Dissolution Amplification by Resonance and Cavitational Stimulation at Ultrasonic and Megasonic Frequencies

Acoustic stimulation offers a green pathway for the extraction of valuable elements such as Si, Ca, and Mg via solubilization of minerals and industrial waste materials. Prior studies have focused on the use of ultrasonic frequencies (20-40 kHz) to stimulate dissolution, but mega sonic frequencies (≥1 MHz) offer benefits such as matching of the resonance frequencies of solute particles and an increased frequency of cavitation events. Here, based on dissolution tests of a series of minerals, it is found that dissolution under resonance conditions produced dissolution enhancements between 4x-to-6x in Si-rich materials (obsidian, albite, and quartz). Cavitational collapse induced by ultrasonic stimulation was more effective for Ca- and Mg-rich carbonate precursors (calcite and dolomite), exhibiting a significant increase in the dissolution rate as the particle size was reduced (i.e. available surface area was increased), resulting in up to a 70x increase in the dissolution rate of calcite when compared to unstimulated dissolution for particles with d50\u3c 100 μm. Cavitational collapse induced by mega sonic stimulation caused a greater dissolution enhancement than ultrasonic stimulation (1.5x vs 1.3x) for amorphous class F fly ash, despite its higher Si content because the hollow particle structure was susceptible to breakage by the rapid and high number of lower-energy mega sonic cavitation events. These results are consistent with the cavitational collapse energy following a normal distribution of energy release, with more cavitation events possessing sufficient energy to break Ca-O and Mg-O bonds than Si-O bonds, the latter of which has a bond energy approximately double the others. The effectiveness of ultrasonic dissolution enhancement increased exponentially with decreasing stacking fault energy (i.e., resistance to the creation of surface faults such as pits and dislocations), while, in turn, the effectiveness of mega sonic dissolution increased linearly with the stacking fault energy. These results give new insights into the use of acoustic frequency selections for accelerating elemental release from solutes by the use of acoustic perturbation

Targeted morphology of copper oxide based electrospun nanofibers

In this work, CuO-based nanofibers were synthesized via electrospinning. Smooth, defect-free fibers with a diameter of 261 ± 63 nm were fabricated and characterized. Thermal treatment under air at 823 K transformed the smooth nanofibers to a network of segmented, macroporous CuO nanoparticles with an average fiber diameter of 160 ± 41 nm and a crystallite size of 55.4 nm. The effects of solution properties (polymer molecular weight, polymer/metal concentration, and solvent identity) and processing conditions (voltage, tip-to-collector distance, extrusion rate, and humidity) were also investigated. Solution properties were found to strongly influence viscosity, conductivity, dielectric constant, density, and surface tension, which invariably affected fiber dimension, morphology and surface structure. Fibers as thick as 536 nm and as thin as 70 nm with cylindrical and fused structures were produced by manipulating the solution properties. Processing conditions were found to moderately affect fiber uniformity and fiber diameter

Targeted morphology of copper oxide based electrospun nanofibers

In this work, CuO-based nanofibers were synthesized via electrospinning. Smooth, defect-free fibers with a diameter of 261 ± 63 nm were fabricated and characterized. Thermal treatment under air at 823 K transformed the smooth nanofibers to a network of segmented, macroporous CuO nanoparticles with an average fiber diameter of 160 ± 41 nm and a crystallite size of 55.4 nm. The effects of solution properties (polymer molecular weight, polymer/metal concentration, and solvent identity) and processing conditions (voltage, tip-to-collector distance, extrusion rate, and humidity) were also investigated. Solution properties were found to strongly influence viscosity, conductivity, dielectric constant, density, and surface tension, which invariably affected fiber dimension, morphology and surface structure. Fibers as thick as 536 nm and as thin as 70 nm with cylindrical and fused structures were produced by manipulating the solution properties. Processing conditions were found to moderately affect fiber uniformity and fiber diameter

Selective Homogeneous and Heterogeneous Catalytic Conversion of Methanol/Dimethyl Ether to Triptane

The demand for specific fuels and chemical feed-stocks fluctuates, and as a result, logistical mismatches can occur in the supply of their precursor raw materials such as coal, biomass, crude oil, and methane. To overcome these challenges, industry requires a versatile and robust suite of conversion technologies, many of which are mediated by synthesis gas (CO + H_2) or methanol/dimethyl ether (DME) intermediates. One such transformation, the conversion of methanol/DME to triptane (2,2,3-trimethylbutane) has spurred particular research interest. Practically, triptane is a high-octane, high-value fuel component, but this transformation also raises fundamental questions: how can such a complex molecule be generated from such a simple precursor with high selectivity? In this Account, we present studies of this reaction carried out in two modes: homogeneously with soluble metal halide catalysts and heterogeneously over solid microporous acid catalysts. Despite their very different compositions, reaction conditions, provenance, and historical scientific context, both processes lead to remarkably similar products and mechanistic interpretations. In both cases, hydrocarbon chains grow by successive methylation in a carbocation-based mechanism. The relative rates of competitive processes−chain growth by methylation, chain termination by hydrogen transfer, isomerization, and cracking−systematically depend upon the structure of the various hydrocarbons produced, strongly favoring the formation of the maximally branched C_7 alkane, triptane. The two catalysts also show parallels in their dependence on acid strength. Stronger acids exhibit higher methanol/DME conversion but also tend to favor chain termination, isomerization, and cracking relative to chain growth, decreasing the preference for triptane. Hence, in both modes, there will be an optimal range: if the acid strength is too low, activity will be poor, but if it is too high, selectivity will be poor. A related reaction, the methylative homologation of alkanes, offers the possibility of upgrading low-value refinery byproducts such as isobutane and isopentane to more valuable gasoline components. With the addition of adamantane, a hydride transfer catalyst that promotes activation of alkanes, both systems effectively catalyze the reaction of methanol/DME with lighter alkanes to produce heavier ones. This transformation has the further advantage of providing stoichiometric balance, whereas the stoichiometry for conversion of methanol/DME to alkanes is deficient in hydrogen and requires rejection of excess carbon in the form of carbon-rich arenes, which lowers the overall yield of desired products. Alternatively, other molecules can serve as sacrificial sources of hydrogen atoms: H2 on heterogeneous catalysts modified by cations that activate it, and H_3PO_2 or H_3PO_3 on homogeneous catalysts. We have interpreted most of the features of these potentially useful reactions at a highly detailed level of mechanistic understanding, and we show that this interpretation applies equally to these two widely disparate types of catalysts. Such approaches can play a key role in developing and optimizing the catalysts that are needed to solve our energy problems

Non-cancer uses of histone deacetylase inhibitors: effects on infectious diseases and β-hemoglobinopathies

After the approval of suberoylanilide hydroxamic acid (SAHA, vorinostat, Zolinza) for the treatment of cutaneous T cell lymphoma (CTCL), a number of HDAC inhibitors (HDACi) are currently in Phase II or III clinical trials (alone or in combination) for the treatment of a great number of tumors. In addition to these cancer uses, HDACi can be successfully used in non-cancer diseases. In this review we focused on the uses of HDACi in some infectious diseases and beta-hemoglobinopaties. In C. albicans cultures, HDACi increased the frequency of cell switching (a relevant virulence trait) in the white-to-opaque transition, reduced the azole trailing effect through reduction in azole-dependent upregulation of CDR and ERG genes, and inhibited the fluconazole-dependent resistance induction. Moreover, they inhibited germination in several strains, and caused 90% reduction in the adherence of C. albicans to human cultured pneumocytes. In HIV-1-infected cells, the treatment with HDACi reactivates the HIV-1 expression in latent cellular reservoirs. Thus, the use of HDACi as adjuvant to highly active antiretroviral therapy (HAART) can represent a new potential therapeutic strategy to eradicate the viral infection. A number of HDACi have been reported as active against P. falciparum infection. Two recent papers show some 2-aminosuberic acid-based compounds as well as a series of phenylthiazolyl suberoyl hydroxamates as very potent and selective antimalarial agents. Among the many agents capable to perform post-natal reactivation of fetal hemoglobin production, HDACi for their capacity to de-repress gamma-globin gene expression in adult red cell, are presently considered promising molecules for personalized therapy of beta-hemoglobinopathies

Catalytic Conversion of Biomass to Monofunctional Hydrocarbons and Targeted Liquid-Fuel Classes

It is imperative to develop more efficient processes for conversion of biomass to liquid fuels, such that the cost of these fuels would be competitive with the cost of fuels derived from petroleum. We report a catalytic approach for the conversion of carbohydrates to specific classes of hydrocarbons for use as liquid transportation fuels, based on the integration of several flow reactors operated in a cascade mode, where the effluent from the one reactor is simply fed to the next reactor. This approach can be tuned for production of branched hydrocarbons and aromatic compounds in gasoline, or longer-chain, less highly branched hydrocarbons in diesel and jet fuels. The liquid organic effluent from the first flow reactor contains monofunctional compounds, such as alcohols, ketones, carboxylic acids, and heterocycles, that can also be used to provide reactive intermediates for fine chemicals and polymers markets

Direct observation of the kinetics of gas-solid reactions using in situ kinetic and spectroscopic techniques

In situ spectroscopic techniques provide kinetic and chemical structure data for elucidation of reaction mechanisms and pathways during reactive separations