Theoretical Study Of The Interactions Of Phenoxyalkanoic Herbicides And Amide Molecules With Kaolinite Cluster Model

In this paper,octahedral（Al-O）surface model（K（o））Al₁₃O₄₈H₅₇ and tetrahedral（Si-O）surface model（K（t））Si₁₃O₃₇H₂₂ were constructed for the investigation of the phenoxyalkanoic herbicides on kaolinite surface and cluster models(Al₅CaO₂₄H₃₀)-,(Si₅AlO₁₈H₁₂)-and(Al₆Si₅CaO₄₂H₄₂)2-were constructed for isomorphously substituted octahedral surface（K（os））,tetrahedral surface（K（ts））and kaolinite surface（Ks）whose basal plane surfaces were negatively charged to investigate the interaction of amides with the isomorphously substituted kaolinite.The calculation was based on B3LYP（Becke,three-parameter,Lee-Yang-Parr exchange-correlation functional）method,and the basis set was set to be 6-31G（d,p）and 6-31G（d）,respectively,to research the interaction of the phenoxyalkanoic herbicides（2,4-dichlorophenoxyacetic acid（2,4-D）,2,4-dichlorophenoxypropanoic acid（2,4-DP）,2,4-dichlorophenoxybutyric acid（2,4-DB）,2-methyl-4-chlorophenoxyacetic acid（MCPA）,2-methyl-4-chlorophenoxypropanoic acid（MCPP）,2-methyl-4-chlorophenoxybutyric acid（MCPB））and amides（formamide（FA）,acetamide（AA）,cis-N-methylformamide（cis-NMFA）,trans-N-methylformamide（trans-NMFA）,cis-N-methylacetamide（cis-NMA）,trans-N-methylacetamide（trans-NMA））with kaolinite,including optimal structures,structural parameters,interaction energies,natural bond orbit（NBO）charge distributions,etc.The investigation of the phenoxyalkanoic herbicides with the kaolinite indicates that the herbicide molecules with the propionyloxy or butyrate have the better adsorption ability due to the larger amount of adsorption sites when comparing to the herbicides with carbethoxy.Simultaneously,the adsorption of MCPP on kaolinite surface was stronger than that of MCPA.Combined with conclusion of experiment that 2,4-D has higher adsorption than MCPA,we can infer that 2,4-D and MCPA tend to be adsorbed on tetrahedral surface.Therefore,interaction of herbicides on kaolinite should be taken full account of to ensure the feasibility of leaching in removing herbiside residues in the process of fertilization.The investigations of the adsorption and intercalation of isomorphously substituted kaolinite and amide molecules reveal that the adsorption of the isomorphously substituted tetrahedral surface becomes stronger and the adsorption of the isomorphously substituted octahedral surface becomes weaker.The order of the stability of the complexes is Ks/amides > K（ts）/amides > K（os）/amides.Overall,the interaction of the isomorphously substituted kaolinite and the amide molecules is stronger than that of the neutral kaolinite and the amides.It can infer that the adsorption and desorption of the guest molecules with the kaolinite may be easily achieved by means of controlling the substitution of the kaolinite.