Metal-organic Frameworks-based Functional Composite Nanomaterials And Their Properties

As a class of porous crystalline materials formed by organic linkers coordinated with metal ions,metal-organic framework(MOF)has attracted intense attention in the past two decades due to its wide application.Recently,combining MOFs with other functional materials to construct MOF-based composite materials has become a blooming research filed.Owing to the synergistic effect,MOF-based composites usually exhibit enhanced or novel properties in some fileds compared with single component counterparts.In order to efficiently and directionally synthesize specific MOF-based composites for specific applications,it is the key to construct well-defined composites and build up their structure-function relationship.For this,this dissertation aims to develop some new methods to accurately control the fabrication of wellstructured MOF-based composites and to identify their structure-function relationship in practical applications.The main results and conclusion are listed below:1)Two kinds of composite catalysts,Pt@ZIF-8 and Pt@ZIF-71,were synthesized with Pt nanoparticles embedded in a flexible or ripid MOF matrix by encapsulation method,respectivley.In the selective hydrogenation of cinnamaldehyde(CAL),owing to the confinement effect of the MOF aperture,the two composite catalysts have high catalytic activity for selective hydrogenation of CAL to cinnamyl alcohol under mild conditions.Moreover,the catalyst with Pt NPs embedded in flexible matrices(i.e.,Pt@ZIF-8)was found to exhibit higher conversion but lower selectivity compaired to the catalyst with embedded in rigid matrices(i.e.,Pt@ZIF-71),which is due to the difference of two MOF shell in strucatural flexibility.2)The flower-like Rh-Ni@MOF catalysts(RhNi@MOF-74)were successufully fabricated by a facile templated dealloying strategy.In this case,the encapsulation state and thickness of MOF shells around the Rh-Ni alloy could be finely controlled by tuning the Ni content in pre-synthesized Rh-Ni self-sacrificial template.With the high surface area of Rh-Ni nanoflowers and the confinement effect of MOF shell,the asprepared Rh-Ni@MOF-74 catalysts exhibited high efficiency in selective hydrogenation of diphenylacetylene to cis-stilbene.3)Two kinds of NP@MOF composites,RhCoNi@ZIF-67(Co)and RhCoNi@MOF-74(Ni)were successfully constructed by using RhCoNi ternary alloy as self-sacrificial template.In the dealloying process,Co or Ni element could be selectively dissoloved by choosing different ligands as etching ageats,thereby forming different MOF shell on the surface of RhCoNi alloy.The as-synthesized RhCoNi@MOFs composites offered us a potential platform to systematically study the relationship between the performance of composites and the structure of MOF shells.In this work,two different size alkenes,1-hexene and cyclohexene,were chosen as probe molecules to test their catalytic performance in hydrogenation reactions.Due to different pore structure of MOFs shell,the two composites showed different selectivity to different sizes of substrate molecules in olefin hydrogenation.4)A well-designed nonenzymatic electrochemical sensor PtCu@MOFs/C,in which PtCu alloy supported on the electro-conductive porous carbon(PC)support was armored by a Cu-based MOF shell,was fabricated via a self-sacrificial templated route.The electrochemical tests showed that this unique MOF-surrounding PtCu heterostructure could be used as an artificial enzyme electrochemical sensor.Compared to unmodified sensor,it exhibited better selectivity and anti-interference capacity in H2O2 detection.Strikingly,this new electrochemical sensor showed an obvious response in the detection of H2O2 generated from living tumor cells.It means that this sensor has a potential application in the high selective detection of H2O2 in complex biological systems.5)A novel multifunctional composite catalyst(PtNi@MOF-74-POM)was constructed by a modified self-sacrificial templated method.Structurally,there are two different kinds of active materials,PtNi alloy as hydrogenation sites and phosphotungstic acid(H3O40PW12)as esterification sites,in the MOF composites.Owing to the cooperation of two different active sites in MOF's cavity,the as-prepared bifunctional catalyst exhibited high conversion and high selectivity in the tandem synthesis of benzocaine,which is a very important amino-ester-type anesthetic and is usually synthesized via a multistep process in traditional industry.More importantly,this multifunctional catalyst proved to be suitable for the tandem synthesis of a wide range of chemical compounds involving hydrogenation and esterification reactions.