Controlled continuous hydrothermal synthesis of cobalt oxide (Co3O4) nanoparticles

Cubic Co3O4 nanoparticles have been produced hydrothermally by mixing high temperature water (sub-, near to supercritical) with an aqueous cobalt acetate precursor at high pressure. The relationship between operating variables such as synthesis temperature and residence time on particle size and conversion rate was examined. An increasing nanoparticle size was observed when synthesis temperature was increased, particularly in the range from 200 °C to 330 °C. Residence times of 0.5 s and 7 s appeared to strongly influence nanoparticle size while residence time greater than 7 s did not show any significant effect. Increasing reaction temperature or residence time both resulted in higher conversion rates. The Langmuir mathematical equation has been proposed as a kinetic expression that models nanoparticle size versus residence time for various reaction temperatures. The data generated using this model agrees well with experimental results which can be used to predict particle size at any given temperature and/or residence time.