Adsorption at gas-solid interfaces is considered in the framework of the Ono-Kondo lattice density functional theory (DFT). A lattice model is derived and applied to macro-, meso-, and microporous adsorbents by imposing different boundary conditions. It is shown that this lattice theory can predict the entire spectrum of behavior observed when gases, liquids, or supercritical fluids adsorb on solid surfaces.; In Chapter 1, using this lattice theory to study a systematic analysis of adsorption behavior is able to predict steps in the isotherms, scaling behavior near saturation conditions, supercritical behavior, and adsorption hysteresis. This analysis leads to a new classification of isotherms for gas-solid equilibria.; In Chapter 2 and 3, adsorbate-adsorbate interactions are analyzed in the framework of off-lattice version of Ono-Kondo model. A new phenomenon, surface compression of adsorbates, is discussed for gases adsorbed on solids. The strong attraction to a surface causes adsorbate molecules to attain much higher densities than that of a normal liquid. Under these conditions, adsorbate molecules are so compressed that they repel each other. This phenomenon is discussed in terms of experimental data, results of Monte Carlo simulations, and theoretical models.; In Chapter 4, a lattice DFT based upon Ono-Kondo theory is used with appropriate boundary conditions for fluid adsorption in slit-like pores of various sizes. It is shown that a lattice DFT can predict adsorption isotherms with hysteresis loops and that different types of hysteresis loops can be obtained by varying energies of adsorbate-adsorbate and adsorbate-adsorbent interactions for different widths and lengths of slit-like pores. A lattice DFT also predicts hysteresis loops with multiple steps. Though such behavior has not been art of the characterization of isotherms with hysteresis loops, there are experimental data that exhibit steps within hysteresis loops.
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