功能化枝状复合材料的设计合成及吸附重金属性能和构效关系研究

The mesoporous silica-based adsorbents were studied extensively due to their unique large surface areas, well-defined pore sizes and pore shapes as well as well-modified surface properties. Nowadays, more and more attraction has been focused on the function of mesoporous silica (SBA-15 and MCM-41) with various organic groups for effective adsorption of heavy metal ions. Polyamidoamine (PAMAM) dendrimers are highly branched, well-defined, synthetic macromolecular available in nanometer dimensions, which consist of globular macromolecules with three covalent bind components: a core, interior branch cells and terminal branch cells. PAMAM is a unique chelating agent because of its high density of nitrogen ligands and the possibility of attaching functional groups, such as primary amines, carboxylates and hydroxymates, which can result in a substantial increase of bonding capacity for a variety of toxic metal ions. But the dendrimers have to.be recycled by ultrafiltration membrane, which is inconvenient and expensive in application for removal of heavy metal. The project is synthesizing with PAMAM-SBA-15 and 2,3-Dimercaptosuccinic acid（DMSA）modified SBA-15 inorganic-organic hybrid materials for the removal of metal ions. Through the structural analysis of functional PAMAM-SBA materials and heavy metal adsorption properties, optimizations of synthesis and adsorption conditions are needed to improve heavy metal adsorption properties and adsorptive selectivity. Supported PAMAM-SBA-15 would enhance adsorption performance of heavy metal ions and can be easily recycled and reused. Through study of the active sites, adsorption strength , surface properties of the adsorbent materials and the nature of heavy metal ions , the structure-activity relationships and adsorption mechanism of adsorption will be revealed. The studies will be helpful for providing theoretical.basis for the design and synthesis of new adsorbent materials.

介孔分子筛材料含有均匀的孔道和排列整齐的孔穴及较高的比表面积和孔容等特点，具有较强的吸附能力和吸附性能；PAMAM化合物属于胺型树枝状高分子，其结构中含有多个胺基官能团，且可形成笼状结构，与重金属离子配位可形成稳定性很强的螯合物，有利于重金属的吸附。然而PAMAM材料需通过回收，成本较高。本项目主要以可调控孔道结构的SBA-15、MCM-41等无机介孔材料为载体，通过化学修饰方法在介孔分子筛孔道中，合成具有枝状结构和笼状结构化合物，并通过化学嫁接改性，嫁接活性基团（如巯基、胺基、羧基等），增加吸附活性位点，并通过形成多个螯环增强吸附能力。通过负载型枝状化合物的合成即增强了对重金属的吸附，同时可通过过滤的方法使吸附剂得以回收，重复利用。通过深入研究活性吸附位、吸附强度、吸附材料表面性质等与重金属离子性质之间的关系，掌握吸附材料的构效关系及吸附机理，为新型吸附材料的设计与合成提供理论依据。

水溶液中重金属去除越来越受到广泛关注。项目利用介孔分子筛具有均匀孔道和较高比表面积及胺型枝状高分子含有多个胺基等优点，以SBA-15等为载体，通过Michael加成和氨化等方法嫁接活性基团（如巯基、胺基等）在孔道中，成功合成枝状高分子吸附剂SBA-15-G3、SBA-15-G3-SH等，采用FT-IR、XRD等进行表征；研究了浓度、温度、pH、离子强度、重金属离子等对吸附影响和再生、循环使用性能；研究了吸附等温线、动力学及热力学参数，计算ΔGθ、ΔHθ等，推断速控步骤，研究了吸附机理。SBA-15-G3对水溶液中的Cr（VI）在pH=2.8，温度298 K，吸附量为39.09 mg·g-1。Zeta电位表明， SBA-15-G3在酸性条件下电位随着pH降低而升高，这是由于吸附剂表面的大量伯胺和次氨基团与H+离子相互作用，易形成阳离子-NH3+基，pH升高时溶液中H+减少，导致吸附剂表面阳离子基减少。FT-IR结果表明在1560和3091 cm-1处吸收峰归属于-NH的弯曲振动和-NH2的伸缩振动。在SBA-15-G3吸附剂的基础上，用巯基乙酸对其改性，成功地引入巯基合成具有高性能性能的SBA-15-G3-SH，其对Cr（VI）的吸附性能明显提升，在pH=2.3，温度298 K，吸附量高达163.54 mg·g-1；FESEM、EDS、FT-IR、XRD的表征结果表明，SBA-15-G3-SH上成功地接枝了-NH2和-SH官能团，且对Cr（VI）的吸附性能明显提升。吸附过程符合Langmuir吸附模型和准二级动力学方程，相关系数达0.999左右。ΔHθ为负值，表明SBA-15-G3和SBA-15-G3-SH对Cr（VI）的吸附是放热反应。研究并揭示吸附反应机理，吸附作用主要归因于接枝的巯基、胺基等与重金属离子间表面络合作用。离子强度对吸附性能影响的实验表明，吸附剂表面与溶液中重金属离子之间可能还存在一定的静电相互作用，也有利于重金属吸附。还对壳聚糖进行了改性，通过水热共沉淀形成磁芯，再经活化，将氨基固定在壳聚糖层表面，成功合成易回收、较好吸附性能的磁性壳聚糖吸附剂HA-MG-CH，其对Cr（VI）吸附量达55.25 mg·g-1。具有易回收，不易造成二次污染优点。项目的实施为新型吸附材料设计、合成提供了理论依据，对水资源污染的防治及修复将起到一定的促进作用。