含硫树状多配体调制催化贵金属纳米束及其补丁约束效应

The activity, durability and recyclability of metallic catalyst lie on the morphological and chemical environment of the metal ligands/supports. This project dedicates to structured ligands to mediate and support green metal nanocluster (NC) catalysts. Introduction of a few thiol/thioether groups to branched polyethylenimine (PEI) so that the thio- and amino groups cooperatively mediate synthesis of quality, active and stable NC nanocoomposite (termed NC-PEI). Slight alkylation of NC-PEI leads to a water-soluble amphiphilic NC composite. The NC-composite can costabilize an oil-in-water emulsion with small surfactants and, after solidification and full washing, NC-composite dictates the surface of the resulting emulsion-based particle as discrete patches. Similarly, for sufficiently alkylated NC-PEI composite, it can lead to an open-cellular monolith via a water-in-oil concentric emulsion, with the monolith’s pore surface dictated by discrete NC-impregnated patches. The discrete patches suppress NC from erosion and ripening. In a word, the dendritic amphiphile can mediate synthesis of quality NC, direct its dictation exclusively on support surface, and confine NC by patch. Such NC is catalytically efficient and well recyclable, and can significantly decrease metal content in either product or medium.

金属催化剂的活性、耐用性和泄漏性取决于其配体/载体的电子结构与物理形态。本项目致力于以结构化载体负载补丁约束的贵金属纳米束(NC)以获取绿色耐用催化材料。在超支化聚乙撑亚胺（PEI）上引入微量强配体硫醇/硫醚，能和氨基弱配体协同作用获得尺寸小、活性高且性能稳定的复合纳米束(NC-PEI)。对NC-PEI进行弱亲油化获得水溶性树状复合两亲体，后者在小分子表面活性剂辅助下共同稳定乳液。待乳液粒固化后除去辅助剂，表面将仅留下由分立树状体补丁约束的NC。反之，对NC-PEI进行充分亲油化，则可通过油包水型浓乳液调制三维通孔骨架，骨架的孔表面类似地仅由分立补丁约束的NC表达。分立补丁能抑制NC的老化和原子态流失。总之，含硫树状配体能调制高质量NC的合成，引导NC在结构化载体表面表达，并作为补丁约束NC。这类易回收NC催化效率高、同时可显著降低产品和介质中的贵金属残留。

高效绿色易回收的金纳米簇催化剂的获取总体上仍然是挑战，其中配体/载体的设计是关键。目前，具有高比表面的金纳米簇大多只能由强配体调制，但强配体抑制其催化活性并窄化其催化谱。本项目采取了新的配体/载体设计策略，期望获得载体化的宽谱高效催化剂。项目将弱的多胺配体以均一的补丁状表达在多孔惰性载体表面，每个补丁由一个多胺大分子构成，因此尺寸均匀。实验表明，这种补丁调制合成金簇时，金原子的自由迁移受到抑制，结果获得颗粒更小更均匀的金颗粒（4 nm）；当进一步在多胺补丁上引入微量的中等强度的配体时，成核作用明显增强，能获得均一的金纳米簇（1.6 nm）。这些纳米簇表现出极高的催化活性（TOF =354/h），且回收方便。该策略可以扩展到更多贵金属和更多配体上。另外，将多胺转变为大分子表面活性剂，可以方便地通过乳液法表达在多孔材料上并进行化学衍生，产生各种吸附剂。例如衍生为多二醇可以吸附淡化海水中的硼酸，衍生为氨基多羧酸可以高效吸附各种硬酸性重金属离子。初步研究表明，进一步衍生为配体性大表面活性剂可以为获得金纳米簇提供更简便的方法。