Development of a microemulsion-based process for synthesis of cobalt (Co) and cobalt oxide (Co₃O₄) nanoparticles from submicrometer rods of cobalt oxalate

Rod-shaped nanostructures of cobalt oxalate dihydrate were synthesized at room temperature by the microemulsion (reverse micellar) route. These rods are highly uniform in length and can be modified with temperature (from ∼6.5 μm at 50 °C to ∼2.5 μm at 150 °C) while keeping the diameter nearly constant (200-250 nm). Thermal decomposition of these rods in a controlled atmosphere (air and H₂) leads to nanoparticles of Co₃O₄ and Co, respectively, while in a helium atmosphere a mixture of Co and CoO nanoparticles is obtained. Co₃O₄ nanoparticles (∼35 nm) were slightly agglomerated, while Co nanoparticles were monodispersed and highly uniform (∼25 nm). The oxalate rods and Co₃O₄ nanoparticles show an antiferromagnetic ordering at 54 and 35 K, respectively.