蒙脱石对赖氨酸和壳聚糖的吸附实验研究

The Study of Adsorption of L-lysine and Chitosan on Montmorillonite

粘土矿物对有机质的吸附是自然界重要的过程之一。科学界对于有机质与粘土矿物的相互作用过程和机制研究仍处于一个比较薄弱的阶段。该文采用天然有机质赖氨酸(左旋)和壳聚糖与蒙脱石进行室内合成模拟实验,通过X射线衍射、化学分析和红外光谱分析的手段对反应产物进行系统研究。结果表明,蒙脱石对赖氨酸和壳聚糖的吸附均存在两种机制:阳离子交换和有机分子间的相互吸引。赖氨酸在蒙脱石层间的排布有三种构型,随着赖氨酸浓度的增加分别以倾斜式、垂直呈"之"字形排列,最后形成第二排并可能生成简单肽;氨基酸的净电荷是影响吸附过程的重要因素,主要与p H值相关。壳聚糖能在蒙脱石层间形成分层结构,溶液的p H值和无机盐的存在都会影响吸附过程。壳聚糖-蒙脱石复合体在常温常压下水溶液中能稳定存在,而相同条件下赖氨酸易从蒙脱石层间释放,这主要是由有机质本身的性质以及有机质和蒙脱石的结合方式决定的。

Organic matter adsorbed onto the surface of clay minerals is one of an important process in the natural environment. However, the process and mechanism of the interaction between natural organic matter and clay minerals is highly debated due to its complexity. To solve this problem, natural organic matter of L-lysine and chitosan are intercalated in montmorillonite. Chemical analysis, infrared spectroscopy and X-ray diffraction have been employed in the characterization of the reaction products. Our data indicated that the adsorption of the L-lysine and chitosan is both firstly dominated by cation exchange and secondly by adsorption of electrically neutral forms. For L-lysine, three configurations seem to form. At low concentrations, L-lysine is inclined in the interlayer. As the concentration of L-lysine increases, the molecules orientate perpendicular to the montmorillonitelayers, maybe in a zig-zag arrangement. When the concentration is higher enough, the second row of L-lysine appears and peptides may formed in the interlayer by L-lysine polymerisation. The net charge of amino acids, which depends on the pH value in both the bulk solution and in the proximity of the clay layer or the interlayer space, is an important factor affecting the adsorption process. For chitosan, a layered structure can form in the interlayer of montmorillonite. The pH value of the solution and the presence of the inorganic salt will affect the adsorption process. Chitosan-montmor illonite complexes in aqueous solution at room temperature and atmospheric pressure is stable, but under the same condition, L-lysine is easily released from the interlayer space of montmorillonite, which is related to the nature of the organic matter itself and its form combined with montmorillonite.