Comparison of the Surface Properties of Hydrothermally Synthesised Fe₃O₄@C Nanocomposites at Variable Reaction Times

The influence of variable reaction time (t_r) on surface/textural properties (surface area, total pore volume, and pore diameter) of carbon-encapsulated magnetite (Fe₃O₄@C) nanocomposites fabricated by a hydrothermal process at 190 °C for 3, 4, and 5 h was studied. The properties were calculated using the Brunauer-Emmett-Teller (BET) isotherms data. The nanocomposites were characterised using Fourier transform infrared spectroscopy, X-ray diffraction analysis, thermogravimetry, and scanning and transmission electron microscopies. Analysis of variance shows t_r has the largest effect on pore volume (F value = 1117.6, p value < 0.0001), followed by the surface area (F value = 54.8, p value < 0.0001) and pore diameter (F value = 10.4, p value < 0.001) with R²-adjusted values of 99.5%, 88.5% and 63.1%, respectively. Tukey and Fisher tests confirmed t_r rise to have caused increased variations in mean particle sizes (11-91 nm), crystallite sizes (5-21 nm), pore diameters (9-16 nm), pore volume (0.017-0.089 cm³ g^-1) and surface area (7.6-22.4 m² g^-1) of the nanocomposites with individual and simultaneous confidence limits of 97.9 and 84.4 (p-adj < 0.05). The nanocomposites' retained Fe-O vibrations at octahedral (436 cm^-1) and tetrahedral (570 cm^-1) cubic ferrite sites, modest thermal stability (37-60 % weight loss), and large volume-specific surface area with potential for catalytic application in advanced oxidation processes.