From nanoparticle networks to metal-organic frameworks: synthesis, structural engineering and applications
Creators: name: Bo, Renheng
Publisher: name: The Australian National University
Year: 2020

description: Nanoparticle networks, self-assembled from flame generated hot aerosols consisting of ceramic nanoparticles with well-controlled particle size, are promising materials for many different applications, especially for photodetectors and VOC sensors. Furthermore, the great structural flexibilities of these self-assembled nanoparticle networks including tuneable thickness and hierarchical porosity, precisely-controlled averaged particle size as well as chemical composition make them as potential platforms for templated materials synthesis via chemical conversion. On the other hand, metal-organic framework (MOF), is a growing family of microporous materials consisting of metal cations connected by organic linkers. Their unique properties, including a narrow pore size distribution (intrinsic porosity), designable topology, high accessible surface area, and chemical mutability, make MOFs promising materials for a variety of applications including gas storage, separation, catalysis, biotechnology, optics, microelectronics and energy production/storage. However, there are still several bottlenecks hindering the structural engineering of metal-organic frameworks, especially for pure crystalline MOF materials, including limited attainable thickness, scalability, poor mechanical stability (i.e. brittle nature of MOFs), hard to realize the morphological control (e.g. tuneable extrinsic hierarchical porosity) and geometric designs on pure crystalline MOF components. Thus, a facile synthetic approach for MOF structuring is highly desirable, which could afford the fabrication of three-dimensional MOF materials with possibly unlimited thickness, free-standing feature, the control over extrinsic hierarchy as well as pre-determined designs of MOFs while maintain their crystalline property and intrinsic extreme accessible surfaces. Firstly, we started with the synthesis of pure ZnO nanoparticle networks and the optimization of their particle size. Later, using the ZnO nanoparticle networks with an optimal particle size, a high-performing UV photodetector has been prepared to show a proof of concept application of such structural engineering. After achieving the first structural control over ZnO nanoparticle networks, a multi-dimensional control has been further investigated associated with its potential use for multi-functional devices including transparent conductive oxides and gas sensors. Given the successful structural control over nanoparticle networks, considering the existing bottlenecks in current MOF fabrication, this multi-dimensional structural control has been successfully replicated to MOF preparation via a means of gas phase conversion. Therefore, in this thesis, a systematic study has been presented from the synthesis and applications of nanoparticle networks to those of metal-organic frameworks in the sequence of: (i) the synthesis of three-dimensional nanoparticle networks (i.e. ZnO-based metal oxide nanoparticle networks), (ii) the realization of a precise particle size control over the synthesized nanoparticle networks (e.g. ZnO) and the use of resulted optimal structure for photodetector application, (iii) the realization of chemical composition manipulation over the synthesized nanoparticle networks (e.g. ZnO nanoparticle networks with varied Al doping concentrations) and the use of the resulted structures as proof of concept applications for both porous conductive electrodes and VOC sensor, (iv) the establishment of a synthetic pathway from nanoparticle networks to metal-organic frameworks based on the replication of the structural control over nanoparticle networks towards metal-organic frameworks, and the proof of concept application of the resulted free-standing metal-organic frameworks monolith for effective molecular sieve in batteries, and (v) the use of the established fabrication approach (i.e. from nanoparticle networks to metal-organic frameworks) for monolithic metal-organic framework patterning.