Chemical and Biomolecular Engineering - Theses

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Author: Cao, Yang × End date: 2023 × Start date: 2020 × Subject: nanomaterials ×

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    Multiscale characterisation and sub-nanometre engineering of reduced graphene oxide membranes
    Cao, Yang ( 2022)
    Multilayered 2D nanomaterial-based membranes with sub-nanometre pores or channels hold great promise for widespread applications such as compact energy storage, ion sieving, membrane separation and bio-electronics. Understanding their assembly structure across multiple length scales, particularly at the sub-nanometre scale, is crucial to realise their precise structural engineering for desired applications but has largely been overlooked in the literature. With the chemical conversion of multilayered graphene oxide membranes to their electroconductive form as a model system, this thesis is devoted to investigating the stacking behaviour of 2D nanoscale building blocks in laminar membranes across multiple length scales during their chemical conversion. With a combined approach of various light scattering techniques and dynamic electrosorption analysis, this study establishes a hierarchical structural model of ultra-dense graphene membranes to describe how the graphitised clusters, sub-nanometre channels and large slit-like voids co-exist in the membranes in an interconnected manner. These structural features and their hierarchical organisation are dependent on the synthetic conditions, including the reduction agent, reduction degree, reduction kinetics, concentration of electrolyte and nature of solvent in the reduction environment. This study also reveals that the (sub-) nanotexture of the graphene membranes, including the size and distribution of the graphitised clusters, the connectivity and structural ordering of the nanochannels, and the extent of graphitisation/crystallinity, can have a significant effect on the transport of ions through the membranes under electrification. The results enable the development of several new methods for engineering their sub-nanometre structure for compact capacitive energy storage and future nanoionics applications.