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Browsing by Author "Smith, Ethan D."

Now showing 1 - 4 of 4
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    Functionalized Cellulose Nanocrystal Nanocomposite Membranes with Controlled Interfacial Transport for Improved Reverse Osmosis Performance
    Smith, Ethan D.; Hendren, Keith D.; Haag, James; Foster, Earl Johan; Martin, Stephen M. (MDPI, 2019-01-20)
    Thin-film nanocomposite membranes (TFNs) are a recent class of materials that use nanoparticles to provide improvements over traditional thin-film composite (TFC) reverse osmosis membranes by addressing various design challenges, e.g., low flux for brackish water sources, biofouling, etc. In this study, TFNs were produced using as-received cellulose nanocrystals (CNCs) and 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs) as nanoparticle additives. Cellulose nanocrystals are broadly interesting due to their high aspect ratios, low cost, sustainability, and potential for surface modification. Two methods of membrane fabrication were used in order to study the effects of nanoparticle dispersion on membrane flux and salt rejection: a vacuum filtration method and a monomer dispersion method. In both cases, various quantities of CNCs and TOCNs were incorporated into a polyamide TFC membrane via in-situ interfacial polymerization. The flux and rejection performance of the resulting membranes was evaluated, and the membranes were characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The vacuum filtration method resulted in inconsistent TFN formation with poor nanocrystal dispersion in the polymer. In contrast, the dispersion method resulted in more consistent TFN formation with improvements in both water flux and salt rejection observed. The best improvement was obtained via the monomer dispersion method at 0.5 wt% TOCN loading resulting in a 260% increase in water flux and an increase in salt rejection to 98.98 ± 0.41% compared to 97.53 ± 0.31% for the plain polyamide membrane. The increased flux is attributed to the formation of nanochannels at the interface between the high aspect ratio nanocrystals and the polyamide matrix. These nanochannels serve as rapid transport pathways through the membrane, and can be used to tune selectivity via control of particle/polymer interactions.
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    Mitigation of bidirectional solute flux in forward osmosis via membrane surface coating of zwitterion functionalized carbon nanotubes
    Zou, Shiqiang; Smith, Ethan D.; Lin, Shihong; Martin, Stephen M.; He, Zhen (Elsevier, 2019-07-08)
    Forward osmosis (FO) has emerged as a promising membrane technology to yield high-quality reusable water from various water sources. A key challenge to be solved is the bidirectional solute flux (BSF), including reverse solute flux (RSF) and forward solute flux (FSF). Herein, zwitterion functionalized carbon nanotubes (Z-CNTs) have been coated onto a commercial thin film composite (TFC) membrane, resulting in BSF mitigation via both electrostatic repulsion forces induced by zwitterionic functional groups and steric interactions with CNTs. At a coating density of 0.97 gm⁻², a significantly reduced specific RSF was observed for multiple draw solutes, including NaCl (55.5% reduction), NH₄H₂PO₄(83.8%), (NH₄)₂HPO₄ (74.5%), NH₄Cl (70.8%), and NH₄HCO₃ (61.9%). When a synthetic wastewater was applied as the feed to investigate membrane rejection, FSF was notably reduced by using the coated membrane with fewer pollutants leaked to the draw solution, including NH₄⁺-N (46.3% reduction), NO₂⁻₋N (37.0%), NO₂⁻₋N (30.3%), K⁺ (56.1%), PO₄³⁻₋P (100%), and Mg²⁺ (100%). When fed with real wastewater, a consistent water flux was achieved during semi-continuous operation with enhanced fouling resistance. This study is among the earliest efforts to address BSF control via membrane modification, and the results will encourage further exploration of effective strategies to reduce BSF.
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    Understanding the Impact of High Aspect Ratio Nanoparticles on Desalination Membrane Performance
    Smith, Ethan D. (Virginia Tech, 2020-04-16)
    Access to clean water is one of the world's foremost challenges that has been addressed on a large scale by membrane-based separation processes for the last six decades. Commercial membrane technology within one operation, reverse osmosis, has remained consistent since the late 1970s, however within the last two decades, access to nanotechnology has created a realm of study involving thin film nanocomposite (TFN) membranes, in which nanoparticles are incorporated into existing membrane designs. Desirable properties of the nanoparticles may positively impact qualities of the membrane like performance, anti-fouling behavior, and physical strength. In the present work, two types of nanoparticles have been evaluated for their potential as TFN additives: cellulose nanocrystals (CNCs) and metal-organic framework (MOF) nanorods. CNCs were chosen due to their high aspect ratios, mechanical strength, and potential for surface functionalization. MOF nanorods are also of interest given their aspect ratios and potential for functionalization, but they also possess defined pores, the sizes of which may be tuned with post-synthetic modification. Both CNCs and MOF nanorods were incorporated into TFN membranes via interfacial polymerization, and the resulting membranes were characterized using a variety of techniques to establish their performances, but also to gain insight into how the presence of each nanoparticle might be affecting the membrane active layer formation. A resulting CNC membrane (0.5 wt% loading) exhibited a 160% increase in water flux and an improvement in salt rejection to 98.98 ± 0.41 % compared to 97.53 ± 0.31 % for a plain polyamide control membrane. Likewise, a MOF nanorod membrane (0.01 wt% loading) with a high ratio of acid chain modification exhibited a 95% flux increase with maintained high salt rejection. For the CNCs, the flux increase is attributed to the formation of nanoscale voids along the length of each particle that form during the interfacial polymerization. These nanochannels introduce new rapid water transport pathways within the active layer of each membrane while maintaining ion rejection. The proposed mechanism for the MOF nanorods also introduces nanochannels into each membrane, but the presence of each nanorod's pore structure may offer another transport pathway for water molecules, one that varies with pore size. In combination, these results have allowed the study of molecular transport of water molecules and various ion species within the active layer of a thin film composite RO membrane. Understanding these phenomena will allow the development of smarter membrane materials to address present-day and future separations challenges. Carbon nanotubes are also demonstrated as surface modifiers for forward osmosis (FO) membranes to address issues unique to the FO process, namely reverse solute flux (RSF). This method shows promise, as a coating density of 0.97 g/m2 reduced RSF for many draw solution species, including a 55% reduction for sodium chloride.
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    Zooming in on adverse birth outcomes in coalfield regions of Central Appalachia
    Marston, Michael L.; Wu, Connor Y. H.; Smith, Ethan D.; Gohlke, Julia M.; Kolivras, Korine N.; Krometis, Leigh-Anne H. (Virginia Tech. Powell River Project, 2018)
    Health disparities account for significant differences in mortality and morbidity risks in Central Appalachia (encompassing parts of WV, KY, TN and VA) compared to other U.S. regions, yet research addressing environmental factors potentially contributing to these health disparities is lacking. Central Appalachia offers a unique opportunity to examine environmental exposures associated with resource extraction. Coal production from large surface mines was the dominant resource extraction method in the 1990s-2000s and is now decreasing as other resource extraction methods increase. We hypothesize that health risks associated with air and water pollution exposure are greater for Central Appalachian residents living within close proximity to active surface mines. The results described here begins to link exposure with health outcomes using individual-level birth record data. We have extended spatiotemporal characterization of boundaries associated with surface mining between 1990 and 2015 in all Central Appalachia counties. Results indicate that from 1990 to 2015, 1806 km2 of land across the study area was disturbed by mining activities, which equates to approximately 4.2% of the study-defined Central Appalachia region. Temporal trends show a decreasing amount of active surface mining sites over the study period. Using a previously developed surface mining dataset that only covered southwest Virginia coalfields, we tested the hypothesis that maternal address proximity to active surface mining was positively associated with preterm birth. No significant association was found; however the sample size (n=5008) was very small due to poor geocoding rates, particularly in earlier years, and overall low number of births between 1990-2015 in this small, rural area (n=14,269). Our next steps will be to improve inference and precision in effect estimates by increasing sample size with inclusion of data from TN, KY and WV, application of the accuracy–assessed surface mining extent dataset described here to improve estimate of proximity to active surface mining, and inclusion of watershed boundaries, drinking water violation datasets, as well as airshed characterization. Ultimately, we hope this research will aid in determining the underpinnings of health disparities in Central Appalachian communities, ultimately leading to research, policy and practice improvements that may be generalizable to other rural areas beyond Central Appalachia.