Study On The Preparation Of 2D Ultrathin Bismuth Oxyhalide Nanosheets And Their Photocatalytic Performance

In recent years,the global energy crisis has been caused by excessive consumption of non-renewable energy sources such as coal and petroleum.In addition,large-scale industrial production activities have caused serious environmental pollution problems.Therefore,there is an urgent need to explore effective solutions to deal with the above problems.As an inexhaustible source of renewable energy,solar energy has the advantages of being clean and easy to obtain,which makes people tirelessly explore how to use solar energy efficiently.In this context,photocatalytic technology came into being.To date,photocatalytic technology has shown considerable prospects in the fields of hydrogen/oxygen generation from water decomposition,CO₂ reduction,and pollutant degradation.As we all know,the prerequisite for the realization of photocatalytic technology lies in the design of photocatalytic materials.Semiconductors have become one of the most concerned photocatalytic materials due to their advantages such as low manufacturing cost,low toxicity,and strong stability.In addition,the microstructure of a material has a great impact on its physical and chemical properties.According to research,when the thickness of bulk materials is reduced to the atomic level?usually less than 5 nm?,local atomic structures,such as coordination number,bond length,bond angle,and degree of disorder of surface atoms,will change significantly.These result in characteristics such as larger specific surface area,high surface atomic occupation ratio,and quantum confinement effects,which make the material have an adjustable band structure,shorter charge carrier migration distance,and higher crystal facet activity etc.Therefore,the preparation of ultrathin two-dimensional semiconductor photocatalytic materials has been the focus of research in the field of photocatalysis.However,most of the current synthesis methods require severe synthesis conditions?such as high temperature,high pressure,etc.?or complicated synthesis processes?such as directional attachment,template orientation,etc.?.Under this background,in this paper,by developing a simple and applicable water-oil two-phase colloidal synthesis method,2D ultrathin BiOX?X=Cl,Br,I?nanosheets with high exposure of{001}facets were prepared,and its photocatalytic performance was studied.Details as follows:In chapter 2,the 2D ultrathin BiOX nanosheets prepared by this synthesis method were first characterized.Based on this,by systematically studying the effects of various reaction parameters on the morphology,size,thickness and composition of the product,the formation mechanism of2D ultrathin BiOX nanosheets was proposed.Inhibiting the hydrolysis of Bi³⁺is essential for the growth of 2D ultrathin BiOX nanosheets with high exposure of{001}facets.Under strongly acidic synthesis conditions,the adsorption of protons can greatly reduce the surface energy of the{001}facets,which will greatly inhibit the growth of BiOX crystals along the[001]crystal axis direction,and also help improve the crystallinity in this direction.In chapter 3,the visible light responsive BiOBr nanosheets prepared by this synthesis method were tested for photocatalytic dye degradation and photocatalytic water oxidation performance.The results show that the photodegradation effect of organic dye molecules is mainly determined by the specific surface area of the BiOBr nanosheets,and the photocatalytic water oxidation performance depends on the photogenerated carrier separation efficiency of the BiOBr nanosheets.Because the ultrathin BiOBr-acid-0.5 nanosheets have a large specific surface area and high photocarrier separation efficiency,they show the best photocatalytic performance in both aspects,and their oxygen production is up to 445.6?mol g^-1h^-1.In summary,the 2D ultrathin BiOX?X=Cl,Br,I?nanosheets with high exposure of{001}facets were successfully prepared by this water-oil two-phase colloidal synthesis method.The ultrathin structure has excellent photocatalytic performance because it reduces the migration distance of photogenerated carriers,increases the specific surface area and surface active sites.