Preparation,adsorption And Wave Absorbing Performance Of Fe₃C-SiO₂ Composite Structures

Iron carbide(Fe₃C)has great application potentials in the fields of catalysis,adsorption and absorbing dues to its stable chemical properties,strong surface activity and high saturation magnetization.However,the adsorption and absorption performance of the pure Fe₃C particles could be reduced due to less surface active sites by agglomeration and poor impedance matching,respectively.As a wave permeable material with high specific surface area,SiO₂ aerogel not only can provide sufficient active sites for the adsorption applications,but also can support good impedance matching with the absorbing material.Therefore,in order to broaden the application of Fe₃C in the fields of adsorption and absorbing,the Fe₃C-SiO₂ composite structures of uniform distribution and core-shell have been prepared by a sol-gel process and an improved St(?)ber method,respectively.The dye adsorption and wave absorption performance of both Fe₃C-SiO₂ composite structures and the corresponding work mechanisms have been investigated as well.Firstly,pure Fe₃C has been successfully prepared by a sol-gel method by using two kinds of carbon sources,which are melamine and polyvinylpyrrolidone(PVP),respectively.Both phase determinations and external magnetic field response measurements confirm that the pure Fe₃C particles prepared with PVP as carbon source present higher crystallinity and faster external magnetic field response compared with the pure Fe₃C particles prepared with melamine as carbon sources.On the basis of Fe₃C preparation,uniform distribution and core-shell Fe₃C-SiO₂ composite structures have been respectively prepared by a sol-gel process and an improved St(?)ber method.The results show that Fe₃C nanoparticles have been uniformly distributed in SiO₂ matrix for the uniform distribution structure and have also been coated by SiO₂ successfully for the core-shell structure.And the specific surface areas of Fe₃C-SiO₂ composite structures have been increased by 95%and 88%,respectively,compared with the pure Fe₃C particles.The successful preparation of two configurations has paved a way for the subsequent researches on the adsorption and absorption performance of Fe₃C-SiO₂composite structures.Secondly,the adsorption effect of Fe₃C-SiO₂ composite structures on rhodamine B(RhB)and the corresponding mechanism have been studied based on the porous characteristics.For the uniformly distributed Fe₃C-SiO₂ composites,when the mass ratio of Fe₃C-SiO₂ to RhB dye is 100:1,the RhB adsorption efficiency and the adsorption rate can reach 96%and 0.003 g·mg^-1·min^-1,respectively.While regarding the core-shell Fe₃C-SiO₂ composites,when the mass ratio of Fe₃C-SiO₂ to RhB dye is 50:1,the adsorption rates can be up to 92%,and the adsorption rate is0.019 g·mg^-1·min^-1.The mechanism analysis shows that the RhB adsorption processes of both Fe₃C-SiO₂ composite structures agree well with Freundlich isotherm model and quasi-second-order kinetic equation.And it can be concluded that the RhB adsorption processes of both Fe₃C-SiO₂ composite structures are mainly multi molecular layer adsorption and natural adsorption dependent since the high specific surface area of Fe₃C-SiO₂ composite structures can provide sufficient active sites.By contrast,although the uniformly distributed Fe₃C-SiO₂ composites presents higher absolute adsorption efficiency,the core-shell Fe₃C-SiO₂ composites can offer a higher relative adsorption efficiency due to its lower dosage.Thirdly,the microwave absorbing performance of Fe₃C-SiO₂ composite structures and corresponding mechanism have been explored thanks their magnetic properties.The results show that the absorption efficiencies of uniform distribution and core-shell Fe₃C-SiO₂ composite structures can reach 99%and 90%,respectively,in the frequency range of 12-18 GHz.And the relationship between the matching thickness and the peak frequency of the electromagnetic wave absorbed by Fe₃C-SiO₂ is subject to the quarter-wavelength matching condition.In addition,uniformly distributed Fe₃C-SiO₂composites reveal larger reflection loss values and wider effective bandwidth than the core-shell Fe₃C-SiO₂ composites.The mechanism analysis indicates that the wave absorption of both Fe₃C-SiO₂ composite structures are mainly dependent on the synergistic effects of dual relaxation polarization,eddy current loss,good impedance matching and high attenuation.