Godwin Mbamalu

Geometric dependence of transport and universal behavior in three dimensional carbon nanostructures

Carbon nanostructures with the spherical voids exhibit interesting temperature and magnetic field dependent transport properties. By increasing the void size, the structures are tuned from metallic to insulating; in addition, the magnetoresistance (MR) is enhanced. Our investigation in the magnetic fields (B) up to 18 T at temperatures (T) from 250 mK to 20 K shows that at high temperatures (T > 2 K), the MR crosses over from quadratic to a non-saturating linear dependence with increasing magnetic field. Furthermore, all MR data in this temperature regime collapse onto a single curve as a universal function of B/T, following Kohlers rule. Remarkably, the MR also exhibits orientation insensitivity, i.e., it displays a response independent of the direction on the magnetic field.The optical absorption spectrums of nanomotors made from double-wall carbon nanotubes have been calculated with the time-dependent density functional based tight binding method. When the outer short tube of the nanomotor moves along or rotates around the inner long tube, the peaks in the spectrum will gradually evolve and may shift periodically, the amplitude of which can be as large as hundreds of meV. We show that the features and behaviors of the optical absorption spectrum could be used to monitor the mechanical motions of the double-wall carbon nanotube based nanomotor.

A quantitative methodology for indexing environmental sensitivity and pollution potential.

A methodology for rating the suitability of sites forthe location of industrial facilities is formulated and appliedto the case of a coal-fired power plant location. The methodologycomprises two major interlinked components: the environmentalplant location indexing component, which involves theidentification, scaling and weighting of environmentalsensitivity factors; and the impact analysis component, whichinvolves the superimposition of the pollution generation impactsof an industrial facility on spatially gridded zones of variousenvironmental sensitivities. For each rectangular areal unitdefined by a square grid, the Unit Pollution Potential Index isdetermined by the severity and distribution of key environmentalsensitivity factors and the coverage of superimposed pollutanteffects as determined by contaminant fate and transport models.For any alternative site of a planned facility, the summation ofthe unit indices over the area of influence of the facilityprovides the quantitative Pollution Index, which can be used as abasis for comparison of alternative sites for planned facilities.For this paper, this methodology is applied to the hypotheticalcase of the siting of a coal-fired power plant in thenortheastern region of the United States, in which threealternative sites are considered. The three sites: A, B and Cyielded indices of 47.83, 47.91 and 47.6, respectively, indicatingthat site C is the most suitable for siting the power plant.

Can molten carbonate be a non-metal catalyst for CO oxidation?

For the first time, we have examined molten carbonate as a non-metal catalyst for CO oxidation in the temperature range of 300–600 °C. The reaction mechanism was analyzed using a classic Langmuir–Hinshelwood model combined with DFT calculations. It was found that the conversion of CO is greatly enhanced by molten carbonate at about 400 °C and increased to 96% at 500 °C. The reaction process involves four steps, including (1) dissociative adsorption of oxygen, (2) adsorption of CO, (3) surface reaction, and (4) desorption of CO2. DFT modeling reveals the formation of (C2O4)2− and (CO4)2− as the intermediate species, and that the first two steps are exothermic and preferred by chemical equilibrium. The energy barrier of oxygen dissociation to form CO42− is calculated to be 23.0 kcal mol−1, which is in good agreement with the measured overall activation energy of 19.1 kcal mol−1. However, the surface reaction (step 3) has a low energy barrier of 10.8 kcal mol−1 only. This confirms that the oxygen dissociation is the rate determing step in the whole process. Further analysis of the reaction kinetics indicates that the reaction is affected by the CO concentration. With low CO concentration, the reaction is first order with respect to CO and half order to O2. From the current report, it has been proven that molten carbonate can serve as an efficient catalyst for CO oxidation and potentially for other oxidation reactions in the temperature range of 400–600 °C. More studies are demanded to further investigate the reaction mechanism and explore more potential industrial applications.