Oxide nanocrystals from a low-temperature, self-limiting sol-gel transition in a coordinating environment: Nanocrystal synthesis, processing of gas-sensing devices and application to organic compounds

SnO2 and In2O3 nanocrystals were prepared by injecting the corresponding metal oxide sols in solutions of amines in organic solvents at
160 oC, followed by heating at the resulting temperature (80-110 oC) for 3 h. The obtained nanoparticles were extracted by centrifugation, washed
and heat-treated at 500 oC for final purification and eventual completion of the crystallization process. The preparation process and the final
products were characterized by X-ray diffraction, Raman and Fourier transform infrared spectroscopy and transmission electron microscopy. Very
small nanoparticles with a mean size of about 6 nm were obtained, generally constituted by single crystals, chemically pure and defect free.
The nanocrystals could be suspended in various solvents, and then deposited by dropping onto alumina substrates with pre-deposited heaters
and electrodes. The resulting gas-sensing devices were tested to such gases as acetone and ethanol, and we observed that tin oxide has a higher
sensitivity towards acetone while indium oxide has a higher sensitivity towards ethanol. Moreover, in the case of indium oxide there is a maximum
in the response around 300 oC while for tin oxide the response increases with the operating temperature.