Hydrothermal Synthesis Of Tin Dioxide And Their Gas Sensing Properties

The sensing of properties of SnO2, the most used semiconductor base material for gas sensors, has been extensively discussed. There are many internal and external factors affecting the sensing properties of gas sensors, such as doping, microstructure and grain size. Thus researches are always focusing on controlling the size and morphology of nanomaterials. The 3D hierarchical nanostructures assembled from low-dimensional nanoscale units are considered to be the most effective and promising candidates due to their porous nanostructures and it is very meaningful to develop a series methods for preparing 3D hierarchical SnO2 nanostructures. In addition, many theoretical studies have shown that heterovalent tin oxides with a better performance than univalent tin oxides in some respects are existed, so it is necessary to develop a simple method to prepare the multivalent tin oxide.In this paper,3D hierarchical SnO2 nanomaterials and novel Sn2O3 nanoflower were synthesized by a facile template-free hydrothermal method. The as-prepared nanomaterials were characterized by XRD、DSC-TG、SEM、TEM、HRTEM and XPS. The growth mechanisms are also discussed by observing the morphology revolution at various reaction times. Further, gas-sensing measurement indicated that the as-prepared samples showed a high response to ethanol, respectively. The main research results are as follows:① Urchin-like SnO2 hierarchical nanostructures were synthesized via a simple Zn(CH3COO)2-assisted hydrothermal process. As increasing the concentration of NaOH in the process of reaction, the diameters of assembly units (nanorods or nanofibers) will continue to reduce and the smallest sizes are below 10 nm. Morphology observation and crystal structure analysis showed that the SnO2 crystal nucleus grow along [110] into nanorods and self assemble to form urchin-like nanostructures. The sample with large specific surface area and small grain size showed a better gas sensitive to ethanol. Further, gas-sensing measurement indicated that the parameters including high surface areas, the smaller grain size and the zinc doping can improve the gas sensitive performance.② Hierarchical SnO2 nanostructures made from ultra-thin nanosheets have been successfully prepared by a hydrothermal method. Here, Na2C2O4 was introduced as an assembling and structure-directing agent to control the synthesis of different forms of SnO2 flakes and it was found that the adding amount of Na2C2O4 played a key role in the preparation of different SnO2 forms. When reducing the content of Sodium oxalate, the prepared material grown in a lower density of nanosheets and as no addition of Na2C2O4, the nanoflakes no longer been assembled orderly but stacked in disorder, which suggested in the Na2C2O4 plays a nucleus in the reaction. The hierarchical nanostructures with highest density of nanosheets show a better gas sensitive to ethanol and the gas response of sensors with nanosheets are higher than the sensors with urchin-like nanostructures. The method in this chapter provides a good reference for continuing to optimize the gas-sensing properties.(3) We successfully synthesized tin trioxide(Sn2O3) by reducing the mixing time dramatically which resulted in divalent tin not able to be oxidized. These Sn2O3 possess hierarchical flower-like nanostructures assembled with many nanosheets as thin as 15 nm. The as-prepared Sn2O3 products have a good thermal stability and will transform into SnO2 in the temperature range 534-800℃. The oxidation states of the Sn2O3 hierarchical nanostructures are confirmed by the shape analysis of corresponding XPS O 1s and Sn 3d peaks using the decomposition procedure. It is estimated that [O]/[Sn] is 1.56±0.05 and [Sn4+]/[Sn2+] is 1.02.