吸附Adsorption

表面原子的配位不饱和，具有剩余力场，表面能较高，吸附外来分子可降低体系的表面自由能，所以吸附通常自发进行（ΔG < 0）；吸附使分子运动受限、熵减小（ΔS < 0），因此吸附一般放热（ΔH < 0），升温不利于吸附。吸附量与压力（或浓度）的关系称为吸附等温线，常用朗缪尔、弗罗因德利希和 BET 方程描述。注意区分吸附（表面）与吸收（体相，如海绵吸水）。

Surface atoms are coordinatively unsaturated, with residual force fields and high surface energy, so taking up foreign molecules lowers the surface free energy and adsorption is usually spontaneous (ΔG < 0); it restricts molecular motion (ΔS < 0), so it is generally exothermic (ΔH < 0) and disfavoured by heating. The relation between amount adsorbed and pressure or concentration is the adsorption isotherm, commonly described by the Langmuir, Freundlich and BET equations. Adsorption (at a surface) differs from absorption (into the bulk, as a sponge takes up water).

古埃及已用木炭净化饮水。1773 年舍勒观察到木炭吸附气体，1785 年洛维茨发现木炭可使溶液脱色。1881 年凯泽创造 adsorption 一词。1916 年朗缪尔提出单分子层吸附理论，因表面化学研究获 1932 年诺贝尔化学奖。1938 年布鲁诺尔、埃米特和特勒提出多分子层吸附的 BET 理论。

Ancient Egyptians purified water with charcoal. Scheele saw charcoal take up gases in 1773, and Lowitz found it decolourises solutions in 1785. Kayser coined the word adsorption in 1881. Langmuir proposed monolayer adsorption theory in 1916 and received the 1932 Nobel Prize in Chemistry for surface chemistry, and Brunauer, Emmett and Teller proposed the BET theory of multilayer adsorption in 1938.

吸附广泛用于水和空气净化（活性炭）、防毒面具、干燥（硅胶、分子筛）、气体分离（变压吸附制氧和制氢）、色谱分离、催化（多相催化的第一步是反应物的化学吸附）、比表面积和孔径测定，以及碳捕集和储氢材料（金属有机框架）。

Adsorption is used to purify water and air (activated carbon), in gas masks, for drying (silica gel, molecular sieves), for gas separation (pressure-swing adsorption for oxygen and hydrogen), in chromatography, in catalysis (the first step of heterogeneous catalysis is chemisorption of reactants), to measure surface area and pore size, and in carbon-capture and hydrogen-storage materials such as metal–organic frameworks.