Highly Efficient Formaldehyde Sensors Based on Au-Decorated SnO2 Nanosheets with High-Energy {001} Facets
Authors: Yin Yan-Yan , Zhang Le-Xi , Xu Ran , Bie Li-Jian 
Published: May 2020

Introduction

Formaldehyde (HCHO) have caused health problems and thus associated with various diseases, so there is an urgent need to develop an effective way for HCHO detection. Metal oxide-based gas sensors (e.g. SnO2) have been fully proved as active materials for monitoring HCHO. Recently, crystal facet engineering opens up a new way for enhanced response for nano SnO2 with exposed high-energy facts, for instance {221} [1], {001} [2], and {332} [3]. Moreover, SnO2 decorated with noble metals is an effective strategy for response improvement. Obviously, comprehensive optimization of gas sensing can be achieved via synergistic effects [4] of small size, high-energy facets and noble metal catalysis, however the related research has not been reported yet. Here, Au decorated SnO2 nanosheets with dominant {001} facets were synthesized, characterized, and HCHO sensing performance. Finally, the reasons of enhanced HCHO sensing were also discussed.

Synthesis of SnO2 and Au-SnO2

Pristine SnO2 nanosheets (P-SnO2) was synthesized by a hydrothermal process: 2.0 mmol SnCl2·2H2O and 6.0 mmol NaOH were dissolved in 20 mL distilled water under stirring, transferred into a 25 mL Teflon-lined stainless steel autoclave, and maintained at 180 °C for 12 h. Precipitates were centrifuged, washed by deionized water and ethanol, dried at 80 °C for 12 h. Au decorated SO2 nanosheets (Au-SnO2) was obtained by a impregnation method: 0.5 mmol SnO2 products were dispersed into 10 mL ethanol by ultrasonication. Afterwards, 0.5 mL HAuCl4·4H2O solution (2 mmol/L) was added, ultrasonicated for 15 min, heated at 80 °C for 6 h, and calcined at 400 °C for 30 min.

S
ensor
F
abrication and Measurement

The fabrication of side-heated SnO2 gas sensors is similar to the procedure [2]. Sensors were measured on a WS-30A static gas sensing system (Weisheng Electronics Co. Ltd., China). The response was defined as the ratio of sensor resistance in air (Ra) to that in a target gas (Rg): Sr = Ra/Rg.

Results and Conclusions

As shown in Fig. 1 (a), Au-SnO2 are featured in nanosheets with lengths of 30-50 nm and thicknesses of only 5-8 nm. The HRTEM indicates the decoration of Au particles on SnO2 in Fig. 1 (b). Temperature dependent HCHO response shows that Au-SnO2 holds the highest response value and the lowest optimum operating temperature (OOT) at 130 °C in all three SnO based HCHO gas sensors, as can be seen in Fig. 1 (c). We believe that the excellent results of Au-SnO2 can be attributed to synergistic effects of nanosheet caused structural sensitization, as well as Au catalysis induced chemical and electronic sensitization.

Fig. 1 TEM (a) and HRTEM (b) images of Au-SnO2. Temperature dependent HCHO response of P-SnO2, Au-SnO2 and C-SnO2 (commercial SnO2 nanopowders).

References

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[3] C.Wang, D.Cai, B.Liu, H.Li, D.Wang, Y.Liu, L.Wang, Y.Wang, Q.Li, T.Wang, Ethanol-sensing performance of tin dioxide octahedral nanocrystals with exposed high-energy {111} and {332} facets, J. Mater. Chem. A 2014, 2, 10623−10628. doi: 10.1039/C4TA00844H.

[4] J.M.Walker, S.A.Akbar, P.A.Morris, Synergistic effects in gas sensing semiconducting oxide nano-heterostructures: A review, Sens. Actuators B 286 (2019) 624–640. doi: 10.1016/j.snb.2019.01.049.

Figure 1