Study On Efficiency And Mechanism Of Oxidation Degradation Of Atrazine By Fe@N-C Activated Persulfate

Atrazine is a typical triazine herbicide that is still widely used in corn fields in the black soil region of Northeast China.Atrazine is chemically stable and is a difficult-to-degrade organic pollutant,and long-term use can increase its residual amount in the soil.Additionally,atrazine has strong mobility,and the residue of atrazine in the soil may further contaminate groundwater and surface water,causing great harm to the environment.In recent years,advanced oxidation technologies based on sulfate radical have been widely used in various pollution remediation scenarios.Among them,iron-based catalysts have been widely used in advanced oxidation technologies due to their low price,environmental friendliness,and ability to efficiently treat pollutants.However,the tendency of iron-based catalysts to agglomerate and deactivate during application has limited their use.Iron-carbon composites improve the dispersibility of iron nanoparticles,and nitrogen atom doping is beneficial to electron transport and provides more active sites for catalysts.In this study,a nitrogen-doped iron-carbon composite catalyst material（Fe@N-C）was prepared by one-step pyrolysis of melamine and Fe₂O₃.The efficiency and mechanism of atrazine degradation by activated persulfate oxidation were studied after optimizing the performance of the catalyst with different pyrolysis temperatures and different ratios of nitrogen to iron.The main results and conclusions of this study are as follows:（1）Results showed that the optimal pyrolysis temperature was 900℃,as determined by studying the atrazine removal efficiency and reaction rate.By changing the ratio of melamine to Fe₂O₃,it was found that the microstructure of the catalyst could be tuned.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）results have shown that the morphology of the catalyst can be controlled by adjusting the ratio of melamine to Fe₂O₃.In addition,the atrazine removal efficiency reached 100%within a melamine to Fe₂O₃ratio range of 5:1 to 1:2.X-ray diffraction analysis（XRD）shows that the catalyst mainly exhibits characteristic peaks of Fe⁰and Fe₃C/Fe₃N.（2）We also conducted tests to assess the catalyst’s stability.The results indicated that the Fe@N-C/900-1:1+PS system was highly adaptable to varying reaction temperatures,and atrazine could be efficiently removed from the system at initial p H values between 3and 9,suggesting that the catalyst was well-tolerated.Although different water samples reduced the reaction rate of atrazine removal,the removal efficiency of atrazine still reached 100%.In the catalyst reusability experiment,the removal efficiencies of atrazine were compared in the Fe@N-C/900-5:1+PS,Fe@N-C/900-1:1+PS,and Fe@N-C/900-1:2+PS systems after five consecutive cycles.The results showed that the removal efficiency of atrazine in the Fe@N-C/900-1:1+PS system still reached 48.51%after five cycles.（3）The successful doping of nitrogen was indicated by the presence of functional groups,such as C-N,C=N,graphitic nitrogen,pyrrole nitrogen,and pyridine nitrogen in the catalyst,as revealed by Fourier-transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）analysis.The changes in the content of nitrogen-containing functional groups before and after the reaction indicated that nitrogen-containing functional groups participated in the catalytic reaction effectively.The disappearance of Fe⁰fitting peak after the reaction indicated that Fe⁰participated in the catalytic reaction.Reactive species such as SO₄^·-,·OH,¹O₂and surface free radicals on the catalyst were detected by electron spin resonance（ESR）and free radical quenching.KI and L-histidine exhibited the most significant inhibition on atrazine among the quenchers tested.Therefore,it is determined that the degradation mechanism of atrazine involves both free radical and non-free radical pathways,but surface free radicals on the catalyst may be the key pathway.Metabolites of atrazine were detected using liquid chromatography-mass spectrometry（LC-MS）,which revealed that atrazine was degraded mainly through Alkylic-hydroxylation,Olefination,Alkylic-oxidation,De-alkylation,and Dechlorination-hydroxylation.The Fe@N-C/900-5:1+PS system resulted in the most thorough degradation of atrazine with few intermediates,and ultimately generated the ring-opening product.Dechlorination products were detected in all three reaction systems.（4）The potential application value of the representative catalytic system in actual water bodies was explored.The effect of atrazine removal efficiency was studied by adding different concentrations of common coexisting anions or humic acid to the Fe@N-C/900-1:1+PS system.The introduction of Cl^-had no significant effect on the removal of atrazine in the reaction system.However,higher concentrations of HCO₃^-and CO₃^2-ions reduced the removal efficiency of atrazine in the system.The addition of humic acid increased the reaction rate of atrazine removal,so that atrazine in the reaction system was completely removed within 20 min.In the presence of different water samples in the Fe@N-C/900-1:1+PS system,tap water would reduce the reaction rate of atrazine removal,the removal efficiency of atrazine still reached 100%.