基于纳米纤维素模板的多级孔分子筛的制备机理及构效关系研究

With rapid development of industrialization and urbanization, the problem of water pollution has intensified and there is an urgent need to develop high efficient sewage treatment for the increasing wastewaters. . Due to its high affinity to various contaminants, zeolites are widely used in the field of wastewater treatment. However, the mass transfer during the adsorption process is seriously inhibited by the small size of micropores inside zeolites, which leads to high transport resistance and low adsorption efficiency. To cope with drawbacks resulting from zeolite microporosity, extra levels of porosity is introduced into the structure of zeolite to form hierarchical zeolite, since mesopores or macropores facilitate the transport and address mass transfer limitations. . In this project, hierarchical zeolites of different pore structures will be synthesized by hydrothermal method via nanocellulose templates of various sizes and shapes. The micro morphology and crystal structure will be characterized by scanning electron microscopy, X-ray diffraction spectra and high resolution transmission electron microscopy. The effect of size, shape, and surface functional groups of nanocellulose onto the crystal growth, crystal structure and micro morphology of zeolite will be carefully investigated. Furthermore, adsorption performance of different size water contaminants onto hierarchical zeolites of different pore structures will also be discussed. Thereafter, the structure-function relationship will be established among the shape structure of nanocellulose, the pore structure of hierarchical zeolite and the adsorption properties of pollutants.. The characteristic and innovation of the project is to design and prepare nanocellulose templates for new structure zeolites, and to figure out the relationship between structure of zeolites and size of contaminants. The research findings will not only enrich the present preparation methods and synthesis mechanisms of hierarchical zeolites, but also provide theoretical basis and technical support for the application of hierarchical zeolite in the field of wastewater treatment.

水污染治理是摆在国人面前的一道必答题，在各种探索高效低成本治理水污染的尝试中，分子筛以其良好的吸附能力而被广泛采用。.传统分子筛普遍存在孔径小、传质阻力大、吸附效率低的问题，限制其吸附效率提升。本项目以结构形态多样的纳米纤维素为模板，通过水热法制备多级孔分子筛，达到显著改善传质性能，提高吸附效率的目的。主要研究纳米纤维素形态、尺寸、表面官能团对分子筛晶体生长、微观形貌、结构的影响规律，继而研究不同孔道结构的多级孔分子筛对不同尺寸水体污染物的吸附特性，建立纳米纤维素模板结构形态→分子筛孔道结构→污染物吸附特性三者间的构效关系。.本项目特色和创新在于对纳米纤维素模板进行设计和制备，通过模板结构的变化制备新结构的多级孔分子筛，进而明确分子筛结构与不同尺寸和特性的污染物之间的作用关系。项目研究成果将丰富多级孔分子筛的制备方法和机理，为多级孔分子筛更广泛地应用于水污染治理提供理论依据和技术支持。

作为应用广泛的吸附剂材料，传统分子筛普遍存在孔径小、传质阻力大、吸附效率低的问题，限制其吸附效率提升。在微孔分子筛中引入介孔或大孔结构形成多级孔分子筛被认为是解决微孔分子筛扩散限制最有效的方法。.本项目以自然界中存在广泛的纤维素为模板剂制备多级孔分子筛材料，研究纤维素的形貌、尺寸、表面性质对分子筛晶化生长的影响机制，并以Cd2+为探针污染物，研究多级孔分子筛的吸附性能，在此基础上探索纤维素模板剂形态结构-多级孔分子筛形貌结构-材料对污染物吸附特性之间的构效关系。.研究结果表明：1）纤维素的形貌和尺寸决定了产物分子筛的微观形貌和结构，当尺寸在微米量级的微晶纤维素（MCC）为模板剂时，产物分子筛包覆在其表面形成葡萄串状团簇结构，而直径在几十到几百纳米的纳米纤维素（NCC）或纤维素超细纤维（CSF）为模板剂时，纤维素被包裹在产物分子筛晶体结构中，通过焙烧处理去除纤维素可在微孔分子筛晶体内部形成介孔、大孔孔道结构；2）纤维素表面改性可以增强产物分子筛晶体和纤维素表面的结合，避免二者在晶化过程中发生两相分离；3）纤维素的尺寸、表面改性和焙烧处理均会影响产物分子筛的吸附性能，以NCC为模板剂的产物分子筛对Cd2+的分配系数比以MCC为模板提高至少两个数量级，纤维素改性提升了产物的吸附能力，焙烧后产物的Cd2+分配系数较焙烧前提升40%以上；4）在分子筛合成过程中添加改性纤维素NCC或CSF可显著提高材料的传质效率，在吸附100 ppm的Cd2+溶液时仅需15 min就可基本达到吸附平衡，较同类型传统微孔分子筛所需时间（80 min）缩短81.3%；5）动力学分析表明，不同于原始微孔分子筛在传质中粒内扩散为决速步，基于NCC和CSF的多级孔分子筛的主要限速步骤为膜扩散。.该项目研究展现了纤维素基多级孔吸附在水污染治理领域的应用潜力，也为纤维素为模板剂的其他功能材料的制备提供理论依据和技术指导。