| The surface layer atoms of multi-metallic oxides were composed of different elements and only specific molecules could be absorbed quickly,the selective oxidation on the surface would be expected to overcome the poor selectivity of the traditional simple metal oxide.In this paper,a variety of multi-metallic oxides semiconductor nanomaterials includingBi2MoO6,NaBi?MoO4?2andFe2?MoO4?3weresynthesizedby hydrothermal/solvothermal method.The intrinsic relationship among compositions,morphologies,structure and sensing performances was systematically investigated.In addition,component design,doping and structural adjustment for nanomaterials have been carried out to improve their gas-sensing properties.The main results are as follows:1.When Bi/Mo molar ratio was 0.4,the tetragonal scheelite NaBi?MoO4?2 nanoflakes were obtained using Bi?NO3?3·5H2O and Na2MoO4·2H2O as raw materials.And the orthorhombic Bi2MoO6 nanoflakes were achieved in the case that the molar ratio of Bi/Mo was changed to 2.The results of gas-sensing properties exhibited that the sensor based on NaBi?MoO4?2 showed high sensing properties including quick response-recovery rate and good stability to H2S.Its sensitivity was 18.5 to 100 ppm H2S at the optimum operating temperature of 370oC,and the response-recovery time was 9 s-4 s.While the sensor based on Bi2MoO6 did not show any response to the tested gas.2.The NaBi?MoO4?2 was modified in two ways:composite and doping modificaion.A series of Bi2MoO6/NaBi?MoO4?2 nano-composites with different molar ratio of Bi/Mo were prepared.However,the modified composites did not increase the gas-sensing property of NaBi?MoO4?2.The gas-sensing materials with different kinds and different concentration doping were also prepared by another way of modification.The different elements doped NaBi?MoO4?2 sensors showed that the enhancement effect of Ru3+on sensitivity was the most obvious.In addition,the Ru3+or Fe3+doping was an efficient approach to improve the H2S selectivity of NaBi?MoO4?2.And the optimum operating temperature of NaBi?MoO4?2 could be reduced from 370oC to 300oC by doping Fe3+.The different concentration of Ru3+doped NaBi?MoO4?2 sensors showed good H2S sensitivity and stability.And the best doping concentration was 1 wt%.The response-recovery time of1 wt%Ru-NaBi?MoO4?2 sensor was 11 s-4 s to 5 ppm H2S at the optimum operating temperature of 370oC,and the sensitivity was 19.0,6.45-fold higher than that of pure NaBi?MoO4?2.It also showed good low concentration?5 ppm?and high concentration?100ppm?selectivity.3.The five kinds of samples with different pH value of 2,1.65,1.4,1,0.8 were prepared using Fe2?NO3?3·9H2O and Na2MoO4·2H2O as raw materials.They were all monoclinic Fe2?MoO4?3 nanoplates.When the pH value equaled 0.8,the obtained Fe2?MoO4?3 was spherical formed by a large number of sheets,and the crystal had special anisotropic growth along the?100?plane.The results of gas-sensing properties exhibited that all of the sensors with different pH values showed low H2S optimum operating temperature and good xylene sensitivity.The obtained Fe2?MoO4?3 sensor with pH equals0.8 exhibited the highest xylene sensitivity.Its sensitivity is 22.3 to 100 ppm xylene at the optimum operating temperature of 340oC,and the response-recovery time is 6 s-8 s. |
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