Sol–Gel Engineering of Nanostructured MgFe2O4 Ferrite: Tunable Microstructure for Thermochemical Energy Conversion Applications
This study investigates the synthesis–structure relationships governing sol–gel-derived nanostructured MgFe2O4 ferrite powders for high-temperature thermochemical energy conversion applications. The effects of key processing parameters, including propylene oxide (PO) concentration, gel aging time, calcination temperature, and calcination duration, were systematically examined to tune the phase composition, specific surface area (SSA), pore volume, crystallite size, and nanoparticle morphology of MgFe2O4. Increasing the PO concentration from 5 to 20 mL shortened the gelation time from 585 to 323 s and increased the SSA from 5.30 to 17.88 m2/g, while the pore volume increased from 0.0074 to 0.0210 cm3/g. In contrast, gel aging time between 24 and 120 h produced negligible changes in SSA, pore volume, and crystallite size, indicating that extended aging is not required for microstructural control. Calcination temperature strongly influenced the nanostructure: increasing the temperature from 600 to 1000 °C decreased SSA and pore volume while increasing crystallite size from 21.33 to 48.76 nm. Longer calcination times produced a similar but less pronounced effect, decreasing SSA from 18.83 to 14.89 m2/g and increasing crystallite size from 17.55 to 30.12 nm. Overall, phase-pure MgFe2O4 with favorable textural properties was obtained using 20 mL of PO, 24 h of aging, and calcination in the 700–800 °C range. Under the identified synthesis conditions, namely 20 mL of PO, 24 h of aging, and calcination in the range of 700–800 °C for 2 h, phase-pure MgFe2O4 nanoparticles with particle sizes of approximately 10–50 nm were obtained. These results establish a processing–microstructure framework for engineering MgFe2O4 nanomaterials with tunable textural properties for solar thermochemical redox cycles and related high-temperature energy applications.