In-situ studies of the growth of two-dimensional covalent organic frameworks

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The development of new materials plays a vital role in the evolution of existing technology. New materials often display unique properties that suggest new ways of solving important societal problems such as making better catalysts or the development of new sensors for medical or environmental applications. The development of graphene is a prominent example of a new material that redefined existing applications and in many cases suggested entirely new ones. A proven approach to developing new materials is to combine different structures to form composite materials where the properties of multiple materials can be combined in a single structure. In addition to simply combining the properties of individual materials, composite materials often lead to entirely new properties that surpass those of either of the components.To discover new composite materials we need to understand how they form and utilise this knowledge to grow complex materials that can be designed to have desirable properties. This project aims to combine two promising types of materials into new composite structures: porous graphene materials and two-dimensional covalent organic frameworks (2D-COFs). 2D-COFs are formed by linking separate molecular building blocks together with covalent bonds to create extended two-dimensional molecular structures. The 2D-COFs studied in this project are surface supported porphyrin 2D-COFs. This means the growth of the 2D-COF takes places on an underlying surface and the main molecular components are porphyrin molecules. Porphyrins are highly versatile and widely used organic molecular components. The potential of porphyrins to provide chemical functionality is demonstrated by their important roles in biological systems, photosynthesis and binding oxygen in red blood cells and technologically in catalysts and sensors.I will use an experimental tool called a quartz crystal microbalance (QCM) to track the growth of 2D-COFs on porous graphene materials in real-time. Porphyrin 2D-COFs will be grown using a condensation reaction to form the covalent links between molecules. These condensation reactions release water molecules and the mass change associated with this can be detected by QCM. These in-situ measurements will allow us to gain insights into how environmental conditions, such as temperature pressure and humidity, influence the growth of 2D-COF structures. Using these insights I will find optimal conditions for 2D-COF growth and the project will investigate the growth on high surface area graphene materials such as graphene foams and graphene hydrogels.A major obstacle to the application of 2D-COFs is their lack of stability in harsh conditions. To produce ordered 2D-COFs it is necessary to use covalent bonds that link molecules together reversibly. If bonds are non-reversible defects in the growing 2D-COF become trapped and disordered structures are produced. However, a limitation to using reversible bond formation processes is that while the resulting 2D-COFs are ordered they are also susceptible to degradation, making them unsuitable for applications that require stability in harsh environments. This project aims to develop post-growth chemical treatments that increase the stability of pre-formed porphyrin 2D-COFs while maintaining their ordered structure. Finally, an approach to adding functionality to pre-formed 2D-COFs by using custom designed molecular building blocks will also be investigated. These building blocks will have chemical groups which are inactive during 2D-COF growth but subsequently can be used to attach other functional components, such as dye molecules or nanoparticles, to the preformed 2D-COFs. This modular approach use 2D-COFs as templates for producing complex and functional materials.This project will lead to a new understanding in the growth of functional organic nanostructures and a new set of composite materials with potential in a wide range of applications.