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

In this work, peculiar porous alpha-Fe(2)O(3) nanospheres were fabricated by a glycine-assisted hydrothermal method. They have large mesopores (ca. 10nm) 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 alpha-Fe(2)O(3) nanospheres. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy were employed to characterize the obtained Fe(2)O(3) nanospheres. Effects of preparation conditions, such as reactants, reaction temperature and reaction duration, were investigated on the morphology and structure of Fe(2)O(3) 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 alpha-Fe(2)O(3). The alpha-Fe(2)O(3) 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 alpha-Fe(2)O(3) nanospheres are also significantly better than those of previously reported Fe(2)O(3) 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. Copyright 2009 Elsevier B.V. All rights reserved.