Lanthanum-doped spinel cobalt ferrite (CoFe2O4) nanoparticles for environmental applications

Magnetic nanomaterials have been widely studied as adsorbents in the removal of contaminants from effluents. In this context, lanthanum-doped cobalt ferrites (CoLa_xFe_2-xO₄) were successfully synthesized via sol-gel method at 300 °C. XRD, TEM and BET analyses showed that minute particle size was achieved, with decreases along increasing La³⁺ content. XRD patterns confirm single cubic spinel CoFe₂O₄ nanoparticles. The average crystallite size confirmed via TEM images ranges between 5 nm and 12 nm. Surface area increased from 74.3 to 109.3 m² g⁻¹ with the addition of La³⁺. Raman spectra indicate a tendency towards inversion of the spinel induced by the addition of the lanthanide. The optical band gap of the samples doped with La showed a progressive decrease from 1.35 to 1.1 eV, which was not expected. Hysteresis loops indicate a transition from hard to soft magnetism. A significant decrease in coercivity from 740 to 158 Oe was observed with increase in La³⁺ (CoFe₂O₄ to CoLa_0.025Fe_1.975O₄). Total magnetization (M* defined for maximum available field H = 20 kOe) decayed from 44.6 to 29.0 emu.g⁻¹. These results show that the produced nanoparticles are ideally suited as magnetic adsorbents in separation of pollutants from wastewater.