Polyol-Mediated Coprecipitation and Aminosilane Grafting of Superparamagnetic, Spinel ZnFe2O4 Nanoparticles for Room-Temperature Ethanol Sensors

A simple wet-chemical procedure is reported for synthesis and subsequent functionalization of spinel ZnFe2O4 nanomaterials for sensitive electrical detection of ethanol. ZnFe2O4 nanoparticles are produced by triethylene glycol-mediated coprecipitation of ZnSO4 and FeSO4 sols in aqueous ammonia. The mechanism for synthesis is described. As-prepared ZnFe2O4 nanoparticles are either thermally-treated at 673 K for 4 h or surface-modified with 3-(triethoxysilyl)propylamine to study the structure-property-sensing relationships. Fourier transform infrared spectroscopy is used to characterize functional groups on ZnFe2O4 surface. X-ray diffraction analysis of thermally-treated and surface-modified ZnFe2O4 nanoparticles coincide with the cubic spinel ZnFe2O4 structure having a crystallite size of 4.8 nm and 5.9 nm, respectively. The microstructure of ZnFe2O4 nanoparticles demonstrates a significant difference in the surface morphology of different samples. Vibrating sample magnetometer analyses demonstrate that ZnFe2O4 nanoparticles are superparamagnetic in nature. Thick-film chemiresistive ethanol sensors are then fabricated and tested at 300 K to determine the sensing characteristics of different ZnFe2O4 nanoparticles. The surface-modified ZnFe2O4 nanoparticles exhibit the highest sensitivity (0.51 ppm−1), good selectivity with 168.2% (2.7 times) higher response toward ethanol compared to major interferents, fast response (τres = 50 s) and recovery (τrec = 116 s) times, and excellent stability with 91.5% efficiency after three weeks of testing.