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1、Synthesis and Gas Sensitivity of In2O3/CdO CompositeAbstract: Indium oxide (In2O3) was synthesized using a hydrothermal process. The crystallography and microstructure of the synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ra

2、y spectroscopy (EDX), and transmission electron microscopy (TEM). The In2O3 had a flower-like hierarchical nanostructure and was composed of tiny near-spherical crystals with a diameter of approximately 20 nm. When In2O3 was mixed with CdO in a 1:1 molar ratio, it was found that the resulting In2O3/

3、CdO composite showed an interesting grape-like porousmicrostructure following calcinations at elevated temperatures. A gas sensor using this In2O3/CdOcomposite as the sensing material showed higher sensitivity to different concentration of formaldehyde than the gas sensor based on pure flower-like I

4、n2O3 nanomaterials. The In2O3/CdO-based sensors showed a high sensitivity to a concentration of 0.0510-6 formaldehyde at the optimized operating temperature of 410 C and a good level of selectivity over other possible interference gases such as ethanol, toluene, acetone, methanol, and ammonia. The g

5、as sensing mechanism of In2O3/CdO sensor has been discussed in detail.1 IntroductionFormaldehyde (HCHO) is a colorless and strong-smellinggas coming from building materials, interior decoration materials,wood furniture, carpet and so on.HCHO is one of the most dangerous indoor pollutants among volat

6、ile organic compounds (VOCs), and is found to be associated with asthma, nasopharyngealcancer, and multiple subjective health complaints. In particular, HCHO is considered as a major cause of sick building syndrome (SBS). World Health Organization (WHO) established a standard of 0.0810-6 (volume fra

7、ction)averaged over 30 min for long-term exposure in formaldehyde vapor. Many methods to detect VOCs have been investigated. Among them, semiconductor gas sensors are widely used since they are cheap and easy to be available. The sensing materials, including SnO2,10-12 ZnO,13 NiO,14 and In2O3,15,16

8、have been explored for formaldehyde detection.In recent years, nanostructure semiconductor materials havebeen extensively studied due to their exceptional propertiesand potential applications in various fields. Among them, indium oxide (energy gap 3.67 eV, Bohr radius 2.14 nm) material has been wide

9、ly studied because of its unique optoelectronic properties, such as high electrical conductivity and high UV transparency. It has been widely used in the optoelectronic devices such as solar cells, window heaters, and liquid crystal displays。It has been also explored for sensing materials for detect

10、ingO3， HCHO, trimethylamine (TMA),NO2 CO,and NH3。Various vapor-phase or physical template methods were developed to prepare In2O3 nanocrystals. For example, In2O3 nanowires were synthesized by using the vapor-liquid- solid technique。The In2O3 nanowire arrays or nanorods were induced by template-assi

11、sted growth, and the In2O3 nanobelts were obtained through thermal evaporation。Besides these physical methods, there are also wet-chemistry methods to prepare specific In2O3 nanostructures. For instance, In2O3 with structures of nanorod bundles, spherelike agglomerates, lotus-root-like, and nanotube

12、s were successfully synthesized by hydrothermal route。Quasi-monodisperse In2O3 nanocrystals were obtained through an organic solution synthetic route。In this work, the flower-like hierachical nanostructure In2O3 composed of the tiny spherical nanocrystallines was fabricated by using the hydrothermal

13、 method. Then, the as-synthesized In2O3 powders were mixed with CdO in a molar ratio of 1:1 to form a gas sensing material. The formaldehyde sensing properties of the In2O3/CdO-based sensors were carried out.2 Experimental2.1 Preparation and characterization of materialsInCl34H2O (99.5%) was obtaine

14、d from Sinopharm Chemical Reagent Co., Ltd., China. Ethylene diamine tetra acetic acid (99.5%, EDTA, C10H16N2O8) and CS(NH2)2 (99.0%) were obtained from Tianjin Kermel Chemical Reagent Co., Ltd.,China. CdO (99.5%) powder was analytical grade with 30 nm particle size, and purchased from Haitai Nanome

15、ter Materials Co., China. All of the reagents used in the experiments were analytical grade and utilized without further purification.Flower-like In2O3 was synthesized by a hydrothermal method. In a typical procedure, 1 mmol InCl34H2O and 2 mmol CS(NH2)2 were dissolved in 30 mL EDTA. A few drops of

16、ammonia were dripped into the solution, and the solution was under the conditions of ultrasonic dispersing and constant stirring alternately for 20 min. Then, the mixture was transferred into a 50 mL Teflon-lined stainless steel autoclave. The autoclave was sealed and maintained in an electric oven at 180 C for 18 h. After that, the autoclave was cooled to room temperature naturally. The pink precipitate was collected and washed with ethanol and deionized water