ORIGINAL RESEARCH article

Front. Mater., 13 May 2022

Sec. Environmental Degradation of Materials

Volume 9 - 2022 | https://doi.org/10.3389/fmats.2022.850362

Facile Construction of Self-Healing Polydopamine-Based Composite Coating Protection of Copper From NaCl Solution

  • The Education Ministry Key Lab of Resource Chemistry, Joint International Research Laboratory of Resource Chemistry, Ministry of Education, and Shanghai Key Laboratory of Rare Earth Functional Materials, College of Chemistry and Materials Science, Shanghai Normal University, Shanghai, China

Abstract

Developing a sufficient composite organic inhibitor coating on the surface of metals is a promising strategy to improve the protection capability of metal materials from corrosive media. In this study, dopamine is polymerized into a polydopamine coating on a copper surface by embedding 8-hydroxyquinoline (denoted as PDA@8-HQ). The formation mechanism of PDA@8-HQ on the surface of copper is confirmed by X-ray photoelectron spectroscopy, Fourier transform infrared reflectance, and Raman methods. Electrochemical and field emission scanning electron microscopic results show that the PDA@8-HQ coating made with the addition of 8-HQ was 0.02 M and had the greatest inhibition efficiency (99.1%). When the optimal composite coating is damaged by external forces, self-healing capability could be obviously found due to generating insoluble complex species between corrosive products of copper ions and 8-HQ and the salt solution in the damaged region. This study provides feasibility for the construction of functional corrosion inhibitors on the metal surface.

Introduction

Nowadays, various metals, such as magnesium alloys, aluminum, carbon steel, and copper, are used in navigation and industrial fields (; ; ; ). Among them, copper, with its perfect mechanical workability, high strength at low temperature, good availability, excellent eminent electrical and thermal conductivity, has been widely applied in the fields of condenser pipes of ships, civilian pipes, and coastal power plant heat exchangers (; ). However, as an active metal, copper tends to be corroded in the environment, especially in media containing chloride ions (Cl). Therefore, for preventing such corrosion, many anticorrosion methods have been developed, including a sacrificial cathode, chromate conversion coatings, self-assembly monolayers (SAMs), chromate-free corrosion inhibitors, and organic–inorganic hybrid coatings (; ; ; ; ), among which organic barrier coatings have gained great interest due to their retention of properties of the metal component ().

Organic polymer coatings are explored extensively due to their stability, low cost, and good mechanical strength (). Dopamine (DA) could form polydopamine (PDA) coating by self-polymerization, which easily attaches onto the surface of materials (; ). However, in corrosive suppression field, some cracks in the PDA coating formed during self-polymerization would result in metal corrosion in chloride ion environments. Additionally, metals with PDA coating used in thermal cycling or damaged by mechanical scratch would increase coating crack and even peel off from the substrate (). Therefore, enforcement of PDA coating by introducing inhibitors is an alternative way.

Inhibitors entrapped into composite coating could diffuse out of coating to heal the cracks produced by external force factors (; ) and such composite coating is known as “smart” coating. The “smart” coating especially means that the damaged area can be self-repaired (). In the literature, some methods were reported to fabricate self-healing films: 1) electrospun coaxial fiber (), 2) ion-exchange organic resins (), 3) sol–gel (), 4) layered double hydroxides, 5) hollow SiO2 (), and silica/polymer hybrid nanotubes (). Typically, self-healing could be achieved via the following pathway: the self-healing coating containing linseed oil-loaded nanocapsules, potassium ethyl xanthate, benzotriazole (), 1H-benzotriazole-loaded mesoporous silica sol–gel coating (), micro-arc oxidation/polymethyltrimethoxysilane composite coating (), and polymer coating containing healing agent and microencapsulated catalyst. In view of those strategies, tedious preparation procedures are unavoidable, and the optimization of the corrosion inhibitor content and self-healing efficiency should be considered ().

Recently, in previous work, a study on functionalized multi-walled carbon nanotube-reinforced coating for metal protection was conducted (). Carbon nanotubes (CNT), due to their high specific surface area, good corrosion inhibition ability, good thermal stability, and good mechanical performance, were added in PDA coating, which exhibited better corrosion inhibition efficiency of 98.8% than pure PDA coating. The promising protection was probably owing to a strong interaction between PDA and functionalized CNT via hydrogen bonds, enforcing passive coating in a uniform and dense way. In this work, 8-hydroxyquinoline (8-HQ) as an effective inhibitor for metal corrosion in chloride solutions has been validated (). We carefully study the possibility of embedding 8-HQ into PDA coating to fill the coating defects to improve inhibition efficiency. In Scheme 1, the self-healing procedure of the PDA@8-HQ coating at the copper surface is illustrated. When such coating is damaged by external forces, the inhibitor in the composite coating will be exposed. Free copper (II) ions will electrostatically adsorb () with 8-HQ and complex to repair the cracks caused by external factors, and then 8-HQ will complex with copper (II) to heal the cracks caused by external force factors, which forms clathrate of bis(8-hydroxyquinoline) copper [Cu (HQ)2] (), as indicated in Supplementary Figure S1B.

SCHEME 1

Experiment

Experimental Method

Dopamine hydrochloride (98 wt.% purity), Tris(hydroxymethyl)aminomethane (99.8% purity), 8-hydroxyquinoline (8-HQ, 98 wt.% purity), and ethanol (AR) were purchased from Sigma-Aldrich Corporation. Hydrochloric acid (AR) and sodium chloride (AR) were obtained from Shanghai Richjoint chemical reagents co., Ltd.

Pretreatment of Copper Electrode

Teflon sealed copper rod (99.999 wt.%) with an area of 0.0314 cm2 was used as the observed electrode. First, to remove the oxide/hydroxide layer, the copper electrode was ground with 500- and 1,000-grit SiC papers. Then, 0.3 µm Al2O3 was used to polish the electrode surface. Finally, the polished copper surface was rinsed with deionized (DI) water (18.2 MΩ cm), pure ethanol, and deionized water successively to remove the loose oxides and alumina residue.

Surface Modification

1) The copper electrode was immersed into 2 mg ml−1 dopamine in 100 ml Tris–HCl (pH = 8.5) buffer solution for 12 h at room temperature. DA is therefore self-polymerized onto the copper surface, which is beneficial to the formation of a uniform and dense coating. The copper electrode with PDA coating, recorded as PDA@Cu in the following text, was first rinsed with deionized water and then air-dried. The self-polymerization process of DA is shown in Supplementary Figure S1A.

2) The electrode was immersed in 0.02 M 8-HQ anhydrous ethanol solution for 12 h, rinsed with DI water, air-dried, and recorded as 0.02 M 8-HQ@Cu.

3) After that, 0.2 g DA was dissolved in 100 ml Tris–HCl (pH = 8.5) buffer with magnetic stirring at room temperature. Following that, 20 ml 8-HQ (with different concentrations) anhydrous ethanol solution was slowly added to dopamine solution under constant stirring. The final electrode ( 8-HQ@Cu) was obtained after the bare copper electrode was immersed in the mixture solution for 12 h at room temperature.

Surface Characterization

The composition of the coating was characterized using X-ray photoelectron spectroscopy (XPS, PHI 5000 VersaProbe, Japan). It provided 1,486.6 eV photons using an Al Ka X-ray source (40 W, 15 KV). The test voltage and the base pressure of the analysis chamber were set at 6 × 10−7 Pa and 2 × 10−8 Pa, respectively. The coatings of PDA@Cu and 8-HQ@Cu were scraped off from the copper surface to conduct structural characterization by FTIR (Thermo Fisher Nicolet iS5, United States ). The FTIR spectral range of 500–4,000 cm−1 was recorded with 4 cm−1 resolution in the transmission mode.

Raman spectra were collected using a confocal micro-Raman spectrometer (Super LabRam II system, Dilor, France). The laser and detector were 632.8 nm He-Ne laser and multichannel air-cooled 1,024 × 800 pixels charge-coupled device, respectively. The laser power, pinhole, and slit for Raman measurements were set at 5 mW, 1,000 μm, and 100 μm, respectively. Each Raman spectrum was acquired by 10 s three times and was calibrated using a silicon line (519.2 cm−1).

The morphologies of electrodes were taken at 5 kV acceleration voltage by scanning electron microscopy (SEM, Hitachi S-4800).

Electrochemical Test

To observe the electrochemical behaviors of the electrodes with coatings, by using a VersaSTAT4 electrochemical workstation (AMETEK Princeton Applied Research), OCP, EIS, and Tafel polarization curves were measured in 3.5 wt.% NaCl aqueous solution. A conventional three-electrode system was used, with copper, Pt wire, and saturated calomel electrode (SCE) as the working, counter, and reference electrodes. In detail, the electrodes were kept in the NaCl solution for 10,000 s before EIS tests to obtain a steady state of OCP. The EIS experiment was carried out in the range from 100 kHz to 0.01 Hz with an AC amplitude of 10 mV. The electrochemical polarization curve was acquired at an open-circuit voltage of OCP ± 0.25 V (vs. SCE) with a scan rate of 1 mV s−1.

Evaluation of the Self-Healing Properties

Bare copper, PDA@Cu, 8-HQ@Cu, and PDA@8-HQ@Cu specimens were scratched to expose the metallic substrates by using a ceramic knife (Analytik Jena). The scratched specimens were immediately immersed in 3.5 wt.% NaCl corrosive solution. The scratched portions of copper electrodes with and without treatment of corrosive media were observed using FE-SEM (Hitachi S-4800) and energy-dispersive X-ray (EDS) microanalysis (Hitachi S-4800).

Bare Cu and modified coppers were scratched and corroded in 3.5 wt.% NaCl solution for 10 h. Then linear sweep voltammetry (LSV) was performed by a VersaSTAT4 electrochemical workstation to evaluate self-healing behavior in three-electrode electrochemical cells. The potential range was from 0 to 1.0 V, and the scan rate was set at 50 mV/s (; ; ).

Results and Discussion

Composition of Surface

The successful preparation of 8-HQ@Cu is confirmed by XPS and ATR-FTIR. Figures 1A,B show C 1s and N 1s XPS spectra of PDA@Cu and 8-HQ@Cu. From Figure 2, the contents of various C species are given in detail in Table 1. Some obvious differences could be found in C=C, C-C, C-N, C-O, and C = O groups after the introduction of 8-HQ, for 8-HQ@Cu in comparison with PDA@Cu. Direct evidence of the existence of 8-HQ in the composite coating could be offered via the comparison of the N 1s spectra. As shown in Figure 2C, N-C (399.7 eV) and N-H (400.9 eV) groups are attributed to PDA modified at the Cu surface, while in Figure 2D, the appearance of the C = N (398.7 eV) group in 8-HQ@Cu indicates the successful dopant of 8-HQ into PDA coating.

FIGURE 1

FIGURE 2

TABLE 1

SampleBond content (at%)
PDA@CuC = CC-CC-NC-OC = O
20.6922.9421.7318.7115.93
PDA@8-HQ@CuC = CC-CC-NC-OC = O
22.6024.0319.3920.0413.94

Bond composition and content of C = C, C-C, C-N, C-O, and C = O of C 1s.

To further ascertain the structure of the coating, the FTIR experiment was conducted. As shown in Figure 1, the FTIR spectrum of 8-HQ presents a peak of C-H stretching at 3,057 cm−1, two bands at 1,287 and 1,274 cm−1 correspond to C–N stretching, and a peak at 1,580 cm−1 is due to C = N stretching (; ), and the peaks at 1,222 and 1,206 cm−1 are also from C-OH stretching of 8-HQ (). All corresponding bands are observed in the FTIR spectrum of 8-HQ coating. Additionally, as compared with the FTIR spectrum of PDA, a new band at 1,613 cm−1 occurring in the FTIR spectrum of 8-HQ coating is assigned to the superposition of phenylic C = C stretching (), and intermolecular hydrogen bonds in PDA present a broad band in the 3,000- to 3,400-cm−1 region (). The previous FTIR investigation depicts the successful formation of a composite coating of PDA and 8-HQ at the copper surface.

Similarly, the Raman experimental results could also show the coating formation. From Supplementary Figure S2, Raman spectra of 8-HQ@Cu present a peak at 950 cm−1 from 8-HQ and two peaks at 1,382 and 1,603 cm−1 from PDA.

Open Circuit Potential

Recorded in 3.5 wt.% NaCl solution, Figure 3 shows the curves plotted by open circuit potential (OCP vs. SEC) versus time for bare copper, PDA@Cu, and different PDA@8-HQ@Cu formed by changing the amount of 8-HQ. OCPs of bare Cu, PDA@Cu, and PDA@8-HQ@Cu with different concentrations of 8-HQ (i.e., 0.005 M, 0.01 M, 0.015 M, 0.02 M, and 0.025 M) are −0.209 ± 0.003, −0.196 ± 0.002, −0.202 ± 0.003, −0.198 ± 0.003, −0.191 ± 0.003, −0.172 ± 0.002, and −0.187 ± 0.001 mV, respectively. Obviously, the low OCP value of PDA@Cu is due to the defects in PDA coating, which could be observed in the SEM image (Supplementary Figure S3). From another aspect, some cracks in the PDA coating formed by self-polymerization would result in the occurrence of metal corrosion in chloride ions. By introducing an inhibitor (8-HQ) to synthesize a composite coating, the PDA coating with 8-HQ at the copper surface could dramatically prevent the attack of chloride ions, and the OCP value is relatively higher due to the defects filled by 8-HQ. In Figure 3, the OCP values first shift to the anodic direction and then to the cathodic direction with the increasing 8-HQ concentration. The RSD results in Figure 3 are acquired by three measurements.

FIGURE 3

Due to external factors, the inhibitor in the composite coating will be exposed, and the free copper (II) ions will electrostatically adsorb with 8-HQ and complex to repair the cracks caused by external factors. Then, 8-HQ will complex with copper (II) to heal the cracks caused by external force factors. The test results showed that the corrosion inhibition effect of the coating is bad at low concentrations. The optimal concentration of 8-HQ to stuff the defects in the coating is 0.02 by observation of OCP at a more positive value, presenting the best anticorrosion ability. When a lower concentration of 8-HQ was used, the coating defects could not be filled completely, and when the 8-HQ concentration was excessive, 8-HQ would precipitate in the crystal form during the reaction, which also affected the integrity of the coating.

Electrochemical Polarization

The potentiodynamic polarization curves (Figure 4) of the bare and modified copper electrodes were acquired in 3.5 wt.% NaCl aqueous solution. The resultant electrochemical parameters are listed in Table 2. As described in the literature (; ; ; ), copper corrosion reactions in chloride could be remarked as follows:

FIGURE 4

TABLE 2

SampleEcorr (V vs.·SCE)jcorr (µA cm−2)βc (V·dec−1)βa (V·dec−1)η (%)
Bare copper0.191 ± 0.0020.776 ± 0.00510.7 ± 0.8623.1 ± 1.12
PDA@Cu0.204 ± 0.0040.129 ± 0.00317.0 ± 1.5118.7 ± 1.6783.38
8-HQ@Cu0.215 ± 0.0040.089 ± 0.00411.6 ± 0.7927.4 ± 0.9888.53
8-HQ@Cu0.227 ± 0.0030.044 ± 0.00219.6 ± 0.9437.6 ± 1.4294.33
8-HQ@Cu0.201 ± 0.0050.023 ± 0.00349.3 ± 2.7263.7 ± 2.7196.78
8-HQ@ Cu0.184 ± 0.0030.0071 ± 0.00237.4 ± 1.7397.2 ± 1.8599.09
8-HQ@ Cu0.197 ± 0.0050.0557 ± 0.00421.3 ± 1.6749.6 ± 2.9892.82

Corrosion parameters obtained from potentiodynamic polarization curves for different samples in 3.5 wt.% NaCl aqueous solution (The error means a standard deviation of three measurements).

The anodic dissolution reactions are given as follows:

The cathodic oxygen reduction reaction is given as follows:

By Tafel line extrapolation, the corrosion current density (jcorr), corrosion potential (Ecorr), anodic Tafel slopes (βa), and cathodic Tafel slopes (βc) could be obtained. The jcorr value of the coated coppers is smaller than that of bare copper. The lowest jcorr could be reached at 8-HQ@Cu, which shows a decrease in magnitude by two orders, compared to bare copper (from 0.776 to 0.0071 µA). The results also suggest that the inhibition efficiency of the composite coating with 0.02 M 8-HQ exhibits the greatest resistance to salt corrosion, and the inhibition efficiency could reach 99.09%. In addition, all coatings retard both the cathodic and anodic reactions to some extent, and the differences in βc are less noticeable than βa. This indicates that after modified copper surface with PDA or PDA@8-HQ, the reduction of dissolved oxygen and the diffusion of CuCl2 are diminished ().

Electrochemical Impedance Spectroscopy

To evaluate the protective ability of the composite coating for copper, EIS is an effective method (). Supplementary Figure S4 shows the Nyquist plots of the coated copper electrodes in 3.5 wt.% NaCl solution, and the inset plot shows that of the bare copper. A capacitive loop in the high-frequency range could indicate the solution resistance, and a straight line in the low-frequency range, Warburg impedance, is associated with the diffusion of CuCl2 (). After modification by PDA and PDA@8-HQ at the copper surfaces, in both EIS spectra, the Warburg impedances disappear and the radius of the capacitive loops increases. 8-HQ@Cu presents the highest impedance modulus.

In the Bode plots in Figure 5A, the impendence value at low frequency (|Z|0.01Hz) increases from 3.48 to 5.16 with respect to bare copper. In the phase angle plots of Figure 5B, bare copper, PDA@Cu, and PDA@8-HQ@Cu have two time constants. PDA@ 0.02 M 8-HQ@Cu shows the maximum phase angle, manifesting the best inhibition efficiency. The result is in good consistency with that of potentiodynamic polarization.

FIGURE 5

For better understanding of the corrosion mechanism, ZsimpWin software was used to fit impedance spectra. The equivalent circuit model shows the minimum error and chi-square value (χ2) less than 1 × 10−3. The fitted electrical circuits are shown in Figure 6, and the corresponding electrochemical parameters are listed in Table 3. The most suitable fitting circuit model for bare copper is R(Q{R[Q(RW)]}), while the equivalent circuit model of R{Q[R(QR)]} is picked out for PDA@Cu. Additionally, R(QR)(QR) is a better mode for fitting the PDA@8-HQ coating. In the equivalent circuits, Rs stands for NaCl solution resistance, and Rct and Rf represent charge transfer resistance and the resistance of the film, respectively. Constant phase elements (Qc and Qf) are with respect to copper oxide, PDA coating, and PDA@8-HQ coating. W is Warburg impedance. The Q impedance is defined as ZQ = Y01 ()-n (), in which Y0 is the values of Q, j is the imaginary number, ω (ω = 2πƒ) is the angular frequency, and n is the phase (–1≤n ≤ 1), which is related to the inhibitor adsorption, surface inhomogeneity, and porous layer formation. When n is −1, 0, 0.5, and 1, the Q represents inductance, resistance, Warburg impedance, and capacitance, respectively. As seen in Table 3, the n value of modified samples ranges from 0.5 to 1, meaning the relatively slow corrosion process ().

FIGURE 6

TABLE 3

SampleRs (Ω cm2)Rf × 103 (Ω cm2)Qfn1WQcn2Rct × 103 (Ω cm2)η (%)
Y0 × 10−4Y0 × 10−3Y0 × 10−4
−1 cm −2·Sn)−1 cm −2·S0.5)−1 cm −2·Sn)
Bare copper0.58 ± 0.0050.001 ± 0.000011.96 ± 0.020.86 ± 0.001541 ± 4117 ± 30.484 ± 0.030.075 ± 0.0006
PDA@Cu2.08 ± 0.160.01 ± 0.0020.960 ± 0.0560.73 ± 0.0017.20 ± 0.050.530 ± 0.030.97 ± 0.0392.27
8-HQ@Cu2.22 ± 0.121.011 ± 0.012.30 ± 0.150.70 ± 0.00329.58 ± 0.210.6325 ± 0.041.64 ± 0.0495.43
8-HQ@Cu1.76 ± 0.140.726 ± 0.032.302 ± 0.170.77 ± 0.0052.12 ± 0.060.6599 ± 0.032.05 ± 0.0596.34
8-HQ@Cu1.87 ± 0.182.123 ± 0.045.783 ± 0.230.64 ± 0.0041.61 ± 0.010.7558 ± 0.050.74 ± 0.0189.86
8-HQ@Cu2.51 ± 0.170.857 ± 0.039.360 ± 0.320.80 ± 0.0062.90 ± 0.020.6618 ± 0.023.10 ± 0.0497.58
8-HQ@ Cu1.53 ± 0.112.632 ± 0.052.887 ± 0.190.70 ± 0.0022.717 ± 0.030.7559 ± 0.020.50 ± 0.0285.00

Electrochemical parameters calculated from EIS measurements for different samples in 3.5 wt.% NaCl aqueous solution (The error means a standard deviation of three measurements).

As for blank copper, Rf and Qf are attributed to the inevitable layer of corrosion products (). Nevertheless, diffusion in such a relatively thin layer then becomes possible, resulting in the presence of W. As for the PDA-modified copper electrode, Rf and Qf are caused by a composite film containing copper oxides and PDA. This thick PDA film therefore hinders the diffusion process causing W disappearance. For 8-HQ coating, since 8-HQ can fill the cracks of PDA, the dense protection layer shows the greatest inhibition efficiency up to 97.58%. Therefore, the first time constant is correlated with the film of 8-HQ coating, and the second time constant is then the double layer ().

Self-Healing Behavior

SEM Observations

Figure 7 shows FE-SEM images of copper with and without PDA or 8-HQ coatings, scratched by external forces, which were taken before and after corroded in 3.5 wt.% NaCl aqueous solution for 10 h. In Figures 7B,D, after immersion, there are many pitting corrosions that occurred at the scratched bare copper and the scratched 0.02M 8-HQ@Cu surface, and the visible corrosion products around the scratched spots indicate severe corrosion. Much seriously, in Figure 7F, the PDA coating has partly peeled off from the copper surface after long-term immersion in NaCl media. Obviously, the protection efficiencies of copper from corrosive solution by only PDA coating or 8-HQ are not satisfactory. Figure 8A shows SEM images and EDS results recorded before immersion of the scratched PDA@ 0.02M 8-HQ@Cu in salt solution. The exposure of copper in the scratched portion of PDA@ 0.02M 8-HQ@Cu could be visible.

FIGURE 7

FIGURE 8

In Figure 8B of scaled SEM images, after the scratched 8-HQ@Cu in 3.5 wt.% NaCl solution for 10 h, some nanorods produced in the vicinity of the scratched trace could be found, and the EDS result indicates that the nanorods are mainly composed of O, N, C, and Cu elements. Supplementary Figure S5 shows the section views of the 8-HQ@Cu. After immersion in 3.5 wt.% NaCl aqueous solution for 10 h, nearly no corrosion occurred in the scratched portion due to the self-healing ability of composite coating. It shows that when the coating is damaged by external forces, 8-HQ embedded in the PDA coating would combine with copper ions through electrostatic attraction, forming insoluble clathrate of bis(8-hydroxyquinoline) copper [Cu (HQ)2]. The preeminent self-healing ability of such 8-HQ composite coating will also be validated by following an electrochemical experiment.

Electrochemical Test

Potentiodynamic polarization was used to characterize self-healing property. PDA@Cu and 8-HQ@Cu were scratched with a knife, and then the scratched coatings were immersed in 3.5 wt.% NaCl solution for 0 h, 10 h, and 20 h. As shown in Figures 9A,B and Table 4, compared to the intact PDA@Cu and 8-HQ@Cu, jcorr values of both scratched coatings increased. However, jcorr value of the scratched PDA@Cu sample kept increasing with increasing immersion time, indicating further corrosion in NaCl aqueous solution. By contrast, for 8-HQ@Cu, jcorr value remarkably decreased (down to 0.003 μA cm−2) as soaking time increased, and after self-healing for 20 h, the inhibition efficiency of the scratched 8-HQ@Cu recovered to the original level of the unscratched one.

FIGURE 9

TABLE 4

SampleEcorr (V vs.·SCE)jcorr (µA cm−2)βc (V·dec−1)βa (V·dec−1)η (%)
Bare copper0.191 ± 0.0020.776 ± 0.00510.7 ± 0.8623.1 ± 1.12
PDA0.204 ± 0.0040.129 ± 0.00317.0 ± 1.5118.7 ± 1.6783.38
Scratched0.222 ± 0.0010.291 ± 0.00321.6 ± 0.9314.1 ± 0.7462.50
Self-healing 10 h0.223 ± 0.0020.296 ± 0.00221.0 ± 0.7911.8 ± 0.8261.86
Self-healing 20 h0.225 ± 0.0030.447 ± 0.00418.6 ± 0.8616.7 ± 1.0142.40
8-HQ0.184 ± 0.0030.007 ± 0.00837.4 ± 1.7397.2 ± 1.8599.10
Scratched0.189 ± 0.0020.268 ± 0.00221.9 ± 0.8939.2 ± 0.7965.46
Self-healing 10 h0.185 ± 0.0010.047 ± 0.00519.5 ± 0.9937.8 ± 0.9393.94
Self-healing 20 h0.184 ± 0.0030.003 ± 0.00419.6 ± 0.8236.8 ± 1.0599.61

Anticorrosion performance obtained from potentiodynamic polarization curves recorded with the self-healing tests on PDA@Cu and M 8-HQ@Cu samples.

Figures 9C,D show the Bode plots of self-healing tests of PDA@Cu and 8-HQ@Cu. At the beginning stage, the impendence values at low frequency for scratched PDA@Cu and 8-HQ@Cu reduce an order of magnitude compared to undamaged coatings. Similarly, after self-healing for 20 h, the impendence value of scratched 8-HQ@Cu increased to the same level as the unscratched coating, hinting that the scratches have been repaired by 8-HQ molecules. By contrast, in the case of scratched PDA@Cu, the impendence value decreased with the time undergoing. From Table 5, EIS measurements with RSD about 2.69% repeated for five batches of scratched samples reveal excellent reproducibility. Figure 9E shows OCP (vs. SCE) curves for scratched PDA@Cu and scratched 8-HQ@Cu in 3.5 wt.% NaCl solution over the immersion time. Both OCP values (vs. SCE) of scratched PDA@Cu and scratched 8-HQ@Cu present a sharp fall in the first 3 h, indicating corrosion occurrence in the cracks by the penetration of the corrosive media. After 3 h, OCP (vs. SCE) of scratched PDA@Cu remained decreased, while OCP (vs. SCE) of scratched 8-HQ@Cu increased due to the self-healing behavior. After 12 h, the OCP value of scratched 8-HQ coating reached 181 mV (vs. SCE), which was close to the undamaged coating (ca. 172 mV). The self-healed coating exhibited a stable protection performance for the copper substrate after immersion in salt solution for 20 h.

TABLE 5

8-HQ@CuRs (Ω cm2)Rf (Ω cm2)Q1n1Q2n2Rct (Ω cm2)RpRSD (%)
Y0 × 10−4Y0 × 10−4
−1 cm−2·Sn)−1 cm−2·Sn)
11.6722,7432.5570.6619.1120.5195327.583,070.582.69
21.8852,4134.6550.67642.1450.6721570.42,983.4
31.2352,9383.5880.71243.4830.7655261.853,199.85
41.8992,5902.5890.68933.9660.6254452.793,042.79
51.5372,6322.8870.69892.7170.7559499.53,131.15

Reproducibility of anticorrosion performance obtained from EIS measurements recorded with the self-healing tests on five different 8-HQ samples.

Conclusion

In summary, a facile strategy to prepare a protection coating with self-healing capability was proposed. We first constructed a composite coating at the copper surface by embedding inhibitor of 8-HQ into the PDA coating by using the one-step method. Under an optimal formation of the composite coating by using 8-HQ at 0.02 M, the suppression efficiency of about 99.1% can be reached. 8-HQ@Cu not only showed the efficient inhibition of corrosion but also demonstrated the self-healing ability in case of mechanical damage. By scratching 8-HQ@Cu electrode, the inhibitor in the composite coating will be exposed, and Cu (II) will electrostatically adsorb with 8-HQ and complex to seal the cracks caused by scratching to produce the complexation, which sufficiently inhibits corrosion occurring in the scratched trace. After 20 h of self-healing, the inhibition efficiency reached 99.61%.

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Statements

Data availability statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding authors.

Author contributions

JF and WC: conceptualization and writing/original draft preparation; YJ and SL: investigation and numeral calculations; and HY and YY: writing—review and editing. All the authors contributed to the article and approved the submitted version.

Funding

This research is funded by the National Natural Science Foundation of China (No. 21707091).

Acknowledgments

We greatly appreciate the support of the National Natural Science Foundation of China (No. 21707091), Joint International Research Laboratory of Resource Chemistry, Ministry of Education, Shanghai Key Laboratory of Rare Earth Functional Materials, Key Laboratory of Resource Chemistry of Ministry of Education, “111” Innovation and Talent Recruitment Base on Photochemical and Energy Materials (No. D18020), Shanghai Engineering Research Center of Green Energy Chemical Engineering (No. 18DZ2254200), and Shanghai Municipal Education Committee Key Laboratory of Molecular Imaging Probes and Sensors.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmats.2022.850362/full#supplementary-material

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Summary

Keywords

copper, polydopamine, 8-hydroxyquinoline, self-healing, inhibition of corrosion

Citation

Chen W, Fan J, Jiang Y, Li S, Ying Y and Yang H (2022) Facile Construction of Self-Healing Polydopamine-Based Composite Coating Protection of Copper From NaCl Solution. Front. Mater. 9:850362. doi: 10.3389/fmats.2022.850362

Received

07 January 2022

Accepted

07 March 2022

Published

13 May 2022

Volume

9 - 2022

Edited by

Brahim El Ibrahimi, Université Ibn Zohr, Morocco

Reviewed by

Omar Dagdag, Sidi Mohamed Ben Abdellah University, Morocco

Smrutiranjan Parida, Indian Institute of Technology Bombay, India

Updates

Copyright

*Correspondence: Ye Ying, ; Haifeng Yang,

† These authors have contributed equally to this work and share first authorship

This article was submitted to Environmental Degradation of Materials, a section of the journal Frontiers in Materials

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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