Yolk–Shell Nanocrystal@ZIF-8 Nanostructures for Gas-Phase Heterogeneous Catalysis with Selectivity Control

Abstract

A general synthetic strategy for yolk-shell nanocrystal@ZIF-8 nanostructures has been developed. The yolk-shell nanostructures possess the functions of nanoparticle cores, microporous shells, and a cavity in between, which offer great potential in heterogeneous catalysis. The synthetic strategy involved first coating the nanocrystal cores with a layer of Cu(2)O as the sacrificial template and then a layer of polycrystalline ZIF-8. The clean Cu(2)O surface assists in the formation of the ZIF-8 coating layer and is etched off spontaneously and simultaneously during this process. The yolk-shell nanostructures were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and nitrogen adsorption. To study the catalytic behavior, hydrogenations of ethylene, cyclohexene, and cyclooctene as model reactions were carried out over the Pd@ZIF-8 catalysts. The microporous ZIF-8 shell provides excellent molecular-size selectivity. The results show high activity for the ethylene and cyclohexene hydrogenations but not in the cyclooctene hydrogenation. Different activation energies for cyclohexene hydrogenation were obtained for nanostructures with and without the cavity in between the core and the shell. This demonstrates the importance of controlling the cavity because of its influence on the catalysis.

Surfactant-assisted ZnO processing as a versatile route to ZIF composites and hollow architectures with enhanced dye adsorption

“…, the oxide core can be effectively and rapidly removed from the composites by soaking in 2M KOH for 10-15 mins. While related templateetch strategies to prepare ZIF-8 capsules from functionalised colloidal polystyrene templates 26 and access to Pd@ZIF-8 yolkshell structures from sacrificial coatings of Cu 2 O on Pd nanoparticles 27 have been reported, we believe this is the first time an oxide has been used both as metal-source and a hard post-synthetically etchable template for the formation of MOF-based hollow structures. Furthermore, etching of those composites prepared using high levels of C 12 Gua such as those shown in figure S14d, selectively removes the oxide particles to leave micron-sized bowl-like ZIF-8 crystals which contain large hollow cavities.…”

Nanocatalysis I: Synthesis of Metal and Bimetallic Nanoparticles and Porous Oxides and Their Catalytic Reaction Studies

“…Recently, core/shell or yolk/shell nanoparticles with metalorganic frameworks (MOFs) were developed. Tsung group reported Pd/ZIF-8 yolk/shell nanoparticles by coating Pd nanoparticle cores with Cu 2 O and polycrystalline zeolitic imidazolate framework 8 (ZIF-8) layers [30]. In this process, the Cu 2 O layer as a sacrificial template in the middle of the structure assisted the formation of the ZIF-8 coating layer and was etched off to create a cavity as shown in Fig.…”

Photoreduction of CO2 on ZIF-8/TiO2 nanocomposites in a gaseous photoreactor under pressure swing

“…Zeolitic imidazolate frameworks (ZIF) are a subclass of MOFs featuring excellent CO2 uptake and simple fabrication. In conjugation with other photocatalytic materials it can improve the photocatalytic activity in aqueous and gaseous media [8,9]. For instance, ZIF-9 is shown to activate CO2 leading to positive shift in the onset potential in photoelectrochemical CO2 conversion process [10].…”