Date of Award

5-31-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Tamara M. Gund

Third Advisor

Robert Benedict Barat

Fourth Advisor

Edgardo Tabion Farinas

Fifth Advisor

Yong Ick Kim

Abstract

Water scarcity is foreseen to be one of the great global issues in the coming decades. The challenges are not only in providing water supply to cope with the growing public demand, but recovering clean water to natural resources. Clean water supply, from brackish and seawater is attractive. Membrane distillation (MD) is an emerging thermal membrane-based process that has been used for desalination and other pollutant separations from water. MD can be operated at low temperature, so low-grade energy sources are a good alternative heat source for MD. High salt rejection and low membrane fouling also make MD interesting for sea water desalination and wastewater treatment. In this dissertation, three major challenges related to water treatment are addressed. Approaches to enhance the MD performance by modifying the commercial membranes with different carbon-based nanomaterials are explored. These are the basis of this dissertation.

In the first application, graphene oxide (GO) is immobilized on the permeate side of a polytetrafluoroethylene (PTFE) membrane for desalination via direct contact membrane distillation (DCMD). The hydrophilicity of the permeate side of the membrane is enhanced by immobilizing the GO to facilitate fast condensation and withdrawal of the permeate water vapors. The graphene oxide immobilized membrane on the permeate side (GOIM-P) improves the performance of DCMD. The water vapor flux of the modified membrane is higher than that of the unmodified membrane for all operating parameters; temperature, feed flow rate, and concentration.

In the second application, the raw carbon nanotubes (CNTs) and the more polar carboxylated carbon nanotubes (referred to as f-CNTs) are employed to create carbon nanotube immobilized membranes (CNIMs) for ammonia separation via direct contact membrane distillation (DCMD). The ammonia removal by both CNIMs are markedly superior to that of the original PTFE membrane, while functionalized CNIM (CNIM-f) shows the best performance in terms of flux, mass transfer coefficients, and selectivity. The enhancement in ammonia removal with f-CNTs is attributed to the favored chemisorption of ammonia with the carboxylic groups of the f-CNTs.

In the third major application, functionalized carbon nanotube immobilized membranes (CNIM-f) and graphene oxide immobilized membranes (GOIM) are applied to separate methyl tert-butyl ether (MTBE) from its aqueous solution via sweep gas membrane distillation (SGMD). CNIM-f provides the best performance in terms of flux, removal efficiency, mass transfer coefficients and overall selectivity. The immobilization of functionalized CNTs (f-CNTs) alters the surface characteristics of the membrane and enhanced partition coefficients, and thus assists MTBE transport across the membrane. The fast adsorption-desorption of organic moiety on f-CNTs results in activated diffusion and lead to high flux enhancement.

This dissertation shows that the modification of the membranes with carbon-based materials namely CNTs, GO and their derivatives is an effective alternative to enhance the performance of MD and the membrane modified by CNTs and GO has the great potentials for water purification and solvent removal from aqueous solution using MD technology

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