Browsing by Author "Wang, Bo"
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Item Analysis of physiological roles of Drosophila calmodulin through in vivo genetic and in vitro structure/function studies(2003) Wang, Bo; Beckingham, Kathleen M.Calmodulin (CaM), a small protein found in all eukaryotes examined, is a major component of Ca2+ signaling pathways and functions as a Ca2+ signal sensor and transducer. A wide variety of targets are regulated by CaM, including enzymes, cytoskeleton elements and ion channels. To dissect the in vivo roles of Drosophila CaM, a series of Cam mutations were previously generated in the Beckingham lab. This thesis primarily concerns investigation of two Cam mutations; Cam7, a point mutation encoding V91G mutant CaM, and a null mutation, Camn339. Cam7 causes unprecedented defects. Cam 7 mutants are sluggish as larvae and form aberrant pupal cases with highly indented rings around the body. Mutant pupae never eclose and most die as pharate adults with head defects. Expression of wild type CaM specifically in the musculature is shown here to partially rescue the Cam7 phenotype, suggesting that muscle function is primarily affected by this mutation. Further, genetic studies performed suggest that misregulation of the ryanodine receptor (RyR), a Ca2+ channel on the sarcoplasmic reticulum, may be largely responsible for the muscle defects. Muscle contraction-associated Ca2+ release is shown here to be drastically altered in the Cam7 mutant. Biochemical studies revealed that the V91G mutation has no detectable effects on Ca2+-binding or the Ca2+-induced conformation of CaM. However, the conformation of Ca2+-free CaM is altered. Examination of the interaction between CaM and the RyR CaM binding region indicates that the V91G mutation would alter regulation of the RyR so as to cause Ca2+ leaking through the RyR channel. The ability of CaM variants with the N- or C-terminal Ca 2+-binding sites inactivated to rescue the Cam7 phenotype was also investigated. Consistent with prior CaM-RyR studies, the C-terminal binding site mutant exacerbated the phenotype. However, the N-terminal binding site mutant showed an "over-rescue" effect causing muscle relaxation. In contrast, the main behavioral defect observed in Cam null mutant larvae was found to be rescued by neural, not muscle, expression of wild type CaM and neither the N-terminal nor C-terminal Ca2+-binding site mutants had any effect on this defective behavior, suggesting a different molecular pathway is affected.Item Boron Nitride Based Photocatalysts for Efficient PFAS Degradation(2023-08-08) Wang, Bo; Wong, MichaelThe strong persistence, pervasiveness, and toxicity of per- and polyfluorinated substances (PFAS) make them recalcitrant contaminants of emerging concern. The stability of C-F bonds and the surfactant properties of PFAS lead to incomplete removal by standard water treatment methods, and ppb (μg/L) levels of PFAS have been detected in human tissues and blood serum. Exposure to parts-per-quadrillion of PFAS in water has negative health effects, including kidney, liver, and reproductive problems in adults, suppressed immune response to vaccines, and neurological/behavioral issues in children. The U.S. EPA published a proposed rule in 2023 establishing Federal Maximum Contaminant Levels (MCLs) for 6 PFAS in drinking water. Current water treatment technologies only physically remove, but not destroy PFAS, and also general PFAS contaminated waste. Photocatalysis has been proved as an efficient approach for degrading PFAS in water with air as the oxidant, and light as the energy source, but identifying photocatalysts is still challenging. The primary goal of this work is to present that boron nitride-based materials are excellent catalysts for the PFAS remediation in water, in which three boron nitride-based photocatalysts were prepared and demonstrated their efficiency for PFAS destruction under UV light or even solar illumination. The corresponding mechanism has also been investigated. These findings present fresh opportunities for materials design and for the re-evaluation of other wide band gap semiconductors for PFAS photocatalytic degradation. The insights also serve as rationally-guided design principles for improved heterogeneous photocatalysts. Boron nitride (BN) was discovered to degrade PFOA upon irradiation with 254 nm (ultraviolet C, UVC) light. The ability of BN to degrade PFOA photocatalytically has previously been unreported and is unexpected, because its band gap is too large for light absorption. Radical scavenging experiments suggest that PFOA degrades in the presence of BN via a hole-initiated reaction pathway similar to the TiO2 case and involves superoxide/hydroperoxyl and hydroxyl radicals. Surface defects were surmised to allow BN to absorb in the UVC range and to photogenerate reactive oxygen species. Sealed batch studies indicated BN was ∼2 and ∼4 times more active than TiO2, before and after ball milling the material, respectively. BN can be reused, showing no decrease in activity over three cycles. BN was active for the photocatalytic degradation of GenX, another PFAS of concern. We then investigated why BN exhibited superior photoreactivity towards PFAS degradation. The role of BN’s surface hydrophobicity on PFOA photocatalysis was investigated by comparing BN (hexagonal phase) with TiO2 (anatase phase) under reaction conditions in which the exposed surface areas were the same. BN exhibited a ~2.5× faster PFOA degradation rate compared to TiO2, with both materials photo-generating holes at nearly identical rates (23 μM EDTA/min for BN vs. 22 μM EDTA/min for TiO2) as quantified through hole scavenging experiments. Sorption experiments indicated that PFOA surface coverage was ~2× higher on BN than on TiO2. Though surface coverage correlates with PFOA activity, it does not completely explain it. Density functional theory calculations highlight the importance of BN hydrophobicity in inhibiting the competing hole reaction with surface-hydroxyls. These insights serve as rationally-guided design principles for improved heterogeneous photocatalysts. Boron nitride (BN) destroys PFAS under UVC irradiation, but is ineffective at longer wavelengths, though. By simple calcination of BN and UVA active titanium oxide (TiO2), it creates a BN/TiO2 composite that is more photocatalytically active than BN or TiO2 under UVA for PFOA. Under UVA, 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. Lastly, we found that commercially available defective BN can produce ammonia due to its hydrolytic instability. We hypothesize that BN hydrolysis can be inhibited by preventing the exposure of edge defect sites to water. In this study, we prepared SiO2-coated BN ("SiO2-BN") with varying amounts of SiO2 through tetraethyl orthosilicate (TEOS) hydrolysis and condensation. We then tested these materials for PFOA photodegradation under UVC illumination. Unexpectedly, the SiO2 coating promoted PFOA sorption and degradation, with 6 wt% SiO2-BN exhibiting a 1.6× faster PFOA photodegradation rate than BN and achieving near complete (95%) defluorination after 24 hours of UVC irradiation. While some enhancement in PFOA degradation is likely due to the increased PFOA sorption, the SiO2 coating also functionally removes B-OH edge sites, thus inhibiting the competing reaction of photogenerated holes with surface hydroxyls. Furthermore, the SiO2 coating stabilizes BN, as evidenced by 6 wt% SiO2-BN exhibiting an approximately 4× lower formation rate of N-containing byproducts compared to BN. These findings provide valuable insights and directions for the design of stable and effective catalysts for PFAS photocatalysis.Item Complete defluorination of per- and polyfluoroalkyl substances — dream or reality?(Elsevier, 2023) Arana Juve, Jan-Max; Wang, Bo; Wong, Michael S.; Ateia, Mohammed; Wei, Zongsu; The Catalysis and Nanomaterials LaboratoryThe consensus of removing per- and polyfluoroalkyl substances (PFAS) from the environment is widely recognized and enlightened by the near-zero standards released from the U.S. Environmental Protection Agency in 2023. The only way to achieve the goal of zero fluoro-pollution is to fully defluorinate or mineralize PFAS, but current technologies only partially defluorinate a limited number of PFAS, which can lead to the creation of potentially more toxic short-chain intermediates. Therefore, we discuss herein the need to broaden the scope of tested PFAS, summarize the state-of-the-art degradation technologies, and provide perspectives to achieve complete defluorination. Besides fundamental knowledge gaps in defluorination reactions, technological gaps in the aspects of water matrix effects, pilot tests, and cost analysis also limit the application and comparison of different treatment technologies. This work would shed light on further research to find solutions in the complete defluorination of PFAS.Item Domain-dependent strain and stacking in two-dimensional van der Waals ferroelectrics(Springer Nature, 2023) Shi, Chuqiao; Mao, Nannan; Zhang, Kena; Zhang, Tianyi; Chiu, Ming-Hui; Ashen, Kenna; Wang, Bo; Tang, Xiuyu; Guo, Galio; Lei, Shiming; Chen, Longqing; Cao, Ye; Qian, Xiaofeng; Kong, Jing; Han, YimoVan der Waals (vdW) ferroelectrics have attracted significant attention for their potential in next-generation nano-electronics. Two-dimensional (2D) group-IV monochalcogenides have emerged as a promising candidate due to their strong room temperature in-plane polarization down to a monolayer limit. However, their polarization is strongly coupled with the lattice strain and stacking orders, which impact their electronic properties. Here, we utilize four-dimensional scanning transmission electron microscopy (4D-STEM) to simultaneously probe the in-plane strain and out-of-plane stacking in vdW SnSe. Specifically, we observe large lattice strain up to 4% with a gradient across ~50 nm to compensate lattice mismatch at domain walls, mitigating defects initiation. Additionally, we discover the unusual ferroelectric-to-antiferroelectric domain walls stabilized by vdW force and may lead to anisotropic nonlinear optical responses. Our findings provide a comprehensive understanding of in-plane and out-of-plane structures affecting domain properties in vdW SnSe, laying the foundation for domain wall engineering in vdW ferroelectrics.Item Electrothermal mineralization of per- and polyfluoroalkyl substances for soil remediation(Springer Nature, 2024) Cheng, Yi; Deng, Bing; Scotland, Phelecia; Eddy, Lucas; Hassan, Arman; Wang, Bo; Silva, Karla J.; Li, Bowen; Wyss, Kevin M.; Ucak-Astarlioglu, Mine G.; Chen, Jinhang; Liu, Qiming; Si, Tengda; Xu, Shichen; Gao, Xiaodong; JeBailey, Khalil; Jana, Debadrita; Torres, Mark Albert; Wong, Michael S.; Yakobson, Boris I.; Griggs, Christopher; McCary, Matthew A.; Zhao, Yufeng; Tour, James M.Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative pollutants that can easily accumulate in soil, posing a threat to environment and human health. Current PFAS degradation processes often suffer from low efficiency, high energy and water consumption, or lack of generality. Here, we develop a rapid electrothermal mineralization (REM) process to remediate PFAS-contaminated soil. With environmentally compatible biochar as the conductive additive, the soil temperature increases to >1000 °C within seconds by current pulse input, converting PFAS to calcium fluoride with inherent calcium compounds in soil. This process is applicable for remediating various PFAS contaminants in soil, with high removal efficiencies ( >99%) and mineralization ratios ( >90%). While retaining soil particle size, composition, water infiltration rate, and cation exchange capacity, REM facilitates an increase of exchangeable nutrient supply and arthropod survival in soil, rendering it superior to the time-consuming calcination approach that severely degrades soil properties. REM is scaled up to remediate soil at two kilograms per batch and promising for large-scale, on-site soil remediation. Life-cycle assessment and techno-economic analysis demonstrate REM as an environmentally friendly and economic process, with a significant reduction of energy consumption, greenhouse gas emission, water consumption, and operation cost, when compared to existing soil remediation practices.Item Niobium Oxide Photocatalytically Oxidizes Ammonia in Water at Ambient Conditions(SciELO, 2024) Elias, Welman; Clark, Chelsea; Heck, Kimberly; Arredondo, Jacob; Wang, Bo; Toro, Andras; Kürtib, László; Wong, Michael; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water TreatmentAmmonia contamination in water is a significant environmental issue since it is toxic and leads to eutrophication. Photocatalysis has been investigated as a strategy for ammonia degradation but can potentially form toxic nitrite (NO2–) and nitrate (NO3–) byproducts. This work reports on the ability of niobium oxide (Nb2O5) to photocatalytically oxidize aqueous-phase ammonia (NH3). Whereas as-synthesized Nb2O5 showed little catalytic activity (< 1% NH3 conversion after 6 h of UV-C irradiation, at room temperature and atmospheric pressure, and under O2 headspace), Nb2O5 treated in basic solution (OH-Nb2O5) was able to photocatalytically degrade NH3 at ca. 9% conversion after six hours, with ca. 70% selectivity to the desired N2, with a first-order rate constant of ca. 12 times higher than the as synthesize catalyst (1.6 × 10–3 min–1 vs. 2.0 × 10–2 min–1). Raman spectroscopic analysis indicated the presence of terminal Nb=O species after base treatment of Nb2O5, implicating them as catalytically active sites. These results underscore how a simple structural modification can significantly affect photocatalytic activity for aqueous ammonia oxidation.Item 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 TreatmentBoron 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.