Synthesis of MnCO₃ nanoparticles by microemulsions: Statistical evaluation of the effects of operating conditions on particle size distribution

Manganese carbonate nanoparticles were produced by microemulsion method. The effects of different operating conditions on nanoparticles' morphology, size, and polydispersity were determined. The reference system was made of cetyl trimethylammonium bromide, cyclohexane (as solvent), pentanol (as cosurfactant), and reactants MnCl₂ and (NH₄) ₂CO₃. Investigated operating conditions were reaction time (30 and 60 min), solvent's type (isooctane and hexane), cosurfactant's dosage (3 and 4.5 g), and reactant's concentration (1.0 and 0.25 mol/L). Produced nanoparticles were characterized by X-ray diffraction, scanning electron microscope, while particle size distribution was determined by image analysis. Significance of investigated factors was assessed by statistical analysis. Cubic-rhombohedral stacked particles with average size of 69 nm and standard deviations of 31 nm were obtained. Morphology was maintained in all the investigated conditions except when cosurfactant's dosage was raised to 4.5 g. Statistical analysis showed that nanoparticles' average size can be significantly increased with respect to the reference condition by augmenting reaction time (+49 nm), by increasing the cosurfactant's dosage (+67 nm) and also by decreasing the reactant's concentration when using hexane as solvent (+110 nm). Conversely, significant diminution of average size was obtained by using isooctane (-30 nm) and hexane (-26 nm) as solvents. Polydispersity of particle size distribution can be significantly diminished by using isooctane (8 nm) and hexane (13 nm) instead of cyclohexane, by decreasing reactant's concentration in the reference condition (10 nm) and by raising cosurfactant's dosage (12 nm).