Publications by authors named "Fred Nesbitt"

3 Publications

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Fabrication, Optimization and Characterization of Natural Dye Sensitized Solar Cell.

Sci Rep 2017 01 27;7:41470. Epub 2017 Jan 27.

Center for Nanotechnology, Department of Natural Sciences, Coppin State University, 2500 W. North Ave, Baltimore, MD, USA.

The dyes extracted from pomegranate and berry fruits were successfully used in the fabrication of natural dye sensitized solar cells (NDSSC). The morphology, porosity, surface roughness, thickness, absorption and emission characteristics of the pomegranate dye sensitized photo-anode were studied using various analytical techniques including FESEM, EDS, TEM, AFM, FTIR, Raman, Fluorescence and Absorption Spectroscopy. Pomegranate dye extract has been shown to contain anthocyanin which is an excellent light harvesting pigment needed for the generation of charge carriers for the production of electricity. The solar cell's photovoltic performance in terms of efficiency, voltage, and current was tested with a standard illumination of air-mass 1.5 global (AM 1.5 G) having an irradiance of 100 mW/cm. After optimization of the photo-anode and counter electrode, a photoelectric conversion efficiency (η) of 2%, an open-circuit voltage (Voc) of 0.39 mV, and a short-circuit current density (Isc) of 12.2 mA/cm were obtained. Impedance determination showed a relatively low charge-transfer resistance (17.44 Ω) and a long lifetime, signifying a reduction in recombination losses. The relatively enhanced efficiency is attributable in part to the use of a highly concentrated pomegranate dye, graphite counter electrode and TiCl treatment of the photo-anode.
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http://dx.doi.org/10.1038/srep41470DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5270247PMC
January 2017

Direct measurement and theoretical calculation of the rate coefficient for Cl+CH3 in the range from T=202-298 K.

J Phys Chem A 2007 Feb 25;111(6):1015-23. Epub 2007 Jan 25.

Solar System Exploration Division, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.

The rate coefficient has been measured under pseudo-first-order conditions for the Cl+CH3 association reaction at T=202, 250, and 298 K and P=0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH3 were generated rapidly and simultaneously by reaction of F with HCl and CH4, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F2 in He. The decay of CH3 was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH3 concentration ([Cl]0/[CH3]0=9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T=202 K, the rate coefficient increases from 8.4x10(-12) at P=0.30 Torr He to 1.8x10(-11) at P=2.00 Torr He, both in units of cm3 molecule-1 s-1. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k2=6.0x10(-11) cm3 molecule-1 s-1, independent of temperature in the range from 200 to 300 K.
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http://dx.doi.org/10.1021/jp066231vDOI Listing
February 2007

Rate Constant for the Recombination Reaction CH + CH → CH at T = 298 and 202 K.

J Phys Chem A 2002 Jun;106(25):6060-6067

Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, Department of Natural Sciences, Coppin State College, Baltimore, Maryland 21216, Department of Chemistry, Millersville University, Millersville, Pennsylvania 17551, and Department of Chemistry, University of Iowa, Iowa City, Iowa 52242.

The recombination of methyl radicals is the major loss process for methyl in the atmospheres of Saturn and Neptune. The serious disagreement between observed and calculated levels of CH has led to suggestions that the atmospheric models greatly underestimated the loss of CH due to poor knowledge of the rate of the reaction CH + CH + M → CH + M at the low temperatures and pressures of these atmospheric systems. In an attempt to resolve this problem, the absolute rate constant for the self-reaction of CH has been measured using the discharge-flow kinetic technique coupled to mass spectrometric detection at T = 202 and 298 K and P = 0.6-2.0 Torr nominal pressure (He). CH was produced by the reaction of F with CH, with [CH] in large excess over [F], and detected by low energy (11 eV) electron impact ionization at m/ z = 15. The results were obtained by graphical analysis of plots of the reciprocal of the CH signal vs reaction time. At T = 298 K, k (0.6 Torr) = (2.15 ± 0.42) × 10 cm molecule s and k (1 Torr) = (2.44 ± 0.52) × 10 cm molecule s. At T = 202 K, the rate constant increased from k (0.6 Torr) = (5.04 ± 1.15) × 10 cm molecule s to k (1.0 Torr) = (5.25 ± 1.43) × 10 cm molecule s to k (2.0 Torr) = (6.52 ± 1.54) × 10 cm molecule s, indicating that the reaction is in the falloff region. Klippenstein and Harding had previously calculated rate constant falloff curves for this self-reaction in Ar buffer gas. Transforming these results for a He buffer gas suggest little change in the energy removal per collision, -〈Δ E〉, with decreasing temperature and also indicate that -〈Δ E〉 for He buffer gas is approximately half of that for Argon. Since the experimental results seem to at least partially affirm the validity of the Klippenstein and Harding calculations, we suggest that, in atmospheric models of the outer planets, use of the theoretical results for k is preferable to extrapolation of laboratory data to pressures and temperatures well beyond the range of the experiments.
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http://dx.doi.org/10.1021/jp014044lDOI Listing
June 2002