Study On The Photocatalytic Synthesis Of Hydrogen Peroxide Over Carbon Nitride By Defect Engineering And Metal Ions Modification

As an environment-friendly oxidant,hydrogen peroxide is an important industrial chemical and be widely used.At present,the anthraquinone method is still the mainly way to product hydrogen peroxide in industry.But this method has a lot of pollution.To develop a green synthetic method of hydrogen peroxide is very urgent.The photocatalytic synthesis route is considered as a green and environment-friendly technological route because sunlight can be used as the driving force,and the basic raw materials to produce hydrogen peroxide is water and oxygen.At present,the development of photocatalyst suitable for this reaction is the key to realize the photocatalytic synthesis technology.Graphite phase carbon nitride material is a kind of polymer with layered structure.As a nonmetallic catalytic material,it has attracted much attention.Carbon nitride material as a photocatalytic material has unique advantages,including the high stability,and the appropriate bandwidth.In recent years,researchers have carried out some explorations on the photosynthesis of hydrogen peroxide by carbon nitride,but the understanding of catalyst performance and reaction mechanism still needs to be further improved.This thesis starts from the source of catalyst preparation,successively uses methods such as adjusting the preparation temperature,alkali metal and alkaline earth metal ion modification,and supporting precious metal nanoparticles to control the properties of the catalyst,and explore the influence of these factors on the performance of the catalyst.Specific contents include:1.By simply controlling the synthesis temperature,carbon nitride materials with different degrees of polymerization were prepared,and the performance of photocatalytic synthesis of hydrogen peroxide was examined.The results show that carbon nitride exhibits the highest hydrogen peroxide activity when it is not completely polymerized.Combined with the characterization results,it is speculated that the interaction of the complete melem structure and the incomplete melem structure of the low polymerized carbon nitride is to increase the activity.The main reason is that the presence of more terminal cyano groups in the oligomeric carbon nitride material facilitates the separation and transfer of charges;when the degree of polymerization of the carbon nitride is high,the incompletely polycondensed groups in the material disappear.At this time,defects become the main reason for enhancing its photocatalytic activity.2.The precursor mixture containing NaOH and melamine was heat-treated to prepare a carbon nitride photocatalyst containing alkali metal ions and defects.Alkali metal modification significantly improves the activity of carbon nitride photocatalytic synthesis of hydrogen peroxide.Various characterization results show that the improvement of the catalyst performance is the result of the synergistic effect of alkali metal modification and defects.The introduction of an appropriate amount of alkali metal broadens the light absorption range,and the existence of defects can quickly capture photo-generated electrons and greatly inhibit the recombination of charges..On this basis,we have further improved the activity of carbon nitride materials by using sodium carbonate instead of sodium hydroxide as the sodium source.In addition,our research also shows that the modification of alkaline earth metal elements can also significantly improve the performance of carbon nitride materials for the photocatalytic synthesis of hydrogen peroxide,while the supported precious metal nanoparticles as a promoter have the opposite effect,which is not conducive to peroxide performance.These works will provide a useful reference for the development of photocatalysts based on carbon nitride materials.