A comparative study on the structural, optical and magnetic properties of Fe3O4 and Fe3O4@SiO2 core–shell microspheres along with an assessment of their potentiality as electrochemical double layer capacitors

Abstract

Herein, we report a comprehensive and comparative study on the crystal structure, and microstructural, optical, magnetic, hyperfine and electrochemical properties of Fe₃O₄ microspheres (S1) of diameter ∼418 nm and Fe₃O₄@SiO₂ core–shell microspheres (S2) of diameter ∼570 nm. Each asymmetric unit of the crystalline Fe₃O₄ has one cation vacancy at the octahedral [B] site. At 300 K the saturation magnetization and coercivity of ferrimagnetically ordered S1 and S2 are 63.5, 38.5 emu g⁻¹ and 200 and 120 Oe, respectively. We have shown that the synthesis procedure, morphology, surface properties, interparticle interaction manifesting the collective properties of the nanoparticle assembly and the average size of individual Fe₃O₄ nanoparticles forming the spherical ensemble play a crucial role in determining the magnetic properties of Fe₃O₄ and Fe₃O₄@SiO₂ microspheres while the diameter of the microsphere does not have significant influence on magnetic properties of such a system. Further, the photoluminescence intensity of Fe₃O₄ microspheres gets significantly enhanced upon SiO₂ coating. A cyclic voltammetric study suggests that S1 can act as a good electrical double layer capacitor (EDLC) above a scan rate of 0.04 V s⁻¹ while S2 exhibits excellent performance as EDLC in a scan range from 0.01 to 0.06 V s⁻¹. Thus, S2 is a potential candidate for fabrication of EDLCs.