Tunable Synthesis And Gas Sensing Properties Of ?-Fe₂O₃ And Their Zn???,Ni???-ferrite Composite Nanomaterials

This paper is focused on the controlled synthesis of ?-Fe2O3 nanomaterials and their composites through hydrothermal routes.The fabrication,formation mechanism and properties of the as-obtained nanometerials were investigated throughly.The contents mainly include the synthesis and gas sensing properties of the oblique parallelepiped polyhedron,polyhedron of cracked-structure and polyhedron ?-Fe2O3 nanoparticles;the synthesis,the formation mechanism and gas sensing properties of polyhedral 20-facet a-Fe2O3 nanoparticles and the facet-etched oblique parallelepiped polyhedron ?-Fe2O3 nanoparticle;the preparation and gas sensing properties of ZnFe2O4/?-Fe2O3 and NiFe2O4/?-Fe2O3Composite nanoparticles.The results show that the gas-sensing ability of sensor is closely associated with their capacity of adsorbing oxygen,and crystal structure,surface energy.The gas-sensing property of the 20-facet ?-Fe2O3 nanoparticles is superior than that of the etched oblique parallelepiped polyhedron a-Fe2O3 nanoparticles.Compared with the pure phase of ?-Fe2O3 nanoparticles,ZnFe2O4/?-Fe2O3 and NiFe2O4/?-Fe2O3 composite nanomaterials are excellent gas sensitive materials and exhibit better gas sensitive properties towards acetone gas due to the synergetic effect of the components and the relative larger specific surface area of the composite.1.Tunable synthesis of ?-Fe2O3 nanoparticles with different morphologies and their morphology/facet-dependent gas-sensing propertiesThree kinds of different ?-Fe2O3 nanoparticles including the oblique parallelepiped polyhedron,polyhedron of cracked-structure and polyhedron were synthesized via a hydrothermal route through regulating the volume ratio of EG/H2O in the solvent.The phase,morphology and microstructure of the products were characterized thoroughly using many techniques.The gas-sensing properties of the three different ?-Fe2O3 nanoparticles were investigated.The results indicated that the ?-Fe2O3 nanparticles exhibit high response,good selectivity and long-term stability.The sensitivity order of three kinds of ?-Fe2O3 nanoparticles is polyhedron>polyhedron of cracked-structure>oblique parallelepiped polyhedron.The gas-sensing ability of the sensor is closely associated with their specific surface areas and the difference of atomic configurations and chemical composition on different crystal facets.According to the analysis,the gas-sensing ability of different crystal planes of ?-Fe2O3 nanoparticles follows the order of {110}>{102}>{104}>{012}.2.Controlled synthesis,gas-sensing properties of polyhedral 20-facet ?-Fe2O3 nanoparticles and the facet-etched oblique polyhedron ?-Fe2O3 nanoparticles.The polyhedral ?-Fe2O3 nanoparticles and the etched oblique parallelepiped polyhedron ?-Fe2O3 nanoparticles were prepared by a hydrothermal process using FeCl3·6H2O and urea as reagents,the mixture of ethylene glycol and distilled water as solvent.SEM and TEM techniques were used to analyze the morphology and size of the products.The size of polyhedral ?-Fe2O3 nanoparticle was in the range of 330-360nm,which were composed of 20 surfaces,including 12 trapezoidal planes,6 rectangular planes and 2 polygonal planes.The etched oblique polyhedron ?-Fe2O3 nanoparticles has oblique hexahedral structure with size is about 360-450 nm.All the six surfaces show different degrees of depression,the diameter of depression is in the range of 200-300 nm.The morphology of the products was strongly dependent on the solvent.The formation mechanism of polyhedron nanoparticles is studied through regulating the reaction time.Finally,the gas-sensing properties of the different of ?-Fe2O3 nanoparticles were investigated.The results indicate that the 20-facet ?-Fe2O3 nanoparticle shows more excellent gas-sensing property than the etched oblique parallelepiped polyhedron ?-Fe2O3 nanoparticle towards n-butyl alcohol gas.3.Controlled synthesis of ZnFe2O4/?-Fe2O3 and NiFe2O4/?-Fe2O3 composite nanoparticles and their gas sensing properties.On the basis of the above chapter,we successfully obtain ZnFe2O4/?-Fe2O3 and NiFe2O4/?-Fe2O3 composites though adding Zn(Ac)2·2H2O and NiCl2·6H2O into synthesis of polyhedral 20-facet ?-Fe2O3 nanoparticles.XRD,SEM,TEM,and TG techniques were used to characterize the phanes,morphology and structure of the products.The size of the two samples are very uniform and the NiFe2O4/?-Fe2O3 is bigger than ZnFe2O4/?-Fe2O3.The gas-sensing results indicate the composite materials exhibit good response towards acetone at a relative low temperature.Compared with pure phase ?-Fe2O3,the composites exhibit higher gas response,mainly due to the synergetic effect of the different components and larger specific surface area of the composite.