Ketosulfone Drug as a Green Corrosion Inhibitor for Mild Steel in

Article pubs.acs.org/IECR

Ketosulfone Drug as a Green Corrosion Inhibitor for Mild Steel in Acidic Medium Prasanna B. Matad,† Praveen B. Mokshanatha,*,‡ Narayana Hebbar,§ Venkatarangaiah T. Venkatesha,∥ and Harmesh Chander Tandon⊥ †

Department of Chemistry, Sri Taralabalu Jagadguru Institute of Technology, Ranebennur, Haveri,Karnataka 581115, India Department of Chemistry, Srinivas School of Engineering, Mukka, Mangalore 574146, India § Department of Chemistry, Bearys Institute of Technology, Mangalore 574199, India ∥ Department of Studies in Chemistry, School of Chemical Sciences, Kuvempu University, Shankaraghatta, Karnataka 577451, India ⊥ Department of Chemistry, Sri Venkateswara College, Dhula Kuan, New Delhi 110021, India ‡

ABSTRACT: Ketosulfone has been evaluated as a green corrosion inhibitor for mild steel in 1 M HCl medium by chemical and electrochemical methods. The effect of Ketosulfone on the corrosion rate was determined at various concentrations and temperature. Polarization measurements reveal that Ketosulfone acts as a mixed-type inhibitor. The adsorption of the inhibitor on the mild steel surface in acid solution was found to obey the Langmuir adsorption isotherm. The activation and thermodynamic parameters of dissolution and adsorption were calculated and discussed. Quantum chemical calculations were calculated and discussed, and it supports the results. SEM images of inhibited strips reveal the likely formation of a protective film.

1. INTRODUCTION

electrochemical, quantum chemical calculations, thermodynamic parameters, and activation parameters.

Mild steel is considered as one of the most excellent alloys of iron. It has wide application in industries and structural uses due to its superior mechanical properties. Generally, mild steel undergoes corrosion in processes such as acid pickling, industrial cleaning, acid descaling, oil well acidizing, and petrochemical processes.1,2 During these processes, there is a possibility of the underlying steel coming into contact with acid, which undergoes corrosion leading to loss of metal. Among the alternatives, the use of inhibitors is the most practical and costeffective method to overcome this lacunae. Inhibitors are organic molecules having hetero atoms, such as phosphorus, sulfur, nitrogen, and π electrons, through which inhibitor molecules interact with the metal surface by which adsorption takes place.3−5 Most of these inhibitors are toxic, even though they exhibit good inhibition action. Presently, there is a need for using eco friendly inhibitors and hence there is an emerging interest in the use of green corrosion inhibitors.6 This has led us to consider using drugs as inhibitors.7−11 Torsemide and Furosemide,12 Ciprofloxacin,13 Sulfa drugs,14 Lamotrigine,15 Rhodanine azosulfa drugs,16 and Risperidone17 are reported to be good inhibitors. The efficiency of an inhibitor is decided by the planarity of the molecule.18,19 Thus, drugs having planar structure are effective inhibitors, which influenced us to choose Ketosulfone as a green corrosion inhibitor.20 Ketosulfone is an anti-inflammatory drug. The presence of electron rich nitrogen oxygen, sulfur atoms, and π- bonds in its structure are in favor of its adsorption on the metal surface, which gives scope to its study as a potential corrosion inhibitor. In the present work, the inhibiting action of Ketosulfone for mild steel in 1 M HCl has been done by chemical, © 2014 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials and Methods. Weight loss measurements were carried out using mild steel strips with dimensions of 4 × 1 × 0.1 cm3 and strips with an exposed area of 1 cm2 were used for the electrochemical method. The samples were abraded with emery paper from grade no. 80 up to 1200 and washed thoroughly with double distilled water. The corrosive media is 1 M HCl solution. 2.2. Inhibitor. The compound, Ketosulfone was purchased from Ramdev Chemicals India Pvt. Ltd., Mumbai. The IUPAC name of Ketosulfone is 1-(6-methylpyridine-3-yl)-2 (4methylsulfonyl) phenyl ethanone. The structure of the inhibitor molecule is as shown in Figure 1. It is a white creamy powder with 180−186 °C melting point and easily soluble in HCl.

Figure 1. Ketosulfone structure. Received: Revised: Accepted: Published: 8436

October 22, 2013 April 10, 2014 April 25, 2014 April 25, 2014 dx.doi.org/10.1021/ie500232g | Ind. Eng. Chem. Res. 2014, 53, 8436−8444

Industrial & Engineering Chemistry Research

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2.3. Weight Loss Measurements. Weight loss measurements were carried out by dipping steel strips in a corrosive media (1 M HCl) with different concentrations of inhibitor. Samples were taken out after 4 h of immersion, then these strips were washed with tap water, dried, and weighed accurately (accuracy: ± 0.1 mg). Triplicate experiments were conducted, and an average value was considered for reporting. 2.4. Electrochemical Measurements. The electrochemical measurements were recorded by the CHI608D workstation (CH Instruments) at 303−333 K. The working electrode (steel), counter electrode (platinum), and reference electrode (SCE) were used for the measurements. In Tafel measurements, potential−current curves were recorded at a scan rate of 0.001 V s−1 in the given potential range. Impedance measurements were taken using an AC signal with amplitude of 5 mV at OCP in the frequency range from 100 kHz to 10 mHz. The chronoamperometric experiments were carried out by polarizing the working electrode anodically at −0.41 V (SCE) for 600 s. 2.5. Quantum Chemical Studies. Quantum chemical calculations for Ketosulfone were performed in the gas phase using a Parametric Method 3 (PM3). The energy parameters in the form of the root-mean-square gradient were kept at 0.05 kcal/A mol and a convergence limit at 0.05. These calculations were carried out using the Hyperchem 7.5 package program. 2.6. Adsorption Isotherm and Thermodynamic Parameters. In order to learn about the mode of adsorption of Ketosulfone on the metal surface in 1 M HCl at different temperatures, attempts were made to fit experimental data with several adsorption isotherms. By using these data, thermodynamic parameters were calculated using standard equations. 2.7. Scanning Electron Microscopic (SEM) Studies. The mild steel strip surface morphology was recorded after immersion in 1 M HCl in the absence and presence of Ketosulfone for 4 h using Scanning Electron Microscopy (JEOL JSM-840A model).

Table 1. Results Obtained from Weight Loss Measurements

W° − W × 100 W°

W° − W × 100 ST

inhibition efficiency (ηw)

blank 25 50 75 100 200

0.266 0.057 0.022 0.020 0.015 0.009

78.57 91.72 92.48 94.36 96.61

ηP =

° − icorr icorr ° icorr

× 100 (3)

where, i°corr and icorr are corrosion current in the absence and presence of inhibitor, respectively. Table 2 clearly shows that the corrosion current density (icorr) values decrease in the presence of different concentrations of inhibitor due to the adsorption of the inhibitor molecule over the mild steel surface. Hence, the inhibition efficiency increases with an increase in inhibitor concentration. Figure 2 shows that the nature of the polarization curves remains constant in the presence of different concentrations of the inhibitor at different temperatures. The curves shifted gradually toward lower current density in the presence of the inhibitor, and it can be safely concluded that the inhibitor molecules retard the corrosion process. The inhibitor caused small changes in the Ecorr value, and it implies that the inhibitor acts as mixed-type inhibitor.23,24 In addition, there is no significant variation in βa and βc value, which indicates that the presence of Ketosulfone in corrosive media does not alter the corrosion reaction mechanism, but acts as an adsorption inhibitor and retards the corrosion process by blocking the active sites. Maximum inhibition was achieved at 200 ppm of the inhibitor and above this concentration, marginal change was observed. 4.2. Electrochemical Impedance Spectroscopy (EIS) Measurements. Figure 3 shows Nyquist plots recorded for the corrosion of steel in 1 M HCl. In this figure, high-frequency (HF) depressed semicircles are observed. The values of polarization resistance (Rp), double-layer capacitance (Cdl), and the calculated inhibition efficiency obtained from the Nyquist plots are reported in Table 2, while the measured impedance data analyzed by fitting into an equivalent circuit is shown in Figure 4. ηz was calculated using the following equation:25

(1)

where W° and W are the weight loss of mild steel in the absence and presence of inhibitor, respectively. The rate of corrosion ρ (g cm−2 h−1) was calculated from the following equation: ρ=

corrosion rate (g/cm2 h)

4. ELECTROCHEMICAL MEASUREMENTS 4.1. Polarization measurements. Polarization curves of mild steel in 1 M HCl are given in Figure 2. Electrochemical corrosion kinetic parameters such as corrosion potential (Ecorr), corrosion current density (icorr), cathodic Tafel slope (βc), anodic Tafel slope (βa), and inhibition efficiency (ηp) are listed in Table 2. The inhibition efficiency (ηp) was calculated from the following relation:

3. RESULTS AND DISCUSSION 3.1. Weight Loss Measurements. The inhibition efficiency of Ketosulfone at 303 K temperature was analyzed by weight loss measurement technique. Inhibition efficiency (ηw) of Ketosulfone was calculated from the following relation: ηw =

corrosive medium of Ketosulfone (ppm)

(2)

where S is the surface area of the steel strips, and T is the immersion time in hours. Corrosion parameters are provided in Table 1. This clearly shows that weight loss decreases significantly with the addition of Ketosulfone inhibitor. The decrease in the rate of corrosion with an increase in concentration of Ketosulfone is because the surface coverage of metal increases as it adsorbs inhibitor molecules.21,22

ηZ =

R p − R po Rp

× 100 (4)

where, Rp and Rp° are polarization resistance values in the presence and absence of inhibitor. The double layer capacitance values (Cdl) were evaluated by the following formula: 8437

dx.doi.org/10.1021/ie500232g | Ind. Eng. Chem. Res. 2014, 53, 8436−8444


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Figure 2. Tafel plots for mild steel in 1 M HCl (A) 303 K, (B) 313 K, (C) 323 K, and (D) 333 K.

Cd1 = (QR ct1− n)1/ n

While considering the current density values in Figure 5, the inhibition efficiency was calculated around 90%.27 It can therefore be concluded that Ketosulfone acts as an efficient corrosion inhibitor for mild steel in 1 M HCl. 4.4. Open-Circuit Potential (OCP) Measurements. The change in the OCP with immersion time for mild steel in the presence and absence of Ketosulfone in 1 M HCl is given in Figure 6. In HCl solution, the potential stood at a virtually stable value of −0.425 V, whereas the solution containing an inhibitor produced a nobler potential value of −0.400 V, which has a tendency to shift toward a positive direction over time in solution with an inhibitor.28,29 4.5. Adsorption Isotherm and Thermodynamic Parameters. The adsorption isotherm gives information about interactions between the inhibitor and the mild steel surface. The efficiency of Ketosulfone as a successful corrosion inhibitor chiefly depends on its adsorption capacity on the metal surface.30 It is crucial to know the mode of adsorption as well as the adsorption isotherm that can give important information on the interaction between the inhibitor and the metal surface. The degree of surface coverage (θ) for different molar concentrations (C) of Ketosulfone in the temperature range (303−333 K) was assessed by EIS data (Table 3). The relationship of C/θ versus C is depicted in Figure 7. The adsorption of Ketosulfone on metal surface obeyed the Langmuir adsorption isotherm. This can be expressed by the following equation:

(5)

where Q is the constant phase element (CPE) (Ω−1 Sn cm−2), and n is the CPE exponent which gives details about the degree of surface inhomogeneity. The analysis of impedance parameters shows that Rp values increase with increasing Ketosulfone concentration. The increase in Rp value can be attributed to the formation of protective layer on the steel surface. Table 2 clearly indicates that Cdl values decrease with Ketosulfone. The Cdl values decrease in the presence of Ketosulfone because the inhibitor molecules adsorb at the inner Helmholtz plane and block the active sites on the metal surface. Further, the decrease in Cdl values with increasing concentration of inhibitor may be due to a decrease in the local dielectric constant and/or an increase in the thickness of the electrical double layer.26 As a result, the 200 ppm concentration of Ketosulfone shows better inhibition efficiency, and it indicates that Ketosulfone is a good corrosion inhibitor for steel in 1 M HCl. 4.3. Chronoamperometric Measurements. To verify the use of Ketosulfone in anodic processes of mild steel, chronoamperometric experiments were carried out by polarizing anodically the electrode potential at −0.41 V for 600 s. The current density values obtained during the electron oxidation process of mild steel were recorded in 1 M HCl in the absence and presence of 200 ppm Ketosulfone. The chronoamperometric data are shown in Figure 5. 8438



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Table 2. Tafel and EIS Results temp (K) inhibitor conn (ppm) 303

313

323

333

blank 25 50 75 100 200 blank 25 50 75 100 200 blank 25 50 75 100 200 blank 25 50 75 100 200

Ecorr (V)

icorr A cm−2

corrosion rate (mpy)

βc mV/decade

βa mV/decade

−0.478 −0.481 −0.485 −0.484 −0.486 −0.452 −0.471 −0.502 −0.502 −0.490 −0.493 −0.498 −0.490 −0.490 −0.495 −0.500 −0.490 −0.500 −0.486 −0.475 −0.494 −0.491 −0.489 −0.494

0.170 0.067 0.061 0.046 0.045 0.042 0.465 0.141 0.113 0.110 0.094 0.076 0.486 0.264 0.208 0.189 0.159 0.158 0.506 0.307 0.261 0.258 0.195 0.181

33.70 13.10 11.80 9.05 8.77 8.50 91.10 27.71 22.13 21.67 19.50 17.50 95.04 51.68 40.70 36.97 31.11 30.90 188.20 163.31 140.66 130.60 60.07 50.52

−5.87 −10.18 −8.90 −8.15 −8.21 −7.57 −5.410 −6.650 −7.050 −7.200 −7.070 −7.073 −5.770 −6..25 −6.50 −6.59 −6.48 −6.466 −5.041 −5.247 −5.364 −5.500 −5.539 −5.781

6.03 10.05 10.14 10.67 11.00 8.94 5.430 8.050 8.690 9.290 8.900 8.710 5.980 6.58 7.72 8.027 8.16 8.03 5.162 5.383 5.550 5.798 6.323 6.693

C 1 = +C θ K

1 0 exp(ΔGads /RT ) 66.6

69.60 75.60 76.30 79.70 83.60 45.00 57.20 61.10 67.20 67.00 39.33 41.01 49.01 61.40 64.22

Rp Ωcm2 Cdl (μF cm−2) 6.727 14.31 20.66 25.40 26.01 30.17 2.36 8.28 10.15 10.22 13.3 16.7 1.881 3.68 4.26 4.91 6.32 6.68 0.887 1.250 1.398 1.492 3.239 4.128

687 297 290 284 123 131 243 135 120 119 115 113 141 105 124 146 125 129 195 631 576 727 177 152

ηz 53.10 67.50 73.50 74.10 77.70 73.00 76.70 76.90 82.00 85.80 49.00 55.80 61.70 70.20 71.80 29.04 36.50 40.54 52.26 60.50

(9)

A plot of ΔG0ads/T v/s 1000/T is provided in Figure 8 with the slope equal to the standard enthalpy of adsorption (ΔH0ads). Generally, the magnitude of ΔH0ads values lesser than −40 kJ/mol involve physisorption processes, and for chemisorption, this value approaches −100 kJ/mol.33,34 In our work, ΔH0ads is −68 kJmol−1, and it suggests that Ketosulfone is adsorbed on the steel surface predominately by the chemisorption method. In this work, ΔS0ads is found to be −107 J/mol/K, and the negative sign of the value indicates that adsorption is accompanied by a decrease in entropy. It can be explained as follows: before the adsorption of inhibitor onto the steel surface, the chaotic degree of the steel surface is high, but when inhibitor molecules are orderly adsorbed onto the steel surface, there is a decrease in entropy.35 4.6. The Effect of Temperature. Temperature has a more marked effect on corrosion rate of metals. In acid medium, υcorr increases exponentially with a corresponding increase in temperature. Hydrogen over voltage also decreased with temperature.36 Typically, corrosion reactions are regarded as Arrhenius processes, and the υcorr can be expressed by the relation:37

(7)

where R is the gas constant, and T is the absolute temperature. The constant value of 55.5 is the concentration of water in solution in mol/L. The values of Kads and ΔG0ads are listed in Table 3. ΔG 0 ads values show that the inhibitor is adsorbed spontaneously onto the mild steel surface. Normally, the magnitude of ΔG0ads around −20 kJ/mol or less negative is assumed for physisorption and those around −40 kJ/mol or more negative are indicative of chemisorption. The values of ΔG0ads are between these two, but modestly closer to −40 kJ/ mol. Therefore, Ketosulphone is adsorbed on the mild steel surface predominately by a chemisorption method.31 The enthalpy and entropy of adsorption (ΔH0ads and ΔS0ads) can be calculated using the Gibbs−Helmholtz equation as follows:32

⎛ ∂G /T ⎞ H ⎜ ⎟ = − ⎝ ∂T ⎠ p T2

60.50 64.10 72.90 73.50 75.20

0 0 0 ΔSads = (ΔHads − ΔGads )/T

(6)

where C is the inhibitor concentration, and K is the equilibrium constant for adsorption−desorption process. The strong adsorption of inhibitor on the mild steel surface obeys Langmuir’s adsorption isotherm. The Kads values were calculated from the intercept of the straight line obtained from the plot of C/θ versus C. This is related to the standard free energy of adsorption (ΔG0ads) with the following equation: K ads =

ηp

ln υcorr = ln A −

Ea* RT

(10)

where υcorr is the corrosion rate, Ea* is the apparent activation energy, R is the gas constant, T is the absolute temperature, and A is the frequency factor. The Arrhenius plot of ln υcorr against 1/T gives straight lines with slope −Ea*/R and the intercept of ln A are given in Figure 9. The obtained values of Ea* and A are tabulated in Table 4. Ea* and A values are greater in the presence of Ketosulfone compared to uninhibited solution. This implies that adding

(8)

The above equation can be rearranged to give the following equation: 8439



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Figure 3. Nyquist plots (A) 303 K, (B) 313 K, (C) 323 K, and (D) 333 K.

Figure 4. Equivalent circuit.

Ketosulfone hinders metal dissolution in 1 M HCl by increasing the energy barrier for the corrosion reaction by the process of adsorption on the metal surface.38 Meanwhile, Ea* for the corrosion process, both in the absence and presence of Ketosulfone are greater than 20 kJ mol−1, and it suggests that the entire process is controlled by surface reaction.39 The change in enthalpy (ΔH*) and entropy (ΔS*) of activation were calculated by the transition-state equation given below. ⎡ Rh ln υcorr ΔS* ⎤ ΔH * = ⎢ln + ⎥− ⎣ Nh T R ⎦ R

Figure 5. Chronoamperometric curve.

where h is the Planck’s constant, and N is the Avogadro’s number. The plots of ln (υcorr/T) versus 1/T are depicted in Figure 10. Straight lines were acquired with a slope of −ΔH

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Figure 9. Arrhenius plot.

Table 4. Activation Parameters for Mild Steel Figure 6. OCP graph for mild steel in 1 M HCl.

Table 3. Thermodynamic Parameters temperature (K)

Kads (kJ/mol)

ΔG0ads (kJ/mol)

ΔH0 ads (kJ/mol)

ΔS0 ads J/mol/K

303 313 323 333

20 000 9708 4273 2000

−35.06 −34.34 −33.23 −32.16

−68.00 −68.00 −68.00 −68.00

−107.7 −107.4 −107.3 −107.3

concentration of inhibitor(ppm)

Ea* (kJ/mol)

blank 25 50 75 100 200

43.81 68.38 67.16 71.49 52.26 49.71

A (kJ mol−1)

ΔH* (kJ mol−1)

ΔS* (J mol−1K−1)

× × × × × ×

12.92 21.25 21.54 23.85 19.83 19.46

−18.52 −14.93 −15.50 −14.67 −16.25 −16.42

13.72 73.08 38.53 17.79 92.69 32.76

108 1011 1011 1011 108 108

and ΔS values were calculated from the intercepts of ln (υcorr/ T) axis and are found in Table 4.

Figure 10. Transition state plot.

The positive values of ΔH* indicates that the dissolution reaction is an endothermic process and dissolution of steel is difficult.40 The increase in the values of ΔS* show that the activated complex in the rate-determining step represents a dissociation rather than an association, meaning that a decrease in disordering takes place going from reactants to the activated complex.41−43 4.7. Quantum Chemical Studies. Quantum chemical methods are a powerful impact on the design and development of corrosion inhibitors using which we can gauge evidence regarding distribution of electron for different molecular geometries. The optimized molecular structure of Ketosulfone is given in Figure 11. The computed quantum chemical data are summarized in Table 5. Structure of HOMO and LUMO are given in Figure 12 and Figure 13. Inhibitor molecules are adsorbed on the metal surface by the donor−acceptor interactions between inhibitor molecules and metal surface. EHOMO relates the electron donating ability of the inhibitor, and higher values of EHOMO indicates a high tendency of inhibitor molecules to donate electrons to the acceptor molecules. ELUMO relates the ability of a metal/molecule to

Figure 7. Langmuir adsorption plot of mild steel.

Figure 8. Relationship between ΔG0ads/T and 1000/T.

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accept electrons and lower value of ELUMO indicates the easier acceptance of electrons from the metal surface.44 The molecules with lower ΔE values give higher inhibition efficiencies because the excitation energy gap is more polarizable and is generally associated with chemical reactivity.45 Lower ΔE values aid in an electron transfer process between the inhibitor molecules and the mild steel surface. The calculated ΔE value for the Ketosulfone is 9.5326 eV, and it justifies the results. Mahendra Yadav et al. studied the corrosion inhibition performance of three Benzmidazole derivatives, and they found ΔE values of 8.059, 7.963, and 7.947 eV for Inhibitor 1, Inhibitor 2, and Inhibitor 3, respectively.46 The inhibition efficiency of these inhibitors decreased with an increase in ΔE values. J. Zhang et al. studied the corrosion inhibition performance of Imidazoline phosphate, and they found a ΔE value of 8.838 eV with an inhibition efficiency of 95%.47 Nataraj et al. studied a few organic compounds, and they found ΔE values of 8.13, 6.56, and 5.47 eV for HYD, TAD, and TRD, respectively.48Generally in the previous studies, corrosion inhibition efficiency decreased with an increase in ΔE values. Dipole moment (μ) is one of the important parameters to decide the adsorption inhibitor molecule on mild steel surfaces. Higher dipole moments increase the adsorption of inhibitors on the mild steel surface and increases the inhibition efficiency. The calculated dipole moment (μ) of Ketosulfone is 4.742. In this present investigation, ηq of Ketosulfone on steel surface by quantum calculation is 85.8%. It shows that Ketosulfone is an excellent green corrosion inhibitor for mild steel in 1 M HCl medium. The inhibitor not only offers electrons from activity centers to the unoccupied orbital of the metal, but also accepts free electrons from the metal, thus forming a more compact protective film on mild steel surface in 1 M HCl solution. 4.8. Scanning Electron Microscopy (SEM) Analysis. The surface morphology of the steel surface was viewed by SEM. Figure 14 shows the SEM photograph of the steel surface. The SEM photographs showed that the surfaces of the metal have pits and corrosive products, but in the presence of inhibitor, they are minimized on the metal surface. It indicates the formation of a passive layer on the metal surface, by which corrosion rate decreases in the presence of inhibitor and diminishes the electrochemical reaction. 4.9. Mechanism of Inhibition. The Ketosulfone drugs contain sulfur, nitrogen, oxygen, fused benzene rings, and N hetero atoms in the benzene ring. Our study indicates that

Figure 11. Optimized molecular structure of Ketosulfone.

Table 5. Quantum Chemical Parameters of Ketosulfone EHOMO

ELUMO (eV)

ΔE (eV)

μ (D)

ηq

−10.3705

−0.8379

9.5326

4.742

85.8

Figure 12. Structure of HOMO energy state of Ketosulfone.

Figure 13. Structure of LUMO energy state of Ketosulfone.

Figure 14. SEM photographs of steel surface (A) absence of inhibitor (1 M HCl) (B) presence of inhibitor. 8442



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(8) Pongsak, L.; Dusit, U.; Pakawadee, S. Tryptamine as a corrosion inhibitor of mild steel in hydrochloric acid solution. Corros. Sci. 2010, 52, 30−36. (9) Obot, I. B.; Obi-Egbedi, N. O. Adsorption properties and inhibition of mild steel corrosion in sulfuric acid solution by ketoconazole: Experimental and theoretical investigation. Corros. Sci. 2010, 52, 198−204. (10) El-Naggar, M. M. Corrosion inhibition of mild steel in acidic medium by some sulfa drugs compounds. Corros. Sci. 2007, 49, 2226− 2236. (11) Abdallah, M. Antibacterial drugs as corrosion inhibitors for corrosion of aluminium in hydrochloric solution. Corros. Sci. 2004, 46, 1981−1996. (12) Pongsak, L.; Dusit, U.; Pakawadee, S. Tryptamine as a corrosion inhibitor of mild steel in hydrochloric acid solution. Corros. Sci. 2010, 52, 30−36. (13) Kumar, S. H.; Karthikeyan, S. Torsemide and Furosemide as Green Inhibitors for the Corrosion of Mild Steel in Hydrochloric Acid Medium. Ind. Eng. Chem. Res. 2013, 52, 7457−7469. (14) Akpan, I. A.; Offiong, N.-A. O. Inhibition of Mild Steel Corrosion in Hydrochloric Acid Solution by Ciprofloxacin Drug. International Journal of Corrosion. Int. J. Corros. 2013, 301689, 1−5. (15) Abdallah, M. Antibacterialdrugs as corrosion inhibitors for corrosion of aluminium in hydrochloric solution. Corros. Sci. 2004, 46, 1981−1996. (16) Shylesha, B. S.; Venkatesha, T. V.; Praveen, B. M.; Nataraja, S. E. Acid Corrosion Inhibition of Steel by Lamotrigine. Int. Schol. Res. Network ISRN Corros. 2012, 932403, 1−8. (17) Nataraja, S. E.; Venkatesha, T. V.; Tandon, H. C. Computational and experimental evaluation of the acid corrosion inhibition of steel by tacrine. Corros. Sci. 2012, 60, 214−223. (18) Prabhu, R. A.; Shanbhag, A. V.; Venkatesha, T. V. Risperidone as a corrosion inhibitor for mild steel in acid media. Bull. Electrochem. 2006, 22, 225−233. (19) Singh, A. K.; Quraishi, M. A. The effect of some bis-thiadiazole derivatives on the corrosion of mild steel in hydrochloric acid. Corros. Sci. 2010, 52, 1373−1385. (20) Riggs, O. L. J. Corrosion Inhibitors, second ed.; C.C. Nathan, Houston, TX, 1973. (21) www.drugbank.com. (22) Emregül, K. C.; Atakol, O. Corrosion inhibition of mild steel with Schiff base compounds in 1 M HCl. Mater. Chem. Phys. 2003, 82, 188−193. (23) Ali, S. A.; El-Shareef, A. M.; Al-Ghandi, R. F.; Saeed, M. T. The isoxazolidines: The effects of steric factor and hydrophobic chain length on the corrosion inhibition of mild steel in acidic medium. Corros. Sci. 2005, 47, 2659−2678. (24) Jayaperumal, D. Effects of alcohol-based inhibitors of corrosion of mild steel in hydrochloric acid. Mater. Chem. Phys. 2010, 119, 478− 484. (25) Ferreira, E. S.; Giancomlli, C.; Giacomlli, F. C.; Spinelli, A. Evaluation of the inhibitor effect of L-ascorbic acid on the corrosion of mild steel. Mater. Chem. Phys. 2004, 83, 129−134. (26) Bentiss, F.; Lebrini, M.; Vezin, H.; Chai, F.; Traisnel, M.; Lagrenee, M. Enhanced corrosion resistance of carbon steel in normal sulfuric acid medium by some macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety: AC impedance and computational studies. Corros. Sci. 2009, 51, 2165−2173. (27) Ramos, R. O.; Battistin, A.; Goncalves, R. S. Alcoholic Mentha extracts as inhibitors of low-carbon steel corrosion in aqueous medium. J. Solid State Electrochem. 2012, 16, 747−752. (28) Musa, A. Y.; Kadhum, A. A. H.; Mohamad, A. B.; Takriff, M. S.; Daud, A. R.; Kamarudin, S. K. On the inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1,2,4-trizole-3-thiol. Corros. Sci. 2010, 52, 526−533. (29) Soror, T. Y.; El-Ziady, M. A. Effect of cetyl trimethyl ammonium bromide on the corrosion of carbon steel in acids. Mater. Chem. Phys. 2002, 77, 697−703.

Ketosulfone is adsorbed on the metal surface by chemisorption method. Ketosulfone gets adsorbed on the mild steel surface by donor−acceptor interactions between the Ketosulfone and the vacant d-orbital of iron atoms. Nitrogen and oxygen atoms of the Ketosulfone may donate a lone pair of electrons to the vacant d orbital of the metal and forms coordinate bond. In addition, π electrons of the aromatic rings also may form the same type of bond with the metal atom.

5. CONCLUSIONS Ketosulfone is found to be a green inhibitor for the corrosion of mild steel in 1 M HCl. Inhibition efficiency increases with an increase in concentration of Ketosulfone and with increase in temperature up to 313 K. The adsorption mechanism of Ketosulfone on the mild steel surface obeyed by Langmuir’s adsorption isotherm and the negative value of the Gibbs free energy of adsorption (ΔGads) indicates a strong interaction between inhibitor molecules and the mild steel surface. Polarization curves prove that Ketosulfone is a mixed type inhibitor. Adsorption of the inhibitor on steel surface is predominately due to chemisorption and is spontaneous, which is confirmed by the activation parameters. Hence, Ketosulfone is an excellent green corrosion inhibitor and could find possible applications in industries.

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Corresponding Author

*Tel.: 91-9980951074. Fax: 0824−2477457. E-mail: bm. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are obliged to the authorities of Srinivas School of Engineering, Mukka, Mangalore, Karnataka, India for providing excellent lab facilities. The authors also express thanks to the Department of Science and Technology, New Delhi, Govt. of India under the fast track scheme for young scientist (DST: Project Sanction No. SR/FT/CS-147 2011dated 13-07-2012) and All India Council for Technical Education, New Delhi, Govt. of India under MODROBS scheme (ref. No 8024/ RIFD/MOD 292/2010-11 dated 31-03-2011) for providing instrumental amenities.

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