Isotherms, kinetics and thermodynamics for adsorption of pyridine vapors on modified activated carbons

The adsorption isotherms of pyridine have been determined gravimetrically on different samples of granulated, fibrous and spherical activated carbons. Several chemical treatments such as oxidation, degassing and impregnation have been carried out on as-received activated carbon cloth (ACC) so as to modify the surface characteristics of the activated carbon. The porous and chemical structure of modified and unmodified activated carbons has been characterised by XRD, TGA–DTG, SEM and pore size distribution techniques. The adsorption increases on oxidation while decreases on degassing which can be correlated to increase and decrease in the concentration of surface oxygen groups. Loading with Ag⁺ and Cu²⁺ increases the adsorption of pyridine compared with the unloaded sample while loading with Cr⁶⁺ decreases the adsorption of these vapors. The adsorption–desorption branches of pyridine vapors on metal impregnated do not meet even at zero relative vapor pressure indicating the chemisorption or other specific interactions. The adsorption kinetics data has been examined using the linear driving force and empirical diffusion models. The initial decrease in isosteric enthalpy of adsorption for modified and unmodified ACC indicates the effect of surface heterogeneity and later increase indicates the influence of lateral interactions between adsorbate molecules. The results suggest that the adsorption of pyridine involves the physisorption as well as specific interactions with carbon oxygen functional groups and metal complexes present on the carbon surface.