| Mild steel and copper,as engineered alloys with excellent thermal stability and mechanical properties,are being used to manufacture a variety of mechanical production equipment and metal structures.However,the corrosion of metal is one of the great threats to limit their long-term usage.Therefore,acid solution is usually used to clean the dirt on the metal surface.Hydrochloric acid is often used as an industrial cleaning agent in pickling process,oil chemical production and oil well practice because of its slow dissolution rate of steel and other base metals.Nonetheless,because of its volatile,easy to pollute the environment,resulting in metal occur surface rust,cracking,local pitting perforation in hydrochloric acid solution.The consequences of corrosion process will not only affect the industrial production benefits,the products of corrosion and the waste of engineering will also threaten human health and life to a certain extent.Therefore,the discussion of metal corrosion mechanism and the appropriate technology to control or inhibit the corrosion of metal in hydrochloric acid solution are the most important problems.Among all the methods to inhibit metal corrosion,the usage of organic corrosion inhibitors,which containing N,O,S and P heteroatoms and aromatic rings,is a simple and economical measure.With the continuous improvement of people's awareness of environmental protection,using cheap,harmless,easily obtained and eco-friendly drug corrosion inhibitors to replace conventional toxic ones,and the discussion of their anti-corrosion mechanism have become a research hotspot in the field of corrosion.Organic corrosion inhibitors through forming protective adsorption films on metal surface,thus playing a shielding corrosion suppression role.The effectiveness of the inhibitor depends on its physicochemical properties,such as the functional groups,the geometry of the molecular structure,the substituent type and its affinity to metal surface,etc.Due to the complex and fuzzy correlation between molecular structure and anti-corrosion efficiency,the main means of developing new organic inhibitors is still blind filter,which poses a great challenge to the design of efficient and environmentally friendly organic inhibitors under harsh corrosion conditions.Sulphonamides,possess-NH2,-SO2-NH,O,N heteroatoms and aromatic rings,have excellent properties of green corrosion inhibitors.As an antimicrobial agent used in clinical medicine,sulphonamides are biodegradable and have negligible negative effects on aquatic environment,have played an important role in pharmaceutical industry.However,their research as corrosion inhibitor is very limited,and their corrosion inhibition mechanisms on various metals have not been elucidated.Clarifying the influence of active functional groups and the adsorption configurations on the corrosion inhibition effect of sulphonamides will broaden the application in the field of corrosion.Consequently,this study focuses on sulphonamides,using electrochemical impedance and electrochemical polarization technology to investigate the corrosion resistance.What's more,Scanning Electron Microscopy(SEM),Energy Dispersive Spectroscopy(EDS)and Near-infrared technology(FTIR-ATR)are used to characterize the morphology of the metal surface inhibitor films.In addition,Density Functional Theory(DFT)calculated the organic inhibitors neutral and protonation model,and further study the interreaction between the inhibitors with metal by the Highest Occupied Molecular Orbit(HOMO),the Lowest Unoccupying Molecule Orbit(LUMO),Energy gap(?E)and dipole moment(?)of the system.What's more,the adsorption configurations and the mechanisms of inhibition on the metal surface were investigated by using Surface-enhanced Raman Spectra(SERS).Due to the good correlation between experimental and theoretical calculations,a virtual screening strategy can be provided,which examines and screens potential performance through computational simulation before experimental operation to accelerate the discovery process of efficient green corrosion inhibitor.The specific studies are as follows:First,using experimental techniques and DFT calculations to investigate the corrosion inhibition effects of three sulphonamides,namely Sulfadiazine(SD),p-toluenesulfonylhydrazide(p-TSH)and Sulfathiazole(STI)in 0.5 mol/L HCl solution on Q235.The electrochemical experiment results and the Langmuir adsorption isotherm observation show that sulphonamides can spontaneously adsorb on the surface of Q235 through the combination of physical and chemical interaction,forming a dense adsorption film.And the inhibition efficiency(?)order is SD(?=92.8%)>p-TSH(?=79.8%)>STI(?=66.8%).The strong interaction of the protonation SD with the metal atoms(Fe)is confirmed by the DFT calculation.Through highly consistent experimental and theoretical results,the correlation between molecular structural effects and anti-corrosion efficiency is clarified,which providing a pave for understanding the corrosion mechanism of sulfonamides with different functional groups.Second,the inhibition efficiency of the inhibitor is closely related to the molecular properties and the adsorption ability of inhibitor on different metals.Exploring the mechanism of inhibitors with different metals will broaden the application range of sulphonamide on metal substrate.Therefore,on the basis of previous work,Sulfaguanidine(SG)of the sulphonamide derivatives was selected to explore the effect of adsorption configurations on different metal surfaces.Electrochemical experiments showed that SG has better corrosion inhibition on copper,reaching 92.2%at 5 mmol/L,while the inhibition efficiency for Q235 is 64.7%at 1 mmol/L.DFT calculations and SERS technology demonstrate that SG takes S=O bond,benzene ring and ammonia group as the main adsorption sites on the copper surface,which causes SG adsorb in a flat way,increasing the metal surface coverage and providing stronger inhibition efficiency for copper.However,the adsorption of SG on Q235 surface mainly depends on the ammonia group and C=N bond,with fewer adsorption sites.SG will accumulate at high concentration and deviate from the Q235 surface,thus resulting in a decrease in inhibition efficiency.Third,the synergistic inhibition effect between inhibitors will significantly improve the inhibition performance of a single inhibitor.Therefore,the anionic surfactant sodium dodecyl phenylsulfonate(SDBS)was introduced based on SG to explore the synergistic mechanism and the inhibition mechanism on copper.Electrochemical experiments results showed that the inhibition efficiency was up to99.9%in 0.5 mol/L HCl solution upon the addition of 5 mmol/L SG+0.1 mmol/L SDBS,showing a excellent corrosion suppression efficiency for copper.The synergy between the SG and SDBS was confirmed by the synergism parameter 12.1.Surface analysis and contact angle test results confirmed that the mixed inhibitor film has good corrosion resistance against metallic copper.The adsorption configuration of SG and SDBS on the copper surface were explored by DFT calculations,molecular docking simulations and SERS.The synergistic inhibition is due to the introduction of the hydrophobic alkyl chain of SDBS effectively improving the hydrophobicity of the SG film,and the interaction between the formed hydrogen bonds and?-conjugation can facilitate the formation of a more denser and compact film on copper surface. |
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