Nanocasting synthesis, magnetic interaction and gas-sensing properties of dispersed, bundled and assembled α-Fe2O3 nanowires

The alpha-Fe2O3 (hematite) nanowires were synthesized with the nanocasting route using the hard template of SBA-15, and then were divided into the dispersed alpha-Fe2O3 nanowires (DNWs), bundled alpha-Fe2O3 nanowires (BNWs) and assembled alpha-Fe2O3 nanowires (ANWs) by the centrifugation technique. All samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption/desorption isotherm, UV-vis spectrum and superconducting quantum interference device (SQUID). All results indicated that all synthesized samples with the same nanowires diameter presented the much different interwires distance. Magnetic measurements showed that Ms of alpha-Fe2O3 ANWs and BNWs was smaller than that of alpha-Fe2O3 DNWs, while Hc and TC were larger than alpha-Fe2O3 DNWs. These should be attributed to the magnetic interaction from the surface spin coupling for the smaller interwires distance between the neighboring nanowires of alpha-Fe2O3 ANWs and BNWs. The gas-sensing behavior indicated that the as-obtained alpha-Fe2O3 ANWs, BNWs and DNWs exhibited the excellent gas-sensing performance to ethanol, resulting from the wide bandgap of alpha-Fe2O3 nanowires. Furthermore, it was proved that the sensitivity increased with the specific surface area, and the sensitivity of alpha-Fe2O3 DNWs based sensors was higher than those of alpha-Fe2O3 BNWs and ANWs. The alpha-Fe2O3 ANWs, BNWs and DNWs based sensors presented the rapid response and recovery times (only 7 s and 1 s) and the excellent gas sensitivity at low concentration. (C) 2017 Elsevier B.V. All rights reserved.