Date of Award

8-9-2014

Document Type

Open Access Thesis

Department

Chemical Engineering

First Advisor

Miao Yu

Abstract

Graphene oxide (GO) was utilized as a novel material for making ultrathin membranes for gas separation and for making functional coatings for nano-/ultra-filtration in oil/water separation. Fundamental separation mechanisms by ultrathin GO membranes/coatings and potential applications were explored. This work can be divided into three parts. In the first part, ultrathin GO membranes supported on flat and smooth anodic aluminum oxide (AAO) substrates, with thickness down to 1.8 nm, were prepared by a facile vacuum filtration method. The as-prepared GO membranes were then studied for single-gas permeation and hydrogen mixture separation. It was revealed that the separation mechanism for the ultrathin GO membranes followed the molecular sieving. Ultrathin GO membranes represent a new type of membranes that may realize high throughput molecular-sieving separation at low energy cost.

In the second part of this work, GO was used as a coating material to modify macroporous polyamide (PA) supports, by a similar vacuum filtration approach. The supported GO membranes showed superoleophobicity and low oil-adhesion underwater. This could be ascribed to the hierarchically rough membrane surface and excellent water “locking” property of GO. The hierarchical roughness was introduced by the combination of the intrinsic micro-scaled roughness of the PA support with the nano-scaled corrugation of GO flakes. Oil/water separation results showed that by optimizing GO coating thickness, antifouling property and 100% pure water flux recovery were achieved.

As an extension of the second section, the third section of the thesis work was focused on tuning oleophobicity of GO coatings under water by gradually modifying the chemistry and structure of GO flakes using ultraviolet (UV) irradiation. The underwater oleophobicity of GO coatings was tuned gradually, simply by controlling the UV treatment time. Oxidative UV etching was shown to generate more and larger structural defects on GO flakes, which increased the nano-scaled roughness on GO flakes. In addition, more hydrophilic oxygen-containing groups, such as carboxyl, carbonyl, hydroxyl and epoxy, introduced by UV irradiation, improved the ability of GO to attract and "lock" water molecules at the coating surface, which effectively lowers oil adhesion. The GO flakes with different UV treatment time were fabricated into GO membranes on PA supports. A series of oil/water separations were conducted for these GO membranes, and membrane recovery capability was greatly improved with the optimized UV etching time.

Rights

© 2014, Hang Li

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