Co 3 O 4 nanoparticles (NPs) and Co 3 O 4 NPs-functionalized with 0.25, 0.50, and 1.00 wt.% Ruthenium (Ru) are synthesized by the precipitation and impregnation methods. X-ray diffraction data confirm that all samples are highly crystalline with a typical cubic Co 3 O 4 NPs structure. Electron microscopic images show spherical morphologies of Co 3 O 4 nanoparticles with the diameters of 10-30 nm and Ru nanoparticles with relatively small diameters of 2-4 nm loaded on Co 3 O 4 surfaces. The gas-sensing results reveal that Ru loading at an optimally low Ru content of 0.25 wt.% led to significantly enhanced ethanol sensing performances. Specifically, the 0.25 wt.%Ru/Co 3 O 4 sensor exhibits a good p-type response of %30 to 100 ppm C 2 H 5 OH, short response time (0.08 s), good recovery time (a few minutes) and high C 2 H 5 OH selectivity against H 2 S, H 2 , NH 3 , NO 2 , and SO 2 . Therefore, the Ru-loaded Co 3 O 4 sensor is a promising alternative p-type gas sensor for ethanol detection.

In this research, molybdenum trioxide (MoO3) nanoflakes were synthesized by a simple and low cost hydrothermal method for gas sensing application. Sodium molybdate (Na2MoO4·2H2O) was used as the precursor. The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). After hydrothermal process, the powders were showed amorphous phase. However, after annealing process the MoO3 was observed as particles having the orthorhombic phase. The average particle sizes of MoO3 nanoflakes were about 80 nm. The morphologies, cross section and elemental compositions of sensing films were analyzed by SEM and EDS line-scan mode analysis. From the SEM image revealed nanoflakes morphologies of MoO3 and the thickness of MoO3 sensing film was about 10 mm. The obtained sensing film can be used as the sensing device to fabricate composited gas sensors for detection of some environmental hazardous gas (including ethanol, carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrogen oxide, and ammonia) will report in the next research.

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