A novel approach for the preparation of AgBr nanoparticles from their bulk solid precursor using CTAB microemulsions

Microemulsions are suitable reaction media to prepare a wide variety of nanoparticles and provide control over their sizes. However, as typically used, microemulsions limit rates of rapid reactions and suffer from low reactant solubilization capacity. This work presents a new application of a novel approach aimed at minimizing these limitations. This approach, which was previously applied for AgCl nanoparticle preparation, involves solubilization of a bulk silver halide in the form of higher halides, by means of reaction with the surfactant counterion of a microemulsion, and the reprecipitation of silver halide nanoparticles in the water pools of individual reverse micelles. CTAB microemulsions were employed because they possess a reactive counterion and are known to have a high solubilization capacity for ionic reactants. Despite their high solubilization capacity, CTAB microemulsions achieved lower nanoparticles uptake (molar concentration of the colloidal nanoparticles) for the same surfactant concentration when compared to our previous study. The effect of the following variables on the nanoparticle uptake and the particle size was investigated: (1) operation variables, including rate of mixing and temperature; and (2) microemulsion variables, including CTAB and n-butanol concentrations, and water-to-surfactant mole ratio, R. These variables provide a comprehensive test to the proposed mechanism and expose the role of the surfactant layer rigidity. The nanoparticle uptake increased as the rate of mixing, temperature, and CTAB concentration increased, and decreased as n-butanol concentration and R increased. High n-butanol concentration and R values reduced the effective surfactant concentration and contributed to less surfactant layer rigidity and to particle aggregation.