Synthesis and characterization of nano-sized nickel ferrites from fly ash for catalytic oxidation of CO

Nano-sized nickel ferrite powders have been synthesized from fly ash via a chemical synthesis route, co-precipitation method. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe2O4, phase can be obtained by thermal treatment of the precursors at temperature >800 °C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range of 500 °C ≤ T ≤ 800 °C, impure low crystalline NiFe2O4 phase is formed. The main impurities are FeO(OH) and Fe2O3·H2O phases. Higher magnetization (32 emu g−1) is obtained for a precursor precipitated at pH 10 and thermally treated at 1200 °C for 120 min. Prepared nickel ferrite samples showed a good response toward CO oxidation. It is concluded that the lower crystal size (∼8.5 nm) enhanced CO adsorption and consequently its oxidation.