Silver Nanoparticles Composite

Subscriber access provided by University of Otago Library

Article

Performance Evaluation of Chitosan/silver Nanoparticles Composite on St37 Steel Corrosion in 15% HCl Solution Moses M Solomon, Husnu Gerengi, Tugce Kaya, and Saviour A. Umoren ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02141 • Publication Date (Web): 07 Nov 2016 Downloaded from http://pubs.acs.org on November 17, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Performance Evaluation of Chitosan/silver Nanoparticles Composite on St37 Steel Corrosion in 15% HCl Solution Moses M. Solomona*, Husnu Gerengia, Tugce Kayaa, and Saviour A. Umorenb a

Corrosion Research Laboratory, Department of Mechanical Engineering, Faculty of Engineering, Duzce University, 81620, Duzce, Turkey b

Centre of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran31261, Saudi Arabia *

[email protected]

Abstract Chitosan/silver nanoparticles(AgNPs/chitosan) composite has been prepared in-situ using natural honey as the reducing and capping agent and its effectiveness as inhibitor for St37 steel in 15% HCl solution assessed using Electrochemical Impedance Spectroscopy (EIS), Potentiodynamic Polarization (PDP), Dynamic Electrochemical Impedance Spectroscopy (DEIS), and Weight Loss (WL) methodscomplemented with surface morphological examination with the aid of Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscope (AFM), and Scanning Electron Microscope (SEM). AgNPs/chitosan was characterized using Fourier Transformed Infrared (FTIR), EDS, and SEM. Results obtained show that AgNPs/chitosan is effective cathodic type inhibitor particularly at higher temperature andprotects the metal surface by formation of protective film. SEM, AFM and EDS confirm the formation of adsorbed film. The adsorption followed Temkin adsorption isotherm as such, the thermodynamic and kinetic parameters governing the adsorption was calculated and discussed. Values of free energy of adsorption suggest that 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

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1.

Page 2 of 44

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 sulphuric acids in the concentration range of 15-28% are deploy in large volume for industrial processes like acid pickling, oil-well acidizing, industrial cleaning, acid descaling, etc. This practice, though intended for high system efficiency, encourage corrosion of metals. It is customary that corrosion inhibitors be added to acid solutions before used for any industrial process. Before now, inorganic compounds like chromates, nitrites, nitrates, phosphates, etc. were utilized as metals corrosion inhibitor because they could oxidize metal surface to form passive films capable of protecting the surface against corrosion2-4. They were however banned because of theirpoisonous nature to both human and the natural environment 5-6. Organic compounds with N, S, O, P, and/ or π-electrons in their molecules replaced inorganic compounds as metal inhibitor leading the inhibitor’s 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 rigorous approach. There have been calls from different quarters drawing the attention of corrosion scientists to why metals corrosion inhibitors should be developed from natural source8, 9. Beside availability, natural substances are harmless to the natural ecosystem and are cheap. In a response, corrosion scientists have tested plant parts extracts polymers

16-22

10-15

and natural

for anticorrosive effect. It is however found that most natural polymers possess

moderate inhibiting ability and are unstable at elevated temperature Umoren and Solomon

9, 23

. As rightly put it by

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 inhibitor. The most recent is the infusion of inorganic substance in minute size into 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 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: ex-situ and in-


Page 3 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


situmethods. The ex-situ technique entails the dispersion of pre-made particles directly into 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 longterm stability against aggregation30. The in-situ method, in 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 onin-situ synthesis of silvernanoparticles/polymer composite in sulphuric acid solution26-29 but none in HCl solution. The reason is not far fetch. Silver ions precipitate chloride ions in solution forming silver chloride salt and this makes it impossible for silver nanoparticles to form. In our effort to overcome this challenge while still upholding the merit of 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 Microscope (SEM) while chemical and electrochemical (Electrochemical impedance Spectroscopy, Potentiodynamic Polarization, and Dynamic Electrochemical Impedance Spectroscopy) methods complemented with surface morphological assessment (Scanning Electron Microscope, Atomic Force Microscopeand EDS) were used for corrosion studies. 2.

Experimental Section

2.1

Chemicals and Materials

Chitosan with properties listed in Table 1 was purchased from Sigma-Aldrich and natural honey (mad honey) was gotten 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 St37-2 steel sheet with chemical composition of (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 series of emery paper (#800 - #2000), washed under 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

running water, degreased with acetone, and dried with warm air

32

Page 4 of 44

. They were preserved in a

dessicator prior to use. 2.2

Solutions

The corrosive medium was 15% HCl solution prepared by dilution of 37% concentrated HCl acid. The concentration of the prepared AgNPs/chitosan studied was 50, 100, 500, 750, and 1000 ppm. 2.3

Synthesis of AgNPs/chitosan Composite

Silver nanoparticles were generated in-situfollowing 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 chitosan was dissolved in 10 ml 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 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 colour solution was obtained and this solution was allowed to stand at ordinary temperature for four days (96 h). The colour change from yellow to dark signaled complete conversion of Ag+ to Ag027, 28 and this was verified chemically by adding NaCl solution to small portion of the dark colour solution. The non-formation of white precipitate suggested absence of Ag+. At this point, the AgNPs/chitosan composite solution was used to prepare 15% HCl solution by diluting concentrated HCl acid. Again, formation of white precipitate was not observed. Other concentrations of AgNPs/chitosan were obtained by dilution of 1000 ppm AgNPs/chitosan with 15% HCl solution. 2.4

Characterization of AgNPs/chitosan

2.4.1 FTIR FTIR spectra for AgNPs/chitosan in water and in HCl solution was recorded and compared with the spectrum for chitosan on Agilent Technologies Cary 630 FTIR spectrometer.AgNPs/chitosan samples were prepared by evaporating to dryness colloidal solutions of AgNPs/chitosan in a 4 ACS Paragon Plus Environment

Page 5 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


petridish at 40 oC.All FTIR spectra were scanned against a blank KBr pellet back-ground in the range of 4000 to 450 cm−1 at a resolution of 4 cm−1. 2.4.2 SEM-EDS Samples for SEM-EDS analysis were prepared by depositing a drop of the colloidal composite solutions on Al grid sample holder and drying at room temperature. Elemental composition of the sample was obtained with the aid of Energy Dispersive X-ray spectroscopy coupled to Scanning Electron Microscope J Quanta FEG 250 model (FEI, Holland). 2.5

Corrosion Studies

2.5.1 Electrochemical Experiments A Gamry instrument potentiostat/galvanostat/ZRA (Reference 600) embedded with 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 platinum plate whose main function was to provide the location of the second electron transfer reaction 25 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 condition for at least four times. For PDP experiments, the potential was swept from cathodic direction to anodic direction at a constant sweep rate of 1 mV/s at −250 to +250 mV interval with respect to corrosion potential ( ). The corrosion current density ( ) and were gotten by extrapolation of the Tafel lines 33. The percentage inhibition efficiency (IE) of various concentrations of AgNPs/chitosan was computed using the values in the absence and presence of AgNPs/chitosan according to the following equation 33:  I % IE = 1 − corr 0  I corr

  × 100 

(1)

is the corrosion current density in the absence of AgNPs/chitosan and , is the where

corrosion current density in the presence of AgNPs/chitosan. The EIS experiments were carried 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 44

out at frequency range of 10 mHz to 100 kHz using AC signal of 10 mV peak-to-peak. Values of charge transfer resistance ( ) and film resistance ( ) were obtained by the analysis of Nyquist plots using Echem 6.32 program. value was computed as = + 34and the inhibition efficiency of the various concentrations of AgNPs/chitosan calculated using Eq. 2 35:  R p − R1p   × 100 % IE =  1  R p  

(2)

where R1p and R p are the polarization resistances in the presenceand 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 of 4.5 kHz to 700 MHz. For the analysis of DEIS impedance, the same Echem 6.32 program used for EIS was utilized. IEof AgNPs/chitosan from this technique was calculated using Eq. 2.

2.5.2 Weight Loss (WL) Experiments WL experiments were performed by freely suspending the pre-cleaned 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 60oC in a thermostated bath. The metal specimens were removed after 10 hours, washed thoroughly in 20% NaOH solution containing 200 g/L of zinc dust26, 28, rinsed in running water, dried with warm air and then re-weighed. 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. 3 26 and 4 37respectively: CR ( mpy ) =

3.45 × 10 6 × W ρAT

 W % IE = 1 − e  W0

(3)

  × 100 

(4)


Page 7 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


where W is the average weight loss (g) , ρ is the density of metal specimen (g cm−3), A is the surface area of the St37 specimen (9 cm2) and T is the immersion duration (hour). and are the weight losses of the coupons in the absence and presence of inhibitor, respectivelyat the same temperature.

2.5.3 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 scanning electron microscope J Quanta FEG 250 model (FEI, Holland) and 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 Electron Dispersive X-ray Spectroscopy (EDS) detector.

3.

Results and Discussion

3.1

Characterization

3.1.1 FTIR Studies Comparative IR spectra of honey, chitosan, and synthesized AgNPs/chitosan composite are shown in Fig. 1. In the honey spectrum, peaks arising from the symmetric stretching of C-O-C and C-O-H bending vibration of protein can be seen at1025.0 cm-138. The peaks at 1653.5 and 1374.5 cm−1 are typical of carboxyl group stretching and deformation vibration of N-H in amide I & II of protein

25, 38

. Also, the strong and broad peak at 3331.8 cm-1 is unequivocally assigned

to hydrogen bonded vibration of O-H group while the weak peak at 2927.8 cm-1 is associated with C-H stretching

26

. The honey spectrum is seen to share some semblance with that of

chitosan. For instance, the C-H stretch, the carboxyl group stretch and deformation vibration NH of primary and secondary amide as well as the symmetric stretching of C-O-C and C-O-H bending vibration of protein noted in the honey spectrum also showed up in chitosan spectrum at 2868.0, 1653.5, 1374.5, and 1024.6 cm-1 respectively. However, in contrast, O-H stretch overlapped with N-H stretch is rather found in the chitosan spectrum at 3304.8 cm-125. There are striking differences in the spectrum of chitosan and that of 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 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 44

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 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 amino acid residue 38, 39. In a case where by stability is achieved through free amine groups, C=O stretching band appears at around 1700 cm−1 in IR spectrum

39

. Absence of such peak infers stability

through carboxylate ions of amino residue. In our case, the C=O peak is absent meaning the stabilization of AgNPs in chitosan matrix is through carboxylate ions of 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 as such no reaction takes place between silver and chloride ions in HCl solution.

3.2

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. Fig. 2 presents the elemental profile of synthesized AgNPs/chitosan in (a) H2O and (b) HCl solution. From previous reports 25-28, 40, elemental silver gives signal arising from Surface Plasmon Resonance (SPR) at approximately 3 keV in the EDS spectrum. In both Fig. 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 chitosan backbone are spherical in shape (Fig. 3). Component elements (C, O, N) of chitosan can as well be seen in the spectrum; an evidence that AgNPs were embedded in chitosan matrix. The S peak also seen in Fig. 2(a) may have arose due to the acetic acid which was used as solvent for chitosan while Al signal is as a result of Al grid.

3.2

Anticorrosion Studies

3.2.1 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 o

C. The results obtained are presented in (a) Nyquist (b) Bode modulus and (c) Phase angle

formats in Fig. 4. From Fig. 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 8 ACS Paragon Plus Environment

Page 9 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


solution devoid 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 on the larger size of the capacitive loops and the displacement of the Bode modulus impedance and Phase angle towards bigger value of log/Z/ (Fig. 4(b)) and larger angle (Fig. 4(c)) respectively in the composite inhibited systems compared to without. This means that the presence of the composite in the corrosive solution only slow down the rate of charge transfer process. This could be possible due to adsorption of composite molecules on the metal surface which block reaction sites

26

.The deviation of the Nyquist

diagrams from perfect semicircle is often referred to as frequency dispersion 26, 41, 43 and has been attributed to roughness and non-uniformity of working electrode

26, 43

, fracture structures

44

,

distribution of activity centres45, 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 Fig. 4 was used. It allows for the determination of solution resistance (Rs), charge transfer resistance ( ), and film resistance (Rf). The 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 semicircles41.The parameter is related in the impedance representation as 26: QCPE = Yo−1 ( jω )

−n

(5)

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

Yω n −1 sin( n(π / 2))

(6)

whereωis the angular frequency (ω = 2πfmax); fmax is the frequency at which the imaginary component of the impedance is maximum and n is the phase shift (−1 ≤ ≤ 1), when = 0, the CPE represents pureresistor, if = −1, the CPE stands for inductor, and if = +1, the 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 44

CPE represents 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 %η also listed in the table was calculated using Eq. 2.Inspection of the table reveals that Rs and Rp values of inhibited systems are bigger while Cdl value is smaller compared to those of the uninhibited system. Increase in AgNPs/chitosan concentration is seen to lead to increase in Rp value and decrease in Cdl value. This may be associated with inhibition of St37 steel corrosion in HCl solution by AgNPs/chitosan composite 26, 47. For instance, the Rp and Cdl values of the corrodent are 11.878 Ωcm2 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 Ωcm2 while the Cdl value decreased to 243.89 µFcm2and the corresponding %IE is 54.24%. By increasing the concentration to 1000 ppm, the Rp value increased to 77.551 Ωcm2, Cdldecreased to 80.19 µFcm-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 effect; larger area was covered on the metal surface. Further inspection of the table reveals that n values are close to unity implying that the interface behaves nearly capacitive 48.

3.2.2 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 instantaneous corrosion process in a non-stationary environment

36, 49, 50

. 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. Fig. 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 oC. 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 Fig. 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 uninhibited system reveals larger capacitive loop in the inhibited systems. It is interesting to note that tail of 10 ACS Paragon Plus Environment

Page 11 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


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 Re/Z/ value of 20 Ωcm2 whereas that of the 50, 500, and 1000 ppm AgNPs/chitosan inhibited solutions terminates at 40, 60, and 80 Ωcm2respectively. This, according to Gerengi et al.50 is indicative of corrosion inhibition.

The DEIS spectra were analyzed using the same equivalent circuit (Fig. 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 similar manner as those from EIS method (Table 2). That is, the Rs and Rp values of inhibitor containing solutions are bigger than those of without and Rp value increase with increasing inhibitor concentration. Again, the values of the n parameter for inhibited systems show a higher heterogeneous 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 gotten from EIS measurements.

3.2.3 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 Fig. 7. The polarization parameters derived from the PDP graphs are given in Table 4. The PDP graphs composed of two branches: the anodic and cathodic which under this experimental condition 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 corrosion potential remarkably towards cathodic direction. The most effect is observed for the higher concentrations of AgNPs/chitosan. This behavior is typical of 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 reactions site on the metal surface without changing the reaction mechanism

43

. This is also supported by the non-pattern demonstrated by βc value with

increasing composite concentration (Table 4).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 44

In the literature22, 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 or equal to + 85 mV. In the present investigation, the difference between the Ecorr value of 50, 100, 500, 750, and 1000 ppm AgNPs/chitosan inhibited acid solution and that of the corrodent is +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 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 of 86.88% obtained from this technique agrees with the ones from other electrochemical techniques.

3.2.4 Weight Loss Measurements The dissolution pattern of St37 steel in 15% HCl solution without and with AgNPs/chitosan composite was also studied by chemical technique. 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 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 oC 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 oC than at 25 oC. The higher values of weight loss and corrosion rate at 60 oC compared to values at 25 oC may be due to intensified molecular thermal motion

53

while that of ϴ and IE may be as a result of a shift in adsorption-

desorption equilibrium towards adsorption 9, 26. The higher values of ϴ and IE at 60 oC also point 12 ACS Paragon Plus Environment

Page 13 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


to 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 ppm AgNPs/chitosan offered 87.88% protection to the metal surface at 25 oC but 97.09 % at 60 oC. Further inspection of Table 5 reveals that weight loss and corrosion rate of the metal was 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 weight loss method at 25 oC is in perfect agreement with those from electrochemical methods (Table 2-4).

3.3

Mechanism of Inhibition by AgNPs/chitosan Composite

It has been reported

25, 33, 41, 43

that 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 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 can interact directly with the metal surface 25, 26. Our PDP results suggest that the protonated form of AgNPs/chitosan compete with hydrogen ions for electrons on the metal surface and decreased the rate of hydrogen evolution without changing the mechanism of the cathodic reactions. Authors

51, 54

have reported that such competitive adsorption is possible in HCl environment. After the release of hydrogen gas, cationic AgNPs/chitosan molecules may have returned to their neutral form

55

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 metal surface can be transferred from d-orbital of Fe to ! ∗ orbital of inhibitor molecules. The retro-donation favors adsorption of inhibitor molecules on metal surface and rise in temperature strengthens the bonds 24

. The variation of IE with temperature in Table 5 supports the proposed mechanism.

3.4 Adsorption Consideration



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 44

Insight into the mode of interaction between inhibitor molecules and metal surface can be gained through the use of adsorption isotherm. To further understand the mode of adsorption of AgNPs/chitosan on 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, Temkin, Frundlich, and Frumkin adsorption isotherms. Normally, isotherm with best fit to data is adjudge by the value of linear regression coefficient (R2)

9, 11, 13

.

For a perfect fit, R2= 1. In our case, the best fit was obtained for Temkin adsorption isotherm. 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 adsorption layer would decrease linearly rather than logarithmically with coverage

56, 57

. Temkin model is defined by the following

equation 26, 28: exp( −2 aθ ) = K ads C

(7)

where a is molecules interaction parameter, θ is the degree of surface coverage, #$% is the equilibrium constant of adsorption process, and C is the concentration of AgNPs/chitosan. The straight line graphs obtained by plotting θ values obtained from EIS and PDP methods at 25 oC against composite concentration is given in Fig. 8(a). Similar plot for values obtained from weight loss method at 25 and 60 oC respectively is presented in Fig. 8(b). The adsorption parameters derived from the graphs are listed in Table 6. The adsorption equilibrium constant#$% is related to the standard free energy of adsorption (∆'$% ) according to the

following equation 58: 0 ∆Gads = − RT ln(1 × 106 K ads )

(8)

where, 1 × 10) is the concentration of water molecules expressed in ppm, is the universal gas constant and * is the absolute temperature. Calculated values of ∆'$% 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 existence of repulsive force in the AgNPs/chitosan adsorbed layer 26. Interestingly, the repulsive force is suppressed at higher temperature and as 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 oC is -0.0529 and the corresponding#$% value is 2.7842 M-1. At 60 oC, the a value becomes more positive, i.e -0.0520 and the #$% value increased to 3.7801 M-1. The∆'$% value


Page 15 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


at 25 oC 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 value interpreted in the literature for mixed adsorption (i.e both physisorption and chemisorption) 41, 43, 59, 60 but the value at 60 oC clearly point to chemical adsorption mechanism61. This result supports the proposed mechanism in sub-section 3.3 for the adsorption of AgNPs/chitosan onto St37 steel surface.

3.5

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 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

1 1  C R2 = Ea  −  C R1 2.303 R  T 1 T 2 

(9)

  θ   θ   T T  Q ads = 2.303R log 2  − log 1  ×  1 2  KJ mol −1  1 − θ 1   T 2 − T 1   1−θ 2 

(10)

where where CR1 and CR2, θ1 and θ2are 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 Ea values of the inhibited systems are smaller than that of the uninhibited and decrease with increasing composite concentration. Similar result has been reported in the literature

64

and was

interpreted as indicative of chemical adsorption. The Qadsvalues are all positive which is characteristic of chemisorption mechanism 62.

3.6

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 protective film on the surface. Fig. 9 presents the SEM pictures and EDS spectra obtained for St37 steel in (a, b) abraded state, (c, d) after exposing to 15% HCl solution, and (e, f) after exposing 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 Fig. 9(a) is seriously damaged upon exposure to the acid solution (Fig. 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 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 44

Fig. 9(d) compared to that in Fig. 9(b). Cracks can be visibly seen on the surface in Fig. 9(c). This shows the level of severity of the damage incurred by the metal surface in 15% HCl solution. In Fig. 9(e), heaps of deposits are seen and the appearance of N and Ag peaks in Fig. 9(f) provide 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 Fig. 9(f) compared to that of Fig. 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 Fig. 10. The lines in Fig. 10(b & d) show the section of which average roughness was measured. As could be seen in Fig. 10 (a & b), the surface is very rough. The average roughness range between 185.891 – 219.973 nm. The metal surface is less damage in the acid solution containing AgNPs/chitosan (Fig. 10 (c &d) as the average roughness is reduced to between 121.481-131.129 nm. This again support the experimental results that AgNPs/chitosan protected the metal surface in the studied environment.

4.

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


Page 17 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5.

Acknowledgements

Moses M. Solomon is grateful to The Scientific and Technological Research Council of Turkey (TÜBITAK) for financial support under the TÜBITAK 2216 – Postdoctoral Research Fellowship (TUBITAK 21514107-115.02-56312) programme and Duzce Unıversity, Turkey for providing the facilities. The authors are thankful to Dr 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. Washington, DC: U.S. Government Printing Office 1995.

(6)

Toxicological profile for chromium, agency for toxic substance. US Public Health Service, Report no. ATSDR/TP-88/10, 1989.

(7)

www.grandviewresearch.com/industry-analysis/corrosion-inhibitors-market 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, 68, 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

(Accessed



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 44

solvent systems and 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 Chemica2012, 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. Res. 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. Comm.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. Ionics2014, 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)

Fekery, A. M.; Mohamed, R. R. Acetyl thiourea chitosan as an ecofriendly inhibitor for mild steel in sulphuric acid medium. Electrochim. Acta2010, 55, 1933-1939.

(20)

Bello, M.; Ochoa, N.; Balsamo, V.; Gonzalez, G. Modified cassava starches as corrosion inhibitors of carbon steel: an electrochemical and morphological approach. Carbohyd. 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. Corr. Sci.2012, 65, 223-30.


Page 19 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(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. Cellulose2010, 17, 635–648

(23)

Umoren, S.A.; Solomon, M. M. Recent Developments on the Use of Polymers as Corrosion Inhibitors -A Review.The 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. Macromolecules2016, 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 Interf. 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

(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. Carbohyd. Polym.2016, 150, 13–20



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 44

(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-2-ylimino)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 Hybrids2013, 4, 87-98

(39)

Philip, D. Honey mediated green synthesis of gold nanoparticles. Spectrochim. Acta2009, A 73, 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: Mol. Bio. Spec. 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 (2-hydroxyethyl) 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 semi-circular arcs in impedanceplots for irreversible electrode reactions. Electrochim. Acta2008, 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.


Page 21 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(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 3-amino-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 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 coppermanganese-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. I & EC Res.2016, DOI: 10.1021/acs.iecr.6b02414

(51)

Gerengi, H.; Ugras, H. I.; Solomon, M. M.; Umoren, S. A.; Kurtay, M.; Atar, N. Synergistic corrosion inhibition effect of 1-ethyl-1- methylpyrrolidinium 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. Carbohyd. Polym.2014, 112, 291–299.

(54)

Kowsari, E.; Payami, M.; Amini, R.; Ramezanzadeh, B.; Javanbakht, M. Taskspecific 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. USSR1940, 12, 327–356.

(57)

Aharoni, C.; Ungarish, M. Kinetics of activated chemisorption. Part 2. Theoretical models. J. Chem. Soc. Faraday Trans.1977, 73, 456–464.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 44

(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. Acta2009, 27(1), 13-22

(64)

Zheng, X.; Zhang, S.; Li, W.; Yin, L.; He, J.; Wu, J. Investigation of 1-butyl-3-methyl1H-benzimidazolium iodide as inhibitor for mild steel in sulfuric acid solution. Corros. Sci. 2014, 80, 383–392


Page 23 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


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

Synopsis: Silver nanoparticles were incorporated into chitosan matrix via green in-situ approach to enhance anticorrosive property.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 44

FIGURE CAPTION Figure 1:FTIR spectra for honey, chitosan, and silver nanoparticles/chitosan composite in water and HCl solution Figure 2: EDS spectrum of AgNPs in (a) water and (b) HCl solution obtained by treating 5 mL honey with 1000 ppm chitosan + 1 mM aqueous AgNO3 solution Figure 3:SEM picture of AgNPs in HCl solution containing the composite obtained by treating 5 mL honey with 1000 ppm chitosan + 1 mM aqueous AgNO3 solution 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 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 oC after 2 h of measurements Figure 7: Potentiodynamic polarization curves obtained for St37 steel in 15% HClsolution without and with different concentrations of AgNPs/chitosan at 25 oC Figure 8:Temkin plot of θ versus log C from (a) EIS and PDP data at 25 oC and (b) WL data at 25 and 60 oC. Figure 9:SEM images and EDS spectra for St37 steel in (a, b) 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 oC 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 oC

ACS Paragon Plus Environment

Page 25 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Table 1: Properties of chitosan used in the study Molecular weight Degree of deactylation

448. 869 g/mol 75.0%

Viscosity

20 – 300 cps

Solubility

1 wt % in 1% acetic acid at

. Also

soluble in dilute aqueous acids



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 26 of 44

Table 2: Electrochemical impedance parameters for St37 steel in 15% HCl in the absence and presence of different concentrations of AgNPs/chitosan at 25 oC. IE Concentration (ppm) 0 50 100 500 750 1000

(

)

(

(µF

)

) 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

Page 27 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


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 oC. IE Concentration (ppm) 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


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 28 of 44

Table 4: Potentiodynamic polarization parameters for St37 steel in 15% HCl in the absence and presence of different concentrations of AgNPs/chitosan at 25 oC. (mpy) %η

Concentration (ppm) (mV/Ag/Ag (µA cm-2)

(mV dec-1)

(mV dec-1)

Cl) 0

193.0

808.0

172.8

86.7

391.4

–

50

290.0

247.0

132.3

86.6

111.3

69.43

100

390.0

207.0

123.1

117.4

83.96

74.38

500

401.0

181.0

130.8

84.5

71.58

77.60

750

409.0

140.0

138.1

103.3

63.79

82.67

1000

417.0

106.0

154.0

104.1

57.49

86.88


Page 29 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


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 60oC from weight loss measurements Concentration

Weight loss (g)

Corrosion rate (mpy)

Surface coverage (ϴ)

%IE

(ppm)

25oC

60 oC

25oC

60 oC

25oC

60 oC

25oC

60 oC

0

0.3894

4.3122

1889.89

20928.55

-

-

-

-

50

0.1706

1.3730

827.98

6663.63

0.5619

0.6816

56.19

68.16

100

0.1385

1.0239

672.19

4969.33

0.6443

0.7626

64.43

76.26

500

0.0973

0.2798

472.23

1357.19

0.7501

0.9351

75.01

93.51

1000

0.0472

0.1253

229.08

608.12

0.8788

0.9709

87.88

97.09



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 30 of 44

Table 6:Adsorption parameters from Temkin isothermfor St37 steel in 15% HCl in the absence and presence of different concentrations of AgNPs/chitosan from different methods (M-1)

Method

Temperature (K)

EIS

298

0.0216

2.7315

36.719

PDP

298

0.0374

4.4916

37.951

WL

298

0.0529

2.7842

36.766

333

0.0520

3.7801

41.931


(kJ/mol)

Page 31 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


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 Concentration (ppm) 0 50 100 500 1000

(KJ/mol) 56.69 49.17 47.16 24.90 23.02

(KJ/mol) 12.077 13.507 35.986 36.983



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Page 32 of 44

Page 33 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1 Figure 1 128x98mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2a Figure 2a 112x85mm (96 x 96 DPI)


Page 34 of 44

Page 35 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2b Figure 2b 114x85mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 36 of 44

Page 37 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60





1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 38 of 44

Page 39 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60





1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 40 of 44

Page 41 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8a Figure 8a 128x77mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8b Figure 8b 128x77mm (96 x 96 DPI)


Page 42 of 44

Page 43 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60





1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 44 of 44

Silver Nanoparticles Composite

Recommend Documents