Study On The Preparation And Corrosion Inhibition Mechanism Of Carbon Nanomaterials

Given the low cost and easy operation,the injection of corrosion inhibitor is one of the most effective methods to inhibit metal corrosion.Nowadays,the researches and developments of green inhibitors have become an important direction in the field of corrosion inhibitors with the increasingly severe environmental problems.At the same time,carbon nanomaterials have been widely studied in the field of environmental protection and medicine owing to the great biocompatibility,which has also been concerned by anti-corrosion researchers.Therefore,it is significant for the development of green corrosion inhibitors in the field of nanomaterials,especially for preparing the series of carbon nanomaterials with excellent inhibition performance,systematically studying their inhibition mechanism,and then summarizing the differences between nanomaterials and traditional corrosion inhibitors in inhibition behavior.In this study,zero-dimensional carbon quantum dots(CD_S),one-dimensional carbon nanotubes(CNTs)and two-dimensional graphene oxide(GO)were used as the main carbon nanomaterials,and then synthetised or functionalized by a variety of modification methods to prepare the functional inhibitors with excellent inhibition performance.The weight loss tests,electrochemical measurements,surface morphology combined with structure characterizations were adopted to investigate the inhibition behavior of carbon nanomaterials on metal surface,and to comprehensively analyze the differences of characteristics with traditional corrosion inhibitors.The changes of inhibition behavior for materials with different dimensions were also studied and the inhibition models of different carbon nanomaterials were established finally.The main research contents and results are as follows:1.Preparation of carbon nanomaterials and evaluation of inhibition performanceN and S co-doped carbon dots(N,S-CDs)were synthesized by hydrothermal method,and the functionalized carbon nanotubes(FCNTs)were prepared by introducing active amide groups via hydrothermal modification method,and the functionalized graphene oxide(FGO)was achieved by chemical coupling grafting with heterocyclic molecules,while the GO-PDA was acquired from the self-polymerization encapsulation of dopamine.The structures and characteristics of products were characterized by electron microscopies,diffraction spectrums,spectroscopy and thermogravimetric analysis,and then the inhibition performances were evaluated in different conditions,and the results showed:(1)The inhibition efficiency of N,S-CDs for carbon steel in CO₂-saturated Na Cl solution reached93%at 50 mg/L,which was a mixed inhibitor mainly for inhibiting anodic reactions.The inhibition efficiency for aluminum alloy in 0.1 M HCl solution was 86%with the concentration of 5 mg/L,and N,S-CDs inhibited cathodic reactions evidently.(2)With the addition of 100 mg/L,the inhibition efficiency of FCNTs for carbon steel in CO₂-saturated Na Cl solution was close to 90%,and FCNTs belonged to the type of mixed inhibition.(3)The inhibition efficiency of FGO for carbon steel in CO₂-saturated Na Cl solution reached83.4%,which was also a mixed inhibitor.Besides that,the inhibition efficiency of GO-PDA for carbon steel in 0.1 M HCl solution was close to 90%at 100 mg/L,and the inhibition in cathodic reactions was more obvious.2.Influencing factors of corrosion inhibition performance of carbon nanomaterialsThe effects of addition concentration and immersion time on the inhibition performance of carbon nanomaterials were investigated,and the results were as follows:(1)The inhibition performances of N,S-CDs,FCNTs and GO-PDA were gradually enhanced with the increase of concentration,but FGO showed the extremum effect in concentration,and the inhibition effect first increased and then decreased with the maximum inhibition efficiency at 20 mg/L.(2)With the prolongation of immersion time,the inhibition performances of four kinds of carbon nanomaterials increased slowly in the initial stage.The results of electrochemical impedance spectroscopy reached the maximum value after immersion for 3 to 6 hours,and then gradually remained stable in Na Cl solution,but gradually declined in HCl solution.3.Inhibition mechanisms of carbon nanomaterialsThe electrochemical response characteristics during the interactions between metal and inhibitors,and both the growth and microstructures of the protective film were studied to analyse the inhibition mechanisms,while the distribution of nanoparticles at interface was characterized and analyzed on nanoscale.The results were as follows:(1)There are large number of polar groups on the surface of nanomaterials after functionalization reactions,which can be combined with carbon steel through chemical adsorption,and N,S-CDs can also chelate with Al³⁺to deposit on metal surface.(2)The interaction between nanoparticles promoted the agglomeration in solution,forming the nanoparticles in larger size and depositing to cover the metal surface,and finally to make up a special protective layer with micro-nano structure.Among them,N,S-CDs had formed a covering layer composed of a large number of nanoparticles,and FCNTs winded and gathered on the surface to form a protective film based on tubular filler,while the FGO and GO-PDA had made up a lamellar isolation layer.Meanwhile,all kinds of protective films were hydrophobic,which could inhibit the diffusion of corrosive mediums and had been confirmed by theoretical calculations.Thus,the inhibition behavior of carbon nanomaterials was composed of the chemical adsorption after the particles migrated to interface,the aggregation and deposition between particles and the growth of protective film.4.The differences of inhibition behavior between carbon nanomaterials and traditional corrosion inhibitorsCombined with the characteristics of larger size,easy aggregation and accumulated charge,the stability and adsorption behavior of nanoparticles in solution were explored,and the results were as follows:(1)The addition of N,S-CDs and GO-PDA would have a significant impact for the interface electric double layer.On the one hand,it affected the structure of the electric double layer so that the interface capacitance was changed.On the other hand,the rearrangement of charge in electric double layer owing to the electrostatic interaction induced by accumulated charge of nanomaterials surface could improve the electrostatic attraction and enhance the physical adsorption,and finally leaded to the significant movement of the self-corrosion potential.(2)According to the special adsorption behavior of carbon nanomaterials,the Redlich-Peterson equation of three parameters introduced in this study accurately fitted the adsorption processes of FCNTs and FGO,and could also be adopted to evaluate the difference degree of particle adsorption.(3)Based on the fluorescence characteristics of N,S-CDs,the adsorption sites and distribution of nanoparticles on metal surface can be observed in situ so that the migration and adsorption state of nanoparticles at interface can be truly evaluated,which provides a new idea for in-situ characterization of corrosion inhibitors.5.The changes of inhibition behavior for carbon nanomaterials with different dimensionsThe inhibition behavior and mechanisms of three kinds of carbon nanomaterials with different dimensions were compared and analyzed,and the results were as follows:(1)The inhibition performance of carbon nanomaterials decreased with the increase of particle size in similar conditions.(2)The protective film at interface of carbon steel thickened correspondingly with the increase of nanomaterials dimension,but its density decreased gradually,and both the permeation and diffusion processes of corrosive mediums increased through the cover layer.(3)The chemisorption between the carbon nanomaterials and carbon steel decreased with the increase of nanomaterials dimension,but the geometric covering effect was gradually enhanced.