Preparation And Photocatalytic Performance Of Porous Metamaterial Based Photocatalysts In Three-dimensional Anisotropic Geometries

As a new type of artificial material,hyperbolic metamaterial has a special"hypersurface" dispersion curve,which can be modulated for the light absorption by adjusting its structure.At present,the use of hyperbolic metamaterials has achieved ultrabroadband spectrum absorption in the microwave region.Therefore,this anisotropic structure can enhance light absorption,and it is expected to be applied in the photocatalytic direction to improve photocatalytic performance.This paper aims to build anisotropic hyperbolic metamaterials photocatalysts based on oriented self-assembled silica particles and explore its photocatalytic properties.The following work was mainly carried out:(1)An anisotropic structure model with periodical arrangement of silver-clad oxidized silica rods was constructed by FDTD Solutions.The calculation of its equivalent dielectric confirmed its dielectric non-definite characteristics.The absorption of anisotropic structures with different silver thicknesses and different rod lengths were simulated by FDTD.It was found that the average absorption rate of the silver layer reached 85%when the thickness of the silver layer was 3 nm and 5 nm,and the length of the bar was 1000 nm.Comparing the absorption characteristics of the isotropic structures which based on the same parameters of silver-clad silica spheres,it was found that the anisotropic structures have relatively high absorptivity at 380 nm-800 nm,and the light fields of the two structures at various wavelengths were simulated by FDTD,which confirmed the above conclusions.(2)The anisotropic three-dimensional porous structure was constructed by template self-assembly method and characterized by SEM morphology and EDS spectroscopy.Firstly,the monodisperse silica colloidal particles were prepared.The colloidal particles with complete morphology were generated by adjusting the proportion of the reagents several times.The colloidal particles were prepared into 5wt%suspensions and constructed into silica vertical templates under the electric field.The conformal deposition of silver particles on the surface of porous silica structures was achieved using electroless plating method at a water bath temperature of 50?.The outer layer was constructed by atomic layer deposition co-type covering titanium oxide.(3)Explore the effects of different silver content,titanium oxide thickness,and different metal depositions on their photocatalytic properties.It was found that the light absorption and photocurrent density increase first and then decrease with the increase of silver content.At a certain concentration of the reaction solution,the light absorption rate and photocurrent density are the maximum at 8-9 min of reaction.The ALD deposition of TiO2 increased with the number of cycles,and the light absorption and photocurrent densities first increased,then stabilized and then decreased.The maximal values were observed during 180-190 cycles of operation.Comparing the deposition of platinum with deposited silver,it was found that the absorptivity of deposited silver at 380 nm-450 nm is about twice that of platinum deposition,and the photocurrent density is about 1.5 times that of deposited platinum.(4)An isotropic structure with silica microspheres as a template was constructed by self-assembly method and characterized by SEM morphology and EDS spectroscopy.The anisotropy structure with the same other parameters was compared in the deposition of different metals.The photocatalytic performance of the anisotropic structure was found to be higher than that of the isotropic structure at 380nm-450nm,and the photocurrent density was almost twice that of the isotropic structure.It was proved that the three-dimensional shape-anisotropy porous structural photocatalysts we constructed have stronger light absorption and photocatalytic properties than isotropic structures.