OPEN ACCESS

Eurasian Journal of Analytical Chemistry ISSN: 1306-3057

2017 12(3):275-294 DOI 10.12973/ejac.2017.00170a

© Authors. Terms and conditions of Creative Commons Attribution 4.0 International (CC BY 4.0) apply.

Correspondence: Karima Toumiat, Department of Materials Sciences & Physical Chemistry Laboratory Materials,

Laghouat University, Algeria.

k.toumiat@lagh-univ.dz

Copper Corrosion Inhibition using BTAH Inhibitor in Sodium Chloride Medium: Experimental and Theoretical Studies

Karima Toumiat Laghouat University, ALGERIA

Abdenacer Guibadj Laghouat University, ALGERIA

Mohamed B. Taouti Laghouat University, ALGERIA

Received 8 June 2016 Revised 15 October 2016 Accepted 19 October 2016

ABSTRACT

The effect of 1H-benzotriazole (BTAH) with ppm (part per million) grade concentrations on

copper corrosion in aerated 0.5 M NaCl solution is studied using chemical method (weight

loss) and electrochemical methods (Potentiodynamic Polarization and Electrochemical

Impedance Spectroscopy (EIS)). The present study confirm that the BTAH acts as a mixed-

type inhibitor of copper corrosion in 0.5 M NaCl. The optimum inhibition efficiency is at 30

ppm of BTAH. The surface characterization performed using Scanning Electron Microscopy

(SEM) to confirm the adsorption of the inhibitor molecules after 21 days of immersion time

in aerated 0.5 M NaCl. The results obtained from different techniques used in this research

are in very good agreement and revealed that the BTAH is a very good inhibitor of copper

corrosion in sodium chloride medium. Computer Simulation techniques confirm that the

BTAH molecules adsorbed on the Cu (111) Surface.

Keywords: Copper, EIS, weight loss, theoretical study, 1H-benzotriazole

INTRODUCTION

From a wide range of metals used in industries, copper extensively used owing to its

remarkable thermal and electric properties. It is usually employed in heating and cooling

systems because of its excellent thermal conductivity [1- 7]. Copper also exclusively used for

piping and delivery of water in marine industry. These pipes used in a medium rich of Cl- [8].

It is known that the corrosion products caused by chloride ions Cl- leads to a reduction in the

efficiency of copper, which causes huge economic loss [9, 10].

The corrosion inhibition is one of several methods of protection against metals

degradation in different aqueous solutions [11-15].

To overcome this problem, an electrochemical monitoring was done by studying the

behaviour of copper in 0.5 M NaCl in presence and absence of the inhibitor BTAH.

K. Toumiat et al.

276

In this context, several studies realized, BTAH known for six decades as a corrosion

inhibitor for copper.1. Cotton and al. [16] are the first contributors in the field of BTAH as

copper corrosion inhibitor. They demonstrated that the pre-treatment of the copper surface by

BTAH induce a long lasting prevention of staining, they elucidate the BTAH inhibitory action

in the terms of physical barrier. Wall and Davies [17] showed that, in the presence of BTAH

dissolution of copper and pick up of copper ions from the solution reduced in closed circuit

systems containing copper. They claimed that BTAH forms an insoluble and invisible chelate

on the copper surface. That is responsible for reducing corrosion attack.

Poling [18] confirmed the linear polymeric Cu (I) BTA structure proposed by Cotton [16]

and stated more decisively that the structure contains Cu(I) ions, the formation of Cu (I) BTA

was not limited to a monolayer, but could grow further to from films up to several thousand

Å thick.

EXPERIMENTAL

Chemicals and preparation of the simples

BTAH (self-prepared 97%), NaCl electrolyte prepared with deionized water. A three-

electrode electrochemical cell was used which contain counter electrode of Platinum (Pt. 1 cm

²) and saturated calomel electrode (SCE) as reference electrode. The working electrodes made

using pure copper 99.99 % cylinder.

The samples were mechanically cut into cylinders (D1= 1.1 cm & D2= 0.8 cm) x 1cm

dimensions. The samples used for the electrochemical study were welded with electric cables

for easier use, then coated with epoxy resin and finally polished with abrasive papers

(1200,1500,2000 and 2500) followed by a finishing polishing (Felt) with Diamond Polishing

Paste (0.1 µm). The samples used for weight loss experiment polished with same way. All

samples has cleaned successively with acetone, distilled water and deionized water.

Electrochemical measurements

The potentiodynamic polarization and EIS measurements had performed using an Auto

lab (PGZ-402) electrochemical workstation and an electrochemical cell (100 ml) with three

electrodes; the solution was not stirred or deaerated. Before the potentiodynamic polarization

measurements, an open circuit measurement for 30 min performed to stabilize the potential.

The potential was scanned from – 400 to 400 mV at a scan rate of 1mV.min-1. The EIS

measurements were performed at open circuit potential for 30 min, in a frequency range from

100 KHz to 100 MHz.

Weight loss and SEM analyses

Samples used for weight loss measurement were prepared by the same method

mentioned previously (Paragraph 2.1.). In a cylindrical shape (d = 0.8 cm & h = 0.3 cm) with

an exposed total area (A=1.76 cm²). After polishing and weighing (m1), the samples

Eurasian J Anal Chem

277

introduced in 100 ml of 0.5 M NaCl solution with and without inhibitor used for (2-21) days.

Subsequently, the tested samples were removed, cleaned and weighed (m2).

In order to see if the BTAH molecules effectively adsorbed on the copper surface

executed the SEM analysis, SEM is widely used to detect the morphological features of metal

surface. The SEM micrograph obtained for copper samples used in weight loss part. The

surface morphology of these copper samples investigated by using SEM analysis (VEGA 3,

TESCAN) at 5, 10 and 20.0 KV.

Theoretical study

Molecular simulation studies carried out using Materials Studio 7 software from accelrys

Inc. to find the correlation between theoretically calculated properties and experimentally

determined inhibition efficiency for copper corrosion in 0.5 M NaCl solution by BTAH organic

inhibitor.

The DFT+ semi-empirical tight binding method was used for building and to optimize

BTAH molecule, determine the electronic properties of BTAH, effect of the frontier molecular

orbital energies The energy of the highest occupied molecular orbital (EHOMO), the energy of

the unoccupied molecular orbital (ELUMO), electronic charges on reactive centres, dipole

moment and the energy of the gap, Equation (1).

𝑬 = 𝑬𝑳𝑼𝑴𝑶 − 𝑬𝑯𝑶𝑴𝑶 (1)

Interaction between BTAH molecules and Cu (111) surface carried out in a simulating

box (14.45 Å×10.22Å × 29.99 Å) with periodic boundary conditions. The Cu (111) surface firstly

built and relaxed by minimizing its energy using molecule mechanics then the surface of Cu

(111) increased by constructing a supercell, a vacuum slab of 30 Å thickness built on the Cu

(111) surface. The number of layers in the structure chosen so that the depth of surface is

greater than the non-bond cutoff used in the calculation; we choose six as a number of layers

which sufficient depth that the inhibitor molecules will only be involved in non-bond

interactions with Cu (111) surface. After minimizing Cu (111) surface and BTAH molecules,

the corrosion system will be built by layer builder to place the inhibitor molecule on Cu (111)

surface using a forcefield COMPASS (Condensed phase Optimized Molecular Potentials for

Atomistic Simulation Studies). The adsorption locator module in Materials Studio 7 software

from accelrys Inc. [19] allows selecting thermodynamic ensemble and associated parameters,

temperature and pressuring and initiating a dynamic calculation. The dynamic simulations

procedures have been described elsewhere [20].

K. Toumiat et al.

278

RESULTS AND DISCUSSION

Potentiodynamic Polarization Results

Figure 1 represent the behavior of pure copper electrodes in aerated 0.5 M NaCl solution

at room temperature, in the absence and in the presence of different concentrations from 0.5

×10-4 M to 3.5 ×10-4 M grade of BTAH after an immersion time of 30 min. as an open circuit

potential measurement.

The cathodic corrosion reaction of copper in NaCl solution is the reaction of oxygen

𝑶𝟐 + 𝟐𝑯𝟐𝟎 + 𝟒𝒆− → 𝟒𝑶𝑯− (2)

usually, the dissolution of copper (anodic corrosion reactions) is:

𝑪𝒖 → 𝑪𝒖+ + 𝟏𝒆− (3)

moreover, Cu+ ions can undergo disproportionation according to Equation (4) [21-24]

𝟐𝑪𝒖+ 𝑪𝒖𝟐+ + 𝑪𝒖 (4)

When we use an aerated corrosive aqueous medium in near neutral pH, which contained

complexing agents such as Cl- , we have to consider the formation of copper complex such as

𝐶𝑢𝐶𝑙2− as indicated by following anodic reactions:

𝑪𝒖𝑪𝒍𝒂𝒅𝒔 + 𝑪𝒍− 𝑪𝒖𝑪𝒍𝟐− (5)

𝑪𝒖 + 𝑪𝒍− 𝑪𝒖𝑪𝒍𝒂𝒅𝒔 + 𝟏𝒆− (6)

Compared with the solution without inhibitor the corrosion potential (Ecorr) shifted to

the more positive values and both the anodic and cathodic currents (icorr) decreased. This

-400 -200 0 200 400

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

log

i (A

/cm

²)

Potential (mV/ECS)

Blank

0.5 ×10-4 M BTAH

1.5 ×10-4 M BTAH

2.5 ×10-4 M BTAH

3.5 ×10-4 M BTAH

Figure 1. Polarisation curves of copper electrode in the absence and in the presence of various

concentrations of BTAH in aerated 0.5 M NaCl solution

Eurasian J Anal Chem

279

indicates that the BTAH inhibitor acts as a mixed-type corrosion inhibitor. The cathodic and

the anodic currents progressively diminish with an increment in BTAH concentration that is

clearer in anodic current. The electrochemical parameters shown in Table 1 extracted from

polarization curves shown in Figure 1 obtained after an electrochemical follow of the behavior

of pure copper in 0.5 M NaCl medium in absence and presence of different concentrations of

BTAH at room temperature. The results obtained using Tafel extrapolation method. Figure 1

shows clearly that the cathodic polarisation curves does not display an extensive Tafel region

which confirm a limiting diffusion current return to the reduction of dissolved oxygen, the

Tafel extrapolation method was used for both anodic and cathodic Tafel region using

Voltamaster 4.0 program. The kinetics of electron transfer at the metal-solution interface can

be shown using Butler-Volmer equation [25]. The Butler –Volmer equation given by Equation

(7).

𝒊 = 𝒊𝒄𝒐𝒓𝒓 − [𝒆𝜶𝒏𝑭(𝑬−𝑬𝒄𝒐𝒓𝒓)/𝑹𝑻 − 𝒆−(𝟏−𝜶)𝒏𝑭(𝑬−𝑬𝒄𝒐𝒓𝒓/𝑹𝑻)] (7)

Where icorr is the corrosion current density at the corrosion potential Ecorr, α is the transfer

coefficient (α = 0.5), and n the number of electrons transferred. When the rate of the back

reaction is negligible, Equation (7) gives:

𝑬 = 𝒂 + 𝒃𝒍𝒐𝒈𝒊 (8)

where a and b constants. In Equation (8), when E=Ecorr and when i=icorr this is the basis of Tafel

exploitation. The inhibition efficiency (ηi (%)) shown in Table 1 was calculated from values of

(icorr) using the following equation:

𝜼𝒊(%) =𝒊𝒄𝒐𝒓𝒓

𝟎 − 𝒊𝒄𝒐𝒓𝒓

𝒊𝒄𝒐𝒓𝒓𝟎

× 𝟏𝟎𝟎 (9)

Where 𝑖𝑐𝑜𝑟𝑟0 and 𝑖𝑐𝑜𝑟𝑟 are the corrosion current densities for Cu electrode in aerated 0.5 M NaCl

in absence and presence of different concentrations of BTAH.

Table 1. Corrosion inhibition parameters of copper in aerated 0.5 M NaCl solution in the absence and

presence of various concentrations of BTAH using Tafel method

C

(×10-4 M)

Ecorr

(mV/SCE)

ba

(mV/dec)

bc

(mV/dec)

icorr

(µA/cm²)

ηi

(%)

Blank -232.4 65.3 205.2 7.865 --

0.5 -153.6 66.7 149.9 0.241 96.93

1.5 -153.1 111.6 144.0 0.208 97.35

2.5 -103.9 88.8 141.6 0.043 99.45

3.5 -190.9 92.9 136.2 0.088 98.88

K. Toumiat et al.

280

The inhibition effect of BTAH on the polarization behaviors of copper in chloride

medium, it known that the corrosion current density of copper usually calculated by the use

of the Stern-Geary equation as:

𝑰𝒄𝒐𝒓𝒓 =𝑩

𝑹𝑷

(10)

where Rp is the polarization resistance and B in a constant, which varies with the expression

with the expression that:

𝑩 =𝒃𝒂𝒃𝒄

𝟐. 𝟑(𝒃𝒂 + 𝒃𝒄)

(11)

where 𝑏𝑎, 𝑏𝑐 are the anodic and the cathodic Tafel slopes obtained from anodic and cathodic

polarization curves of copper [26].

Generally, the calculation of the determination of Rp and rarely gives attention on the

value of B [27]. The value of B commonly considered being between 10 and 30 mV for almost

metals. Table 2 shows the calculated parameters obtained using Stern-Geary method.

It can be conclude that the corrosion current density decreased and the inhibition

efficiency increased with the increase of BTAH concentration, The BTAH adsorbed on copper

surface acted as a barrier layer to block corrosion process. The addition of 0.5 ×10-4 M of BTAH

to the electrolyte can reduces to great importance of inhibition efficiency. The optimal

inhibition efficiency of 99.45% was obtains for 2.5 ×10-4 M of BTAH. The parameters calculated

using linear polarization method or Stern-Geary method confirmed the results from Tafel

method.

EIS results

In this experimental part of electrochemical measurements the Electrochemical

Impedance Spectroscopy (EIS) used to confirm results of the potentiodynamic polarization

step and to get further information of the inhibition process with the same concept with

potentiodynamic measurement, The EIS is an excellent tool to investigate the corrosion and

the adsorption phenomena. [25] Several experiences done using copper electrode in different

electrolytes in the absence and in the presence of four different concentrations of the inhibitor

Table 2. Corrosion inhibition parameters of copper in aerated 0.5 M NaCl solution in the absence and

presence of various concentrations of BTAH using Stern-Geary method

C

(×10-4 M)

Rp

(KΩ/cm²)

Ecorr*

(mV/SCE)

icorr*

(µA/cm²)

B Constant

(mV)

ηi*

(%)

Blank 3.26 -236.48 7.975 21.84 --

0.5 94.55 -155.67 0.274 20.06 96.56

1.5 147.58 -152.5 0.176 21.64 97.79

2.5 597.45 -103.79 0.043 22.79 99.46

3.5 240.97 -190.29 0.107 23.84 98.65

Eurasian J Anal Chem

281

(BTAH) in aerated 0.5 M NaCl medium at room temperature. The results obtained at an open

circuit potential immersed for 30 min represented as typical Nyquist and Bode plots, shown

in (Figures 2, 3 and 4).

In the presence of BTAH the impedance spectra for the Nyquist plots Figure 2 shows a

depressed semicircle in the high frequency region. This high frequency semicircle attributed

to the charge transfer and double layer capacitance [28].

The lowest frequency area generally known as Warburg impedance related to the

diffusion of soluble copper species from electrode surface to bulk solution [28]. The diameter

of semicircles in extent with the increasing of the inhibitor concentrations. The Bode plots

Figure 3 show that the impedance values over the whole frequency range increased with

increasing the BTAH concentration.

0 1000 2000 3000 4000 5000 6000-200

0

200

400

600

800

1000

1200

1400

1600

Blank

0.5 ×10-4 M BTAH

1.5 ×10-4 M BTAH

2.5 ×10-4 M BTAH

3.5 ×10-4 M BTAH

-Zi

(oh

m.c

m²)

Zr (ohm.cm²)

Figure 2. Nyquist plots of copper electrode at an open-circuit potential after 30 min in aerated 0.5 M

NaCl solution without and with various concentrations of BTAH

K. Toumiat et al.

282

It can be obtains from Bode phase plots Figure 4 that the corrosion process-taking place

at the electrode surface has one relaxation time constant related to the relaxation of the

electrical double layer capacitor. We can also observe that the increasing of BTAH

concentrations results an increase in the maximum phase angle, which confirm the inhibiting

action of BTAH on copper in the study medium.

The equivalent circuit model used to construe impedance characteristics is shown in this

circuit was reported in several studies for copper/solution interface [28, 30].

-1 0 1 2 3 4 5

0.5

1.0

1.5

2.0

2.5

3.0

3.5 Blank

0.5 ×10-4 M BTAH

1.5 ×10-4 M BTAH

2.5 ×10-4 M BTAH

3.5 ×10-4 M BTAH

log

|Z|(

ohm

.cm

²)

log f (Hz)

Figure 3. Bode plot for copper electrode in aerated 0.5 M NaCl solution without and with different

concentrations of BTAH

-1 0 1 2 3 4 5-80

-70

-60

-50

-40

-30

-20

-10

0

10

Blank

0.5 ×10-4 M BTAH

1.5 ×10-4 M BTAH

2.5 ×10-4 M BTAH

3.5 ×10-4 M BTAH

Ph

ase

(deg

ree)

log f (Hz) Figure 4. Phase angle plot for copper electrode in aerated 0.5M NaCl solution without and with different

concentrations of BTAH

Eurasian J Anal Chem

283

The parameters obtained by fitting the equivalent circuit and the inhibition efficiency

represented in Table 3.

Here Rs represented the solution resistance. 𝑄 represents the constant phase element

(CPE), Rt represent the charge transfer resistances and W is the Warburg impedance.

The impedance of CPE represented by the following equation:

𝑸 = 𝒀𝒐(𝒋𝝎 )𝒏 (12)

where 𝑌0 is the modulus, j is the imaginary root, 𝛚 is the angular frequency and n is the phase.

In the practical electrode system, the impedance spectra are offer depressed semicircles

with their centres below the real axis. This phenomenon known as the dispersing effect [31].

The inhibition efficiency (ηi) is calculated using charge transfer resistance as follow:

𝜼𝒊 = (𝟏 −𝑹𝒕𝒐

𝑹𝒕) × 𝟏𝟎𝟎

(13)

Weight loss and SEM analyses results

In this part the variation of the weight loss of copper at different immersion times in

aerated 0.5 M NaCl solution, at room temperature 25°C for (2, 4, 7, 10, 14 and 21) days, without

inhibitor and with 2.5 10-4 M of BTAH results shown in Figure 6.

Figure 5. Equivalent circuit used to fit experimental EIS data in Figure 2, symbols in the circuit indicated

in the text

Table 3. Impedance parameters for copper electrode in 0.5 M NaCl solution in the absence and

presence of various concentrations of BTAH inhibitor at room temperature

Solution

Parameters

Rs(Ω) Q

Rt (Ω) W (Ω.s-1/2) ηi (%) Y

0(µF.sa-1) a

Blank 11.43 66.27 0.920 797.6 784.9 --

0.5 ×10-4 M 8.414 54.97 0.736 2 047 674.2 61.03

1.5 ×10-4 M 10.25 40.34 0.775 2 832 439.0 71.83

2.5 ×10-4 M 6.814 47.24 0.727 5 241 148.8 84.78

3.5 ×10-4 M 8.467 43.68 0.736 2 761 26.58 71.11

K. Toumiat et al.

284

The concentration of inhibitor used in this part has chosen as the optimal concentration

confirmed in the electrochemical study part.

The loss of weight mentioned (∆m: mg.cm-²). The corrosion rate (Rcorr: mg.cm-1.day-1)

and the inhibition efficiency (ηw %) were calculated as follow [32, 33] :

𝚫𝒎 =𝒎𝟏 − 𝒎𝟐

𝑨 (14)

𝑹𝒄𝒐𝒓𝒓 =𝚫𝒎

𝑨𝒕

(15)

𝜼𝒘% =𝑹𝒄𝒐𝒓𝒓

𝒖𝒏 − 𝑹𝒄𝒐𝒓𝒓𝒊𝒏

𝑹𝒄𝒐𝒓𝒓𝒖𝒏

(16)

Here, 𝐴 is the total area exposed to the solution, 𝑡 is the time of immersion, 𝑹𝒄𝒐𝒓𝒓𝒖𝒏 is the

corrosion rate without inhibitor and 𝑹𝒄𝒐𝒓𝒓𝒊𝒏 is the corrosion rate with inhibitor.

We found that the inhibition efficiency of BTAH on copper immersed in aerated solution

of 0.5 M NaCl, varied from 50% after two days of immersion time to 84.84 % after 21 days

immersion time Figure 7, it’s clear that the BTAH has a very good effect against copper

corrosion in the study solution, also it stays effective after 21 days of immersion. Without

forget the low concentration of inhibitor used in this part.

-2 0 2 4 6 8 10 12 14 16 18 20 22 24

0.0000

0.0004

0.0008

0.0012

0.0016

0.0020

wei

gh

t lo

ss (

mg.c

m-²

)

t (day)

Blank

2.5 ×10-4 M BTAH

Figure 6. Variation of the weight loss as function of time for copper coupons in in aerated solution of

0.5 M NaCl without and with 2.5 ×10-4 M of BTAH

Eurasian J Anal Chem

285

The SEM micrograph for the copper samples immersed in aerated 0.5 M NaCl in absence

and presence of BTAH with concentration equals to 2.5 ×10-4 M for 21 days shown in Figure

8 and 9 . It is obvious that the BTAH molecules partially distributed on the copper surface. The

surface coverages obtained from:

𝜽 =𝒎 − 𝒎𝒊𝒏𝒉

𝒎 (17)

where 𝑚, 𝑚𝑖𝑛ℎ are weight loss obtained from previous measurements. The corrosion rates

obtained from equation (15).

The inhibition efficiency, coverages and corrosion rates tabulate in Table 4.

The Figure 8 represents the copper sample before immersion, the Figure 9(a) shows the

surface morphology of the copper sample immersed in solution without inhibitor, it is clear

that the surface strongly corroded by the Sodium Chloride solution.

0 2 4 6 8 10 12 14 16 18 20 22 240

20

40

60

80

100

57.14

84.84

78.94

66.66

50

81.81

inh

ibit

ion

eff

icie

ncy

%

t (day)

2.5 ×10-4

M BTAH

50

Figure 7. Variation of the inhibition efficiency as function of time for copper coupons in aerated solution

of 0.5 M NaCl containing 2.5 ×10-4 M of BTAH

Table 4. The inhibition efficiency (𝜂w %), changes of the degree of copper surface coverages (𝜃) and

corrosion rates (𝑅𝑐𝑜𝑟𝑟𝑖𝑛 : with 2.5 ×10-4 M of BTAH and 𝑅𝑐𝑜𝑟𝑟

𝑢𝑛 solution without inhibitor) obtained from

weight loss data in aerated 0.5 M NaCl solutions

2.5 ×10-4 M BTAH Time (day)

2 4 7 10 14 16 21

𝜂 w (%) 50 50 57.14 66.66 78.94 81.81 84.84

𝜃 (10-4) 0.203 0.406 0.601 0.881 1.442 1.559 2.441

𝑹𝒄𝒐𝒓𝒓𝒖𝒏 (10-5 cm/d) 3.23 3.23 3.23 3.87 4.38 4.44 5.07

𝑹𝒄𝒐𝒓𝒓𝒊𝒏 (10-5 cm/d) 1.61 1.61 1.38 1.29 0.92 0.80 0.79

K. Toumiat et al.

286

The Figure 9(b) shows the morphology of the copper sample, immersed in the presence

of 2.5 ×10-4 M of BTAH. Protection layers formed on the copper surface, which indicate that

the BTAH adsorbed on the copper surface.

In addition, we conclude that the BTAH has a good inhibiting effect on copper corrosion

which confirmed in weight loss part, at 2.5 ×10-4 M of BTAH an after 21 days the inhibition

efficiency attain 84.84 %.

Theoretical Calculation methods results

DFT simulation results

The present part focus on the geometry optimization step of the BTAH molecule using

DFT+ module, this optimization step aim to calculate the Mullikan charge distributions of

BTAH as well as HOMO and LUMO were calculated and represented in Figure 10. We find

that the HOMO is located on the Benzene ring, which indicate that the preferred active sites

for an electronic attack and the favourite sites for interactions with the metal surface are

Figure 8. SEM image for polished copper electrode

(a) (b)

Figure 9. SEM images for copper electrodes after 21 days immersion in aerated 0.5 M NaCl solution without inhibitor (a) and with 2.5 ×10-4 M of BTAH (b).

Eurasian J Anal Chem

287

located within the region around the Nitrogen (azole function) atoms belonging to the benzene

ring [34].

According to DFT-Koopmans’ theorem [35], the ionization potential I written as follow:

𝑰 = −𝑬𝑯𝑶𝑴𝑶 (18)

Then the negative of the energy of the LUMO represent the electron affinity A Equation

(17):

𝑨 = −𝑬𝑳𝑼𝑴𝑶 (19)

Other quantum chemical parameters has been correlated recently using DFT modules

[36], these calculated parameters such as dipole moment µ which given as follow:

𝝁 = 𝒒𝑹 (20)

Where 𝑞 represents the charge and 𝑅 is the distance.

The value of the electronegativity and the chemical potential [37] given by Equation

(19):

𝑿 = (𝑰 + 𝑨)/𝟐 (21)

Figure 9. Molecular structure, Charge distribution, Electron density and frontier molecular orbitals for

the optimized BTAH by DFT+ module

K. Toumiat et al.

288

Other parameters [38, 39] calculated such as the global hardness and the global softness

where the global hardness given by Equation (20):

𝜼 = (𝑰 − 𝑨)/𝟐 (22)

The global softness S or the absolute hardness defined by the inverse of the global

hardness where:

𝑺 = 𝟏 / 𝟐𝜼 (23)

The propensity of chemical species to accept electrons defined as the global

electrophilicity 𝝎 it given by Par et Al. [40] as follow:

𝝎 = 𝝁𝟐 / 𝟒𝜼 (24)

The Equation (22) becomes as follow:

𝝎 =(𝑰 + 𝑨)𝟐

𝟖(𝑰 + 𝑨)

(25)

Finally and according to Person [41] the fraction of electrons transferred from the

inhibitor molecule to the metallic surface gives by:

𝚫𝑵 = 𝑿𝑴 − 𝑿𝒊𝒏𝒉 / 𝟐(𝜼𝑴 + 𝜼𝒊𝒏𝒉) (26)

where 𝑋𝑀 and 𝑋𝑖𝑛ℎ denote the absolute electronegativity of metal and inhibitor molecule,

𝜂𝑀and 𝜂𝑖𝑛ℎ are the absolute hardness of the metal and the inhibitor.

Obtained results for BTAH molecule and interaction of BTAH molecule with copper

surface calculated with DFT+ module shows in Table 5.

Table 5. Quantum chemical and molecular dynamics parameters for BTAH molecule calculated with

DFT+ module in aqueous phase

Propriety Value

ET, KJ.mol-1 -51679.558

µ, D 4.210

EHOMO, eV -5.743

ELUMO, eV -1.816

∆E, eV 3.927

Ionization potential (I) 5.743

Electron affinity (A) 1.816

Chemical potential ( ) 3.779

Global hardness (𝜂) 1.96

Global softness (S) 0.25

Global electrophilicity (𝛚) 0.944

(∆N) 0.479

Eurasian J Anal Chem

289

According to Lukovits [42], if ΔN < 3.6 (our case Δ𝑁 = 0.479) the inhibition efficiency

of organic inhibitor increase with increasing electron donating ability at the metal surface. We

concluded the BTAH could adsorbed on the copper surface by donating the unshared pair of

electrons from the N atoms to the vacant d orbitals of copper.

The high value of 𝐸𝐻𝑂𝑀𝑂 (-5.743 eV) indicate the tendency of BTAH molecule to donate

electrons to the appropriate acceptor molecule with the low energy and the empty molecular

orbital. Whereas the value of 𝐸𝐿𝑈𝑀𝑂 (-1.816 eV) indicate the ability of BTAH molecule to accept

electrons. Observing the value of the energy of the gap ∆E, which indicate the stability of the

formed complex (Cu-BTAH).

Molecular dynamics simulation

Forcite tools, adsorption locator, molecular dynamics in Materials Studio 7 software

from accelrys Inc. [20] performed on a system comprising BTAH molecule and Cu (111)

surface.

0 10 20 30 40 50 60 7060

80

100

120

140

160

180

200

Ene

rgy/

Kca

l.mol

-1

Optimization step

BTAH

Figure 10. DFT+ geometry optimization and energy step of BTAH

The BTAH molecule placed on the surface of copper, optimized then quench molecular

dynamics run. Figure 11 shows the optimization energy step for BTAH molecule, before

putting it on the Cu (111) surface.

Total energy, average energy, Van der Waals energy, electrostatic energy and

intermolecular energy in interaction of BTH/Cu (111) surface figured in Figure 12. The

adsorption locator process tries to get to the lowest energy for the system in comprising

BTAH/Cu (111).

K. Toumiat et al.

290

The possibility of BTAH adsorption on Cu (111) surface simulated in Figure 13(a). We

can see that BTAH molecule moves near to the copper surface, indicating that the BTAH

adsorbed at copper surface [43].

Figure 13(a) shows that the adsorption occurred through the Nitrogen atoms. The

adsorption density of BTAH on Cu (111) surface shown in Figure 13(b). Therefore, the studied

molecules are likely to the copper surface to form a stable adsorption layer and protect copper

from corrosion.

The parameters tabulated in Table 6 include total energy of the BTAH-Cu (111)

configuration. The total energy is defined is the sum of the energies of the adsorbate

components, the rigid adsorption energy and the deformation energy. In the present study,

the energy of the substrate (Cu (111) surface) taken as zero. Then adsorption energy reports

energy required when the relaxed adsorbate BTAH adsorbed on the substrate surface Cu (111).

The adsorption energy defined as the sum of rigid adsorption energy and the deformation

energy for BTAH molecule.

0.0 5.0x104

1.0x105

1.5x105

2.0x105

2.5x105

-40

-20

0

20

40

60

80

100

120

Total energy

Avearge total energy

Van der Waals energy

Electrostatic energy

Intermolecular energy

En

ergy

/ K

cal.m

ol-1

Step Figure 11. Total energy distribution for BTAH/Copper system during energy optimization process

Eurasian J Anal Chem

291

The rigid adsorption energy released when the unrelaxed BTAH molecule (before

geometry optimization step) adsorbed on Cu (111) surface. The deformation energy required

when the BTAH molecule is relaxed on the Cu (111) surface. The report (dEads/ dNi) of

BTAH-Cu (111) configurations where one of the BTAH molecule removed is also shows in

Table 6.

CONCLUSIONS

The BTAH known as a very good inhibitor for copper corrosion in aerated 0.5 M NaCl

solution. The inhibition mechanism is attributable to the adsorption of the inhibitor on the

copper surface and blocking its active sites. All results obtained from electrochemical

measurements and chemical measurement are reasonably in good accord.

To go so far and follow the stability of the inhibition efficiency, BTAH stays stable and

it has a very good inhibition efficiency 84.84 % after 21 days of immersion time in aerated 0.5

M NaCl solution. The molecular modelling as well as quantum chemical simulation precisely

(a) (b)

Figure 12. (a) Most suitable configuration for adsorption of BTAH on the Cu (111) surface obtained by

Adsorption locator module; (b) Adsorption density of BTAH on the Cu (111) substrate

Table 6. Outputs and descriptors calculated with adsorption locator for BTAH on Cu (111) surface

Inhibitor BTAH

Total energy (Kcl.mol-1) 39.59

Adsorption energy (Kcl.mol-1) -50.51

Rigid adsorption energy (Kcl.mol-1) -36.32

Deformation energy (Kcl.mol-1) -14.18

dEads/ dNi (Kcl.mol-1) -50.51

K. Toumiat et al.

292

the calculation of the both energies EHOMO and ELUMO indicate that the preferred active sites for

an electronic attack and the favourite sites for interaction with the copper surface are located

within the region around the Nitrogen atoms, which confirm that the BTAH molecule adsorb

on the Cu (111) surface.

REFERENCES

1. Jafari, A. H., Hosseini, S. M., & Jamalizadeh, E. (2010). Investigation of Smart Nanocapsules Containing Inhibitors for Corrosion Protection of Copper. Electrochimica Acta, 55, 9004-9009.

2. Hong, S., Chen, W., Luo, H. Q., & Li, N. B. (2010). Inhibition Effect of 4-amino-antipyrine on the Corrosion of Copper in 3wt. % NaCl Solution. Corrosion Sci., 57, 270-278.

3. Annibaldi, V., Rooney, A. D., & Breslin, B. C. (2012). Corrosion Protection of Copper using Polypyrrole Electrosynthesised from a Salicylate Solution. Corrosion Sci., 59, 179-185.

4. Nüñez, L., Reguera, E., Corvo, F., Gonzãlez, R., & Vazquez, C. (2005). Corrosion of Copper in Seawater and its Aerosols in a Topical Island. Corrosion Sci., 47, 464-481.

5. Sherif, E. M., Erasmus, R. M., & Comins, J. D. (2007). Corrosion of Copper in Aerated Synthetic Seawater Solutions and its Inhibition by 3-amino-1,2,4-triazole. J. Colloid Interface Sci., 309, 470-477.

6. Hammouti, B., Dafali, A., Touzani, R., & Bouachrine, M. (2012). Inhibition of Copper Corrosion by Bipyrazole Compound in Aerated 3%NaCl. J. Saudi Chemical Soc., 16, 413-418.

7. Zhang, D. Q., Wu, H., & Gao, L. X. (2012). Synergistic Inhibition Effect of L-Phenylalanine and Rare Earth Ce(IV) Ion on the Corrosion of Copper in Hydrochloric Acid Solution. Materials Chemistry and Physics, 133, 981-986.

8. Hack, H. P., & Pickering, H. W. (1991). AC Impedance study of Cu and Cu-Ni Alloys in Aerated Salt Water I. Pd Coating and Corrosion Product Stripping. J. Electrochem. Soc., 138, 690-695.

9. Benedetti, A. V., Sumodjo, P. T. A., Nobe, K., Cabot, P. L., & Proud, W. G. (1995). Electrochemical Studies of Copper, Copper-aluminium and Copper-aluminium-silver Alloys: Impedance Results in 0.5 M NaCl. Electrochimica Acta, 40, 2657.

10. Zhou, G., Shao, H., & Loo, B. H. (1997). A study of the copper electrode behavior in borax buffer solutions containing chloride ions and Benzotriazole-type inhibitors by voltammetry and the photocurrent response method. J. Electroanal. Chem, 421, 129.

11. Walker, R. (1973). Benzotriazole as a Corrosion Inhibitor for Immersed Copper. Corrosion, 29, 290-296.

12. Brusic, V., Frisch, M. A., Eldridge, B. N., Novak, F. P., Kaufman, F. B., Rush, B. M., & Frankel, G. S. (1991). Copper Corrosion with and without Inhibitors. J. Electrochem. Soc., 138, 3483.

13. Tromans, D., & Sun, R. (1991). Anodic Polarization Behavior of Copper in Aqueous Chloride/Benzotriazole Solutions. J. Electrochem. Soc., 138, 3235.

14. Antonijevic, M. M., & Petrovic, M. B. (2008). Copper Corrosion Inhibition. A review. Int. J. Electrochem. Sci., 3, 1.

15. Tuck, C. D. S., Powell, C. A., & Nuttall, J. (2010). Corrosion of Copper and its Alloys. Shereir’s Corrosion, 3, 1937-1973.

16. Cotton, & Scholes, I. R. (1967). Benzotriazole and Related Compounds as Corrosion Inhibitors for CopperBrit. Corros. J., 2, 1-5.

17. Wall, K. H., & Davies, I. (1965). Corrosion Control in Water Cooled Stator. J. Appl. Chem., 15, 389-392.

18. Wall, K. H., & Davies, I. (2007). Corrosion Control in a water Cooled Stator. J. Appl. Chem., 15, 389-392.

19. Poling, G. W. (1970). Reflection Infra-red Studies of films formed by Benzotriazole on Cu. Corrosion Sci., 10, 359-370.

Eurasian J Anal Chem

293

20. Bariga, J., Coto, B., & Fernandez, B. (2007). Molecular Dynamics Study of Optimal Packing Structure of OTS Self-assembled Monolayers on SiO2 Surface. Tribol. Int., 40, 960-966.

21. Khaled, K. F. (2009). Monte Carlo simulations of corrosion inhibition of mild steel in 0.5 M sulfuric acid by some green corrosion inhibitors. J. Solid Stat. Electrochem, 13, 1743.

22. Strehblow, H. H., & Titze, B. (1980). The investigation of the passive behaviour of copper in weeklyacid and alkaline solutions and the examination of the passive film by ESCA and ISS. Electrochimca Acta, 25, 839-850.

23. Hashemi, T., & Hogarth, C. A. (1988). The mechanism of corrosion inhibition of copper in NaCl solution by benzotriazole studied by electron spectroscopy. Electrochimca Acta, 33, 1123-1127.

24. Gardiner, D. J., Gorvin, A. C., Gutteridge, C., Jackson, A. R. W., & Raper, E. S. (1985). In Situ Characterization of Corrosion Inhibition Complexes on Copper Surfaces using Raman Microscopy. Corrosion Sci., 25, 1019-1027.

25. Scendo, M. (2005). Potassium Ethyl Xanthate as Corrosion Inhibitor for Copper in Acidic Chloride Solutions. Corrosion Sci., 47, 1738-1749.

26. Stern, M., & Geary, A. L. (1957). Electrochemical Polarization. J. of Electrochemical Soceity. 27. Keenan, A. G., Webb, C. A., & Karmen, D. A. (1976). Polarisation Resistance Study of the Effect

of Alpha-amino Acids on Copper Corrosion Kinetics. Anodic Oxide of Vanadium, 123, N 02. 28. Schlesinger, M. (2009). Mathematical Modeling in Electrochemistry, Modern Aspect of

Electrochemistry No. 43. Modeling and Numerical Simulations. 29. Amin, M. M. (2006). Weight loss, Polarization, Electrochemical Impedance Spectroscopy, SEM

and EDX Studies of the Corrosion Inhibition of Copper in Aerated NaCl Solutions. J. Appl. Electrochem., 36, 215-216.

30. Rao, A., Iqbal, Y., & Sreedhar, B. (2010). Electrochemical and Surface Analytical Studies of the Self-assembled Monolayer of 5-methoxy-2-(octadecalthio) benzamidazole in Corrosion Protection of Copper. Electrochim. Acta, 55, 620-631.

31. Wu, X., Ma, H., Chem, S., Xu, Z., & Sui, A. (1999). General Equivalent Circuits for Faradic Electrode Processes under Electrochemical Reaction Control. Electrochem. Soc., 146, 1847-1853.

32. Sherif, E. M., & Park, S. M. (2006). Inhibition of Copper Corrosion in Acidic Picking solutions by N-phenyl-1, 4-phenylenediamine. Electrochimica Acta, 51, 4655-4673.

33. Sherif, E. M., & Almajid, A. A. (2010). Surface Protection of Copper in Aerated 3.5 % Sodium Chloride Solutions by 3-amino-5-mercapto-1, 2, 4-triazole as a Copper Corrosion Inhibitor. J. Appl. Electrochem., 40, 1555-1562.

34. Liao, Q. Q., Yue, Z. W., Wang, Z. H., Li, Z. H., Ge, H. H., & Li,Y. J. (2011). Inhibition of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium diethyldithiocarbamate. Corrosion Science, 53, 1999-2005.

35. Koopmans, T. (1934). Über Die Zuordnug von Wellenfunktionen und Eigenwerten zu den Einzelnen Elektronen Eines Atoms. Physica, 1, 104-113.

36. Atkins, P., & De Paula, J. (2006). ATKINS’ Physical Chemistry. 37. Chermette, H. (1999). Chemical Reactivity Indexes in Density Functional Theory. J. Comp. Chem.,

20, 129-154. 38. Parr, R. G., & Pearson, R. G. (1991). Principle of Maximum Hardness. J. Am. Chem. Soc., 105,

7512-7516. 39. Yang, W., & Parr, R. G. (1985). Proc. Natl, Hardness, Softness and the Fukui Function in the

Electronic Theory of Metals and Catalysis. Acad. Sci., 82, 6723-6726. 40. Parr, R. G., Sventpaly, L., & Liu, S. (1999). Electrophilicity Index. J. Am. Chem. Soc., 121, 1922-

1824. 41. Pearson, R. G. (1963). Hard and Soft Acids and Bases. J. Am. Chem. Soc., 85, 3533-3539. 42. Lukovits, I., Kálmán, E., & Zucchi, F. (2001). Corrosion Inhibitors-Correlation between

Electronic Structure and Efficiency. Corrosion, 57, 3-8.

K. Toumiat et al.

294

43. Al-Mubarak, N. A., Khaled, K. F., Hamed, M. N. H., Abdel-Azim, K. M., & Abdelshafi, N. S. (2010). Corrosion inhibition of copper in chloride media by 2-mercapto-4-(p-methoxyphenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile: Electrochemical and theoretical study. Arab. J. Chem., 3, 233-242.

http://iserjournals.com/journals/ejac