Fig 7 Response and recovery time of sensor for 5010 6 CO as function of

Fig 7 response and recovery time of sensor for 5010 6

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Fig. 7 Response and recovery time of sensor for 50×10 6 CO as function of temperature: (a) Pure-SnO 2 ; (b) GNP-SnO 2 4 Gas-sensing mechanism The detection mechanism of our sensors in the presence of a reducing gas such as CO involves the partial chemical reduction of the sensitive layer surface [13]. At higher temperatures, the O 2 molecules ionized on the SnO 2 nanoparticles to form active ionic oxygen species like [O ]. Due to the high electron affinity of oxygen and because metal oxide semiconductors are n -type, they extract electrons from the semiconductor conduction band and create a depletion area on the surface of the grains, decreasing the effective radius of the grains for electron transport. By introducing CO gas, a reaction between the ionic oxygen atoms [O ] and CO molecules occurs [CO+O CO 2 +e]. This interaction releases electrons and re-injects them into the depletion region created in SnO 2 nanoparticles surfaces. This significantly reduces the height of barriers created
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A. BORHANINIA, et al/Trans. Nonferrous Met. Soc. China 27(2017) 1777 1784 1782 Fig. 8 Transient response of sensors at optimal temperature: (a) Pure-SnO 2 at 50×10 6 CO; (b) GNP-SnO 2 at 50×10 6 CO; ( c ) Pure- SnO 2 at (20 60)×10 6 CO; (d) GNP-SnO 2 at (20 60)×10 6 CO Fig. 9 Response of sensors at different 50×10 6 gases between neighboring particles, resulting in an increase in sensor conductance. GNPs also cover SnO 2 nanoparticles to some extent but CO molecules can penetrate through the free spaces between the particles and react with ionic oxygen species (O 2 , O 2− , O ) [14,21,25]. Through reducing the activation energy required for interactions as mentioned, GNPs increase the sensor response. Besides, as GNPs contact with SnO 2 nanoparticles, a Schottky barrier forms between them and electrons flow from the SnO 2 nanoparticles to the GNP S . This occurs because of the work function difference between the gold and SnO 2 nanoparticles. This widens the depletion region into the SnO 2 nanoparticles and tends to further reduce the sensor conductivity. So, when CO molecules interact with pre-adsorbed oxygen ionic atoms to release and re-inject electrons into the depletion region created in SnO 2 nanoparticles, the changes of the sensor conductivity will be improved [14,21,25]. The GNPs affect the rate of attraction and repulsion of the gas molecules and improves the response and recovery time. These improvements are dependent on the interaction of the CO molecules and ionic oxygen species (O 2 , O 2− , O ) under the catalytic effect of the GNPs [21,38,39]. 5 Conclusions The amount of GNPs optimized was used to create high performance GNP-SnO 2 sensors (Au/Sn= 3.7663×10 4 ). The optimal operating temperature is about 260 °C and the responses at concentrations of (20 80)×10 6 are 8.3 29.5. This means that the operating temperature decreases by about 80 °C and the response improved by more than 2-fold compared with
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A. BORHANINIA, et al/Trans. Nonferrous Met. Soc. China 27(2017) 1777 1784 1783 the pure samples. At 50×10 6 CO gas, the response and recovery time for the pure SnO 2 sensor were approximately 10 and 14 s, and for the GNP-SnO 2 sensor, these values were approximately 4 and 6 s, respectively. This means that the sensor speed increases by more than 2-fold. The selectivity of the sensor
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  • Summer '18
  • Peter
  • Oxide, Gas sensors, Operating temperature, GNPs

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