Effects of surface heterogeneity in adsorption from binary liquid mixtures

Ordered assembly of two different metal clusters with the same topological connectivity in one single coordination network

The introduction of heterogeneous components within one single coordination network leads to the multifunctionality of the final material. However, it is hard to precisely control the local distribution of these different components in such a coordination network, especially for different components with identical topological connectivity. In this study, we successfully achieved the ordered assembly of [Mn3(μ3-O)] nodes and [Mn6(μ3-O)2(CH3COO)3] nodes within one pacs coordination network. The resulting new structure (NPU-6) with heterogeneous metal nodes simultaneously inherits the advantages of both parent networks (good thermal stability and high pore volume). The significant effect of the reaction concentration of competing ligand CH3COO- on the mixed assembly of these two nodes in NPU-6 is revealed by a series of control experiments. This method is anticipated to offer a valuable reference for orderly assembling heterogeneous components in coordination networks.

Microporous Coordination Polymers for Efficient Recovery of Chloromethane from Organic Silicon Industrial Exhaust Gas

Removal and recovery of methyl chloride (CH3Cl) from exhaust gas of organic silicon industry is highly important from the perspective of environment and economy. For the first time, a tailor-made microporous coordination polymer (Mn-BDC-TPA) was synthesized and applied to the efficient capture and recovery of CH3Cl from related gas mixtures. The high adsorption capacity of CH3Cl (163.4 cm3/g) and high adsorption selectivity of CH3Cl over other impurity gases (1965 for N2, 65 for CH4, and 16 for C2H6) were achieved at 298 K and 100 kPa due to the dual-cage pore system and larger polarizability of CH3Cl. Dynamic breakthrough experiments demonstrate the excellent CH3Cl recovery performance (capacity of >98 cm3/g and purity of >95%) in one adsorption-desorption cycle from the CH3Cl-involved binary, ternary, or quaternary gas mixture.

Application of the Dubinin–Radushkevich Equation for Describing Adsorption from Solutions on to Various Carbons

Dozens of papers have been published recently describing adsorption processes from solutions on to solid surfaces, but a certain lack of understanding of this problem is still observed. This article deals with the description of adsorption from binary solutions of non-electrolytes on to solids. This description covers adsorption both on homogeneous and heterogeneous surfaces from ideal and non-ideal liquid mixtures. Some important factors determining the adsorption process, i.e. the heterogeneity of the solid surface, interactions between the species in the bulk and surface phases, differences in molecular sizes of the adsorbate molecules, etc., have been discussed. The main attention has been focused on the Dubinin–Radushkevich equation and its application in the description of adsorption from solutions on to energetically, heterogeneous adsorbents. Numerous model calculations have been reported for this equation and several experimental systems have been analyzed. The application of the Dubinin–Radushkevich equation in characterizing liquid adsorption on to various carbons has been demonstrated.

Nonlinearity of cationic aromatic amine sorption to aluminosilicates and soils: role of intermolecular cation-π interactions

Through the study of substituted anilines and benzylamines, we demonstrated that cooperative cation-π, π-π, and van der Waals interactions can increase aromatic cationic amine sorption to Na/Ca-montmorillonite well beyond the extent expected by cation exchange alone. Cationic amines exhibiting cooperative interactions displayed nonlinear S-shaped isotherms and increased affinity for the sorbent at low surface coverage; parallel cation exchange and cooperative interactions were noted above a sorption threshold of 0.3-2.3% of exchange sites occupied. Our experiments revealed the predominance of intermolecular cation-π interactions, which occurred between the π system of a compound retained on the surface via cation exchange and the cationic amine group of an adjacent molecule. Compounds with greater amine charge/area and electron-donating substituents that allowed for greater electron density at the center of the aromatic ring showed a greater potential for cation-π interactions on montmorillonite surfaces. However, benzylamine sorption to nine soils, at charge loadings comparable to the experiments with montmorillonite, revealed no significant cooperative interactions. It appears that cation-π interactions may be likely in soils with exceptionally high cation exchange capacities (>0.7 mol charge/kg) and low organic matter contents, abundant in montmorillonite and other expanding clay minerals.

Adsorption--from theory to practice

Adsorption at various interfaces has concerned scientists since the beginning of this century. This phenomenon underlies a number of extremely important processes of utilitarian significance. The technological, environmental and biological importance of adsorption can never be in doubt. Its practical applications in industry and environmental protection are of paramount importance. The adsorption of substrates is the first stage in many catalytic processes. The methods for separation of mixtures on a laboratory and on an industrial scale are increasingly based on utilising the change in concentration of components at the interface. Moreover, such vital problems as purification of water, sewages, air and soil are involved here too. On the other hand, many areas in which technological innovation has covered adsorption phenomena have been expanded more through art and craft than through science. A basic understanding of the scientific principles is far behind; in part because the study of interfaces requires extremely careful experimentation if meaningful and reproducible results are to be obtained. In recent years, however, considerable effort has been increasingly directed toward closing the gap between theory and practice. Crucial progress in theoretical description of the adsorption has been achieved, mainly through the development of new theoretical approaches formulated on a molecular level, by means of computer simulation methods and owing to new techniques which examine surface layers or interfacial regions. Moreover, during the last 15 years new classes of solid adsorbents have been developed, such as activated carbon fibres and carbon molecular sieves, fullerenes and heterofullerenes, microporous glasses and nanoporous--both carbonaceous and inorganic--materials. Nanostructured solids are very popular in science and technology and have gained extreme interest due to their sorption, catalytic, magnetic, optical and thermal properties. Although the development of adsorption up to the 1918s has been following rather a zig-zag path, this arm of surface science is now generally considered to have become a well-defined branch of physical science representing an intrinsically interdisciplinary area between chemistry, physics, biology and engineering. This review presents in brief the history of adsorption and highlights the progress in theoretical description of the phenomenon under consideration. The paper deals with the above problems critically, showing the development of adsorption, presenting some of the latest important results and giving a source of up-to-date literature on it. Moreover, in this paper the most important aspects are overviewed referring to today's trends and visions in application of adsorption science in industry, environmental protection and in environmental analysis. The relationship between development of adsorption theory and adsorption practice is pointed out. Current understanding and perspectives pertaining to applications of adsorption phenomena on laboratory and on industrial scale as well as environmental protection are discussed and illustrated by means of a few spectacular examples.