杉木活性炭吸附处理水溶液中的尼古丁

用不同孔径及化学性质的活性炭对尼古丁水溶液进行吸附研究. 以杉木屑为原料, 分别用氯化锌化学活化法和水蒸气物理活化法制备活性炭, 并分别命名为AC-Z和AC-H. 同时选用椰壳基商品活性炭作为对比吸附剂, 命名为AC-C. 采用比表面积孔径测定分析仪及Boehm滴定法对活性炭进行表征, 分别测定其比表面积、孔径分布和表面官能团含量. 吸附实验主要考虑吸附时间、温度和尼古丁溶液的初始浓度三个因素, 实验数据分析结果表明微孔有利于物理吸附的进行, 而表面酸性官能团及金属原子作为吸附活性位的作用更加重要. 由改变温度对各样品的吸附量影响也能说明活性位在吸附中的作用. AC-Z拥有较多的活性位, 温度变化时尼古丁的吸附量先升高后减小, 这主要是由于适合的温度能加快尼古丁分子的离解并促使其与活性位相结合, 而过高的温度会造成尼古丁分子动能增加, 导致分子间碰撞的机率和强度增大, 使吸附在活性炭表面的尼古丁分子脱落. AC-H和AC-C由较多的微孔和不同程度的活性位组成, 优先发生物理吸附, 并且伴随发生吸附剂表面分子团簇现象, 其吸附趋势与AC-Z相反. 动力学研究表明活性炭对尼古丁的吸附反应非常迅速, 并且符合准二阶动力学程模型. 各热力学参数ΔG⁰, ΔH⁰和ΔS⁰的计算结果表明吸附剂对尼古丁的吸附为吸热和自发性过程.AC-Z和AC-H的ΔH⁰值远低于AC-C, 说明吸附剂表面的活性位对尼古丁分子有强烈的吸引作用, 所以吸附相同数量吸附质分子所需的吸附热更小, 这也说明了活性位在吸附过程中发生作用.

Adsorption of Nicotine from Aqueous Solution by Activated Carbons Prepared from Chinese Fir Sawdust

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.