Graphene oxide (GO) is a heavily oxidized version of graphene, which is often made by oxidative chemical exfoliation from graphite powders. The reaction decorates the graphene sheets with oxygen-containing functional groups including hydroxyl and epoxide groups on the basal plane, as well as carboxyl groups on the edge, rendering the sheets dispersible in water. GO dispersions and gels are widely used to assemble bulk GO architectures, which can be converted to chemically modified graphene or reduced GO (r-GO) materials. In this thesis, I will first discuss the discovery of a long-missing state of GO in water called dough. It has a GO mass loading of 20% to 60%. GO dough is highly malleable and can be dried into a dense isotropic glassy GO solid with disordered stacking of sheets. To preserve the shape and microstructure in the final graphene-based materials, a topochemical method is developed for reduction of GO doughs. By heating a dough in a sealed autoclave, the high pressure generated by water vapor from the dough itself helps to prevent fracture and maintain structural integrity, which cannot be easily achieved by conventional reducing methods such as simple heating or chemical reduction. The limitation of this method and potential ways for improvement are also discussed (Chapter 2).In addition, GO dough can be redispersed in water as single layers without significantly altering the sheet morphology. Therefore, the compact size of dough makes it a good form for GO manufacturing, especially during storage and transportation. It offers drastic space and weight saving in comparison to dispersions and avoids safety hazards associated with dry GO solids (Chapter 2). The initial way to make doughs starts from freeze-drying a dispersion into a foam followed by carefully rehydrating the foam using a minute amount of water, often delivered by an aerosol generator. Later it is found that long time drying can lead to decreased processability of the final dough. Over-dried, dehydrated foam is no longer dispersible in water and neither does the dough. Further investigation reveals that over-drying triggers irreversible interlayer crosslinking between GO sheets through esterification reaction between carboxyl and hydroxyl groups, which is supported by spectroscopy studies, mass change during dehydration/rehydration, and microscopy observation at single layer level. This new insight updates our knowledge about a fundamental chemical property of GO and how the sheets might interact with each other, which is a foundational structure feature in all GO-based materials (Chapter 3). It also offers guidance over how GO should be processed during manufacturing and applications. Circling back to the dough making process, it is now clear that freeze-drying inevitably introduces crosslinking of GO sheets, at least in partial, and is unsuitable for this purpose. Therefore, a new method is developed to create the dough state from the dispersion without forming foams through agitated evaporation, which avoids over-drying (Chapter 4). As is with the rest of the world, my research about GO was also interrupted by the COVID-19 pandemic. In addition to viruses, panic and despair were also spreading among people. However, in the face of the grave tragedy and uncertainty, the struggle, sacrifice and resilience demonstrated by ordinary people and healthcare workers in Wuhan so deeply moved my heart that I felt I had to do something, at least trying. Therefore, I joined my advisor in studying literature and textbooks in the field of virology and public health, and discussing with healthcare professionals. I was surprised to quickly realize that there is actually much we can do in this global crisis. Chapter 6 elaborates what I have learned about virion structures and what we think can be done by physical scientists to help slow down the transmission of infectious respiratory diseases. This led to several new “essential” pandemic related research projects in the lab, including two that I have led, i. e., a public health concept of on-mask chemical modulation layer for respiratory droplets (Chapter 7) and a self-sanitizing coating on stainless steels (Chapter 8), both of which aim to curb transmission by making droplets less infectious. Transmission of infectious respiratory diseases starts from pathogen-laden respiratory droplets released during coughing, sneezing, or speaking. An on-mask chemical modulation strategy is discussed in Chapter 7, whereby droplets escaping a masking layer are chemically “contaminated” with antipathogen molecules (e.g., mineral acids or copper salts) preloaded on polyaniline-coated fabrics. A colorimetric method based on the color change of polyaniline and a fluorometric method utilizing fluorescence quenching microscopy are developed for visualizing the degree of modification of the escaped droplets by H+ and Cu2+, respectively. An algorithm is developed to extract information about size and the degree of modulation from microscopy images. It is found that even fabrics with low fiber-packing densities (e.g., 19%) can readily modify 49% of the escaped droplets by number, which accounts for about 82% by volume. The chemical modulation strategy highlights and strengthens the public health function of face coverings. It could be applied to enhance protection for healthcare workers in patient wards or temporary shelter hospitals. It could also add outward protection when applied to some of the current valved masks. Stainless steels are widely used in hospitals and public transportation vehicles as one of the most common touch surfaces. Retrofitting stainless steel surfaces with an antimicrobial layer can bring potential public health benefits by reducing the ability of inanimate objects, or fomites, to transmit infections. Chapter 8 discusses a facile surface conversion reaction that coats stainless steel with a conformal and robust oxyhydroxide layer. Microscopy observations show that the layer is amorphous, continuous, and pinhole free with a thickness of only 10-15 nm. The coating releases Cu ions, a broad-spectrum antimicrobial agent, in the presence of water. It adheres strongly to stainless steel and can resist aggressive rubbing in simulated friction tests, which is attributed to its gradient distribution of elements without forming a sharp interface with the substrate.

Creator

• Huang, Haiyue

DOI

• https://doi.org/10.21985/n2-nmzq-bg06

Subject

• Materials Science

Language

• en

Alternate Identifier

• etdadmin_upload_887181
• http://dissertations.umi.com/northwestern:15970

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright