Adsorption of pure and mixed CO 2 and N 2 is simulated in a mimetic MCM-41. The full-atom MCM-41 model is constructed by caving cylindrical pores from an amorphous silica matrix and energetically optimized. Dreiding force field is used for the dispersive interaction with the atomic charges estimated from the densityfunctional theory calculations. The optimized MCM-41 maintains a hexagonal array of the mesoscopic pores as evidenced by the three characteristic peaks in the XRD pattern. The pore surface of MCM-41 is corrugated and coated with hydroxyls and defects. The pore size exhibits a Gaussian distribution with an average radius of 14.38 Å close to the experimental value. Simulated adsorption isotherms and isosteric heats of CO 2 match well with the experimental data. CO 2 adsorbs preferentially at the active sites near the pore surface, while N 2 tends to adsorb homogeneously on the pore surface. In CO 2 and N 2 mixture as a flue gas, CO 2 is more adsorbed than N 2 . The selectivity of CO 2 over N 2 drops rapidly with increasing temperature and depends weakly on pressure. At temperatures higher than 400 K, the selectivity approaches a constant and pressure has no discernible effect.

A molecular dynamics simulation study is reported to investigate a CO(2)-induced microstructure transition of surfactant AOT4 in aqueous solution. The lamellar bilayer changes into a spherical micelle induced by CO(2) at ambient temperature, while a thermotropic aggregate transition occurs in the absence of CO(2) above 140 degrees C. In the lamellar bilayer, AOT4 shows a bimodal density distribution. The bilayer thickness and the average area per AOT4 are estimated to be 19.2 A and 83.3 A(2). The AOT4 bilayer possesses a sandwich structure and consists of a hydrophobic region in the center and a hydrated layer on both sides. Upon CO(2) dissolving, the lamellar bilayer is swollen and becomes loose and unstable. CO(2) molecules in the lamellar bilayer are initially near the ester groups of AOT4 and then accumulate in the center of the hydrophobic region. With increasing amounts of CO(2), the AOT4 bilayer expands gradually and the density distribution of each leaflet becomes broader. Driven by surface tension, the lamellar bilayer tends to reduce the surface area. The lamellar bilayer changes into a 3D cubic network in a small simulation box, attributed to the influence of neighboring images. In a sufficiently large box, the lamellar bilayer transforms into spherical micelles. CO(2)-active surfactants such as fluorinated surfactants and oxygenated AOT analogues are proposed to substitute CO(2)-inactive AOT and may reduce the critical pressure in microstructure transition.

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