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Photons to Formate: Semiconductor Photocatalyzed Reduction of Bicarbonate to Solar Fuels
Başlık:
Photons to Formate: Semiconductor Photocatalyzed Reduction of Bicarbonate to Solar Fuels
Yazar:
Pan, Hanqing, author.
ISBN:
9780438028135
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (144 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Michael D. Heagy Committee members: Pabitra Choudhury; Sanchari Chowdhury; Paul Fuierer; Mahinda Ranasinghe; Rodolfo Tello-Aburto.
Özet:
Rising levels of anthropogenic carbon dioxide and the rapid depletion of fossil fuels are raising concerns about the environment and the future of our energy supply. The continual increase in atmospheric CO 2 is not only causing a rise in the global temperature, it is also increasing the hydronium ion concentration in the ocean, causing its acidification. One potential approach towards generating renewable fuels is to use solar energy to directly reduce atmospheric or locally produced CO2 to liquid fuels. This approach, referred to as "chemical carbon mitigation" can lead to methanol as an end product, a useful solar fuel. The concept of "The Methanol Economy", championed by Chemistry Nobel laureate George Olah, highlights methanol as an alternative to hydrogen as a renewable and readily transportable fuel. Furthermore, methanol surpasses compressed hydrogen in energy density. Inspired by this concept, our lab is focused on the solar-driven conversion of carbon dioxide to formic acid and ultimately to methanol.
This dissertation is focused on the photocatalytic reduction of bicarbonate to formate. Specifically, it aims to achieve this reduction by utilizing earth-abundant, non-toxic, and low-cost semiconductors. Three semiconductors were evaluated in detail by characterizing their size, morphology, band gap, and crystal structure. To improve semiconductor efficiency, plasmonic noble-metal nanoparticles and organic dyes were used as photosensitizers to extend optical absorption into the visible wavelengths. Photocatalysis also requires a sacrificial reducing agent to scavenge the photogenerated holes, and in this dissertation, we highlight glycerol as a green chemistry solvent with superior efficiency.
Chapter 1 outlines the background and current state of the research area. This chapter focuses on different groups of photocatalysts used for the photocatalytic reduction of CO2 to formate. In current literature, next to inorganic ruthenium complexes, semiconductors are the most prominent catalysts used. Phthalocyanines adsorbed onto Nafion membranes allowed the membranes to possess properties similar to p-type semiconductors, which enabled the membrane to successfully reduce CO2 to formate. Lastly, metal-organic frameworks (MOFs) are a class of emerging catalyst possessing an inorganic metal cluster held together by organic linkers. These species are porous, have extremely high surface area, have easily tunable properties, and have been shown to have exquisite photocatalytic efficiency.
Chapters 2 and 3 evaluates three semiconductors under the parameters of size, crystal structure, band gap, and surface area. Chapter 2 is focused on copper (I) oxide and a silver-copper oxide nanocomposite (Ag/Cu2O). Silver nanoparticles were used as a sensitizer to enhance semiconductor efficiency via plasmon-induced electron transfer from metal to semiconductor. Based on the success of Cu2O as a photocatalyst and continuing with the idea of utilizing earth-abundant, non-toxic, and low-cost semiconductors, several different nanostructures of ZnO and Fe2O3 were synthesized and their photochemical properties were examined in chapter 3. It was found that these hierarchical nanostructures such as nanowires and nanoflowers tend to possess the largest surface area and are able to delay electron/hole recombination. As a result, formate production is greatly enhanced.
Chapter 4 is focused on six hole scavengers and their ability to donate electrons to fill photogenerated holes. Sodium sulfite, ethylenediaminetetraacetic acid, triethanolamine, 2-propanol, ethylene glycol, and glycerol were tested for their hole scavenging efficiency. As predicted, the results showed that glycerol gives the highest product yield of formate. Compared to petroleum-derived 2-propanol, green-chemistry solvent glycerol proved to be a superior sacrificial agent due to its abundance of hydroxyl groups.
Chapters 5 and 6 are focused on enhancing semiconductor efficiency. Plasmonic noble-metal nanoparticles and organic dyes were used to expand optical absorption into the visible region of the solar spectrum. In chapter 5, a gold nanoparticle-TiO 2 nanocomposite (Au/TiO2) was synthesized and tested for bicarbonate reduction under solar irradiation and 365 nm irradiation. Formate production was significantly enhanced with the addition of gold nanoparticles under solar irradiation. To confirm this effect, the photo-reduction of organic dye resazurin to resorufin was studied. The reduction rate increased with the addition of gold nanoparticles. To study the parallel oxidation reaction, the oxidation of organic dye rhodamine B was carried out. Interestingly, the addition of gold nanoparticles had an adverse effect on the oxidation reaction. The decreased reaction rate was attributed to the fact that gold nanoparticles are able to scavenge hydroxyl radicals and therefore hindered the reaction. In chapter 6, a novel solid-state thin film device was constructed with a thin layer of semiconductor and another thin layer of phthalocyanine as a photosensitizer. The photon to formate conversion efficiency of the device reached 40%. Lastly, chapters 7 and 8 summarize the results and discuss future directions.
Notlar:
School code: 0295
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(681364.1) | 681364-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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