Modification Of G-C₃N₄-Based Nanophotocatalysts And Study Of Pollutant Degradation Mechanism

In recent years,the harm of pesticides to water environment has become a hot issue of global concern.Agriculture is the main pillar of human survival,and the transition and excessive use of pesticides have existed for a long time.Some pesticides are retained in the environment for a long time due to their long half-life and stable structure,and can be further diffused through infiltration and migration between soil and water.Atrazine,as a commonly used triazine herbicide,has attracted increasing attention due to its properties of environmental hormones.In particular,environmental hormones can cause biological and human sex hormone secretion and activity decline,reproductive organ abnormalities,cancer and other morbidity increase,and then affect human reproductive ability and offspring health level and survival rate decline.Effective degradation of atrazine has become an urgent environmental problem.In the aspect of pollution control,photocatalysis technology has become the key technology to solve the problem of environmental pollution because of its effective use of the sun,green and convenient.However,poor charge separation,short charge lifetime and low utilization rate of visible light have seriously affected the development of photocatalysts.In particular,there are few studies on the effect of the generation of active groups on the degradation mechanism and path of pollutants,and the internal relationship among them.There are few studies on whether there are specific active groups that can better degrade the pollutant atrazine.Based on the above reasons,in this paper,the construction of nano-heteronode photocatalyst system can effectively promote photogenic charge separation,improve the activation of oxygen,and trigger the corresponding active groups to efficiently degrade atrazine.In this paper,atrazine was taken as the research object,and g-C₃N₄,a typical photocatalytic material,was taken as an example to prepare a photocatalyst with high oxygen activity by means of heterojunction construction and synergistic Fenton effect,and the effects of heterojunction construction and synergistic Fenton effect on the separation of photogenic carrier,the active species and degradation mechanism of atrazine photocatalytic degradation were discussed.In order to establish a new photocatalytic system which can be used for green photocatalytic degradation,so as to better deal with the problem of environmental pollution.The thesis work is focused on two main areas:In view of the key scientific problems in graphitic carbon nitridate（g-C₃N₄）materials,such as low photogenerated carrier separation efficiency,insufficient oxygen activation ability and unclear degradation mechanism of atrazine,P-NT/CN heterojunction was constructed by wet chemical method and used for photocatalytic degradation of atrazine under visible light.The results of photophysical and photochemical tests showed that NT platform could transfer photogenerated electrons from CN and effectively promote charge separation.H₃PO₄ on its surface could effectively promote surface oxygen adsorption,and activated oxygen by photogenerated electrons to form·O₂^-free radicals,thus promoting charge separation and improving the photocatalytic degradation activity of atrazine.The results showed that the activity of 4P-5NT/CN and 5NT/CN was 3.9 and 2.1 times stronger than that of CN in visible light degradation,respectively.In addition,the dual-radical attack pathway of·O₂^-dominated·O₂^-and·OH degraded atrazine was realized.At the same time,using liquid chromatography-tandem mass spectrometry,free radical capture experiment and ESR test and other methods,through the analysis of active groups and intermediates,it was found that·O₂^-free radical played a key role in the initial degradation of photocatalysis.In order to solve the problem of insufficient oxygen activation ability of g-C₃N₄,porous graphite phase carbon nitdrive（PCN）with N defect was designed and prepared,and the Fenton-assisted photocatalytic composite system of MO/PCN and H₂O₂ was prepared by in-situ synthesis of transition metal oxide-manganese dioxide（MO）.It was also used to study the photocatalytic degradation of atrazine under visible light.The photocatalytic degradation results showed that the Fenton-assisted photocatalytic composite system of MO/PCN and H₂O₂ showed 2.69 times more photocatalytic degradation activity than that of PCN.By means of photophysical and photochemical tests,the mechanism of improving the performance of MO/PCN composite photocatalyst was revealed,that is,the heterojunction constructed by MO and PCN effectively promoted charge separation,oxygen adsorption and oxygen activation,and finally generated·OH radical with H₂O₂.·OH and·O₂^-biradical were formed to attack the degradation pathway.