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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.


Average SnO2 crystal size (dXRD) of the SnO2-SiO2 nanocomposites as a function of the sintering time at 600 °C for several SiO2 contents.
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biosensors-02-00221-f003: Average SnO2 crystal size (dXRD) of the SnO2-SiO2 nanocomposites as a function of the sintering time at 600 °C for several SiO2 contents.

Mentions: Reduction of the long-term drift of the SnO2 and SnO2-SiO2 sensors may be obtained by pre-sintering of the films at temperatures above the operational ones (e.g., at 600 °C) [7] leading to the achievement of a thermodynamically stable grain size prior to sensor testing (e.g., at 400 °C). Figure 3 shows the average SnO2 crystal size of several SnO2-SiO2 nanocomposites as a function of such a pre-sintering step at 600 °C. The 1 wt% SnO2-SiO2 crystal size (Figure 3, triangles up) increased from 9.7 to 15.4 with increasing sintering time at 600 °C from 0 to 24 h. This shows that even the smallest addition of SiO2 leads to stabilization of the SnO2 crystal size far below that of pure SnO2 at 400 °C (Figure 1, solid triangles). In particular, the 1.4 wt% SnO2-SiO2 reached a size of 11.4 nm already after 4 h sintering (Figure 3, circles). This is more than the thermodynamically stable size (≈10.5 nm) at 400 °C and thus pre-sintering of the sensing films prior to sensor utilization may be utilized to considerably shorten the time required for achievement of a stable sensor response. Furthermore, up to 4 wt% SiO2, the as-prepared SnO2 crystal size (Figure 3) of these nanocomposites was very close (ca. 10 ± 1.5 nm) suggesting further that SiO2 may condense directly on the formed SnO2 nanoparticles inhibiting further crystal and grain growth during flame-synthesis. In comparison, the initial crystal size of the pure SnO2 nanoparticles was 12 nm (Figure 1, solid squares) which is attributed to particle coagulation during the residence time in the flame. In line, the as-prepared powder SSA increased from 100 to 211 m2/g with increasing SiO2 content from 0 to 15 wt%. The 15 wt% SiO2-SnO2 demonstrated the highest long-term stability growing only from 4.5 to 5 nm (Figure 3, diamonds) with increasing sintering time from 0 to 24 h. This is in agreement with the grain growth inhibition demonstrated by SiO2 cosynthesis [7]. However, utilization of such high SiO2 contents results in the formation of insulating domains and a drastic drop of the sensing performance [7] and thus, here, the dynamics of the sensor response stabilization has been investigated at low SiO2 content (1–4 wt%).


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

Tricoli A - Biosensors (Basel) (2012)

Average SnO2 crystal size (dXRD) of the SnO2-SiO2 nanocomposites as a function of the sintering time at 600 °C for several SiO2 contents.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-02-00221-f003: Average SnO2 crystal size (dXRD) of the SnO2-SiO2 nanocomposites as a function of the sintering time at 600 °C for several SiO2 contents.
Mentions: Reduction of the long-term drift of the SnO2 and SnO2-SiO2 sensors may be obtained by pre-sintering of the films at temperatures above the operational ones (e.g., at 600 °C) [7] leading to the achievement of a thermodynamically stable grain size prior to sensor testing (e.g., at 400 °C). Figure 3 shows the average SnO2 crystal size of several SnO2-SiO2 nanocomposites as a function of such a pre-sintering step at 600 °C. The 1 wt% SnO2-SiO2 crystal size (Figure 3, triangles up) increased from 9.7 to 15.4 with increasing sintering time at 600 °C from 0 to 24 h. This shows that even the smallest addition of SiO2 leads to stabilization of the SnO2 crystal size far below that of pure SnO2 at 400 °C (Figure 1, solid triangles). In particular, the 1.4 wt% SnO2-SiO2 reached a size of 11.4 nm already after 4 h sintering (Figure 3, circles). This is more than the thermodynamically stable size (≈10.5 nm) at 400 °C and thus pre-sintering of the sensing films prior to sensor utilization may be utilized to considerably shorten the time required for achievement of a stable sensor response. Furthermore, up to 4 wt% SiO2, the as-prepared SnO2 crystal size (Figure 3) of these nanocomposites was very close (ca. 10 ± 1.5 nm) suggesting further that SiO2 may condense directly on the formed SnO2 nanoparticles inhibiting further crystal and grain growth during flame-synthesis. In comparison, the initial crystal size of the pure SnO2 nanoparticles was 12 nm (Figure 1, solid squares) which is attributed to particle coagulation during the residence time in the flame. In line, the as-prepared powder SSA increased from 100 to 211 m2/g with increasing SiO2 content from 0 to 15 wt%. The 15 wt% SiO2-SnO2 demonstrated the highest long-term stability growing only from 4.5 to 5 nm (Figure 3, diamonds) with increasing sintering time from 0 to 24 h. This is in agreement with the grain growth inhibition demonstrated by SiO2 cosynthesis [7]. However, utilization of such high SiO2 contents results in the formation of insulating domains and a drastic drop of the sensing performance [7] and thus, here, the dynamics of the sensor response stabilization has been investigated at low SiO2 content (1–4 wt%).

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.