Glycine-assisted hydrothermal synthesis of peculiar porous α-Fe2O3 nanospheres with excellent gas-sensing properties

In this work, peculiar porous α-Fe2O3 nanospheres were fabricated by a glycine-assisted hydrothermal method. They have large mesopores (ca. 10 nm) in the core and small mesopores (<4 nm) in the shell. To our best knowledge, there have been so far no reports on the synthesis of such peculiar porous α-Fe2O3 nanospheres. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy were employed to characterize the obtained Fe2O3 nanospheres. Effects of preparation conditions, such as reactants, reaction temperature and reaction duration, were investigated on the morphology and structure of Fe2O3 nanospheres. It was shown that the morphology and structure could be readily controlled by the time and temperature of hydrothermal treatment. The formation mechanism was proposed based on experimental results, which shows that glycine molecules play an important role in the formation of the morphology and porous structure of α-Fe2O3. The α-Fe2O3 porous nanospheres were used as gas sensing layer, and exhibited excellent gas-sensing properties to ethanol in terms of response and selectivity. The sensors showed good reproducibility and stability as well as short response (9 s) and recovery time (43 s) even at an ethanol concentration as low as 50 ppm. The gas-sensing properties of porous α-Fe2O3 nanospheres are also significantly better than those of previously reported Fe2O3 nanoparticles (ca. 30 nm). The sensitivity of the former is over four times higher than that of the latter at varied ethanol concentrations. The gas-sensing mechanism was discussed in details. Both fast response and steady signal make these peculiar nanostructures a promising candidate for ethanol detection.