Mass transport through graphene oxide laminates.

Graphene-based materials have been intensively investigated as semi-permeable membranes because they are ultra-thin, mechanically strong, and possess a large surface area with small pore size. Graphene oxide is a 2D material consisting of a basal plane of sp2 carbon atoms attached with oxygenated functional groups on the plane. The interlayer space, which is formed by stacking graphene oxide sheets, serves as a pathway for various molecules and selectively blocks ions and molecules based on size exclusion. The graphitic wall within interlayer channels allows almost frictionless water flow, and the porosity of this material provides lots of accessible sites for gas adsorption. These advantages render graphene oxide a promising candidate in waterand gas-related applications. However, when the size of target ions or molecules is generally below one nanometer, the ideal membrane requires tuneable porosity on the angstrom level to precisely prohibit undesired ions and molecules. Many studies, therefore, have been directed to tuning the porosity of graphene oxide through various approaches, such as crosslinking, physical controlling, and reduction processing. Nevertheless, the practical applications of most methods are limited by difficulties of massive energy consumption, intensive chemical involvements, and complex operations. The realization of pore engineering via a facile and green method could be a big step forward. In this work, by using thermal and chemical reducing treatments to adjust the porosity of graphene oxide, we explore and understand the fundamentals of controlling the structure and functionalities of graphene oxide. In doing so, we aim to figure out an energy-efficient, environmentally friendly, and easy way of controlling the porosity of graphene oxide to improve its performance in water- and gas-related applications. This thesis is divided into six chapters. Chapter 1 gives basic information of graphene oxide and the outline of this thesis. Chapter 2 introduces the structure and properties of graphene-based materials and their applications in water- and gas-related fields. Chapter 3 describes the synthesis routes of samples and characterization methods used in this work. Chapter 4 presents the investigation on the performance of mild annealing graphene oxide membranes on salt-rejection. Chapter 5 compares the gas permeation through interlayer channels of graphene oxide, thermally treated graphene oxide and chemically reduced graphene oxide. Chapter 6 summarizes the studies conducted in this thesis and the future scope of graphene-based material