Browsing by Author "Westerhoff, Paul"

Now showing 1 - 5 of 5
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    Catalytic Converters for Water Treatment
    (American Chemical Society, 2019) Heck, Kimberly N.; Garcia-Segura, Sergi; Westerhoff, Paul; Wong, Michael S.; Nanotechnology Enabled Water Treatment (NEWT) Center
    Fresh water demand is driven by human consumption, agricultural irrigation, and industrial usage and continues to increase along with the global population. Improved methods to inexpensively and sustainably clean water unfit for human consumption are desired, particularly at remote or rural locations. Heterogeneous catalysts offer the opportunity to directly convert toxic molecules in water to nontoxic products. Heterogeneous catalytic reaction processes may bring to mind large-scale industrial production of chemicals, but they can also be used at the small scale, like catalytic converters used in cars to break down gaseous pollutants from fuel combustion. Catalytic processes may be a competitive alternative to conventional water treatment technologies. They have much faster kinetics and are less operationally sensitive than current bioremediation-based methods. Unlike other conventional water treatment technologies (i.e., ion exchange, reverse osmosis, activated carbon filtration), they do not transfer contaminants into separate, more concentrated waste streams. In this Account, we review our efforts on the development of heterogeneous catalysts as advanced reduction technologies to treat toxic water contaminants such as chlorinated organics and nitrates. Fundamental understanding of the underlying chemistry of catalytic materials can inform the design of superior catalytic materials. We discuss the impact of the catalytic structure (i.e., the arrangement of metal atoms on the catalyst surface) on the catalyst activity and selectivity for these aqueous reactions. To explore these aspects, we used model metal-on-metal nanoparticle catalysts along with state-of-the-art in situ spectroscopic techniques and density functional theory calculations to deduce the catalyst surface structure and how it affects the reaction pathways and hence the activity and selectivity. We also discuss recent developments in photocatalysis and electrocatalysis for the treatment of nitrates, touching on fundamentals and surface reaction mechanisms. Finally, we note that despite over 20 years of growing research into heterogeneous catalytic systems for water contaminants, only a few pilot-scale studies have been conducted, with no large-scale implementation to date. We conceive of modular, on- or off-grid catalytic units that treat drinking water at the household tap, at a community well, or for larger-scale reuse of agricultural runoff. We discuss how these may be enhanced by combination with photocatalytic or electrocatalytic processes and how these reductive catalytic modules (catalytic converters for water) can be coupled with other modules for the removal of potential water contaminants.
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    Inhibition of biofouling on reverse osmosis membrane surfaces by germicidal ultraviolet light side-emitting optical fibers
    (Elsevier, 2022) Rho, Hojung; Yu, Pingfeng; Zhao, Zhe; Lee, Chung-Seop; Chon, Kangmin; Perreault, François; Alvarez, Pedro J.J.; Amy, Gary; Westerhoff, Paul; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    Biofouling of membrane surfaces poses significant operational challenges and costs for desalination and wastewater reuse applications. Ultraviolet (UV) light can control biofilms while reducing chemical usage and disinfection by-products, but light deliveries to membrane surfaces in spiral wound geometries has been a daunting challenge. Thin and flexible nano-enabled side-emitting optical fibers (SEOFs) are novel light delivery devices that enable disinfection or photocatalytic oxidation by radiating UV light from light-emitting diodes (LEDs). We envision SEOFs as an active membrane spacer to mitigate biofilm formation on reverse osmosis (RO) membranes. A lab-scale RO membrane apparatus equipped with SEOFs allowed comparison of UV-A (photocatalysis-enabled) versus UV-C (direct photolysis disinfection). Compared against systems without any light exposure, systems with UV-C light formed thinner—but denser—biofilms, prevented permeate flux declines due to biofouling, and maintained the highest salt rejection. Results were corroborated by in-situ optical coherence tomography and ex-situ measurements of biofilm growth on the membranes. Transcriptomic analysis showed that UV-C SEOFs down-regulated quorum sensing and surface attachment genes. In contrast, UV-A SEOFs upregulated quorum sensing, surface attachment, and oxidative stress genes, resulting in higher extracellular polymeric substances (EPS) accumulation on membrane surfaces. Overall, SEOFs that deliver a low fluence of UV-C light onto membrane surfaces are a promising non-chemical approach for mitigating biofouling formation on RO membranes.
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    Superparamagnetic nanoadsorbents for the removal of trace As(III) in drinking water
    (Elsevier, 2021) Marcos-Hernández, Mariana; Arrieta, Roy A.; Ventura, Karen; Hernández, José; Powell, Camilah D.; Atkinson, Ariel J.; Markovski, Jasmina S.; Gardea-Torresdey, Jorge; Hristovski, Kiril D.; Westerhoff, Paul; Wong, Michael S.; Villagrán, Dino
    A series of novel zeolitic imidazolate framework (ZIF) decorated superparamagnetic graphene oxide hybrid nanoadsorbents were synthesized, characterized, and tested for their As(III) adsorbed amount in simulated drinking water. The three composite nanomaterials are based each on three isostructural and water stable ZIFs, (C-1 based on ZIF-8, C-2 based on ZIF-67, and C-3 based on ZIF-Zn/Co). The composite nanomaterials and there parent materials were characterized through pXRD, TEM, FTIR, BET and magnetometry methods (SQUID), and were tested as adsorbents in a representative drinking water matrix containing arsenite (As(III)) at an initial trace concentration (realistic in some natural drinking water sources) of 35 µg/L. The nanoadsorbents were magnetically captured and removed after adsorption in batch conditions. Out of the three composites, C-2 shows the highest As(III) adsorbed amount at an initial concentration of 35 µg/L (q0) of 202 µg/g, followed by C-3 with 102 µg/g and C-1 with 82 µg/g.
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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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    Utilizing the broad electromagnetic spectrum and unique nanoscale properties for chemical-free water treatment
    (Elsevier, 2021) Westerhoff, Paul; Alvarez, Pedro J.J.; Kim, Jaehong; Li, Qilin; Alabastri, Alessandro; Halas, Naomi J.; Villagran, Dino; Zimmerman, Julie; Wong, Michael S.; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT)
    Clean water is critical for drinking, industrial processes, and aquatic organisms. Existing water treatment and infrastructure are chemically intensive and based on nearly century-old technologies that fail to meet modern large and decentralized communities. The next-generation of water processes can transition from outdated technologies by utilizing nanomaterials to harness energy from across the electromagnetic spectrum, enabling electrified and solar-based technologies. The last decade was marked by tremendous improvements in nanomaterial design, synthesis, characterization, and assessment of material properties. Realizing the benefits of these advances requires placing greater attention on embedding nanomaterials onto and into surfaces within reactors and applying external energy sources. This will allow nanomaterial-based processes to replace Victorian-aged, chemical intensive water treatment technologies.