Control of Surface Area and Porosity of Co3O4 via Intercalation of Oxidative or Nonoxidative Anions in Hydrotalcite-like Precursors

Monometal hydrotalcite-like compounds of CoII0.74CoIII0.26(OH)2.01(NO3)0.21(CO3) 0.02·0.6H2O and CoII0.74CoIII0.26(OH)1.99(CO3)0.13(NO3)0.01·0.7H2O have been prepared via precipitation and anion-exchange methods. After being heated at 150−600 °C, the two precursor compounds were oxidatively converted to product spinel Co3O4. The chemical nature of the anions intercalated in the interlayer space of the compounds determines the ultimate crystallite size, surface area, and porosity of the oxide spinel. By selection of carbonate anions, Co3O4 with crystallite size of 7−34 nm and surface area of 17−150 m2/g can be prepared at 150−600 °C. In particular, nanometer size Co3O4 crystallites (7−10 nm) has been synthesized at a temperature as low as 150−250 °C from the precursor compound CoII0.74CoIII0.26(OH)1.99(CO3)0.13(NO3)0.01·0.7 H2O. The roles of the different anions in the interlayer space are also discussed with respect to the thermal decomposition of the precursor compounds.