Bystromite (MgSb2O6) nanorods were prepared using a colloidal method in the presence of ethylenediamine, after a calcination step at 800 °C in static air. From X-ray powder diffraction analyses, a trirutile-type structure with lattice parameters a = 4.64 Å and c = 9.25 Å and space group P42/mnm was identified. Using scanning electron microscopy (SEM), microrods with sizes from 0.2 to 1.6 μm were observed. Transmission electron microscopy (TEM) analyses revealed that the nanorods had a length of ~86 nm and a diameter ~23.8 nm. The gas-sensing properties of these nanostructures were tested using pellets elaborated with powders of the MgSb2O6 oxide (calcined at 800 °C) at temperatures 23, 150, 200, 250 and 300 °C. The pellets were exposed to different concentrations of carbon monoxide (CO) and propane (C3H8) at these temperatures. The results showed that the MgSb2O6 nanorods possess excellent stability and high sensitivity in these atmospheres.

LaCoO3nanoparticles with perovskite-type structure were prepared by a microwave-assisted colloidal method. Lanthanum nitrate, cobalt nitrate, and ethylenediamine were used as precursors and ethyl alcohol as solvent. The thermal decomposition of the precursors leads to the formation of LaCoO3from a temperature of 500°C. The structural, morphological, and compositional properties of LaCoO3nanoparticles were studied in this work by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Pellets were manufactured in order to test the gas sensing properties of LaCoO3powders in carbon monoxide (CO) and propane (C3H8) atmospheres. Agglomerates of nanoparticles with high connectivity, forming a porous structure, were observed from SEM and TEM analysis. LaCoO3pellets presented a high sensitivity in both CO and C3H8at different concentrations and operating temperatures. As was expected, sensitivity increased with the gas concentration and operation temperature increase.

Experimental work on the synthesis of the CoSb 2 O 6 oxide and its CO 2 sensing properties is presented here. The oxide was synthesized by a microwave-assisted colloidal method in presence of ethylenediamine after calcination at 600 °C. This CoSb 2 O 6 oxide crystallized in a tetragonal structure with cell parameters = 4.6495 and = 9.2763 Å, and space group P4 2 /mnm. To prove its physical, chemical and sensing properties, the oxide was subjected to a series of tests: Raman spectroscopy, Scanning Electron Microscopy (SEM) and impedance (Z) measurements. Microstructures, like columns, bars and hollow hemispheres, were observed. For the CO 2 sensing test, a thick film of CoSb 2 O 6 was used, measuring the impedance variations on the presence of air/CO 2 flows (0.100 sccm/0.100 sccm) using AC (alternating current) signals in the frequency-range OPEN ACCESSSensors 2014, 14 15803 0.1-100 kHz and low relative temperatures (250 and 300 °C). The CO 2 sensing results were quite good.