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Dissertation-Yuxin Zhai-3.pdf (11.39 MB)

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Spectroscopic Studies of Adsorbed CO2 on Polyamines and Photo-generated Electrons in Photocatalytic Synthesis

Zhai, Yuxin
http://orcid.org/0000-0002-1651-0975
http://rave.ohiolink.edu/etdc/view?acc_num=akron1538145926835136

Abstract Details

2018, Doctor of Philosophy, University of Akron, Polymer Science.
CO2 capture and sequestration from stationary sources, i.e., coal-fired and natural gas-fired power plants, has been conceived as an effective strategy to slow down the increase of atmospheric CO2 concentration. One promising and cost-effective approach for controlling CO2 emission from stationary sources is the use of polyamine-based adsorbents for thermal swing CO2 capture processes. The critical aspects of the development of polyamine adsorbents include (i) the structure of adsorbed CO2 and their adsorption/desorption pathway in the CO2 capture process and (ii) the durability of amine sites under high-temperature regeneration in the presence of CO2, steam, and air. These scientific issues could be addressed by an in-situ Fourier transform infrared (FTIR) spectroscopy, which is a powerful technique that could provide insights from the molecular level. This dissertation is focusing on employing the in-situ FTIR spectroscopy in the fields of CO2 capture and photocatalysis, including (i) the nature of adsorbed CO2 on solid amine adsorbents during CO2 capture from air and simulated flue gas, (ii) mechanism of CO2-H2O-amine interactions on liquid and solid amine adsorbents, (iii) enhancing degradation resistance of amines by a cross-linked polymeric support, and (iv) photocatalytic synthesis of amino acid on TiO2 and modified TiO2. The in situ IR study of the structure and nature of adsorbed CO2 on tetraethylenepentamine-immobilized silica adsorbents (TEPA/SiO2) (i) provided evidence to support the zwitterion pathway for CO2 adsorption/desorption and (ii) allowed determination of the nature of adsorbed species. The results revealed that CO2 adsorbs on the primary amine site as strongly adsorbed species in the form of ammonium carbamate, and on the secondary amine site as weakly adsorbed species in the form of carbamic acid. Another form of weakly adsorbed species could be ammonium carbamate on the secondary amine. Raising the concentration of CO2 in the stream increased CO2 capture capacity, fractions of strongly adsorbed CO2, and binding energy of adsorbed species. Water vapor in flue gas plays a significant role in polyamine adsorbents in the CO2 capture process. To determine how the H2O-CO2-amine interactions affect amine efficiency and binding energy of adsorbed CO2, we employed an in situ FTIR spectroscopy to determine the structure of adsorbed CO2 and H2O as well as their relations to adsorption/desorption kinetics and CO2 capture capacity on TEPA films and TEPA/SiO2 adsorbents. The results unraveled that H2O enhanced amine efficiency of TEPA films and TEPA/SiO2 adsorbents by increasing the accessibility of secondary amine sites to CO2 and promoting the formation of hydronium carbamate and carbamic acid. Thick amine films and high amine loading adsorbents contain high-density amine sites which produce mainly strongly adsorbed CO2 through the formation of hydronium carbamate. The results obtained from this study could provide a clear picture of how molecular interactions of H2O-CO2-amine control the formation of adsorbed species and provide an insight into the role of water in controlling amine efficiency and binding energy of adsorbed CO2 in CO2 capture process by amine sorbents. Poly(vinyl alcohol) (PVA) has found a wide range of applications in the area of separation and biochemical processes because of its non-toxicity, high flexibility, and low-cost. We have fabricated PVA with polyethyleneimine (PEI) composites to serve as adsorbents in the CO2 capture process. The degradation behavior of partially cross-linked PEI/PVA adsorbents was evaluated by the in situ FTIR spectroscopy. In situ FTIR study revealed that the secondary amine is more liable to degrade than the primary amine on PEI/SiO2. On PEI/PVA, the PVA’s OH groups interacted mainly with the secondary amine of branched PEI through a hydrogen bonding, which could contribute to enhancing the resistance of PEI against degradation. This new finding could provide new pathways in the development of low-cost and highly durable amine sorbents by using highly porous polymeric supports with -OH groups. In situ IR spectroscopy has been applied in the investigation of photocatalytic redox reaction of L-Lysine (L-Lys) on titanium dioxide (TiO2), which is one of the most commonly used photocatalysts. Photocatalysis of L-Lys on TiO2 produced photo-generated holes and electrons to oxidize and reduce L-Lys. Photo-generated electrons, located at conduction band or trapped levels, were evidenced by a broad featureless IR spectrum under UV irradiation. Fitting the photo-generated electrons into simulated conduction-band/trapped electrons (e-CB and e-ST) revealed the accumulation of e-CB and e-ST from 0 to 0.05 min and the consumption of e-CB and e-ST from 0.05 to 25 min in the photocatalysis of L-Lys, indicating the oxidation and reduction of L-Lys, respectively. The direct observation of e-CB and e-ST in redox reaction will provide an in-depth insight into the role of photo-generated charge carriers in photocatalysis. The products, pipecolic acid (PCA) or L-PCA, were determined by NMR, circular dichroism, and ESI-MS. The results from liquid-phase and solid-phase photocatalysis of L-Lys unraveled that the chiral property of PCA is governed by the adsorbed states and structures of L-Lys on TiO2, which may open up a new low-cost route to the synthesis of high valued-added amino acid.
Steven Chuang, Dr. (Advisor)
Toshikazu Miyoshi, Dr. (Committee Chair)
Darrell Reneker, Dr. (Committee Member)
Chris Wesdemiotis, Dr. (Committee Member)
Yu Zhu, Dr. (Committee Member)
300 p.
Chemical Engineering; Chemistry; Energy; Molecular Chemistry; Molecules; Organic Chemistry; Polymer Chemistry; Polymers; Technology

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Citations

  • Zhai, Y. (2018). Spectroscopic Studies of Adsorbed CO2 on Polyamines and Photo-generated Electrons in Photocatalytic Synthesis [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1538145926835136

    APA Style (7th edition)

  • Zhai, Yuxin. Spectroscopic Studies of Adsorbed CO2 on Polyamines and Photo-generated Electrons in Photocatalytic Synthesis. 2018. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1538145926835136.

    MLA Style (8th edition)

  • Zhai, Yuxin. "Spectroscopic Studies of Adsorbed CO2 on Polyamines and Photo-generated Electrons in Photocatalytic Synthesis." Doctoral dissertation, University of Akron, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1538145926835136

    Chicago Manual of Style (17th edition)

akron1538145926835136
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