Matching Items (5)
Description
A new photocatalytic material was synthesized to investigate its performance for the photoreduction of carbon dioxide (CO2) in the presence of water vapor (H2O) to valuable products such as carbon monoxide (CO) and methane (CH4). The performance was studied using a gas chromatograph (GC) with a flame ionization detector (FID) and a thermal conductivity detector (TCD). The new photocatalytic material was an ionic liquid functionalized reduced graphite oxide (IL-RGO (high conductive surface))-TiO2 (photocatalyst) nanocomposite. Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV-vis absorption spectroscopy techniques were employed to characterize the new catalyst. In the series of experiments performed, the nanocomposite material was confined in a UV-quartz batch reactor, exposed to CO2 and H2O and illuminated by UV light. The primary product formed was CO with a maximum production ranging from 0.18-1.02 µmol(gcatalyst-hour)-1 for TiO2 and 0.41-1.41 µmol(gcatalyst-hour)-1 for IL-RGO-TiO2. A trace amount of CH4 was also formed with its maximum ranging from 0.009-0.01 µmol(gcatalyst-hour)-1 for TiO2 and 0.01-0.04 µmol(gcatalyst-hour)-1 for IL-RGO-TiO2. A series of background experiments were conducted and results showed that; (a) the use of a ionic liquid functionalized reduced graphite oxide -TiO2 produced more products as compared to commercial TiO2, (b) the addition of methanol as a hole scavenger boosted the production of CO but not CH4, (c) a higher and lower reduction time of IL-RGO as compared to the usual 24 hours of reduction presented basically the same production of CO and CH4, (d) the positive effect of having an ionic liquid was demonstrated by the double production of CO obtained for IL-RGO-TiO2 as compared to RGO-TiO2 and (e) a change in the amount of IL-RGO in the IL-RGO-TiO2 represented a small difference in the CO production but not in the CH4 production. This work ultimately demonstrated the huge potential of the utility of a UV-responsive ionic liquid functionalized reduced graphite oxide-TiO2 nano-composite for the reduction of CO2 in the presence of H2O for the production of fuels.
ContributorsCastañeda Flores, Alejandro (Author) / Andino, Jean M (Thesis advisor) / Forzani, Erica (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2014
Description
Over the past years, an interest has arisen in resolving two major issues: increased carbon dioxide (CO2) emissions and depleting energy resources. A convenient solution would be a process that could simultaneously use CO2 while producing energy. The photocatalytic reduction of CO2 to fuels over the photocatalyst titanium dioxide (TiO2) is such a process. However, this process is presently inefficient and unsuitable for industrial applications. A step toward making this process more effective is to alter TiO2 based photocatalysts to improve their activity. The interactions of CO2 with oxygen-deficient and unmodified (210) surfaces of brookite TiO2 were studied using first-principle calculations on cluster systems. Charge and spin density analyses were implemented to determine if charge transfer to the CO2 molecule occurred and whether this charge transfer was comparable to that seen with the oxygen-deficient and unmodified anatase TiO2 (101) surfaces. Although the unmodified brookite (210) surface provided energetically similar CO2 interactions as compared to the unmodified anatase (101) surface, the unmodified brookite surface had negligible charge transfer to the CO2 molecule. This result suggests that unmodified brookite is not a suitable catalyst for the reduction of CO2. However, the results also suggest that modification of the brookite surface through the creation of oxygen vacancies may lead to enhancements in CO2 reduction. The computational results were supported with laboratory data for CO2 interaction with perfect brookite and oxygen-deficient brookite. The laboratory data, generated using diffuse reflectance Fourier transform infrared spectroscopy, confirms the presence of CO2- on only the oxygen-deficient brookite. Additional computational work was performed on I-doped anatase (101) and I-doped brookite (210) surface clusters. Adsorption energies and charge and spin density analyses were performed and the results compared. While charge and spin density analyses showed minute charge transfer to CO2, the calculated adsorption energies demonstrated an increased affinity for CO2adsorption onto the I-doped brookite surface. Gathering the results from all calculations, the computational work on oxygen-deficient, I-doped, and unmodified anatase and brookite surface structures suggest that brookite TiO2 is a potential photocatalysts for CO2 photoreduction.
ContributorsRodriguez, Monique M (Author) / Andino, Jean M (Thesis advisor) / Nielsen, David R (Committee member) / Dai, Lenore (Committee member) / Arizona State University (Publisher)
Created2012
Description
Volatile Organic Compounds (VOCs) are central to atmospheric chemistry and have significant impacts on the environment. The reaction of oxygenated VOCs with OH radicals was first studied to understand the fate of oxygenated VOCs. The rate constants of the gas-phase reaction of OH radicals with trans-2-hexenal, trans-2-octenal, and trans-2 nonenal were determined using the relative rate technique. Then the interactions between VOCs and ionic liquid surfaces were studied. The goal was to find a material to selectively detect alcohol compounds. Computational chemistry calculations were performed to investigate the interactions of ionic liquids with different classes of VOCs. The thermodynamic data suggest that 1-butyl-3-methylimindazolium chloride (C4mimCl) preferentially interacts with alcohols as compared to other classes of VOCs. Fourier transform infrared spectroscopy was used to probe the ionic liquid surface before and after exposure to the VOCs that were tested. New spectral features were detected after exposure of C4mimCl to various alcohols and a VOC mixture with an alcohol in it. The new features are characteristic of the alcohols tested. No new IR features were detected after exposure of the C4mimCl to the aldehyde, ketone, alkane, alkene, alkyne or aromatic compounds. The experimental results demonstrated that C4mimCl is selective to alcohols, even in complex mixtures. The kinetic study of the association and dissociation of alcohols with C4minCl surfaces was performed. The findings in this work provide information for future gas-phase alcohol sensor design. CO2 is a major contributor to global warming. An ionic liquid functionalized reduced graphite oxide (IL-RGO)/ TiO2 nanocomposite was synthesized and used to reduce CO2 to a hydrocarbon in the presence of H2O vapor. The SEM image revealed that IL-RGO/TiO2 contained separated reduced graphite oxide flakes with TiO2 nanoparticles. Diffuse Reflectance Infrared Fourier Transform Spectroscopy was used to study the conversion of CO2 and H2O vapor over the IL-RGO/TiO2 catalyst. Under UV-Vis irradiation, CH4 was found to form after just 40 seconds of irradiation. The concentration of CH4 continuously increased under longer irradiation time. This research is particularly important since it seems to suggest the direct, selective formation of CH4 as opposed to CO.
ContributorsGao, Tingting (Author) / Andino, Jean M (Thesis advisor) / Forzani, Erica (Committee member) / Kavazanjian, Edward (Committee member) / Arizona State University (Publisher)
Created2012
Description
The mitigation and conversion of carbon dioxide (CO2) to more useful carbon chemicals is a research topic that is at the forefront of current engineering and sustainability applications. Direct photocatalytic reduction of CO2 with water (H2O) vapor to C1-C4 hydrocarbons has significant potential in setting substantial groundwork for meeting the increasing energy demands with minimal environmental impact. Previous studies indicate that titanium dioxide (TiO2) containing materials serve as the best photocatalyst for CO2 and H2O conversion to higher-value products. An understanding of the CO2-H2O reaction mechanism over TiO2 materials allows one to increase the yield of certain products such as carbon monoxide (CO) and methane (CH4). The basis of the work discussed in this thesis, investigates the interaction of small molecules (CO, CH4,H2O) over the least studied TiO2 polymorph - brookite. Using the Gaussian03 computational chemistry software package, density functional theory (DFT) calculations were performed to investigate the adsorption behavior of CO, H2O, and CH4 gases on perfect and oxygen-deficient brookite TiO2 (210) and anatase TiO2 (101) surfaces. The most geometrically and energetically favorable configurations of these molecules on the TiO2 surfaces were computed using the B3LYP/6-31+G(2df,p) functional/basis set. Calculations from this theoretical study indicate all three molecules adsorb more favorably onto the brookite TiO2 (210) surface. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was used to investigate the adsorption and desorption behavior of H2O and CH4 on Evonik P25 TiO2. Results from the experimental studies and theoretical work will serve as a significant basis for reaction prediction on brookite TiO2 surfaces.
ContributorsRollins, Selisa F (Author) / Andino, Jean M (Thesis advisor) / Dai, Lenore L (Committee member) / Forzani, Erica S (Committee member) / Arizona State University (Publisher)
Created2012
Description
The release of organophosphorus compounds (OPs) and subsequent exposure to these compounds is of concern to humans and the environment. The goal of this work was to control the concentrations of gaseous OPs through interaction with sorbent oxides. Experimental and computational methods were employed to assess the interactions of dimethyl phosphite (DMHP), dimethyl methylphosphonate (DMMP), dimethyl ethylphosphonate (DMEP), diethyl ethylphosphonate (DEEP), and triethyl phosphate (TEP) with amorphous silica (a-silica), ã-alumina, and monoclinic zirconia (m-zirconia) for applications in air pollution control. Interactions of the selected OPs with a-silica were chosen as a baseline to determine the applicability of the computational predictions. Based on the a-silica results, computational methods were deemed valid for predicting the trends among materials with comparable interactions (e.g. -OH functionality of a-silica interacting with the phosphonyl O atoms of the OPs). Computational evaluations of the interactions with the OPs were extended to the oxide material, m-zirconia, and compared with the results for ã-alumina. It was hypothesized that m-zirconia had the potential to provide for the effective sorption of OPs in a manner superior to that of the a-silica and the ã-alumina surfaces due to the surface charges of the zirconium Lewis acid sites when coordinated in the oxidized form. Based on the computational study, the predicted heats of adsorption for the selected OPs onto m-zirconia were more favorable than those that were predicted for ã-alumina and a-silica. Experimental studies were carried out to confirm these computational results. M-zirconia nanoparticles were synthesized to determine if the materials could be utilized for the adsorption of the selected OPs. M-zirconia was shown to adsorb the OPs, and the heats of adsorption were stronger than those determined for commercial samples of a-silica. However, water interfered with the adsorption of the OPs onto m-zirconia, thus leading to heats of adsorption that were much weaker than those predicted computationally. Nevertheless, this work provides a first investigation of m-zirconia as a viable sorbent material for the ambient control of the selected gaseous OPs. Additionally, this work represents the first comparative study between computational predictions and experimental determination of thermodynamic properties for the interactions of the selected OPs and oxide surfaces.
ContributorsSiu, Eulalia Yuen-Yi (Author) / Andino, Jean M (Thesis advisor) / Forzani, Erica S (Committee member) / Hristovski, Kiril (Committee member) / Nielsen, David R (Committee member) / Pfeffer, Robert (Committee member) / Arizona State University (Publisher)
Created2011