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Structural Stability and Performance of Noble Metal-Free SnO2-Based Gas Sensors.

Tricoli A - Biosensors (Basel) (2012)

Bottom Line: The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms.In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration.Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland. atricoli@ethz.ch.

ABSTRACT
The structural stability of pure SnO2 nanoparticles and highly sensitive SnO2-SiO2 nanocomposites (0-15 SiO2 wt%) has been investigated for conditions relevant to their utilization as chemoresistive gas sensors. Thermal stabilization by SiO2 co-synthesis has been investigated at up to 600 °C determining regimes of crystal size stability as a function of SiO2-content. For operation up to 400 °C, thermally stable crystal sizes of ca. 24 and 11 nm were identified for SnO2 nanoparticles and 1.4 wt% SnO2-SiO2 nanocomposites, respectively. The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms. In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration. Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

No MeSH data available.


Cross-sensitivity to relative humidity (20 °C) of as prepared SnO2 nanoparticles (solid triangles), and of 1 wt% (empty triangles) and 2.5 wt% (squares) SnO2-SiO2 nanocomposites at 320 °C.
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biosensors-02-00221-f009: Cross-sensitivity to relative humidity (20 °C) of as prepared SnO2 nanoparticles (solid triangles), and of 1 wt% (empty triangles) and 2.5 wt% (squares) SnO2-SiO2 nanocomposites at 320 °C.

Mentions: The stability of the sensor response toward variations in relative humidity is of major importance for several applications [2,22]. Doping of SnO2 nanoparticles with Ti has been reported to drastically decrease their cross-sensitivity to humidity [9]. Recently, this has been attributed to thermodynamically dictated enrichment of the SnO2 surface with Ti atoms [23] that lower the adsorption energy of dissociatively adsorbed H2O [24]. The effect of SiO2 cosynthesis on the cross-sensitivity (CS) to humidity of SnO2 nanoparticles, however, has not been investigated yet. This is particularly important as flame-made SiO2 has high surface concentration of hydroxyl groups that facilitate the binding of H2O molecules [10] and thus may result in a strong enhancement of the CS to humidity. Figure 9 shows the CS to humidity during EtOH detection, defined as change of the sensor response in dry air (Equation (2)), of the pure SnO2 (triangles solid), 1 wt% (empty triangles) and 2.5 wt% (empty squares) SnO2-SiO2 nanocomposites as a function of the relative humidity. The CS to humidity of the pure SnO2 sensors (Figure 9, solid triangles) increased from 51 to 74% with increasing r.h. from 20 to 60%. This is in agreement with the drastic change in sensor response reported for SnO2 nanoparticles with increasing r.h. content [9]. The continuous increase in CS above 20% r.h. (Figure 9, solid triangles) indicates that the SnO2 surface has not yet been saturated with adsorbed H2O species. More important, the CS of both SnO2-SiO2 sensors (Figure 9, empty squares and triangles) was comparable to that of the pure SnO2 (Figure 9, solid triangles). This is different than the effect of Ti-doping [7] and in contrast to the super-hydrophilic properties of flame-made SiO2 [10]. However, as SiO2 is an isolator, localized SiO2 molecules/clusters on the SnO2 surface may act as active sites for H2O binding but still have minimal impact on the sensing properties of the SnO2 nanocrystals due to its inefficient electron conduction properties. As a result, SiO2 cosynthesis leads to the same CS than pure SnO2 nanoparticles. This is in contrast to the modification of SnO2 crystals with hydrophilic zeolites [25,26] where notable variations from the sensing response of the pure SnO2 were observed. Minimization of the CS while improving the long-term stability and sensitivity of SnO2-based gas sensors may be achieved by synthesis of Sn1−xTixO2-SiO2 nanocomposites [9].


Structural Stability and Performance of Noble Metal-Free SnO2-Based Gas Sensors.

Tricoli A - Biosensors (Basel) (2012)

Cross-sensitivity to relative humidity (20 °C) of as prepared SnO2 nanoparticles (solid triangles), and of 1 wt% (empty triangles) and 2.5 wt% (squares) SnO2-SiO2 nanocomposites at 320 °C.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263576&req=5

biosensors-02-00221-f009: Cross-sensitivity to relative humidity (20 °C) of as prepared SnO2 nanoparticles (solid triangles), and of 1 wt% (empty triangles) and 2.5 wt% (squares) SnO2-SiO2 nanocomposites at 320 °C.
Mentions: The stability of the sensor response toward variations in relative humidity is of major importance for several applications [2,22]. Doping of SnO2 nanoparticles with Ti has been reported to drastically decrease their cross-sensitivity to humidity [9]. Recently, this has been attributed to thermodynamically dictated enrichment of the SnO2 surface with Ti atoms [23] that lower the adsorption energy of dissociatively adsorbed H2O [24]. The effect of SiO2 cosynthesis on the cross-sensitivity (CS) to humidity of SnO2 nanoparticles, however, has not been investigated yet. This is particularly important as flame-made SiO2 has high surface concentration of hydroxyl groups that facilitate the binding of H2O molecules [10] and thus may result in a strong enhancement of the CS to humidity. Figure 9 shows the CS to humidity during EtOH detection, defined as change of the sensor response in dry air (Equation (2)), of the pure SnO2 (triangles solid), 1 wt% (empty triangles) and 2.5 wt% (empty squares) SnO2-SiO2 nanocomposites as a function of the relative humidity. The CS to humidity of the pure SnO2 sensors (Figure 9, solid triangles) increased from 51 to 74% with increasing r.h. from 20 to 60%. This is in agreement with the drastic change in sensor response reported for SnO2 nanoparticles with increasing r.h. content [9]. The continuous increase in CS above 20% r.h. (Figure 9, solid triangles) indicates that the SnO2 surface has not yet been saturated with adsorbed H2O species. More important, the CS of both SnO2-SiO2 sensors (Figure 9, empty squares and triangles) was comparable to that of the pure SnO2 (Figure 9, solid triangles). This is different than the effect of Ti-doping [7] and in contrast to the super-hydrophilic properties of flame-made SiO2 [10]. However, as SiO2 is an isolator, localized SiO2 molecules/clusters on the SnO2 surface may act as active sites for H2O binding but still have minimal impact on the sensing properties of the SnO2 nanocrystals due to its inefficient electron conduction properties. As a result, SiO2 cosynthesis leads to the same CS than pure SnO2 nanoparticles. This is in contrast to the modification of SnO2 crystals with hydrophilic zeolites [25,26] where notable variations from the sensing response of the pure SnO2 were observed. Minimization of the CS while improving the long-term stability and sensitivity of SnO2-based gas sensors may be achieved by synthesis of Sn1−xTixO2-SiO2 nanocomposites [9].

Bottom Line: The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms.In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration.Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland. atricoli@ethz.ch.

ABSTRACT
The structural stability of pure SnO2 nanoparticles and highly sensitive SnO2-SiO2 nanocomposites (0-15 SiO2 wt%) has been investigated for conditions relevant to their utilization as chemoresistive gas sensors. Thermal stabilization by SiO2 co-synthesis has been investigated at up to 600 °C determining regimes of crystal size stability as a function of SiO2-content. For operation up to 400 °C, thermally stable crystal sizes of ca. 24 and 11 nm were identified for SnO2 nanoparticles and 1.4 wt% SnO2-SiO2 nanocomposites, respectively. The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms. In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration. Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

No MeSH data available.