Study On Structural Design And Photocatalytic Performance Of Silver-loaded Titanium Dioxide Hollow Spheres

Titanium dioxide?TiO₂?is widely used in the field of sewage treatment for its advantages of high photosensitivity,good chemical stability,non-toxicity and low cost.However,because of its wide bandgap width,poor adsorption capacity and high recombination rate of photogenerated electron-hole pairs,it can only have good photocatalytic effect under ultraviolet light.Therefore,it is necessary to propose methods to improve the photocatalytic activity of TiO₂ under visible light.In this paper,using melamine-formaldehyde resin?MF?microspheres as templates,silver loaded titanium dioxide hollow spheres with different silver contents?Ag@TiO₂HS?,ytterbium-doped silver loaded titanium dioxide hollow spheres?Yb-Ag@TiO₂HS?and yttrium oxide/silver-loaded titanium dioxide hollow spheres?Y₂O₃/Ag@TiO₂HS?composites with double shell structure were successfully prepared by sol-gel method and high-temperature reduction method.The morphology and structure of the samples were characterized by X-ray diffraction analysis?XRD?,X-ray photoelectron photoelectron spectroscopy?XPS?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,and ultraviolet-visible light diffuse reflection spectra?UV-vis DRS?analysis.The photocatalytic degradation of methyl orange by hollow spheres in visible light was studied.The main research results are as follows:?1?Using MF microsphere as templates and n-butyl titanate and silver nitrate as raw materials,Ag@TiO₂HS were successfully prepared through sol-gel method and high-temperature calcinations and reduction,and the influence of Ag content on the photocatalytic effect of methyl orange under visible light was studied.The results show that with the increase of Ag content,the anatase TiO₂ gradually transformed to brookite,the prepared TiO₂HS had a structure of two-phase.In addition,the light absorption range is redshifted and the forbidden band width is gradually reduced.The existence of Ag elements and heterostructure promotes the separation of photo-generated electron-hole pairs and reduces the probability of electron hole recombination.After being irradiated for 180 min under visible light,the degradation effect of samples on methyl orange was gradually improved with the increase of Ag content.When the Ag content was 4%,the degradation efficiency of methyl orange reached 86.2%,and the degradation rate was increased to 0.01245 min^-1,which is about 8 times and 27 times of TiO₂HS,respectively.?2?Using MF microsphere as templates and n-butyl titanate,silver nitrate and ytterbium nitrate hexahydrate as raw materials,Yb-Ag@TiO₂HS were successfully prepared by sol-gel method and high-temperature calcinations and reduction,and the influence of Ag and Yb co-doping on the photocatalytic effect of methyl orange in visible light was studied.The results show that in the process of co-doping,Yb³⁺does not affect the reduction of Ag⁺,and Ag does not affect the substitution of Yb³⁺for Ti⁴⁺into the lattice of anatase phase TiO₂.The introduction of Yb³⁺creates impurity energy levels in the TiO₂ band gap,which broadens the light absorption range and shortens the band gap width.At the same time,Ag has strong electron conduction ability and improves the carrier transfer speed.Under the combined action of Yb and Ag,the photo-degradation efficiency of co-doping TiO₂HS on methyl orange in visible light was significantly improved compared with that of undoping and single doping.The degradation efficiency of Yb-Ag@TiO₂HS on methyl orange reached 76.3%,which was 7 times,3 times and 4times higher than that of TiO₂HS,1%Ag@TiO₂HS and 0.5%Yb@TiO₂HS,respectively.?3?Using MF microspheres as the templates,butyl titanate,silver nitrate and six water yttrium nitrate as raw materials,via the sol gel method and high temperature calcination reduction,Y₂O₃/Ag@TiO₂HS with double shell structure was prepared successfully,and TiO₂ as the inner shell,Y₂O₃ as the outer shell.The photocatalytic activity of double shell shell structure and the position of Ag load on methyl orange under visible light were studied.The results show that TiO₂ and Y₂O₃ have a good synergistic effect,and the photocatalytic performance of Y₂O₃/TiO₂HS is better than that of TiO₂HS and Y₂O₃HS.At the same time,it can widen light absorption range,reduce band gap width and improve photocatalytic activity when Ag existed in TiO₂ layer.The photocatalytic efficiency of Y₂O₃/Ag@TiO₂HS on methyl orange in visible light was 68%,which is about 6 times and 1.4 times than that of the original TiO₂HS and Ag@Y₂O₃/TiO₂HS,respectively.This indicates that Ag,Y₂O₃ and TiO₂ have a good synergistic effect and jointly promote the photocatalytic activity of the samples.