Study On The Composite Structure And Function Of Novel Nanometer Iron Oxides

Recently,a huge variety of materials has been designed with different morphology,makeup and sizes.Out of which,the development of new fashioned nanocomposite materials are the lime light of modern research.Out of these materials,the ferrite is a kind of traditional material and with the development of synthesis technology nanoferrites of different structures are grown up.It is noteworthy that the nanoferrites having the advantages of both nano-materials and ferrites can be employed in varying fields.In this work,the nanoring shaped ferrite nanoparticles are synthesized and applied in the field of electromagnetic wave absorption and ethanol gas sensor.Herein,the uniformα-Fe₂O₃ nanorings are successfully synthesized by a simple hydrothermal method with an average particle size of 90 nm and the inner hole of 20-40 nm.Then,the uniform Fe₃O₄@C composite structure is developed by CCVD method usingα-Fe₂O₃ nanorings as raw materials and in the presence of C₂H₂ gas to decorate a uniform carbon layer on nanorings’surface.At the same time,due to the catalytic effect of C₂H₂,theα-Fe₂O₃ is converted into Fe₃O₄.The average particle size of Fe₃O₄@C composite is increased to 110 nm due to the uniform coating of the carbon layer on the surface of nanoring structure.Subsequently,Fe₃O₄@C composite structure was reduced in H₂ atmosphere and the orderly Fe-Fe₃O₄@C（FFC）composite structure is obtained.In particular,the nanoring morphology remains intact during the calcination and reduction reactions as the Fe₃O₄@C is calcined toα-Fe₂O₃@C composite and the Fe₃O₄is reduced toα-Fe₂O₃ at 300°C.The α-Fe₂O₃,Fe₃O₄@C and Fe-Fe₃O₄@C are tested the electromagnetic parameters as wave absorbing materials.The results reveal the effective electromagnetic wave absorbing capacity of Fe₃O₄@C and Fe-Fe₃O₄@C nanomaterials.When the thickness of FFC50 is 2 mm and the frequency is 15.9 GHz,it gives the highest reflection loss of-39.16 dB;when the thickness of FFC50 is 2 mm and the frequency is17.1 GHz,the reflection loss is-32.9 dB;and finally,when the thickness of FFC60 is 3mm and the frequency is 8.9 GHz,the lowest reflection loss is-18.4 dB.Further,natural ferromagnetic resonance,eddy current effect,Debye relaxation and multi-interface polarization exist in the absorbing process of Fe₃O₄@C and Fe-Fe₃O₄@C,which are mainly attributed to the unique ring structure,reasonable material composition and multiple interfaces of Fe₃O₄@C and Fe-Fe₃O₄@C.Additionally,the composite structuresα-Fe₂O₃,andα-Fe₂O₃@Care studied as ethanol gas sensor materials.In this paper,par thermal gas sensor is used which mainly consists of SiO₂ ceramic tube,heating wire and base to study the optimum operating temperature and response sensitivity.It is found that the optimum working temperature ofα-Fe₂O₃ is 370°C,while that ofα-Fe₂O₃@C composite structure is 300°C.The lowest detection limit ofα-Fe₂O₃ is 100 ppm while that ofα-Fe₂O₃@C composite structure is 10 ppm,which shows that the detection ability ofα-Fe₂O₃@C composite structure for ethanol gas is better than that ofα-Fe₂O₃@C composite structure.