Water coadsorption effect on the physical adsorption of N2 and O2 at room temperature on carbon molecular sieve fibers

The effect of water vapours on the physical adsorption of nitrogen and oxygen from air, on the surface of an activated carbon molecular sieve fibre, was studied by temperature-programmed desorption mass spectrometry with a supersonic molecular beam inlet system. During exposure of the carbon surface at room temperature to moist air, the adsorption kinetics for oxygen and nitrogen are fast, with oxygen being slightly faster, however, the water adsorption kinetics are much slower. When water starts to fill the pore volume, the adsorbed nitrogen and oxygen are removed, with oxygen being more easily removed. At high relative humidity, hydrogen bonding between neighbouring water molecules leads to the formation of clusters of adsorbed water, which trap the nitrogen molecules and form new sites for nitrogen adsorption. The effect of surface modification of carbon molecular sieves, by evacuation at high temperatures, on the adsorption sites of nitrogen and oxygen was also explored.