Plasmonic Photodecomposition of Gas-phase Toxic Molecules
| dc.contributor.advisor | Halas, Naomi J. | |
| dc.creator | Lou, Minghe | |
| dc.date.accessioned | 2022-09-23T18:29:02Z | |
| dc.date.available | 2023-06-01T05:01:11Z | |
| dc.date.created | 2022-12 | |
| dc.date.issued | 2022-08-24 | |
| dc.date.submitted | December 2022 | |
| dc.date.updated | 2022-09-23T18:29:02Z | |
| dc.description.abstract | 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. | |
| dc.embargo.terms | 2023-06-01 | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.citation | Lou, Minghe. "Plasmonic Photodecomposition of Gas-phase Toxic Molecules." (2022) Diss., Rice University. <a href="https://hdl.handle.net/1911/113291">https://hdl.handle.net/1911/113291</a>. | |
| dc.identifier.uri | https://hdl.handle.net/1911/113291 | |
| dc.language.iso | eng | |
| dc.rights | Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder. | |
| dc.subject | plasmonic photocatalysis | |
| dc.subject | Gas-phase decomposition | |
| dc.subject | plasmon-induced chemistry | |
| dc.subject | plasmonic hot charge carriers | |
| dc.subject | rotational spectroscopy | |
| dc.subject | ||
| dc.title | Plasmonic Photodecomposition of Gas-phase Toxic Molecules | |
| dc.type | Thesis | |
| dc.type.material | Text | |
| thesis.degree.department | Chemistry | |
| thesis.degree.discipline | Natural Sciences | |
| thesis.degree.grantor | Rice University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy |
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