Author ORCID Identifier

https://orcid.org/0000-0001-6234-953X

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Chemical and Materials Engineering

First Advisor

Dr. Dibakar Bhattacharyya

Abstract

Microfiltration polyvinylidene fluoride (PVDF) membranes have distinct advantage for open structure in terms of high internal surface area and ease of access in the pore domain. Functionalization of PVDF membranes with different functional groups (-COOH, -OH, -SH) enables responsive (pH, temperature) properties to membrane, tuning of effective pore size, controlling permeate flux. PVDF microfiltration membrane functionalization with suitable responsive polymer such as poly acrylic acid (PAA) to incorporate carboxyl (-COOH) group enables further modification of functionalized PAA-PVDF membranes for different application ranging from catalysis, bio reactor to heavy metal sorption platform. As a catalytic reactor bed, this PAA-PVDF membranes are very desirable platform for in-situ synthesis of catalytic nanoparticles for conducting a wide range of reactions. As a bio reactor, PAA-PVDF membrane with a net charge have been used to electrostatically immobilize enzymes for conducting catalytic reactions. Functionalization of PVDF membrane also allow for the development of high capacity heavy metal sorbents by modifying existing functional groups (-COOH) to other functional groups (-SH) to adsorb heavy metal cations from contaminated water.

Hydrophilic polymers with carboxylic (-COOH) groups are studied in different functionalization processes especially in preparation of responsive (pH) membranes. To understand the role of membrane pore polymerization condition on the properties of functionalized membrane a systematic study has been conducted, specifically, the effects of polymerization on the membrane mass gain, water permeability, Pd-Fe nanoparticle (NP) loading, of pore functionalized polyvinylidene fluoride (PVDF) membranes. In this study, monomer (acrylic acid (AA)) and cross-linker (N, N′- methylene-bis (acrylamide)) concentrations were varied from 10 to 20 wt% of polymer solution and 0.5-2 mol% of monomer concentration, respectively. Results showed that responsive behavior of membrane could be tuned in terms of water permeability over a range of 270-1 Lm-2 h-1 bar-1, which is a function of water pH. The NP size on the membrane surface was found in the range of 16-23 nm. NP loading was found to vary from 0.21 to 0.94 mg per cm2 of membrane area depending on the variation of available carboxyl groups in membrane pore domain.

The NPs functionalized membranes were then tested as a platform for the degradation of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) and understand the effect of NP loading of the rate of degradation of PCB 126. The observed batch reaction rate (Kobs) for PCB 126 degradation for per mg of catalyst loading was found 0.08-0.1 h-1. Degradation study in convective flow mode shows 98.6% PCB 126 is degraded at a residence time of 46.2 s. The corresponding surface area normalized reaction rate (Ksa) is found about two times higher than Ksa of batch degradation; suggesting elimination of the effect of diffusion resistance for degradation of PCB 126 in convective flow mode operation.

A layer-by-layer approach to immobilize laccase enzyme into PAA functionalized PVDF microfiltration membranes for degradation of 2,4,6-trichlorophenol (TCP) from water was demonstrated to offer bioinspired remediation. Over 80% of the initial TCP was degraded at optimum flow rate under an applied air pressure of about 0.7 bar or lower. This corresponds to degrading a substantial amount of the initial substrate in only 36 seconds residence time, which in a batch reaction take hours. This, in fact, demonstrates an energy efficient flow through system with potential large-scale applications. Comparison of the stability of the enzyme in solution phase vs. immobilized on membrane phase showed a loss of some 65% of enzyme activity in the solution phase after 22 days, whereas the membrane-bound enzyme lost only a negligible percentage of activity in comparable time span. Finally, the membrane was exposed to rigorous cycles of TCP degradation trials to study its reusability. The primary results reveal a loss of only 14% of the initial activity after four cycles of use in a period of 25 days, demonstrating its potential to reuse. Regeneration of the functionalized membrane was also validated by dislodging the immobilized enzyme followed by immobilization of fresh enzyme on to the membrane.

A multi-enzyme functionalized membrane reactor for bioconversion of lignin model compound involving enzymatic catalysis was also developed. Layer-by-layer approach was used to immobilize three different enzymes (glucose oxidase, peroxidase and laccase) into pH-responsive membranes. This novel membrane reactor couples the in-situ generation of hydrogen peroxide (by glucose oxidase) to oxidative conversion of a lignin model compound, guaiacylglycerol-B-guaiacylether (GGE). Preliminary investigation of the efficacy of these functional membranes towards GGE degradation is demonstrated under convective flow mode. Over 90% of the initial feed could be degraded with the multienzyme immobilized membranes at a residence time of approximately 22 seconds. GGE conversion product analysis revealed formation of oligomeric oxidation products with peroxidase, which might be potential hazard to membrane bioreactors. These oxidation products could be further degraded by laccase enzymes in the multi-enzymatic membranes explaining the potential of multienzyme membrane reactors. The multi-enzyme incorporated membrane reactors were active for about a month time of storage at 4 oC, and retention of activity was demonstrated after repetitive use.

Further, PAA functionalized PVDF membranes are immobilized with thiol (-SH) groups for metal sorption from industrial effluent water. The sorption capacity of mercury for CysM immobilized membrane is 2446 mg/g PAA and the efficiency of Hg removal is 99.1±0.1% respectively from synthetic water. For 1300 minutes CysM-PAA-PVDF membrane is used to remove Hg2+ cations from effluent water. The adsorption efficiency in this long-term study is around 97%. In presence of Ca2+ cations adsorption efficiency drops to 82% for CysM-PAA-PVDF membrane and to 40% for Cys-PAA-PVDF membrane. A mathematical model on heavy metal adsorption by thiol (-SH) functionalized membrane was developed to predict experimental results over a wide range of operating conditions. These diverse functional approaches of microfiltration membranes and its application towards water remediation offer superior performance over traditional treatment process thus anticipates immediate industrial application.

Finally, hollow Fe-Pd nanoparticles were synthesized for the application towards degradation of chlorinated compounds. This fabricated Fe hollow spheres have 2.6 times higher surface area and 4.28 times pore volume compare to commercial Fe catalyst. Initial investigation reveals in presence of palladium, these prepared hollow NPs can completely degrade polychlorinated biphenyl (PCB-1) anticipating future potential for water remediation application.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.303

Funding Information

This research was funded by the National Institute of Environmental Health Sciences (NIEHS) Superfund program (Grant no: PE42ES007380), National Science Foundation (NSF)- Established Program to Stimulate Competitive Research (EPSCoR) (Grant no: 1355438) and Chevron Corporation. (2015-2020)

Available for download on Wednesday, July 21, 2021

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