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Acetohydroxamic acid adsorbed at copper surface: electrochemical, Raman and theoretical observations

Acetohydroxamic acid adsorbed at copper surface: electrochemical, Raman and theoretical observations Int J Ind Chem (2017) 8:285–296 DOI 10.1007/s40090-017-0111-6 RESEARCH Acetohydroxamic acid adsorbed at copper surface: electrochemical, Raman and theoretical observations 1 1 1 1 1 • • • • • Juan Du Ye Ying Xiao-yu Guo Chuan-chuan Li Yiping Wu 1 1 Ying Wen Hai-Feng Yang Received: 14 June 2016 / Accepted: 11 January 2017 / Published online: 4 February 2017 The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Corrosion inhibition effect of AHA film formed However, copper and its alloys suffer serious corrosion in on the copper surface by self-assembled monolayers tech- chloride environments, causing huge economy losses nique was estimated in 3 wt% NaCl solution by electro- [6–8]. Thus, a considerable amount of efforts have been chemical impedance spectroscopy and polarization made to improve the corrosion resistance properties of methods. Polarization data indicated that AHA was an copper using effective organic inhibitors with aromatic anodic inhibitor. The maximum inhibition efficiency rings, and electronegative functional groups involving the reached 93.5% in the case of assembly 3 h in 10 mM AHA heteroatoms of sulfur, nitrogen and oxygen, which may solution. The adsorption of AHA on the copper surface fits adsorb at the copper surface to form inhibitive coatings Langmuir adsorption isotherm. Surface-enhanced Raman [9–15]. scattering together with quantum chemical studies Unfortunately, among them, some are toxic and demonstrated that N–O and C=O groups were attached to expensive. In recent years, various types of nontoxic the copper surface, predicting the feasible adsorption cen- organic compounds have been investigated to meet the ters and confirming the relationship between the molecular recommendation using eco-friendly inhibitors as substi- structures of AHA and its inhibition property. tutes for restricted toxic inhibitors [16–21]. Some hydrox- amic acids and their derivatives with biological activities, Keywords Acetohydroxamic acid  EIS  Polarization  such as anti-inflammatory and anti-asthmatic, are used as SERS  Anodic inhibitor pesticides and plant growth promoters [22]. In addition, hydroxamic acids could chelate with metal ions to form complexes [23, 24]. Thus, hydroxamic acid derivatives Introduction have already been reported as effective corrosion inhibitors for carbon steel and copper corrosion [25–27]. AHA as a potential corrosion inhibitor could form a protection film Highly electrical and thermal conductivities, as well as good mechanical workability of copper and its alloys on the copper surface due to multiple adsorption centers of enable them to have a diverse range of applications in a nitrogen atom and two oxygen atoms in its structure (see pipelines for domestic and industrial water systems, ship- Scheme 1). So far, the adsorption behavior of AHA on building, seawater desalination and heat exchanger [1–5]. copper surface as well as its corrosion inhibition efficiency has not been observed in detail. In this work, AHA was adsorbed on copper surface by & Ye Ying self-assembled monolayers (SAMs) technique and the yingye@shnu.edu.cn efficiency against corrosion in 3 wt% NaCl solution was & Hai-Feng Yang estimated by electrochemical impedance spectroscopy haifengyang@yahoo.com (EIS) and polarization methods. SERS technique as a powerful tool to provide molecular fingerprint information The Education Ministry Key Lab of Resource Chemistry, was used to elucidate formation mechanism of AHA Department of Chemistry, Shanghai Normal University, coating on the copper surface as well as Langmuir Shanghai 200234, People’s Republic of China 123 286 Int J Ind Chem (2017) 8:285–296 integration time and 39 repeats. The line of silicon posi- -1 tioned at 519 cm was used for spectral calibration. The electrochemical measurements were carried out using CHI 750C electrochemistry workstation (CH Instruments, Inc.). Pretreatment for electrode The copper electrode was constructed from polycrystalline copper (99.999%) rod inside of a Teflon sheath, and the exposure area of surface was 0.0314 cm . Before the Raman spectroscopic and electrochemical measurements, the copper electrode was sequentially abraded with 500- and 1000-grit papers, followed by 0.3 lm alumina powders to get a shiny mirror-like electrode surface, and then cleaned with Milli-Q water and pure ethanol in an ultra- sonic bath to remove any remaining alumina particles and possible rust. For SERS detection, to obtain the necessary roughness of the copper surface, copper surface was first treated in 2 M H SO solution using an oxidation–reduc- 2 4 tion cycle (ORC) process in the potential range from -0.55 to 0.45 V (vs. SCE) with scan rate at 0.02 V/s and 10 sweep segments and final potential was applied at -0.55 V Scheme 1 Optimized structure of acetohydroxamic acid (vs. SCE) for 60 s [28]. In a conventional three-electrode cell, the AHA-modified copper electrode (or bare copper adsorption isotherm measurement. Furthermore, quantum specimen) and a platinum electrode were used as working chemical studies were used to predict the feasible adsorp- electrode and the counter electrode, respectively. All tion centers and confirm the relationship between the potentials referred to in this paper are reported relative to molecular structures of AHA and its inhibition property. the saturated calomel electrode (SCE), which was used as reference electrode. Experimental Coating the copper surface with AHA Materials and chemicals The cleaned copper electrodes were immersed immediately into the deoxygenated AHA solutions with various con- Acetohydroxamic acid (AHA) was purchased from Sigma- centrations. The assembly time effect on the formation of Aldrich. Analytical grade NaCl was dissolved in ultrapure AHA film at the Cu surface was also considered. Before water (18 MX cm) to prepare 3 wt% NaCl corrosion spectroscopic and electrochemical experiments, the AHA media. Sulfuric acid and ethanol were analytical reagents, solution was removed and the electrode surface with AHA purchased from Sinopharm Chemical Reagents Company. film was rinsed using Milli-Q water, and then dried by flowing nitrogen gas. Apparatus Electrochemical measurements Raman spectroscopic measurement was conducted using LabRam II confocal Laser Raman system (Dilor, France). The impedance spectra were performed in a three-electrode A 1024 9 800 pixels charge-coupled device detector cell starting from open circuit potential (OCP) with the AC cooled by semiconductor was used, and the excitation voltage amplitude of 5 mV (vs. SCE) in the frequency source was a He–Ne laser at 632.8 nm with power of ca. 5 range from 0.01 Hz to 100 kHz. The impedance results mW. The slit and pinhole were controlled at 100 and were simulated with a compatible electronic equivalent 1000 lm, respectively. The laser was focused onto the circuit fitting. The electrochemical polarization curves copper surface through a long-working-length of 509 were obtained from -0.1 V (vs. SCE) to -0.3 V (vs. SCE) -1 objective. Each Raman spectrum was taken with 8 s with a scan rate of 1 mV s . 123 Int J Ind Chem (2017) 8:285–296 287 a 2000 a 1800 1800 17.38 mHz 17.38 mHz 30. 9 mHz 30. 9 mHz 210.5 mHz 210. 5 mHz 976.6 mHz 976.6 mHz 800 1.758 kHz a bare a bare b 1 mM 1.758 kHz b 1 h c 5 mM 600 c 3 h d 10 mM d 5 h e 50 mM e 8 h 200 e Simulated Simulated 0 500 1000 1500 2000 2500 3000 3500 4000 2 0 500 1000 1500 2000 2500 3000 3500 4000 Zre /Ω cm Z /Ω cm re 4.0 4.0 3.5 3.5 bare 3.0 1 mM bare 3.0 5 mM 1 h 2.5 10 mM 3 h 2.5 5 h 50 mM 2.0 8 h 2.0 1.5 1.5 1.0 1.0 0.5 0.5 0.0 0.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 log f (Hz) log f (Hz) bare bare 1 mM 1 h 5 mM 3 h 10 mM 5 h 50 mM 8 h -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 log f (Hz) log f (Hz) Fig. 2 Nyquist (a), Bode (b) and phase angle (c) plots of copper Fig. 1 Nyquist (a), bode (b) and phase angle (c) plots of copper electrodes in the absence and presence of film formed in 10 mM electrodes with acetohydroxamic acid films formed in different acetohydroxamic acid solution for different time, recorded in 3 wt% concentrations of acetohydroxamic acid solutions, acquired in 3 wt% NaCl solution NaCl solution Phase (degree) log|Z|(Ω cm ) -Z /Ω cm im -Z /Ω cm im log|Z|(Ω Phase (degree) 288 Int J Ind Chem (2017) 8:285–296 observed using GaussView 5.0. The SERS bands of AHA molecule were tentatively assigned according to the com- putation result obtained using B3LYP/Lanl2DZ method on the basis of AHA-Cu mode. Additionally, the calculations of the frequencies have been scaled by a factor of 0.9940 for B3LYP/6-31G(d) level and a uniform scaling factor of 0.9762 for B3LYP/LanL2DZ method. Results and discussion EIS spectra Electrochemical impedance spectroscopy for studying the inhibitor against corrosion does not result in any destruc- tion of the film state on the electrode surface [29]. Nyquist plots along with bode and phase angle plots for the copper electrodes with AHA films formed in various AHA concentration solutions and under different assembly time corroded in 3 wt% NaCl solutions are shown in Figs. 1 and 2. The shape of the Nyquist plot for bare copper electrode is different from those of AHA-modified elec- trodes. The latter ones are composed of a high-frequency imperfect semicircle and a straight line seen as Warburg Fig. 3 The electrical equivalent circuit models for impedance data of impedance in the low frequency [30]. copper electrode without film (a) with AHA film (b) Clearly, the Warburg impedance for copper is connected with the diffusion of many oxide species due to lacking Theory computation details protection film [31]. In Fig. 1a, compared with that of bare copper electrode, semicircle diameters of the electrodes The geometry optimization of AHA molecule and its with AHA increase visibly and it reaches a maximum when Raman spectral calculation were performed at the density functional theory (DFT) based on B3LYP/6-31G(d) level the film was formed in 10 mM AHA solution. It means that formed in an optimized assembly concentration of AHA using Gaussian 03 package and the vibrations were Table 1 Electrochemical parameters calculated from EIS measurements for copper electrodes without the AHA films, in 3 wt% NaCl solution C E R (X cm ) Q R Q R R W g (%) AHA OCP s f f dl ct p 2 2 2 (mM) (V vs. SCE) (X cm ) (X cm ) (X cm ) -3 -4 Y 9 10 n Y 9 10 n Y 0 1 0 2 0 -1 -2 n1 -1 -2 n2 -1 -2 0.5 (X cm s ) (X cm s ) (X cm n ) Bare -0.193 1.45 5.37 0.565 227 1.08 0.858 4.84 232 0.0109 – Table 2 Electrochemical parameters calculated from EIS measurements for copper electrodes with the AHA films formed in different con- centrations of AHA solutions, in 3 wt% NaCl solution C E (V vs. R C R Q R R W g AHA OCP s f f dl ct p 2 -2 2 2 2 (mM) SCE) (X cm ) (lFcm ) (X cm ) (X cm ) (X cm ) (%) -4 -3 Y 9 10 nY 9 10 0 0 -1 -2 n -1 -2 0.5 (X cm S ) (X cm S ) 1 -0.200 1.59 7.61 24.5 5.93 0.515 764 789 5.92 70.7 5 -0.225 1.62 7.24 39.0 1.77 0.611 1638 1677 2.83 86.2 10 -0.236 1.72 6.31 54.7 2.46 0.540 3489 3544 1.68 93.5 20 -0.224 1.64 8.31 32.4 3.81 0.536 1996 2028 2.21 88.6 40 -0.225 1.62 6.48 29.0 3.05 0.485 1457 1486 4.00 84.4 50 -0.230 1.62 8.07 16.2 4.36 0.536 2789 2805 2.16 91.7 123 Int J Ind Chem (2017) 8:285–296 289 Table 3 Electrochemical impedance parameters for copper electrodes in 3 wt% NaCl solution, in the absence and presence of film formed in 10 mM AHA solution for different time Time E (V vs. R C R Q R R W g OCP s f f dl ct p 2 -2 2 2 2 (h) SCE) (X cm ) (lFcm ) (X cm ) (X cm ) (X cm ) (%) -4 -3 Y 9 10 nY 9 10 0 0 -1 -2 n -1 -2 0.5 (X cm S ) (X cm S ) 1 -0.212 1.62 5.98 26.6 2.44 0.576 1586 1613 4.18 85.6 3 -0.236 1.72 6.31 54.7 2.46 0.540 3489 3544 1.68 93.5 5 -0.222 1.61 7.68 20.9 3.66 0.569 2008 2029 3.30 88.6 8 -0.251 1.05 13.7 0.111 5.02 0.655 1270 1270 5.39 81.8 -2.0 -2.0 -2.5 -2.5 -3.0 -3.0 -3.5 -3.5 -4.0 -4.0 -4.5 -4.5 -5.0 -5.0 a bare -5.5 -5.5 a bare b 1 mM c 5 mM b 1 h -6.0 a -6.0 c d d 10 mM c 3 h -6.5 e 50 mM d 5 h -6.5 e 8 h -7.0 -7.0 -7.5 -7.5 -0.30 -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 -0.30 -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 E (V vs. SCE) E(V vs. SCE) Fig. 4 Anodic and cathodic polarization curves of the copper without Fig. 5 Anodic and cathodic polarization curves for copper electrodes and with AHA film formed at different concentrations for 3 h: a bare, without and with AHA films formed in 10 mM AHA solution for b 1 mM, c 5 mM, d 10 mM, e 50 mM, in 3 wt% NaCl solution different time: a bare, b 1h, c 3h, d 5h, e 8 h in 3 wt% NaCl solution solution, molecular adsorption layer on the copper surface is compact for enhancing corrosion protection [32]. Simi- evaluating the least error for each parameter routinely less larly, the Z value of the bode plot (Fig. 1b) and phase than 10% and the Chi-square values (v ) less than mod -3 angle value from phase angle plot (Fig. 1c) for the film- 1 9 10 . modified electrodes formed in 10 mM AHA solution are In Fig. 3a, the equivalent circuit model of highest, indicating a superior protection performance. In R(Q(RW))(QR) is fitting the Nyquist plot of the bare Fig. 2a, semicircle diameter of the electrode with AHA copper while R(C(R(Q(RW)))) equivalent circuit in Fig. 3b formed in 10 mM AHA solution for 3 h assembly time is for the AHA-modified copper. comes to the greatest value; the same results have been R is the solution resistance, and R , the charge transfer s ct observed in the bode plots (Fig. 2b) and phase angle plots resistance is attributed to the corrosion reaction at the (Fig. 2c). If the assembly time is less than 3 h, the AHA electrode/solution interface [33]. R represents the resis- layer adsorbed on the electrode might not be dense enough tance of the film formed on the copper surface, and W while more than 3 h, accumulation of AHA molecules indicates the Warburg impedance. Q and Q are defined as dl f occurs on the surface, which also affects the compact constant phase elements (CPE), representing film capaci- structure of film and hinders inhibition of copper corrosion. tance and a modified double-layer capacitance [34], The equivalent circuit models for analyzing impedance described by the following equation [35]: characteristics of electrodes with and without AHA are 1 n Z ¼ Y ðÞ jx ð1Þ CPE displayed in Fig. 3. Such equivalent circuit models were selected, considering the possible adsorption fashion and where Y is the modulus, j is the imaginary root, x is the the film structure of AHA at the copper surface as well as angular frequency and n is the phase (-1 B n B? 1). -2 Log ( i / A cm ) -2 Log( i / A cm ) 290 Int J Ind Chem (2017) 8:285–296 Table 4 Corrosion parameters obtained from potentiodynamic polarization curves for copper surface without and with AHA film formed in different concentrations of AHA solutions for 3 h assembly time, in 3 wt% NaCl solutions -2 -1 -1 C (mM) E (V vs. SCE) i (uA cm ) b (V dec ) b (V dec ) g (%) AHA corr corr c a Bare -0.241 78.89 4.323 12.84 _ 1 -0.201 17.25 6.748 18.21 78.13 5 -0.206 13.29 6.712 17.61 83.15 10 -0.199 10.13 9.460 19.61 87.16 50 -0.197 11.12 8.770 18.91 85.90 Table 5 Polarization parameters for the copper without and with AHA film formed in 10 mM AHA solution for different time, in 3 wt% NaCl solution -2 -1 -1 Time (h) E (V vs. SCE) i (uA cm ) b (v dec ) b (v dec ) g (%) corr corr c a Bare -0.241 78.89 4.323 12.84 – 1 -0.218 13.2 4.207 17.81 83.27 3 -0.199 10.13 9.460 19.61 87.16 5 -0.216 12.2 5.454 17.61 84.54 8 -0.220 17.09 3.055 17.71 78.34 Table 6 Comparison of the inhibition efficiencies of different copper inhibitors Inhibitor Concentration (mM) Medium g (%) References AHA 10 3 wt% NaCl 93.5 This work DMTD 10 0.5 M HCl 84.3 Qin et al. [40] PU 10 1 M NaCl 76.0 Scendo [41] MPTT 20 0.5 M NaCl 94.4 Chen et al. [42] BBTD 1 3 wt% NaCl 87.6 Zhang et al. [5] AAP 10 3 wt% NaCl 90.6 Song et al. [30] Relying on the different values of n, CPE may be induc- Observation from the three Tables reveals that the R tance (n =-1, Q = L), resistance (n = 0, Q = R), War- values for the AHA-modified copper electrodes increase burg impedance (n = 0.5, Q = W) or capacitance (n = 1, visibly and the W values tend to decrease obviously com- Q = C). pared to the bare copper electrode. Under the above-men- Electrochemical parameters calculated from EIS mea- tioned optimized condition, R reaches the maximum surements for copper electrodes without and with AHA value, W reaches the minimum value and the maximum films are listed in Table 1 (bare copper), Table 2 (with inhibition efficiency reaches 93.5%. The RSD (relative films formed in different AHA concentrations solutions) standard deviation) of the inhibition efficiencies calculated and Table 3 (with films under different assembly time). from electrochemical impedance parameters for three All the n values are over 0.5, indicating the relatively copper electrodes with film is 0.13%. In all, impedance low corrosion of the electrode [36]. The inhibition effi- data suggest that the AHA monolayer has a remarkable ciency (g%) is described in the following equation [37]: protection behavior for copper. R  R gð%Þ¼ 100 ð2Þ Polarization measurements R refers the polarization resistance of the bare copper, Polarization curves of the electrodes with different AHA and R is the polarization resistance of the AHA-modified concentrations and different assembly time recorded in electrode (R is the sum of R and R )[38]. 3 wt% NaCl solutions are given in Figs. 4 and 5, p ct f 123 Int J Ind Chem (2017) 8:285–296 291 Fig. 6 Micrographs of copper surfaces with AHA film formed in 10 mM AHA solution for 3 h assembly time (a), and with AHA film formed in same condition as a and exposed to 3 wt% NaCl for 5 h (corrosion time) at 298 K (b). Bare copper before (c) and after (d) exposed to 3 wt% NaCl for 5 h (corrosion time) at 298 K respectively. The reaction of the cathodic oxygen reduction the best uniform and compact film of AHA at the copper is depicted as follows: surface just formed under optimal concentration and assembly time. O þ 4e þ 2H O ! 4OH ð3Þ 2 2 The comparison of this work with other inhibitors, such Also, in the presence of Cl , the anodic dissolution as 4-amino-antipyrine (AAP) [30], as well as 2,5-dimer- process of copper consists of the following steps (the capto-1,3,4-thiadiazole (DMTD) [40], bis-(1-benzotria- - - ionization of copper with Cl and the diffusion of CuCl zolymethylene)-(2,5-thiadiazoly)-disulfide (BBTD) [5], to the bulk solution) [39]: purine (PU) [41], 5-Mercapto-3-phenyl-1,3,4-thiadiazole- 2-thione potassium (MPTT) [42], is listed in Table 6.By Cu þ Cl ! CuCl þ e ð4Þ contrast, it can be seen that the AHA is an effective cor- CuCl þ Cl ! CuCl ð5Þ rosion inhibitor for copper in 3 wt% NaCl. 2þ CuCl ! Cu þ 2Cl þ e ð6Þ Microscopic analysis The related electrochemical parameters obtained from the polarization curves, such as cathodic and anodic Tafel Figure 6 shows the surface morphologies of AHA-modified slopes (b and b ), corrosion potential (E ), corrosion c a corr copper and bare copper electrode corroded in 3 wt% NaCl current density (i ) and the inhibition efficiency (g%), are corr solutions for 5 h. In Fig. 6d, after 5 h immersion in high- given in Tables 4 and 5. E and i were estimated by corr corr salt media, the porous structure and rough surface of the the method of Tafel extrapolation. bare copper indicate serious corrosion occurrence while the It can be seen from Figs. 4 and 5 that the Tafel slopes corrosion behavior of the AHA-modified copper surface is greatly change after the addition of AHA. Besides, current less severe under the same condition (see Fig. 6b). The densities shift to lower values obviously at the same above observation confirms that AHA is an effective potential, compared with the bare electrode. Additionally, inhibitor for copper corrosion, acquired from electro- corrosion potential shifts to the positive direction signifi- chemical measurement. cantly, indicating that AHA has more pronounced influence in the anodic dissolution process of copper with respect to the cathodic oxygen reduction. It might point out that in Adsorption isotherm Fig. 4 the plot c (5 mM) looks tricky in comparison with others. We repeated the each experiment more than 59 and For further shedding insight on adsorption mechanism of the results were quite similar. A possible reason was that inhibitor interaction with the copper surface, many 123 292 Int J Ind Chem (2017) 8:285–296 (y = 1.06463x ? 0.2659), with the linear correlation coefficient R = 0.9999, and its nearly unit slope confirms that the adsorption of AHA on the copper surface fits Langmuir adsorption isotherm. Additionally, adsorption isotherm drawn from potentiodynamic polarization results in Table 4 is also given in Fig. 7b. A plot of c/h against c shows a straight line (y = 1.16282x ? 0.0452), with the linear correlation coefficient R = 0.9999. In addition, the standard free energy of adsorption, DG , is obtained from the following equation [46]: ads DG ¼RT lnðÞ 55:5K ð8Þ ads ads -1 -1 where R is the general gas constant (8.314 J mol K ), the temperature in Kelvin (298.15 K) is the absolute tem- 0 -1 perature, and the value of 55.5 mol L is the concentra- 0 5 10 15 20 25 30 35 40 45 50 55 tion of water in pure solution. The calculated K values ads C / (mM) 3 -1 4 -1 are 3.76 9 10 M and 2.21 9 10 M , based on EIS b 60 and potentiodynamic polarization results, respectively. The -1 relevant DG is -30.4 kJ mol (EIS results) or ads 50 -1 -34.8 kJ mol (potentiodynamic polarization results). 45 0 The large negative value of DG indicates that AHA was ads strongly adsorbed on the copper surface [47, 48]. Raman studies Figure 8a, b illustrates the normal Raman spectrum of AHA powder and SERS spectrum of the AHA-modified copper electrode formed in 10 mM AHA solution for 3 h assembly time, respectively. Table 7 shows density func- tional theory (DFT) calculation results for Raman and 0 SERS analysis. The corresponding assignments for Raman 0 5 10 15 20 25 30 35 40 45 50 spectral analysis were performed on the basis of B3LYP/6- C / (mM) 31G(d) calculation. Also, to assign SERS spectrum of Fig. 7 Langmuir adsorption isotherm plot for AHA film formed AHA, DFT calculation for geometry optimization and under the optimized condition at the copper surface in 3 wt% NaCl vibration modes based on B3LYP/LanL2DZ was per- solution at 298 K according to a EIS results and b potentiodynamic polarization results formed with model AHA-Cu [49]. The optimized geom- etry model AHA-Cu can be seen in Fig. 9. It should be mentioned that in inset of Fig. 8 with adsorption modes such as the Langmuir, Temkin and -1 spectral range from 200 to 750 cm , the Raman bands Frumkin isotherms could be investigated [43]. Therefore, -1 around 528 and 618 cm are from the oxide species of the surface coverage (h) for different concentrations of copper, indicating that the oxide layers were inevitably AHA modification film was calculated from EIS parame- generated in ORC pretreatment process for SERS activity ters in Table 1ðÞ gðÞ % = 100h . of copper [50]. It is found that the adsorption of AHA on the copper Combined with the calculation results in Table 7,we surface can be described by Langmuir adsorption isotherm can better understand the vibrational modes in Fig. 8a, b. In equation [44, 45]: -1 Fig. 8a, the Raman peaks at 967 and 989 cm represent c 1 = + c ð7Þ N–O–H bending in plane and C–H bending in plane. The h K ads stretching vibration modes of N–O,C–C,C=O and C–H -1 where K is the equilibrium constant, h is the degree of appear at 1088, 1366, 1619 and 2998 cm . The asym- ads surface coverage on the metal surface and c is the AHA metric stretching vibration mode of C–H appears at -1 -1 concentration. According to EIS experimental results, a 2941 cm . The Raman peaks at 1390 cm represent OH plot of c/h against c (Fig. 7a) showed a straight line bending and C-N bending out of plane. C/ θ (mM) C/ θ (mM) Int J Ind Chem (2017) 8:285–296 293 Fig. 8 a Normal Raman spectrum of AHA in powder, b SERS spectrum of AHA film at the copper electrode formed in 10 mM AHA solution for 3 h assembly time, inset showing the SERS spectrum -1 (200–750 cm ) of the oxide layers Table 7 Assignment for Raman vibrational modes of AHA and SERS vibrational modes of AHA-Cu based on DFT calculation -1 -1 -1 -1 Raman (cm ) Calculated Raman (cm ) Approximate assignment SERS (cm ) Calculated SERS (cm ) Approximate assignment (B3LYP/6-31G(d)) (AHA-Cu ) s ip.bend str. 967 957 N–O–H 940 C–N–H s ip.bend m ip.bend 989 1011 C–H 1011 1011 C–H op.bend m op.bend 1022 C–H 1035 1020 C–H w str. s str. 1088 1096 N-O 1088 1085 N–O str. 1122 O–H bend m bend 1286 N–H 1305 1309 N–H s deformation 1327 1355 CH m str. 1366 1371 C–C m bend bend 1390 1410 OH 1410 OH op.bend op.bend C–N C–N str. m str. bend 1507 C–N 1495 1503 C–N N–H m str. s str. 1619 1667 C=O 1600 1627 C=O s as.str. str. 2941 2945 C–H 2967 O–H m str. deformation 2998 3019 C–H 3066 CH -1 Wavenumber is given in cm w weak, m medium, s strong, as asymmetric, str. stretching, ip in plane, op out plane, bend bending -1 In Fig. 8b, the peaks at 1011 and 1035 cm represent intensities. The proposed adsorption model of AHA at the C–H bending in plane and C–H bending out of plane. The copper surface is shown in Fig. 10. -1 bands with medium intensities at 1305 and 1495 cm could be assigned to N–H bending and C-N stretching, Quantum chemistry calculations -1 while the strong bands at 1088 and 1600 cm are from N– O stretching and C=O stretching. According to the surface As mentioned in SERS spectrum analysis, AHA molecule selection rule for SERS [51, 52] and the SERS mechanism may adsorb at the copper surface by transferring electrons [53, 54], the enhanced bands in the SERS spectrum might from the N–O and C=O groups to the unfilled hybrid orbital correspond to either the vibrational moieties attached to the of copper; quantum chemical calculations are used to predict surface or the vibration direction perpendicular to the metal the feasible adsorption centers of a free single molecule on surface; in contrast, the intensities of vibrational modes the bare metal surface to confirm the relationship between with parallel polarized components to the surface will be the AHA molecular structures and its inhibition property. In decreased. Thus, the N–O and C=O groups might be per- addition, note that all the calculated parameters obtained in pendicular to the surface, due to their high SERS the gas phase and the solvent effects were ignored. 123 294 Int J Ind Chem (2017) 8:285–296 Table 8 Quantum chemical parameter comparison of some mole- cules in literature with the AHA molecule calculated with DFT method -1 E E DE (kJ mol ) l LUMO HOMO -1 -1 (kJ mol ) (kJ mol ) (Debye) AHA -175.9 -427.6 251.8 5.413 MPTT -0.072 -0.186 0.114 9.834 AAP -0.505 -5.296 4.791 4.257 The geometry of the AHA is fully optimized based on the method of B3LYP/LANI2DZ. The illustration of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is given in Fig. 11. The quantum chemical parameters, such as E E , HOMO, LUMO dipole moment, l, the energy gap, DE (DE = E - - LUMO Fig. 9 The geometry model of AHA-Cu optimized by B3LYP/ E ), are listed in Table 8. 4 HOMO LANI2DZ method Clearly in Table 8, the high value of E HOMO -1 (E =-427.64 kJ mol ) indicates the strong ability HOMO of AHA molecule donating electrons to form covalent bond with unoccupied d-orbitals of metal [55], while the low -1 value of E (E =-175.86 kJ mol ) indicates LUMO LUMO that the AHA molecule has a tendency to accept electrons from d-orbitals of metal to form back-donating bond. The values of the high dipole moment (l = 5.4125 D) and the -1 low energy gap (DE = 251.78 kJ mol ) facilitate adsorption to the copper surface and, therefore, enhance the inhibition efficiency [56], which is in good agreement with the experimental results. It can be found in Fig. 11 that the HOMO is located within the region around the N–O and C=O groups, which could be regarded as the feasible sites for interaction with the copper surface. Additionally, the nitrogen atom and two oxygen atoms have large electron densities and their Mulliken atomic charges are -0.302, -0.357 and -0.363, respectively. Thus, AHA can adsorb on the copper surface by donating the electrons from the two O atoms to the d-orbitals of copper. Fig. 10 The proposed adsorption model of AHA on the copper surface Fig. 11 Molecular orbital plots for acetohydroxamic acid 123 Int J Ind Chem (2017) 8:285–296 295 7. Tian HW, Cheng YF, Li WH, Hou BR (2015) Triazolyl-acyl- Conclusions hydrazone derivatives as novel inhibitors for copper corrosion in chloride solutions. Corros Sci 100:341–352 Consequently, the above investigations confirm that the 8. 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Electrochem Acta 53:5953–5960 of copper corrosion in 0.5 M NaCl solution by modification of http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Industrial Chemistry Springer Journals

Acetohydroxamic acid adsorbed at copper surface: electrochemical, Raman and theoretical observations

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Abstract

Int J Ind Chem (2017) 8:285–296 DOI 10.1007/s40090-017-0111-6 RESEARCH Acetohydroxamic acid adsorbed at copper surface: electrochemical, Raman and theoretical observations 1 1 1 1 1 • • • • • Juan Du Ye Ying Xiao-yu Guo Chuan-chuan Li Yiping Wu 1 1 Ying Wen Hai-Feng Yang Received: 14 June 2016 / Accepted: 11 January 2017 / Published online: 4 February 2017 The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Corrosion inhibition effect of AHA film formed However, copper and its alloys suffer serious corrosion in on the copper surface by self-assembled monolayers tech- chloride environments, causing huge economy losses nique was estimated in 3 wt% NaCl solution by electro- [6–8]. Thus, a considerable amount of efforts have been chemical impedance spectroscopy and polarization made to improve the corrosion resistance properties of methods. Polarization data indicated that AHA was an copper using effective organic inhibitors with aromatic anodic inhibitor. The maximum inhibition efficiency rings, and electronegative functional groups involving the reached 93.5% in the case of assembly 3 h in 10 mM AHA heteroatoms of sulfur, nitrogen and oxygen, which may solution. The adsorption of AHA on the copper surface fits adsorb at the copper surface to form inhibitive coatings Langmuir adsorption isotherm. Surface-enhanced Raman [9–15]. scattering together with quantum chemical studies Unfortunately, among them, some are toxic and demonstrated that N–O and C=O groups were attached to expensive. In recent years, various types of nontoxic the copper surface, predicting the feasible adsorption cen- organic compounds have been investigated to meet the ters and confirming the relationship between the molecular recommendation using eco-friendly inhibitors as substi- structures of AHA and its inhibition property. tutes for restricted toxic inhibitors [16–21]. Some hydrox- amic acids and their derivatives with biological activities, Keywords Acetohydroxamic acid  EIS  Polarization  such as anti-inflammatory and anti-asthmatic, are used as SERS  Anodic inhibitor pesticides and plant growth promoters [22]. In addition, hydroxamic acids could chelate with metal ions to form complexes [23, 24]. Thus, hydroxamic acid derivatives Introduction have already been reported as effective corrosion inhibitors for carbon steel and copper corrosion [25–27]. AHA as a potential corrosion inhibitor could form a protection film Highly electrical and thermal conductivities, as well as good mechanical workability of copper and its alloys on the copper surface due to multiple adsorption centers of enable them to have a diverse range of applications in a nitrogen atom and two oxygen atoms in its structure (see pipelines for domestic and industrial water systems, ship- Scheme 1). So far, the adsorption behavior of AHA on building, seawater desalination and heat exchanger [1–5]. copper surface as well as its corrosion inhibition efficiency has not been observed in detail. In this work, AHA was adsorbed on copper surface by & Ye Ying self-assembled monolayers (SAMs) technique and the yingye@shnu.edu.cn efficiency against corrosion in 3 wt% NaCl solution was & Hai-Feng Yang estimated by electrochemical impedance spectroscopy haifengyang@yahoo.com (EIS) and polarization methods. SERS technique as a powerful tool to provide molecular fingerprint information The Education Ministry Key Lab of Resource Chemistry, was used to elucidate formation mechanism of AHA Department of Chemistry, Shanghai Normal University, coating on the copper surface as well as Langmuir Shanghai 200234, People’s Republic of China 123 286 Int J Ind Chem (2017) 8:285–296 integration time and 39 repeats. The line of silicon posi- -1 tioned at 519 cm was used for spectral calibration. The electrochemical measurements were carried out using CHI 750C electrochemistry workstation (CH Instruments, Inc.). Pretreatment for electrode The copper electrode was constructed from polycrystalline copper (99.999%) rod inside of a Teflon sheath, and the exposure area of surface was 0.0314 cm . Before the Raman spectroscopic and electrochemical measurements, the copper electrode was sequentially abraded with 500- and 1000-grit papers, followed by 0.3 lm alumina powders to get a shiny mirror-like electrode surface, and then cleaned with Milli-Q water and pure ethanol in an ultra- sonic bath to remove any remaining alumina particles and possible rust. For SERS detection, to obtain the necessary roughness of the copper surface, copper surface was first treated in 2 M H SO solution using an oxidation–reduc- 2 4 tion cycle (ORC) process in the potential range from -0.55 to 0.45 V (vs. SCE) with scan rate at 0.02 V/s and 10 sweep segments and final potential was applied at -0.55 V Scheme 1 Optimized structure of acetohydroxamic acid (vs. SCE) for 60 s [28]. In a conventional three-electrode cell, the AHA-modified copper electrode (or bare copper adsorption isotherm measurement. Furthermore, quantum specimen) and a platinum electrode were used as working chemical studies were used to predict the feasible adsorp- electrode and the counter electrode, respectively. All tion centers and confirm the relationship between the potentials referred to in this paper are reported relative to molecular structures of AHA and its inhibition property. the saturated calomel electrode (SCE), which was used as reference electrode. Experimental Coating the copper surface with AHA Materials and chemicals The cleaned copper electrodes were immersed immediately into the deoxygenated AHA solutions with various con- Acetohydroxamic acid (AHA) was purchased from Sigma- centrations. The assembly time effect on the formation of Aldrich. Analytical grade NaCl was dissolved in ultrapure AHA film at the Cu surface was also considered. Before water (18 MX cm) to prepare 3 wt% NaCl corrosion spectroscopic and electrochemical experiments, the AHA media. Sulfuric acid and ethanol were analytical reagents, solution was removed and the electrode surface with AHA purchased from Sinopharm Chemical Reagents Company. film was rinsed using Milli-Q water, and then dried by flowing nitrogen gas. Apparatus Electrochemical measurements Raman spectroscopic measurement was conducted using LabRam II confocal Laser Raman system (Dilor, France). The impedance spectra were performed in a three-electrode A 1024 9 800 pixels charge-coupled device detector cell starting from open circuit potential (OCP) with the AC cooled by semiconductor was used, and the excitation voltage amplitude of 5 mV (vs. SCE) in the frequency source was a He–Ne laser at 632.8 nm with power of ca. 5 range from 0.01 Hz to 100 kHz. The impedance results mW. The slit and pinhole were controlled at 100 and were simulated with a compatible electronic equivalent 1000 lm, respectively. The laser was focused onto the circuit fitting. The electrochemical polarization curves copper surface through a long-working-length of 509 were obtained from -0.1 V (vs. SCE) to -0.3 V (vs. SCE) -1 objective. Each Raman spectrum was taken with 8 s with a scan rate of 1 mV s . 123 Int J Ind Chem (2017) 8:285–296 287 a 2000 a 1800 1800 17.38 mHz 17.38 mHz 30. 9 mHz 30. 9 mHz 210.5 mHz 210. 5 mHz 976.6 mHz 976.6 mHz 800 1.758 kHz a bare a bare b 1 mM 1.758 kHz b 1 h c 5 mM 600 c 3 h d 10 mM d 5 h e 50 mM e 8 h 200 e Simulated Simulated 0 500 1000 1500 2000 2500 3000 3500 4000 2 0 500 1000 1500 2000 2500 3000 3500 4000 Zre /Ω cm Z /Ω cm re 4.0 4.0 3.5 3.5 bare 3.0 1 mM bare 3.0 5 mM 1 h 2.5 10 mM 3 h 2.5 5 h 50 mM 2.0 8 h 2.0 1.5 1.5 1.0 1.0 0.5 0.5 0.0 0.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 log f (Hz) log f (Hz) bare bare 1 mM 1 h 5 mM 3 h 10 mM 5 h 50 mM 8 h -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 log f (Hz) log f (Hz) Fig. 2 Nyquist (a), Bode (b) and phase angle (c) plots of copper Fig. 1 Nyquist (a), bode (b) and phase angle (c) plots of copper electrodes in the absence and presence of film formed in 10 mM electrodes with acetohydroxamic acid films formed in different acetohydroxamic acid solution for different time, recorded in 3 wt% concentrations of acetohydroxamic acid solutions, acquired in 3 wt% NaCl solution NaCl solution Phase (degree) log|Z|(Ω cm ) -Z /Ω cm im -Z /Ω cm im log|Z|(Ω Phase (degree) 288 Int J Ind Chem (2017) 8:285–296 observed using GaussView 5.0. The SERS bands of AHA molecule were tentatively assigned according to the com- putation result obtained using B3LYP/Lanl2DZ method on the basis of AHA-Cu mode. Additionally, the calculations of the frequencies have been scaled by a factor of 0.9940 for B3LYP/6-31G(d) level and a uniform scaling factor of 0.9762 for B3LYP/LanL2DZ method. Results and discussion EIS spectra Electrochemical impedance spectroscopy for studying the inhibitor against corrosion does not result in any destruc- tion of the film state on the electrode surface [29]. Nyquist plots along with bode and phase angle plots for the copper electrodes with AHA films formed in various AHA concentration solutions and under different assembly time corroded in 3 wt% NaCl solutions are shown in Figs. 1 and 2. The shape of the Nyquist plot for bare copper electrode is different from those of AHA-modified elec- trodes. The latter ones are composed of a high-frequency imperfect semicircle and a straight line seen as Warburg Fig. 3 The electrical equivalent circuit models for impedance data of impedance in the low frequency [30]. copper electrode without film (a) with AHA film (b) Clearly, the Warburg impedance for copper is connected with the diffusion of many oxide species due to lacking Theory computation details protection film [31]. In Fig. 1a, compared with that of bare copper electrode, semicircle diameters of the electrodes The geometry optimization of AHA molecule and its with AHA increase visibly and it reaches a maximum when Raman spectral calculation were performed at the density functional theory (DFT) based on B3LYP/6-31G(d) level the film was formed in 10 mM AHA solution. It means that formed in an optimized assembly concentration of AHA using Gaussian 03 package and the vibrations were Table 1 Electrochemical parameters calculated from EIS measurements for copper electrodes without the AHA films, in 3 wt% NaCl solution C E R (X cm ) Q R Q R R W g (%) AHA OCP s f f dl ct p 2 2 2 (mM) (V vs. SCE) (X cm ) (X cm ) (X cm ) -3 -4 Y 9 10 n Y 9 10 n Y 0 1 0 2 0 -1 -2 n1 -1 -2 n2 -1 -2 0.5 (X cm s ) (X cm s ) (X cm n ) Bare -0.193 1.45 5.37 0.565 227 1.08 0.858 4.84 232 0.0109 – Table 2 Electrochemical parameters calculated from EIS measurements for copper electrodes with the AHA films formed in different con- centrations of AHA solutions, in 3 wt% NaCl solution C E (V vs. R C R Q R R W g AHA OCP s f f dl ct p 2 -2 2 2 2 (mM) SCE) (X cm ) (lFcm ) (X cm ) (X cm ) (X cm ) (%) -4 -3 Y 9 10 nY 9 10 0 0 -1 -2 n -1 -2 0.5 (X cm S ) (X cm S ) 1 -0.200 1.59 7.61 24.5 5.93 0.515 764 789 5.92 70.7 5 -0.225 1.62 7.24 39.0 1.77 0.611 1638 1677 2.83 86.2 10 -0.236 1.72 6.31 54.7 2.46 0.540 3489 3544 1.68 93.5 20 -0.224 1.64 8.31 32.4 3.81 0.536 1996 2028 2.21 88.6 40 -0.225 1.62 6.48 29.0 3.05 0.485 1457 1486 4.00 84.4 50 -0.230 1.62 8.07 16.2 4.36 0.536 2789 2805 2.16 91.7 123 Int J Ind Chem (2017) 8:285–296 289 Table 3 Electrochemical impedance parameters for copper electrodes in 3 wt% NaCl solution, in the absence and presence of film formed in 10 mM AHA solution for different time Time E (V vs. R C R Q R R W g OCP s f f dl ct p 2 -2 2 2 2 (h) SCE) (X cm ) (lFcm ) (X cm ) (X cm ) (X cm ) (%) -4 -3 Y 9 10 nY 9 10 0 0 -1 -2 n -1 -2 0.5 (X cm S ) (X cm S ) 1 -0.212 1.62 5.98 26.6 2.44 0.576 1586 1613 4.18 85.6 3 -0.236 1.72 6.31 54.7 2.46 0.540 3489 3544 1.68 93.5 5 -0.222 1.61 7.68 20.9 3.66 0.569 2008 2029 3.30 88.6 8 -0.251 1.05 13.7 0.111 5.02 0.655 1270 1270 5.39 81.8 -2.0 -2.0 -2.5 -2.5 -3.0 -3.0 -3.5 -3.5 -4.0 -4.0 -4.5 -4.5 -5.0 -5.0 a bare -5.5 -5.5 a bare b 1 mM c 5 mM b 1 h -6.0 a -6.0 c d d 10 mM c 3 h -6.5 e 50 mM d 5 h -6.5 e 8 h -7.0 -7.0 -7.5 -7.5 -0.30 -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 -0.30 -0.28 -0.26 -0.24 -0.22 -0.20 -0.18 -0.16 -0.14 -0.12 -0.10 E (V vs. SCE) E(V vs. SCE) Fig. 4 Anodic and cathodic polarization curves of the copper without Fig. 5 Anodic and cathodic polarization curves for copper electrodes and with AHA film formed at different concentrations for 3 h: a bare, without and with AHA films formed in 10 mM AHA solution for b 1 mM, c 5 mM, d 10 mM, e 50 mM, in 3 wt% NaCl solution different time: a bare, b 1h, c 3h, d 5h, e 8 h in 3 wt% NaCl solution solution, molecular adsorption layer on the copper surface is compact for enhancing corrosion protection [32]. Simi- evaluating the least error for each parameter routinely less larly, the Z value of the bode plot (Fig. 1b) and phase than 10% and the Chi-square values (v ) less than mod -3 angle value from phase angle plot (Fig. 1c) for the film- 1 9 10 . modified electrodes formed in 10 mM AHA solution are In Fig. 3a, the equivalent circuit model of highest, indicating a superior protection performance. In R(Q(RW))(QR) is fitting the Nyquist plot of the bare Fig. 2a, semicircle diameter of the electrode with AHA copper while R(C(R(Q(RW)))) equivalent circuit in Fig. 3b formed in 10 mM AHA solution for 3 h assembly time is for the AHA-modified copper. comes to the greatest value; the same results have been R is the solution resistance, and R , the charge transfer s ct observed in the bode plots (Fig. 2b) and phase angle plots resistance is attributed to the corrosion reaction at the (Fig. 2c). If the assembly time is less than 3 h, the AHA electrode/solution interface [33]. R represents the resis- layer adsorbed on the electrode might not be dense enough tance of the film formed on the copper surface, and W while more than 3 h, accumulation of AHA molecules indicates the Warburg impedance. Q and Q are defined as dl f occurs on the surface, which also affects the compact constant phase elements (CPE), representing film capaci- structure of film and hinders inhibition of copper corrosion. tance and a modified double-layer capacitance [34], The equivalent circuit models for analyzing impedance described by the following equation [35]: characteristics of electrodes with and without AHA are 1 n Z ¼ Y ðÞ jx ð1Þ CPE displayed in Fig. 3. Such equivalent circuit models were selected, considering the possible adsorption fashion and where Y is the modulus, j is the imaginary root, x is the the film structure of AHA at the copper surface as well as angular frequency and n is the phase (-1 B n B? 1). -2 Log ( i / A cm ) -2 Log( i / A cm ) 290 Int J Ind Chem (2017) 8:285–296 Table 4 Corrosion parameters obtained from potentiodynamic polarization curves for copper surface without and with AHA film formed in different concentrations of AHA solutions for 3 h assembly time, in 3 wt% NaCl solutions -2 -1 -1 C (mM) E (V vs. SCE) i (uA cm ) b (V dec ) b (V dec ) g (%) AHA corr corr c a Bare -0.241 78.89 4.323 12.84 _ 1 -0.201 17.25 6.748 18.21 78.13 5 -0.206 13.29 6.712 17.61 83.15 10 -0.199 10.13 9.460 19.61 87.16 50 -0.197 11.12 8.770 18.91 85.90 Table 5 Polarization parameters for the copper without and with AHA film formed in 10 mM AHA solution for different time, in 3 wt% NaCl solution -2 -1 -1 Time (h) E (V vs. SCE) i (uA cm ) b (v dec ) b (v dec ) g (%) corr corr c a Bare -0.241 78.89 4.323 12.84 – 1 -0.218 13.2 4.207 17.81 83.27 3 -0.199 10.13 9.460 19.61 87.16 5 -0.216 12.2 5.454 17.61 84.54 8 -0.220 17.09 3.055 17.71 78.34 Table 6 Comparison of the inhibition efficiencies of different copper inhibitors Inhibitor Concentration (mM) Medium g (%) References AHA 10 3 wt% NaCl 93.5 This work DMTD 10 0.5 M HCl 84.3 Qin et al. [40] PU 10 1 M NaCl 76.0 Scendo [41] MPTT 20 0.5 M NaCl 94.4 Chen et al. [42] BBTD 1 3 wt% NaCl 87.6 Zhang et al. [5] AAP 10 3 wt% NaCl 90.6 Song et al. [30] Relying on the different values of n, CPE may be induc- Observation from the three Tables reveals that the R tance (n =-1, Q = L), resistance (n = 0, Q = R), War- values for the AHA-modified copper electrodes increase burg impedance (n = 0.5, Q = W) or capacitance (n = 1, visibly and the W values tend to decrease obviously com- Q = C). pared to the bare copper electrode. Under the above-men- Electrochemical parameters calculated from EIS mea- tioned optimized condition, R reaches the maximum surements for copper electrodes without and with AHA value, W reaches the minimum value and the maximum films are listed in Table 1 (bare copper), Table 2 (with inhibition efficiency reaches 93.5%. The RSD (relative films formed in different AHA concentrations solutions) standard deviation) of the inhibition efficiencies calculated and Table 3 (with films under different assembly time). from electrochemical impedance parameters for three All the n values are over 0.5, indicating the relatively copper electrodes with film is 0.13%. In all, impedance low corrosion of the electrode [36]. The inhibition effi- data suggest that the AHA monolayer has a remarkable ciency (g%) is described in the following equation [37]: protection behavior for copper. R  R gð%Þ¼ 100 ð2Þ Polarization measurements R refers the polarization resistance of the bare copper, Polarization curves of the electrodes with different AHA and R is the polarization resistance of the AHA-modified concentrations and different assembly time recorded in electrode (R is the sum of R and R )[38]. 3 wt% NaCl solutions are given in Figs. 4 and 5, p ct f 123 Int J Ind Chem (2017) 8:285–296 291 Fig. 6 Micrographs of copper surfaces with AHA film formed in 10 mM AHA solution for 3 h assembly time (a), and with AHA film formed in same condition as a and exposed to 3 wt% NaCl for 5 h (corrosion time) at 298 K (b). Bare copper before (c) and after (d) exposed to 3 wt% NaCl for 5 h (corrosion time) at 298 K respectively. The reaction of the cathodic oxygen reduction the best uniform and compact film of AHA at the copper is depicted as follows: surface just formed under optimal concentration and assembly time. O þ 4e þ 2H O ! 4OH ð3Þ 2 2 The comparison of this work with other inhibitors, such Also, in the presence of Cl , the anodic dissolution as 4-amino-antipyrine (AAP) [30], as well as 2,5-dimer- process of copper consists of the following steps (the capto-1,3,4-thiadiazole (DMTD) [40], bis-(1-benzotria- - - ionization of copper with Cl and the diffusion of CuCl zolymethylene)-(2,5-thiadiazoly)-disulfide (BBTD) [5], to the bulk solution) [39]: purine (PU) [41], 5-Mercapto-3-phenyl-1,3,4-thiadiazole- 2-thione potassium (MPTT) [42], is listed in Table 6.By Cu þ Cl ! CuCl þ e ð4Þ contrast, it can be seen that the AHA is an effective cor- CuCl þ Cl ! CuCl ð5Þ rosion inhibitor for copper in 3 wt% NaCl. 2þ CuCl ! Cu þ 2Cl þ e ð6Þ Microscopic analysis The related electrochemical parameters obtained from the polarization curves, such as cathodic and anodic Tafel Figure 6 shows the surface morphologies of AHA-modified slopes (b and b ), corrosion potential (E ), corrosion c a corr copper and bare copper electrode corroded in 3 wt% NaCl current density (i ) and the inhibition efficiency (g%), are corr solutions for 5 h. In Fig. 6d, after 5 h immersion in high- given in Tables 4 and 5. E and i were estimated by corr corr salt media, the porous structure and rough surface of the the method of Tafel extrapolation. bare copper indicate serious corrosion occurrence while the It can be seen from Figs. 4 and 5 that the Tafel slopes corrosion behavior of the AHA-modified copper surface is greatly change after the addition of AHA. Besides, current less severe under the same condition (see Fig. 6b). The densities shift to lower values obviously at the same above observation confirms that AHA is an effective potential, compared with the bare electrode. Additionally, inhibitor for copper corrosion, acquired from electro- corrosion potential shifts to the positive direction signifi- chemical measurement. cantly, indicating that AHA has more pronounced influence in the anodic dissolution process of copper with respect to the cathodic oxygen reduction. It might point out that in Adsorption isotherm Fig. 4 the plot c (5 mM) looks tricky in comparison with others. We repeated the each experiment more than 59 and For further shedding insight on adsorption mechanism of the results were quite similar. A possible reason was that inhibitor interaction with the copper surface, many 123 292 Int J Ind Chem (2017) 8:285–296 (y = 1.06463x ? 0.2659), with the linear correlation coefficient R = 0.9999, and its nearly unit slope confirms that the adsorption of AHA on the copper surface fits Langmuir adsorption isotherm. Additionally, adsorption isotherm drawn from potentiodynamic polarization results in Table 4 is also given in Fig. 7b. A plot of c/h against c shows a straight line (y = 1.16282x ? 0.0452), with the linear correlation coefficient R = 0.9999. In addition, the standard free energy of adsorption, DG , is obtained from the following equation [46]: ads DG ¼RT lnðÞ 55:5K ð8Þ ads ads -1 -1 where R is the general gas constant (8.314 J mol K ), the temperature in Kelvin (298.15 K) is the absolute tem- 0 -1 perature, and the value of 55.5 mol L is the concentra- 0 5 10 15 20 25 30 35 40 45 50 55 tion of water in pure solution. The calculated K values ads C / (mM) 3 -1 4 -1 are 3.76 9 10 M and 2.21 9 10 M , based on EIS b 60 and potentiodynamic polarization results, respectively. The -1 relevant DG is -30.4 kJ mol (EIS results) or ads 50 -1 -34.8 kJ mol (potentiodynamic polarization results). 45 0 The large negative value of DG indicates that AHA was ads strongly adsorbed on the copper surface [47, 48]. Raman studies Figure 8a, b illustrates the normal Raman spectrum of AHA powder and SERS spectrum of the AHA-modified copper electrode formed in 10 mM AHA solution for 3 h assembly time, respectively. Table 7 shows density func- tional theory (DFT) calculation results for Raman and 0 SERS analysis. The corresponding assignments for Raman 0 5 10 15 20 25 30 35 40 45 50 spectral analysis were performed on the basis of B3LYP/6- C / (mM) 31G(d) calculation. Also, to assign SERS spectrum of Fig. 7 Langmuir adsorption isotherm plot for AHA film formed AHA, DFT calculation for geometry optimization and under the optimized condition at the copper surface in 3 wt% NaCl vibration modes based on B3LYP/LanL2DZ was per- solution at 298 K according to a EIS results and b potentiodynamic polarization results formed with model AHA-Cu [49]. The optimized geom- etry model AHA-Cu can be seen in Fig. 9. It should be mentioned that in inset of Fig. 8 with adsorption modes such as the Langmuir, Temkin and -1 spectral range from 200 to 750 cm , the Raman bands Frumkin isotherms could be investigated [43]. Therefore, -1 around 528 and 618 cm are from the oxide species of the surface coverage (h) for different concentrations of copper, indicating that the oxide layers were inevitably AHA modification film was calculated from EIS parame- generated in ORC pretreatment process for SERS activity ters in Table 1ðÞ gðÞ % = 100h . of copper [50]. It is found that the adsorption of AHA on the copper Combined with the calculation results in Table 7,we surface can be described by Langmuir adsorption isotherm can better understand the vibrational modes in Fig. 8a, b. In equation [44, 45]: -1 Fig. 8a, the Raman peaks at 967 and 989 cm represent c 1 = + c ð7Þ N–O–H bending in plane and C–H bending in plane. The h K ads stretching vibration modes of N–O,C–C,C=O and C–H -1 where K is the equilibrium constant, h is the degree of appear at 1088, 1366, 1619 and 2998 cm . The asym- ads surface coverage on the metal surface and c is the AHA metric stretching vibration mode of C–H appears at -1 -1 concentration. According to EIS experimental results, a 2941 cm . The Raman peaks at 1390 cm represent OH plot of c/h against c (Fig. 7a) showed a straight line bending and C-N bending out of plane. C/ θ (mM) C/ θ (mM) Int J Ind Chem (2017) 8:285–296 293 Fig. 8 a Normal Raman spectrum of AHA in powder, b SERS spectrum of AHA film at the copper electrode formed in 10 mM AHA solution for 3 h assembly time, inset showing the SERS spectrum -1 (200–750 cm ) of the oxide layers Table 7 Assignment for Raman vibrational modes of AHA and SERS vibrational modes of AHA-Cu based on DFT calculation -1 -1 -1 -1 Raman (cm ) Calculated Raman (cm ) Approximate assignment SERS (cm ) Calculated SERS (cm ) Approximate assignment (B3LYP/6-31G(d)) (AHA-Cu ) s ip.bend str. 967 957 N–O–H 940 C–N–H s ip.bend m ip.bend 989 1011 C–H 1011 1011 C–H op.bend m op.bend 1022 C–H 1035 1020 C–H w str. s str. 1088 1096 N-O 1088 1085 N–O str. 1122 O–H bend m bend 1286 N–H 1305 1309 N–H s deformation 1327 1355 CH m str. 1366 1371 C–C m bend bend 1390 1410 OH 1410 OH op.bend op.bend C–N C–N str. m str. bend 1507 C–N 1495 1503 C–N N–H m str. s str. 1619 1667 C=O 1600 1627 C=O s as.str. str. 2941 2945 C–H 2967 O–H m str. deformation 2998 3019 C–H 3066 CH -1 Wavenumber is given in cm w weak, m medium, s strong, as asymmetric, str. stretching, ip in plane, op out plane, bend bending -1 In Fig. 8b, the peaks at 1011 and 1035 cm represent intensities. The proposed adsorption model of AHA at the C–H bending in plane and C–H bending out of plane. The copper surface is shown in Fig. 10. -1 bands with medium intensities at 1305 and 1495 cm could be assigned to N–H bending and C-N stretching, Quantum chemistry calculations -1 while the strong bands at 1088 and 1600 cm are from N– O stretching and C=O stretching. According to the surface As mentioned in SERS spectrum analysis, AHA molecule selection rule for SERS [51, 52] and the SERS mechanism may adsorb at the copper surface by transferring electrons [53, 54], the enhanced bands in the SERS spectrum might from the N–O and C=O groups to the unfilled hybrid orbital correspond to either the vibrational moieties attached to the of copper; quantum chemical calculations are used to predict surface or the vibration direction perpendicular to the metal the feasible adsorption centers of a free single molecule on surface; in contrast, the intensities of vibrational modes the bare metal surface to confirm the relationship between with parallel polarized components to the surface will be the AHA molecular structures and its inhibition property. In decreased. Thus, the N–O and C=O groups might be per- addition, note that all the calculated parameters obtained in pendicular to the surface, due to their high SERS the gas phase and the solvent effects were ignored. 123 294 Int J Ind Chem (2017) 8:285–296 Table 8 Quantum chemical parameter comparison of some mole- cules in literature with the AHA molecule calculated with DFT method -1 E E DE (kJ mol ) l LUMO HOMO -1 -1 (kJ mol ) (kJ mol ) (Debye) AHA -175.9 -427.6 251.8 5.413 MPTT -0.072 -0.186 0.114 9.834 AAP -0.505 -5.296 4.791 4.257 The geometry of the AHA is fully optimized based on the method of B3LYP/LANI2DZ. The illustration of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is given in Fig. 11. The quantum chemical parameters, such as E E , HOMO, LUMO dipole moment, l, the energy gap, DE (DE = E - - LUMO Fig. 9 The geometry model of AHA-Cu optimized by B3LYP/ E ), are listed in Table 8. 4 HOMO LANI2DZ method Clearly in Table 8, the high value of E HOMO -1 (E =-427.64 kJ mol ) indicates the strong ability HOMO of AHA molecule donating electrons to form covalent bond with unoccupied d-orbitals of metal [55], while the low -1 value of E (E =-175.86 kJ mol ) indicates LUMO LUMO that the AHA molecule has a tendency to accept electrons from d-orbitals of metal to form back-donating bond. The values of the high dipole moment (l = 5.4125 D) and the -1 low energy gap (DE = 251.78 kJ mol ) facilitate adsorption to the copper surface and, therefore, enhance the inhibition efficiency [56], which is in good agreement with the experimental results. It can be found in Fig. 11 that the HOMO is located within the region around the N–O and C=O groups, which could be regarded as the feasible sites for interaction with the copper surface. Additionally, the nitrogen atom and two oxygen atoms have large electron densities and their Mulliken atomic charges are -0.302, -0.357 and -0.363, respectively. Thus, AHA can adsorb on the copper surface by donating the electrons from the two O atoms to the d-orbitals of copper. Fig. 10 The proposed adsorption model of AHA on the copper surface Fig. 11 Molecular orbital plots for acetohydroxamic acid 123 Int J Ind Chem (2017) 8:285–296 295 7. Tian HW, Cheng YF, Li WH, Hou BR (2015) Triazolyl-acyl- Conclusions hydrazone derivatives as novel inhibitors for copper corrosion in chloride solutions. Corros Sci 100:341–352 Consequently, the above investigations confirm that the 8. 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Electrochem Acta 53:5953–5960 of copper corrosion in 0.5 M NaCl solution by modification of

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International Journal of Industrial ChemistrySpringer Journals

Published: Feb 4, 2017

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