Synthesis of magnetic iron oxide particles: Development of an in situ coating procedure for fibrous materials

We report on the synthesis of magnetic iron oxide particles; study of the particles' formation was undertaken to investigate conditions of precipitation in order to apply it efficiently to cellulose fibre coating procedures. Synthesis of magnetic particles was performed, comprised of variations of molar concentrations of precursor solutions as well as different addition protocols of reactants into the reaction system. This allowed us to investigate the formation of iron oxide particles from different starting points. Following the synthesis, an evaluation of particles' formation in different stages of synthesis procedure i.e. at different pH values and analysis of particles' properties was carried out. Structural properties (crystallinity, size of the single magnetite crystals), their magnetic and colloidal properties were correlated with the synthesis procedure used. Procedure with controlled addition of ammonium hydroxide solution into a solution of precursor iron salts results in magnetic particles with largest crystallite size and the most intense X-ray diffraction patterns. Size and crystallinity of formed particles are also dependent upon the molar concentrations of Fe²⁺ and Fe³⁺ ions. Highest values of saturation magnetization are again exhibited by particles, produced with controlled addition of catalyst into a solution of precursor, a consequence of their ordered structure, which also favourably influences their colloidal properties when dispersed in an aqueous-based ferrofluid. Gained insight of the presented synthesis study will prove useful when in situ precipitation of magnetic iron oxide particles will be used for the preparation of magnetic solid cellulose substrates, since it will allow for the optimal adjustment of process conditions.