Structural Control Of Au/TiO 2 And Its Visible Light Catalytic Properties

In recent years,environmental pollution has become increasingly harsh.There are a variety of methods to deal with environmental pollution.Photocatalytic purification of polluted water is an environmental-friendly technology,its research and application in recent years becomes a rapid developmental field.Titanium oxide is one of the most common catalysts.Beause of stable chemical properties,cheap and easy to get,it has great potential in the photocatalytic degradation of pollutants.The electron band structure of TiO₂ semiconductor determines that it can use the ultraviolet in photocatalytic reaction.However,ultraviolet in the solar spectrum of the Earth’s surface only 3% 5%,the use of solar light is extremely low efficiency in TiO₂.In addition,the electrons and holes that are excited by ultraviolet are seriously recombined in their interior and surface,resulting in a very low quantum efficiency（≤4%）.In order to expand the utilization of titanium dioxide on the light,one of the methods is the use of metal modification.Metals loaded the photocatalytic properties of semiconductors change the distribution of electrons.The deposition of metals can reduce the combination of photogenerated electrons and holes,the quantum efficiency of light can be improved,which provides a new way to expand its visible light response.Gold nanoparticle size,shape can be controlled,and its’ preparation method is mature.The Au/TiO₂ photocatalyst was prepared by dispersing it on the surface of TiO₂,and the light absorption of the material was extended to the visible region.However,Au/TiO₂ photocatalyst has low photogenerated electrons and hole separation efficiency,which limites its’ application.One of the key issues for photocatalytic materials is to promote the separation of charge carrier.This paper focuses on the Au/TiO₂ material.The relationship between the crystal phase composition,nanostructure,the loading of gold nanoparticles and the interface between gold and titanium dioxide was studied.The aim of this paper is to enhance the visible photocatalytic reduction performance of Au/TiO₂.The main works were as follows:（1）Combining the gold nanoparticles with different crystal phase composite of titanium oxide,investigating the separation efficiency of the photoelectrons and holes of the Au/TiO₂ composite phase.The properties of Au/TiO₂ composites are affected by many factors,such as the size and morphology of Au NPs.The first part of this paper focuses on the study of the crystal structure of titanium dioxide.The titanium dioxide was prepared by solvothermal process and calcined at different temperatures to get different crystallinity of the samples.Anatase,the mixture of anatase and rutile,and rutile structure were obtained by calcination at high temperature.The morphology and structure of the prepared materials were analyzed by XRD,BET,TEM,XPS and DRS.The visible light reduction activity of Cr（Ⅵ）solution was used as a probe to evaluate the catalytic performance of the Au/FLT samples.The results show that the Au/ FLT-700 exhibits the best performance,and Au-FLT-700 is the best for the rapid separation of electrons and holes.（2）By constructing the multi-stage structure of titanium oxide to enhance utilization of light in the Au/TiO₂ composite material.Au/TiO₂ composites extend the light absorption of titanium dioxide into the visible region,but the utilization of light is not high.The second part of the work focuses on the morphology of titanium dioxide,hoping to improve the visible light utilization of Au/TiO₂ composite material.The three-dimensional structure of titanium dioxide,constructed by the solvothermal process,has an open structure.The flaky petals are connected to each other,and the edge exposure favors the light absorption.The three-dimensional structure of titanium dioxide was destroyed by grinding method.The samples were prepared by combining TiO₂ and Au NPs before and after grinding,and their morphologies and structures were characterized by a series of experiments.The visible light reduction performance of Au/FLT on Cr（Ⅵ）solution before and after grinding was investigated.Compared with the sample Au/ground-FLT,it is concluded that the three-dimensional structure of titanium dioxide enhances the absorption of Au/FLT in the visible region and enhances the utilization of light.（3）Exploring the effect of inert layer of alumina layer on the the separation efficiency of the photoelectrons and holes of Au/TiO₂ photocatalyst.Relevant literature reported that the alumina can improve the performance of dye-sensitized batteries,because the alumina layer plays a hindrance on the combination of electrons and holes.The third part of the paper focuses on the interface of Au/TiO₂.It is desirable to construct an alumina layer at the Au/TiO₂ interface.The Au/Al₂O₃/TiO₂ composites with different content of alumina were prepared by changing the amount of aluminum source.The morphology and structure of Au/Al₂O₃/TiO₂ were characterized.The visible light reduction performance of Cr（Ⅵ）solution was investigated.Experiments show that the presence of alumina layer can indeed hinder the recombination of electrons and holes.