Effects of Surface Functionalities on Gas Adsorption

By more intense oxidation of the carbon, the amount of water vapor adsorbed at low relative pressures ( 4 Torr at 25 °C) can be drastically increased. For example. Walker and co-workers showed a 100-fold increase in water vapor adsorption by activated carbon after strong surface oxidation by HNO3 (Mahajan et al 1982). Exchange of the surface H-ions by cations (Li, Na, K, Ca) on the oxidized carbon further increased the moisture capacity at low vapor pressures to amounts comparable with that on zeolites. The ion-exchanged carbon was fully regenerated at 140 °C, in contrast to temperatures 350 °C that are required for zeolite regeneration (Mahajan et al., 1982). 

Although the effects of oxidation on water adsorption are expected, the effects of incorporation with other atoms do not yield expected results. Mild chlorination of the surface of activated carbon results in slightly more hydrophobicity (Hall and Holmes, 1993). Mild fluorination has shown drastically increased 

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