An-Najah Staff

Ultradispersed metal oxide nanoparticles have applications as heterogeneous catalysts for organic reactions. Their catalytic activity depends primarily on their surface area, which in turn, is dictated by their size, colloidal concentration and stability. This work presents a microemulsion approach for in situ preparation of ultradispersed copper oxide nanoparticles and discusses the effect of different microemulsion variables on their stability and highest possible time-invariant colloidal concentration (nanoparticle uptake). In addition, a model which describes the effect of the relevant variables on the nanoparticle uptake is evaluated. The preparation technique involved solubilizing CuCl2 in single microemulsions followed by direct addition of NaOH. Upon addition of NaOH, copper hydroxide nanoparticles stabilized in the water pools formed in addition to a bulk copper hydroxide precipitate at the bottom. The copper hydroxide nanoparticles transformed with time into copper oxide. After reaching a time-independent concentration, mixing had limited effect on the nanoparticle uptake and particle size. Particle size increased with increasing the surfactant concentration, concentration of the precursor salt, and water to surfactant mol ratio; while the nanoparticle uptake increased linearly with the surfactant concentration, displayed an optimum with R and a power function with the concentration of the precursor salt. Surface areas per gram of nanoparticles were much higher than literature values. Even though lower area per gram of nanoparticles was obtained at higher uptake, higher surface area per unit volume of the reverse micellar system was attained. A model based on water uptake by Wisor type II microemulsions, and previously used to describe iron oxide nanoparticle uptake by the same microemulsions, agreed well with the experimental results.

Nanoparticles serve the need for advanced materials with specific chemical, physical, and electronic properties. These properties can be attained by manipulating the particle size. Consequently, size control has been recognized as a key factor for selecting a nanoparticle preparation technique. (w/o) Microemulsions, or reverse micelles, have been successfully used to prepare wide variety of nanoparticles with controlled sizes. Studies showed that adjusting microemulsion and/or operation variables provides a key to controlling nanoparticle size and polydispersity. The effect of a given variable, however, relies heavily on the reactant addition scheme. The mixing of two microemulsions scheme has been widely used in the literature, and the effect of microemulsion and operation variables on intermicellar nucleation and growth was detailed. The single microemulsions reactant addition scheme, on the other hand, enables intramicellar nucleation and growth, and therefore, may lead to a different response. Moreover, studies on nanoparticle preparation using the single microemulsions scheme involved more of reactive surfactants and introduced the concept nanoparticle uptake, which pertains to the maximum colloidal concentration of nanoparticles that can be stabilized in a microemulsion system. This review looks into the mechanisms controlling nanoparticle formation and compares literature trends reported for the effect of microemulsion and operation variables on the nanoparticle size and polydispersity for the single microemulsions reactant addition scheme. Moreover, it sheds some light on nanoparticle uptake and its significance.

Ultradispersed catalysts significantly enhance rates of reaction and mass transfer by virtue of their extended and easy accessible surface. These attractive features were exploited in this study to effectively capture H2S(g) from an oil phase by ultradispersed sorbents. Sorption of H2S(g) from oil phases finds application for scavenging H2S(g) forming during heavy oil extraction and upgrading. This preliminary investigation simulated heavy oil by (w/o) microemulsions having 1-methyl-naphthalene; a high boiling point hydrocarbon, as the continuous phase. H2S(g) was bubbled through the microemulsions which contained the ultradispersed sorbents. The type and origin of sorbent were investigated by comparing in situ prepared FeOOH and commercial α-Fe2O3 nanoparticles as well as aqueous FeCl3 and NaOH solutions dispersed in the (w/o) microemulsions. The in situ prepared FeOOH nanoparticles captured H2S(g) in a chemically inactive form and displayed the highest sorption rate and capacity. Temperature retarded the performance of FeOOH particles, while mixing had no significant effect.

Water-in-oil (w/o) microemulsions are very appealing reaction media due to their ability to provide huge surface of contact between water-soluble and oil-soluble reactants. Their application as reaction media, including the preparation of nanoparticles, is, however, limited to water soluble precursors. In this study, we present a first step scheme in a two-step process for the preparation of metal oxide nanoparticles starting from their water-insoluble metal oxide bulk powder. This step involves solubilizing the metal oxide in the water pools of the microemulsion with the aid of a solubilizing agent. The variables affecting the solubilizing capacity of iron and copper oxides,as examples of important metal oxides, in single HCl-containing AOT/water/isooctane microemulsions were investigated. The effect of the following variables on the solubilization capacity is reported, namely, mixing time, surfactant concentration, water to surfactant mole ratio (R),and the nominal concentration of HCl in the water pool. At 300-rpm, time-invariant concentration of the metals in the microemulsions was achieved in about 6 hours. These values were quoted as the solubilization capacity of the metal oxide at the corresponding conditions.Solubilization capacity increased linearly with the surfactant concentration and R, and portrait a power function with the nominal concentration of HCl in the water pool. A mathematical model previously derived to describe nanoparticle uptake by single microemulsion accurately accounted for the effect of the aforementioned variables on the solubilization capacity.