The Microwave Absorption And Photocatalytic Properties Of Yolk-shell Structured Zinc Ferrite@Graphene@Titanium Dioxide

Due to the unique structure with distinctive core@void@shell,yolk-shell structured nanocomposites possess some unique properties,and can facilitate multiple reflection and refraction on the incoming light or electromagnetic wave?EMW?,which will enhance the capture of them effectively and improve greatly the photocatalytic and EMW absorption properties of the composites.In addition,the components of the yolk-shell structured composites are relatively independent and still maintain their own characteristics.Attributing to the synthetic effects of these components and the easy movement of the core,the overall combined performances are greater than the summation of various components exhibiting.Furthermore,the performance of the composites can be easy tunable by changing the composition,interstitial void size and shell thickness,which has attracted extensive attention by scientists.As an important magnetic functional material,ZnFe₂O₄ has always been applied in photocatalytic fields due to its narrow bad gap,but the application in the microwave absorption is rarely reported.Additional,when ZnFe₂O₄ is served as photocatalytic degradation,the easy recombination of photoinduced electron-holes has limited its photocatalytic efficiency.Reduced graphene oxide?RGO?is a two-dimensional carbon material,and lots of researches have shown that composites wrapped with RGO sheets have been proved to be an ingenious and effective way to obtain an new typed RGO-based composites with enhanced performance.And compared with the traditional RGO-based materials,the new typed RGO-based materials have a broader application prospects.On the other hand,it is known that TiO2 is a classic semiconductor material,and it not only has excellent photocatalytic performance but also is an ideal additive in absorbing materials,which can improve the dieletric loss properties of the composites and adjust the impedance matching.Based on the above assumptions,choosing the ZnFe₂O₄,RGO and TiO2 as the based material,a series of composites have been prepared by a layer-by-layer coating process and chemical etching route herein,and its photocatalytic and EMW absorption properties are further study.The main research contents and results of this work are as follows:?1?Hierarchical core-shell structured ZnFe₂O₄@SiO2@RGO nanocomposites have been prepared by a“coating-coating”route.And its EMW absorption properties have been study throughly by changing the content of RGO and tuning the thickness of interstitial SiO2 layer.The results show that the S-2 sample possess the best EMW absorption performance,its minimum RL reaches-43.92 dB at 13.9 GHz,and its effective absorption bandwidth is up to 6.0 GHz?12?18 GHz?in thickness of 2.8 mm.The enhanced EMW absorption performance of the composites is summation of the conductive loss and dielectric loss caused by RGO and the magnetic loss resulting from ZFO,as well as the interfacial polarization and relaxation effects between three components.In addition,SiO2 with good wave-transmissivity can improve the impedance matching of ZFO@SiO2@RGO composites,and further increase the absorption ability of absorber on EMW.?2?A multifunctional hierarchical structured ZnFe₂O₄@RGO@TiO2 composite has been successfully synthesized in this work.ZnFe₂O₄ nanoparticles are encapsulated by RGO which is then coated by anatase TiO2.The photocatalytic activity of the as-prepared ternary catalyst has been explored for the degradation of FA.And the results show that the enhanced catalytic activity of the catalyst is due to the synergistic effect of the excellent adsorption of RGO,Fenton oxidation of ZnFe₂O₄ and photocatalytic degradation of TiO2.Through exploring the influence of the experimental parameters,it has been found that the H2O2 dosage,solution pH and catalyst dosage all have a great influence on catalytic activity of ZnFe₂O₄@RGO@TiO2.In addition,the catalyst is reusable and shows 90%efficiency up to 5 cycles.?3?The obtained ZnFe₂O₄@SiO2@GO microspheres in the second chapter are further coated by TiO2 through a templating approach.And the yolk-shell ZnFe₂O₄@GO@TiO2 nanomicrospheres are then obtained after the SiO2 layer is etched.By tuning the amount of TEOS,a series of yolk-shell ZnFe₂O₄@RGO@TiO2 microspheres with different void sizes and shell thicknesses can be obtained and its EMW absorption properties are also investigated.The electromagnetic data demonstrate that the as-prepared yolk-shell microspheres possess enhanced microwave absorption properties in high frequency compared to pure ZnFe₂O₄ and hierarchical ZnFe₂O₄@SiO2@RGO@TiO2 due to its unique core@void@shell structure.Among which,the sample with void size of?190 nm and TiO2 thickness of?45 nm exhibits the optimal reflection loss which can reach up to-44.3 dB at 15.92 GHz,and the effective absorption bandwidths is 4.1 GHz.