Browsing by Author "Wang, Zhe"

Now showing 1 - 6 of 6
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    Construction of active sites for electrocatalysis on carbon materials
    (2021-11-30) Wang, Zhe; Tour, James M.
    With the rapid increase of greenhouse gas emissions, there is an urgent need to produce fuels like dihydrogen (H2) and chemicals like ammonia (NH3) and hydrogen peroxide (H2O2) in a cleaner and more efficient way. Electrochemical conversions of dinitrogen (N2), dioxygen (O2), carbon dioxide (CO2) and water (H2O) can afford fuels and chemicals with high selectivity, efficiency and reaction rates under mild conditions. These processes also help to store and redistribute renewable energy to better match societal needs. However, electrocatalysts with high efficiency are still in need of further development. Carbon materials, which exhibit high electrical conductivity, larger specific surface area and good chemical stability, are promising candidates for making electrocatalysts. Since well-defined hexagonal defect-free carbon materials are electrochemically inert, it is difficult to synthesize highly active catalysts with single-atomic sites and requisite carbon defects which are required for efficient conversion reactions. This thesis begins with the introduction of single-atomic sites on carbon materials. In Chapter 1, single-atomic Mo was anchored on holey nitrogen-doped graphene, which proved to be an efficient catalyst to selectively reduce N2 to ammonia (NH3). This method could be a possible alternative to the traditional Haber-Bosch process that operates at a high temperature and pressure. In Chapter 2, a new method to introduce single atoms into the carbon frame, namely flash Joule heating, was present, with which high-purity pyrrole-type FeN4 active sites were prepared. These iron-rich carbon materials exhibited good performance in both the oxygen reduction reaction and the CO2 reduction reaction. In both chapters, the single-atomic nature and coordination environment were confirmed with a series of microscopic and spectroscopic methods, including X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption near-edge structure (XANES). O-containing functional groups and N-dopants are normally considered as the active sites for the 2-electron oxygen reduction reaction. However, the carbon defects formed during the preparation process were ignored. By decoupling the formation of carbon defects with heteroatom doping, the critical role of carbon defects in the catalytic process was illustrated in Chapter 3 and Chapter 4. The synergistic effect of carbon defects and semiconductor materials in the 2-electron oxygen reduction reaction was analyzed using commercial carbon black and titanium dioxide (TiO2) as the model in Chapter 5.
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    High-surface-area corundum nanoparticles by resistive hotspot-induced phase transformation
    (Springer Nature, 2022) Deng, Bing; Advincula, Paul A.; Luong, Duy Xuan; Zhou, Jingan; Zhang, Boyu; Wang, Zhe; McHugh, Emily A.; Chen, Jinhang; Carter, Robert A.; Kittrell, Carter; Lou, Jun; Zhao, Yuji; Yakobson, Boris I.; Zhao, Yufeng; Tour, James M.; Smalley-Curl Institute; NanoCarbon Center; Welch Institute for Advanced Materials
    High-surface-area α-Al2O3 nanoparticles are used in high-strength ceramics and stable catalyst supports. The production of α-Al2O3 by phase transformation from γ-Al2O3 is hampered by a high activation energy barrier, which usually requires extended high-temperature annealing (~1500 K, > 10 h) and suffers from aggregation. Here, we report the synthesis of dehydrated α-Al2O3 nanoparticles (phase purity ~100%, particle size ~23 nm, surface area ~65 m2 g−1) by a pulsed direct current Joule heating of γ-Al2O3. The phase transformation is completed at a reduced bulk temperature and duration (~573 K, < 1 s) via an intermediate δʹ-Al2O3 phase. Numerical simulations reveal the resistive hotspot-induced local heating in the pulsed current process enables the rapid transformation. Theoretical calculations show the topotactic transition (from γ- to δʹ- to α-Al2O3) is driven by their surface energy differences. The α-Al2O3 nanoparticles are sintered to nanograined ceramics with hardness superior to commercial alumina and approaching that of sapphire.
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    Integrated building analysis and design system using distributed object computing
    (1999) Wang, Zhe; Terk, Michael
    This study describes a new approach to building integrated design using distributed object technology. It identifies a number of issues involved in integrating tools initially developed for stand-alone use into an integrated design environment and shows how this approach can be used to address these issues. The benefits of this approach are illustrated by the description of IBADS, an integrated building analysis and design environment, implemented during this research effort. IBADS uses the proposed approach to integrate commercial off-the-shelf software packages AutoCAD, Etabs and Steeler into an environment for design of 2-D frames.
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    Oxidized Activated Charcoal Nanozymes: Synthesis, and Optimization for In Vitro and In Vivo Bioactivity for Traumatic Brain Injury
    (Wiley, 2024) McHugh, Emily A.; Liopo, Anton V.; Mendoza, Kimberly; Robertson, Claudia S.; Wu, Gang; Wang, Zhe; Chen, Weiyin; Beckham, Jacob L.; Derry, Paul J.; Kent, Thomas A.; Tour, James M.; Smalley-Curl Institute;NanoCarbon Center;Welch Institute for Advanced Materials
    Carbon-based superoxide dismutase (SOD) mimetic nanozymes have recently been employed as promising antioxidant nanotherapeutics due to their distinct properties. The structural features responsible for the efficacy of these nanomaterials as antioxidants are, however, poorly understood. Here, the process–structure–property–performance properties of coconut-derived oxidized activated charcoal (cOAC) nano-SOD mimetics are studied by analyzing how modifications to the nanomaterial's synthesis impact the size, as well as the elemental and electrochemical properties of the particles. These properties are then correlated to the in vitro antioxidant bioactivity of poly(ethylene glycol)-functionalized cOACs (PEG-cOAC). Chemical oxidative treatment methods that afford smaller, more homogeneous cOAC nanoparticles with higher levels of quinone functionalization show enhanced protection against oxidative damage in bEnd.3 murine endothelioma cells. In an in vivo rat model of mild traumatic brain injury (mTBI) and oxidative vascular injury, PEG-cOACs restore cerebral perfusion rapidly to the same extent as the former nanotube-derived PEG-hydrophilic carbon clusters (PEG-HCCs) with a single intravenous injection. These findings provide a deeper understanding of how carbon nanozyme syntheses can be tailored for improved antioxidant bioactivity, and set the stage for translation of medical applications.
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    Phase controlled synthesis of transition metal carbide nanocrystals by ultrafast flash Joule heating
    (Springer Nature, 2022) Deng, Bing; Wang, Zhe; Chen, Weiyin; Li, John Tianci; Luong, Duy Xuan; Carter, Robert A.; Gao, Guanhui; Yakobson, Boris I.; Zhao, Yufeng; Tour, James M.; Smalley-Curl Institute; NanoCarbon Center and the Welch Institute for Advanced Materials
    Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr2C3, MoC, and W2C) and covalent carbides (B4C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including β-Mo2C and metastable α-MoC1-x and η-MoC1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>104 K s−1). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with β-Mo2C showing the best performance.
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    Urban mining by flash Joule heating
    (Springer Nature, 2021) Deng, Bing; Luong, Duy Xuan; Wang, Zhe; Kittrell, Carter; McHugh, Emily A.; Tour, James M.; Smalley-Curl Institute; NanoCarbon Center; Welch Institute for Advanced Materials
    Precious metal recovery from electronic waste, termed urban mining, is important for a circular economy. Present methods for urban mining, mainly smelting and leaching, suffer from lengthy purification processes and negative environmental impacts. Here, a solvent-free and sustainable process by flash Joule heating is disclosed to recover precious metals and remove hazardous heavy metals in electronic waste within one second. The sample temperature ramps to ~3400 K in milliseconds by the ultrafast electrical thermal process. Such a high temperature enables the evaporative separation of precious metals from the supporting matrices, with the recovery yields >80% for Rh, Pd, Ag, and >60% for Au. The heavy metals in electronic waste, some of which are highly toxic including Cr, As, Cd, Hg, and Pb, are also removed, leaving a final waste with minimal metal content, acceptable even for agriculture soil levels. Urban mining by flash Joule heating would be 80× to 500× less energy consumptive than using traditional smelting furnaces for metal-component recovery and more environmentally friendly.