Study On The Quantitative Structure-activity Relationship Of A New Type Of Ionic Liquid Corrosion Inhibitor

Metal corrosion commonly exists,which brings serious harm to the economic life,industrial production,science and technology and orther fields.Adding corrosion inhibitors is cost-effective.Ionic liquids?ILs?have many advantages including good thermal stability,high chemical stability and wide electrochemical window etc.Ionic liquids have been one of the most potential corrosion inhibitors.Nowadays,the selection and experimental study of ILs corrosion inhibitors are mostly carried out by trial-and-error method,which have problems of blindness,long cycle and high cost.In addition,the corrosion inhibition mechanism of ILs corrosion inhibitors on metal surface is not clear.In terms of these problems,in my paper,quantitative structure-activity relationship?QSAR?,quantum chemistry and molecular dynamics?MD?simulations were combined to design new ionic liquids corrosion inhibitors and study the interaction and corrosion inhibition mechanism on carbon steel,aluminum and copper surface,which provide theoretical guidance for the selection,design and development of ionic liquid corrosion inhibitors.The correlations between physicochemical properties and 15 structural parameters of 65 ILs were established by the combination of quantum chemistry and QSAR.Correlation coefficients are above 0.7.The results show as follows.With the increase of alkyl chain on imidazole ring,the introduction of methyl substituent on imidazole ring or the increase of alkyl chain on anion,the electrons transferred number,polarizability and molar volume increase,whereas the energy gap and interaction energy decrease,which cause larger viscosity,smaller conductivity,density and surface tension as well as wider electrochemical window.The correlations of corrosion inhibition efficiency,structural parameters and concentrations of corrosion inhibitors for carbon steel,aluminum and copper were established by the combination of quantum chemistry and QSAR.Correlation coefficients are above 0.8,which predicts the corrosion inhibition efficiency and concentration well.With the increase of the alkyl chain or introduction of the methyl substituent on the imidazole ring,the polarizability,molar volume and electrons transferred number increase,whereas the energy gap decrease,which cause higher inhibition efficiency.Combining the hard and soft acid theory and synergistic effect,we introduced the methyl substituent and increased the side alkyl chain to maximum on 3-Decyl-1-methyl-imidazolium?[C₄MIM]⁺?.According to the QSAR,the suitable anions were selected and the composite corrosion inhibitors were constituted,which had better corrosion inhibition performance.The cation was designed as[C₁₅DMIM]⁺.The NO₃^-and Ac^-were anions of carbon steel corrosion inhibitor.The Br^-and TfO^-were anions of aluminum corrosion inhibitors.The HSO₄^-and Br^-were anions of copper corrosion inhibitors.The combination of MD simulations and quantum chemistry was used to study the corrosion inhibition mechanisms for ionic liquid corrosion inhibitors named3-Decyl-1-methyl-imidazolium tetrafluoroborate([C₁₀MIM]BF₄),3-Dodecyl-1-methyl-imidazolium tetrafluoroborate([C₁₂MIM]BF₄),3-Decyl-1,2-dimethyl-imidazolium tetrafluoroborate([C₁₀DMIM]BF₄)and 3-Dodecyl-1,2-dimethyl-imidazolium tetrafluoroborate([C₁₂DMIM]BF₄)on carbon steel.The results show as follow.The imidazolium ring is main reactive site.With the increase of the alkyl chain or the introduction of the methyl substituent on imidazolium ring,the electrons donor role of imidazolium ring,molecular reactivity,the interaction between corrosion inhibitors and Fe surface and the ability of diffusion inhibition for corrosive media particles increases gradually.The order of corrosion inhibition efficiency predicted by QSAR between inhibition efficiencies and structural parameters is[C₁₀MIM]BF₄<[C₁₂MIM]BF₄<[C₁₀DMIM]BF₄<[C₁₂DMIM]BF₄,which agrees with the experimental result.The interaction between N atoms and Fe surface is stronger than C atoms on imidazolium ring.N atoms can donate electrons to Fe³⁺or Fe²⁺to form coordinate bond.Corrosion inhibitors are adsorbed on the Fe surface through chemical effect,which result in the decrease in diffusion coefficients and number density of corrosive medium particles.The corrosion inhibition mechanisms of 1-butyl-3-methyl-imidazolium hydrogen sulfate?[BMIM]HSO₄?,1-hexyl-3-methyl-imidazolium hydrogen sulfate?[HMIM]HSO₄?and 1-octyl-3-methyl-imidazolium hydrogen sulfate?[OMIM]HSO₄?on the Cu surface were studied.The results show as follow.With the increase of the alkyl chain on imidazolium ring,the molecular reactivity,electrostatic interaction between corrosion inhibitors and Cu surface and the ability of diffusion inhibition for corrosive media particles increase.The order of corrosion inhibition efficiency predicted by QSAR between inhibition efficiencies and structural parameters is[BMIM]HSO₄<[HMIM]HSO₄<[OMIM]HSO₄,which agrees with the experimental result.The interaction between C atoms and Cu surface is stronger than N atoms on imidazolium ring.Corrosion inhibitors are adsorbed on Cu surface as protective films through physical adsorption,which cause the decrease of diffusion coefficients and number density for corrosive medium particles.The corrosion inhibition efficiency and concentration predicted by QSAR between inhibition efficiencies and structural parameters are consistent with the experimental values,indicating that QSAR models establihed are reliable.The corrosion inhibitor can inhibit th e interaction between the corrosive medium and the metal surface effectively,which inhibits the electrochemical reaction and the ionization process of the metal.Thus corrosion inhibitors have good corrosion inhibition effects.MD simulations were used to study the corrosion inhibition performance of new ionic liquids corrosion inhibitors?carbon steel corrosion inhibitors,aluminum corrosion inhibitors and copper corrosion inhibitors?.The corrosion inhibition efficiencies predicted by QSAR between inhibition efficiencies and structural parameters for carbon steel corrosion inhibitors([C₁₅DMIM]NO₃ and[C₁₅DMIM]Ac),aluminum corrosion inhibitors([C₁₅DMIM]TfO and[C₁₅DMIM]Br)and copper corrosion inhibitors([C₁₅DMIM]HSO₄ and[C₁₅DMIM]Br)are above 87%.The carbon atoms on alkyl chain attached with imidazolium ring increase to 15,the corrosion inhibition performance is optimal.The new ionic liquids corrosion inhibitors are adsorbed on metal surface as protective films respectively,which cause the decrease of diffusion and number density of corrosive medium particles on metal surface.The new ionic liquids corrosion inhibitors could hider the interaction between corrosive medium particles and metal surface effectively.New ionic liquids corrosion inhibitors have good corrosion inhibition effects.