Synthesis and characterization ofα-Fe₂O₃nanoparticles showing potential applications for sensing quaternary ammonium...

P-type and n-type metal oxide semiconductors are widely used in the manufacture of gas sensing materials, due to their excellent electronic, electrical and electrocatalytic properties. Hematite (α-Fe₂O₃) compound has been reported as a promising material for sensing broad types of gases, due to its affordability, good stability and semiconducting properties. In the present work, the efficient and easy-to-implement sol-gel method has been used to synthesizeα-Fe₂O₃nanoparticles (NPs). The TGA-DSC characterizations of the precursor gel provided information about the phase transformation temperature and the mass percentage of the hematite NPs. X-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy data analyses indicated the formation of two iron oxide phases (hematite and magnetite) when the NPs are subjected to thermal treatment at 400 °C. Meanwhile, only the hematite phase was determined for thermal annealing above 500 °C up to 800 °C. Besides, the crystallite size shows an increasing trend with the thermal annealing and no defined morphology. A clear reduction of surface defects, associated with oxygen vacancies was also evidenced when the annealing temperature was increased, resulting in changes on the electrical properties of hematite NPs. Resistive gas-sensing tests were carried out using hematite NPs + glycerin paste, to detect quaternary ammonium compounds. Room-temperature high sensitivity values (S_r ∼ 4) have been obtained during the detection of ∼1 mM quaternary ammonium compounds vapor. The dependence of the sensitivity on the particle size, the mass ratio of NPs with respect to the organic ligand, changes in the dielectric properties, and the electrical conduction mechanism of gas sensing was discussed.