Synthesis And Visible Light Photo-Fenton Properties Of Iron-based Composite Photocatalysts

In recent years,the treatment of organic pollutants in water,which are highly toxic,easily soluble,and carcinogenic,has gradually become an urgent environmental problem.As a promising method,semiconductor photocatalysis technology is considered to be an effective strategy to decompose organic pollutants from wastewater.Among them,iron oxide as a photocatalyst with great potential has been extensively studied due to its easy preparation,low cost and good visible light absorption ability.However,due to the high recombination rate of photogenerated carriers in a single photocatalyst,the degradation effect is still far from the actual requirements.Therefore,in order to solve the above problems,this article combines photocatalytic technology with heterogeneous Fenton technology to construct a photocatalytic-Fenton system by synthesizing iron-based semiconductor composite materials to treat water pollutants（including dyes and tetracycline）.Therefore,in order to solve the above problems,a synergistic system of photocatalytic and Fenton reaction was constructed by synthesizing two-dimensional iron-based semiconductor composites to treat pollutants in water（including dyes and tetracycline）.The formation of two-dimensional/two-dimensional structure and Z-scheme（S-scheme）heterojunctions effectively improves the transport efficiency of photogenerated carriers and retains the strong redox ability of the catalyst.Combining the advantages of photocatalytic technology and Fenton technology,the addition of trace amounts of hydrogen peroxide and the cycle between Fe²⁺/Fe³⁺significantly improve the degradation activity of the composite material to methyl blue and tetracycline.In addition,the capture experiment of the photo-Fenton catalytic reaction process proved that holes and hydroxyl radicals are the most important active substances in the photo-Fenton system.The main contents that have been completed are as follows:（1）The 2D/2D Z-scheme Fe₂O₃/g-C₃N₄photo-Fenton catalyst was prepared by a simple and quick hydrothermal method,and the chemical composition,crystal structure,morphology structure and photoelectric properties of the composites were analyzed in detail..Under visible light irradiation,the degradation efficiency of Fe₂O₃/g-C₃N（50:100）for tetracycline can reach 78%within 20 minutes,which is 3.47 times and 5.82 times that of single Fe₂O₃and g-C₃N₄,respectively.This study combines the advantages of the photocatalytic reaction and the Fenton reaction.The electrons generated by the photocatalytic process promote the reduction of iron ions in the Fenton reaction.At the same time,due to the transfer of electrons,the separation efficiency of the photogenerated electrons and holes in the catalyst is also improved.In addition,the two-dimensional Z-scheme heterojunction also improves the transmission efficiency of photo-generated charges,increases reactive sites and maintains the redox performance of the material itself,which promotes the improvement of catalyst degradation activity.（2）In order to further study the effect of photogenerated charge transfer mechanism on the activity of the catalyst,Fe₂O₃/Bi₂Mo O₆photocatalyst with 2D/2D S-scheme heterojunction structure was designed and synthesized.The photocatalytic activities of Fe₂O₃/Bi₂Mo O₆were investigated by degradation of tetracycline under visible light irradiation.The results showed that Fe₂O₃/Bi₂Mo O₆exhibited significantly enhanced photocatalytic activity due to the synergistic effect of photocatalysis and Fenton reaction.The activities of Fe₂O₃/Bi₂Mo O₆with the optimal ratio are 3.2 and 2.0 times higher than that of Fe₂O₃and Bi₂Mo O₆,respectively.The trapping experiments of active substances show that the hole and hydroxyl radical are the main active substances in the process of photo Fenton reaction.Based on the photo-Fenton catalytic reaction,2D/2D S-scheme heterojunction structure was further constructed.The built-in electric field and band bending can promote the separation of photo-generated carriers and retain the redox ability of the catalyst itself.（3）In the above research,the results of active substance capture experiments of Fe₂O₃/g-C₃N₄and Fe₂O₃/Bi₂Mo O₆show that the holes and hydroxyl radicals are the main active substances in the photo-Fenton reaction.Therefore,Bi₂WO₆with more positive valence band positions（3.35 e V）than g-C₃N₄and Bi₂Mo O₆were introduced into the photo-Fenton system to prepare 2D/2D S-scheme Fe₂O₃/Bi₂WO₆photo-Fenton catalysts.Under visible light irradiation,the degradation activities of Fe₂O₃/Bi₂WO₆composite for methyl blue are 11.06times and 3.29 times of that of single Fe₂O₃and Bi₂WO₆,respectively.At the same time,photoluminescence and photocurrent experiments show that Fe₂O₃/Bi₂WO₆has higher photogenerated charge transfer efficiency than single Fe₂O₃and Bi₂WO₆.The significant improvement of its catalytic activity comes from the synergistic effect of photocatalytic reaction and Fenton reaction and the contribution of 2D/2D S-scheme heterostructure.The two-dimensional/two-dimensional morphology of surface-to-surface contact shortens the transmission distance and time of photogenerated carriers,and increases the active sites on the composites.The S-scheme heterojunction realizes the spatial separation of photogenerated electrons and holes,and retains the good oxidation-reduction performance of the catalyst.The construction of the photo-Fenton catalytic system provides more abundant hydroxyl radicals and accelerates the degradation of methyl blue.