Photocatalytic Oxygen Reduction Synthesis Of H₂O₂ From Phenolic Resins Regulated By Functional Group

H₂O₂is a kind of very important chemicals,which has been widely used in organic pollutant treatment,chemical synthesis,disinfectant and some other fields.It is also an ideal carrier of clean energy due to high energy density,environmentally friendly feature,and easy storage.At present,more than 95%of H₂O₂is derived from the anthraquinone method.This method is energy intensive,involving cumbersome and complex steps,and producing a large number of by-products that are harmful to the environment.The photocatalytic method requires only O₂,water and the earth’s abundant sunlight to produce H₂O₂,representing an ideal green and sustainable technology.However,despite nearly a century of photocatalytic development,none of the current photocatalysts perform to industrial requirements.As a result,many efforts have been made to develop cheap,stable and safe photocatalysts.Among the many photocatalysts,resorcinol–formaldehyde（RF）resins are a promising new polymeric photocatalyst with a small band gap,a wide range of light absorption and good product stability.However,for practical applications,the activity of the photocatalyst still needs to be further improved.The rational introduction of specific organic functional groups can modulate the activity of the photocatalytic material.The introduction of sulfhydryl groups into the carbon material can enhance the oxygen adsorption capacity of the carbon material.The use of sulfhydryl groups instead of hydroxyl groups can also reduce the influence of hydrogen bonding forces during the reaction process,and thus probably improving order degree of theπ-stacking of the material.On the other hand,the sulfonic acid group is a strongly acidic group,which can provide in situ protons for the oxygen reduction process.The sulphonic acid group is negatively charged and the introduction of the sulphonic acid group can,to a certain extent,induce self-assembly of the material and thus control the surfaceπ-stacking structure.In addition,the introduction of the sulphonic acid group can also modulate its band gap.Based on the above considerations,this thesis focuses on the functionalization of RF resins to enhance their photocatalytic H₂O₂production activity by using 3-hydroxybenzenethiol instead of resorcinol and introducing sulfonic acid groups on RF resins,respectively.The main research contents are as follows:1)The 3-hydroxybenzenethiol-formaldehyde（S-RF）resin was prepared by ammonia-catalyzed high-temperature hydrothermal reaction using 3-hydroxybenzenethiol and paraformaldehyde as raw materials.The products were characterized in detail using FE-SEM,XRD,IR,TSPV,and some other characterization techniques.The results showed that the introduction of the sulfhydryl group effectively enhanced the H₂O₂-producing activity of the resin.As a result,the H₂O₂concentration could reach 2 m M within 1 h,which was 3.4 times higher than that of RF.The introduction of the sulfhydryl group led to an increase in the reactive sites,improving the oxygen adsorption capacity of S-RF,increasing its crystallinity,improving theπstacking of the material,and enhancing its carrier separation efficiency.S-RF showed good photocatalytic activity for the degradation activity of oxytetracycline,combined with the Fenton reaction.Our work not only provides a new strategy to enhance the photocatalytic activity of phenolic resins for H₂O₂production but also develops a new technology for organic pollution treatment.2)Using RF synthesized with resorcinol and paraformaldehyde under high-temperature hydrothermal conditions as raw material,RF-SO₃H was prepared by introducing sulfonic acid groups on the surface of the resin at 0 ^oC.The-synthesized products were characterized in detail by FE-SEM,Raman,UV and XRD.It was found that the introduction of the sulphonic acid group improved the performance by a factor of 1.9,and the H₂O₂concentration in the solution could reach 1.2 m M for 1 h.The introduction of the sulphonic acid group into RF improves the crystallinity,carrier separation efficiency of photogenerated carriers,and the oxygen adsorption capacity,thus increasing its photocatalytic activity.In addition,the introduction of the sulphonic acid group reduces the band gap of the RF resin and shows a certain absorption in the infrared region.Thus,we further investigate the photothermal-assisted photocatalytic oxygen reduction toward H₂O₂generation of RF-SO₃H,utilizing its own photothermal effect.After 2 h of illumination,the temperature of the aqueous solution containing RF-SO₃H increased by 22 ^oC and the cumulative concentration of H₂O₂reached3.3 m M.