Adsorption behavior of propylamine on activated carbon fiber surfaces as induced by oxygen functional complexes.
In this study, the surfaces of activated carbon fibers (ACFs) were modified by nitric acid to introduce surface oxygen complexes and to observe the influence of those complexes on the propylamine adsorption of the ACFs. It was found that the oxygen complexes including carboxylic and phenolic groups were predominantly increased, resulting in the increase of total surface acidity. However, the specific surface areas and the total pore volumes of the modified ACFs were decreased by 5-8% due to the increased blocking (or demolition) of micropores in the presence of newly introduced complexes. Despite the decrease of textural properties, it was found that the amount of propylamine adsorbed by the modified ACFs was increased by approximately 17%. From the XPS results, it was observed that propylamine reacted with strong or weak acidic groups, such as COOH or OH, on the ACF surfaces, resulting in the formation of pyrrolic-, pyridonic-, or pyridine-like structures.
Role of surface oxygen groups in incorporation of nitrogen to activated carbons via ethylmethylamine adsorption.
Coal origin and wood origin activated carbons were used in this study. To broaden the spectrum of surface features, the surface of the initial samples was modified using oxidation with nitric acid or impregnation with urea followed by heat treatment. Boehm and potentiometric titrations, thermal analysis, and sorption of nitrogen were used to characterize the pore structure and surface chemistry. Then adsorption of ethylmethylamine from aqueous solutions was carried out without controlling the pH of the carbon suspension. The isotherms were measured at 299 K and fitted to the Freundlich equation. The results showed that the amount of ethylmethylamine adsorbed on all carbons at a high concentration is dependent on the total number of surface groups whereas at low concentration it depends on the type of surface groups. The latter was observed exclusively for initial and oxidized carbons where acidic groups are present. The ethylmethylamine adsorption is mainly governed by dipole-dipole, hydrogen bonding, or specific acid-base interactions. Those interactions play a crucial role in incorporation of nitrogen to the carbon matrix at elevated temperatures.
Adsorption of NH3 onto activated carbon prepared from palm shells impregnated with H2SO4.
Adsorption of ammonia (NH3) onto activated carbons prepared from palm shells impregnated with sulfuric acid (H2SO4) was investigated. The effects of activation temperature and acid concentration on pore surface area development were studied. The relatively large micropore surface areas of the palm-shell activated carbons prepared by H2SO4 activation suggest their potential applications in gas adsorption. Adsorption experiments at a fixed temperature showed that the amounts of NH3 adsorbed onto the chemically activated carbons, unlike those prepared by CO2 thermal activation, were not solely dependent on the specific pore surface areas of the adsorbents. Further adsorption tests for a wide range of temperatures suggested combined physisorption and chemisorption of NH3. Desorption tests at the same temperature as adsorption and at an elevated temperature were carried out to confirm the occurrence of chemisorption due to the interaction between NH3 and some oxygen functional groups via hydrogen bonding. The surface functional groups on the adsorbent surface were detected by Fourier transform infrared spectroscopy. The amounts of NH3 adsorbed by chemisorption were correlated with the contents of elemental oxygen present in the adsorbents. Mechanisms for chemical activation and adsorption processes are proposed based on the observed phenomena.