Date of Award

4-24-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Systems Engineering

First Advisor

Alexandru Biris

Abstract

Surfaces that have a water contact angle (WCA) above 150° and a negligible difference between the receding and advancing contact angles are superhydrophobic, meaning that a simple, minimal tilt will cause water droplets to roll off the surfaces. Superhydrophobic surfaces are found in nature and can possess several fascinating properties, including the ability to self-clean. A typical superhydrophobic surface has micro/nanostructure roughness and low surface energy, which combine to give it its unusual anti-wetting properties. Because of their unique capabilities, superhydrophobic surfaces have interested scientists in research and industry fields for years. In recent decades, researchers have developed a number of synthetic methods for producing novel superhydrophobic surfaces that mimic natural phenomena. These synthetic surfaces have been applied on different types of substrates for widespread, practical applications. Recently, much research has focused on the use of superhydrophobic surfaces for oil-water separation. Due to increased production, transportation, and use of oils and toxic organic solvents, the possibility of spills that cause serious environmental threats and pollution has grown. As a result, efficient, affordable remediation of oil spills and chemical leaks is crucial. This need demands cost-effective, simple fabrication processes, easily reproducible for largescale manufacturing, that produce functional, porous materials that separate and absorb oil from water, particularly salt water. In this study, two projects focusing on novel oil-sorbent materials are discussed. In the first project, we created a free-standing carbon nanofiber-polydimethylsiloxane (CNF/PDMS) nanocomposite block via a solution process using one-step vacuum filtration, a simple, cost-effective fabrication method. The block showed excellent superhydrophobicity and superoleophilicity (water contact angle = 163°, oil contact angle = ~0°), high mechanical stability, good absorbance capacity, and recyclability. It also exhibited rapid, selective absorption of several types of oils and organic liquids floating on the water surface, as well as heavy oils sunken in water. These findings suggest that the CNF/PDMS block is a promising, practical material for oil spill clean-up. In the second project, we developed the first simple, cost-effective, magnetic, porous material based on PDMS and steel wool (SW) that may meet the urgent need for efficient oil clean-ups. The solution immersion process used to prepare the PDMS-SW is easily scaled up, not requiring multiple steps or complicated equipment. Our experiments demonstrated that the PDMS-SW is superhydrophobic, superoleophilic, and capable of absorbing and separating oils and organic solvents from water. The material is highly mechanically and chemically stable, even in salty environments, and can be magnetically guided. It not only exhibited good selectivity, recyclability, and sorption capacity, but it was also able to absorb and remove large amounts of oils and organic solutions from both stationary and turbulent water quickly and continuously. In addition, the PDMS-SW’s inherent high porosity enables direct, gravity-driven oil-water separation with permeate flux as high as ~32,000 L/m2.h (liters per square meter per hour) and separation efficiency of over 99%. Its high flexibility and selective wettability also contributed to efficient oil-water separation. Therefore, all findings indicate that the PDMS-modified SW has great practical potential for oil absorption and oil-water separation in real conditions.

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