Browsing by Author "Lou, Minghe"
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Item Plasmonic Photodecomposition of Gas-phase Toxic Molecules(2022-08-24) Lou, Minghe; Halas, Naomi J.Plasmonic nanomaterials have recently attracted much research interest with regard to their applications in photocatalysis and photochemistry. The collective oscillation of conductive electrons in metal nanostructures, also known as local surface plasmon, allow the nanostructures to interact with light in a cross section far larger than the physical cross section. This higher uptake of photon on the nanostructure further makes photochemical conversion with higher efficiency possible. During plasmonic photocatalysis or photochemical conversion, decay of the local surface plasmons could generate energetic hot charge carriers that are capable of either selectively facilitating specific reaction pathways through electron transfer or energy transfer or heating up the system through electron-phonon scattering. This feature makes plasmonic photocatalysis a promising approach for endothermic decomposition reactions, where the selectivity towards specific decomposition products is favored. This is even more important in the decomposition or decontamination of harmful toxic molecules since the toxicity of the target product is expected to be lower than the reactants. In this thesis, I investigate several aspects of applying plasmonic photocatalysis to decomposition of gas-phase toxic molecules like H2S (Chapter 3) and 2-chloroethylethylsulfide (Chapter 4). To realize more sensitive and accurate quantification of the complicated decomposition products, I also develop a method for quantitative analysis using frequency-modulated rotational spectroscopy (Chapter 2). Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. In chapter 2, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for quantitative gas-phase detection, identification, and quantification. Plasmonic metal nanostructures have shown significant potential in photocatalysis by facilitating chemical bond activation and overcoming the high energy demands of conventional fossil-fuel-based thermal catalysis. In chapter 3, we introduce highly efficient, sustainable heterogeneous plasmonic photocatalysis of the direct decomposition of hydrogen sulfide into hydrogen and sulfur, an alternative to the industrial Claus process. Under visible-light illumination and with no external heat source, up to a 20-fold reactivity enhancement compared to thermocatalysis can be observed. We show that the substantially enhanced reactivity can be attributed to plasmon-mediated hot carriers that modify the reaction energetics. With a shift in the rate-determining step of the reaction, a new reaction pathway is made possible with a lower apparent reaction barrier. Light-driven one-step decomposition of hydrogen sulfide represents an exciting opportunity for high-efficiency hydrogen production and sulfur recovery at low temperatures, leading to a more sustainable petrochemical industry. Benefiting from the strong interactions with photons and multiple energy decay mechanisms, plasmonic nanostructures have also been reported to enhance reactivity and tune selectivity. In chapter 4, we introduce plasmonic aluminum nanoparticles as a promising detoxifier of chemical warfare agent simulant 2-chloroethylethylsulfide through gas-phase photodecomposition. Under visible light illumination, a maximum conversion rate of 72% could be achieved in the constant flow of the feed gas. The post-reaction aluminum nanoparticles could be regenerated with no obvious reactivity loss through simple surface treatment and annealing. Analysis of the decomposition products indicated that C-S breaking was facilitated under illumination while C-Cl breaking and HCl elimination were favored in dark. This difference in reaction pathways sheds light on the potential of plasmonic nanoparticles to tune the selectivity towards less toxic products in the detoxification of chemical warfare agents.Item Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy(AIP Publishing LLC, 2019) Lou, Minghe; Swearer, Dayne F.; Gottheim, Samuel; Phillips, Dane J.; Simmons, Jay G. Jr.; Halas, Naomi J.; Everitt, Henry O.; Laboratory for NanophotonicsRotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.Item Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy(AIP Publishing LLC, 2019) Lou, Minghe; Swearer, Dayne F.; Gottheim, Samuel; Phillips, Dane J.; Simmons, Jay G.; Halas, Naomi J.; Everitt, Henry O.Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.Item Sustainable valorization of asphaltenes via flash joule heating(AAAS, 2022) Saadi, M.A.S.R.; Advincula, Paul A.; Thakur, Md Shajedul Hoque; Khater, Ali Zein; Saad, Shabab; Shayesteh Zeraati, Ali; Nabil, Shariful Kibria; Zinke, Aasha; Roy, Soumyabrata; Lou, Minghe; Bheemasetti, Sravani N.; Bari, Md Abdullah Al; Zheng, Yiwen; Beckham, Jacob L.; Gadhamshetty, Venkataramana; Vashisth, Aniruddh; Kibria, Md Golam; Tour, James M.; Ajayan, Pulickel M.; Rahman, Muhammad M.The refining process of petroleum crude oil generates asphaltenes, which poses complicated problems during the production of cleaner fuels. Following refining, asphaltenes are typically combusted for reuse as fuel or discarded into tailing ponds and landfills, leading to economic and environmental disruption. Here, we show that low-value asphaltenes can be converted into a high-value carbon allotrope, asphaltene-derived flash graphene (AFG), via the flash joule heating (FJH) process. After successful conversion, we develop nanocomposites by dispersing AFG into a polymer effectively, which have superior mechanical, thermal, and corrosion-resistant properties compared to the bare polymer. In addition, the life cycle and technoeconomic analysis show that the FJH process leads to reduced environmental impact compared to the traditional processing of asphaltene and lower production cost compared to other FJH precursors. Thus, our work suggests an alternative pathway to the existing asphaltene processing that directs toward a higher value stream while sequestering downstream emissions from the processing.