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Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.〔(【引用サイトリンク】title=Glossary )〕 This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a fluid (the ''absorbate'') permeates or is dissolved by a liquid or solid (the ''absorbent'').〔(【引用サイトリンク】title=absorption (chemistry) )〕 Adsorption is a surface-based process while absorption involves the whole volume of the material. The term ''sorption'' encompasses both processes, while ''desorption'' is the reverse of it. Adsorption is a ''surface phenomenon''. Similar to surface tension, adsorption is a consequence of surface energy. In a bulk material, all the bonding requirements (be they ionic, covalent, or metallic) of the constituent atoms of the material are filled by other atoms in the material. However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and therefore can attract adsorbates. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (characteristic of weak van der Waals forces) or chemisorption (characteristic of covalent bonding). It may also occur due to electrostatic attraction. Adsorption is present in many natural, physical, biological, and chemical systems, and is widely used in industrial applications such as activated charcoal, capturing and using waste heat to provide cold water for air conditioning and other process requirements (adsorption chillers), synthetic resins, increase storage capacity of carbide-derived carbons, and water purification. Adsorption, ion exchange, and chromatography are sorption processes in which certain adsorbates are selectively transferred from the fluid phase to the surface of insoluble, rigid particles suspended in a vessel or packed in a column. Pharmaceutical industry applications, which use adsorption as a means to prolong neurological exposure to specific drugs or parts thereof, are lesser known. However, it should be remarked that the distinction between adsorption and absorption vanishes as we go from perfectly crystalline macroscopic materials to porous/structured materials, aggregates and composites made out of increasingly smaller grains, viz., micron-sized particles to nanoparticles, sub-nano particles and finally molecules (or atoms). In such nano-composites, the internal surface area of particulate matter is very large. Then the adsorption on internal surfaces simply becomes absorption when viewed from the bulk. Then the distinction between adsorption and absorption vanishes. On the other hand, the distinction is clearest between bulk solids without internal structure, but having only surfaces where only adsorption can occur on the outer surfaces, and nanocomposites or aggregates with internal structure where absorption by the host material is simply adsorption on internal surfaces of the host material. As an example, we may consider a crystalline piece of silicon dioxide (quartz) which can adsorb water molecules on its surface. However, if the quartz is ground into very fine sand, the pile of sand (an aggregate) has a very large internal surface area. A very large amount of water can be adsorbed by the "internal" surfaces of the grains in the pile of sand, and this absorption is simply "internal adsorption. If water is made to flow thorugh such a pile of sand, ions and toxins in the water may be preferentially adsorbed by the surfaces of the grains of sand, providing a simple, well-known water purification application. The word "adsorption" was coined in 1881 by German physicist Heinrich Kayser (1853-1940).〔 . In this study of the adsorption of gases by charcoal, the first use of the word "adsorption" appears on page 527: "Schon Saussure kannte die beiden für die Grösse der Adsorption massgebenden Factoren, den Druck und die Temperatur, da er Erniedrigung des Druckes oder Erhöhung der Temperatur zur Befreiung der porösen Körper von Gasen benutzte." (Saussaure already knew the two factors that determine the quantity of adsorption – () the pressure and temperature – since he used the lowering of the pressure or the raising of the temperature to free the porous substances of gases.)〕 ==Isotherms== Adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (if liquid) at constant temperature. The quantity adsorbed is nearly always normalized by the mass of the adsorbent to allow comparison of different materials. To date, 15 different isothem models were developed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Adsorption」の詳細全文を読む スポンサード リンク
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