Thesis
Carbon nanotube membranes for the purification of water from uranium
University of Iowa
Master of Science (MS), University of Iowa
Autumn 2020
DOI: 10.17077/etd.005686
Abstract
Carbon nanotubes (CNT) are unique materials with inner diameters as small as one to several nanometers. There has been a growing interest to use CNTs to develop the next generation of membranes to use the inner diameters to selectively sieve chemicals based on their sizes. Scientists have shown that combining the fast transport of water through CNTs and the uniform structures of CNTs results in an improved and efficient membrane. We applied CNT membranes to the separation of uranium from water. Uranium is found in the environment in multiple oxidation states, with the primary oxidation state in aqueous solution being U(VI). The uranyl cation U(VI)O22+ readily complexes with carboxylic acids, carbonate, phosphate, or sulfate ions and in these forms is soluble and easily transported. With this in mind, we investigated how CNT membranes separated uranium from water. Complexation of uranium with citric acid led to large complexes that could not permeate the membranes, but the uranium in water without citric acid permeated. Raman spectroscopy confirmed the presence of uranium species, [(UO2)2(HCit)2]2- and [(UO2)3O(Cit)3]5-, and provided further insight into the size of the uranyl-citrate complexes. In my thesis I will describe our hypothesis that the presence of a sodium ion in the water led to the formation of a supramolecular complex that is much larger than the inner diameter of a CNT. This work can offer insight on complex aqueous systems involving uranium, and further our understanding of CNT membrane technology.
Details
- Title: Subtitle
- Carbon nanotube membranes for the purification of water from uranium
- Creators
- Katherine Sulaitis
- Contributors
- Tori Forbes (Advisor)Ned Bowden (Advisor)Sara Mason (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Autumn 2020
- Publisher
- University of Iowa
- DOI
- 10.17077/etd.005686
- Number of pages
- vii, 48 pages
- Copyright
- Copyright 2020 Katherine Sulaitis
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Access to drinking water has been a growing problem for many countries around the world, including the United States. More specifically, in the southwest part of the United States people living in the Navajo Nation region are consuming water filled with many potentially harmful contaminants such as uranium. The EPA limit for uranium in drinking water is 30 μg/L, and in some areas the concentration of uranium may be up to 700 μg/L. Presently, there are a variety of membrane technologies that have great ability to purify water and are being used to try and address this issue. However, since the discovery of carbon nanotubes (CNT), there has been a growing interest to use CNTs to develop the next generation of membranes. This is due to the fact that the permeation of water through CNTs is up to five orders of magnitude faster than through a polymeric membrane. With this in mind, we will investigate how carbon nanotube membranes (CNMs) separate uranium from water, which has not been studied to the best of our knowledge.
An initial experiment has shown that CNMs can reject up to 95% of uranium in aqueous solution at a pH of 7.4. With promising initial data, we would like to explore how different concentrations of uranium and different pH solutions affect the rejection profile of CNMs, and if they potentially will yield higher rejections of uranium. In addition, we want to add safe, environmentally friendly ligands that would coordinate to the uranium, which can increase the size of the complex in solution, making it too large to permeate through the membrane. We have shown some results in using the ligand citric acid, which increased the rejection of uranium. We hypothesize that through optimizing various parameters in the separation we will be able to achieve purified water that is below the EPA limits for uranium concentration in drinking water.
- Academic Unit
- Chemistry
- Record Identifier
- 9984036789902771
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