Influence of the temperature and insertion of cerium on morphology of magnetite nanoparticles

Full text: Iron oxides present strong adsorption capacity, natural abundance and low cost; among them magnetite has been applied as catalyst in the heterogeneous Fenton processes for degradation of organic contaminants, due to presence of Fe²⁺ in the structure and magnetic properties, the latter, important for catalyst separation. The present work discusses the influence of temperature on the conversion of amorphous oxide to the crystalline phase (70 and 140 °C) and the insertion of different amounts of cerium (2%, 1% and 0.5% (m/m)) in the crystalline structure of the material. These materials were prepared by co-precipitation method from FeCl₃.6H₂O, FeCl₂.4H₂O and different amounts of Ce(NO₃)₃.6H₂O. After washing step, the material was heated at 3 °C min^-1 until 70 or 140 °C, remaining under this condition during 12 h. The materials were characterized by scanning electron microscope, X-ray diffractometry, nitrogen adsorption-desorption isotherms for specific surface area (BET) and vibrating sample magnetometry. The micrography images showed that the morphology is sensitive to the insertion of cerium atoms, conferring loss of uniform spheric shape and presenting undefined forms. As for the microstructure, the insertion of the lowest amount of cerium caused an increase of crystallite size and of specific surface area, important parameters for the efficiency of degradation processes. The magnetization decreased considerably with the 140 °C temperature and especially with cerium insertion. The decrease of magnetization with the increase of temperature is probably due to a conversion to the maghemite phase. The material containing 1% Ce was applied in dark Fenton process resulting in 55% degradation of the antibiotic cephalexin (1 mg L^-1) after 150 min reaction. The material showed also catalytic activity under solar irradiation, achieving 67% degradation after 90 min, demonstrating efficiency under visible radiation. (author)