Synthesis And Gas Sensitive Properties Of Indium Oxide Based Nanomaterials

As an important low resistance sensitive material, In₂O₃ especially play an important role in the detection of oxidizing gases. It has great significance to study the relationship between indium oxide microstructure and gas sensing performance, due to its sensing mechanism is surface resistivity controlled mode. In this paper, different crystal and morphology of indium oxide nonmaterials have been synthesized by hydrothermal / solvothermal method, and their gas sensitivity and sensing mechanism have been deeply studied. The results can be summarized as follows:1. Cubic phase In₂O₃ cubes were successfully synthesized by a simple hydrothermal reaction. The changes of the alkali concentration can regulate the size of the cubes during the reaction. Under the aid of ammonia, we can get monodisperse In₂O₃ cubes（1 mm）. In the absence of ammonia, the size of the cube increased, and it is easily broken in the calcination process. When ammonia was substituted with alkali hydroxide, smaller size cubes can be obtained, but easy to agglomeration. The sensor based on1 mm In₂O₃ cubes exposed high sensitivity to ethanol vapor, and has certain selectivity.2. Porous h-In₂O₃ nanosheets which have a special footprints shape were successfully prepared by solvothermal. The length of the synthesized h-In₂O₃ nanosheets is about 1 mm, and the thickness is not more than 50 nm. The dispersion of nanosheets is great and the specific surface area of which is 24.2 m2/g. Many uniform pores can be seen on the nanosheets obviously. It is shown that ethylene plays an important role in the regulation of the morphology of indium oxide. When the reaction system has not glycol, only uniformly dispersed indium oxide nanoparticles can be obtained. Through regulating the amount of ethylene glycol, great dispersion and completed structure indium oxide nanosheets can be obtained. The addition of ethylene promote the self-assembly of nanoparticles, thus contributing to the synthesis of stability porous nanosheets. Through comparing with nonporous In₂O₃ nanosheets about the photoluminescence and gas sensing performance, it is found that porous h-In₂O₃ nanosheets have high fluorescence intensity and good performance to NO2 gas.3 Porous h-In₂O₃ nanoflowers were prepared by solvothermal with the aid of PVP. The conditions which could affect the morphology and crystalline of material were studied in detail, for example, reaction solvent, surfactant, reaction temperature, p H value, and reaction time. When only water involved in the reaction, c-In₂O₃ cubes can be obtained. However, using ethanol and ethanol / ethylene glycol as the solvent, h-In₂O₃ nanoparticles and nanosheets can be obtained. The addition of surfactant PVP to ethanol / ethylene glycol solvent thermal reaction is favor to the formation of nanoflower structure. The diameter of h-In₂O₃ nanoflowers are about 400-600 nm which were assembled by nanosheets and nanorods. The dispersion of the nanoflowers is good. With increasing reaction time, the precursor In（OH）3 is gradually transformed into In OOH, which is consistent with the TG analysis result. The finnally product transformed from bcc-In₂O₃ to h-In₂O₃. Gas sensing performance results showed that the porous h-In₂O₃ nanoflowers gas sensor has high sensitivity, fast response and good selectivity to ethanol vapor. XPS analysis showed that the material has more chemisorption oxygen O- at 280 ℃, which is consistent with the larger value of gas sensing performance at 280 ℃. Based on the above analysis, it showed that the gas sensing mechanism of In₂O₃ is surface resistance controlled mode.4 Porous h-In₂O₃ nanorods and mesoporous Ce O2 were successfully prepared by solvothermal. The synthesized porous structure h-In₂O₃ nanorods are conducive to rapid gas adsorption and desorption. The length of the nanorods is about 500 nm, which is favor of more active sites because of the smaller one dimensional nanostructure, and thus contributes to the increase of gas sensing performance. The diameter of synthesized Ce O2 nanosphere which has many small holes is about 100 nm. Adopting impregnation composite method, different ratio of Ce O2/In₂O₃ nanocomposites was prepared. Ce O2 was beneficial to improve the sensing properties of the sensor to ethanol vapor. When loading 5 mol% Ce O2, the sensitivity of composite material to 50 ppm ethanol is three times than unloaded In₂O₃ and it can detect 1ppm ethanol with sensitivity of 2.4. The sensor has good selectivity to ethanol.5 Mg O/In₂O₃ nanosheets composite were synthesized by solvothermal, and their gas-sensing performances were studied in detail. The size of the uniform morphology In₂O₃ nanosheets is about 1 mm, and thickness of the nanosheets is not more than 50 nm. The Mg O nanoparticles which were loaded on the nanosheets uniformly are about 100 nm. When the working temperature of 200 ℃, the Mg O/In₂O₃ composite showed good performance to NO2 gas. Compared with uncompleted In₂O₃ nanosheets material, the composite has high sensitivity to 0.1-40 ppm NO2. The sensitivity of composite to 40 ppm NO2 gas is 323, which is two times than pure In₂O₃ nanosheets. The gas sensitivity improvement of the composite material to NO2 is eight times more than other gases, indicating its good selectivity.