Encapsulation of Active Liquids Using a Pickering Emulsion Platform

Emulsions are mixtures of two immiscible fluids, where droplets of one are dispersed in the continuous phase of the other. The stability of emulsions can be improved through the addition of a small molecule surfactant, such as sodium dodecyl sulfate. Alternatively, Pickering emulsions are those that are stabilized by solid particles instead of small molecule surfactants. Of particular interest are Pickering emulsions stabilized by graphene oxide (GO) nanosheets because of the planar nature of the nanosheets and their ability to be both covalently and non-covalently modified. Such chemical modification allows for the wettability of the nanosheets to be tuned to stabilize a variety of emulsion platforms (e.g., not only oil-in-water). Pickering emulsions can be used in conjunction with simple chemistries to prepare a variety of composite structures. This dissertation advances the preparation and application of GO-stabilized Pickering emulsions as a platform to include a variety of active liquids, specifically task specific ionic liquids (ILs), poly(α-olefins) (PAOs), and deep eutectic solvents (DESs). These liquids are considered “active” as they have unique properties beyond those inherent with being a liquid. However, these active liquids are often very viscous, resulting in slow mass transfer rates and handling difficulties. To overcome such issues, these liquids were successfully encapsulated in a GO/polyurea shell via interfacial polymerization utilizing a Pickering emulsion template. Encapsulation increases the surface area of the active liquid, which facilities mass transfer by making more active liquid accessible (provided permeability of the composite shell), and allows the user to handle the active liquid as a solid, mitigating many handling difficulties. Potential applications of the active liquid capsules were then examined, and a study was done to determine how polymer structure impacts capsule shell permeability to small molecules. Finally, transition metal oxides, another class of 2D nanosheets, were studied as a Pickering emulsion co-surfactant with GO, demonstrating that surfactant composition can also be tailored, opening new opportunities. The work reported here lays a foundation for the use of capsules of active liquids as media for separations and offers insight into how surfactant, discontinuous phase, and polymer choice impact the application of a capsule system

Organic Carbon Amendments for Enhanced Biological Attenuation of Trace Organic Contaminants in Biochar-Amended Stormwater Biofilters

This study sought to evaluate how dissolved organic carbon (DOC) affects attenuation of trace organic contaminants (TOrCs) in biochar-amended stormwater biofilters. It was hypothesized that (1) DOC-augmented runoff would demonstrate enhanced TOrC biodegradation and (2) biochar-amended sand bearing DOC-cultivated biofilms would achieve enhanced TOrC attenuation due to sorptive retention and biodegradation. Microcosm and column experiments were conducted utilizing actual runoff, DOC from straw and compost, and a suite of TOrCs. Biodegradation of TOrCs in runoff was more enhanced by compost DOC than straw DOC (particularly for atrazine, prometon, benzotriazole, and fipronil). 16S rRNA gene quantification and sequencing revealed that growth-induced microbial community changes were, among replicates, most consistent for compost-augmented microcosms and least consistent for raw runoff microcosms. Compost DOC most robustly enhanced utilization of TOrCs as carbon substrates, possibly due to higher residual nutrient levels upon TOrC exposure. Sand columns containing just 0.5 wt % biochar maintained sorptive TOrC retention in the presence of compost-DOC-cultivated biofilms, and TOrC removal was further enhanced by biological activity. Overall, these results suggest that coamendment with biochar and compost may robustly enhance TOrC attenuation in stormwater biofilters, a finding of significance for efforts to mitigate the impacts of runoff on water quality