Study On The Efficiency And Mechanism Of Photocatalytic Degradation Of Atrazine By Persulfate Based On GC₃N₄

At present,pesticides still play an important role in agricultural development.They can not only effectively reduce the loss of agricultural products,but also significantly improve grain yield and quality.However,compared to other pollutants,the concentration of pesticides in aqueous solutions is much higher,posing a potential threat to the aquatic environment.Although a series of measures have been taken to reduce the ecological risks of pesticides,it is still necessary to develop an efficient and reliable technology to address the root cause of pesticide pollution.Currently,most conventional persulfate photocatalytic technologies use UV as the excitation light source,but it must be mentioned that UV light accounts for only 5%of the solar spectrum and about 48%of the energy of daylight is concentrated in the visible region.Therefore,in the field of water treatment,if the oxidant can be used in combination with visible light,it means a significant reduction in treatment costs,and the process operation can better achieve the goal of environmental protection.This study selected ATZ as the target pollutant,studied and prepared two types of photocatalysts,graphite nitride carbon（g-C₃N₄）and N-Zn O/g-C₃N₄（g-N-Z）,and characterized their morphology and optical properties.A comparative study was conducted on the degradation efficiency and mechanism of ATZ between the PDS system and the g-C₃N₄/PDS system under visible light.The light source and photocatalyst in the g-C₃N₄/PDS/Vis system were optimized,and a series of explorations were conducted on the removal and mechanism of ATZ in the g-N-Z/PDS/solar system.The research mainly includes examining the effects of water background components and main process parameters on ATZ removal efficiency under two different systems,and analyzing and summarizing the reasons for the fluctuation of degradation rate;The types of main active ingredients in the system were identified through free radical capture experiments and EPR technology;Detected the intermediate products generated during the degradation process of ATZ and speculated on their possible degradation pathways;Finally,based on the above experimental results,an enhanced mechanism for ATZ degradation was proposed.The main research findings are as follows:Based on the characterization results of XRD,SEM,and XPS,g-C₃N₄ was successfully prepared using melamine as the precursor through a simple thermal shrinkage method.Meanwhile,we prepared g-N-Z photocatalysts using hydrothermal and high-temperature calcination methods.The introduction of N-Zn O significantly enhanced the light absorption performance of g-C₃N₄ in the Uv-visible region,accelerated the separation of photo generated carriers,and improved its utilization of sunlight.Corresponding kinetic experiments were conducted.In the pure water system,the degradation effect of g-N-Z/PDS/solar system on ATZ is better than that of g-C₃N₄/PDS/Vis system.In the PDS/Vis system,the degradation rate of ATZ within 70 minutes was 71.77%,while in the g-C₃N₄/PDS/Vis system and g-N-Z/PDS/solar system,the degradation rate of ATZ within 25 minutes had reached 78.44%and 83.18%,respectively.In the experiment of operating parameter influence,moderately increasing the dosage of photocatalyst and PDS concentration can accelerate the degradation process of ATZ in the g-C₃N₄/PDS/Vis system and g-N-Z/PDS/solar system.However,increasing the concentration of ATZ in the solution will have an inhibitory effect on its own degradation,and the inhibitory effect is proportional to the concentration of ATZ.When exploring the impact of p H,it was found that the degradation rate of ATZ was the fastest when the system was in a strongly acidic environment,while alkaline environments would inhibit the degradation of ATZ.The addition of Cl^-,CO₃^2-/HCO₃^-and NOM can inhibit the degradation of ATZ in both systems,but even if inhibited,the degradation rate of ATZ in g-C₃N₄/PDS/Vis system is still significantly higher than that in PDS/Vis system under ideal conditions.Similarly,a similar phenomenon exists in the g-N-Z/PDS/solar system.Although the degradation performance of ATZ in different actual water environments is affected to different degrees,the low residual persulfate and the recyclability of catalyst indicate that g-N-Z/PDS/solar system still has great application potential.The active ingredients present in the systems were verified by adding tert-butanol（TBA）,methanol（Me OH）,disodium ethylenediaminetetraacetate（EDTA-2Na）,and p-benzoquinone（p-BQ）as trapping agents to both systems,and it was concluded that the active ingredients that play a major role in the degradation of ATZ in both systems are·OH,SO₄^·-,h⁺and O₂^·-.Among them,SO₄^·-,h⁺and O₂^·-were the active components that dominated the ATZ degradation in the g-C₃N₄/PDS/Vis system,while h⁺and O₂^·-were the active components that dominated the ATZ degradation in the g-N-Z/PDS/solar system.The results of the tests also provide direct evidence for the presence of active species in the system.The oxidation products of ATZ in the two systems were detected by LC-MC/MC technique.A total of 7 ATZ intermediates were detected in the g-C₃N_4/PDS/Vis system and 12 ATZ intermediates were detected in the g-N-Z/PDS/solar system.Based on this,the degradation pathways of ATZ in the two systems were speculated.The degradation of ATZ in the g-C₃N₄/PDS/Vis system was mainly achieved through the three pathways of dealkylation,dechlorination and oxidation,while the degradation of ATZ in the g-N-Z/PDS/solar system included the alkenylation process in addition to the above three pathways.The changes of TOC in the solution showed that the ATZ existed mainly in the form of small organic molecules in the system.A possible photocatalytic enhancement mechanism is proposed.The coupling between g-C₃N₄ and PDS was substantially enhanced in visible light,and PDS as an electron acceptor not only improved the separation efficiency of photogenerated carriers in g-C₃N₄,but also promoted the formation of·OH,SO₄^·-and O₂^·-in the system.In the g-N-Z/PDS/solar system,the enhanced mechanism of ATZ degradation was attributed to the formation of Z-type heterojunctions that further improved the photocatalytic performance of g-C₃N₄ and also accelerated the transfer of photogenerated carriers to PDS,which in turn led to the enhancement of the generation rate of active components in the system.