Author ORCID Identifier

https://orcid.org/0000-0002-0175-4782

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Chemical and Materials Engineering

First Advisor

Dr. T. John Balk

Second Advisor

Dr. Dibakar Bhattacharyya

Abstract

Novel metallic thin film composite membranes are synthesized and evaluated in this work for improved separations and catalysis capabilities. Advances in technology that allow for improved membrane performance in solvent separations are desirable for low molecular weight organic separation applications such as those in pharmaceutical industries. Additionally, the introduction of catalytic materials into membrane systems allow for optimization of complex processes in a single step. By adding a nanostructured metallic thin film to its surface, a polymer membrane may be modified to exhibit these improved properties. Using magnetron sputtering, thin metal films may be deposited on commercially available membranes to modify separations properties. Alloy films may then be deposited onto the membrane surface and dealloyed to produce a porous structure with a small feature size for catalysis.

Multiple composites were studied in this research. Metallic thin film composites (MTFCs) of 10 nm Ta films deposited on top of commercially available ultrafiltration polysulfone (UF PSf) membranes were fabricated and characterized to study the film’s effect on effective pore size of the membrane. A significant water flux drop from the UF PSf (168 LMH/bar) to the resulting MTFC (8.8 LMH/bar) was found. Effective pore size was studied using rejection experiments with molecules of known sizes as markers. The UF PSf rejected about 90% of the 70 kDa while all smaller molecules were rejected minimally. The MTFC, however, rejected down to 5 kDa dextran indicating a reduction in effective pore size through the addition of 10 nm of Ta. Further experiments with IPA and water indicated that the structure was stable in this solvent.

Two different alloy systems were studied as precursors to nanoporous films for further catalysis. Both were Fe/Pd (80/20 at. %) and Mg/Pd (75/25 at.%) precursors were used to produce nanoporous Pd. In all cases the alloy films were anchored to the membrane substrate with a thin Ta film, then dealloyed to produce a nanoporous metal thin film composite (npMTFC). In both cases the npMTFC was produced to catalyze a dechlorination reaction using hydrogen gas. Chlorinated organic compounds were the target compound for this system, as they are a persistent pollutant.

Fe/Pd alloy films were dealloyed using a solution of 25% sulfuric acid to etch away the iron and generate porosity. The Fe/Pd npMTFCs were then tested for both batch mode dechlorination and permeation testing with a model COC, chlorobiphenyl (PCB-1). Permeation of a 5 ppm solution of PCB-1 through a similar membrane degraded 28% of PCB-1 from solution with a single pass under H2 pressurization. For the Mg/Pd precursor system only water was needed in order to etch magnesium, preserving the pore structure of the underlying UF PSf substrate with little deformation from dealloying. Under convective flow, the membrane removed over 70% of PCB-1 from solution with a single pass at 4 bar H2 pressurization. Successful fabrication of a novel composite membrane type has been demonstrated with applications for improved separations in solvents and in catalysis. The catalytic applications here may be easily modified for a variety of reactions.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.192

Funding Information

This research has been supported through the NSF KY EPSCoR grant (Grant 1355438) and NIH-NIEHS-SRC (Award No. 5P42ES007380-21 and 2P42ES007380-22).

Available for download on Monday, May 17, 2021

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