Zameer Shervani

Synthesis of Ag2S quantum dots in water-in-CO2 microemulsions

Ag2S nanocrystals with a mean diameter of 5.9 nm (sigma= 1.65 nm) and characteristic surface plasmon resonance absorption at 330 nm have been synthesized in water-in-supercritical CO2 reverse microemulsion using the commonly used AOT surfactant with 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (F-pentanol) as cosurfactant.

Compartmentalization of reactants in supercritical fluid micelles

The hydrolysis of acetylsalicylic acid, a model reaction, in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/supercritical ethane reverse micelles has been studied in the presence of imidazole catalyst using in situ UV-vis spectroscopy. An increase of rate constant by 55 times was observed in AOT/supercritical ethane micellar medium compared to the reaction carried out in aqueous buffer. The reaction had a strong dependence on the water content of micelles, which decelerated to a large extent when the water content of the micelles was increased. The acceleration of the reaction in micelles compared to aqueous buffer and the water content dependence of the reaction rate have been confirmed to be due to compartmentalization of the water-soluble reactant and catalyst in the aqueous core of the micelles. The local concentration of substrate and catalyst increases when they are enclosed in the aqueous core of the micelles, resulting in an increase in the rate constant and shortening of the reaction time, rather than the existence of a diluted solution in the aqueous buffer. No pressure dependence of the reaction has been found in the pressure range of 27 to 44 MPa at 310 K.

The promotion of hydrolysis of acetylsalicylic acid in AOT/near-critical propane microemulsion

A significant acceleration of the hydrolysis of acetylsalicylic acid was accomplished by the introduction of an AOT/near-critical propane microemulsion at lower W0 values; the rate constant at W0 = 1 was found to be 54 times that in aqueous buffer medium in the presence of imidazole catalyst.

Development of ‘Green and Clean’ Reaction Media for Inorganic and Organic Nanomaterials

We have developed new water-in-CO₂ microemulsions under supercritical conditions of CO₂ bulk phase. Using fluorinated AOT surfactants and hydrogenated n-butanol as a cosurfactant, microemulsion solutions were obtained which could dissolve large amount of water as large as W₀=49 at 35°C. Where W₀ is the molar ratio of water-to-surfactant. Using varieties of surfactants and amount of cosurfactant, the composition of microemulsion has been established which gives capabilities to prepare different size nanomaterials in the range of 3 to 10 nm depending on the size of the core of microemulsion droplets. Size of the nanomaterials can be controlled with narrow size distribution by adjusting the W₀ values of microemulsion solution. In this presentation, I shall describe the preparation of water-in-CO₂ microemulsions as a function of water content, pressure of CO₂, surfactant concentration, and amount of cosurfactant added. The new CO₂ microemulsions will replace the existing conventional media used for preparation of nanomaterials until now because of non-toxic, cheap, easily recyclable bulk phase CO₂ used in these solutions at moderately low temperature of 35°C.