Browsing by Author "Clark, Chelsea A."

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    Highly Defective UiO-66 Materials for the Adsorptive Removal of Perfluorooctanesulfonate
    (American Chemical Society, 2019) Clark, Chelsea A.; Heck, Kimberly N.; Powell, Camilah D.; Wong, Michael S.; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    Perfluorooctanesulfonate (PFOS) is a persistent organic pollutant that is bioaccumulative and toxic. While its use in most countries has been restricted to certain industrial applications due to environmental and health concerns, chrome plating and semiconductor manufacturing facilities are industrial point sources of PFOS-containing wastewater. Current remediation technologies are ineffective at treating these highly concentrated industrial effluents. In this work, UiO-66 metal–organic frameworks (MOFs) of several defect concentrations were studied as sorbents for the removal of PFOS from concentrated aqueous solutions. PFOS sorption isotherms indicated that defective UiO-66, prepared with HCl as a modulator, had a maximum Langmuir sorption capacity of 1.24 mmol/g, which was ∼2× greater than powdered activated carbon (PAC), but ∼2× less than that of a commercial ion-exchange resin. Defective UiO-66 adsorbed PFOS 2 orders of magnitude faster than the ion-exchange resin. Large pore defects (∼16 and ∼20 Å) within the framework were critical to the increased adsorption capacity due to higher internal surface area and an increased number of coordinatively unsaturated Zr sites to bind the PFOS head groups. Of the common co-contaminants in chrome plating wastewaters, chloride ions have a negligible effect on PFOS sorption, while sulfate and hexavalent chromium anions compete for cationically charged adsorption sites. These materials were also effective adsorbents for the shorter-chain homologue, perfluorobutanesulfonate (PFBS). The enhanced PFOS and PFBS adsorptive properties of UiO-66 highlight the advantage of structurally defective MOFs as a water treatment approach toward environmental sustainability.
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    Titanium oxide improves boron nitride photocatalytic degradation of perfluorooctanoic acid
    (Elsevier, 2022) Duan, Lijie; Wang, Bo; Heck, Kimberly N.; Clark, Chelsea A.; Wei, Jinshan; Wang, Minghao; Metz, Jordin; Wu, Gang; Tsai, Ah-Lim; Guo, Sujin; Arredondo, Jacob; Mohite, Aditya D.; Senftle, Thomas P.; Westerhoff, Paul; Alvarez, Pedro; Wen, Xianghua; Song, Yonghui; Wong, Michael S.; Center for Nanotechnology Enabled Water Treatment
    Boron nitride (BN) has the newly-found property of degrading recalcitrant polyfluoroalkyl substances (PFAS) under ultraviolet C (UV-C, 254 nm) irradiation. It is ineffective at longer wavelengths, though. In this study, we report the simple calcination of BN and UV-A active titanium oxide (TiO2) creates a BN/TiO2 composite that is more photocatalytically active than BN or TiO2 under UV-A for perfluorooctanoic acid (PFOA). Under UV-A, BN/TiO2 degraded PFOA ∼ 15 × faster than TiO2, while BN was inactive. Band diagram analysis and photocurrent response measurements indicated that BN/TiO2 is a type-II heterojunction semiconductor, facilitating charge carrier separation. Additional experiments confirmed the importance of photogenerated holes for degrading PFOA. Outdoor experimentation under natural sunlight found BN/TiO2 to degrade PFOA in deionized water and salt-containing water with a half-life of 1.7 h and 4.5 h, respectively. These identified photocatalytic properties of BN/TiO2 highlight the potential for the light-driven destruction of other PFAS.
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    Treating Water by Degrading Oxyanions Using Metallic Nanostructures
    (American Chemical Society, 2018) Yin, Yiyuan B.; Guo, Sujin; Heck, Kimberly N.; Clark, Chelsea A.; Coonrod, Christian L.; Wong, Michael S.; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    Consideration of the water–energy–food nexus is critical to sustainable development, as demand continues to grow along with global population growth. Cost-effective, sustainable technologies to clean water of toxic contaminants are needed. Oxyanions comprise one common class of water contaminants, with many species carrying significant human health risks. The United States Environmental Protection Agency (US EPA) regulates the concentration of oxyanion contaminants in drinking water via the National Primary Drinking Water Regulations (NPDWR). Degrading oxyanions into innocuous compounds through catalytic chemistry is a well-studied approach that does not generate additional waste, which is a significant advantage over adsorption and separation methods. Noble metal nanostructures (e.g., Au, Pd, and Pt) are particularly effective for degrading certain species, and recent literature indicates there are common features and challenges. In this Perspective, we identify the underlying principles of metal catalytic reduction chemistries, using oxyanions of nitrogen (NO2–, NO3–), chromium (CrO42–), chlorine (ClO2–, ClO3–, ClO4–), and bromine (BrO3–) as examples. We provide an assessment of practical implementation issues, and highlight additional opportunities for metal nanostructures to contribute to improved quality and sustainability of water resources.