4 resultados para surface electronic phenomena (work function, surface potential, surface states. etc.)

em Bucknell University Digital Commons - Pensilvania - USA


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There is a need for biomethane capture and carbon dioxide sequestration to mitigate evident global climate change. This research work investigated the potential for microalgae to remove CO2 from biogas as a biotechnical method for upgrading the thermal value for subsequent compression, liquification, or introduction to natural gas pipelines. Because biogas is largely methane, the effect of high methane environments on mixed microalgae was explored and found that specific carbon utilization rates were not statistically different when microalgae were exposed to biogas environments (70% v/v CH4) , relative to high CO2 environment. The uses of conventional bubbled column photobioreactors (PBR) were assessed for CO2 removal and subsequent CH4 enrichment. A continuously-bubbled biogas PBR (cB-PBR5) and intermittently-bubbled biogas PBR (iB-PBR) experienced CO2 loading rates of about 1664 and 832 mg C/L*day and showed 30.0 and 60.1 % carbon removal, respectively. However, a lack of biogas enrichment and issues associated growth inhibition due to high CO2 environments as well as stripping the dissolved gases, namely oxygen and nitrogen, from the bulk liquid and introduction to the outlet gas prompted the consideration for gas/liquid separation using nonporous hollow-fiber (HF) membranes for CO2 transfer. The potential for two non-porous HF membrane materials [polydimethylsiloxane (PDMS) and composite polyurethane (PU)] were modeled along fiber length using a mechanistic model based on polymeric material transport properties (Gilmore et al., 2009). Based on a high CO2:CH4 permeability selectivity for PU of 76.2 the model predicted gas enrichment along an 8.5 cm fiber length. Because PDMS permeability selectivity is low (3.5), evident gas transfer was not predicated along a 34.3 cm length. Both of these HF materials were implemented in hollow-fiber membrane-carbonated biofilm (HFMcB) PBRs for microalgal-mediated biogas enrichment. Phototrophic biofilm colonization occurred on the membrane, where CO2 concentration was greatest. The presence of a biofilm demonstrated greater resiliency to high CO2 environments, compared to the conventional PBRs. However, as the PDMS model predicted, the PDMS HFMcBs did not demonstrate gas enrichment. These reactors received CO2 loading rates of 200 mg C/L*day based on PDMS permeability flux and showed approximately 65% removal of the total C transferred across the membrane. Thus, the HFMcBs demonstrated controlled carbonation of the bulk liquid via a nonporous HF membrane. Likewise, the experimental PU HFMcB did not show gas enrichment yet this result should be further explored due to the high permeability selectivity of the polymeric material. Chemical stratifications, namely pH and dissolved O2, present in a PDMS membrane-carbonated biofilm were analyzed using electrochemical microsensors. Results indicated that high DO (20 mg L-1) exists at surface of the biofilm where light availability is greatest and low pH microenvironments (pH=5.40) exist deep in the biofilm where the diffusive flux of CO2 drives transfer through the biofilm. The presence of a 400-600 ¿m liquid phase boundary layer was evident from microsensor profiles. Cryosectioning of the biofilm samples showed the biofilm to be approximately 1.17 ± 0.07 mm thick, suggesting that the high localized concentration of biomass associated with the phototrophic biofilm aided in overcoming inhibition in a microenvironment dominated by CO2(aq). Challenges of biofilm detachment and PBR fouling as well as microalgal growth inhibition in the presence of high CO2 content remain for applications of microalgae for biogas enrichment.

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Conducted work with two potential alternatives to Ni, La0.8Sr0.2Cr0.5Mn0.5 (LSCM) and Sr doped LaVO3 (LSV) to serve as the electron conductor in the anode of solid oxide fuel cells SOFCs.

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The potential energy surface for the first step of the alkaline hydrolysis of methyl acetate was explored by a variety of methods. The conformational search routine within SPARTAN was used to determine the lowest energy am1 and pm3 structures for the anionic tetrahedral intermediate. Ab initio single point and geometry optimization calculations were performed to determine the lowest energy conformer, and the linear synchronous transition (lst) method was used to provide an initial structure for transition state optimization. Transition states were obtained at the am1, pm3, 3-21G, and 3-21 + G levels of theory. These transition states were compared with the anionic tetrahedral intermediates to examine the assumption that the intermediate is a good model for the transition state. In addition, the Cramer/Truhlar sm3 solvation model was used at the semiempirical level to compare gas phase and aqueous alkaline hydrolysis of methyl acetate.

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Land surface temperature (LST) plays a key role in governing the land surface energy budget, and measurements or estimates of LST are an integral part of many land surface models and methods to estimate land surface sensible heat (H) and latent heat fluxes. In particular, the LST anchors the potential temperature profile in Monin-Obukhov similarity theory, from which H can be derived. Brutsaert has made important contributions to our understanding the nature of surface temperature measurements as well as the practical but theoretically sound use of LST in this framework. His work has coincided with the wide-spread availability of remotely sensed LST measurements. Use of remotely sensed LST estimates inevitably involves complicating factors, such as: varying spatial and temporal scales in measurements, theory, and models; spatial variability of LST and H; the relationship between measurements of LST and the temperature felt by the atmosphere; and the need to correct satellite-based radiometric LST measurements for the radiative effects of the atmosphere. This paper reviews the progress made in research in these areas by tracing and commenting on Brutsaert's contributions.