关键词: 尼古丁, 吸附, 孔径, 化学特征, 动力学

Abstract:

Adsorption of nicotine from aqueous solution by activated carbons with different pore sizes and chemical properties was studied. Activated carbons were prepared from Chinese fir sawdust by chemical activation with zinc chloride (called AC-Z) or physical activation with steam (called AC-H). The properties of the samples were compared with those of a commercial coconut-based activated carbon, named AC-C. The surface area and pore structure of the samples were determined by a surface area and porosity analyzer, and surface oxygen groups were characterized by Boehm titration. Adsorption experiments were performed under varying contact time, initial concentration, and temperature. The experimental data suggested that micropores, acidic groups, and the metal atoms play important roles in adsorption of nicotine. The different effects of temperature on the three samples also explain the role of the activated sites. The amount of nicotine adsorbed by AC-Z, which contained more activated sites than the other samples, first increased and then decreased with increasing temperature. This is because increased temperature accelerated the decomposition of nicotine molecules and their conjugation with activated sites, but if it became too high, the probability and strength of molecular collisions increased, causing adsorbed molecules to dissociate from activated sites. AC-H and AC-C, which both contained micropores and activated sites, showed different performance. Nicotine was physically adsorbed first: the surface oxygen groups bonded to nicotine molecules, which blocked the micropores of the adsorbents. Pseudofirst order, pseudo-second order, and intraparticle diffusion kinetic models were used to interpret the adsorption mechanism. Kinetic studies showed adsorption of nicotine was rapid and followed a pseudosecond order model. Thermodynamic parameters ΔG⁰, ΔH⁰ and ΔS⁰ were also calculated to predict the nature of adsorption, and indicated that adsorption was endothermic and spontaneous. The low ΔH⁰ values of AC-Z and AC-H show that nicotine molecules interacted strongly with activated sites, so they require less isosteric heat to adsorb the same amount of nicotine as AC-C, and also indicate that the activated sites play a role in adsorption.

Key words: Nicotine, Adsorption, Pore size, Chemical character, Kinetics