Study Of Noble Metal Nanoparticles And Imidazole Derivatives Compounds Self-Assembled Films On Iron Surface

The corrosion of metal is a common phenomenon that causes changes in its appearances,color and mechanical properties.The corrosion may lead to damages of devices,leakage of pipelines,pollution of products as well as other accidents and waste of resources and energy,which will bring great loss to the national economy.It is estimated that in many developed countries the economic loss caused by metal corrosion accounts for 1%-4%of their gross domestic product and 20%annul produced iron corrodes.The total loss of corrosion will exceed all that caused by disasters each year,including fire hurricanes and earthquakes.Many domestic fields,such as oil,petrochemical, hydropower,bridge and naval architecture,have marked a significant development.So it is of great importance to our national economic to study the corrosion mechanisms and protection measures.With the development of life science,nanotechnology and material science,the techniques of self-assembled ordered molecular monolayers/multilayers are becoming widely concemed.The SAM techniques could form ordered molecular systems with thermodynamic stability and lowest energy by spontaneous adsorptions of molecules on solid/liquid or solid/gas interfaces.SAMS has many advantages,including good orientation, compactness,ordered molecules arrangements and easy preparations as well. So they are playing an increasingly important role in the fields of biochemistry, medicine,chemistry separation,material science and corrosion protection.In recent years,the awareness of environmental protection and sustainable development are being widely accepted,which brings new requirements for the development and application of inhibitors.Concerning the properties and profits,the development of environmental-friendly inhibitors by means of Green Chemistry is widely accepted.The use of Green Chemistry technology in the development of inhibitors could reduce or avoid the use of toxic substances and develop environmental-friendly inhibitors,which have value of practical application.In this dissertation,by exploring different inorganic and organic compounds and proper experiment conditions,SAMs with good inhibition efficiency was prepared on the surface of iron,which could protect the iron from corrosion effectively by isolating the iron from its environment.The inorganic noble metal nanoparticles,imidazole and amino acid compounds were self-assembled on the iron surface after pretreatment.Electrochemical measurements such as electrochemistry impedance spectroscopy and polarization curves were used to study the inhibition properties of the SAMs in the 0.5mol dm^-3 H₂SO₄ solution.Electrochemistry parameters such as charge transfer resistance,double-layer capacitance,corrosion potential and corrosion current were measured.The effects of different factors on the inhibition properties of SAMs,including the assembly time and temperature,the concentration of inhibitors and the characteristic of the substituents were also studied.The relative impedance spectra were fitted by means of equivalent circuits.The components and morphologies of the SAMs were characterized through XPS,FT-IR and SEM.In order to explain the experiment results, attempts were made to study the theory of the adsorption of SAMs on electrode surfaces through quantitum chemistry calculation and molecular simulation.The main contents and research results are as following:1.Study the inorganic noble metal nanoparticles self-assembled films on iron surfaceThrough a one-step thermal reaction,Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface.TEM image indicates that the Au nanopartiles are composed of quasi-spheroid and quasi-triangle shape particles.SEM images show that the Au nanoparticles can be assembled on the iron surface and the size of the nanoparticles is the same as that of the TEM image.Results of electrochemical impedance spectroscopy indicate that self-assembled mixed films of PVA-protected Au nanoparticles can prevent iron from corrosion effectively.The iron electrode was immersed into Au nanoparticles solution for 1h to make the Au nanoparticle self-assembled films.The protection efficiency for Au nanoparticle films is 77.0%.After 1 h's immersion,the iron electrode was washed with ultra pure water and anhydrous ethanol thoroughly,and then immersed in n-hexylthiol solution for 1 h to make the n-hexylthiol/Au nanoparticle self-assembled mixed films.We also made the n-hexylthiol self assembled films and EIS result showed the protection efficiency of n-hexylthiol self assembled films is 89.2%.While the protection efficiency for mixed films-modified iron electrode is promoted to 97.1%.That is to say the n-hexylthiol/Au nanoparticle films are of good effect for protection of iron in acidic solution.Au,Pt and Ag nanoparticles were prepared in aqueous solution through a chemical reduction method and transferred from water phase to toluene phase with the protection of 1-dodecanethiol(DDT).The polished iron electrode was immersed in the DDT-protected metal nanoparticles toluene solutions to form DDT/metal nanoparticles self-assembled mixed films.With the immersion time up to 16 h,the inhibition efficiency(IE) of the DDT/Au nanoparticles self-assembled mixed films was 98.9%;the IE of DDT/Ag nanoparticles self-assembled mixed films was 98.3%;the IE of DDT/Pt nanoparticles self-assembled mixed films was 98.3%.The appearance of the peaks of elements such as S,Au,Ag and Pt for XPS tests identified the presence of DDT,Au nanoparticles,Ag nanoparticles and Pt nanoparticles.2.Self-assembled films of imidazole and its derivatives on the iron surfaceSelf-assembled films of imidazole and its derivatives were formed on the iron surface.The corrosion inhibition ability of the self-assembled films in acidic solutions was studied by means of electrochemical methods.The effect of immersion time,assembling temperature,concentration of the inhibitor etc. on the inhibition ability was also investigated.The longer the immersion time is,the better the protection ability of imidazole self-assembled films on the iron electrode is.When the immersion time prolonged 16 h,the quality of the film will not be improved significantly by further prolonging the immersion time.The iron electrode was immersed in 0.01 mol dm^-3 IMZ solution at different temperatures for 1 h,the assembling temperature was set at 0℃,20℃, 40℃and 60℃respectively.With the rise in temperature,the inhibition efficiency was also increased,but the extent of increase was not noticeable. That is to say,the assembling temperature has little effect on the inhibition efficiency of the self-assembled films.So we choose 25℃as our working temperature.At the same assembling temperature,with the increase in the inhibitor concentration,the time of getting stabled self-assembled film shorted and correspondingly the inhibition efficiency also increased.Imidazole derivatives were synthesized and formed self-assembled films on the iron surface.Comparing with the inhibition efficiency(IE) of imidazoie films and imidazole derivative films,all the IE of imidazole derivatives increased in various degrees.When the assembling time was 24 h,the IE of imidazole self-assembled films was 77.7%;the IE of 1-butyl-1H-imidazole self-assembled films was 81.0%;the IE of 1-benzyl-1H-imidazole self-assembled films was 84.4%;the IE of 1-tosyl-1H-imidazole self-assembled films was 84.6%;the IE of(E)-3-(4-((1H-imidazol-1-yl)methyl)phenyl)acrylic acid self-assembled films was 85.6%;the IE of(E)-methyl3-(4-((1H-imidazol-1-yl) methyl)phenyl)acrylate self-assembled films was 86.8%.The imidazole molecule shows three different possible anchoring sites suitable for bonding: pyridine like nitrogen atom 3N,pyrrole like nitrogen atom 1N and aromatic ring itself and probably the substituent may act as an active center.With the addition of the adsorption atoms and the increasing of the SA films' thickness the IE of the SA films may be improved.Quantum chemical calculations showed that the atomic charge of N,S,O atoms are negative,they can bond to iron through those atoms andÏ€electron.3.Study of L-Glutamine self-assembled films on the iron surfaceL-Glutamine self-assembled films were formed on iron surface and the inhibition efficiency was investigated with the change of the assembling time. Electrochemical tests indicated that L-Glutamine self-assembled films could prevent iron from corrosion effectively in 0.5 mol dm^-3 H₂SO₄ solution.With the increase in the assembling time,the IE of the self-assembled films boost up. EIS results showed that R_ct of L-Glutamine self-assembled films increased quickly for the first 30 minutes,but with the increase of the immersion time the R_ct increase slightly and remains constant.FT-IR results show that the characterization peaks correspond to the groups in the compounds.Scanning electron microscope was used to observe the morphology of the iron sheets including bare iron sheet and L-Glutamine modified iron sheet,which had been corroded in 0.5 mol dm^-3 H₂SO₄ solutions for 2 h.There were distinct differences between the two photographs.The bared iron surface suffered more severe corrosion than the L-Glutamine modified one.The surface of the bare iron sheet was damaged completely,while the L-Glutamine-modified iron sheet was not damaged so severely,which means the presence of the L-Glutamine films can protect iron from corrosion effectively.Quantum chemical calculations showed that N or O atoms in L-Glutamine bear more negative charges than other atoms,so the two N atoms and two O atoms in L-Glutamine molecule may act as active center on iron surface.