Preparation Of Carbon Nitride-based Photocatalytic Materials And Study On The Performance Of Photocatalytic Synergistic Degradation Of Phenolic Pollutants With Persulfate

Photocatalytic technology uses green,clean and renewable sunlight as energy to convert solar energy into chemical energy,and is applied in such aspects as environmental degradation,energy production,and green sterilization.Especially in terms of environmental degradation,photocatalysis has the advantages of environmental protection,high efficiency,and low secondary pollution,which can make up for the lack of water pollution control at this stage,and has broad application prospects.However,the application of traditional catalysts in photocatalysis also exposes many key problems:for example,he quantum utilization efficiency of sunlight is low,and the shortcomings of photo-generated carriers that are easy to recombine after being excited.Therefore,it is urgent to prepare a new type of photocatalyst with efficient solar light utilization.Graphite carbon nitride（g-C₃N₄）has been discovered in the past ten years.It is a new type of photocatalyst with visible light response.It has the advantages of non-toxicity,environmental protection,and low price,which has attracted wide attention of investigators.But similarly,the shortcomings of g-C₃N₄cannot be ignored,such as:light absorption range,low light utilization rate,easy recombination of photo-generated carriers,and low photocatalytic activity.Through its element doping,semiconductor recombination,surface interface modification and other methods,it can effectively improve the light response ability,accelerate the separation of carriers,and enhance the active site.Advanced oxidation methods based on persulfate have been extensively studied in recent years.Persulfate can be used as an electron capture agent to promote electron transfer at the interface of photocatalytic semiconductors,and then generate strongly oxidized sulfate radicals（·SO₄^-）,which can efficiently and quickly oxidize organic pollutants in water.Therefore,the photocatalytic technology and the persulfate oxidation technology are combined,on the one hand,the photocatalytic material itself will be modified to promote its degradation of pollutants;on the other hand,the persulfate can obtain the electrons generated by the semiconductor excitation to form sulfate radicals.Free radicals（·SO₄^-）have a strong oxidizing effect,and at the same time,other active oxygen free radicals with a higher concentration will be produced,which promotes the rapid,efficient and low removal of pollutants.Advanced oxidation methods based on persulfate have been extensively studied in recent years.Persulfate can be used as an electron capture agent to promote electron transfer at the interface of photocatalytic semiconductors,and then generate strongly oxidized sulfate radicals（·SO₄^-）,which can efficiently and quickly oxidize organic pollutants in water.Therefore,the photocatalytic technology and the persulfate oxidation technology are combined,on the one hand,the modification of the photocatalytic material itself will promote its degradation efficiency of pollutants;on the other hand,the persulfate can obtain the electrons generated by the semiconductor excitation to form sulfate radicals.Free radicals（·SO₄^-）have a strong oxidizing effect,and at the same time,other active oxygen free radicals with a higher concentration will be produced,which promotes the rapid and efficient removal of pollutants..In this paper,modification methods are used to construct surface or internal electron transfer channels to improve the separation efficiency of photo-generated carriers and inhibit the recombination of e^--h⁺.Through the photocatalytic synergistic degradation experiment of persulfate,a reaction mechanism in which multiple free radicals act together is proposed.It provides new ideas and ways for the experiment and design of photocatalysis.The specific content of this article is as follows:1.The semi-metallic structure and the g-C₃N₄ structure are coupled together by the in-situ pyrolysis process of the ionic liquid,and an electron transfer path is constructed on the surface to synthesize the ionic liquid modified g-C₃N₄（hm-CN）.The photocurrent analysis of the catalyst shows that the semi-metallic structure coupled to the g-C₃N₄ framework has a good promotion of electron transfer.This greatly increases the separation efficiency of electron-hole pairs and improves the photocatalytic activity.Next,bisphenol A（BPA）was designated as the main impurity,and the photocatalytic activity of the catalyst on BPA was detected.The degradation efficiency of the best-performing 30hm-CN catalyst is 4.5 times higher than that of the monomer catalyst.The photocatalytic degradation mechanism of 30hm-CN was further analyzed.Finally,the degradation mechanism is analyzed.Superoxide radicals（·O₂^-）and holes（h⁺）are the main active species.2.The photocatalyst was constructed by potassium ion intercalation modification g-C₃N₄（KCN）and oxygen-doped red g-C₃N₄（RCN）.At the same time,the surface of the S-type catalyst is modified with boron nitride quantum dots（BNQDs）to promote the efficient separation of electron-hole pairs.The synthesized composite catalyst BRKCN improves the performance of photocatalysis and persulfate in removing pollutants.Various characterization of the material to analyze the structure of the catalyst.It is proved that the two carbon nitride materials are well combined together,and the BNQDs are uniformly supported on the composite.The photocurrent,impedance,and fluorescence（PL）experiments confirmed that the catalyst effectively reduced the recombination of photogenerated carriers and improved the photocatalytic activity.Then,photocatalysis and persulfate degradation of BPA and other target pollutants were carried out.The activity of the 3BRKCN composite has the most obvious improvement,and the combined degradation efficiency and monomer have increased by 4 times.Analyze the reaction mechanism of degradation through capture experiment and electron spin resonance（ESR）technology.The degradation reaction mechanism was analyzed by capture experiment and electron spin resonance（ESR）technology.It is speculated that h⁺,·O₂^-,and singlet oxygen（¹O₂）are the main active species,and sulfate radicals（·SO₄^-）and hydroxyl radicals（·OH）are the secondary active species.The reaction mechanism of the co-degradation of multiple free radicals.3.The alkaline earth metal chloride（MCl₂,M=Ca,Sr,Ba）and melamine are melted and calcined to obtain the alkaline earth metal intercalation g-C₃N₄（MCN,M=Ca,Sr,Ba）.Since alkaline earth metal ions can chemically bond with the atoms of two adjacent layers to form a"bridge"connecting the upper and lower layers,this allows the charge to be efficiently transferred between the g-C₃N₄ layers.Through infrared（FTIR）and X-ray diffractometer（XPS）characterization tests,it is found that the cyano groups appearing on the MCN skeleton have a strong electron attracting effect,which has a good guiding effect on promoting the separation of electrons and holes.Finally,the pollutant BPA was photocatalyzed and synergistically degraded by persulfate.It was found that the Ba CN catalyst had the best degradation activity,the time required for degradation was shortened,and the efficiency was increased by 12times.The possible reaction mechanism in the degradation process was analyzed through ESR experiment and capture experiment.Holes（h⁺）,superoxide radicals（·O₂^-）,singlet oxygen（¹O₂）,and sulfate radicals（·SO₄^-）work together.