence of polar sites on the surface of all the investigated minerals but does not allow us to propose an unequivocal assignment for such sites.

The isoflurane-saving and CO2-retaining effects of a charcoal filter were compared with a Siemens standard heat and moisture (HME) exchanger and an emptied specimen (dummy). Isoflurane was delivered during the inspiratory phase and consumption investigated at 10, 15 and 25 cycles min−1. The investigation was performed by ventilation with humidified air with a constant end-tidal CO2 and temperature. For a comparison, isoflurane was delivered in a conventional manner via the ventilator. The arrangement with a charcoal filter reduced the isoflurane consumption by a factor of 2.0−2.6, depending on ventilatory rate. Most of the saving was a result of the method of isoflurane delivery (factor 1.4−2.0), while adding the reflector gave a further reduction (factor 1.3−1.5). One circumstance that reduced the net efficiency of the charcoal filter was that it also reflected CO2; consequently, total minute ventilation had to be increased to maintain constant end-tidal CO2.