Water Vapour Adsorption of Microporous Carbon Films Prepared from Fluorinated Aromatic Polyimides

The adsorption of water vapour onto microporous carbon films derived from fluorinated aromatic polyimides was studied at 25 degrees C over the relative pressure range 0-0.95. The carbon films prepared were microporous with a high micropore volume ranging up to 0.44 ml/g and a sharp pore-width distribution at ca. 0.6 nm. The adsorption/desorption isotherm of water vapour onto the carbon films was of type V with slight hysteresis. The carbon films derived from fluorinated polyimides were found to exhibit a much higher water vapour adsorption at low relative pressure regions relative to commercially available activated carbon fibres, with their saturated adsorption capacities being dependent on their micropore volumes. The microporous carbon derived from the polyimide with the highest fluorine content (31.3 mass%) showed the highest saturated adsorption capacity of ca. 465 mg/g, with 90 mass% of the water vapour being adsorbed at a relative pressure below 0.46. Both the high micropore volume and the high water vapour adsorption were maintained even after heat treatment at 1300 degrees C, although the steep uptake of water vapour was shifted to higher relative pressures to some extent.