Preparation And Properties Of Photocatalytic Materials Based On Bimetallic MOFs

With the rapid development of industry,the exploitation and consumption of fossil fuels is increasing seriously,and energy crisis and environmental pollution have become global problems,so it is an urgent need to develop and utilize a clean source of energy.In the exploration of new energy,solar energy has advantages of being renewable and easy to obtain,which makes people explore it widely.But it is also an important question about how to convert light energy into chemical energy.In such a context,photocatalytic technology came into being.So far,photocatalytic technology has shown a considerable development in the fields of hydrogen/oxygen evolution from water splitting,pollutant degradation and CO₂reduction etc.Among them,the photocatalytic hydrogen evolution technology based on photocatalysts can directly realize the storage and conversion of solar energy,which plays a vital role in the direction of photocatalysis.Therefore,the preparation and development of highly efficient and stable photocatalytic materials have become a research hotspot in various fields.And there are many high requirements for the photocatalysts of the photocatalytic water decomposition for hydrogen production:appropriate energy band position,strong stability,easy separation of photogenerated carriers,high cost performance,non-toxic,harmless and easy recycling,etc.Metal-organic frameworks（MOFs）have become the focus of research on photocatalytic materials in recent years due to their advantages such as adjustable energy band structure,large specific surface area and inherent photocatalytic activity,etc.However,MOFs are often modified by doping,loading,coating and other methods due to the poor stability and low photocatalytic activity,in order to enhance the photocatalytic activity.Among them,MOFs-derived single-component/multi-component materials loaded with porous carbon structure not only retain the MOFs skeleton,but also enhance the stability and interfacial electron transfer efficiency,which has also attracted extensive attention.In this context,we are committed to preparing a kind of bimetallic MOFs as photocatalysts.For the purpose of preparing simple materials by simple methods,reduce the energy band gap through in-situ doping.Thus,the visible light absorption range will be increased,so as to improve the catalytic activity.In this paper,Ti-Ni bimetallic MOFs were prepared by one-pot hydrothermal method,and we explored the properties of photocatalytic water decomposition for hydrogen production.N,C doped（A/R）TiO₂-Ni TiO₃multi-component composites were prepared by in-situ pyrolysis on this basis,.It was found that the composites had higher stability and photocatalytic activity.This work laid a foundation for the practical application of photocatalytic water decomposition for hydrogen evolution.The specific content as follows:In the second chapter,a series of Ti-Ni bimetallic MOFs with different metal molar ratios were prepared by one-pot hydrothermal method,and their morphologies and structures were characterized.Then we used water as reaction system and triethanolamine as sacrifice agent to test the properties of hydrogen production by photocatalytic water decomposition of the samples.It was found that Ti₃Ni₁-MOF with appropriate molar ratio of metal significantly improved photocatalytic activity compared with single MOFs.This phenomenon has aroused our interest in the study of material structure and catalytic mechanism.Further characterization and analysis showed that Ni element acts as the electron donor center in Ti₃Ni₁-MOF,which increases the number of free electrons in the system.Moreover,the 3d orbital of Ni participates in the formation of the conduction band bottom in the bimetallic MOFs,which reduces the energy band gap and increases the visible light absorption range,so that the photocatalytic activity has improved.On this basis,in order to enhance the stability of the materials under the condition of maintaining the frame structure of MOFs,N-C doped multi-component composite（A/R）TiO₂-Ni TiO₃was obtained by in-situ themolysis,so as to prepare a multi-component heterojunction structure,thereby enhancing the electron transfer efficiency and improving the photocatalytic activity.Based on the previous work,a simple and effective method for the preparation of high efficiency multi-component composite photocatalyst was proposed.In the third chapter,firstly,the effects of different calcination temperatures on the structure and properties of the prepared materials were investigated;secondly,the changes of properties and structure before and after calcination were studied;finally,the performance changes of different materials（compared with single metal materials）were researched under the optimal temperature（600℃）.In addition,we also further explored its properties in other directions of photocatalysis,such as photocatalytic oxygen evolution.This paper lays a foundation for the application of bimetallic MOFs in the field of photocatalytic hydrogen production,and provides an idea for the preparation of cheap,efficient,simple and stable photocatalytic materials.