Degradation Mechanism Of Atrazine Catalyzed By Montmorillonite

Atrazine and montmorillonite are two main targets in our research,and the influence of montmorillonite on the photo-catalytic degradation of atrazine was investigated.Basing on these results of photo reaction,an environmental functional material was designed for rapid degradation of atrazine.Quantum chemical method was employed to study the aromaticity of atrazine and to predict the reaction sites of atrazine,explaining the degradation behavior of atrazine in the "photo-catalytic" and the "environmental functional material catalytic" degradation,which provides the scientific evidence and theoretical basis for the environmental behavior,risk assessment and pollution remediation of atrazine.Under solar light irradiation,the dominant reactive oxygen species(ROS)in Fe3+-montmorillonite system was ·OH,because the reaction could be significantly inhibited by methanol,and the benzoic acid(BA)yielded the product,para-hydroxyl benzoic acid(pHBA),which is the product of BA by attacking of ·OH.The yield of ·OH in Fe3+-montmorillonite was controlled with pH value and sodium cation(Na+)could enhance the efficiency of the photo reaction,because of the ion-exchange effect.The type and amount of anion came along with Na+ also had effect on the Fe3+-montmorillonite photo reactions,if the anion was the perchlorate(CIO4-),then no effect was observed;If the anion was chloride(Cl-),then the effect termed as "enhanced at the low and depressed at the high" would be observed.At low concentration of NaCl,the ion-exchange reaction dominated,and at high concentration of NaCl,the Cl-could consume ·OH to yield chlorine radical(Cl·),which could not react with atrazine and therefore depressed the efficiency of the photo reaction.Under natural light irradiation,the dominant ROS in SRFA system was 1O2,because the inhibition of methanol was not observed and the inhibition of NaN3 was found,the production of 1O2 was affected with pH and the degradation rate of atrazine in SRFA system had no significantly difference under different pH.Increasing of SRFA concentration from 5 mg L-1 to 20 mg L-1 could not elevate the degradation rate,while the higher level of SFRA consumed the ROS in system.In anther hand,high level of SFRA would also reduce the available photo intensity in system through their chromophore groups.The dominant ROS in SRFA/Fe3+-montmorillonite hybrid system depended on pH,·OH was dominant at low pH and the 1O2 was the main ROS at high pH.Because the-OH produced with Fe3+-montmorillonite was inhibited at higher pH and the 1O2 consistently yielded with SRFA despite the change of pH.Dissolved oxygen(DO)is the critical element in the Fe3+-montmorillonite system,the SRFA system and the SRFA/Fe3+-montmorillonite hybrid system.In Fe3+-montmorillonite system,DO was reduced with photo-reduced ferrous ion,the yielded superoxide radical(O2-)turned into hydroperoxyl radical(HO2)after protonation,H2O2 is the final production of the reduction of DO,which was decomposed with ferrous ions to produce ·OH to remove the atrazine.In sole SRFA system,DO was inspired with SRFATS to yield 1O2,1O2 was capable to remove atrazine,which was confirmed in a pure 1O2 generation system consist of molybdate and H2O2.High level of SRFA could consume the ·OH and 1O2 in the system,and could reduce the available irradiation in system.The results of the anerobic experiment indicated that the SRFATS could not remove atrazine.The results of quantum chemical calculation suggested that the ferrous ion adsorbed on the surface of the montmorillonite was easier to be oxidized with molecular oxygen than that in a free solution,the change of the first ionic potential before and after adsorption was 0.24 eV.After fully understanding the effect of montmorillonite on degradation of atrazine.By using the confined space of montmorillonite,the zero-valent copper was prepared in the interlayer(termed as ZVMMMT)and its particle diameter was smaller than 1 nanometer,under a proper condition,ZVCMMT could remove atrazine(15 ?M)in less than 2 min.The initial reaction rate of ZVCMMT was 72 times and 2 times larger than that of commercially available zero valent copper(CZVC)and that of nano-sized zero valent copper(nZVC)that synthetized without montmorillonite.Toxicity of ATRA after degradation was carried out by detecting the inhibition ofPhotobacterium phosphoreum(P.phosphoreum)by following the National standard(GB/T 15441-1995).The inhibition in Fe3+-montmorillonite,SRFA and SRFA/Fe3+-montmorillonite system was 9.14%,4.93%and 6.37%,respectively,suggesting the overall toxicity decreasing after photo degradation.The presence of SRFA could relieve the toxicity of atrazine after photo-degradation,given that the Fe3+-montmorillonite and SRFA were widely distributed in natural environment.Therefore the photo-degradation of atrazine with Fe3+-montmorillonite and SRFA could be a detoxification pathway of atrazine under natural condition.In the degradation of atrazine with ZVCMMT,the inhibition decreased from 25%to-0.52%after the reaction,suggesting that the overall toxicity of atrazine solution reduced significantly,and the toxicity of ZVCMMT after reaction was negligible,ZCVMMT is an environment-friendly material.In third part of our research,the molecule of atrazine was studed with quantum chemical methods.The results of density functional theory(DFT)quantum chemical calculation could describe the molecular characters of atrazine.Frontier-electron theory(FET)was selected to analysis the result of the wave function of DFT calculation,the results suggested that the reaction sites of atrazine under attack with ·OH was over the N atoms in the side chain,however,the prediction of the relative reactivity between the sites was not satisfactory by using FET.Dual descriptor(DD)was one of the functions belonged to conceptual density functional theory(CDFT),the result of wave function analyzed with DD also suggested that reaction sites of atrazine were over the side chain,the values of DD over N atom attached with ethyl group and with isopropyl group was-0.1561 and 0.0134,respectively.DD values of N atom in side chain of DIA was-0.1561 and-0.1539 of that in DEA.Two N atoms in DEDIA was with a identical values of DD at-0.0651.The values of these N atoms were in agreement of the results of the experiments.With the breaking of side chains,the calculated DD value of N atom increased,indicating those N atoms were with lower reactivity and more stable under the attack of-OH.Given the results of prediction of reaction sites of atrazine,DD method was with a better performance than FET method.Localized orbital locator(LOL)could well investigate the aromaticity of s-triazine ring structure of atrazine molecule.The delocalization of electron of ring in atrazine was confirmed with the change of different substituents by using the function of LOL.With the increasing of substituents over the ring,the aromaticity of s-triazine was weakened and finally disappeared.The aromaticity of atrazine was mainly contributed with ? electron,the contribution of ? electron was manageable.S-triazine had aromaticity and atrazine did not.After all mentioned above,our research started with the degradation of atrazine under solar irradiation.A novelty environmental functional matrieal was designed and applied to remove atrazine after learning from the nature.Aromaticity was investigated with quantum chemical method.Our research provided therogy basis and technology support for the study of atrazine environmental behavior and pollution control project.