Preparation, structure and properties of micro-spherical alumina with magnetic spinel ferrite cores Original Research Article

Layered double hydroxide (LDH) precursors with the compositions Mg2+–Fe2+–Fe3+–CO32−–LDHs, Ni2+–Fe2+–Fe3+–CO32−–LDHs and Co2+–Fe2+–Fe3+–CO32−–LDHs have been synthesized by a method involving separate nucleation and aging steps (SNAS). After calcination at 900 °C, MgFe2O4, NiFe2O4 and CoFe2O4 spinel ferrites were obtained. Vibrating sample magnetization (VSM) measurements indicate that NiFe2O4 has the best combination of soft magnetic properties with high specific saturation magnetization, low remanence and low coercivity. Silica was coated onto the surface of the NiFe2O4 spinel ferrite particles, and the coated particles were used as magnetic cores for the preparation of porous magnetic micro-spherical alumina particles (NiFe2O4–SiO2–Al2O3) by the oil column method. Scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and low temperature nitrogen adsorption measurements indicate that the sphericity, magnetic properties and pore structure of NiFe2O4–SiO2–Al2O3 are suitable for practical applications as a catalyst or catalyst support.