Structural, magnetic and optical properties and photocatalytic activity of magnesium-calcium ferrite powders

Single-phase magnesium-calcium ferrite powders were prepared by solution combustion synthesis method. The phase and structure characterized by infrared and X-ray diffractometry methods showed that Ca2+ cations entered into octahedral sites and pushed Mg2+ cations to tetrahedral sites. The particle size decreased from similar to 50 to similar to 30 nm with addition of Ca2+ as observed by scanning and transmission electron microscopy. Magnetic properties measured by vibrating sample magnetometry technique showed that magnetic saturation initially increased from 27.1 to 33.2 emu/g and then decreased up to 30.1 emu/g due to the rearrangement of Fe3+ cations between tetrahedral and octahedral sites and the reduction in particle size. The band gap energy calculated from diffuse reflectance spectra decreased from 1.97 to 1.87 eV with addition of Ca2+ cations. The pristine magnesium ferrite powders photodegraded about 63% of methylene blue during 60 min of visible light illumination. However, the photodegradation rate was lower for Ca-substituted MgFe2O4 powders, due to the reduction of light absorption capability.