Contents lists available at ScienceDirect

Journal of Electroanalytical Chemistry

journal homepage: www.elsevier.com/locate/jelechem

1-(4-Nitrophenylo-imino)-1-(phenylhydrazono)-propan-2-one as corrosioninhibitor for mild steel in 1 M HCl solution: Weight loss, electrochemical,thermodynamic and quantum chemical studies

Hanane Hamania, Tahar Douadia, Djamel Daouda,b,⁎, Mousa Al-Noaimic, Rahma Amina Rikkouha,Salah Chafaaa

a Laboratoire d'Electrochimie des Matériaux Moléculaires et Complexes (LEMMC), Département de Génie des Procèdes, Faculté de Technologie, Université Ferhat ABBASde Sétif-1, 19000 Sétif, Algeriab Unité de Recherche Appliquée en Energies Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133 Ghardaïa, Algeriac Department of Chemistry, Hashemite University, P.O. Box 150459, Zarqa 13115, Jordan

A R T I C L E I N F O

Keywords:Corrosion inhibitorMild steelEISSEMDFT

A B S T R A C T

1-(4-Nitrophenylo-imino)-1-(phenylhydrazono)-propan-2-one (NO2AM) was studied as a corrosion inhibitor formild steel in 1 M HCl solution by weight loss, polarization, electrochemical impedance spectroscopy (EIS),scanning electron microscopy (SEM) and UV–visible spectroscopy. The inhibition efficiency was found to in-crease with increasing inhibitor concentration and to decrease with increasing temperature. Some thermo-dynamic and kinetic parameters were calculated and discussed. The adsorption of the inhibitor on the mild steelsurface obeyed the Langmuir adsorption isotherm. Polarization studies showed that the inhibitor behaves as amixed-type inhibitor. SEM was performed for surface analysis of the uninhibited and inhibited mild steelsamples. The density functional theory (DFT) was employed for theoretical calculations. The results obtainedfrom experimental measurements and those from theoretical calculations are in good agreement.

1. Introduction

The hydrochloric acid solution is used in industrial processes duringpickling and cleaning of metals and alloys; that causes significant metalloss [1]. Inhibitors are added to the acid solution to minimize acid at-tack on metal. Heterocyclic compounds are used as a corrosion in-hibitor for preventing metal dissolution in acid media [2,3]. Thesecompounds are adsorbed on the metal surface and bring down thecorrosion rate of metals. Most of the commercial inhibitors exhibitadverse effects on the environment. In view of this, current researchactivities are being focused on the development of eco-friendly corro-sion inhibitors [4]. However, the inhibition mechanisms for most or-ganic inhibitors are usually related to their adsorption, either physi-sorption or chemisorption of heteroatoms such as nitrogen, oxygen orsulfur aromatic compounds, or some unsaturated functional groupssuch as azo (eN]Ne), olefinic (R]R), and carbonyl (eC]O) [5–10].Compounds with an imine group (eC]Ne) conjugated to an azo group(eN]Ne) are known as an azoimine (eN]NeC]Ne) [5,11]. Pre-viously, various N-heterocyclic compounds are reported as good cor-rosion inhibitors for steel in acidic media, such as azo-azomethine

derivatives [12], p-amino azobenzene derivatives [13], 2-amino-5-ni-trothiazole [14] and azomethine derivatives [15]. They exhibit inhibi-tion by adsorption on the metal surface, and the adsorption takes placethrough N, O, and S atoms, as well as those with triple or conjugateddouble bonds or aromatic rings in their molecular structures. Further-more, the adsorption of the inhibitor on steel/solution interface is in-fluenced by the chemical structure of inhibitor, the nature and chargedsurface of metal, the distribution of charge over the whole inhibitormolecule and the type of aggressive media. If a substitution polar group(eNH2, eOH, eSH, etc.) is added to the N-heterocyclic ring, the elec-tron density of N-heterocyclic ring is increased, and subsequently, itfacilitates the absorbability.

A number of studies have been focusing on the relationship betweenthe structural properties of the organic inhibitor molecules and theirinhibitory effects, in order to appraise the organic compounds as in-hibitors. A.S. Fouda and A.S. Ellithy [3] studied the corrosion inhibitionof 4-phenylthiazole derivatives 304L stainless steel in 3.0 M HCl at30 °C, and the results showed that the inhibition efficiency (g) of thesecompounds follows the order: 1 > 2 > 3 > 4 > 5, which is due tothe difference in the substituants (the active centers) in each compound:

http://dx.doi.org/10.1016/j.jelechem.2017.08.031Received 2 March 2017; Received in revised form 12 August 2017; Accepted 14 August 2017

⁎ Corresponding author.E-mail address: djdaoud@uraer.dz (D. Daoud).

Journal of Electroanalytical Chemistry 801 (2017) 425–438

Available online 15 August 20171572-6657/ © 2017 Elsevier B.V. All rights reserved.

MARK

eOCH3 > eCH3 > H > eBr > eNO2, respectively. K.R. Ansariet al. [16] reported the corrosion inhibition by (4-Nitrobenzylidene)amino)-5-(pyridine-4-yl)-4H-1,2,4-triazole-3- thiol (SB-3) for carbonsteel in 1 M HCl, and the maximum inhibition efficiency (g) at 150 mg/L is 85.7%. According to work [17,18], N-[(1E)-(2-chloroquinolin-3-yl)methylene]-N-(4-nitrophenyl) amine (CNPA) and N,N′-bis-(4-ni-trobenzylidene)-2,2′-diaminodiphenyl disulfide also act as good in-hibitors on the corrosion of steel in 1.0 M HCl. Through these studies,there is a great the correlation between the molecular structure andinhibitive performance. As ligands, these compounds are stronger π-acceptor compared to 2,2′-bipyridine and other N-donor heterocyclicligands [19–22]. Also, the azoimine, eN]NeC]Ne, functional grouphas been implanted into a coumarine backbone for the synthesis of aphotoactive coumarinyl-azoimine motif [23–28]. The objective of thepresent work is to investigate the inhibitory efficiency of azoimine: 1-(4-Nitrophenylo-imino)-1-(pheny-lhydrazono)-propan-2-one (NO2AM)for mild steel in 1 M HCl solution using weight loss, potentiodynamicpolarization, electrochemical impedance spectroscopy, SEM techniqueand quantum chemical calculation method to correlate molecularstructure parameters and inhibition efficiency of corrosion inhibitor[29,30]. The superiority of this compound lies in that it is completelysoluble, easy to prepare, cheap, non-toxic and biodegradable; the ex-amination of its anti-corrosive proprieties is significant in the context ofthe current priority to synthesize inhibitors with low environmentalimpact. In addition this derivative has eNO2 as electro-attractive group.The Scheme 1, shows the chemical structure of the (NO2AM).

2. Experimental

2.1. Material and sample preparation

The mild steel specimen with the chemical composition (wt%):C = 0.39; P = 0.024; Si = 0.23; Mn = 0.78; Cr = 0.14; Cu = 0.20;Al = 0.023; Ni = 0.23; S = 0.031; Mo = 0.030 and the rest is Fe, isused in this study. The mild steel specimens of dimensions(4 × 3 × 0.3 cm) are used for weight loss method. Prior to each ex-periment the exposed mild steel surface is abraded with emery papers(grade 800 to 2000), followed by washed with distilled water, de-greased with acetone and dried with cool air. The 1 M HCl solution isprepared by dilution of analytical grade 37% HCl (Merck) solution withdistilled water. The synthesis and the characterization of the examinedcompound (NO2AM) is published [20], it is totally soluble in 1 M HC.The concentration of the (NO2AM) is kept in the range of 5 × 10−6 to7.5 × 10−5 M. The solubility (in g/L) of the inhibitor (NO2AM) in 1 MHCl solution was 0.00149 (5 × 10−6 M), 0.00298 (1 × 10−5 M),0.00745 (2.5 × 10−5 M), 0.01490 (5 × 10−5 M) and 0.02235(7.5 × 10−5 M).

2.2. Weight loss measurements

Mild steel specimens in triplicate are immersed in 1 M HCl for 24 hat temperature 25 °C in the absences and presence of various con-centrations of (NO2AM). The average mass of each mild steel specimenis determined before and after immersion. The corrosion rate and in-hibition efficiency EIW(%) are determined by using the following

equations [31]:

= ∆×

= −×

C WS t

W WS tRW1 2

(1)

⎜ ⎟= ⎛⎝

− ⎞⎠

×°

°EIC C

C% 100W

RW RW

RW (2)

where W1 and W2 are the weight of specimens before and after im-mersion, respectively, ΔW is the average weight loss, S is the surfacearea of the specimen, t is the immersion time, CRW

° and CRW are cor-rosion rates in the absence and presence of inhibitor, respectively.

2.3. Electrochemical measurements

Electrochemical studies were conducted in a three-electrode cellconsisting of mild steel specimen of 0.19 cm2 exposed area as workingelectrode, a platinum counter electrode and a saturated calomel elec-trode (SCE) as a reference electrode. Prior to each electrochemical test,the working electrode is immersed in the test solution for about 30 minto attain open circuit potential (EOCP) at 25 °C. Potentiodynamic po-larization curves were obtained at a scan rate of 0.5 mV s−1 in thepotential range of −800 to −250 mV vs. SCE at open circuit potential(EOCP). The linear Tafel segments of anodic and cathodic curves wereextrapolated to obtain corrosion current densities (icorr). The inhibitionefficiency (EIP%) and surface coverage (θ) are determined by using thefollowing equations [32]:

⎜ ⎟= ⎛⎝

− ⎞⎠

×°

°EIi i

i% 100P

corr corr

corr (3)

=−°

°θi i

icorr corr

corr (4)

where icorr° and icorr are the corrosion current densities in the absenceand presence of inhibitors, respectively.

The polarization resistance (Rp) was calculated from the cathodic(Bc) and anodic (Ba) Tafel slopes for the cathodic and anodic branchesusing Stern–Geary relation shown in Eq. (5) [33]:

=+

×R B BB B i2.303( )

1p

a c

a c corr (5)

The inhibition efficiency ELPR(%) is calculated as follows:

= + ×E R RR

(%) 100LPRPinh P

Pinh (6)

where RP and RPinh are the polarization resistance values without andwith inhibitor, respectively.

The electrochemical impedance measurements (EIS) were per-formed in the frequency range of 100 kHz to 10 mHz with at 10 mVamplitude at the open circuit potential (EOCP). The inhibition efficiency(EISIE%) was calculated from charge transfer resistance values obtainedfrom impedance measurements using the following equation [34]:

=−

×− −

−EIR R

R(%) 100SIE

ct1

ct1

ct1

0

0 (7)

where Rct0 and Rct are charge transfer resistance in the absence andpresence of inhibitor, respectively. The values of double layer capaci-tance (Cdl) were calculated from charge transfer resistance and CPEparameters (Q and n) using the equation [35,36]:

= −C Q( R )dl ct1 n 1 n (8)

where Q is CPE constant and n is CPE exponent. The value of n re-presents the deviation from the ideal behavior and it lies between 0 and1. Potentiodynamic polarization and electrochemical impedance spec-troscopy (EIS) experiments were carried out using a PGZ 301 Voltalab-40 model potentiostat/galvanostat.

N

N

N

COCH3

NO2

Scheme 1. Chemical structure of 1-(4-Nitrophenylo-imino)-1(phenylhydrazono)-propan-2-one (NO2AM).

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

426

2.4. Scanning electron microscopic (SEM)

For a surface morphological study of the uninhibited and inhibitedmild steel samples, SEM images were recorded using the JOEL-JSM-7001F-Japan instrument. The surface morphological characteristics ofthe specimen immersed in the corrosive medium with and without in-hibitor separately were analyzed at an accelerating voltage of 4.0 kV.

2.5. Quantum chemical calculation

All computations were performed using the Gaussian 09 (G09)program. Full geometry optimization was carried out using the DFTmethod at the B3LYP level of theory [29]. The C, H, N, and O elementswere assigned the 6-31G (d,p) basis. The important molecular para-meters such as highest occupied molecular orbital energy (EHOMO),lowest unoccupied molecular orbital energy (ELUMO), energy gap(ΔE=ELUMO−EHOMO), dipole moment (μ), ionization potential (I),electron affinity (E), hardness (γ) and electronegativity (χ) are obtainedfor the corrosion inhibitor (NO2AM).

3. Results and discussion

3.1. Weight loss studies

Table 1 shows the values of inhibition efficiency EIW(%) and thecorrosion rate (CRW) obtained from weight loss measurements at dif-ferent concentrations of (NO2AM) at 25 °C after 24 h of immersion. Thecorrosion rate is decreased with increasing inhibitor concentration,while the inhibition efficiency EIW(%) is increased, reaching a max-imum of 91.33% at 7.5 × 10−5 M. This may be due to the adsorptionof azomethine (NO2AM) onto the mild steel surface through non-bonding electron pairs of the azo and oxygen atoms of nitro group aswell as π-electrons of the aromatic rings. The high inhibitive perfor-mance of azomethine suggests a higher bonding ability of this com-pound on mild steel surface. A similar observation has been reported inthe literature [37–40].

3.2. Open circuit potential

Before each electrochemical test, the electrodes immersed in thecorrosive test solution and the open circuit potential (Eocp) valuesmonitored with time, until a steady state was reached on the surface.The results are summarized in Fig. 1, for various inhibitor concentra-tions and blank test solution. It was understood that almost 30 minexposure period is sufficient for reaching stable interface conditions.From Fig. 2, a relatively steady value of the OCP was reached afterabout 700 s of immersion in all cases. The initial decrease in OCP of theblank system is as a result of dissolution of air oxide film at the mildsteel surface [41,42]. The Eocp value reached after 30 min immersionperiod was regarded as the corrosion potential value Ecorr [43]. It isclear, that the corrosion potential (Ecorr) of carbon steel electrode in 1 MHCl solution is shifted to more noble direction until steady state po-tential is established. The results clearly indicate that (Ecorr) was shiftedto noble direction. This suggests that the kinetic of the anodic reaction

of carbon steel in 1 M HCl solution was affected more strongly in thepresence of inhibitor. This may be due to immediate formation ofprotective layer of the inhibitor on the electrode surface therebyshielding it from the corrosive attack of the environment. This is a resultof the formation of protective film of the inhibitor on the steel surface[43].

3.3. Potentiodynamic polarization curves

Fig. 2 shows the potentiodynamic polarization curves for mild steelin 1 M HCl solution in the absence and presence of different con-centrations of azomethine(NO2AM). The electrochemical parameterssuch as corrosion potential (Ecorr), corrosion current density (icorr),corrosion inhibition efficiency (EIP), anodic Tafel slope (Ba) andcathodic Tafel slope (Bc) were derived from extrapolation method andsummarized in Table 2. In addition, both cathodic and anodic currentdensities are decreased distinctly when the NO2AM is added in the acidsolution. The variation of cathodic current densities with inhibitorconcentration is more noticeable. Both anodic metal dissolution andcathodic hydrogen evolution reactions are markedly inhibited by theNO2AM compound. The values of cathodic Tafel slope (Bc) for azo-methine are found to increase in the presence of inhibitor. The Tafelslope variations suggest that NO2AM influence the kinetics of the

Table 1Weight loss results of mild steel corrosion in 1 M HCl with addition of various con-centrations of NO2AM at 25 °C.

Inhibitor C (M) CRW (mg cm−2 h−1) EIW (%)

Blank 1.236 ± 0.015 –NO2AM 5× 10−6 0.516 ± 0.0021 55.22

1 × 10−5 0.248 ± 0.0024 79.852.5 × 10−5 0.224 ± 0.0046 84.835 × 10−5 0.156 ± 0.0038 87.367.5 × 10−5 0.107 ± 0.0031 91.33

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200-555

-550

-545

-540

-535

-530

-525

-520

-515

-510

-505

-500

HCl 1M

5 x 10-6

M

1 x 10-5M

2.5 x 10-5M

5 x 10-5M

7.5 x 10-5M

E (

mV

/SC

E)

Time (s)

Fig. 1. Time variation of the OCP of mild steel samples immersed in 1 M HCl solutionscontaining different concentrations of NO2AM after 30 min immersion at 25 °C.

-800 -700 -600 -500 -400 -300 -200-3

-2

-1

0

1

2

3

HCl 1M

5X10-6M

1X10-5M

2.5X10-5M

5X10-5M

7.5X10-5M

E (mV/SCE)

log

i (m

A c

m-2)

NO2AM

Fig. 2. Potentiodynamic polarization curves of mild steel in 1 M HCl solution without andwith different concentrations of NO2AM at 25 °C.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

427

hydrogen evolution reaction [44]. This indicates an increase in theenergy barrier for proton discharge, leading to less gas evolution[44,45]. The approximately constant values of anodic Tafel slope (Ba)for azomethine indicate that these compound was first adsorbed ontothe metal surface and impeded by merely blocking the reaction sites ofthe metal surface without affecting the anodic reaction mechanism[45].

The inhibiting effect becomes more pronounced by gradual in-creasing of the inhibitor concentration without any distinct trend in theshift of Ecorr values. The observation is very much clear with NO2AMinhibitor, showing almost coinciding corrosion potentials and hencemay be treated as a mixed inhibitor. The displacement in Ecorr value inthe absence and presence of the inhibitor is< 85 mV which states thatthe inhibitor is a mixed type [39,40]. Besides, it can be found that thecathodic branches of the polarization current-potential curves give riseto Tafel lines that are almost parallel. This phenomenon indicates thatthe addition of the inhibitor does not modify the hydrogen evolutionmechanism, and most probably the reduction of hydrogen ions on themild steel surface takes place mainly through a charge transfer me-chanism [46,47]. In this way, actual surface area available for H+ ionsis decreased, while the actual reaction mechanism remains unaffected[48,49]. Similar observations in the literature have been attributed thevalues of Bc are very low [5–8].

In an anodic domain, it is also observed that, for the potentialshigher than −350 mV, the anodic current density sharply increasedwith the increase of potential, suggesting that the inhibitor starts todesorbs if the potential is over a definite potential, which is usuallydefined as desorption potential. This may be the result of the metaloxidation leading to desorption of the inhibitor molecules on the elec-trode surface, it means that the inhibitory effect is dependent on elec-trode potential [50,51]. In this case, moreover, the desorption rate ofNO2AM compound is raised more than its adsorption rate.

As it can be seen from Table 2, when the concentration of inhibitorincreases, the corrosion current density decreases while the polarizationresistance increases. This may be due to adsorption of inhibitor mole-cules on the metal surface. The inhibition efficiencies increased withinhibitor concentration, the maximum value of inhibition efficiency of92.63 and 94.07% at 7.5 × 10−5 M were obtained from potentiody-namic polarization and linear polarization resistance techniques, re-spectively. The inhibition efficiencies values calculated by bothmethods are in good agreement.

3.4. Electrochemical impedance spectroscopy (EIS)

Fig. 3 shows the Nyquist plots for mild steel in 1 M HCl solution inthe absence (blank) and presence of different concentrations of NO2AMat 25 °C. All the impedance spectra obtained show a single depressedcapacitive loop which is related to charge transfer of the corrosionprocess [52] and the diameters of the capacitive loops increase sharplywith increasing NO2AM concentration. It is noticed that the impedanceloops do not yield perfect semicircle. Such phenomenon is generallyattributed to the frequency dispersion as well as heterogeneousroughness of the metal surface and mass transfer process [53]. The plotsobtained in the real system represent a general behavior where thedouble layer on the interface of metal/solution does not behave as a

real capacitor. This anomalous behavior is generally referred to asfrequency dispersion which is attributed to irregularities and hetero-geneities of the solid surfaces. When the electrode surface is in-homogeneous or rough, the impedance diagram is deformed because ofgeometrical factors [54]. Metal/solution interface, on the other handcannot behave as a real capacitor due to the charge separation betweenthe two phases in contact. It is well known for a real condenser that thecharge distribution on both plates is controlled by electrons. However,considering the metal/solution interface, electrons control the chargedistribution on the metal side of the double layer whereas on the so-lution side it is controlled by ions. As ions tend to be much larger thanelectrons, equivalent ions parallel to the charge on the metal surfaceoccupy a larger volume on the solution side of the double layer [54].

The EIS spectra (Fig. 4) were analyzed using an equivalent circuit ofcomprises a parallel combination of the polarization resistance (Rp),which corresponds to the diameter of Nyquist's plot, includes the chargetransfer resistance (Rct), diffuse layer resistance (Rd), the accumulatedspecies at the metal/solution interface (Ra) and the resistance of in-hibitor film at the steel surface (Rf) (Rp = Rct + Rd + Ra + Rf) [55]and the constant phase element (CPE in series with the solution re-sistance (Rs). This type of electrochemical equivalent circuit was re-ported previously to model the iron/acid interface [56,57]. Constantphase element (CPE) is introduced instead of pure double layer capa-citance to give more accurate fit as the double layer at interface doesnot behave as an ideal capacitor. The excellent fit with this model wasachieved as follows for all experimental impedance data. As an ex-ample, the Nyquist and Bode plots of both experimental and simulateddata of mild steel in 1 M HCl solution without and with 7.5 × 10−5 MNO2AM are shown in Figs. 5 and 6, respectively. The measured im-pedance plots are in agreement with those calculated by means of theequivalent circuit model. The electrochemical parameters obtainedfrom the fitting of the impedance spectra are presented in Table 3. Thedata shown in Table 3 reveal that the Rp values in the presence of in-hibitor are larger than the Rp for the blank. The increase in Rp values isattributed to the formation of insulating protective layer the metal/solution interface. The Rp value increases, CPE decreases with in-creasing inhibitor concentration, which can be attributed to an en-hancement in the electrical double layer thickness [55]. The doublelayer between the charged metal surface and the solution can be con-sidered as an electrical capacitor. The adsorption of compound decreasethe metal/solution electrical capacity by displacing the water moleculesand other ions originally adsorbed on the surface [55]. The value of n isrelated to surface roughness. Generally surface roughness increaseswith the decrease in the value of n [58]. It can be observed that thevalues on n in presence of NO2AM are larger (0.892 for NO2AM) thanthat in their absence suggesting that surface smoothness increases inpresence of inhibitor due to the adsorption of NO2AM on mild steelsurface.

Table 3 shows that the Cdl values decrease in the presence of in-hibitors, the similar observations have been documented in the litera-ture [53,59,60].This decrease may be due to a decrease in local di-electric constant and/or increase in thickness of the double layer of theinhibitor, thus making it a protective film on mild steel surface in acidsolution [61]. This decrease in Cdl value with increasing thickness of theelectric double layer can be explained using a Helmholtz model [62]:

Table 2Polarization parameters for the corrosion of mild steel in 1 M HCl solution without and with different concentrations of NO2AM at 25 °C.

Inhibitor C (M) −Ecorr (mV/SCE) −BC (mV/dec) Ba (mV/dec) icorr (mA cm−2) RP (Ω cm2) EILPR (%) EIP (%) θ

Blank 511.6 63.7 65.4 0.5157 26.872 – – –NO2AM 5× 10−6 521.9 74.9 89.3 0.1015 174.263 84.58 80.31 0.80

1 × 10−5 516.8 79.4 73.0 0.0653 252.910 89.37 87.33 0.872.5 × 10−5 503.3 84.7 59.1 0.0471 320.923 91.62 90.86 0.905 × 10−5 509.5 75.2 57.9 0.0412 344.768 92.20 92.01 0.927.5 × 10−5 550.8 85.3 74.3 0.0380 453.768 94.07 92.63 0.92

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

428

=C εεd

Sdl0

(9)

where ε is the dielectric constant of the medium, ε0 is the permittivity ofthe free space, S is the effective surface area of the working electrode,and d is the thickness of the electric double layer formed by the adsorbinhibitors. From the Helmholtz equation, it can be concluded that in-creased in thickness of the double layer was responsible for the decreasein Cdl values [63,64].

The impedance Bode plots for mild steel in 1 M HCl solution withoutand with the various concentrations of NO2AM at 25 °C are shown inFig. 7. The single peak obtained in Bode plots for the inhibitor impliesthat the simple one-time constant equivalent Randle's circuit modelused unfitting the impedance spectra was appropriate. The Bode plotsshow that only one phase maximum for the inhibitor, indicating thatthe electrochemical system involves only one relaxation process, whichis the charge transfer process taking place at the metal–electrolyte in-terface [65]. As shown in Fig. 3, the impedance values in the presenceof inhibitor is larger than in the absence of inhibitor and increase withincreasing concentration of the studied inhibitor. The inhibition effi-ciency IE (%) obtained from weight loss, polarization and impedancemeasurements are comparable to a fair degree.

3.5. Effect of temperature

In order to calculate the activation parameters of the corrosionprocess and the heat of adsorption process and to investigate the in-hibition mechanism affected by temperature, polarization measure-ments were performed at various temperatures (25–55 °C), in the ab-sence and presence of different concentration of NO2AM, as shown inTable 4 and Fig. 8. It is apparent that the increase of corrosion currentdensity is pronounced with the rise of temperature in both uninhibitedand inhibited solutions. Table 4 shows that the inhibition efficiencydecreases slowly with increasing temperature. This type of behavior canbe described on the basis that increases in temperature leads to a shiftof the equilibrium position of the adsorption/desorption phenomenontowards desorption of the inhibitor molecules on the surface of mildsteel [66].

The activation energy (Ea) of the corrosion process can be

determined by the Arrhenius equation [67,68]:

= ⎛⎝

⎞⎠

i A ERT

exp –corr

a

(10)

where Ea is the activation energy of the corrosion process, T is thetemperature, R is the gas constant, A is the Arrhenius constant and icorris corrosion current density. The Arrhenius plots of log icorr vs. 1/T ofmild steel 1 M HCl solution is shown in Fig. 9 from which the values ofEa were calculated from the slope and listed in Table 5.

The tabulated data revealed that the value of Ea for inhibited so-lution is greater than that of the uninhibited solution. This increase inEa in the presence of NO2AM indicates the formation of the higherenergy barrier for corrosion process, suggesting that the adsorbed filmof NO2AM on mild steel surface prevents the charge/mass transfer re-action occurring on the surface [69,70]. Moreover, the decrease in in-hibition efficiency with increasing temperature signifies the physicaladsorption that occurs during the first stage of adsorption process[70,71]. The increased value of Ea also suggests that presence ofNO2AM rate of mild steel dissolution decreased due to the formation ofa metal-inhibitor complex [70]. Similar observation has been reportedin literature [72,73].

The values of standard enthalpy of activation (ΔHa°) and standard

entropy of activation (ΔSa°) were calculated by using the followingequation:

⎜ ⎟ ⎜ ⎟= ⎛⎝

∆ ⎞⎠

⎛⎝

−∆ ⎞⎠

° °i RT

NhSR

HRT

exp expcorra a

(11)

where, h is Planck's constant and N is Avogadro's number, respectively.A plot of ln(icorr/T) against 1/T (Fig. 10) gave straight lines with a

slope of −ΔHa°/R and an intercept of [ln(R/Nh)+(−ΔSa°/R)], from

which the value of activation thermodynamic parameters ΔHa° and ΔSa°

were calculated, as listed in Table 5. The positive sign of the enthalpyreflects the endothermic nature of the mild steel dissolution process.The negative value of ΔSa° for the inhibitor NO2AM indicates that theformation of the activated complex in the rate determining step re-presents an association rather than a dissociation step, meaning that adecrease in disorder takes place during the course of the transition fromreactants to the activated complex [71].

0 20 40 60 80 100 120 140 160 180 200

0

20

40

60

80 HCl 1M

5X10-6 M

1X10-5 M

2.5X10-5 M

5X10-5 M

7.5X10-5 M

-Zi (

ohm

cm

2 )

Zr (ohm cm2)

NO2AM 10.7 Hz

15.6 Hz

51.6 Hz

23.6 Hz

24.8 Hz

22.4 Hz

0.71Hz

0.15Hz0.18Hz0.12Hz

0.17Hz

0.10Hz

79.3Hz 62.2Hz 74.3Hz

64.3Hz

75.4Hz

Fig. 3. Nyquist plots for mild steel in 1 M HCl solutionwithout and with different concentrations of NO2AMat 25 °C.

Fig. 4. The equivalent circuit model for corro-sion process of the mild steel for uninhibited (a)and inhibited solutions (b). Rp = Rct + Rd + Ra

for diagram (a). Rs: uncompensated solution re-sistance, Rp: polarization resistance, Rct: chargetransfer resistance, Rd: diffuse layer resistance,Ra: resistance of accumulated species (corrosionproducts, any existing molecules or ions, etc.), Rf:film resistance, CPE1: double layer capacitance,CPE2: film capacitance.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

429

3.6. Adsorption isotherm

Basic information on the interaction between the organic inhibitorsand the mild steel surface are obtained from various adsorption iso-therms. The most commonly used adsorption isotherms are Langmuir,Temkin and Frumkin. The surface coverage values (θ) for variousconcentrations of the investigated NO2AM have been used to illustratethe best adsorption isotherm. According to the values obtained frompotentiodynamic polarization data, it can be concluded that the bestdescription of the adsorption behavior of NO2AM can be demonstratedby adsorption isotherm of Langmuir [74]:

= +Cθ K

C1inh

adsinh (12)

where Cinh is the inhibitor concentration, Kads is the equilibrium con-stant for the adsorption-desorption process. The plots of ( )C

θinh vs. Cinh

at different temperatures yielded straight lines as shown in Fig. 11. Thecorrelation coefficient (R2) values for the Langmuir adsorption plots arein Fig. 11. The correlation coefficient (R2) values are near to unity,indicating that the adsorption of this inhibitor on mild steel surfaceobeys Langmuir adsorption isotherm. From the intercepts of Fig. 11, thevalues of Kads were calculated. Large values of Kads obtained for thestudied inhibitor imply more efficient adsorption and hence bettercorrosion inhibition efficiency. Using the values of Kads, the values ofΔGads

° were evaluated by using the equation [74]:

∆ = −°G RT Kln(55.5 )ads ads (13)

where R is the universal gas constant, T is the absolute temperature inK, and the numerical value 55.5 represents the molar concentration ofwater in acid solution. The calculated values of Kads and ΔGads

° aregiven in Table 6. The higher value of Kads associated with strong

adsorption of the inhibitor on the surface of the mild steel in 1 M HCl[75]. The negative values of ΔGads

° indicate that the adsorption ofNO2AM molecule was a spontaneous process and stability of the ad-sorbed film on the mild steel surface [75]. In the present study, thevalues of ΔGads

° vary from −38.98 to −40.77 kJ mol−1, at differenttemperatures (303−333 K), signifying that NO2AM molecules adsorbon the mild steel surface in 1 M HCl by physico-chemisorption me-chanism [76].

The standard enthalpy change (ΔHads°) and standard enthalpy

change (ΔSads°) for the adsorption of inhibitor were determined fromthe thermodynamic equation:

∆ = ∆ − ∆° ° °G H T Sads ads ads (14)

The plot of ΔGads° versus T was linear (Fig. 12) with the intercept

equal to ΔHads° and slope equal to ΔSads° as represented in Table 6. It

has been reported in the literature that an endothermic adsorptionprocess (ΔHads

° > 0) is due to chemisorption while an exothermic ad-sorption process (ΔHads

° < 0) may be attributed to physisorption,chemisorption or a mixture of them [77,78]. Therefore, we can con-clude that the adsorption of NO2AM on the metal surface is a mixture ofbetween physical and chemical process. The ΔSads° values are a positivesign, which means an increase of disorder is due to the adsorption ofonly one molecule of NO2AM by desorption of more water molecules[78].

3.7. Surface analysis by SEM

The scanning electron micrographs for mild steel in 1 M HCl inabsence and presence of NO2AM are shown in Fig. 13, Parallel featureson the polished steel surface before exposure to the corrosive solutionwere observed in Fig. 13a, which are associated with polishing

...................Experim ental Result

HCl 1M

151050

-10

-5

0

Zr ohm cm2

Zi o

hm

cm

2

F itResult ................Experim ent Result

HCl 1M

10-1

100

101

102

103

104

105

10-1

100

101

102

Frequency (Hz)

|Z|

oh

m c

m2

F itResult

-75

-50

-25

0

Phase a

ngle

(D

egree)

Fig. 5. Nyquist (a) and Bode (b) plots for mildsteel in 1 M HCl solution: (…) experimental; (−)fitted data.

.....................Experim ental Result

-NO 2

0 100 200 300

-200

-100

0

Zr ohm cm2

Zi

oh

m c

m2

F itResult

.................Experim ental Result-NO 2

10-1

100

101

102

103

104

105

10-1

100

101

102

103

Frequency (Hz)

|Z| o

hm

cm

2

F itResult-75

-50

-25

0

Ph

ase

an

gle

(D

eg

re

e)

Fig. 6. Nyquist (a) and Bode (b) plots for mild steel in 1 M HCl + 7.5 × 10−5 M inhibitor solution: (…) experimental; (−) fitted data.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

430

scratches. Fig. 13b and c show the steel surface after 24 h of immersionin 1 M HCl without and with 7.5 × 10−5 M of NO2AM. The Fig. 13brepresents the SEM micrograph in absence of the NO2AM which is se-verely corroded due to attack of acid on mild steel. However, in pre-sence of NO2AM (Fig. 13c) the surface morphologies remarkably im-proved due to the adsorption of NO2AM on mild steel surface thatprotects the surface from acid corrosion.

3.8. Mechanism of corrosion inhibition by azomethine NO2AM

Generally, it is assumed that the first stage in the action mechanismof the inhibition in acid medium is the adsorption of the inhibitor ontothe metal surface. The process of adsorption is influenced by the natureand the charge of the metal, by the chemical structure of the organicinhibitor and the type of aggressive electrolyte. The charge of the metal

surface can be determined from the potential of zero charge (pcz) on thecorrelative scale (φc) [79] by the equation:

= − =φ E Ec qcorr 0 (15)

where Eq=0 is the potential of zero charge. The pcz of iron in HCl so-lution is −530 mV vs. SCE [80]. In the present system, the obtainedvalue of Ecorr in 1 M HCl is −511,6 mV vs. SCE. So, the value of φc is+18.4 mV vs. SCE. The steel surface charge positive in 1 M HCl solu-tion because the value of φc > 0. There is a tendency of the acid anions(Cl− ions) to be specifically adsorbed creating an excess negativecharge towards the solution and favor more adsorption of the azo-methine cations [81].

The adsorption of NO2AM on mild steel surface by following ways:(i) electro-static interaction of protonated inhibitor molecules with pre-adsorbed Cl− ions (physisorption) (ii) interaction between unsharedelectron pairs of hetero-atoms (N,O) and vacant d-orbital of Fe-atoms(chemisorption) and (iii) donor–acceptor interactions between the π-electrons of aromatic ring and vacant d-orbital of Fe-atoms. The pro-tonated sites of inhibitor molecules may adsorb the on the metal surfacethrough a synergistic effect with pre-adsorbed Cl−. The positivelycharged inhibitor molecules start competing with H+ for electrons onmild steel surface and after releasing H2 gas, the NO2AM moleculesreturn to the neutral stage having free lone pairs of electron availablefor empty d orbitals of Fe-atoms. The accumulation of extra negativecharges on the mild steel surface can be transferred from the d orbital of

Table 3EIS parameters for the corrosion of mild steel in 1 M HCl solution without and with different concentrations of NO2AM at 25 °C.

Inhibitor C (M) Rs (Ω cm2) Rct (Ω cm2) CPE Cdl (μF cm−2) EISIE (%)

n Q (Ω−1Sn cm2)

Blank 0.172 11.23 0.816 286.12 1764.55 –NO2AM 5 × 10−6 0.532 73.200 0.884 74.33 229.56 84.65

1 × 10−5 0.519 115.80 0.889 46.84 136.53 90.302.5 × 10−5 0.511 150.01 0.895 37.05 101.75 92.315 × 10−5 0.572 155.90 0.896 31.35 84.00 92.607.5 × 10−5 0.458 205.90 0.892 21.68 59.95 94.54

-1 0 1 2 3 4 5

0

-20

-40

-60

-80

Log f (Hz)

HCl 1M

5 x 10-6 M

1 x 10-5M

2.5 x 10-5M

5 x 10-5M

7.5 x 10-5M

Phas

e an

gle

(D

egre

e)

-1 0 1 2 3 4 5

-1

0

1

2

HCl 1M

5 x 10-6M

1 x 10-5M

2.5 x 10-5M

5 x 10-5M

7.5 x 10-5M

Log

Z (

ohm

cm

2 )

Log f (Hz)

Fig. 7. Bode plots for mild steel in 1 M HCl solution without and with different con-centrations of NO2AM at 25 °C.

Table 4Influence of temperature on electrochemical parameters of mild steel electrode immersedin 1 M HCl at different concentrations of NO2AM.

T (°C) C (M) −Ecorr(mV/SCE)

−Bc

(mV/dec)Ba

(mV/dec)icorr(mA cm−2)

EIP(%)

θ

Blank 511.6 63.7 65.4 0.5157 – –25 5 × 10−6 521.9 74.9 89.3 0.1015 80.31 0.80

1 × 10−5 516.8 79.4 73.0 0.0653 87.33 0.872.5 × 10−5 503.3 84.7 59.1 0.0471 90.86 0.905 × 10−5 509.5 75.2 57.9 0.0412 92.01 0.927.5 × 10−5 550.8 85.3 74.3 0.0380 92.63 0.92Blank 480.1 87.2 86.0 0.9895 – –

35 5 × 10−6 471.7 72.5 68.5 0.2204 77.72 0.771 × 10−5 474.2 73.6 73.4 0.1778 82.03 0.822.5 × 10−5 496.3 71.8 86.6 0.1055 88.28 0.885 × 10−5 475.4 98.3 79.4 0.0982 90.01 0.907.5 × 10−5 506.3 76.4 80.7 0.0898 90.92 0.90Blank 462.7 71.9 87.4 1.5780 – –

45 5 × 10−6 487.7 73.7 82.5 0.3810 75.85 0.751 × 10−5 504.5 68.2 86.3 0.3055 80.64 0.802.5 × 10−5 495.5 70.8 85.5 0.2680 85.55 0.855 × 10−5 477.5 98.4 77.7 0.1708 89.17 0.897.5 × 10−5 495.8 75.5 69.9 0.1537 90.25 0.90Blank 461.5 64.9 75.5 2.0668 – –

55 5 × 10−6 478.7 82.8 93.0 0.5596 72.92 0.721 × 10−5 465.7 62.4 75.7 0.4621 77.64 0.772.5 × 10−5 450.7 75.1 61.6 0.3749 81.86 0.815 × 10−5 478.7 75.2 80.2 0.2581 87.51 0.877.5 × 10−5 442.6 82.3 87.0 0.2297 88.88 0.88

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

431

Fe to unoccupied π∗ (anti-bonding) of NO2AM molecules (retro-dona-tion). The combination of all ways of adsorption strengthens adsorptionof NO2AM molecules on mild steel surface [82]. Finally, a layer ofadsorbed inhibitor film is formed on the steel surface and acts as abarrier between the metal and corrosive medium, to prevent the cor-rosion of metal. On the basis of the above analysis and speculation, onecan conclude that the studied (NO2AM) inhibitor is of mixed-type, andthe adsorption of the inhibitor contains two modes of interaction, i.e.physisorption and chemisorption. In Section 3.2, the values of ΔGads

°

are between −20 and −40 kJ mol−1, which also confirms the twomodes of interaction between inhibitor molecules and steel surface, i.e.physisorption and chemisorption? To more clearly show the inhibitionmechanism for mild steel corrosion in hydrochloric acid media, anadsorption and protection model is proposed as shown in Fig. 14.

3.9. Quantum chemistry calculations

Quantum chemical calculations can provide the information aboutthe structural parameters of the inhibitor molecule, while the inhibitionmechanism can be accounted for the chemical reactivity of the com-pound. The quantum chemical calculation was also performed to es-tablished relation between molecular structure and inhibition efficiencyof the investigated NO2AM [83,84]. The optimized molecular structure

and the frontier molecule orbital density distributions of the moleculeNO2AM are calculated using the DFT approach with the B3LYP/6-31G(d,p) level, which are shown in Figs. 15 and 16. The quantum chemicalparameters are listed in Table 7.

The molecular electrostatic potential (MEP) is related to the

-800 -700 -600 -500 -400 -300 -200-2

-1

0

1

2

3

log

i (m

A c

m-2

)

E (mV/SCE)

25 °C 35 °C 45 °C 55 °C

(a)

-800 -700 -600 -500 -400 -300 -200-3

-2

-1

0

1

2

3

log

i (m

A c

m-2

)

E (mV/SCE)

25 °C 35 °C 45 °C 55 °C

(b)

Fig. 8. Potentiodynamic polarization curves of mild steel in 1 M HCl solution (a) in theabsence and (b) presence of 7.5 × 10−5 M NO2AM at various temperatures.

300 305 310 315 320 325 330 335

-4

-3

-2

-1

0

1

Blank

5x10-6 M

1x10-5 M

2.5x10-5 M

5x10-5 M

7.5x10-5 M

ln i co

rr(m

A c

m-2)

10 T -1 (K-1)

Fig. 9. Arrhenius plots for mild steel in 1 M HCl in the absence and presence of differentconcentrations of NO2AM.

Table 5Activation parameters for mild steel in 1 M HCl in the absence and presence of differentconcentrations of NO2AM.

Inhibitor C (M) Ea (KJ mol−1) ΔHa0 (KJ mol−1) ΔSa0 (J mol−1)

Blank 37.97 28.134 −137.636NO2AM 5× 10−6 45.70 40.515 −128.307

1 × 10−5 51.06 43.955 −127.3072.5 × 10−5 57.83 46.767 −122.1555 × 10−5 79.40 48.950 −114.3067.5 × 10−5 79.40 52.028 −109.583

305 310 315 320 325 330 335

-10

-8

-6

-4

-2

0

2

Blank

5x10-6 M

1x10-5 M

2.5x10-5 M

5x10-5 M

7.5x10-5 M

ln i co

rr(m

A c

m-2)

10T -1 (K-1)

Fig. 10. Alternative Arrhenius plots for mild steel in 1 M HCl in the absence and presenceof different concentrations of NO2AM.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

432

electronic density. It is a very useful descriptor in understanding thesites for the electrophilic and nucleophilic attack [6,83]. The contourand the total electron density surface mapped with molecular electro-static potential (MEP) of NO2AM are shown in Fig. 15b and c, respec-tively. The negative (red) regions of the MEP are related to nucleophilic

reactivity and the positive (blue) regions to electrophilic reactivity. Ascan be seen from this figure, it is clear that more electron rich regionsare mainly localized around the heteroatoms and the conjugated doublebonds. As noticed that NO2AM can promote the formation of a chelateon the mild steel surface by transferring electrons from benzene ring toiron atom d-orbital and forming a coordinate covalent bond through thechemical adsorption. In this way, the mild steel acting as an electro-phile is susceptible to attract the negatively charged sites of inhibitormolecule, and the nucleophilic centers of inhibitor molecules are nor-mally heteroatoms with free electron pairs, functional electronegativegroups and π-electrons in conjugated double bonds, which are readilyavailable to form chemical bonds [84].

EHOMO is often associated with the capacity of a molecule to donatean electron. A high value of EHOMO probably indicates a tendency of themolecule to donate electrons to appropriate acceptor molecules withlow energy and empty molecular orbital. ELUMO indicates the ability ofthe molecule to accept electrons. The lower value of ELUMO, the moreprobable is that the molecule would accept electrons [85]. The groundstate geometry of the inhibitor, as well as the nature of its frontiermolecular orbitals, namely, the HOMO and LUMO is involved in theactivity properties of the inhibitor (Fig. 16a and b). Noteworthy, theshape of the HOMO and LUMO is structurally dependent and theelectron density of the HOMO location in the inhibitor under study ismostly distributed on the atoms having a delocalized character in-dicating that these atoms are the favorite adsorption sites. The HOMOand LUMO are strongly delocalized in the conjugated system of themolecule NO2AM. According to the frontier molecular orbital theory(FMO) of chemical reactivity, the transition of an electron is due to theinteraction between highest occupied molecular orbital (HOMO) andlowest unoccupied molecular orbital (LUMO) of reacting species[86,87]. Therefore, higher values of EHOMO indicate a better tendencytowards the donation of the electron, enhancing the adsorption of theinhibitor on mild steel and therefore better inhibition efficiency. Thebinding ability of the inhibitor to the metal surface increases with in-creasing of the HOMO and decreasing of the LUMO energy values. It isclear from Table 7 that the neutral form of NO2AM exhibits the lowestEHOMO, making the neutral form the most likely form for the interactionof carbon steel with NO2AM molecule. The ELUMO of the neutral in-hibitor also decreased resulting in an increase in its ability towardsaccepting electrons from the filled d-orbital of the metal. The main rolein adsorption phenomena occurs on LUMO orbitals, the low ELUMO ispreferred because the feedback bonds are formed between d orbitals ofmetal and inhibitor. Formation of feedback bonds increases the che-mical adsorption of inhibitor molecules on the metal surface and thusincreases the inhibition efficiency. A similar report has been docu-mented [7].

According to the frontier orbital theory, the reaction of reactantsmainly occurs in HOMO and LUMO [88]. So, the smaller gap (ΔE)between EHOMO and ELUMO is the more probable to donate and acceptelectrons. The values of ΔE in Table 7, suggesting the strongest abilityof the inhibitor to form coordinate bonds with d-orbitals of metalthrough donating and accepting electrons. It is in good agreement withthe experimental results. Consequently, concerning the value of theenergy gap (ΔE), larger values of the energy difference will provide lowreactivity to a chemical species. Lower values of the ΔE will rendergood inhibition efficiency because the energy required to remove anelectron from the lowest occupied orbital will be low [89]. Energy bandgap ΔE is an important parameter as a function of reactivity of theinhibitor molecule towards the adsorption on the metallic surface(physisorption and chemisorption). In this work, NO2AM shows a goodinhibitory effect against the iron corrosion in acid solution [89,90]. Thisparameter provides a measure of the stability of the inhibitor moleculetowards the adsorption on the metal surface. As ΔE gap decreases, thereactivity of the molecule increases, leading to increasing the inhibitionefficiency of the molecule. The calculation in Table 7 shows thatNO2AM in the neutred form has the smallest energy gap value

Fig. 11. Langmuir adsorption isotherm of NO2AM on mild steel in 1 M HCl at differenttemperatures.

Table 6Thermodynamic parameters of adsorption for mild steel in 1 M HCl at different tem-peratures from Langmuir adsorption isotherm.

Inhibitor T (°C) 105 × Kads

(M−1)−ΔGads

0

(KJ mol−1)−ΔHads

0

(KJ mol−1)ΔSads0

(J−1 K−1)

NO2AM 25 0.8092 38.98 22.20 38.8235 1.0659 39.6045 1.5786 39.8555 1.8347 40.77

295 300 305 310 315 320 325 330

-41,1

-40,8

-40,5

-40,2

-39,9

-39,6

-39,3

-39,0

G 0 ad

s(K

J m

ol-1

)

T (K)

NO2AM

Fig. 12. The relationship between ΔGads° and 1/T for NO2AM in 1 M HCl medium.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

433

indicating that it is in this form that azomethine can easily adsorb onthe metal surface causing higher protection [7].

Additionally, for the dipole moment (μ), a higher value of μ willfavor the enhancement of corrosion inhibition. The high value of (μ)probably increases the adsorption between the chemical compound andthe metal surface [90]. The energy of the deformability increases withthe increase in μ, making the molecule easier to adsorb on the iron (Fe)surface. From Table 7, the value of μ is higher, which is also in agree-ment with the experimental results mentioned above. In the presentstudy the high values of μ (9.45 D and 15.40 D for the neutral andprotonated species respectively) are in favor of high adsorption of theinhibitor molecule on the surface of the mild steel.

HOMO and LUMO energies of the inhibitor molecule are related toionization potential (I) and electron affinity (A), respectively:

= −I EHOMO (16)

= −A ELUMO (17)

Then absolute electronegativity (χ), and global hardness (γ) of theinhibitor molecule are calculated as follows [91]:

= +χ I A2 (18)

= −γ I A2 (19)

As hardness (γ), softness (σ) is a global chemical descriptor mea-suring the molecular stability and reactivity and is given by [92]:

=σγ1

(20)

Ionization energy (I) is a fundamental descriptor of the chemicalreactivity of atoms and molecules. High ionization energy indicateshigh stability and chemical inertness, while small ionization energyindicates high reactivity of the atoms and molecules [84]. Absolutehardness (γ) and softness (σ) are important properties to measure themolecular stability and reactivity. It is apparent that the chemicalhardness fundamentally signifies the resistance towards the deforma-tion or polarization of the electron cloud of the atoms, ions or moleculesunder a small perturbation of chemical reaction. A hard molecule has alarge energy gap and a soft molecule has a small energy gap [84].

(a) (b)

(c)

Fig. 13. SEM images of mild steel in 1 M HClsolution at 25 °C before and after 24 h immer-sion: (a) before immersion (polished), (b) in HCl1 M without NO2AM and (c) in HCl 1 M withNO2AM at 7.5 × 10−5 M.

Fe2+Fe

2+Cl

-Cl

-

N+

N

N+

N

O

O

O+

CH3

Fe3+

Fe3+

Fe3+Fe

2+Cl

-Cl

-Cl

-

physisorption

chemisorption

ritro-donation

" "

""

" "

Fig. 14. Schematic illustration of the adsorption mechanism ofinhibitor on mild steel surface in 1 M HCl solution.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

434

Normally, the inhibitor with the least value of global hardness (hencethe highest value of global softness) is expected to have the highestinhibition efficiency. For the simplest transfer of an electron, adsorptioncould occur at the part of the molecule where softness (σ), which is alocal property, has the highest value [85]. Table 7 shows the neutralform to have the lowest γ and highest σ. Thus, the neutred form of theinhibitor having the maximum value of softness (σ), adsorbs strongly at

the surface of mild steel and shows maximum inhibition efficiency.Thus the fraction of electrons transferred from the inhibitor to

metallic surfaceΔN is given by equation [92]:

∆ =−+

Nχ χγ γ2( )Fe inh

Fe inh (21)

where χFe and χinh represent the absolute electronegativity of the ironatom (Fe) and the inhibitor molecule, respectively; γFe and γinh re-present the absolute hardness of Fe atom and the inhibitor molecules,respectively. A theoretical value for the electronegativity of bulk ironwas used χFe = 7 eV and a global hardness of γFe = 0, by assuming thatfor a metallic bulk I = A because they are softer than the neutral me-tallic atoms [91,92]. The calculated results are presented in Table 7.Generally, value of ΔN shows inhibition efficiency resulting fromelectron donation, and the inhibition efficiency increases with the in-crease in electron donating ability to the metal surface. The value of the

(a)

(b)

(c)

Neutral form

Protonated form

Fig. 15. Quantum chemical results of NO2AM molecule calculated by the DFT/B3LYPmethod with 6-31G (d, p) basis set: (a) optimized molecular structure neutral and pro-tonated form; (b) contour map of electrostatic potential and (c) total electron densitysurface mapped with electrostatic potential. (For interpretation of the references to colourin this figure, the reader is referred to the web version of this article.)

Fig. 16. Frontier molecule orbital density distributions of NO2AM: HOMO (a) and LUMO(b).

Table 7The quantum chemical parameters of the neutral and protonated form of NO2AM ob-tained from DFT/B3LYP/6-31G (d,p) method.

Parameters Inhibitor (NO2AM)

Neutral form Protonated form

EHOMO (eV) −7.08 −5.39ELUMO (eV) −3.331 −2.442ΔE (eV) −3.749 −2.95μ (Debye) 9.458 15.404I (eV) 7.08 5.39A (eV) 3.33 2.442χ (eV) 5.2 3.916γ (eV) 1.88 2.948σ (eV)−1 0.53 0.33ΔN 0.48 0.52

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

435

ΔN shows inhibition effect resulted from electron donation. Accordingto Lukovits' study [93], if ΔN < 3.6, the inhibition efficiency increaseswith increasing electron-donating ability of the metal surface. Based onthese calculations, it is expected that the synthesized inhibitor is adonor of electrons, and the steel surface is the acceptor, and this favorschemical adsorption of the inhibitor on the electrode surface. Here theinhibitor binds to the steel surface and forms an adsorption layeragainst corrosion. The inhibitor shows the highest inhibition efficiencybecause it has the highest HOMO energy and this reflects the greatestability (the lowestΔN) of offering electrons. The number of electronstransferred is higher in the neutral specie than in the protonated spices.All these factors indicate that the neutral specie has the least tendencyto donate electrons to the metal surface. Therefore, its interaction withthe metal surface would preferentially involve electrostatic interactionrather than chemical bond formation [94]. It can be seen from Table 6that the ability of the inhibitor to donate electrons to the metal surface,which is in good agreement with the higher inhibition efficiency of theinhibitor NO2AM.

The use of Mulliken population analysis to estimate the adsorptioncenters of inhibitors has been widely reported and it is mostly used forthe calculation of the charge distribution over the whole skeleton of themolecule [90,95]. There is a general consensus by several authors thatthe more negatively charged heteroatom is, the more is its ability toabsorb on the metal surface through a donor-acceptor type reaction[6,96]. Variation in the inhibition efficiency of the inhibitor depends onthe presence of electronegative eOe and ]Ne atoms as substitutes intheir Fig. 15a representing the effective atomic charges from Mullikenpopulations in the neutral and protonated forms of NO2AM inhibitor,shows that oxygen and nitrogen (eOe, ]Ne) atoms and some carbonatoms carry more negative charges, while the remaining carbon atomscarry more positive charges. This means that the atoms carrying ne-gative charges are the negative charge centers, which can offer elec-trons to the Fe atoms to form coordinate bond, and the atoms carryingpositive charges are the positive charge centers, which can acceptelectrons from orbital of Fe atoms to form feedback bond. We empha-size also that the highest negative charges were found for the atomsN15, O17, O33, O34, C18, N13 and N12 with values of −0.451,−0.417, −0.403, −0.402 -0.382, −0.263 and −0.260, respectively(Fig. 15a. neutral). On the other hand these values were found to be−0.721, −0.563,-0.458, −0.457, −0.434, −0.491 and−0.0.417 forthe protonated molecule, respectively. As observed a small decrease inthe charges are revealed except for N15 whose negative charge in-creases as a result of protonation which has an effect on the azomethinedouble bond. While the highest positive charges were found for theatom C14, C16, C22 and C29. These findings are attributed to theelectronegativity of the oxygen and nitrogen atoms. Thus, the opti-mized structure is in accordance with the fact that excellent corrosioninhibitors cannot only offer electrons to an unoccupied orbital of themetal but also accept free electrons from the metal. Therefore, it can beinferred that triazole (eC]Ne, eN]Ne), the anisyl substituent (eOe)for NO2AM are the possible active adsorption sites.

Natural bonding orbital (NBO) analysis provides an efficient methodfor studying intra and inter-molecular bonding and interaction amongbonds, and also provides a convenient basis for investigating chargetransfer or conjugative interaction in molecular systems [97]. In orderto investigate the interactions between the filled orbitals of one sub-system and vacant orbitals of other system NBO values are calculated.The oxygen, nitrogen and some carbon atoms of the benzene ring ofNO2AM have the negative charges, which are the most favored sites forbonding to mild steel surface through donating electrons.

4. Conclusions

Corrosion inhibition properties of 1-(4-Nitrophenylo-imino)-1-(phenylhydrazono)-propan-2-one (NO2AM), on mild steel in 1 M HClhave been investigated using weight loss, electrochemical methods,

spectroscopic and morphologic techniques and theoretical calculations.The following conclusions were drawn:

➢ The azomethine NO2AM shows good inhibition efficiency for thecorrosion of mild steel in 1 M HCl solution. The inhibition perfor-mance increases with increase in inhibitor concentration and de-creases with increase in temperature. The maximum inhibition ef-ficiency was observed around 96.06% at 7.5 × 10−5 M at 25 °C.

➢ The potentiodynamic polarization study revealed that NO2AM be-haved as a mixed type inhibitor.

➢ Electrochemical impedance spectroscopy (EIS) measurementshowed that the polarization resistance (Rp) increases and doublelayer capacitance (Cdl) decreases in the presence of inhibitor, whichsuggests the adsorption of the inhibitor molecules on mild steelsurface.

➢ The NO2AM adsorbs spontaneously on the metal surface and itsadsorption behavior obeys Langmuir adsorption isotherm featuringcompetitive physisorption and chemisorption mechanisms.

➢ SEM technique confirmed the formation of a protective film byNO2AM on mild steel surface.

➢ Quantum chemical calculations showed a good agreement betweenthe theoretical and experimental results.

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.jelechem.2017.08.031.

References

[1] R. Yildiz, An electrochemical and theoretical evaluation of 4,6-diamino-2-pyr-imidinethiol as a corrosion inhibitor for mild steel in HCl solutions, Corros. Sci. 90(2015) 544–553.

[2] S.M. Shaban, A.A. Abd-Elaal, S.M. Tawfik, Gravimetric and electrochemical eva-luation of three nonionic dithiol surfactants as corrosion inhibitors for mild steel in1 M HCl solution, J. Mol. Liq. 216 (2016) 392–400.

[3] A.S. Fouda, A.S. Ellithy, Inhibition effect of 4-phenylthiazole derivatives on corro-sion of 304L stainless steel in HCl solution, Corros. Sci. 51 (2009) 868–875.

[4] H. Hamani, T. Douadi, D. Daoud, M. Al-Noaimi, S. Chafaa, Corrosion inhibitionefficiency and adsorption behavior of azomethine compounds at mild steel/hy-drochloric acid interface, Measurement 94 (2016) 837–846.

[5] H. Hamani, T. Douadi, M. Al-Noaimi, S. Issaadi, D. Daoud, S. Chafaa,Electrochemical and quantum chemical studies of some azomethine compounds ascorrosion inhibitors for mild steel in 1 M hydrochlori cacid, Corros. Sci. 88 (2014)234–245.

[6] D. Daoud, T. Douadi, H. Hamani, M. Al-Noaimi, S. Chafaa, Corrosion inhibition ofmild steel by two new S-heterocyclic compounds in 1 M HCl: experimental andcomputational study, Corros. Sci. 94 (2015) 21–37.

[7] D. Daoud, T. Douadi, S. Issaadi, S. Chafaa, Adsorption and corrosion inhibitionofnew synthesized thiophene Schiff base on mild steel X52 in HCl and H2SO4 solu-tions, Corros. Sci. 79 (2014) 50–58.

[8] S. Issaadi, T. Douadi, A. Zouaoui, S. Chafaa, M.A. Khan, G. Bouet, Novel thiophenesymmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidicmedia, Corros. Sci. 53 (2011) 1484–1488.

[9] S. Issaadi, T. Douadi, S. Chafaa, Adsorption and inhibitive properties of a newheterocyclic furan Schiff base on corrosion of copper in HCl 1 M: experimental andtheoretical investigation, Appl. Surf. Sci. 316 (2014) 582–589.

[10] C. Verma, M.A. Quraishi, A. Singh, A thermodynamical, electrochemical, theore-tical and surface investigation of diheteroaryl thioethers as effective corrosion in-hibitors for mild steel in 1 M HCl, J. Taiwan Inst. Chem. Eng. 58 (2016) 127–140.

[11] H. Shokry, Molecular dynamics simulation and quantum chemical calculations forthe adsorption of some Azo-azomethine derivatives on mild steel, J. Mol. Liq. 1060(2014) 80–87.

[12] H. Shokry, Molecular dynamics simulation and quantum chemical calculations forthe adsorption of some Azo-azomethine derivatives on mild steel, J. Mol. Struct.1060 (2014) 80–87.

[13] Mehdi Salih Shihab, Hanan Hussien Al-Doori, Experimental and theoretical study of[N-substituted] p-aminoazobenzene derivatives as corrosion inhibitors for mildsteel in sulphuric acid solution, J. Mol. Struct. 1076 (2014) 658–663.

[14] A. Reza, H. Zadeh, I. Danaee, M.H. Maddahy, Thermodynamic and adsorption be-haviour of medicinal nitramine as a corrosion inhibitor for AISI steel alloy in HClsolution, J. Mater. Sci. Technol. 29 (2013) 884–892.

[15] T. Douadi, H. Hamani, D. Daoud, M. Al-Noaimi, S. Chafaa, Effect of temperatureand hydrodynamic conditions on corrosion inhibition of an azomethine compoundsfor mild steel in 1 M HCl solution, J. Taiwan Inst. Chem. Eng. 71 (2017) 388–404.

[16] K.R. Ansari, M.A. Quraishi, A. Singh, Schiff's base of pyridyl substituted triazoles as

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

436

new and effective corrosion inhibitors for mild steel in hydrochloric acid solution,Corros. Sci. 79 (2014) 5–15.

[17] R.A. Prabhu, T.V. Venkatesha, A.V. Shanbhag, G.M. Kulkarni, R.G. Kalkhambkar,Inhibition effects of some Schiff's bases on the corrosion of mild steel in hydro-chloric acid solution, Corros. Sci. 50 (2008) 3356–3362.

[18] A. Asan, S. Soylu, T. Kiyak, F. Yildirim, S.G. Oztas, N. Ancin, M. Kabasakaloglu,Investigation on some Schiff bases as corrosion inhibitors for mild steel, Corros. Sci.48 (2006) 3933–3944.

[19] I. Warad, M. Al-Noaimi, O.S. Abdel-Rahman, F.F. Awwadi, B. Hammouti,T.B. Hadda, Trans/cis isomerization of [RuCl2{H2C]C(CH2PPh2)2}(diamine)]complexes: synthesis, spectral, crystal structure and DFT calculations and catalyticactivity in the hydrogenation of a,b-unsaturated ketones, Spectrochim. Acta A 117(2014) 250–258.

[20] M. Al-Noaimi, H. Saadeh, S.F. Haddad, M.I. El-Barghouthi, M. El-khateeb,R.J. Crutchley, Syntheses, crystallography and spectroelectrochemical studies ofruthenium azomethine complexes, Polyhedron 26 (2007) 3675–3685.

[21] M. Al-Noaimi, M.A. Al-Damen, Ruthenium complexes incorporating azoimine anda-diamine based ligands: synthesis, crystal structure, electrochemistry and DFTcalculation, Inorg. Chim. Acta 387 (2012) 45–51.

[22] M.S. Masoud, M.K. Awad, M.A. Shaker, M.M.T. El-Tahawy, The role of structuralchemistry in the inhibitive performance of some amino pyrimidines on the corro-sion of steel, Corros. Sci. 52 (2010) 2387–2396.

[23] B. Schade, V. Hagen, R. Schmidt, R. Herbrich, E. Krause, T. Eckardt, J. Bendig,Deactivation behavior and excited state properties of (coumarin-4yl)methyl deri-vatives. 1. Photocleavage of (7-methoxycoumarin-4-yl)methyl-caged acids withfluorescence enhancement, J. Org. Chem. 64 (1999) 9109–9117.

[24] S. Nad, H. Pal, Unusual photophysical properties of coumarin-151, J. Phys. Chem. A105 (2001) 1097–1106.

[25] H. Yu, H. Mizufune, K. Uenaka, T. Moritoki, H. Koshima, Synthesis and properties ofcoumarin-derived organogelators, Tetrahedron 61 (2005) 8932–8938.

[26] O.D. Kachkovski, O.I. Tolmachev, L.O. Kobryn, E.E. Bila, M.I. Ganushchak,Absorption spectra and nature of electron transitions in azomethine dyes as 6-de-rivatives of 2H-2-chromenone, Dyes Pigments 63 (2004) 203–211.

[27] P. Frohberg, I. Schulze, C. Donner, F. Krauth, Remarkable stereoselectivity switch insynthesis of carbonyl substituted N2-arylamidrazones with low lipophilicity,Tetrahedron Lett. 53 (2012) 4507–4509.

[28] D.M. Wilson, A.P. Termin, L. Mao, M.M. Ramirez-Weinhouse, V. Molteni,P.D.J. Grootenhuis, K. Miller, S. Keim, G. Wise, Arylamidrazones as novel cortico-tropin releasing factor receptor antagonists, J. Med. Chem. 45 (2002) 2123–2126.

[29] Y. Sasikumar, A.S. Adekunle, L.O. Olasunkanmi, I. Bahadur, R. Baskar,M.M. Kabanda, I.B. Obot, E.E. Ebenso, J. Mol. Liq. 211 (2015) 105–118.

[30] G. Gece, The use of quantum chemical methods in corrosion inhibitor studies,Corros. Sci. 50 (2008) 2981–2992.

[31] M. Behpoura, S.M. Ghoreishi, N. Mohammadi, N. Soltani, M. Salavati-Niasari,Investigation of some Schiff base compounds containing disulfide bond as HClcorrosion inhibitors for mild steel, Corros. Sci. 52 (2010) 4046–4057.

[32] R. Solmaz, Investigation of adsorption and corrosion inhibition of mild steel inhydrochloric acid solution by 5-(4 Dimethylaminobenzylidene) rhodanine, Corros.Sci. 79 (2014) 169–176.

[33] I. Danaee, O. Ghasemi, G.R. Rashed, M. Rashvand Avei, M.H. Maddahy, Effect ofhydroxyl group position on adsorption behavior and corrosion inhibition of hy-droxybenzaldehyde Schiff bases: electrochemical and quantum calculations, J. Mol.Struct. 1035 (2013) 247–259.

[34] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson,H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox,H.P. Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann,O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala,K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski,S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck,K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford,J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara,M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez,J.A. Pople, Gaussian 03, Revision B.03, Gaussian Inc., Pittsburgh PA, 2003.

[35] I. Ahamad, M.A. Quraishi, Mebendazole: new and efficient corrosion inhibitor formild steel in acid medium, Corros. Sci. 52 (2010) 651–656.

[36] N.O. Obi-Egbedi, I.B. Obot, Xanthione: a new and effective corrosion inhibitor formild steel in sulphuric acid solution, Arab. J. Chem. 6 (2010) 211–223.

[37] M.A. Quraishi, H.K. Sharma, 4-Amino-3-butyl-5-mercapto-1, 2, 4-triazole: a newcorrosion inhibitor for mild steel in sulphuric acid, Mater. Chem. Phys. 78 (2002)18–21.

[38] I.B. Obot, N.O. Obi-Egbedi, Indeno-1-one [2, 3-b] quinoxaline as an effective in-hibitor for the corrosion of mild steel in 0.5 M H2SO4 solution, Mater. Chem. Phys.122 (2010) 325–328.

[39] V. Rajeswari, D. Kesavan, M. Gopiraman, P. Viswanathamurth, Physicochemicalstudies of glucose, gellan gum, and hydroxypropyl cellulose–inhibition of cast ironcorrosion, Carbohydr. Polym. 95 (2013) 288–294.

[40] S. Dahiya, S. Lata, R. Kumar, O.S. Yadav, O.S. Yadav, Comparative performance ofUroniums for controlling corrosion of steel with methodical mechanism of inhibi-tion in acidic medium, J. Mol. Liq. 221 (2016) 124–132.

[41] L.O. Olasunkanmi, M.M. Kabanda, E.E. Ebenso, Quinoxaline derivatives as corro-sion inhibitors for mild steel in hydrochloric acid medium: electrochemical andquantum chemical studies, Physica E76 (2016) 109–126.

[42] Sudheer, M.A. Quraishi, 2-Amino-3, 5-dicarbonitrile-6-thio-pyridines: new and ef-fective corrosion inhibitors for mild steel in 1 M HCl, Ind. Eng. Chem. Res. 53(2014) 2851–2859.

[43] M. Lebrini, F. Robert, H. Vezin, C. Roos, Electrochemical and quantum chemicalstudies of some indole derivatives as corrosion inhibitors for C38 steel in molarhydrochloric acid, Corros. Sci. 52 (2010) 3367–3376.

[44] S.T. Selvi, V. Raman, N. Rajendran, Corrosion inhibition of mild steel by benzo-triazole derivatives in acidic medium, Appl. Surf. Elec. 33 (2003) 1175–1182.

[45] M. Behpour, S.M. Ghoreishi, A. Gandomi-Niasar, N. Soltani, M. Salavati-Niasari,The inhibition of mild steel corrosion in hydrochloric acid media by two Schiff basecompounds, J. Mater. Sci. 44 (2009) 2444–2453.

[46] X. He, Y. Jiang, C. Li, W. Wang, B. Hou, L. Wu, Inhibition properties and adsorptionbehavior of imidazole and 2-phenyl-2-imidazoline on AA5052 in 1.0 M HCl solu-tion, Corros. Sci. 83 (2014) 124–136.

[47] R. Solmaz, G. Kardas, M. Culha, B. Yazici, M. Erbil, Investigation of adsorption andinhibitive effect of 2-mercaptothiazoline on corrosion of mild steel in hydrochloricacid media, Electrochim. Acta 53 (2008) 5941–5952.

[48] B. Qian, J. Wang, M. Zhang, B.R. Hou, Synergistic effect of polyaspartic acid andiodide ion on corrosion inhibition of mild steel in H2SO4, Corros. Sci. 75 (2013)184–192.

[49] R. Fuchs-Godec, The adsorption, CMC determination and corrosion inhibition ofsome N-alkyl quaternary ammonium salts on carbon steel surface in 2 M H2SO4,Colloids Surf. A 280 (2006) 130–139.

[50] H. Bentrah, Y. Rahali, A. Chala, Gum arabic as an eco-friendly inhibitor for API 5LX42 pipeline steel in HCl medium, Corros. Sci. 82 (2014) 426–431.

[51] X. Li, X. Xie, S. Deng, G. Du, Two phenylpyrimidine derivatives as new corrosioninhibitors for cold rolled steel in hydrochloric acid solution, Corros. Sci. 87 (2014)27–39.

[52] M. Behpour, S.M. Ghoreishi, Investigation some Schiff base compounds containingdisulfide bonds as HCl corrosion inhibitors for mild steel, Corros. Sci. 52 (2010)4046–4057.

[53] M. Lebrini, M. Lagrenée, H. Vezin, M. Traisnel, F. Bentiss, Experimental and the-oretical study for corrosion inhibition of mild steel in normal hydrochloric acidsolution by some new macrocyclic polyether compounds, Corros. Sci. 49 (2007)2254–2269.

[54] Nurdane Yilmaz, Alper Fitozc, Umit Ergun, Kaan C. Emregul, A combined electro-chemical and theoretical study into the effect of 2-((thiazole-2-ylimino)methyl)phenol as a corrosion inhibitor for mild steel in a highly acidic environment, Corros.Sci. 111 (2016) 110–120.

[55] A.O. Yüce, R. Solmaz, G. Kardaş, Investigation of inhibition effect of rhodanine-N-acetic acid on mild steel corrosion in HCl solution, Mater. Chem. Phys. 131 (2012)615–620.

[56] A. Döner, G. Kardaş, N-Aminorhodanine as an effective corrosion inhibitor for mildsteel in 0.5 M H2SO4, Corros. Sci. 53 (2011) 4223–4232.

[57] R. Yıldız, An electrochemical and theoretical evaluation of 4, 6-diamino-2-pyr-idinethiol as a corrosion inhibitor for mild steel in HCl solutions, Corros. Sci. 90(2015) 544–553.

[58] N.K. Gupta, C. Verma, M.A. Quraishi, A.K. Mukherjee, Schiff's bases derived from L-lysine and aromatic aldehydes as green corrosion inhibitors for mild steel: experi-mental and theoretical studies, J. Mol. Liq. 215 (2016) 47–57.

[59] M. Lebrini, F. Bentiss, H. Vezin, M. Lagrene, Inhibiting effects of some oxadiazolederivatives on the corrosion of mild steel in perchloric acid solution, Appl. Surf. Sci.252 (2005) 950–958.

[60] M. Outirite, M. Lagrenee, M. Lebrini, M. Traisnel, C. Jama, H. Vezin, F. Bentiss,Impedance, X-ray photoelectron spectroscopy and density functional theory studiesof 3,5-bis (n-pyridyl)-1,2,4-oxadiazoles as efficient corrosion inhibitors for carbonsteel surface in hydrochloric acid solution, Electrochim. Acta 55 (2010) 1670–1681.

[61] C. Verma, M.J. Reddy, M.A. Quraishi, Microwave assisted eco-friendly synthesis ofchalcones using 2, 4-dihydroxy acetophenone and aldehydes as corrosion inhibitorsfor mild steel in 1 M HCl, Anal. Bioanal. Electrochem. 6 (2014) 321–340.

[62] I. Ahamad, R. Prasad, M.A. Quraishi, Adsorption and inhibitive properties of somenew Mannich bases of Isatin derivatives on corrosion of mild steel in acidic media,Corros. Sci. 52 (2010) 1472–1481.

[63] C. Bataillon, S. Brunet, Electrochemical impedance spectroscopy on oxide formid onzir-caloy in high temperature water, Electrochim. Acta 39 (1994) 455–465.

[64] C. Verma, A. Singh, G. Pallikonda, M. Chakravarty, M.A. Quraishi, I. Bahadur,E.E. Ebenso, Aryl sulfon amido methyl phosphonates as new class of green corrosioninhibitors for mild steel in 1 M HCl: electrochemical, surface and quantum chemicalinvestigation, J. Mol. Liq. 209 (2015) 306–319.

[65] A. Döner, R. Solmaz, M. Özcan, G. Kardas, Experimental and theoretical studies ofthiazoles as corrosion inhibitors for mild steel in sulphuric acid solution, Corros. Sci.53 (2011) 2902–2913.

[66] N. Kıcır, G. Tansuğ, M. Erbil, T. Tüken, Investigation of ammonium (2,4-di-methylphenyl)-dithiocarbamate as a new, effective corrosion inhibitor for mildsteel, Corros. Sci. 105 (2016) 88–99.

[67] Z. Tao, S. Zhang, W. Li, B. Hou, Corrosion inhibition of mild steel in acidic solutionby some oxo-triazole derivatives, Corros. Sci. 51 (2009) 2588–2595.

[68] S.R. Kumar, I. Danaee, M. RashvandAvei, M. Vijayan, Quantum chemical and ex-perimental investigations on equipotent effects of (+) R and (−) S enantiomers ofracemic amisulpride as eco-friendly corrosion inhibitors for mild steel in acidicsolution, J. Mol. Liq. 212 (2015) 168–186.

[69] N.I. Kairi, J. Kassim, The effect of temperature on the corrosion inhibition of mildsteel in 1 M HCl solution by curcuma longa extract, Int. J. Electrochem. Sci. 8(2013) 7138–7155.

[70] M. Faustin, A. Maciuk, P. Salvin, C. Roos, M. Lebrini, Corrosion inhibition of C38steel by alkaloids extract of Geissospermum laeve in 1 M hydrochloric acid:

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

437

electrochemical and phytochemical studies, Corros. Sci. 92 (2015) 287–300.[71] S.M. Tawfik, N.A. Negm, Synthesis, characterization and evaluation of some anionic

surfactants with phosphate group as a biodegradable corrosion inhibitor for carbonsteel in acidic solution, J. Mol. Liq. 215 (2016) 185–196.

[72] L.C. Murulana, M.M. Kabanda, E.E. Ebenso, Investigation of the adsorption char-acteristics of some selected sulphonamide derivatives as corrosion inhibitors at mildsteel/hydrochloric acid interface: experimental, quantum chemical and QSAR stu-dies, J. Mol. Liq. 215 (2016) 763–779.

[73] M. Prajila, A. Joseph, Controlling the rate of dissolution of mild steel in sulfuric acidthrough the adsorption and inhibition characteristics of (4-(4-Hydroxybenzylideneamino)-4H-1,2,4-Triazole-3,5-diyl) dimethanol (HATD), J. Bio.Tribo. Corros. (2017) 3–10.

[74] Y.A. Albrimi, A.A. Addi, J. Douch, R.M. Souto, M. Hamdani, Inhibition of the pittingcorrosion of 304 stainless steel in 0.5 M hydrochloric acid solution by heptamo-lybdate ions, Corros. Sci. 90 (2015) 522–528.

[75] R. Yıldız, T. Doğan, İ. Dehri, Inhibition of the pitting corrosion of 304 stainless steelin 0.5 M hydrochloric acid solution by heptamolybdate ions, Corros. Sci. 85 (2014)215–221.

[76] H.M. Abd El-Lateef, Experimental and computational investigation on the corrosioninhibition characteristics of mild steel by some novel synthesized imines in hy-drochloric acid solutions, Corros. Sci. 92 (2015) 104–117.

[77] G. Quartarone, M. Battilana, L. Bonaldo, T. Tortato, Investigation of the inhibitioneffect of indole-3-carboxylic acid on the copper corrosion in 0.5 M H2SO4, Corros.Sci. 50 (2008) 3467–3474.

[78] M.A. Hegazy, S.M. Rashwan, M.M. Kamel, M.S. El Kotb, Synthesis, surface prop-erties and inhibition behavior of novel cationic gemini surfactant for corrosion ofcarbon steel tubes in acidic solution, J. Mol. Liq. 211 (2015) 126–134.

[79] M.S. Morad, Inhibition of iron corrosion in acid solutions by Cefatrexyl: behaviournear and at the corrosion potential, Corros. Sci. 50 (2008) 436–448.

[80] C. Gabrielli, M. Keddam, Review of applications of impedance and noise analysis touniform and localized corrosion, Corrosion 48 (1992) 794–811.

[81] S.K. Shukla, M.A. Quraishi, The effects of pharmaceutically active compound dox-ycycline on the corrosion of mild steel in hydrochloric acid solution, Corros. Sci. 52(2010) 314–321.

[82] R. Solmaz, G. Kardas, B. Yazici, M. Erbil, Adsorption and corrosion inhibitiveproperties of 2-amino-5-mercapto-1,3,4-thiadiazole on mild steel in hydrochloricacid media, Colloids Surf. A Physicochem. Eng. Asp. 312 (2008) 7–17.

[83] K.F. Khaled, Adsorption and inhibitive properties of a new synthesized guanidinederivative on corrosion of copper in 0.5 M H2SO4, Appl. Surf. Sci. 255 (2008)1811–1818.

[84] H. Ma, S. Chen, Z. Liu, Y. Sun, Theoretical elucidation on the inhibition mechanismof pyridine–pyrazole compound: a Hartree Fock study, J. Mol. Struct. THEOCHEM774 (2006) 19–22.

[85] M.A. Hegazya, A.M. Badawi, S.S. Abd El Rehim, W.M. Kamel, Corrosion inhibitionof carbon steel using novel N-(2-(2-mercaptoacetoxy) ethyl)-N,N-dimethyl dodecan-1 aminium bromide during acid pickling, Corros. Sci. 69 (2013) 110–122.

[86] A.Y. Musa, A.H. Kadhum, A.B. Mohamad, A.B. Rohoma, H. Mesmari,Electrochemical and quantum chemical calculations on 4,4-dimethyloxazolidine-2-thione as inhibitor for mild steel corrosion in hydrochloric, J. Mol. Struct. 969(2010) 233–237.

[87] G. Gece, S. Bilgiç, Quantum chemical study of some cyclic nitrogen compounds ascorrosion inhibitors of steel in NaCl media, Corros. Sci. 51 (2009) 1876–1878.

[88] N. Khalil, Quantum chemical approach of corrosion inhibition, Electrochim. Acta48 (2003) 2635–2640.

[89] S. Deng, X. Li, X. Xie, Hydroxymethyl urea and 1,3-bis(hydroxymethyl) urea ascorrosion inhibitors for steel in HCl solution, Corros. Sci. 80 (2014) 276–289.

[90] M. ElBelghitia, Y. Karzazi, A. Dafali, B. Hammouti, F. Bentiss, I.B. Obot, I. Bahadur,E.E. Ebenso, Experimental, quantum chemical and Monte Carlo simulation studiesof 3,5-disubstituted-4-amino-1,2,4-triazoles as corrosion inhibitors on mild steel inacidic medium, J. Mol. Liq. 218 (2016) 281–293.

[91] R.G. Parr, R.G. Pearson, Absolute hardness: companion parameter to absoluteelectronegativity, J. Am. Chem. Soc. 105 (1983) 7512–7516.

[92] R.G. Pearson, Absolute electronegativity and hardness: application to inorganicchemistry, Inorg. Chem. 27 (1988) 734–740.

[93] I. Lukovits, E. Kálmán, F. Zucchi, Corrosion inhibitors–correlation between elec-tronic structure and efficiency, Corros. Sci. 57 (2001) 3–8.

[94] A. Zarrouk, H. Zarrok, Y. Ramli, M. Bouachrine, B. Hammouti, A. Sahibed-dine,F. Bentiss, Inhibitive properties, adsorption and theoretical study of 3,7-dimethyl-1-(prop-2-yn-1-yl) quinoxalin-2(1H)-one as efficient corrosion inhibitor for carbonsteel in hydrochloric acid solution, J. Mol. Liq. 222 (2016) 239–252.

[95] M. Sahin, G. Gece, E. Karei, S. Bilgic, Experimental and theoretical study of theeffect of some heterocyclic compounds on the corrosion of low carbon steel in 3.5%NaCl medium, J. Appl. Electrochem. 38 (2008) 809–815.

[96] N.O. Obi-Egbedi, K.E. Essien, I.B. Obot, E.E. Ebenso, 1,2-Diamino anthrax quino-neas corrosion inhibitor for mild steel in hydrochloric acid: weight loss andquantum chemical study, Int. J. Electrochem. Sci. 6 (2011) 913–930.

[97] M. Snehalatha, C. Ravikumar, I. Hubert Joe, N. Sekar, V.S. Jayakumar,Spectroscopic analysis and DFT calculations of a food additive Carmoisine,Spectrochim. Acta A 72 (2009) 654–662.

H. Hamani et al. Journal of Electroanalytical Chemistry 801 (2017) 425–438

438