Preparation And Gas-sensing Properties Of Iron Molybdate Nano-composites

Fe₂（MoO₄）₃,which has a certain catalytic activity and can rapidly absorb specific gas molecules to the surface and occur selective oxidation,has a wide range of development prospects in the application of gas sensors.In this paper,considering the effect of grain size and the exposure of active crystal surface on the gas-sensing performance of the material,pure Fe₂（MoO₄）₃ nano-materials were prepared by hydrothermal process.Four ways,which is adjusting the solution pH value,stirring,adding surfactant and common ion effect,was used to improve the microstructure of Fe₂（MoO₄）₃.The composition,structure and morphology of the prepared nanomaterials were measured by XRD,SEM and BET,the effects of the above methods on the Fe₂（MoO₄）₃ morphologies were analyzed,the gas sensitivity of Fe₂（MoO₄）₃ to different gases was tested,and the gas-sensing mechanism of Fe₂（MoO₄）₃ was investigated.The main conclusions are as follows:1.Fe（NO₃）₃·9H₂O and Na₂MoO₄·2H₂O are reactants raw materials,according to the stoichiometric of Fe/Mo,Fe₂（MoO₄）₃ nanomaterials of different micro structure are synthesized by adjusting the pH value of the solution,stirring,adding surfactant and the same ionic effect.The prepared nano-materials are single oblique crystal structure,the size is between 36⁸5 nm,the morphology is nano-flake.2.According to the gas sensing tests,it is found that Fe₂（MoO₄）₃ gas sensor,which was made of by stirring and adding surfactants,have a faster response-recovery rate to ethanol,n-butanol and xylene.The gas sensitivity of Fe₂（MoO₄）₃ gas sensor made by stirring at pH=3 to 100 ppm ethanol is 24 higher than that at static reaction at optimum operating temperature,indicating that stirring reduces the particle diameter and enhances the gas-sensing performance.The Fe₂（MoO₄）₃ gas sensors made by adding surfactant have the optimum operating temperature of 370℃to 100ppm ethanol and toluene,and the sensitivity maximum to 100ppm ethanol and toluene gas at this temperature is 24 and 20,respectively.3.Gas-sensing tests results show that the optimum temperature has a great variation of 300⁴00℃when the Fe₂（MoO₄）₃ gas sensor made by changing the pH value were tested with 100 ppm ethanol.When contacting 100ppm ethanol and100ppm xylene,the Fe₂（MoO₄）₃ gas sensors,which were made owing to common ion effect,has the optimum operating temperature of 340℃and 370℃,the corresponding sensitivity maximum is 40 and 28,respectively.4.The particle size of Fe₂（MoO₄）₃ materials are reduced by stirring and surfactant PVP,and the effect of the common ions of NO₃^-enhanced the grain surface growth to some extent,which all improved the gas sensitivity of Fe₂（MoO₄）₃.The decrease of pH value of the solution promoted the growth of grains,which resulted in the decrease of gas sensitivity of Fe₂（MoO₄）₃.