金属有机骨架材料(Metal-Organic Frameworks,MOFs)是一类由无机金属离子与有机配体通过配位作用自组装形成的具有周期性网络结构的多孔晶体材料。MOFs除了具有高比表面积、结构可设计性和功能可编程性等特点,同时存在热稳定性和化学稳定性较差等缺点。为此,科学家们将MOFs与各种功能材料进行复合制备出一系列多功能纳米复合材料,不仅解决了以上问题,而且拓宽了MOFs基新材料的应用领域。本论文基于MOFs与不同的功能材料进行复合,开展了一系列工作,主要针对MOFs基复合材料在催化、人工模拟酶和生物医学领域的应用进行了系统地研究。主要取得以下三部分成果: 一、以金属有机骨架材料Zeolitic imidazolate frameworks-8(ZIF-8)为基底材料,采用原位合成法制备了碳稳定钯的非均相纳米复合催化剂[Pd/ZIF-8]@C。该复合催化剂可以直接用于烯烃的加氢反应,其中碳的存在可以有效阻碍反应过程中钯纳米粒子的迁移与团聚,提高了钯纳米粒子的催化活性;ZIF-8的多孔结构有利于反应过程中反应物与生成物的传输。经过五次循环反应,与无碳稳定的催化剂和商业的Pd/C催化剂相比,[Pd/ZIF-8]@C仍能保持较高的催化活性和更加优异的循环稳定性。 二、以物理化学性质稳定的锆基金属有机骨架材料UiO-66-NH₂为基底材料,采用后合成修饰法制备了类谷胱甘肽过氧化物酶的模拟酶复合催化剂UiO-66-Se。模拟酶催化研究表明,接枝在MOFs骨架上的含硒分子能够提供更多的催化活性中心,提高反应的效率;此外,MOFs的孔道能为催化过程中分子的传输提供一个很好的路径。该模拟酶复合催化剂基于固体MOFs材料,可以实现多次循环回收使用的目的,不仅节约了成本,而且循环使用的模拟酶催化剂仍能表现出高效的类酶活性。 三、以具有pH响应性的金属有机骨架材料ZIF-8和具有氧化还原响应性的含硒高分子为基础材料,制备了一种智能的多级刺激响应性纳米药物缓释材料P@ZIF-8,可以实现药物的可控释放。研究表明,P@ZIF-8复合药物缓释材料需在pH和氧化/还原剂的共同作用下,实现抗癌药物阿霉素的释放,同时限制其单一刺激释放过程,有利于药物缓释材料到达特定的病变部位进行释放。由于肿瘤细胞附近的环境极其复杂,因此多级刺激响应性的特点使得药物缓释材料能够更加准确的定位到病变部位,从而进行靶向治疗。相比于其它多孔材料,MOFs的种类多样性也为其在生物医学方面的研究和应用提供了更多的选择性。此外,该多级响应性复合材料的合成相对简单,所采用的两种功能材料均具有生物可降解性,表现出非常好的应用前景。 关键词:金属有机骨架材料 纳米复合材料 贵金属催化 人工模拟酶 药物缓释
Metal-organic frameworks (MOFs), which are composed of metal ions and organic ligands, have received considerable attention because of their attractive characteristics, like high surface area, well-defined porosity and special functional programmability. However, the poor thermal and chemical stability hinder the applications of MOFs in many fields. To address the above limitations, nanocomposites that combine MOFs with various functional materials have been made. Such nanocomposites can provide new unique features and extend the applications. The dissertation is focused on addressing some problems existed in the catalysis, enzyme mimic and biomaterials. The work is divided into three parts as follows: Firstly, an effective in situ approach for preparing heterogeneous catalysts from ZIF-8 supported carbon-stabilized Pd nanoparticles (NPs). Due to efficient stabilization by the carbon matrix, the migration and agglomeration of Pd NPs onto the ZIF-8 can be limited, and the [Pd/ZIF-8]@C catalysts have exhibited high activity in the hydrogenation of olefins. In addition, the porous channels of ZIF-8 improve the transfer of substracts and products. Compared with Pd/ZIF-8, [Pd/ZIF-8]@C can be used 5 times without significant loss of the catalytic activity, showing a satisfactory reusability. Secondly, a general and facile method to fabricate efficient catalysts acting as GPx mimics by grafting selenium-containing molecules to a Zr-based UiO-66-NH₂ frameworks. In this enzyme mimic system, the selenium-containing molecules served as function donators, while the MOFs with high specific surface area and uniform porosity supplied more catalytic active centers to create a special catalytic environment, which resulted in a high catalytic activity. In addition, the selenium-containing MOFs enzyme mimic exhibited good reproducibility and cycling stability due to the structural stability. Thirdly, a facile approach for preparing multiple stepwise responsive drug release carriers by combining selenium-containing polymers with a redox-triggered property and ZIF-8 with a pH-triggered property, which together formed a promising platform for controlled drug release. In the presence of external redox agents and pH stimuli, the novel drug release carrier could release encapsulated Doxorubicin (DOX) and exhibit good selectivity to release DOX in acidic environment. Given that the encapsulated DOX needed to diffuse into ZIF-8 structures before release, the ZIF-8 shell played a significant role in prolonging the release period. The as-prepared P@ZIF-8 displayed excellent biocompatibility, good loading capacity, and controllable drug release and was therefore suitable for DOX storage/release as a smart drug delivery system. KEYWORDS: Metal-organic frameworks; Nanocomposites; Nobel metal catalyst; Enzyme mimic; Drug delivery