Design,Corrosion Inhibition Performance And Theoretical Calculation Of Eco-Friendly Amino Acid Inhibitors

Carbon steel(CS)is widely used in industrial production due to its high strength and low cost.However,it is susceptible to be corroded and damaged in aggressive environment.Although there are many methods to prevent the corrosion of CS,the addition of corrosion inhibitors is one of the most cost-efficient method.As an ubiquitous biomolecules,the development of amino acids corrosion inhibitors has attracted widespread attention.However,the inhibition efficiency and stability of amino acids in most corrosive environments need to be improved.In this paper,amino acid corrosion inhibitors were developed through simple chemical modification and combination.The corrosion inhibition performances of these developed amino acid derivatives were evaluated by electrochemical tests and surface analysis.In addition,the inhibition mechanism of CS was explored through quantum chemical calculation,molecular dynamics simulation,GFN-xTB(Geometries,Frequencies,Noncovalent interactions e Xtended Tight Binding).The main research contents of this work are as follows:1.Two amino acid derivatives(MPT,BPT)were synthesized through modification with phenyl isothiocyanate.The electrochemical test results show that both MPT and BPT exhibit high inhibition efficiencies.At the concentration of 0.1 mM,the inhibition efficiencies of MPT and BPT are 99.26% and 99.44%,respectively.The theoretical calculations show that the corrosion inhibition efficiency of BPT is higher than that of MPT,which may be due to the fact that the introduced benzyl group in BPT molecule could provide a strong electron donating ability and improve the hydrophobicity of BPT molecule.Therefore,BPT molecule exhibits excellent corrosion inhibition performance.2.Two amino acid derivatives(LDT and S-LDT)were synthesized by modifying L-cysteine and S-benzyl-L-cysteine with dextran.The electrochemical test results show that these two corrosion inhibitors act as mixed-type inhibitors with predominant anodic effectiveness.The adsorption mechanism of LDT and S-LDT on CS surface were investigated by molecular dynamics simulation and GFN-xTB calculation,which indicates that LDT or S-LDT molecules can adsorb on the CS surface through the bonding of S,O and N atoms to the steel surface with a flat orientation,thereby forming a dense corrosion inhibitor film and effectively inhibiting the CS corrosion.3.Based on the synergistic effect of corrosion inhibitors,mixing is an effective strategy to improve the inhibition performance of corrosion inhibitors.S-benzyl-L-cysteine(SBLC)and thiourea(TU),as compounded corrosion inhibitors,were investigated through electrochemical tests.The results show that SBLC and TU exhibited obvious synergistic inhibition effect.The GFN-xTB calculations results show that SBLC and TU molecules could bond together through intermolecular interaction.The intermolecular interaction leads to more heteroatoms bonding to Fe surface.Then a more compact and stronger protective film could be formed after co-adsorption of SBLC and TU.Molecular dynamics simulation indicates that the co-adsorbed SBLC + TU film can effectively inhibit the diffusion of corrosive particles compared to the individual SBLC or TU film,thus SBLC + TU can effectively prevent the corrosion of CS.4.L-histidine(LHD)and 1-phenylthiourea(PT)were mixed as combined corrosion inhibitors(LHD + PT).Meanwhile,LHD was also modified with phenyl isothiocyanate to obtain(phenylcarbamothioyl)histidine(PT-HD)inhibitor,which has a similar combined structure of LHD and PT.Then the LHD + PT combined corrosion inhibitors could be regarded as the “intermolecular synergism”,while the developed PT-HD could be regarded as the “intramolecular synergism” of LHD and PT.The inhibition performances of LHD + PT and PT-HD for CS corrosion were evaluated by electrochemical tests and surface analyses.The results show that the PT-HD has better inhibition performance than LHD + PT,i.e.,the “intramolecular synergism” is stronger than the “intermolecular synergism”.Meanwhile,the intrinsic difference in the inhibition performance and mechanism of “intermolecular synergism”(LHD + PT)and “intramolecular synergism”(PT-HD)were in-depth revealed by theoretical calculations.Compared with LHD + PT,PT-HD has stronger adsorption ability.The LHD and PT fragments in PT-HD molecule are closely linked by chemical bonds,and then a more compact adsorbed inhibitor film is formed for the PT-HD adsorption on CS surface,thereby more effectively inhibiting the corrosion of CS.