Year of Publication
Doctor of Philosophy (PhD)
Chemical and Materials Engineering
Dr. Dibakar Bhattacharyya
Among the next generation materials being investigated for membrane development, partially reduced Graphene Oxide (rGO) has received increasing attention from the membrane community. rGO-based nanofiltration membranes have shown promising results in applications such as partial desalination, organic contaminant removal, gas-phase separations, and separations from solvent media. rGO offers a unique platform compared to common polymeric membranes since it can be used for separation applications in both aqueous and organic solvent media. An rGO-based platform could also be utilized to synthesize reactive membranes, giving rGO membranes the additional capability of reactively removing organic contaminants. This research focuses on the synthesis of rGO and nanocomposite membranes for applications including the separation of high-value phenolic compounds from a solvent-water mixture, removal of organic contaminants, and treatment of refinery wastewater.
First, the behavior of a rGO membrane in water and isopropanol was investigated along with its ability to separate high-value, lignin-derived oligomeric compounds from a solvent-water mixture. This study revealed the formation of stable sorbates of water in the GO channels that resulted in declined membrane permeance and improved size-exclusion cutoff. Through controlled reduction of GO by heat treatment, it was demonstrated that physicochemical properties of the GO membrane could be modulated and separation performance tuned based on the extent of reduction. A varying degree of interlayer spacing was attained between the GO laminates by controlling the O/C ratio of GO. This allowed the rGO membrane to achieve tunable molecular separation of lignin-derived model oligomeric compounds from a solvent-water mixture.
Second, the mechanism of ionic transport through the rGO membrane was studied as well as its application in partial desalination and removal of persistent organic contaminants from water. Through comprehensive experimental investigations and mathematical analysis, along with the aid of the extended Nernst Planck equation, the impacts of steric hindrance and charge interactions on the underlying ion transport mechanism were quantified. Charge interactions were observed to be the dominant exclusion mechanism for the rGO membranes. The application of rGO membranes for treatment of high TDS produced water was investigated with the goal of partial hardness and dissolved oil removal. In addition, this study demonstrated the removal of emerging organic contaminants, specifically perfluorooctanoic acid, by rGO membranes and elucidated a charge interaction-dominated exclusion mechanism for this contaminant, as well.
Finally, rGO-based and microporous polyvinylidene fluoride (PVDF)-based catalytic membrane platforms were synthesized for removal of organic contaminants via an oxidative pathway. Herein, an advanced oxidation process was integrated with membrane technology by the in-situ synthesis of Fe-based nanoparticles. The unique capability to oxidatively remove contaminants in a continuous mode of operation was explored in addition to the separation performance of the membrane. The rGO-based platform achieved high oxidative removal of trichloroethylene via a sulfate-free, radical-mediated pathway, while simultaneously removing humic acids from water and potentially eliminating undesired side reactions. A PVDF-based microporous catalytic membrane platform was shown to effectively remove organic impurities, such as Naphthenic acids, from high TDS produced water by the same pathway. The enhancement of reaction extent for elevated temperatures and longer residence times was also quantified in this study.
These studies benefit the membrane community in the following ways: 1) The work identifies the critical role of the physicochemical properties of GO, such as the O/C ratio and water sorption, for determining the permeability-selectivity of rGO membranes for solvent nanofiltration. 2) Investigations of ion transport through rGO membranes led to an understanding of a charge-dominated separation mechanism for ion retention. The Nernst-Planck equation-based approach employed in this study would enable further assessment and comparison of rGO membranes under a wide set of parameters. 3) Catalytic membrane platforms (rGO and microporous PVDF-based) were synthesized for conducting advanced oxidation reactions in the porous membrane domain, demonstrating potential applications in environmental remediation of organic contaminants.
Digital Object Identifier (DOI)
This research was funded by the NIEHS Superfund program (Grant no: PE42ES007380; Years: 2015-2019), NSF-EPSCOR (Grant no: 1355438; Years: 2015-2019), Chevron Corp. (Years: 2015-2019), and by Australian Research Council (through an A ARC Linkage LP140100959 grant; Years: 2015-2018).
Aher, Ashish, "SYNTHESIS, CHARACTERIZATION AND APPLICATIONS OF REDUCED GRAPHENE OXIDE AND COMPOSITE MEMBRANES FOR SELECTIVE SEPARATIONS AND REMOVAL OF ORGANIC CONTAMINANTS" (2019). Theses and Dissertations--Chemical and Materials Engineering. 111.