摘要/Abstract
传统水热法合成的金属有机框架（MOFs）普遍是颗粒尺寸较大的粉末材料，作为多相催化剂虽然便于回收利用，但在液相反应中会存在分散性差、传质阻力大、可接触活性位少的缺点，对催化活性有不利影响.若将MOF多相催化剂均相化，则可兼备均相和多相催化剂的优势.本工作采用了微波辅助合成法成功制备了一种可溶性的卟啉MOF，记为S-Al-PMOF.相比于传统水热法合成Bulk-Al-PMOF需要180℃反应16 h，微波辅助合成法只需140℃反应30 min，更加简单高效.S-Al-PMOF经超声分散可完全溶于乙腈形成澄清的胶体溶液，并且能够一直保持澄清状态而不会聚沉，而Bulk-Al-PMOF分散在溶剂中只能形成悬浊液且很快便会沉降.与此同时，S-Al-PMOF可通过抽滤法从溶液中分离出来，再次超声分散于新的溶剂中则又可以重新形成澄清的胶体溶液，此过程可以重复多次，证明其具有多相催化剂便于分离回收的优势.作为卟啉类MOF，Al-PMOF具有优异的敏光能力，为了验证其同时具备均相和多相催化剂的优势，引入Pd作为共催化剂，测试了S-Al-PMOF在液相光催化分解水制氢反应中的催化性能，并与Bulk-Al-PMOF进行了对比.结果显示，由于能完全溶于液相反应体系，S-Al-PMOF的光催化制氢活性约为Bulk-Al-PMOF活性的14倍，且S-Al-PMOF可以通过抽滤后再溶解分散的方式回收利用，在三轮循环反应的测试中，S-Al-PMOF的活性可以很好地维持.本工作成功实现了可溶性MOF催化剂的制备，为MOF多相催化剂的均相化提供了一种新的思路.
关键词: 金属有机框架, 多相催化剂的均相化, 微波辅助合成法, 光催化, 分解水制氢
Metal-organic frameworks (MOFs), a class of promising heterogeneous catalysts, though readily recyclable, usually suffer from poor dispersity and ease of sedimentation in liquid-phase reaction systems, which may lead to limited exposure of active sites and unsatisfied activity. Conventional hydrothermal synthesis often results in large MOF particles in bulk form and poor dispersity. The homogenization of MOF catalysts is an exciting but challenging task to integrate the advantages of both homogeneous and heterogeneous catalysts. Herein, by means of microwave-assisted synthetic approach, a soluble porphyrinic MOF, denoted as S-Al-PMOF, has been successfully fabricated. In contrast to the Bulk-Al-PMOF synthesized by the conventional hydrothermal route, which requires 180℃ and 16 h, the S-Al-PMOF obtained by the microwave-assisted method is very efficient and takes 30 min only at 140℃. While the as-synthesized S-Al-PMOF can be completely soluble in acetonitrile by ultrasonic dispersion to give a clear and transparent colloidal solution, the Bulk-Al-PMOF can form a turbid suspension liquid by continuous stirring, which easily aggregate with sedimentation in a short time after standing. Furthermore, the S-Al-PMOF can be easily separated from the solution by suction filtration and then re-dissolved in acetonitrile. This separation and re-dissolution process can be repeated several times to prove its good recovery and recycling. Given the outstanding light harvesting ability of Al-PMOF, photocatalytic H2 production by water splitting has been adopted to examine the activity of both S-Al-PMOF and Bulk-Al-PMOF. As a result, the activity of S-Al-PMOF is around 14 times higher than that of Bulk-Al-PMOF, owing to excellent solubility of the former. Moreover, S-Al-PMOF also exhibits good recyclability in the consecutive three cycles of reaction. We believe that the successful synthesis of soluble Al-PMOF opens a new avenue to the homogenization of heterogeneous catalysts.
Key words: metal-organic frameworks, homogenization of heterogeneous catalysts, microwave-assisted synthesis, photocatalysis, water splitting
PDF全文下载地址:
点我下载PDF
