Richards, Evan
(2023)
Development of a Selective Cation Exchanger to Adsorb Ammonium by Coating with a Gas-permeable and Hydrophobic Membrane.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
A sorbent with a high enough capacity for NH4+ could serve as an oral binder to lower urea levels in end-stage kidney disease patients. A hydrogen-loaded cation exchanger such as zirconium phosphate Zr(HPO4)2·H2O (ZrP) is a promising candidate for this application. However, the NH4+ binding selectivity versus other ions must be improved. A gas-permeable and hydrophobic surface coating was first developed on an amorphous form of ZrP using tetraethyl orthosilicate and methoxy-terminated polydimethylsiloxane. The hydrophobic coating served as a barrier to ions in water solution from reaching the ion-exchanger’s surface. Meanwhile, its gas-permeable nature allowed for gaseous ammonia transfer to the cation exchanger. In vitro studies replicated the small intestine’s expected ion concentrations and exposure time to the sorbent. The effectiveness of the coating was measured with NH4+ and Ca2+ solutions and uncoated ZrP as the negative control. X-ray photoelectron spectroscopy and scanning electron microscopy measurements showed the coating successfully modified the surface of the cation exchanger. Water contact angle (WCA) studies indicated that coated ZrP was hydrophobic with an angle of (149.8 ± 2.5). Simulated small intestine solution studies showed the coated ZrP removed 94% (± 11%) more NH4+ than uncoated ZrP in the presence of Ca2+. Meanwhile, Ca2+ binding decreased by 64% (± 6%). The nearly four-fold increase in NH4+ selectivity can be attributed to the gas-permeable and hydrophobic coating applied on ZrP’s surface. But the material’s selectivity decreased by 72% after exposure to stimulated stomach acid conditions.
An alternative hydrophobic (WCA = 145.0 ± 3.2) and gas permeable coating made of a perfluorocarbon backbone was next investigated – perfluorooctyltriethoxysilane. The coating was attached to a polysiloxane-formed membrane on ZrP’s surface. Calculated Langmuir equilibrium and removal rate plots showed that decreasing %1H,1H,2H,2H-perfluorooctyltriethoxysilane in coating solution from 10% to 4% improved total NH4+ removal by 27% and removal rate by nearly 675%. In vitro studies indicated the perfluorocarbon-based coating attached to ZrP offers complete selectivity for NH4+ over Ca2+ with similar NH4+ capacity as the PDMS coating. Perfluorooctyltriethoxysilane-coated ZrP maintained its selectivity and NH4+ removal capacity after simulated stomach acid exposure. The results indicated perfluorooctyltriethoxysilane-coated ZrP is promising as an oral sorbent for ESKD patients.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
13 June 2023 |
| Date Type: |
Publication |
| Defense Date: |
18 October 2022 |
| Approval Date: |
13 June 2023 |
| Submission Date: |
11 April 2023 |
| Access Restriction: |
2 year -- Restrict access to University of Pittsburgh for a period of 2 years. |
| Number of Pages: |
143 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical and Petroleum Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
gas-permeable hydrophobic, polymers, ammonium selectivity, end-stage kidney disease (ESKD), zirconium phosphate |
| Date Deposited: |
13 Jun 2024 05:00 |
| Last Modified: |
13 Jun 2024 05:00 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/44509 |
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