Date of Award

May 2023

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Xiaoli Ma

Committee Members

Benjamin C Church, Yin Wang

Keywords

covalent organic framework membrane, desalination, rapid interfacial polymerization

Abstract

As a consequence of disrupting the water cycle via human interventions, such as climate change, humanity is facing global water crises. The water crises are wide ranging, but often associated with the deterioration of a local water cycle’s capacity to support a population. This capacity is reduced on a global scale through the atmosphere via climate change, but on a local scale, it can be reduced because of an over extraction of resources, alteration of ecosystems, and water pollution. The deployment of desalination plants is growing around the world. Reverse osmosis (RO) desalination is much more efficient than the thermal processes that came before it, such as distillation. However, RO desalination plants are large and still consume commensurate amounts of energy. By increasing the efficiency of potable water production, capital costs for implementation of RO solutions become more viable. The reliability and efficiency of membrane separation will be affected by the materials the membrane is made of. Generally, all membranes exhibit a behavior that is known as the tradeoff between selectivity and permeability. Membranes with high selectivity will have a low permeability/permeance and vice versa. Covalent Organic Framework materials as membranes may have the potential to exceed the current performance limits of state-of-the-art RO thin film composite (TFC) membranes. COF materials are 2D or 3D networks with intrinsic microporosity that are made with geometric linker molecules. The goal of this study is to enhance the desalination performance of COF membranes. The objective of this study was to utilize rapid interfacial polymerization to produce dual-layered COF membranes to enhance desalination. The hypothesis was that the presence of a second layer would increase rejection. This question has been studied with long reaction times, but never with rapid synthesis. The performance of the membranes was tested by measuring water permeances and the rejection rates of salts. The membranes were able to remove salts from the water, and the characterization of the membranes showed that the introduction of a second layer shifted the pore size distribution to smaller mean pore sizes in the COF membranes which led to improved salt rejection.

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