Fabrication and characterization of CoxMn0.25−xMg0.75Fe2O4 nanoparticles for H2S sensing applications

Cobalt-doped manganese–magnesium ferrite nanoparticles CoxMn0.25−xMg0.75Fe2O4 (0.00 ≤ x ≤ 0.20) were successfully synthesized via an autocombustion (sol–gel) technique. The X-ray diffraction patterns of nanoparticles with different compositions revealed that all of the produced samples were composed of a single spinel ferrite phase. The lattice constants of the nanoparticles increased from 8.36743 to 8.38741 as the Co2+ content was increased. Crystallite sizes measured by using Scherrer formula ranged from 24 to 28 nm, indicating that the materials produced were nanocrystalline. Microstructural investigation verified that the nanoparticles had porous morphology due to autoignition during combustion. The results of elemental analysis by energy dispersive X-ray were in good agreement with the composition predicted on the basis of the stoichiometry of the reactant solutions. Magnetic measurements were taken at room temperature by using a vibrating magnetometer. Magnetization measurements showed a maximum coercivity of 440 Oe at a crystallite size of ~ 24 nm. The trend of crystallinity was consistent with the increase in magnetic characteristics (coercivity and retentivity). The samples contained unblocked superparamagnetic nanoparticles. Hysteresis loop area is almost non-existent, reflecting typical soft magnetic materials. Additionally, the conductivity responses of CoxMn0.25−xMg0.75Fe2O4 nanoparticles were measured via exposing particles to the reducing (H2S) gas at various operating temperatures. The results of the H2S gas-sensing tests demonstrated that the synthesized nanoferrite had a high sensitivity of approximately 85.18% at x = 0.20 and a short response and recovery time of 1.6–4.2 s.