Enhanced magnetic properties of highly crystalline cobalt ferrite fibers and their application as gas sensors

In this study, ferromagnetic cobalt ferrite (CoFe2O4) fibers were synthesized by electrospinning technique using a DMF/ethanol mixed precursor solution of poly (vinyl pyrrolidone) (PVP) and cobalt and iron (III) nitrates. The as-spun precursor fibers were characterized using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analyses and calcined at 500, 600 and 800 degrees C with a heating rate of 2 degrees C/min to obtain CoFe2O4 fibers. Morphological studies confirmed the formation of a continuous bead-free fiber structure in the calcined samples with an average fiber diameter and particle size of 208 nm and 48 nm respectively. Magnetic hysteresis loops of CoFe2O4 fibers revealed their ferromagnetic nature, with a maximum saturation magnetization of 76.5 emu/g and a coercivity of 948 Oe. At room temperature, the variation of resistance and the corresponding response toward various test gases of different concentrations were systematically investigated. The sensing response of CoFe2O4 fibers toward ammonia was found to be better than toward other test gases such as ethanol, methanol, acetone, and 2-propanol. CoFe2O4 fibers showed good reproducibility and a maximum response of 0.42 at 900 ppm concentration of ammonia. They also exhibited the ability to sense a very low concentration of ammonia (even at 25 ppm) at room temperature.