Hollow Magnetic Ferrites MFe₂O₄ (M = Fe, Mn, Co, Zn) Fabrication and Comparison by Using Double Ammonium Salts Orientation

Hollow MFe₂O₄(M = Fe, Mn, Co, Zn) particles were synthesized via facile solvothermal route employing ammonium bicarbonate (NH₄HCO₃ and ammonium acetate (NH₄Ac) as structureorientated reagents. Among the targeted ferrites, hollow Fe₃O₄ particles (MFe₂O₄, M = Fe) were formed by adding NH₄HCO₃ and NH₄Ac, or by only one of them. However, the ferrite MFe₂O₄(M = Mn, Co, Zn) samples as-prepared with NH₄HCO₃ and NH₄Ac presented two different morpholo- gies which distinguished from the hollow Fe₃O₄ particles under the same condition. Meanwhile, the monodisperse hollow MFe₂O₄ (M = Mn, Co, Zn) particles were obtained with NH₄Ac, but that similar particles couldn't be obtained with NH₄HCO₃ only. The results prove that the NH₄HCO₃ is vital to the formation of hollow MFe₂O₄ (M = Mn, Co, Zn) particles, and both the concentration of NH₄HCO₃ and NH₄Ac highly determined the composition and structure evolution (whether it is hollow or solid) of magnetic ferrites MFe₂O₄ (M = Fe, Mn, Co, Zn) particles. Also, a possible mechanism of ferrite hollow spheres formation and evolution is proposed and discussed. Such a reaction system of double ammonium salts orientation provides useful references for nanoscale hollow fabrication.