Corrosion Inhibition And Structure-activity Relationship Of Organic Heterocyclic Molecules On Copper And Steel In Acidic Medium

With the progress of society,people have paid close attention to the ecological environment and sustainable development.Effectively preventing the corrosion of metals and their alloys is a major strategy related to national livelihoods.The development of inexpensive and efficient corrosion inhibitor molecules is one of the important research directions for metal corrosion and protection.This thesis focuses on the design and development of green and highly efficient corrosion inhibitor molecules by theoretical and experimental methods,combining electrochemical and scanning electron microscope,X-ray photoelectron spectroscopy,quantum computing methods and the molecular dynamics simulation.The structure-activity relationship between the structures of corrosion inhibitor molecules and corrosion inhibition performance was studied at the atomic scale,providing theoretical guidance for the development of efficient corrosion inhibitor molecules in the future.This paper mainly has the following findings:First,the chain length of inhibitor molecules has an effect on the corrosion inhibition efficiency.Three ionic liquids with different chain lengths,1-vinyl-3-methylimidazolium iodide([VMIM]I),1-vinyl-3-proplylimidazolium iodide([VPIM]I)and 1-vinyl-3-butylimidazolium iodide([VBIM]I),were used to investigate the corrosion inhibition on X70 steel in 0.5 M sulfuric acid solution by surface morphology,weight loss and electrochemistry tests.The result shows that the longer the chain length of substituent,the higher the inhibition efficiency.And the corrosion inhibitor molecules are spontaneously adsorbed to the surface of X70 steel through the mixed physical and chemical adsorption to protect copper from adsorption isothermal simulation and molecular dynamics simulation.The corrosion inhibitor molecules with longer chain length are more easy to donate electrons to metal due to its stronger electron donation effect of alkyl group,thus showing better corrosion inhibition effect.Second,the polarity of the inhibitor molecule substituents has an effect on the corrosion inhibition efficiency.4-hydroxy pyrazolo-pyrimidine(HPP),4-amino pyrazolo-pyrimidine(APP)and 4-mercapto pyrazolo-pyrimidine(MPP)were selected as inhibitors for Q235 steel in 0.5 M sulfuric acid solution.The corrosion inhibition performance and mechanism were investigated by means of electrochemistry,surface topography,adsorption simulation,quantum chemical calculation and molecular dynamics simulation.It is found that the inhibition ability of MPP is better than APP and HPP.This is mainly due to the large atomic radius of S,which is easy to polarize,so-SH has a stronger electron-giving capacity than-NH₂ and-OH,and is easier to adsorb to the metal surface.Thirdly,the steric hindrance of corrosion inhibitor molecule has an effect on the inhibition efficiency.The corrosion inhibition of bio-functional cefpirome and cefixime on copper in 0.5 M sulfuric acid solution was investigated by electrochemistry and surface morphology tests.As a result,cefixime has a better corrosion inhibition effect than cefipime,which is mainly attributed to the fact that cefixime with a smaller steric hindrance is easier to adsorb to the copper surface.In addition,the corrosion inhibitor adsorption membrane has a better inhibition effect on Escherichia coli and Staphylococcus aureus by the bacteriostatic circle tests.Fourth,heterocyclic substituent of corrosion inhibitors has an effect on corrosion inhibitionefficiency.Corrosioninhibitormolecules3,3'-(thiophen-2-ylmethylene)bis(1H-indole)(TYBI)and3,3'-(Furan-2-ylmethylene)bis(1H-indole)(FYBI)were designed and synthesized successfully.The target molecules can self-assemble on the surface of copper by simple immersion self-assembly method.The ellipsometry and contact angle were used to study the thickness and hydrophobicity of the self-assembled film.And the inhibition efficiency and mechanism of the self-assembled film was investigated by means of experiments and theoretical calculations.As a result,the inhibition performance of TYBI is better than FYBI,which is mainly owing to the stronger electron supply capacity of thiazole ring,so it is easier to assemble on the copper surface,showing a thicker self-assembly film and better corrosion inhibition effect.Fifth,the number of molecular substituents has an effect on the corrosion inhibition efficiency.4-((1H-indol-3-yl)methyl)phenol(IMP)with unilateral indole and4-(di(1H-indol-3-yl)methyl)phenol(DIMP)with bilateral indole were designed and synthesized,respectively.In 0.5 M sulfuric acid solution,the target molecules will self-aggregate by intermolecular forces and adsorb to the copper surface to form the aggregate protective films.Electrochemistry and surface morphology show that the self-aggregation film has an excellent corrosion inhibition ability on copper.Contact angle test,adsorption simulation,X-ray photoelectron spectroscopy(XPS)analysis and theoretical calculation were used to further analyze the kinetic mechanism of self-aggregation corrosion inhibitors.It can be found that the inhibition efficiency of IMP is less than DIMP,which is due to the fact that the bilaterally substituted DIMP has more self-aggregation active sites than the unilateral IMP,which will have stronger driving force to self-aggregation.In addition,the bilateral DIMP has stronger electron feeding capacity,and it is easier to absorb and assemble on the copper surface,which makes the self-aggregation protective film show stronger corrosion inhibition performance.