Green sol-gel route for the synthesis of cobalt ferrite mediated by cassava starch

Abstract

In this study, cobalt ferrite (CoFe₂O₄) was synthesized via the sol-gel method using cassava starch as a natural chelating agent. Two different masses of cassava starch were employed: 5 g (sample CFO#M5) and 10 g (sample CFO#M10). The corresponding powders were compacted and sintered into ceramic pellets, identified as CFO#M1 (derived from CFO#M5) and CFO#M2 (derived from CFO#M10), respectively. The samples were characterized by thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and electrical impedance spectroscopy (EIS). TG/DTA curves revealed multiple stages of mass loss associated with solvent evaporation and starch decomposition, with the crystalline phase forming above 700 °C. XRD patterns confirmed the formation of a pure cubic spinel phase of CoFe₂O₄ with no secondary peaks, and average crystallite sizes of 56.7 nm (CFO#M5) and 64.5 nm (CFO#M10). FTIR analysis indicated bands between 948 and 3660 cm⁻¹, attributed to residual organic groups such as hydroxyls, CO₂, C ≡ N, and C–H bonds from starch. SEM images showed spherical to semi-spherical grains with average sizes of 124 nm (CFO#M5) and 143 nm (CFO#M10). EIS measurements revealed two semicircular arcs in the Nyquist plots, indicating distinct conduction processes in grains and grain boundaries. Among the sintered samples, CFO#M2 exhibited higher AC electrical conductivity (σ′) and lower real impedance (Z′), which can be attributed to enhanced grain connectivity and improved intergranular pathways.