基于微观结构重构的纳米层叠薄片状Linde F (K) 沸石的合成及其对重金属的强化吸附机制

Linde F (K) zeolite is a new product gaining from strong potassium hydroxide hydrothermal environment. The zeolite owns rich active adsorption sites. Heavy metal pollution has become a serious threat to human health and environment. Early experiments show that Linde F (K) zeolite could adsorb some heavy metals. However, due to its microcosmic structure, the adsorption properties of Linde F (K) zeolite for heavy metals have not been fully showed and absorption potential has been seriously limited. The main aim of this project is to prepare a special Linde F (K) zeolite which has multilamellar stacking nanosheets morphology through optimizing and reconstruction its microcosmic structure. Then, its ability to strengthen heavy metals adsorption and adsorption mechanism will be studied. In the preparation process, a diquaternary long-chain organic compound will be used as a structure-directing agent, by which the microcosmic structure will be transferred from regular hexahedral structure to multilamellar stacking nanosheets. The inside adsorption sites will be activated and diffusion resistance of the adsorption process will be reduced. On the basis of a comprehensive analysis of microscopic and macroscopic properties of multilamellar stacking nanosheets zeolite, its effects on strengthening heavy metals adsorption will be proved. Then, with the help of modern analytical technologies, an advanced “step and step” adsorption isotherm equation which is developed from classical isotherm equations will be applied to study special enhanced adsorption mechanism of multilamellar stacking nanosheets zeolite.

Linde F(K)沸石是在强氢氧化钾水热环境下合成的一种新型沸石，具有较为丰富的吸附活性位点。重金属污染对人体健康和生态环境构成严重威胁。前期研究表明，Linde F(K)沸石对重金属具有吸附作用。然而，由于其微观结构的限制，Linde F(K)沸石对重金属的吸附性能并未得到完全发挥。本项目通过优化重构Linde F(K)沸石的微观结构，制备具有纳米层叠薄片状特殊形貌的Linde F(K)沸石，并研究其对重金属的强化吸附能力。在制备过程中引入具有双特征官能团长链有机物作为结构模板，使沸石的微观结构从四棱柱状转变成纳米层叠薄片状，激发其内部吸附活性位点，减小吸附过程扩散阻力。在分析纳米层叠薄片状Linde F(K)沸石各种特性的基础上，通过实验证明其对重金属的强化吸附效应。在强化吸附机制的研究过程中引入以经典方程为基础的“进阶式”吸附等温线方程，辅以现代分析手段，阐明其特殊强化吸附机制。

重金属元素是废水中常见的污染物之一。Linde F(K)沸石材料可有效吸附液相中存在的重金属元素。本项目在沸石合成过程中加入丙撑基双[十八烷基二甲基氯化铵]作为模板剂的基础上，通过合成条件优化，在没有改变基本晶体结构的前提下，将Linde F(K)沸石材料的微观尺寸从微米级别降低至纳米级别，合成出了具有层叠结构的纳米Linde F(K)沸石材料，该材料对重金属元素具有良好的吸附效果。提高溶液pH值和温度可有效提高吸附效果和速率。吸附过程的表观动力学符合准二级动力学模型。吸附过程存在内扩散和外扩散两个扩散动力学阶段。在竞争中越是占优势的离子，其保持自身吸附过程的能力越强，而在竞争吸附中越弱势的离子，由于强势离子的干扰，越是无法保持自身的吸附过程。通过引入“进阶式”方程的概念，建立了适用于解释纳米K沸石强化吸附重金属过程的“进阶式”吸附等温线方程。数据拟合结果表明，重金属离子在纳米K沸石上的吸附过程和重金属离子之间的干扰作用被限制在类Langumiur吸附等温线模型的框架下进行。不同初始浓度条件下，重金属离子的竞争优势各不相同，其直接影响各重金属离子在多元吸附体系中的吸附行为。