On the equilibrium and dynamic behavior of alcohol vapors in activated carbon

As alcohol molecules such as methanol and ethanol have both polar and non-polar groups, their adsorption behavior is governed by the contributions of dispersion interaction (alkyl group) and hydrogen bonding (OH group). In this paper, the adsorption behavior of alcohol molecules and its effect on transport processes are elucidated. From the total permeability (B-T) of alcohol molecules in activated carbon, an adsorption mechanism is proposed, describing well the experimental data, by taking combination effects of clustering, entering micropores, layering and pore filling processes. Unlike the case of non-polar compounds, it was found that at low pressures there are two rises in the BT of alcohol molecules in activated carbon. The first rise is due to the major contribution of surface diffusion to the transport (which is the case of non-polar molecules) and the second one may be associated with cluster formation at the edge of micropores and entering micropores when the clusters are sufficiently large enough to induce a dispersive energy. In addition the clusters formed may enhance surface diffusion at low pressures and hinder gas phase diffusion and flow in meso/macropores. (c) 2006 Elsevier Ltd. All fights reserved.

Postsynthesis stabilization of free-standing mesoporous silica films

Mixed ammonia-water vapor postsynthesis treatment provides a simple and convenient method for stabilizing mesostructured silica films. X-ray diffraction, transmission electron microscopy, nitrogen adsorption/desorption, and solid-state NMR (C-13, Si-29) were applied to study the effects of mixed ammonia-water vapor at 90 degreesC on the mesostructure of the films. An increased cross-linking of the silica network was observed. Subsequent calcination of the silica films was seen to cause a bimodal pore-size distribution, with an accompanying increase in the volume and surface area ratios of the primary (d = 3 nm) to secondary (d = 5-30 nm) pores. Additionally, mixed ammonia-water treatment was observed to cause a narrowing of the primary pore-size distribution. These findings have implications for thin film based applications and devices, such as sensors, membranes, or surfaces for heterogeneous catalysis.

Genetic variation for carbon isotope discrimination in sunflower: Association with transpiration efficiency and evidence for cytoplasmic inheritance

Plants accumulate isotopes of carbon at different rates because of discrimination against C-13 relative to C-12. In plants that fix carbon by the C-3 pathway, the amount of discrimination correlates negatively with transpiration efficiency (TE) where TE is the amount of dry matter accumulated per unit water transpired. Therefore, carbon isotope discrimination (Delta) has become a useful tool for selecting genotypes with improved TE and performance in dry environments. Surveys of 161 sunflower (Helianthus spp.) genotypes of diverse origin revealed a large and unprecedented range of genetic variation for Delta (19.5-23.8parts per thousand). A strong negative genetic correlation (r(g)) between TE and Delta (r(g) = -0.87, P < 0.001) was observed in glasshouse studies. Gas exchange measurements of field grown plants indicated that Delta was strongly correlated with stomatal conductance to water vapor (g), (r(g) 0.64, P < 0.01), and the ratio of net assimilation rate (A) to g, (r(g) = 0.86, P < 0.001), an instantaneous measure of TE. Genotype CMSHA89MAX1 had the lowest TE (and highest Delta) of all genotypes tested in these studies and low yields in hybrid combination. Backcrossing studies showed that the TE of this genotype was due to an adverse effect of the MAX1 cytoplasm, which was inherited from the diploid perennial H. maximiliani Schrader. Overall, these studies suggested that there is an excellent opportunity for breeders to develop sunflower germplasm with improved TE. This can be achieved, in part, by avoiding cytoplasms such as the MAX1 cytoplasm.