Date of Award
Doctor of Philosophy (PhD)
Environmental technologies, such as for water treatment, have advanced significantly due to the rapid expansion and application of nanoscale material science and engineering. In particular, two-dimensional graphene oxide (GO), has demonstrated considerable potential for advancing and even revolutionizing some of these technologies, such as engineered photocatalysts and membranes. To realize such potential, an industrially scalable process is needed to produce monomeric and aggregation-resistant GO nanostructures/composites, in addition to new knowledge of material properties, behavior, and performance within an environmental context.
Research presented in this thesis addresses both scientific and engineering gaps through the development of a simple, yet robust aerosol-based synthesis approach and demonstrations of two applications, photocatalysts and membranes. The aerosol-based process was developed to engineer the 2D GO nanosheets into 3D crumpled balls (crumpled GO, CGO), which have excellent aggregation- and compression-resistant properties, while allowing for the incorporation (encapsulation) of other (multi)functional particles inside. The five focus areas of this dissertation are: 1) Crumpling and thermal reduction of GO nanosheets in aerosolized droplets, 2) (Multi)functional nanocomposite synthesis, 3) Colloidal behavior in water as a function of material properties and selected environmental constituents/conditions, 4) Photocatalytic applications, 5) Composite assemblies/nanoscale fillers for advanced water treatment membranes.
Results reveal that the evaporation rate of water droplets plays a critical role in controlling the crumpling process, and thermal reduction leads to temperature-dependent removal of oxygen functional groups. (Multi)functional composites can be achieved through encapsulation of single or multiple types of nanoparticles, such as TiO2, magnetite, and silver. Morphological transformation by crumpling, increased degree(s) of oxidation, and presence of natural organic matters act to enhance the stability of GO in water. CGO-TiO2 composites are shown to possess superior aqueous-based photocatalytic properties, including efficient photo-reduction reaction pathways. Furthermore, assemblies of CGO nanoparticles show superior permeation, separation, and reactive (photo-reactive and antimicrobial) properties. In addition, in situ surface-based photocatalyzed synthesis of Ag nanoparticles at the surface of membrane assemblies, is demonstrated as an approach to (re)generate, thus maintain, enhanced antimicrobial activity.
This work identifies and solves several key issues regarding the industrially attractive processing and applications of (crumpled) graphene-based materials for water treatment technologies. Knowledge obtained, as part of this thesis, will impact aerosol processing of materials, environmental nanotechnology, environmental catalysis, and water treatment membrane technology, among other fields.
John D. Fortner, Pratim Biswas
Fuzhong Zhang, Parag Banergee, Baolin Deng, Wei-Ning Wang, Viatcheslav Freger