Synthesis of cerium/cobalt phosphate nanostructures in catanionic reverse micelles

Abstract

Nanofilaments/nanorods of cerium phosphate or cobalt phosphate are produced by reaction of aqueous hexadecyltrimethylammonium phosphate [(CTA)₃PO₄] micelles with either [Ce(AOT)₃] or [Co(AOT)₂] reverse micelles prepared in isooctane. The nanostructures are hydrophobic, highly uniform in width (4–5 nm) and variable in length (up to 1200 nm). Whereas the particle width is constrained by the size of the catanionic reverse micelles, changes in the reaction conditions such as the concentration of the surfactant salts and [Ce(AOT)₃]/[(CTA)₃PO₄] molar ratio, markedly influence the length of the inorganic nanostructures. The CePO₄ nanofilaments are crystalline and morphologically invariant with regard to changes in the reaction conditions, whereas the Co₃(PO₄)₂ nanorods are amorphous and more sensitive to modifications in the surfactant salt molar ratio. The results are consistent with a mechanism based on the slow uni-directional aggregation/crystallization of nanoscale surfactant-coated inorganic building blocks.