Article pubs.acs.org/IECR
Synthesis, Characterization, and Electrochemical Studies of Novel Biphenyl Based Compounds R. Baskar,† M. Gopiraman,‡,§ D. Kesavan,§ Ick Soo Kim,‡ and K. Subramanian*,† †
Department of Chemistry, Anna University, Chennai, India Nano Fusion Technology Research Group, Department of Functional Machinery and Mechanics, Faculty of Textile Science and Technology, Shinshu University, Nagano 386-8567, Japan § Department of Chemistry, National Institute of Technology, Tiruchirappalli, India ‡
ABSTRACT: (2E)-1-(Biphenyl-4-yl)-3-(4-nitrophenyl)prop-2-en-1-one (BNO), (2E)-3-(4-aminophenyl)-1-(biphenyl-4-yl) prop-2-en-1-one (BNH), and (2E)-1-(biphenyl-4-yl)-3-(4-hydroxyphenyl)prop-2-en-1-one (BOH) were synthesized and characterized by FT-NMR, FT-IR, and elemental analysis. The synthesized compounds were investigated for corrosion inhibition of mild steel in hydrochloric acid medium by means of weight loss measurements, polarization studies, electrochemical impedance spectra, and the adsorption isotherm. Among the biphenyl chalcone derivatives, BOH showed higher efficiency against corrosion of mild steel. All the inhibitors were predominantly found to be cathodic in nature. The thermodynamic parameter values of the free energy of adsorption (ΔGads) reveals that inhibitor was adsorbed on the mild steel surface and the adsorption mechanism of inhibition was supported by FT-IR, surface analysis (SEM-EDS), and adsorption isotherms.
1. INTRODUCTION A corrosion inhibitor is a substance that effectively suppresses or reduces the rate of corrosion upon its addition to the destructive environment of a metal. The corrosion of mild steel in acid solutions can be inhibited by a variety of substances, particularly those containing elements such as nitrogen, phosphorus, oxygen, and sulfur. Organic compounds containing the above-mentioned elements along with multiple bonds are demonstrated as effective inhibitors of corrosion on metals in acidic environment.1−4 The compounds containing α,β-unsaturated keto groups had been reported as effective inhibitors against acid corrosion of metals.5−10 The surface of the metal is degraded during the process of corrosion, which greatly influences the subsequent behavior of the metallic material. These modifications also affect the electrochemical response of the material when it is subjected to voltage or current perturbation during electrochemical monitoring, for example. In the present study we introduce biphenyl chalcones (see Figure 1) as a new class of inhibitors, to prevent corrosion on mild steel in aqueous acidic conditions. The synthesized chalcones were confirmed through 1 H NMR, 13C NMR, and Fourier transform infrared (FT-IR) spectra. The present investigation also deals with the electrochemical studies of corrosion inhibition of mild steel in aqueous hydrochloric acid solution along with weight loss measurements and the adsorption isotherm.
Figure 1. General structure of inhibitor (R = OH, NO2, and NH2).
Prior to all measurements, the steel samples (Mn, 0.340%, C; 0.100%; Cr, 0.220%; Fe, 99.34) are abraded with a series of emery papers from 400 to 1200 grade. The specimens are washed thoroughly with double distilled water, degreased with acetone, and air-dried. The solutions are prepared by the dilution of analytical grade 37% HCl with double distilled water in the absence and presence of inhibitors in the concentration range from 100 to 400 ppm. 2.2. Synthesis. 2.2.1. Synthesis of (2E)-1-(Biphenyl-4-yl)3-(4-nitrophenyl)prop-2-en-1-one (BNO). A solution of 1 mol of 4-acetylbiphenyl and 1 mol of sodium hydroxide in methanol was constantly stirred at room temperature. One mole of 4-nitrobenzaldehyde was dissolved in the required amount of methanol; it was slowly added with constantly stirred solution and the stirring was allowed for 4 h. After the reaction mixture was neutralized with dilute HCl solution and an extract was taken with ethyl acetate, the organic layer was washed with a brine solution and dried over anhydrous sodium sulfate. Volatiles were removed through vacuum and purified by column chromatography. The compound was obtained as a pale yellow solid. Yield: 87%. mp: 234 °C. 1H NMR (500 MHz,
2. EXPERIMENTAL SECTION 2.1. Materials and Methods. Biphenyl, 4-hydroxybenzaldehyde, acetyl chloride, aluminum trichloride, nitrobenzene, potassium hydroxide, stannous chloride, and 4-nitrobenzaldehyde were purchased from Merck and used without further purification. Solvents were purified and dried according to standard procedure. © 2012 American Chemical Society
Received: Revised: Accepted: Published: 3966
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CDCl3) δ ppm 7.45 (t, J = 7.95 Hz, 1H), 7.52 (t, J = 7.95 Hz, 2H), 7.68 (d, J = 7.95 Hz, 2H), 7.72 (d, J = 19.95 Hz, 1H), 7.78 (d, J = 9.01 Hz, 2H), 7.84 (d, J = 9.01 Hz, 2H), 7.88 (d, J = 15.9 Hz, 1H), 8.15 (d, J = 7.95 Hz, 1H), 8.32 (d, J = 9.01 Hz, 2H). 13C NMR (126 MHz, CDCl3) δ ppm 124.24, 125.70, 127.31, 127.47, 128.41, 129.03, 129.23, 136.23, 139.73, 141.11, 141.42, 146.15, 148.59, 189.04. IR (KBr, cm−1) 1345, 1520, 1601, 1659, 2852, 2925, 3079. Anal. Calcd for C21H15NO3 (MW 329.34): C, 76.58; H, 4.59; N, 4.25; O, 14.57. Found: C, 76.52; H, 4.63; N, 4.24; O, 14.58. 2.2.2. Synthesis of (2E)-3-(4-Aminophenyl)-1-(biphenyl-4yl)prop-2-en-1-one (BNH). One mole of nitrochalcone and 5 mol of stannous chloride in methanol were refluxed at 60 °C under a nitrogen atmosphere. After 1 h the reaction mixture was neutralized with sodium bicarbonate solution and extracted with ethyl acetate. The organic layer was washed with a brine solution and dried over anhydrous sodium sulfate. Volatiles were removed through vacuum and purified by column chromatography. The compound was obtained as a brown solid. Yield: 85%. mp: 216 °C. 1H NMR (500 MHz, CDCl3) δ ppm 6.69 (d, J = 7.42 Hz, 2H), 7.42 (t, J = 7.92 Hz, 1H), 7.44 (d, J = 15.02 Hz, 1H), 7.50 (t, J = 7.28 Hz, 2H), 7.53 (d, J = 7.32 Hz, 2H), 7.68 (d, J = 7.28 Hz, 2H), 7.74 (d, J = 8.74 Hz, 2H), 7.82 (d, J = 15.52 Hz, 1H), 8.11 (d, J = 8.73 Hz, 2H). 13C NMR (126 MHz, CDCl3) δ ppm 114.88, 117.94, 125.22, 127.20, 127.29, 128.09, 128.12, 128.99, 130.57, 135.57, 140.10, 145.09, 145.44, 149.29, 190.25. IR (KBr, cm−1) 1602, 1642, 2853, 2924, 3030, 3435. Anal. Calcd for C21H17NO (MW 299.36): C, 84.25; H, 5.72; N, 4.68; O, 5.34. Found: C, 84.21; H, 5.68; N, 4.73; O, 13.17. 2.2.3. Synthesis of (2E)-1-(Biphenyl-4-yl)-3-(4hydroxyphenyl)prop-2-en-1-one (BOH). Inhibitor (BOH) was prepared as described in the literature.11 4-Acetylbiphenyl (10.2 mmol) was added (30 mL) with potassium hydroxide (0.0408 mol) in methanol. To the above reaction mixture, 4-hydroxybenzaldehyde (10.2 mmol) in 10 mL of methanol was added dropwise with constant stirring at 60 °C. The reaction mixture was refluxed for 24 h; it was then neutralized with dilute hydrochloric acid and extracted using ethyl acetate. The organic layer was washed with brine solution and dried over anhydrous sodium sulfate. Volatiles were removed through vacuum and purified by column chromatography. The compound obtained as a yellow solid. Yield: 72%. mp: 203 °C.
H NMR (500 MHz, CDCl3) δ ppm 6.92 (d, J = 8.50 Hz, 2H), 7.41 (t, J = 7.25 Hz, 1H), 7.48 (t, J = 7.57 Hz, 2H), 7.54 (d, J = 15.76 Hz, 1H) 7.64 (d, J = 7.26 Hz, 2H), 7.67−7.71 (d, J = 8.51 Hz, 2H), 7.73 (d, J = 8.51 Hz, 2H), 7.79−7.87 (d, J = 15.45 Hz, 1H), 8.10 (d, J = 8.51 Hz, 2H). 13C NMR (126 MHz, CDCl3) δ ppm 116.33, 119.04, 127.38, 127.47, 128.79, 129.56, 131.30, 131.50, 137.30. 139.49, 144.69, 144.93, 160.65, 188.93. IR (KBr, cm−1) 1511, 1602, 1638, 2847, 2936, 3026, 3223. Anal. Calcd for C21H16O2 (MW 300.35): C, 83.98; H, 5.37; O, 10.65. Found: C, 83.94; H, 5.44; O, 10.61. 2.3. Weight Loss Measurements. The weight loss experiment was performed at 300 ± 2 K with different concentrations of inhibitors. The optimized immersion time is 2 h. Each time a fresh specimen was treated with 100 mL of fresh acid solution, the experiments were repeated in triplicate to have reproducibility. The inhibition efficiency (IE, %) was calculated using the following equation:
Figure 2. Equivalent circuit model for electrochemical impedance measurements.
Figure 3. Variation of inhibition efficiency with different inhibitors (BNH, BOH, and BNO) concentrations.
1
IE (%) =
W0 − W ·100 W0
(1)
where W0 and W are the weight losses of the mild steel in the absence and presence of inhibitor, respectively. The inhibition efficiency values of inhibitors in all methods were used to calculate the surface coverage (θ) of the inhibitor on the steel surface according to the following equation: θ = IE (%)/100
(2)
where IE is the inhibition efficiency of an inhibitor. 2.4. Electrochemical Techniques. CH electrochemical analyzer Model 604B was used to record Tafel polarization curves. A Pt electrode and saturated calomel electrode (SCE)
Table 1. Surface Coverage and Inhibition Efficiency for Various Concentrations of Inhibitors for the Corrosion of Mild Steel in 1.0 M HCl BNH
a
BOH
BNO
inhibitor concn (ppm)
IE (%)
σa
θ
σb
IE (%)
σa
θ
σb
IE (%)
σa
θ
σb
0 100 200 300 400
− 84.6 87.1 90.1 92.9
− 0.11 0.09 0.06 0.06
− 0.846 0.871 0.901 0.929
− 0.09 0.05 0.10 0.08
− 86.6 88.1 93.8 94.6
− 0.06 0.12 0.04 0.07
− 0.866 0.881 0.938 0.946
− 0.02 0.01 0.01 0.02
− 70.7 82.6 86.8 88.1
− 0.03 0.02 0.05 0.04
− 0.707 0.826 0.868 0.881
− 0.01 0.06 0.01 0.06
Standard deviation (σ) calculated for IE for different concentrations of inhibitors. bStandard deviation (σ) for surface coverage (θ). 3967
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Figure 4. Tafel curves of mild steel in the presence and absence of inhibitors (a) BNH, (b) BOH, and (c) BNO.
Table 2. Polarization Parameters for Mild Steel in 1.0 M HCl Containing Different Concentrations of Inhibitors inhibitor BNH
BOH
BNO
inhibitor concn (ppm)
Icorr (μA cm−2)
Ecorr (mV vs SCE)
0 (blank) 100 200 300 400 100 200 300 400 100 200 300 400
3936 518 441 359 244 503 435 201 171 1105 679 501 402
−0.481 −0.525 −0.529 −0.516 −0.523 −0.513 −0.524 −0.553 −0.520 −0.531 −0.535 −0.533 −0.523
bc (mV/ ba (mV/ decade) decade) 42.36 41.69 58.56 49.85 47.98 49.52 54.98 56.25 44.25 55.89 60.23 49.62 55.36
48.85 42.55 59.97 49.91 49.87 50.14 55.25 58.45 44.89 56.52 62.15 50.65 57.45
Table 3. Impedance Parameters for Mild Steel in 1.0 M HCl Containing Different Concentrations of Inhibitors
IE (%) − 86.84 88.79 90.87 93.80 87.22 88.95 94.89 95.66 71.92 82.74 87.26 89.77
inhibitor
inhibitor concn (ppm)
Rct (Ω cm2)
Cdl (μF cm2)
IE (%)
BNH
0 (blank) 100 200 300 400 100 200 300 400 100 200 300 400
14.19 103.56 123.98 150.93 230.19 109.99 141.23 255.68 290.51 50.02 82.44 110.00 141.89
280.54 38.44 25.69 17.58 8.19 36.19 11.27 6.92 4.77 159.17 64.38 36.19 20.40
− 86.30 88.55 90.60 93.84 87.09 88.95 94.45 95.12 71.63 82.79 87.10 89.99
BOH
BNO
rate of 0.5 mV s−1. Inhibition efficiency (IE %) values were calculated from Icorr as follows:12
were used as auxiliary and reference electrodes, respectively. The working electrode was in the form of a square cut from mild steel with surface area 1.0 cm × 1.0 cm. Prior to the measurements, the working electrode was polished mechanically, washed with acetone, rinsed several times with double distilled water, and dried. All the tests were performed with a freshly polished electrode in deaerated acid or inhibitor solution under continuous stirring at 300 ± 2 K. The linear Tafel segments of the anodic and cathodic curves were extrapolated to the corrosion potential to obtain the corrosion current densities. The Tafel curves were recorded by a sweep
IE (%) =
I ′corr − Icorr ·100 I ′corr
(3)
where I′corr and Icorr are corrosion current densities in the absence and presence of inhibitor. ac impedance measurements were carried out at the range from 100 kHz to 10 mHz at an amplitude of 10 mV.13 The impedance diagrams are given in Nyquist representation. The electrical equivalent circuit for the system is shown in 3968
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Figure 5. Nyquist plots for mild steel in the presence and absence of inhibitors (a) BNH, (b) BOH, and (c) BNO.
Table 4. Thermodynamic Parameters for Mild Steel in 1.0 M HCl in the Absence and Presence of Inhibitors at Different Concentrations methods EIS
Tafel
weight loss
inhibitor
R2
slope
ΔGads (kJ/ mol)
Kads (kJ/mol)
BOH BNH BNO BOH BNH BNO BOH BNH BNO
0.999 0.999 0.999 0.999 0.999 0.999 0.999 0.999 0.999
1.036 1.020 1.016 1.039 1.002 1.022 1.041 1.015 1.041
−31.18 −31.68 −29.66 −32.05 −31.52 −29.72 −31.99 −31.60 −29.81
6379 5932 2631 6868 5555 2694 6698 5729 2799
Figure 2. Inhibition efficiency values were calculated using eq 4. IE (%) =
R ct − R′ct ·100 R ct
(4)
where Rct and R′ct are charge transfer resistances in the absence and presence of inhibitor. In the given electrical equivalent circuit, Rs is the solution resistance, Rct is the charge transfer resistance, and Cdl is the double layer capacitance. IE was calculated from the charge transfer resistance (Rct) values.14
Figure 6. FT-IR spectra of compounds BNH, BOH, and BNO before and after corrosion. 3969
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Figure 7. Langmuir adsorption isotherm fitted using data from (a) EIS measurements, (b) Tafel plots, and (c) weight loss measurements.
2.5. Physical Measurements. The infrared spectra were recorded on a Perkin-Elmer Spectrum One instrument with a frequency range of 4000−450 cm−1, using the KBr pellet method. NMR spectra were recorded on a BRUKER 500 MHz AVANCE III instrument using CDCl3 as solvent, with TMS as an internal standard. 2.6. SEM and EDS Analysis. Mild steel specimens were immersed in 100 mL of 1.0 M HCl with an inhibitor concentration of 400 ppm for 2 h. After termination of the experiment, the specimens were dried and examined for their surface morphology using a scanning electron microscope (SEM) with energy dispersive spectrometer (EDS), FEI Quanta 200F.
molecules on the surface of the active site of a mild steel specimen is a possible mechanism of inhibition. 3.2. Potentiodynamic Polarization Measurements. Figure 4 shows the cathodic and anodic polarization Tafel plots of mild steel in both the absence and presence of different concentrations of inhibitors. The electrochemical parameters such as corrosion potential (Ecorr), cathodic and anodic Tafel slopes (bc and ba), and corrosion current density (Icorr) were determined by Tafel plots and are listed in Table 2. All the values were calculated as an average of three experiments, and the standard deviations for bc and ba ranged from 0.02 to 0.08 and from 0.04 to 0.10, respectively. From the Tafel curves, it could be observed that the values of the corrosion current density (Icorr) of mild steel were lower in inhibitor-containing solutions than those for the inhibitor-free solutions, which defines the effective inhibition of acid corrosion of mild steel by the chalcone inhibitors. The corrosion current densities in all inhibitor concentrations were found to be decreasing in the following order: BOH > BNH > BNO. As seen from Figure 4, even though there were slight changes in the anodic and cathodic Tafel slopes, ba and bc remain almost unchanged, which indicates that the inhibitory role of these compounds is not through the interference on the reactions of metal dissolution and reduction of protons.13 This indicates that the chalcone derivatives act as adsorptive inhibitors; i.e.,
3. RESULTS AND DISCUSSION 3.1. Effect of Concentration on Inhibition Efficiency. The inhibition efficiencies for different concentrations of inhibitiors are given in Table 1 and Figure 3. It is obvious that increasing inhibitor concentration increases the percent IE. The BNH inhibitor showed ∼93% IE at 400 ppm. For BOH and BNO inhibitors IE was estimated as 95 and 88%, respectively. Among the investigated inhibitors, BOH showed higher efficiency to inhibit corrosion of mild steel and the order of inhibition is as follows: BOH > BNH > BNO. The high surface coverage values suggest that adsorption of inhibitor 3970
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Figure 8. SEM images of (a) polished mild steel specimen, (b) mild steel specimen in 1.0 M HCl, and mild steel specimen in 1.0 M HCl with (c) BNH, (d) BOH, and (e) BNO.
Table 5. EDS Analysis Results of Mild Steel and Mild Steel in 1.0 M Hydrochloric Acid in the Absence and Presence of Inhibitors composition medium mild steel (Figure 9a) mild steel in 1.0 M HCl (Figure 9b) mild steel in 1.0 M HCl with BNH (Figure 9c) BOH (Figure 9d) BNO (Figure 9e)
Fe
O
C
Cl
Mn
Cr
99.34 76.32
− 9.83
0.10 −
− 13.12
0.34 0.32
0.22 0.41
− −
N
82.83 85.43 82.71
5.22 2.09 4.27
9.30 11.78 10.34
0.86 0.08 1.28
1.12 0.51 0.58
0.26 0.11 0.24
0.40 − 0.58
contain a depressed semicircle, with the center below the real X-axis, where the size increased with an increasing inhibitor concentration, indicating that the corrosion is mainly a charge transfer process.15 A loop is also seen at low frequencies which could arise from the adsorbed intermediate products such as (FeCl−)ads in the absence of inhibitor and/or (FeCl−Inh+)ads in the presence of inhibitor,16 for the corrosion of mild steel in 1.0 M HCl solution. The depressed semicircle is the characteristic of solid electrodes and often refers to frequency dispersion, which arises due to the roughness and other inhomogeneities on the surface. It is clear that the impedance response of mild steel is significantly changed after addition of chalcone derivatives. It is noteworthy that the change in the concentration of chalcone derivatives did not alter the style of the impedance curves, suggesting a similar mechanism of inhibition involved. The impedance parameters derived from these plots are given in Table 3.
they reduce anodic dissolution and also retard the hydrogen evolution reaction via blocking of the active reaction sites on the metal surface or can even screen the covered part of the electrode and therefore protect it from the action of the corrosion medium. Additionally, a shift in the values of Ecorr reveals that the inhibitors predominantly affect the cathodic reaction. In this way, it could be expected that the inhibition efficiency (IE) increases with the increasing concentration of inhibitor; the IE valeus obtained from Tafel polarization measurements are in good agreement with weight loss measurements. 3.3. Electrochemical Impedance Spectroscopy (EIS). The effect of inhibitor concentration on the impedance behavior of mild steel is presented in Figure 5. The curves show a typical Nyquist plot for mild steel in the presence of various concentrations of BOH, BNH, and BNO. The values of Rct, Cdl, and IE were determined with standard deviations ranging from 0.02 to 0.11. As seen from Figure 5, Nyquist plots 3971
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Figure 9. EDS spectra of (a) polished mild steel specimen, (b) mild steel specimen in 1.0 M HCl, and mild steel specimen in 1.0 M HCl with (c) BNH, (d) BOH, and (e) BNO.
As seen from Table 3, the Rct values in the presence of inhibitors increased with the concentration. On the other hand, the values of Cdl are decreased with the increase in inhibitor concentration, which could be due to the possible replacement of water molecules by the adsorption of inhibitors on the mild steel surface. This results in the decrease of the local dielectric constant and/or increase in the thickness of the electrical double layer. This suggests that the biphenyl chalcone derivatives act via adsorption at the metal/solution interface.10,12 The inhibition efficiencies calculated from EIS (Table 3)
showed the same trend as those obtained from potentiodynamic polarization plots (Table 2). 3.4. FT-IR Spectra. The FT-IR spectra were recorded for inhibitors and for inhibitors adsorbed on the mild steel surface. In order to prepare the inhibitor adsorbed on the mild steel surface, the mild steel specimens were coated with the inhibitor by immersion in a solution of the inhibitor containing hydrochloric acid for 2 h. Then the specimens were air-dried and the adsorbed surface film was scraped carefully for recording FT-IR spectra.17 For inhibitor BNH the characteristic 3972
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peak of CO stretching at 1743 cm−1 and the NH2 vibrations at 3342 cm−1 were observed. The bending vibration frequency of CC linkages appeared at 1516 cm−1. After the 2 h immersion with 1.0 M HCl, CO and NH2 peaks disappeared; BNH may be bound with the metal surface, protecting it from metal corrosion. In the same manner for compounds BOH and BNO the CO peak had shifted after the immersion with HCl solution. Moreover, in Figure 6, broadening of the O−H band at 3435 cm−1 and the C−O−C band at 1065 cm−1 suggests that the inhibitors make coordination bonds with the metal surface through heteroatoms.18 Significant changes in the regions (C O, O−H, and N−H) are indicated by circles in Figure 6. 3.5. Adsorption Isotherm. The mechanism of corrosion inhibition could be explained on the basis of the adsorption behavior. The degree of surface coverage (θ) for different inhibitor concentrations was calculated from weight loss measurements, polarization studies, and electrochemical impedance spectra. Data were fitted to various isotherms. It was observed that the plot obeys the Langmuir adsorption isotherm. Figure 7 shows the Langmuir isotherm. The values of ΔGads, Kads, and R2 are listed in Table 4. The expected linear relationship was well approximated in the Langmuir isotherm, and the slopes of BNH, BOH, and BNO are shown in Table 4. Since the values of the slope calculated by means of different methods such as weight loss measurements, polarization studies, and electrochemical impedance spectra were very close to each other and were just above unity, it could be concluded that each chalcone unit occupies almost one adsorption site on the mild steel surface. This reveals the perfect molecular design of the synthesized compounds for inhibition of acid corrosion of mild steel. As can be seen from Table 4, the addition of inhibitors causes negative values of ΔGads, which indicates that the adsorption of chalcone inhibitors was a spontaneous process. The values of ΔGads up to −20 kJ mol−1 were consistent with the electrostatic interaction between the charged molecules and the charged metal (physisorption), while those between −80 and −400 kJ mol−1 were associated with chemisorptions as a result of sharing or transfer of electrons from the inhibitor molecules to the metal surface to form a coordinate type of bond. The calculated ΔGads values in the range of −29 to −32 kJ mol−1 indicate that the adsorption mechanism of the chalcone derivatives on mild steel in 1 M HCl was both electrostatic adsorption and chemisorption.19 3.6. SEM and EDS Analysis. Scanning electron microscope images with corresponding energy dispersive spectra were recorded (Figure 8) in order to determine the interaction of inhibitor molecules with the metal surface during the corrosion in the presence and absence of inhibitors. Figure 8a indicates the finely polished characteristic surface of mild steel and shows some scratches which had arisen during polishing, and Figure 8b reveals that the surface was severely corroded due to the aggressive attack by 1.0 M HCl. Figure 8c−e shows scanning electron microscope images of the surface of mild steel specimens immersed for the same period of time interval in 1.0 M HCl solution containing 400 ppm chalcone derivatives BNH, BOH, and BNO, revealing the formation of a protective film by the inhibitors on the mild steel surface which inhibits the corrosion significantly in acidic medium. The scanning electron microscope images in Figure 8c−e also show that the scratches formed during metal polishing were also covered well
by the inhibitors. Hence the chalcone derivatives BNH, BOH, and BNO protect mild steel in 1.0 M HCl solution. Figure 9a and Table 5 represent the EDS spectra of mild steel, which revealed that the surface has no chlorine content due to the absence of 1.0 M HCl solution. However, in the case of mild steel with 1.0 M HCl solution, Figure 9b shows very high chloride content due to aggressive attack of 1.0 M HCl. Figure 9c−e and Table 5 show EDS spectra of the mild steel specimens immersed for the same period of time interval in 1.0 M HCl solution containing 400 ppm inhibitors; these spectra reveal that inhibitors protect mild steel from 1.0 M HCl solution, which indicates a very low chloride content compared to a mild steel coupon in 1.0 M HCl.20 In addition, the nitrogen concentration on the mild steel surface for BNH and BNO inhibitors (Table 5) supports that they cover the mild steel surface effectively. From these results, it is concluded that inhibitors form an adsorbed layer on the mild steel surface by means of coordination and thus retard corrosion.4
4. CONCLUSION Novel biphenyl chalcone derivatives BNH, BOH, and BNO were successfully synthesized and characterized with 1H NMR, 13 C NMR, and FT-IR spectra and elemental analysis. The corrosion inhibition of mild steel in hydrochloric acid medium by these inhibitors was investigated by means of weight loss measurement, electrochemical studies, and the adsorption isotherm. The inhibitors were found to be cathodic in nature. Among the investigated inhibitors, BOH showed higher efficiency against corrosion of mild steel. The IE values calculated from different methods were in good agreement with each other. The Langmuir adsorption isotherm clearly indicates that the chalcone derivatives inhibit predominantly through adsorption on the mild steel surface. Also, it was supported by FT-IR spectroscopy and surface analysis (SEM-EDS).
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: 044-22358660.
ACKNOWLEDGMENTS The authors acknowledge SAIF, IIT-Madras, for the analytical support. We thank Dr. V. Kesavan, Department of Biotechnology, IIT-Madras, for his support in this work. This work was supported in part by a Grant-in-Aid for Global COE program by the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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REFERENCES
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dx.doi.org/10.1021/ie201470j | Ind. Eng. Chem. Res. 2012, 51, 3966−3974
