Morphological properties of ultra-fine (Ni,Zn)-ferrites and their ability to decompose CO2

Ultra-fine oxygen-deficient ferrites can decompose CO2 gas, which causes the greenhouse effect, into C and O-2 at a low temperature of about 300 degreesC. In the present study, two ultra-fine powders of ternary ferrites of composition (Ni, Zn)Fe2O4, as potential catalysts for CO2 decomposition, were prepared by hydrothermal synthesis or a coprecipitation method, and their abilities to decompose CO2 investigated. X-Ray diffraction measurements identified the crystal structure of the ferrites as spinel-type. The Brunauer-Emmett-Teller (BET) surface area of the ferrite prepared by hydrothermal synthesis was above 110 m(2) g(-1) and larger than for the sample obtained by the coprecipitation method. Particle sizes were very small, about 5-10 nm, in the both specimens. The CO2 decomposition efficiency of the reduced oxygen-deficient ternary ferrite prepared by hydrothermal synthesis was better than that of the coprecipitation sample. The difference of the CO2 decomposition efficiency is discussed in terms of the morphology and crystallinity based on TEM observations.