Study On Hydrogen Peroxide Production Performance Of Carbon Nitride Composites Under Visible Light

Hydrogen peroxide（H₂O₂）has the highest reactive oxygen content（47.1%w/w）,with only water and oxygen（O₂）.H₂O₂ is not only a mild and environmentally friendly oxidant for organic synthesis and environmental remediation,but also a promising new liquid fuel.It is very necessary to find an environmentally friendly and safe hydrogen peroxide production process.The photocatalytic production of H₂O₂ is a green and environmentally friendly method,it does not use dangerous hydrogen,only needs the rich water and oxygen on the earth as raw materials,renewable sunlight as energy,and there is no emission of pollutants in the whole process.Graphite-like carbon nitride（g-C₃N₄）is considered as a new class of multifunctional materials for catalytic,and energy applications because of its unique electrical,optical,structural,and physicochemical properties.In addition,g-C₃N₄ has a suitable energy band structure,and its conduction band is located in a suitable position,which is favorable for the reduction of O₂,and the valence band potential is lower than that of metal oxides,so it can effectively prevent the oxidative decomposition of H₂O₂.However,g-C₃N₄ has some disadvantages that limit the photocatalytic activity of g-C₃N₄.In this paper,g-C₃N₄was choosen as a research object,a nitrogen-deficient 3D carbon nitride and iron-supported 3D carbon nitride were prepared by one-step calcination method and impregnation method,respectively.The photocatalytic activity of H₂O₂ production and pollutant degradation performance of as-prepared samples were also investigated.（1）Using melamine and cyanuric acid as carbon nitride precursors,by controlling the calcination atmosphere and temperature,nitrogen defects are introduced into the structure of three-dimensional carbon nitride.In this paper,the effects of different heating programs and different sacrificial agents on the activity of H₂O₂ production were explored.The 3D carbon nitride rich in nitrogen defects has a high activity of 1.22 mmol·g^-1·h^-1 for the production of H₂O₂ under visible light（≥420 nm）irradiation.When 20 ppm Rhodamine B was used as the solvent,the efficiency of synthesizing H₂O₂ and degrading Rhodamine B was 5 and 12 times higher than that of bulk g-C₃N₄,respectively.Through characterization,it is found that nitrogen defects can act as active sites to trap electrons and lead to the efficient separation of photogenerated carriers,and the three-dimensional structure can provide a larger specific surface area and more active sites.Both experimental and theoretical calculation results show that the existence of nitrogen defects accelerates the separation of electron holes,accelerates the generation of superoxide radicals,and promotes the two-step one-electron oxygen reduction to hydrogen peroxide.More importantly,organic pollutants are degraded in the valence band at the same time,and the synergistic utilization of electrons and holes is carried out.（2）Iron-based nitrogen-defective three-dimensional carbon nitride（Fe（III）/3D CN-Nv）with different mass fractions was prepared by impregnation method,and a photocatalytic self-fenton system coupled with photocatalysis and Fenton technology was constructed.Under visible light,the results show that the 1.5%Fe（III）/3D CN-Nv photocatalyst has the best degradation activity,and the removal rate of tetracycline within60 min is 75.8%,which is 6 times that of bulk g-C₃N₄ and 1.8 times that of unimpregnated Fe（III）.In this system,H₂O₂ can be generated in situ under visible light irradiation,and then a strong oxidizing hydroxyl radical（·OH）can be generated by Fenton reaction,which is used for the degradation of tetracycline hydrochloride in wastewater.The photo-Fenton reaction conditions were optimized by exploring the p H value and Fe species loaded with different mass fractions,and the main active species for degrading tetracycline were elucidated through various analytical tests.