Well-ordered mesoporous silicate films were prepared by infusion and selective condensation of silicon alkoxides within microphase-separated block copolymer templates dilated with supercritical carbon dioxide. Confinement of metal oxide deposition to specific subdomains of the preorganized template yields high-fidelity, three-dimensional replication of the copolymer morphology, enabling the preparation of structures with multiscale order in a process that closely resembles biomineralization. Ordered mesoporous silicate films were synthesized with dielectric constants as low as 1.8 and excellent mechanical properties. The films survive the chemical-mechanical polishing step required for device manufacturing.
Activated carbon remains one of the most economical adsorbents for the removal of contaminants
from water. In particular, activated carbon is known to have an extremely high affinity for
phenol and its derivatives. This has been shown to be the result of a catalytic process wherein
activated carbon catalyzes the oxidative coupling reactions of phenol in aqueous solution when
molecular oxygen is present. These reactions are believed to be the source of the difficulty of
regenerating activated carbon loaded with phenol. This paper reports on our efforts toward
using supercritical fluids to regenerate activated carbon combined with a concurrent temperature-programmed desorption study to identify reaction products and their binding strength to the
carbon surface. The results show unequivocally that part of the phenol is chemisorbed on the
surface and part of it undergoes polymerization. Dihydroxybiphenyls and phenoxyphenols are
the major reaction products present on the surface. Isotope studies showed that surface carbon
atoms do not directly participate in these reactions. Supercritical extraction was found to perform
as well as solvent extraction for the regeneration of activated carbon loaded with phenol.
However, due to the chemisorbed nature of these oxidative coupling products, the reduced mass-transfer limitations afforded by supercritical extraction cannot improve the overall extent of
extraction even though the rate is improved with the addition of cosolvents.
An experimental apparatus has been developed for real time measurements of fluid–solid adsorption (or desorption) rates and equilibria at elevated pressures. In addition to controlling pressure and flow rates simultaneously, this setup is able to operate at higher flow rates than previously possible in supercritical fluid experiments. The system consists of a high pressure microbalance, two high pressure syringe pumps, and an absorbance detector. The microbalance enables the collection of data at a greater time resolution, resulting in a more accurate measurement of rate data. Because of the dual syringe pump design, there is no pressure drop in the system, making it possible to operate at a wide range of flow rates (at experimental conditions). The buoyancy force was measured with helium experiments, while the hydrodynamic forces were measured using a clean solid sample and supercritical carbon dioxide at different flow rates. It was found that the hydrodynamic force increased with flow rate as expected. The apparatus was tested by conducting two desorption experiments of phenol from activated carbon at 141±0.07 bar, 36.0±0.02 °C, and 0.47 ml/min (at experimental conditions). The amount of phenol removed was 16.4% and 18%, respectively, in the two runs which is consistent with previously published results and indicates the difficulty of regenerating activated carbon loaded with phenol.
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