Highly enhanced gas-sensing properties of indium-doped mesoporous hematite nanowires

Mesoporous indium (In)-doped hematite (alpha-Fe2O3) nanowires were synthesized with mesoporous SBA-15 silica as a hard template, and then the influence of In dopant on the microstructure and gas-sensing performance was investigated in detail. With characterization by transmission electron microscopy, X-ray diffraction, UV-vis spectroscopy, and nitrogen physisorption experiments, it was shown that the average grain size increased for up to 1 mol% In dopant and then decreased with increasing In dopant content, while the surface area changed in the inverse manner. Because of the low melting point of In, In acted as a fluxing agent and entered the alpha-Fe2O3 lattice when the In content was low, and the average grain size increased. With higher In content, In precipitated out the lattice and existed at the grain boundary, and the grain size decreased. It is concluded that In in the lattice increased lattice distortion and In at the boundary increased the surface area and oxygen vacancies, which were both beneficial for improving the gas-sensing performance. The response of In-doped alpha-Fe2O3 nanowires increased by about 30%-50% as compared with that of pure alpha-Fe2O3 nanowires. The gas sensor based on 3 mol% In-doped alpha-Fe2O3 nanowires exhibited the best gas response and a rapid response-recovery time toward ethanol at the optimum temperature. Owing to the same valence, In dopant affected only the microstructure and components of the alpha-Fe2O3 lattice, which was necessary to improve the gas-sensing behavior.