Silver ... - ACS Publications

Research Article pubs.acs.org/journal/ascecg

Performance Evaluation of a Chitosan/Silver Nanoparticles Composite on St37 Steel Corrosion in a 15% HCl Solution Moses M. Solomon,*,† Husnu Gerengi,† Tugce Kaya,† and Saviour A. Umoren‡ †

Downloaded via UNIV OF PENNSYLVANIA on June 26, 2018 at 21:57:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Corrosion Research Laboratory, Department of Mechanical Engineering, Faculty of Engineering, Duzce University, 81620 Duzce, Turkey ‡ Centre of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia ABSTRACT: A chitosan/silver nanoparticles (AgNPs/chitosan) composite has been prepared in situ using natural honey as the reducing and capping agent, and its effectiveness as an inhibitor for St37 steel in 15% HCl solution was assessed using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), dynamic electrochemical impedance spectroscopy (DEIS), and weight loss (WL) methods complemented with surface morphological examination with the aid of energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). AgNPs/chitosan was characterized using Fourier transformed infrared (FTIR), EDS, and SEM. The results obtained show that AgNPs/chitosan is an effective cathodic type inhibitor particularly at higher temperature and protects the metal surface by formation of a protective film. SEM, AFM, and EDS confirm the formation of an adsorbed film. The adsorption followed the Temkin adsorption isotherm; as such, the thermodynamic and kinetic parameters governing the adsorption were calculated and discussed. The values of the free energy of adsorption suggest that a mixed adsorption mechanism characterized the adsorption of AgNPs/ chitosan molecules at lower temperature while chemisorption defined the adsorption process at higher temperature. KEYWORDS: Chitosan, Nanocomposite, Synthesis, Acid corrosion, Inhibition, AgNPs/chitosan

■

inhibitors should be developed from natural sources.8,9 Beside availability, natural substances are harmless to the natural ecosystem and are cheap. In a response, corrosion scientists have tested plant parts extracts10−15 and natural polymers16−22 for anticorrosive effects. It is however found that most natural polymers possess moderate inhibiting ability and are unstable at elevated temperature.9,23 As rightly put by Umoren and Solomon,24 abandoning polymers and looking elsewhere for effective, low price, and eco-friendly inhibitors might not be a good idea. Corrosion scientists have therefore devised several approaches in an attempt to improve the stability and performance of polymers as metals corrosion inhibitors. The most recent is the infusion of an inorganic substance in minute size into a polymer matrix,25−29 a modification method referred to as compositing. A composite is a material composed of two or more chemically distinct constituents on a minute scale, separated by a distinct interface, and with characteristics that are different from the properties of the constituents working in isolation. There are numerous methods of preparing metals/polymers composites. However, they can be broadly grouped into two:

INTRODUCTION The industrial demand for steel and its alloys is on the increase owing to its superior mechanical strength in comparison with other metals.1 However, the greatest challenge with the use of steel is its proneness to corrosion. Acid solutions, mostly hydrochloric and sulfuric acids in the concentration range 15− 28%, are deploy in large volume for industrial processes such as acid pickling, oil-well acidizing, industrial cleaning, acid descaling, etc. This practice, though intended for high system efficiency, encourages corrosion of metals. It is customary that corrosion inhibitors be added to acid solutions before use for any industrial process. Before now, inorganic compounds such as chromates, nitrites, nitrates, phosphates, etc. were utilized as metals corrosion inhibitors because they could oxidize a metal surface to form passive films capable of protecting the surface against corrosion.2−4 They were however banned because of their poisonous nature to both humans and the natural environment.5,6 Organic compounds with N, S, O, P, and/or πelectrons in their molecules replaced inorganic compounds as metal inhibitors, leading the inhibitors’ market at present by almost 70%.7 Nevertheless, corrosion scientists are not very comfortable with organic inhibitors because they are expensive and synthesis of many of them requires a rigorous approach. There have been calls from different quarters drawing the attention of corrosion scientists to why metals corrosion © 2016 American Chemical Society

Received: September 6, 2016 Revised: October 13, 2016 Published: November 7, 2016 809

DOI: 10.1021/acssuschemeng.6b02141 ACS Sustainable Chem. Eng. 2017, 5, 809−820

Research Article

ACS Sustainable Chemistry & Engineering

chitosan was dissolved in 10 mL of 0.1 M acetic acid at ordinary temperature. Complete dissolution took 5 h under constant stirring. The solution was poured into a 1000 cm3 capacity flask and the volume made to the mark with distilled water. The chitosan solution was used to prepare a 1 mM AgNO3 solution. Thereafter, 5 mL of natural honey (which serves as reducing and stabilizing agent) was added to every 100 cm3 of the chitosan−AgNO3 solution. A yellowish solution was obtained, and this solution was allowed to stand at ordinary temperature for 4 days (96 h). The color change from yellow to dark signaled complete conversion of Ag+ to Ag0,27,28 and this was verified chemically by adding NaCl solution to a small portion of the dark color solution. The nonformation of white precipitate suggested the absence of Ag+. At this point, the AgNPs/chitosan composite solution was used to prepare a 15% HCl solution by diluting concentrated HCl acid. Again, formation of a white precipitate was not observed. Other concentrations of AgNPs/chitosan were obtained by dilution of 1000 ppm AgNPs/chitosan with a 15% HCl solution. Characterization of AgNPs/Chitosan. FTIR. FTIR spectra for AgNPs/chitosan in water and in HCl solution were recorded and compared with the spectrum for chitosan on an Agilent Technologies Cary 630 FTIR spectrometer. AgNPs/chitosan samples were prepared by evaporating to dryness colloidal solutions of AgNPs/chitosan in a Petri dish at 40 °C. All FTIR spectra were scanned against a blank KBr pellet background in the range 4000−450 cm−1 at a resolution of 4 cm−1. SEM-EDS. Samples for SEM-EDS analysis were prepared by depositing a drop of the colloidal composite solutions on an Al grid sample holder and drying at room temperature. The elemental composition of the sample was obtained with the aid of an energy dispersive X-ray spectroscope coupled to a scanning electron microscope J Quanta FEG 250 model (FEI, Holland). Corrosion Studies. Electrochemical Experiments. A Gamry instrument potentiostat/galvanostat/ZRA (Reference 600) embedded with a Gamry framework system composed of ESA 410 was used for EIS and PDP experiments. The instrument applications have software DC 105 for PDP measurements and EIS 300 for EIS experiments. The prepared St37 steel (exposed area = 0.75 cm2) was used as the working electrode, Ag/AgCl was the reference electrode, and a platinum plate whose main function was to provide the location of the second electron transfer reaction25 was the counter electrode. Before commencing each experiment, the working electrode was immersed in the test solution for 1 h to attain a stable open circuit potential (OCP). For the purpose of reproducibility of experimental data, each experiment was performed under the same conditions for at least four times. For PDP experiments, the potential was swept from the cathodic direction to the anodic direction at a constant sweep rate of 1 mV/s at −250 to +250 mV interval with respect to corrosion potential (Ecorr). The corrosion current density (Icorr) and Ecorr were obtained by extrapolation of the Tafel lines.33 The percentage inhibition efficiency (IE) of various concentrations of AgNPs/chitosan was computed using the Icorr values in the absence and presence of AgNPs/chitosan according to the following equation:33

ex-situ and in situ methods. The ex-situ technique entails the dispersion of premade particles directly into the polymer matrix. The problem with this method is the difficulty associated with preparing inorganic particles that exhibit good dispersibility in the polymer backbone and also have long-term stability against aggregation.30 The in situ method, on the other hand, enjoyed higher patronage in that it is simple and involves on-step fabrication.30 In this method, the inorganic component is generated inside the polymer matrix, and this prevents particle agglomeration and also maintains good spatial distribution in the polymer backbone.30 There are reports in the literature on in situ synthesis of silver nanoparticles/ polymer composites in sulfuric acid solution26−29 but none in HCl solution. The reason is not far fetched. Silver ions precipitate chloride ions in solution, forming a silver chloride salt, and this makes it impossible for silver nanoparticles to form. In our effort to overcome this challenge, while still upholding the merits of an in situ technique, we first used water as the solvent during synthesis before transferring the formed silver nanoparticles into the corrosive medium. This communication reports, for the first time, the modification of unmodified chitosan by incorporation of silver nanoparticles and the effect of the composite on St37 steel corrosion in 15% HCl solution. Characterization of chitosan/silver nanoparticles (AgNPs/chitosan) was done using Fourier transformed infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) while chemical and electrochemical (electrochemical impedance spectroscopy, potentiodynamic polarization, and dynamic electrochemical impedance spectroscopy) methods complemented with surface morphological assessment (scanning electron microscopy, atomic force microscopy, and EDS) were used for corrosion studies.

■

EXPERIMENTAL SECTION

Chemicals and Materials. Chitosan with properties listed in Table 1 was purchased from Sigma-Aldrich, and natural honey (mad

Table 1. Properties of Chitosan Used in the Study Molecular weight Degree of deactylation Viscosity Solubility

448. 869 g/mol ≥75.0% 20−300 cps 1 wt % in 1% acetic acid at 25 °C. Also soluble in dilute aqueous acids

honey) was obtained from Duzce University Bee Keeping Research, Development and Application Centre in Yigilca, Turkey. All other chemicals used in the study were of analytical grade. Corrosion studies were performed on specimens from a St37-2 steel sheet with chemical composition (wt %): C 0.17, Mn 1.40, P 0.05, Si 0.30, S 0.05, and the balance Fe31 (For convenience, St37 is used instead of St37-2 throughout the text). Before specimens were used, they were abraded mechanically with a series of emery paper (#800 to #2000), washed under running water, degreased with acetone, and dried with warm air.32 They were preserved in a desiccator prior to use. Solutions. The corrosive medium was a 15% HCl solution prepared by dilution of 37% concentrated HCl acid. The concentrations of the prepared AgNPs/chitosan studied were 50, 100, 500, 750, and 1000 ppm. Synthesis of AgNPs/Chitosan Composite. Silver nanoparticles were generated in situ following the procedure previously reported.26−29 However, unlike previous reports, distilled water was used as the solvent rather than the corrosive solution. This was to prevent precipitation reaction between silver and chloride ions. 1.0 g of

⎛ I ⎞ ⎟ × 100 %IE = ⎜⎜1 − corr ° ⎟ Icorr ⎝ ⎠

(1)

where I°corr is the corrosion current density in the absence of AgNPs/ chitosan and Icorr is the corrosion current density in the presence of AgNPs/chitosan. The EIS experiments were carried out in the frequency range of 10 mHz to 100 kHz using an AC signal of 10 mV peak-to-peak. Values of charge transfer resistance (Rct) and film resistance (Rf) were obtained by the analysis of Nyquist plots using the Echem 6.32 program. The Rp value was computed as Rp = Rct + Rf,34 and the inhibition efficiencies of the various concentrations of AgNPs/ chitosan were calculated using eq 2:35

⎛ R − R1 ⎞ p p ⎟ × 100 %IE = ⎜⎜ ⎟ 1 R ⎝ ⎠ p 810

(2) DOI: 10.1021/acssuschemeng.6b02141 ACS Sustainable Chem. Eng. 2017, 5, 809−820

Research Article

ACS Sustainable Chemistry & Engineering where R1p and Rp are the polarization resistances in the presence and absence of AgNPs/chitosan, respectively. DEIS measurements were recorded with a frequency response analyzer (FRA) which has a galvanostat model. The current perturbation was generated with a National Instruments Ltd. PCI-4461 digital-analog card.36 The same card was employed in recording current and voltage signals. The sampling frequency was 12.8 kHz, and the perturbation signal had a package composed of current sinusoids of the frequency range 4.5 kHz to 700 MHz. For the analysis of DEIS impedance, the same Echem 6.32 program used for EIS was utilized. IE of AgNPs/chitosan from this technique was calculated using eq 2. Weight Loss (WL) Experiments. WL experiments were performed by freely suspending the precleaned St37 steel samples (in triplicate) in glass reaction vessels containing 100 mL of test solutions (15% HCl and 15% HCl + various concentrations of AgNPs/chitosan) at 25 and 60 °C in a thermostated bath. The metal specimens were removed after 10 h, washed thoroughly in a 20% NaOH solution containing 200 g/L of zinc dust,26,28 rinsed in running water, dried with warm air, and then reweighed. The weight loss (g), was calculated by subtracting the final weight from the initial weight of the metal sample, and the average weight loss was reported. The corrosion rate (CR) and inhibition efficiency were calculated from eqs 326 and 4,37 respectively:

CR(mpy) =

3.45 × 106 × W ρAT

⎛ W⎞ %IE = ⎜1 − e ⎟ × 100 W0 ⎠ ⎝

(3)

(4)

where W is the average weight loss (g), ρ is the density of the metal specimen (g cm−3), A is the surface area of the St37 specimen (9 cm2), and T is the immersion duration (hour). W0 and We are the weight losses of the coupons in the absence and presence of inhibitor, respectively, at the same temperature. Surface Morphology. The morphologies of the surface of St37 specimens exposed to 15% HCl solutions in the absence and presence of 1000 ppm AgNPs/chitosan for 10 h were observed using a scanning electron microscope J Quanta FEG 250 model (FEI, Holland) and an atomic force microscope Park Systems XE-100E model. Elemental compositional analysis of the metal samples before and after exposure to test solutions was recorded using an electron dispersive X-ray spectroscopy (EDS) detector.

Figure 2. EDS spectrum of AgNPs in (a) water and (b) HCl solution obtained by treating 5 mL of honey with 1000 ppm chitosan + 1 mM aqueous AgNO3 solution.

■

RESULTS AND DISCUSSION Characterization. FTIR Studies. Comparative IR spectra of honey, chitosan, and the synthesized AgNPs/chitosan composite are shown in Figure 1. In the honey spectrum, peaks arising from the symmetric stretching of C−O−C and the C−O−H bending vibration of the protein can be seen at

Figure 3. SEM picture of AgNPs in HCl solution containing the composite obtained by treating 5 mL of honey with 1000 ppm chitosan + 1 mM aqueous AgNO3 solution.

1025.0 cm−1.38 The peaks at 1653.5 and 1374.5 cm−1 are typical of carboxyl group stretching and the deformation vibration of N−H in amide I and II of the protein.25,38 Also, the strong and broad peak at 3331.8 cm−1 is unequivocally assigned to the hydrogen bonded vibration of the O−H group while the weak peak at 2927.8 cm−1 is associated with C−H stretching.26 The

Figure 1. FTIR spectra for honey, chitosan, and silver nanoparticles/ chitosan composite in water and HCl solution. 811


Research Article


secondary amide as well as the symmetric stretching of C−O− C and the C−O−H bending vibration of the protein noted in the honey spectrum also showed up in the chitosan spectrum at 2868.0, 1653.5, 1374.5, and 1024.6 cm−1, respectively. However, in contrast, the O−H stretch overlapping with the N−H stretch is rather found in the chitosan spectrum at 3304.8 cm−1.25 There are striking differences in the spectrum of chitosan and that of the AgNPs/chitosan composite in both water and HCl. By comparing the spectra, it could be seen that the broad O−H stretch peak at 3331.8 cm−1 in the chitosan spectrum becomes sharper and shifted to 3003.17 cm−1 in the composite spectra; the carboxyl group stretching peak of amide I at 1653.5 cm−1 appears stronger while the weak C−H peak at 2927.8 cm−1 disappears completely in the composite spectra. All these point to the involvement of proteins in honey in the reduction and stabilization of AgNPs in the chitosan matrix. However, there are two ways in which proteins can induce stability of metals nanoparticles. It can be through free amine groups or through carboxylate ions of the amino acid residue.38,39 In a case whereby stability is achieved through free amine groups, the CO stretching band appears at around 1700 cm−1 in the IR spectrum.39 The absence of such a peak infers stability through the carboxylate ions of the amino residue. In our case, the CO peak is absent, meaning the stabilization of AgNPs in the chitosan matrix is through carboxylate ions of the protein amino residue. It is pertinent to mention that the FTIR spectra of AgNPs/chitosan in H2O and HCl are similar, supporting the claim that silver ions were completely converted to elemental silver, and as such, no reaction takes place between silver and chloride ions in HCl solution. EDS and SEM Studies. EDS is a useful tool for the characterization of a new compound, as it is capable of providing both qualitative and quantitative information. Figure 2 presents the elemental profile of synthesized AgNPs/chitosan in (a) H 2 O and (b) HCl solution. From previous reports,25−28,40 elemental silver gives a signal arising from Surface Plasmon Resonance (SPR) at approximately 3 keV in the EDS spectrum. In both Figure 2(a) and (b), the SPR peak can be seen, thus providing experimental evidence to the claim of AgNPs/chitosan formation. The formed AgNPs in the chitosan backbone are spherical in shape (Figure 3). The component elements (C, O, N) of chitosan can as well be seen in the spectrum: an evidence that AgNPs were embedded in the chitosan matrix. The S peak also seen in Figure 2(a) may have arisen due to the acetic acid which was used as solvent for chitosan while the Al signal is as a result of the Al grid. Anticorrosion Studies. EIS Measurements. Electrochemical impedance spectroscopy was employed to study the behavior of St37 steel in 15% HCl solution without and with various concentrations of AgNPs/chitosan composite at 25 °C. The results obtained are presented in (a) Nyquist, (b) Bode modulus, and (c) Phase angle formats in Figure 4. From Figure 4(a), it is observed that the Nyquist diagram has one depressed capacitive loop in each studied system. This indicates that the corrosion of St37 steel in 15% HCl solution devoid of and containing composite is controlled by a charge transfer process.41,42 The Nyquist diagrams for St37 steel in acid solution without and with composite are similar, implying that the presence of AgNPs/chitosan in the solution did not stop the corrosion of St37 steel. However, the influence of the composite on the corrosion process, which is found to be concentration dependent, is reflected in the larger size of the

Figure 4. Electrochemical impedance spectra for St37 steel in 15% HCl solution in the absence and presence of various concentrations of AgNPs/chitosan composite in (a) Nyquist and (b) Bode modulus representations.

Figure 5. Equivalent circuit used for EIS and DEIS analysis.

honey spectrum is seen to share some semblance with that of chitosan. For instance, the C−H stretch, the carboxyl group stretch, and the deformation vibration N−H of the primary and 812


Research Article


Table 2. Electrochemical Impedance Parameters for St37 Steel in 15% HCl in the Absence and Presence of Different Concentrations of AgNPs/Chitosan at 25 °C Conc (ppm)

Rs (Ωcm2)

CPEdl (Ω−1 s2 cm−2)

ndl

Rct (Ωcm2)

CPEf (Ω−1 s2 cm−2)

nf

Rf (Ωcm2)

Rp = Rct + Rf (Ω cm2)

Cdl (μF cm−2)

R2 × 10−4

%IE

0 50 100 500 750 1000

0.4897 0.4932 0.5345 0.5142 0.5217 0.5234

2.664 2.537 2.573 3.577 3.049 5.273

0.7573 0.8487 0.7368 0.8552 0.8557 0.6272

9.194 23.950 24.960 30.510 37.730 76.150

0.561 1.775 2.533 6.880 5.296 1.105

0.9903 0.7415 0.8713 0.6237 0.6152 0.8968

2.684 2.008 2.634 2.146 2.930 1.401

11.878 25.958 27.594 32.656 40.660 77.551

428.72 243.89 195.88 155.37 146.16 80.19

6.132 5.375 3.386 2.630 2.736 2.508

54.24 56.95 63.63 70.79 84.68

Figure 6. DEIS spectra for St37 steel in (a) 15% HCl solution, (b) HCl solution containing 50 ppm AgNPs/chitosan, (c) acid solution containing 500 ppm AgNPs/chitosan, and (d) acid solution containing 1000 ppm AgNPs/chitosan at 25 °C after 2 h of measurements.

Table 3. Dynamic Electrochemical Impedance Parameters for St37 Steel in 15% HCl in the Absence and Presence of Different Concentrations of AgNPs/Chitosan at 25 °C Conc (ppm)

Rs (Ω cm2)

CPEdl (Ω−1 s2 cm−2)

ndl

Rct (Ω cm2)

CPEf (Ω−1 s2 cm−2)

nf

Rf (Ω cm2)

Rp = Rct + Rf (Ω cm2)

%IE

0 50 500 1000

0.4920 0.5339 0.5467 0.8383

1.755 1.594 1.577 7.318

0.7568 0.6215 0.8015 0.8721

15.61 35.41 64.40 98.09

2.345 4.256 6.047 3.532

0.6774 0.7303 0.5397 0.9109

0.843 3.506 3.388 5.744

16.453 38.916 67.788 103.834

57.72 75.73 84.15

semicircle is often referred to as frequency dispersion26,41,43 and has been attributed to roughness and nonuniformity of a working electrode,26,43 fracture structures,44 distribution of activity centers,45 as well as inhibitors adsorption and formation of porous layers.41,46 For the analysis of the Nyquist impedance data, a R(QR)(QR) equivalent circuit shown in Figure 5 was used. It allows for the determination of solution resistance (Rs), charge transfer resistance (Rct), and film resistance (Rf). The

capacitive loops and the displacement of the Bode modulus impedance and phase angle toward a larger value of log/Z/ (Figure 4(b)) and a larger angle (Figure 4(c)), respectively, in the composite inhibited systems compared to without. This means that the presence of the composite in the corrosive solution only slows down the rate of the charge transfer process. This could be possible due to adsorption of composite molecules on the metal surface, which block reaction sites.26The deviation of the Nyquist diagrams from a perfect 813


Research Article


values of the corrodent are 11.878 Ω cm2 and 428.72 μFcm−2, respectively. The presence of 50 ppm AgNPs/chitosan in the acid solution raised the value of Rp to 25.958 Ω cm2, while the Cdl value decreased to 243.89 μF cm−2 and the corresponding %IE is 54.24%. By increasing the concentration to 1000 ppm, the Rp value increased to 77.551 Ω cm2, Cdl decreased to 80.19 μF cm−2, and the percentage protection is at 84.68%. It could be argued that as the concentration of the composite was increased, more of the inhibitor molecules were available for adsorption, and as an effect, a larger area was covered on the metal surface. Further inspection of the table reveals that the n values are close to unity, implying that the interface behaves nearly capacitive.48 DEIS Measurements. DEIS results have been used in recent times to support results from the conventional EIS owing to the fact that DEIS can measure an instantaneous corrosion process in a nonstationary environment.36,49,50 The EIS method requires a steady state and an unperturbed environment for an accurate measurement to be achieved. As a matter of fact, a completely stable environment is technically impossible to achieve. Figure 6 shows the DEIS spectra obtained after 2 h of measurements for St37 steel in (a) 15% HCl solution, (b) HCl solution containing 50 ppm AgNPs/chitosan, (c) acid solution containing 500 ppm AgNPs/chitosan, and (d) acid solution containing 1000 ppm AgNPs/chitosan at 25 °C. In all cases, a flattened semicircle in the high frequency region with a tail which terminated at the low frequency region is seen. This again indicates that the corrosion of the metal in the studied environment is a charge controlled process. The similarity in the spectra of the uninhibited and inhibited systems in Figure 6 infers that the presence of AgNPs/chitosan did not change the corrosion mechanism of the metal.50 However, a comparison of the spectra of the inhibited systems to the spectrum of the uninhibited system reveals a larger capacitive loop in the inhibited systems. It is interesting to note that the tail of the inhibited spectra terminated at a higher Re/Z/ value compared to that of the blank solution. For instance, the tail of the capacitive loop of the free acid solution terminates at an Re/Z/ value of 20 Ω cm2 whereas that of the 50, 500, and 1000 ppm AgNPs/chitosan inhibited solutions terminates at 40, 60, and 80 Ω cm2, respectively. This, according to Gerengi et al.,50 is indicative of corrosion inhibition. The DEIS spectra were analyzed using the same equivalent circuit (Figure 5) used for EIS spectra analysis, and the parameters derived are presented in Table 3. As could be seen from the table, the listed parameters vary in a similar manner as those from the EIS method (Table 2). That is, the Rs and Rp values of inhibitor-containing solutions are larger than those of solutions without inhibitor, and Rp values increase with increasing inhibitor concentration. Again, the values of the n parameter for inhibited systems show a higher heterogeneous

Figure 7. Potentiodynamic polarization curves obtained for St37 steel in 15% HCl solution without and with different concentrations of AgNPs/chitosan at 25 °C.

constant phase element (CPE) was used in place of double layer capacitance (Cdl). This was necessary for a more accurate fitting following the imperfectness of the Nyquist semicircles.41 The parameter CPE is related in the impedance representation as26 Q CPE = Y o−1(jω)−n

(5)

where Y0 is the CPE constant; n is the CPE exponent; j = (−1)1/2, which is an imaginary number; and ω is the angular frequency in rad/s. The double-layer capacitance (Cdl) values were computed from the expression:26 Cdl =

Yωn − 1 sin(n(π /2))

(6)

where ω is the angular frequency (ω = 2πf max); f max is the frequency at which the imaginary component of the impedance is maximum; and n is the phase shift (−1 ≤ n ≤ 1); when n = 0, the CPE represents a pure resistor, if n = −1, the CPE stands for an inductor, and if n = +1, the CPE represents a pure capacitor.47 The quite small chi-square values (Table 2) show the goodness of the equivalent circuit fitting and validate the derived parameters. All the derived parameters are presented in Table 2. The %IE also listed in the table was calculated using eq 2. Inspection of the table reveals that Rs and Rp values of inhibited systems are larger while the Cdl value is smaller compared to those of the uninhibited system. An increase in AgNPs/chitosan concentration is seen to lead to an increase in Rp value and a decrease in Cdl value. This may be associated with inhibition of St37 steel corrosion in HCl solution by a AgNPs/chitosan composite.26,47 For instance, the Rp and Cdl

Table 4. Potentiodynamic Polarization Parameters for St37 Steel in 15% HCl in the Absence and Presence of Different Concentrations of AgNPs/Chitosan at 25 °C Conc (ppm)

−Ecorr (mV/Ag/Ag Cl)

Icorr (μA cm−2)

βa (mV dec−1)

βC (mV dec−1)

CR (mpy)

%η

0 50 100 500 750 1000

193.0 290.0 390.0 401.0 409.0 417.0

808.0 247.0 207.0 181.0 140.0 106.0

172.8 132.3 123.1 130.8 138.1 154.0

86.7 86.6 117.4 84.5 103.3 104.1

391.4 111.3 83.96 71.58 63.79 57.49

69.43 74.38 77.60 82.67 86.88

814


Research Article


Table 5. Calculated Values of Weight Loss (g), Corrosion Rate (mpy), Surface Coverage (Θ), and Inhibition Efficiency (%IE) for St37 Steel in 15% HCl in the Absence and Presence of Different Concentrations of AgNPs/Chitosan at 25 and 60 °C from Weight Loss Measurements Weight loss (g)

Corrosion rate (mpy)

%IE

Surface coverage (Θ)

Conc (ppm)

25 °C

60 °C

25 °C

60 °C

25 °C

60 °C

25 °C

60 °C

0 50 100 500 1000

0.3894 0.1706 0.1385 0.0973 0.0472

4.3122 1.3730 1.0239 0.2798 0.1253

1889.89 827.98 672.19 472.23 229.08

20928.55 6663.63 4969.33 1357.19 608.12

0.5619 0.6443 0.7501 0.8788

0.6816 0.7626 0.9351 0.9709

56.19 64.43 75.01 87.88

68.16 76.26 93.51 97.09

Table 7. Calculated Values of Activation Energy (Ea) and Heat of Adsorption (Qads) for St37 Steel in 15% HCl in the Absence and Presence of Different Concentrations of AgNPs/Chitosan

Table 6. Adsorption Parameters from the Temkin Isotherm for St37 Steel in 15% HCl in the Absence and Presence of Different Concentrations of AgNPs/Chitosan from Different Methods Temp (K)

−a

Kads (M−1)

−ΔG°ads (kJ/mol)

EIS PDP WL

298 298 298 333

0.0216 0.0374 0.0529 0.0520

2.7315 4.4916 2.7842 3.7801

36.719 37.951 36.766 41.931

Ea (kJ/mol)

Qads (kJ/mol)

0 50 100 500 1000

56.69 49.17 47.16 24.90 23.02

12.077 13.507 35.986 36.983

parameters derived from the PDP graphs are given in Table 4. The PDP graphs are composed of two branches: the anodic and cathodic, which under these experimental conditions correspond to St37 steel dissolution and hydrogen evolution reactions, respectively. It is seen from the figure that the presence of the composite in the acid solution shifted the corrosion potential remarkably toward the cathodic direction. The greatest effect is observed for the higher concentrations of AgNPs/chitosan. This behavior is typical of a cathodic type inhibitor.51 The cathodic curves are found to give rise to Tafel lines, indicating that AgNPs/chitosan prevented the dissolution of St37 steel in 15% HCl solution by simply blocking the reactions site on the metal surface without changing the reaction mechanism.43 This is also supported by the nonpattern demonstrated by the βc value with increasing composite concentration (Table 4). In the literature,22,26,43,50,51 inhibitor can only be classed under cathodic type if the difference between the corrosion potential of the inhibited solution and that of the uninhibited is greater than or equal to +85 mV. In the present investigation, the differences between the Ecorr values of 50, 100, 500, 750, and 1000 ppm AgNPs/chitosan inhibited acid solution and those of the corrodent are +97, +197, +208, +216, and +224 mV/Ag/ AgCl. These values are higher than the benchmark value; hence, we submit that AgNPs/chitosan functioned as a cathodic type inhibitor in the studied corrosive environment. It is pertinent to mention that the corrosion current density and the corrosion rate recorded in the inhibited systems are significantly lower than those recorded in the uninhibited acid solution. For instance, the Icorr and CR values obtained for the metal in free HCl solution are 808.0 μAcm−2 and 391.4 mpy, whereas those for 50 ppm AgNPs/chitosan-containing solution are 247.0 μAcm−2 and 111.3 mpy, respectively. These values are further reduced on increasing the composite concentration, and the least values are obtained in 1000 ppm AgNPs/chitosan-containing solution. This shows that the composite protected the metal surface against corrosive attack in the studied environment. The optimum inhibition efficiency

Figure 8. Temkin plot of θ versus log C from (a) EIS and PDP data at 25 °C and (b) WL data at 25 and 60 °C.

Method

Conc (ppm)

surface compared to the surface in the free acid solution. This might have been caused by the adsorption of inhibitor molecules onto the surface. The optimum inhibition efficiency obtained from this method is 84.15%, which is in perfect agreement with that obtained from EIS measurements. PDP Measurements. To characterize AgNPs/chitosan as anodic, cathode, or mixed type inhibitor, PDP experiments were undertaken. The polarization curves obtained for St37 steel in 15% HCl solution in the absence and presence of AgNPs/chitosan are shown in Figure 7. The polarization 815


Research Article


Figure 9. SEM images and EDS spectra for St37 steel (a, b) in an abraded state, (c, d) exposed to 15% HCl solution, and (e, f) exposed to 15% HCl solution containing 1000 ppm AgNPs/chitosan for 10 h at 25 °C.

of 86.88% obtained from this technique agrees with the ones from other electrochemical techniques. Weight Loss Measurements. The dissolution pattern of St37 steel in 15% HCl solution without and with AgNPs/ chitosan composite was also studied by a chemical technique. The weight loss (WL) method is considered the “gold standard” for corrosion assessment because of its simplicity.52 Compared with the electrochemical techniques, it gives the average corrosion rate while the electrochemical methods measure the instantaneous corrosion rate.9 WL thus requires a reasonable immersion time during measurement. WL experiments were performed for St37 steel in 15% HCl in the absence and presence of different concentrations of AgNPs/chitosan for 10 h at 25 and 60 °C, respectively. The calculated weight loss

(g), corrosion rate (mpy), surface coverage (Θ), and inhibition efficiency (%IE) are given in Table 5. Clearly, from the table, it can be seen that weight loss, corrosion rate, Θ, and IE values are higher at 60 °C than at 25 °C. The higher values of weight loss and corrosion rate at 60 °C compared to values at 25 °C may be due to intensified molecular thermal motion53 while those of Θ and IE may be as a result of a shift in the adsorption−desorption equilibrium toward adsorption.9,26 The higher values of Θ and IE at 60 °C also point to the chemisorption mode of adsorption of AgNPs/chitosan molecules on the metal surface. It appears as if a more compact and rigid film that was capable of effective corrosion inhibition was formed on the metal surface at higher temperature than at lower temperature. For instance, 1000 816


Research Article


Figure 10. AFM images for St37 steel after (a, b) exposure to 15% HCl solution, and (c, d) exposure to 15% HCl solution containing 1000 ppm AgNPs/chitosan for 10 h at 25 °C.

on the metal surface and decreased the rate of hydrogen evolution without changing the mechanism of the cathodic reactions. Authors51,54 have reported that such competitive adsorption is possible in an HCl environment. After the release of hydrogen gas, cationic AgNPs/chitosan molecules may have returned to their neutral form55 such that the neutral molecules chemisorbed on the St37 steel surface through donor interactions between the heteroatoms and the empty d-orbital of Fe. AgNPs may have also interacted directly with the metal surface. According to Zhang et al.,55 extra electrons on the metal surface can be transferred from the d-orbital of Fe to the π* orbital of inhibitor molecules. The retro-donation favors adsorption of inhibitor molecules on a metal surface, and a rise in temperature strengthens the bonds.24 The variation of IE with temperature in Table 5 supports the proposed mechanism. Adsorption Consideration. Insight into the mode of interaction between inhibitor molecules and metal surface can be gained through the use of the adsorption isotherm. To further understand the mode of adsorption of AgNPs/chitosan on an St37 steel surface in 15% HCl solution, surface coverage values (Table 5) were fitted into various adsorption isotherms including Langmuir, El-Awady et al. kinetic/thermodynamic,

ppm AgNPs/chitosan offered 87.88% protection to the metal surface at 25 °C but 97.09% at 60 °C. Further inspection of Table 5 reveals that the weight loss and corrosion rate of the metal were considerably reduced in the presence of composite and the order of reduction is 1000 ppm < 500 ppm < 100 ppm < 50 ppm. The inhibition efficiency obtained from the weight loss method at 25 °C is in perfect agreement with those from electrochemical methods (Tables 2−4). Mechanism of Inhibition by AgNPs/Chitosan Composite. It has been reported25,33,41,43 that the steel surface is hydrated with chloride ions in HCl solution. This specific adsorption of chloride ions renders the surface negatively charged.25,33 In 15% HCl solution, AgNPs/chitosan may exist as either protonated species or neutral species. Adsorption onto the St37 steel surface may be through any of the following ways: (i) electrostatic interaction between the protonated form of the composite and the negatively charged steel surface; (ii) electron transfer or sharing between O and/or N heteroatoms of the neutral form of the composite and the vacant orbital of Fe; (iii) the nanoparticles interacting directly with the metal surface.25,26 Our PDP results suggest that the protonated form of AgNPs/chitosan competes with hydrogen ions for electrons 817


Research Article


⎡ ⎛ θ ⎞ ⎛ θ ⎞⎤ 2 Q ads = 2.303R ⎢log⎜ ⎟ − log⎜ 1 ⎟⎥ ⎢⎣ ⎝ 1 − θ2 ⎠ ⎝ 1 − θ1 ⎠⎥⎦

Temkin, Frundlich, and Frumkin adsorption isotherms. Normally, the isotherm with the best fit to the data is adjudged by the value of the linear regression coefficient (R2).9,11,13 For a perfect fit, R2 = 1. In our case, the best fit was obtained for the Temkin adsorption isotherm. The Temkin adsorption isotherm contains a factor that clearly describes the adsorbent−adsorbate interactions. By ignoring too low or large value of concentration, the model assumes that the heat of adsorption (function of temperature) of molecules in the adsorption layer would decrease linearly rather than logarithmically with coverage.56,57 The Temkin model is defined by the following equation:26,28 exp( − 2aθ ) = KadsC

⎛ TT ⎞ × ⎜ 1 2 ⎟ kJ mol−1 ⎝ T2 − T1 ⎠

where CR1 and CR2, θ1, and θ2 are the corrosion rates and surface coverage at temperatures T1 and T2, respectively. The calculated values are presented in Table 7. It is clear from the table that the Ea values of the inhibited systems are smaller than those of the uninhibited ones, and they decrease with increasing composite concentration. Similar results have been reported in the literature64 and were interpreted as indicative of chemical adsorption. The Qads values are all positive, which is characteristic of a chemisorption mechanism.62 Surface Morphological Examination. SEM and EDS measurements were performed on St37 steel surfaces unexposed and exposed to 15% HCl solution without and with 1000 ppm AgNPs/chitosan composite to show that the protection of the metal surface in the acid solution containing AgNPs/chitosan composite was due to formation of a protective film on the surface. Figure 9 presents the SEM pictures and EDS spectra obtained for St37 steel (a, b) in an abraded state, (c, d) after exposure to 15% HCl solution, and (e, f) after exposure to 15% HCl solution containing 1000 ppm AgNPs/chitosan for 10 h at ordinary temperature. As could be seen from the figure, the smooth surface in Figure 9(a) is seriously damaged upon exposure to the acid solution (Figure 9(c)). The corrosive attack resulted in loss of some of the component elements of the metal, as evidenced in the less intense Fe peak in Figure 9(d) compared to that in Figure 9(b). Cracks can be visibly seen on the surface in Figure 9(c). This shows the level of severity of the damage incurred by the metal surface in 15% HCl solution. In Figure 9(e), heaps of deposits are seen, and the appearance of N and Ag peaks in Figure 9(f) provides evidence that the deposits are adsorbed AgNPs/ chitosan molecules. This adsorbed film was capable of protecting the metal surface, as indicated by the experimental results (Table 2−5) and the more intense Fe peak in Figure 9(f) compared to that of Figure 9(d). To further study the influence of AgNPs/chitosan on the progress of corrosion at the metal/solution interface, the topography of the tested samples was observed using AFM. The 3D and 2D images of the surfaces of St37 steel samples exposed to (a, b) 15% HCl solution and (c, d) 15% HCl solution containing 1000 ppm AgNPs/chitosan are shown in Figure 10. The lines in Figure 10(b and d) show the section for which average roughness was measured. As could be seen in Figure 10(a and b), the surface is very rough. The average roughness ranges between 185.891 and 219.973 nm. The metal surface is less damaged in the acid solution containing AgNPs/ chitosan (Figure 10(c and d), as the average roughness is reduced to between 121.481 and 131.129 nm. This again supports the experimental results that AgNPs/chitosan protected the metal surface in the studied environment.

(7)

where a is the molecules interaction parameter, θ is the degree of surface coverage, Kads is the equilibrium constant of the adsorption process, and C is the concentration of AgNPs/ chitosan. The straight line graphs obtained by plotting θ values obtained from EIS and PDP methods at 25 °C against composite concentration are given in Figure 8(a). Similar plots for values obtained from the weight loss method at 25 and 60 °C, respectively, are presented in Figure 8(b). The adsorption parameters derived from the graphs are listed in Table 6. The adsorption equilibrium constant Kads is related to the standard free energy of adsorption (ΔGads ° ) according to the following equation:58 ° ΔGads = −RT ln(1 × 106Kads)

(8)

where 1 × 106 is the concentration of water molecules expressed in ppm, R is the universal gas constant, and T is the absolute temperature. Calculated values of ΔGads ° are also given in Table 6. From the table, it is seen that the value of the interaction parameter (a) is negative in all cases, indicating the existence of a repulsive force in the AgNPs/chitosan adsorbed layer.26 Interestingly, the repulsive force is suppressed at higher temperature and, as an effect, the strength of the bond between the inhibitor and the metal surface becomes stronger. For instance, the value of a from WL at 25 °C is −0.0529 and the corresponding Kads value is 2.7842 M−1. At 60 °C, the a value becomes more positive, i.e −0.0520, and the Kads value increased to 3.7801 M−1. The ΔGads ° value at 25 °C from all the methods (i.e. 36.719, 37.951, and 36.766 kJ/mol for EIS, PDP, and WL, respectively) is within the range of values interpreted in the literature for mixed adsorption (i.e. both physisorption and chemisorption),41,43,59,60 but the value at 60 °C clearly points to a chemical adsorption mechanism.61 This result supports the proposed mechanism in the section Mechanism of Inhibition by AgNPs/Chitosan Composite for the adsorption of AgNPs/chitosan onto an St37 steel surface. Corrosion Kinetics Analysis. The apparent activation energies (Ea) for the corrosion process of St37 steel in 15% HCl solution in the absence and presence of a AgNPs/chitosan composite were calculated using eq 9,62,63 while the heat of adsorption of the composite on the metal surface was computed from eq 10.62,63 log

Ea ⎛ 1 CR 2 1⎞ = ⎜ − ⎟ CR1 T2 ⎠ 2.303R ⎝ T1

(10)

■

CONCLUSION AgNPs/chitosan composite has been successfully synthesized by using natural honey as the reducing and stabilizing agent. The prepared composite is effective in retarding the corrosion of St37 steel in 15% HCl solution, particularly at higher temperature. EIS results indicate that charge transfer resistance

(9) 818


Research Article


synergistic effect of iodide ions: Ethanol and acetone extracts. J. Environ. Chem. Eng. 2014, 2, 1048−1060. (11) Akalezi, C.; Enenebaku, C.; Okolue, B.; Oguzie, E. Potentials of Hyppocratea pallens planch leave extract as inhibition towardsthe corrosion of mild steel in acidic media. Der Pharma Chemica 2012, 4 (3), 1195−1205. (12) Okafor, P. C.; Osabor, V. I.; Ebenso, E. E. Eco-friendly corrosion inhibitors: inhibitiveaction of ethanol extracts of Garcinia kola forthe corrosion of mild steel in H2SO4 solutions. Pigm. Resin Technol. 2007, 36 (5), 299−305. (13) Umoren, S. A.; Ekanem, U. F. Inhibition of mild steel corrosion in H2SO4 using exudate gum from Pachylobus edulis and synergistic potassium halide additives. Chem. Eng. Commun. 2010, 197, 1339− 1356. (14) Krishnaveni, K.; Ravichandran, J.; Selvaraj, A. Inhibition of mild steel corrosion by Morinda tinctoria leaves extract in sulphuric acid medium. Ionics 2014, 20, 115−126. (15) Obi-Egbedi, N. O.; Obot, I. B.; Umoren, S. A. Spondias mombin L. as a green corrosion inhibitor for aluminium in sulphuric acid: Correlation between inhibitive effect and electronic properties of extracts major constituents using density functional theory. Arabian J. Chem. 2012, 5, 361−373. (16) Bayol, E.; Gurten, A. A.; Dursun, M.; Kayakirilmaz, K. Adsorption behavior and inhibition corrosion effect of sodium carboxylmethyl cellulose on mild steel in acidic medium. Acta Physco-Chim. Sin. 2008, 24, 2236. (17) Arukalam, I. O.; Nleme, K. I.; Anyanwu, A. E. Comparative inhibitive effect of hydroxyethylcellulose on mild steel and aluminium corrosion in 0.5 M HCl solution. Academic Res. Int. 2011, 1 (3), 492− 498. (18) Bentrah, H.; Rahali, Y.; Chala, A. Gum Arabic as an eco-friendly inhibitor for API 5L X42 pipeline steel in HCl medium. Corros. Sci. 2014, 82, 426−431. (19) Fekry, A. M.; Mohamed, R. R. Acetyl thiourea chitosan as an ecofriendly inhibitor for mild steel in sulphuric acid medium. Electrochim. Acta 2010, 55, 1933−1939. (20) Bello, M.; Ochoa, N.; Balsamo, V.; onzalez, G. Modified cassava starches as corrosion inhibitors of carbon steel: an electrochemical and morphological approach. Carbohydr. Polym. 2010, 82, 561−568. (21) Fares, M. M.; Maayta, A. K.; Al-Mustafa, J. A. Corrosion inhibition of iota-carrageenan natural polymer on aluminum in presence of zwitterions mediator in HCl media. Corros. Sci. 2012, 65, 223−30. (22) Umoren, S. A.; Solomon, M. M.; Udosoro, I. I.; Udoh, A. P. Synergistic and antagonistic effects between halide ions and carboxymethyl cellulose for the corrosion inhibition of mild steel in sulphuric acid solution. Cellulose 2010, 17, 635−648. (23) Umoren, S. A.; Solomon, M. M. Recent Developments on the Use of Polymers as Corrosion Inhibitors -A Review. Open Mater. Sci. J. 2014, 8, 39−54. (24) Umoren, S. A.; Solomon, M. M. Effect of halide ions on the corrosion inhibition efficiency of different organic species − A review. J. Ind. Eng. Chem. 2015, 21, 81−100. (25) Hefni, H. H.H.; Azzam, E. M.; Badr, E. A.; Hussein, M.; Tawfik, S. M. Synthesis, characterization and anticorrosion potentials ofchitosan-g-PEG assembled on silver nanoparticles. Int. J. Biol. Macromol. 2016, 83, 297−305. (26) Solomon, M. M.; Umoren, S. A. In-situ preparation, characterization and anticorrosion property of polypropylene glycol/ silver nanoparticles composite for mild steel corrosion in acid solution. J. Colloid Interface Sci. 2016, 462, 29−41. (27) Solomon, M. M.; Umoren, S. A.; Israel, A. U.; Ebenso, E. E. Polypropylene glycol-silver nanoparticle composites:A novel anticorrosion material for aluminum in acid medium. J. Mater. Eng. Perform. 2015, 24, 4206−4218. (28) Solomon, M. M.; Umoren, S. A.; Abai, E. J. Poly(methacrylic acid)/silver nanoparticles composites: In-situpreparation, characterization and anticorrosion property formild steel in H2SO4 solution. J. Mol. Liq. 2015, 212, 340−351.

increases while double layer capacitance decreases in the presence of AgNPs/chitosan composite, suggesting the adsorption of the composite molecules on an St37 steel surface. SEM, AFM, and EDS results confirmed the adsorption, which followed the Temkin adsorption isotherm model. The values of the free energy of adsorption suggest that the adsorption of AgNPs/chitosan composite molecules onto an St37 steel surface involves both physisorption and chemisorption mechanisms. According to PDP results, AgNPs/ chitosan composite acted as a cathodic type inhibitor in 15% HCl solution.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Saviour A. Umoren: 0000-0002-8564-4897 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS M.M.S. is grateful to The Scientific and Technological Research Council of Turkey (TÜ BITAK) for financial support under the TÜ BITAK 2216 − Postdoctoral Research Fellowship (TUBITAK 21514107−115.02-56312) programme and Duzce Unıversity, Turkey for providing the facilities. The authors are thankful to Kazimierz Darowicki and Pawel Slepski for providing the DEIS software.

■

REFERENCES

(1) Strickland, D. M. The resistivity of iron and its application to the chemical industry. Ind. Eng. Chem. 1923, 15, 566−569. (2) Li, X.; Deng, S.; Fu, H.; Mu, G. Synergistic inhibition effect of rare earth cerium(IV) ion and 3,4-dihydroxybenzaldehye on the corrosion of cold rolled steel in H2SO4 solution. Corros. Sci. 2009, 51, 2639−2651. (3) Gunasekaran, G.; Palniswamy, N.; Apparao, B. V.; Muralidharan, V. S. Enhanced synergistic inhibition by calcium gluconate in low chloride media. Part 1: kinetics of corrosion. Proc. Indian Acad. Sci. (Chem. Sci.) 1996, 108 (4), 399−405. (4) Li, X.; Deng, S.; Fu, H.; Mu, G. Synergistic inhibition effect of rare earth cerium(IV) ion and anionic surfactant on the corrosion of cold rolled steel in H2SO4 solution. Corros. Sci. 2008, 50, 2635−2645. (5) U.S. Congress, Office of Technology Assessment. Environmental Policy Tools: A User’s Guide, OTA-ENV-634; U.S. Government Printing Office: Washington, DC, 1995. (6) Toxicological profile for chromium, agency for toxic substance; US Public Health Service, Report no. ATSDR/TP-88/10; 1989. (7) Corrosion Inhibitors Market Analysis by Product (Organic, Inorganic), By Application (Water-based, Oil-based), By End-use (Power Generation, Oil & Gas, Metal Processing, Pulp & Paper, Chemical Processing) And Segment Forecasts to 2024; www.grandviewresearch. com/industry-analysis/corrosion-inhibitors-market (Accessed 27th August, 2016). (8) Raja, P. B.; Sethuraman, M. G. Natural products as corrosion inhibitors for metals in acidic media − a review. Mater. Lett. 2008, 62, 113. (9) Solomon, M. M.; Umoren, S. A.; Udosoro, I. I.; Udoh, A. P. Inhibitive and adsorption behaviour of carboxymethyl cellulose on mild steel corrosion in sulphuric acid solution. Corros. Sci. 2010, 52, 1317−1325. (10) Umoren, S. A.; Solomon, M. M.; Eduok, U. M.; Obot, I. B.; Israel, A. U.Inhibition of mild steel corrosion in H2SO4 solution by coconut coir dust extract obtained from different solvent systems and 819


Research Article


inhibitors for mild steel in sulfuric acid solution. Corros. Sci. 2015, 95, 168−179. (49) Gerengi, H.; Slepski, P.; Bereket, G. Dynamic electrochemical impedance spectroscopy andpolarization studies to evaluate the inhibition effect ofbenzotriazole on copper-manganese-aluminium alloyin artificial seawater. Mater. Corros. 2013, 64 (11), 1024−1031. (50) Gerengi, H.; Mielniczek, M.; Gece, G.; Solomon, M. M. Experimental and quantum chemical evaluation of 8-hydroxyquinoline as a corrosion inhibitor for copper in 0.1 M HCl. Ind. Eng. Chem. Res. 2016, 55, 9614. (51) Gerengi, H.; Ugras, H. I.; Solomon, M. M.; Umoren, S. A.; Kurtay, M.; Atar, N. Synergistic corrosion inhibition effect of 1-ethyl-1methylpyrrolidinium tetrafluoroborate and iodide ions for low carbon steel in HCl solution. J. Adhes. Sci. Technol. 2016, 30 (21), 2383−2403. (52) Anupama, K. K.; Ramya, K.; Joseph, A. Electrochemical and computational aspects of surface interaction and corrosion inhibition of mild steel in hydrochloric acid by Phyllanthus amarus leaf extract (PAE). J. Mol. Liq. 2016, 216, 146−155. (53) Arukalam, I. O. Durability and synergistic effects of KI on the acid corrosion inhibition of mild steel by hydroxypropyl methylcellulose. Carbohydr. Polym. 2014, 112, 291−299. (54) Kowsari, E.; Payami, M.; Amini, R.; Ramezanzadeh, B.; Javanbakht, M. Task-specific ionic liquid as a new green inhibitor of mild steel corrosion. Appl. Surf. Sci. 2014, 289, 478−486. (55) Zhang, W.; Ma, R.; Liu, H.; Liu, Y.; Li, S.; Niu, L. Electrochemical and surface analysis studies of2-(quinolin-2-yl)quinazolin-4(3H)-one as corrosion inhibitor for Q235steel in hydrochloric acid. J. Mol. Liq. 2016, 222, 671−679. (56) Tempkin, M. I.; Pyzhev, V. Kinetics of ammonia synthesis on promoted iron catalyst. Acta Phys. Chim. USSR 1940, 12, 327−356. (57) Aharoni, C.; Ungarish, M. Kinetics of activated chemisorption. Part 2. Theoretical models. J. Chem. Soc., Faraday Trans. 1 1977, 73, 456−464. (58) Roy, P.; Sukul, D. Protein-surfactant aggregate as potential corrosion inhibitor for mild steel in sulphuric acid: zein-SDS system. RSC Adv. 2015, 5, 1359−1365. (59) Mobin, M.; Khan, M. A. Adsorption and corrosion inhibition behavior of polyethylene glycol and surfactants additives on mild steel in H2SO4. J. Mater. Eng. Perform. 2014, 23, 222−229. (60) Solomon, M. M.; Umoren, S. A. Performance evaluation of poly (methacrylic acid) as corrosion inhibitor in the presence of iodide ions for mild steel in H2SO4 solution. J. Adhes. Sci. Technol. 2015, 29 (11), 1060−1080. (61) Zhang, J.; Liu, Z.; Han, G. C.; Chen, G. L.; Chen, Z. Inhibition of copper corrosion by the formation of Schiff base self-assembled monolayers. Appl. Surf. Sci. 2016, 389, 601−608. (62) Oguzie, E. E. Corrosion inhibition of aluminium in acidic andalkaline media by Sansevieria trifasciata extract. Corros. Sci. 2007, 49, 1527−1539. (63) Ebenso, E. E.; Eddy, N. O.; Odiongenyi, A. O. Corrosion inhibition and adsorption properties of methocarbamol on mild steel in acidic medium. Portugaliae Electrochim. Acta 2009, 27 (1), 13−22. (64) Zheng, X.; Zhang, S.; Li, W.; Yin, L.; He, J.; Wu, J. Investigation of 1-butyl-3-methyl-1H-benzimidazolium iodide as inhibitor for mild steel in sulfuric acid solution. Corros. Sci. 2014, 80, 383−392.

(29) Solomon, M. M.; Umoren, S. A. Performance assessment of poly (methacrylic acid)/silver nanoparticles composite as corrosion inhibitor for aluminium in acidic environment. J. Adhes. Sci. Technol. 2015, 29 (21), 2311−2333. (30) Hanemann, T.; Szabó, D. V. Polymer Nanoparticle Composites: From Synthesis to Modern Applications. Materials 2010, 3, 3468− 3517. (31) Hassan, S. A.; Hadi, A. K. Sudan III as corrosion ınhıbıtor for carbon steel St37−2 in H2SO4 solutıons. Int. J. Recent Sci. Res. 2015, 6 (7), 5445−5453. (32) Chidiebere, M. A.; Oguzie, E. E.; Liu, L.; Li, Y.; Wang, F. Corrosion inhibition of Q235 mild steel in 0.5 M H2SO4 solution by phytic acid and synergistic Iodide additives. Ind. Eng. Chem. Res. 2014, 53, 7670−7679. (33) Sangeetha, Y.; Meenakshi, S.; Sundaram, C. S. Corrosion inhibition of aminated hydroxyl ethyl cellulose on mild steel in acidic condition. Carbohydr. Polym. 2016, 150, 13−20. (34) Wang, Z. B.; Hu, H. X.; Zheng, Y. G.; Ke, W.; Qiao, Y. X. Comparison of the corrosion behavior of pure titanium and its alloysin fluoride-containing sulfuric acid. Corros. Sci. 2016, 103, 50−65. (35) Yilmaz, N.; Fitoz, A.; Ergun, U.; Emregül, K. C. A combined electrochemical and theoretical study into the effect of2-((thiazole-2ylimino)methyl)phenol as a corrosion inhibitor for mild steel in a highly acidic environment. Corros. Sci. 2016, 111, 110−120. (36) Gerengi, H.; Bereket, G.; Kurtay, M. A morphological and electrochemical comparison of the corrosion process of aluminum alloys under simulated acid rain conditions. J. Taiwan Inst. Chem. Eng. 2016, 58, 509−516. (37) Verma, C.; Quraishi, M. A.; Ebenso, E. E.; Obot, I. B.; El Assyry, A. 3-Amino alkylated indoles as corrosion inhibitors for mild steel in 1M HCl: Experimental and theoretical studies. J. Mol. Liq. 2016, 219, 647−660. (38) Haiza, H.; Azizan, A.; Mohidin, A. H.; Halin, D. S. C. Green synthesis of silver nanoparticles using local honey. Nano Hybrids 2013, 4, 87−98. (39) Philip, D. Honey mediated green synthesis of gold nanoparticles. Spectrochim. Acta, Part A 2009, A73, 650−653. (40) Rao, Y. S.; Kotakadi, V. S.; Prasad, T.N.V.K.V.; Reddy, A. V.; Sai Gopal, D. V. R. Green synthesis and spectral characterization of silver nanoparticles from Lakshmitulasi (Ocimum sanctum) leaf extract. Spectrochim. Acta, Part A 2013, 103, 156−159. (41) Yüce, A. O.; Telli, E.; Mert, B. D.; Kardaş, G.; Yazıcı, B. Experimental and quantum chemical studies on corrosion inhibitioneffect of 5,5 diphenyl 2-thiohydantoin on mild steel in HCl solution. J. Mol. Liq. 2016, 218, 384−392. (42) Vashisht, H.; Kumar, S.; Bahadur, I.; Singh, G. Evaluation of (2hydroxyethyl) triphenylphosphonium bromide as corrosion inhibitor for mild steel in sulphuric acid. Int. J.Electrochem. Sci. 2013, 8, 684− 699. (43) Yadav, M.; Gope, L.; Kumari, N.; Yadav, P. Corrosion inhibition performance of pyranopyrazole derivatives for mildsteel in HCl solution: Gravimetric, electrochemical and DFT studies. J. Mol. Liq. 2016, 216, 78−86. (44) Mulder, W. H.; Sluyters, J. H. An explanation of depressed semicircular arcs in impedanceplots for irreversible electrode reactions. Electrochim. Acta 1998, 33, 303−310. (45) Hermas, A. A.; Morad, M. S.; Wahdan, M. H. Effect of PgTPhPBr on the electrochemicaland corrosion behaviour of 304 stainless steel in H2SO4solution. J. Appl. Electrochem. 2004, 34, 95− 102. (46) Erbil, M. The determination of corrosion rates by analysis of AC impedance diagrams. Chim. Acta Turc. 1988, 1, 59−70. (47) Obot, I. B.; Madhankumar, A. Synergistic effect of iodide ion addition on the inhibition of mild steel corrosion in 1 M HCl by 3amino-2 methylbenzylalcohol. Mater. Chem. Phys. 2016, 177, 266− 275. (48) Zheng, X.; Zhang, S.; Li, W.; Gong, M.; Yin, L. Experimental and theoretical studies of two imidazolium-based ionic liquids as 820


Silver ... - ACS Publications

Recommend Documents