Startseite Naturwissenschaften Study of the corrosion-inhibiting activity of the green materials of the Posidonia oceanica leaves’ ethanolic extract based on PVP in corrosive media (1 M of HCl)
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Study of the corrosion-inhibiting activity of the green materials of the Posidonia oceanica leaves’ ethanolic extract based on PVP in corrosive media (1 M of HCl)

  • Ghalia A. Gaber EMAIL logo , Mohamed Mohamady Ghobashy , Mohamed Madani , Dalal Mohamed Alshangiti , Sheikha A. Alkhursani , Samera Ali Al-Gahtany und Norhan Nady
Veröffentlicht/Copyright: 13. September 2021
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Green Processing and Synthesis
Aus der Zeitschrift Green Processing and Synthesis Band 10 Heft 1

Abstract

Since the corrosion protection of mild steel samples in corrosive media (1 M of hydrochloric acid [HCl]) was cheap and successful, the ethanol extract of Posidonia oceanica leaves based on polyvinylpyrrolidone (P. oceanica/PVP) was analyzed using the weight reduction, the open circuit potential, and the potentiodynamic polarization methods. The obtained results explained that the productivity of hindrance increments had the greatest restraint efficiency of ∼81% at 1,000 ppm, as the concentration of the extract increased. Liable for adsorption as a thin layer on the surface of mild steel to protect it, the creation of kaolin-traced phenolic and polysaccharide compounds was confirmed by the Fourier transform infrared spectroscopy analysis. A scanning electron microscope was used to evaluate the inhibitive action of P. oceanica/PVP against steel in corrosive media and the change in surface morphology was considered. It is presumed that the ethanol removed from the Posidonia oceanica leaves can fill in as a compelling consumption inhibitor for gentle steel in HCL solution (1 M).

Keywords: polyvinylpyrrolidone; corrosion; Posidonia oceanica ; ethanolic extract

1 Introduction

Posidonia oceanica is an indigenous aquatic plant that forms vast meadows, prevents erosion, and hosts several marine creatures in the Mediterranean Sea. Extracts of P. oceanica containing antioxidant capacity have been mentioned [1]. Different studies have shown that natural plant-based parts containing different natural mixes have an inhibitive corrosion effect [2]. Plant extracts and natural species, inferred as an ecologically maintainable, sustainable, promptly accessible, and appropriate source of corrosion inhibitors, are essential for their application [3,4,5,6]. Amino acids, alkaloids, tannins, and pigments are portions of the constituents of plant products [7]. The amazing green coerosion inhibiting has been utilized. A new generation of corrosion inhibitive pigment based on zinc acetate-Cichorium intybus L. leaf extract (ZnA-CIL.L) has been synthesized. Results showed promising corrosion inhibition performance of the hybrid ZnA-CIL.L complex on the steel surface in saline solution [8,9]. Polyvinylpyrrolidone (PVP) is an ecofriendly hydrophilic polymer that is used in this work due to its features, such as its low cost, highly hydrophilic character, and amorphous form [10]. PVP is synthesized by radiation techniques [11,12,13]. It is a soluble polymer that can form free-standing, thin films (thickness from 50 to 200 µm) using the solution casting method and is easy to remove from the substrate [14]. The absence of PVP causes aggregates or irregular dispersion of P. oceanica. Wang and Wang proved that absence of PVP caused the aggregates of Pd nanosheets and PVP did not make any obvious difference in the morphology of nanosheets [15]. In this contact, PVP has a good, free-standing, thin film forming capability. Additionally, it is a candidate to be used as a film formation in corrosion inhibitor applications because it is cheap and eco-friendly, and is made as a transparent, thin film by a simple casting method.

The current work tests the inhibitive activity of the Posidonia oceanica leaves’ ethanolic extract based on PVP as a green erosion inhibitor in control of the steel consumption movement in corrosive media (1 M of HCl) using gravimetric techniques and electrochemical strategies.

2 Experimental methods

2.1 Materials

An ethanol-soluble polymer, PVP with an average molecular weight (M w) of 100 kDa (highly viscous), was purchased from Sigma-Aldrich Chemicals Co. Posidonia oceanica leaves were collected from the Mediterranean Sea in Alexandria city.

2.2 Preparation of the ethanolic extracts of Posidonia oceanica leaves based on PVP using the solid dispersion technique

Posidonia oceanica leaves were collected from Alexandria in Egypt in July 2019. They were rinsed three times with water (H2O) to remove gravel and sand before being dried in the drier oven at a temperature of 50°C. Then, they were put in a dry blender to give a fine powder of Posidonia oceanica leaves. Finally, the dried powder, along with 30–70% ethanol and isopropanol, refluxed at 75°C for 7 h was recovered three times. Next the appropriate weight of the Posidonia oceanica leaves’ ethanolic extracts and the PVP powder were dissolved in isopropanol in a ratio of 1:1 wt% to ensure that the ethanolic extracts of Posidonia oceanica leaves are well linked to the PVP matrix. The clear solution of the ethanolic extracts of Posidonia oceanica leaves and PVP was dried under vacuum. The obtained Posidonia oceanica extracts and the PVP powder were ready for corrosion experiments.

2.3 Corrosion experimental setup

The following chemicals were used to make the working electrode of mild steel rod: 0.316 wt% of C; 0.218 wt% of Si, 0.825 wt% of Mn, 0.0869 wt% of Cr, and balance Fe. The rod was inserted into a glass tube and secured with araldite, leaving a 1 cm2 circular geometric shape to be in touch with the testing solution. For weight-loss measurements, the rod was cut into several coupons; each one has a surface area of 0.785 cm2. The working anode was cleaned with coarseness emery paper preceding each trial and washed with (CH3)2CO. Lastly, it was washed with two-fold double-distilled H2O. While saturated calomel electrode SCE (Hg/Hg2Cl2-Sat. KCl) was attached as a reference electrode of normal 25 mL electrolytic cell size, the auxiliary electrode was a platinum layer. By analytically diluting 37% of HCl with double-distilled H2O, the corrosive media was prepared. This compound ranged in concentration from 100 to 1,000 ppm. To decide the corrosion behavior of the mild steel, chemical and various electrochemical techniques, such as weight reduction estimations, potentiodynamic polarization (PP), and open circuit potential (OCP), were utilized.

2.4 Gravimetric method (weight loss)

Weight reduction estimations were done in a beaker by adding 25 mL of acidic solution (1 M of HCl) with and without (free of) the various concentrations of P. oceanica/PVP. The coupons were removed after immersion, then rinsed with double-distilled water and (CH3)2CO. The experiment was repeated twice and the mean weight-loss value was recorded. The average rate of steel corrosion is calculated using Eqs. 1 and 2 as follows [16]:

(1) Δ W = W 1 − W 2

(2) C .R . ( mm/year ) = Δ W × K A × T × D

where K is a constant (8.76 × 104), T is time (h), A is section area (cm2), ∆W is loss of sample weight (g), and D is density (7.9 g/cm3). The surface coverage degree (θ) was calculated using Eq. 3:

(3) θ = W 0 − W i W 0

where W i and W 0 are estimates of mild steel coupon weight loss in constrained and uninhibited solutions, respectively. The efficiency of inhibition (IE%) was calculated according to Eq. 4:

(4) IE % = θ × 100

2.5 OCP estimations

By studying the alteration in corrosion potential (E corr) over time, the electrochemical characteristic of steel samples in corrosive media was intensified. In the steady-state condition of corrosion excrement, the OCP and the electrochemical calculations were performed. The variation in mild steel corrosion ability in 1 M of HCl was calculated versus SCE in the absence and existence of the diverse inhibitor concentrations of P. oceanica/PVP. Over a 30 min exposure interval, the time dependence of OCP was recorded for different experiment conditions. The same sample was used for PP experiments.

2.6 PP estimations

PP curves of steel sample in corrosive media were swept at the rate of 0.5 mV/s between –0.8 and +0.8 V. Prior to the corrosion experiment, the operating electrode was submerged in the test solution for 30 min to provide a quasi-stationary estimate of the OCP. Faraday’s law can be used to calculate the rate of corrosion (CR) (weight of steel consumption per year) using Eq. 5 [17]:

(5) CR (µm/year) = 3.3 I corr M / z d

where z is an ionic charge that equals 3 for iron (Fe), M is the atomic weight (at wt) of metal that equals 55.85 for Fe, d is the iron (Fe) density that equals 7.9 g/cm3, and I corr is the current density of corrosion which is expressed as µA/cm2.

The values of corrosion current and potential (I corr and E corr) were measured using the intersection of the linear cathodic and anodic branches of Tafel plots in the presence and absence of various amounts of Posidonia oceanica ethanolic extracts. Each experiment was carried out at least three times. Stern–Geary equation was used to resolve the polarization resistance (R p) values. Eq. 6 [18] is:

(6) R p = β a ⋅ β c 2.303 I corr ( β a + β c )

The surface inclusion degrees (θ) were calculated using potentiodynamic measurements by Eq. 7:

(7) θ = 1 − I corr / I corr °

where I corr ° and I corr are the densities of corrosion current in the absence and existence of P. oceanica/PVP, respectively. The inhibitive efficiency (IE%) was measured by Eq. 8:

(8) IE % = θ × 100

2.7 Surface characterization

Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) were used to examine the surface morphology of corrosive sample products on mild steel after 120 h of immersion in corrosive media of 1 M of HCl in the existence and absence of several concentrations of P. oceanica/PVP extracts.

2.8 Fourier transforms infrared (FTIR) spectroscopy

Fourier transform infrared spectrometer (FTIR) (Thermo Scientific-NICOLET iS10 USA) was used to acquire absorption spectra in the infrared band. This method is used to identify the primary functional groups of Posidonia oceanica/PVP. Samples were combined with KBr, crushed, and pressed with a specific press to produce a disc with a standard diameter.

2.9 Electrochemical impedance spectroscopy (EIS)

EIS measurements of mild steel were carried out in frequency range from 100 kHz to 100 mHz with amplitude of 10 mV peak-to-peak using ac signals at OCP. The inhibition efficiencies (IE%) and the surface coverage (θ) obtained from the impedance measurements are defined by the following Eq. 9:

(9) IE % = θ × 100 = [ 1 − ( R ct / R ct(inh) ) ] × 100

where R ct and R ct(inh) are the charge transfer resistances in the absence and presence of inhibitor, respectively.

The main parameters deduced from the analysis of Nyquist diagram are the resistance of charge transfer R ct (diameter of high frequency loop) and the capacitance of double layer C dl which is defined as Eq. 10:

(10) C dl = ( 2 Π R ct F max ) − 1

where F max is the maximum frequency at which the imaginary component (Zimag) of the impedance is maximum; since the electrochemical theory assumed that 1/R ct is directly proportional to the capacity of double layer.

3 Results and discussion

3.1 FTIR spectroscopy of P. oceanica/PVP

The FTIR of P. oceanica/PVP extracts in Figure 1 shows that the broad IR peak is located at 3,332 cm−1 and this may be attributed to the νst of the O−H and N−H groups interested in the compounds of phenolic and proteins, respectively. In addition, the νast and νst of C–O–C polysaccharide glycosidic linkage are located at 1,250 and 1,044 cm−1, respectively [19,20]. The two sharp IR peaks are centered at 2,915 and 2,849 cm−1 corresponding to the νast and νst of CH2 in fatty acids, respectively [21]. This indicates that the ethanolic extracts of Posidonia oceanica are lipid-rich materials. Furthermore, the FTIR peaks arising from the existence of C═O located at 1,727 and 1,634 cm−1 are corresponding to the ester and carboxylic group of lipids and PVP, respectively. The FTIR peak located at 1,170 cm−1 is attributed to the (C−O) group. This IR peak confirmed the existence of fatty acids long-chain (C22−C34), such as palmitic molecules, linoleic, palmitoleic, and oleic acids [22].

Figure 1 FTIR of ethanolic Posidonia oceanica based on PVP extracts.
Figure 1

FTIR of ethanolic Posidonia oceanica based on PVP extracts.

Figure 1 shows that the “fingerprint” region (i.e., 900–400 cm−1) was detected for the polysaccharide molecules, such as the intense FTIR peak located at 867 cm−1 which is considered to conform to the mannose and galactose pyranose rings [23]. Additionally, the peaks located at ∼718 and 648 cm−1 are assigned to the existence of xylans-type polysaccharides [24]. These peaks support the presence of carbohydrate compounds [25]. The two weak FTIR peaks centered at 3,740 and 3,696 cm−1 are attributed to the inner OH of kaolin [26,27]. The FTIR confirmed the existence of phenolic and polysaccharide compounds with traces of kaolin.

3.2 Gravimetric estimation (weight loss approach)

To examine the impact of the concentrates expansion of ethanolic Posidonia oceanica based on PVP, various focuses on the erosion of steel in corrosive media of 1 M of HCl arrangement were tried and concentrated by weight reduction estimations at 20°C after a period of 120 h. Figure 2 outlines the weight reduction time bent for the erosion of mild steel in corrosive media in the absence and existence of the numerous contents of ethanolic extracts inhibitor of P. oceanica/PVP at 20°C. The current results indicated that the weight losses of steel samples in the existence of P. oceanica/PVP were lower than that of free (blank) samples in the corrosive media. It expanded and shifted directly over time for all focuses. The acquired linearity demonstrated the lack of insoluble surface film through erosion. First, the P. oceanica/PVP inhibitor was immobilized onto the metal sample surface, blocking the corrosion process in this way [28]. These observations led to the conclusion that the ethanolic extracts of P. oceanica/PVP are selected as a steel disintegration inhibitor in the corrosive solution. Table 1 outlines the corresponding inhibition effectiveness, the coverage of the surface, and the erosion rate percentage data measured using the 120 h weight reduction results. This tends to be observed from the fact that the expansion of extracts reduces the erosion rate and indicates obvious consumption restraint conducted against the erosion of steel in corrosive media. The inhibitory impact is incrementing through expanding the convergence of ethanolic extracts of P. oceanica based on PVP. The maximum IE% of 79% was obtained at 1,000 ppm for this inhibitor. The change in the value of IE% with the concentrations (Table 1) revealed that the ethanolic extracts were concentration-dependent inhibitors. It was postulated that the exceptionally low corrosion rates with the use of an inhibitor which is relative to the free solution were due to the influence on the metal surface of a thin and stable passive layer [29]. In groups C–O, O–H, and C═O and other aromatic molecules, the concentrates contain oxygen atoms which are rich in electrons and can fill in the metal surface along these lines as a good adsorption site that restricts the mild steel corrosion in corrosive media.

Figure 2 Weight loss-time dependence curve for the corrosion of steel in corrosive media of 1 M of HCl in the presence and absence of various concentrations of ethanolic extracts of P. oceanica/PVP at a temperature of 20°C.
Figure 2

Weight loss-time dependence curve for the corrosion of steel in corrosive media of 1 M of HCl in the presence and absence of various concentrations of ethanolic extracts of P. oceanica/PVP at a temperature of 20°C.

Table 1

Corrosion parameters such as CR, θ, and IE% of mild steel in corrosive media (1 M of HCl) in the presence and absence of various concentrations of ethanolic extract of P. oceanica/PVP obtained by weight-loss approach at a temperature of 20°C

Inhibitor concentration (ppm) Corrosion rate (CR) (mm/year) Surface coverage (θ) Inhibition efficiency (IE) (%)
Blank 210.440 — —
100 55.456 0.741 74
300 52.000 0.754 75
500 50.230 0.759 76
700 46.240 0.782 78
1,000 45.376 0.787 79

3.3 OCP estimations

The steel electrochemical activity in corrosive media was evaluated over time by measuring the alternation of the corrosion potential (E corr). Changes in OCP in the existence and absence of P. oceanica/PVP inhibitor in corrosive media of 1 M of HCl are presented in Figure 3. The potential accomplishes a consistent state at 30 min after the introduction. It has been observed that the OCP rapidly changes toward negative qualities without the inhibitor of P. oceanica/PVP. This displays the pre-immersion, the disintegration mechanism of air-framed oxide layer, and the attack on the surface of the metal. Compared with the free sample, a steady potential was easily achieved. For various concentrations, the steady-state potential of mild steel in corrosives media shifted further toward a positive value. This is due to the inhibitor adsorption of P. oceanica/PVP on the surface of the metal sample and this results in metal passivation [30]. Physical adsorption takes place among the positive (+ve) charge of the protonated P. oceanica/PVP inhibitor and the negative (−ve) charge of the steel surface (FeCl3) in corrosive media of HCl. As a result, E corr drifts to more +ve values in the steady-state. In any case, it is shown from Figure 3 that the positive move of E corr is too little for a sensible arrangement dependent on the results of the OCP estimations.

Figure 3 Corrosion potential–time dependence curve for the corrosion of mild steel in corrosives media (1 M of HCl) in the absence and presence of the various concentrations of P. oceanica/PVP at a temperature of 20°C.
Figure 3

Corrosion potential–time dependence curve for the corrosion of mild steel in corrosives media (1 M of HCl) in the absence and presence of the various concentrations of P. oceanica/PVP at a temperature of 20°C.

3.4 PP estimation

Figure 4 shows the PP curves of steel samples in the corrosive media in the absence and existence of various Posidonia oceanica ethanolic extracts dependent on the PVP inhibitor concentrations. Numerous corrosion parameters, such as corrosion potential (E corr), anodic and cathodic Tafel slopes (β a and β c), corrosion current density (I corr), polarization resistance (R p), and inhibition efficiency (IE%), are shown in Table 2. It can be very well shown that the inhibitor extract of P. oceanica/PVP has a small impact on the anodic Tafel consistent estimates and a more important impact on the cathodic Tafel steady estimates. This demonstrates that the inhibitor can alert the instrument of cathodic response and may not have an effect on the anodic disintegration phase [31]. Figure 4 shows that the hydrogen advancement is activation-controlled. In addition, it demonstrates that the decrease instrument of anodic is not influenced by the existence of the P. oceanica/PVP inhibitor. The change in the values of the cathodic Tafel slope (β c) is proposing that the response component of hydrogen decrease is not equivalent to the existence and absence of P. oceanica/PVP. The information in Table 2 clearly shows that the current density (I corr) values decrease, and the polarization values (R p) increase as predicted by the existence of different percentages of P. oceanica/PVP. The values of mild steel I corr in the inhibited solution are more modest than those of the free solution of the inhibitor. Due to the reverse relationship between R p and I corr through expanding the concentration of the P. oceanica/PVP inhibitor, it is commonly assumed that the adsorption of the P. oceanica/PVP inhibitor particles takes place on the metal surfaces by creating physical and charge-transfer barriers to protect the metal surfaces in a high degree. The inhibiting activity expanded by the concentration is at the highest estimation of 81% at 1 g/L (1,000 ppm). The E corr value moved toward the negative direction by incorporating the ethanolic extracts of Posidonia oceanica. In addition, the change in the negative corrosion potential suggests that the compounds examined by P. oceanica/PVP are considered cathodic inhibitor [32]. The abatement of the erosion current density and the expansion of the hindrance effectiveness might be credited to the physical adsorption of the investigated compounds of the P. oceanica/PVP inhibitors on the metal surface sample. The results of the tests based on polarization curves revealed that I corr decreases dramatically in the presence of the P. oceanica/PVP inhibitor at all studied concentrations. The Tafel polarization technique affirmed the results of the main weight reduction, giving some extra data. They are dictated by the extrapolation of Tafel lines to the corrosion potentials. Table 3 shows the examination of hindrance productivity estimated by weight reduction technique and PP. Additionally, it is observed from Table 3 that polarization studies have a close relationship with the estimations of inhibition efficiencies which were obtained by using the P. oceanica/PVP inhibitors through weight reduction estimations.

Figure 4 PP curve for mild steel in corrosive media of 1 M of HCl solutions in the absence and existence of the different concentrations of P. oceanica/PVP at a temperature of 20°C.
Figure 4

PP curve for mild steel in corrosive media of 1 M of HCl solutions in the absence and existence of the different concentrations of P. oceanica/PVP at a temperature of 20°C.

Table 2

The parameters of the corrosion experiment obtained from polarization curves for mild steel in 1 M of HCl solution in the absence and existence of the various P. oceanica/PVP concentrations at a temperature of 20°C

Inhibitor concentration (ppm) E corr (V) I corr (µA/cm2) β a (V/dec) β c (V/dec) R p (Ω·cm−2) CR (µm/year) θ IE (%)
1 M of HCl (blank) −0.345 7.925 1.20 0.66 21916.27 61.629 — —
100 −0.428 3.548 0.40 0.10 24475.0 27.592 0.5523 55
300 −0.463 2.512 1.20 0.30 41487.5 19.534 0.6830 68
500 −0.481 1.995 1.86 0.34 63031.7 15.516 0.7482 75
700 −0.475 1.585 1.20 0.30 65753.0 12.325 0.8000 80
1,000 −0.416 1.514 1.33 0.40 88266.9 11.770 0.8090 81
Table 3

Comparison of inhibition efficiency of P. oceanica/PVP measured by weight reduction method and PP

Inhibitor concentration (ppm) Inhibition efficiency (%)
Weight loss method PP
100 74 55
300 75 68
500 76 75
700 78 80
1,000 79 81

3.5 EIS

EIS is a non-destructive method that provides information about surface properties. The Nyquist and Bode plots of mild steel in 1 M of HCl with and without the various concentrations of P. oceanica/PVP at OCP are shown in Figure 5. The Nyquist plot in Figure 5a is a semicircle which shows that its diameter increases with the increase in the P. oceanica/PVP concentration. The high half-circle is credited to the double-layer capacitance [33]. It is obvious that the impedance spectra are not an ideal half-circle and are a discouraged capacitive circle compared with the surface heterogeneity which might be the consequence of the surface unpleasantness or adsorption of the inhibitor atoms [33,34,35]. The charge transfer resistance value increases with the increase in the P. oceanica/PVP concentration. Its value is a measure of electron transfer across the surface and is inversely proportional to the corrosion rate [36]. Figure 5b and c shows that the Bode plot shapes for the inhibited and uninhibited mild steel does not change. This indicates that the P. oceanica/PVP inhibitor does not change the corrosion mechanism. Figure 5d demonstrates the proposed inhibitor corrosion mechanism of P. oceanica/PVP. The EIS parameters are listed in Table 4. From R ct, the IE% increases with the increase in the P. oceanica/PVP concentration. The results obtained from EIS are consistent with the results observed by the polarization and weight-loss measurements. This indicates the ability of P. oceanica/PVP as a corrosion inhibitor for mild steel in 1 M of HCl solution.

Figure 5 EIS plots as (a) Nyquist plot, (b) Bode plot, (c) phase angle plot for mild steel in 1 M of HCl with and without the various concentrations of P. oceanica/PVP and (d) proposed mechanism of P. oceanica/PVP as corrosion inhibitor.
Figure 5

EIS plots as (a) Nyquist plot, (b) Bode plot, (c) phase angle plot for mild steel in 1 M of HCl with and without the various concentrations of P. oceanica/PVP and (d) proposed mechanism of P. oceanica/PVP as corrosion inhibitor.

Table 4

EIS parameters for mild steel in 1 M of HCl with and without the various concentrations of P. oceanica/PVP

Inhibitor concentration (ppm) R s (Ω·cm2) R ct (Ω·cm2) C dl (μF·cm2) Phase angle IE (%)
1 M of HCl (blank) 3.25 12.13 183.1 −10.4 —
100 1.210 16.51 152.3 −26.2 26.5
300 1.958 102.1 21.27 −20.4 88.1
500 2.460 241.8 17.83 −18.5 94.9
700 3.354 319.1 8.633 −20.8 96.2
1,000 4.250 333.6 1.331 −18 96.4

3.6 Adsorption isotherm

The inhibitor compounds’ adsorption depends on several factors: the charge on the surface of the metal and their composition, the electronic characteristics of the metal surface when the other ionic species and solvents are adsorbed, the electrochemical potential, and the corrosion reaction temperature at the interface of the metal solution [37]. As a result, the division of surface covered with inhibitor species (θ) will occur as a part of inhibitor fixation and solution temperature. The information on surface inclusion (θ) is extremely valuable in discussing the adsorption attributes. Adsorption isotherm could be assessed at harmony condition at the point when the covered part of the surface is resolved as a component of the fixation at a consistent temperature. The level of surface inclusion θ for various P. oceanica/PVP concentrations in acidic corrosive media has been assessed by weight reduction and potentiodynamic estimations. The adsorption isotherms and connected mechanisms were drawn. Several mathematical formulae of adsorption isotherms have been proposed to match the experimental data in this study, but the best fit was found through the equation of Langmuir adsorption isotherm, which is as follows [35]:

(11) C / θ = 1 / K ads + C

where K ads and C are the equilibrium constants of both the desorption and adsorption process and the various concentrations of P. oceanica/PVP, respectively. K ads values can be calculated by the intercepts of the straight line of the C/θ axis which is related to the standard free energy of adsorption ( Δ G ads 0 ), as calculated in the following Eqs. 12 and 13:

(12) K ads = 1 / 55.5 exp ( − ( Δ G ads / R T ) )

or

(13) Δ G ads 0 = − R T ln ( 55.5 K ads )

where R and T are the gas constant and the absolute temperature, respectively. The water concentration in the bulk solution has a value of 55.5. The values of free energy, Δ G ads 0 , were calculated.

Table 4 displays the calculated free energy values ( Δ G ads 0 ) of mild steel samples in corrosive media of 1 M of HCl in the existence and absence of the various concentrations of P. oceanica/PVP. The −ve values of free energy ( Δ G ads 0 ) indicate the continuous adsorption of the P. oceanica/PVP inhibitors on the surface of steel samples [35]. Generally, the estimations of free energy ( Δ G ads 0 ) up to −20 kJ·mol−1 are steady with electrostatic interactions (physical adsorption) among charged metal and atoms, while the estimations of free energy ( Δ G ads 0 ) around or higher than −40 kJ·mol−1 are related to a direct chemisorption result by moving or sharing electrons from the P. oceanica/PVP inhibitor particles to the metal surface to frame coordinate bonds. The adsorption modes, such as physisorption adsorption modes and chemisorption adsorption modes, could be ascribed to the fact that the investigated P. oceanica/PVP inhibitors contain several chemical compounds that may be adsorbed physically or chemically [38]. The plot of the C/θ virus contraction of the P. oceanica/PVP inhibitors for mild steel in corrosive media with and without the various concentrations of P. oceanica/PVP is a linear relationship, as shown in Figure 6. This indicates that the physical adsorption approach of P. oceanica/PVP to the metal surface sample is following Langmuir adsorption isotherm (Table 5).

Figure 6 Langmuir adsorption isotherm model for mild steel in corrosive media (1 M of HCl) in the existence and absence of P. oceanica/PVP at a temperature of 20°C through weight loss and potentiodynamic approach.
Figure 6

Langmuir adsorption isotherm model for mild steel in corrosive media (1 M of HCl) in the existence and absence of P. oceanica/PVP at a temperature of 20°C through weight loss and potentiodynamic approach.

Table 5

Parameters of Langmuir adsorption isotherm in corrosive media of 1 M of HCl for mild steel in the presence and absence of P. oceanica/PVP at a temperature of 20°C through weight loss and potentiodynamic approach

Investigated inhibitor Weight reduction method Potentiodynamic method
Slope K ads R 2 ∆G ads Slope K ads R 2 ∆G ads
P. oceanica/PVP 1.2575 56.863 0.9996 −19.627 1.1573 12.802 0.9989 −15.995

3.7 The effect of temperature on inhibition process

To detect the stability of the formed protective film, the corrosion rate of the investigated inhibitor was studied at different temperatures (20°C, 40°C, and 50°C) for 3 h. The effect of temperature on the corrosion rate of mild steel in 1 M of HCl solutions in the absence and presence of the best P. oceanica/PVP concentration (1,000 ppm) was obtained by the weight-loss method. The effect of temperatures on the inhibited steel surface is highly complex because many changes occur on the metal surface. As the temperature increases, the degree of the surface coverage decreases due to the inhibitors’ desorption from the steel surface. The surface becomes less protected and the inhibition, therefore, gradually looses its effectiveness.

The apparent activation energy value (E a) was calculated using the Arrhenius equation as given in Eq. 14:

(14) C .R . = A exp − E a / R T

where C.R. is the corrosion rate of the mild steel surface, A is the Arrhenius constant or the pre-exponential factor, R is the universal gas constant, and T is the absolute temperature.

Figure 7 shows that the linear regression plots between ln C.R. and 1/T give a slope of −E a/R. The calculated activation energy (E a) and regulation factor (R) for mild steel in 1 M of HCl solutions in the absence and presence of P. oceanica/PVP are displayed in Table 6. The values of E a may be explained by the modification of the corrosion process mechanism in the presence of inhibitor molecules. The activation energy of the inhibited metal is higher than the uninhibited one. This indicates that more energy barriers are required for the corrosion reaction. According to several reports, the activation energy E a due to chemical adsorption (>80 kJ·mol−1) is considerably larger than that due to physical adsorption (<80 kJ·mol−1).

Figure 7 A plot of ln C.R. versus 1/T for mild steel in 1 M of HCl solutions in the absence and presence of the best P. oceanica/PVP concentration (1,000 ppm).
Figure 7

A plot of ln C.R. versus 1/T for mild steel in 1 M of HCl solutions in the absence and presence of the best P. oceanica/PVP concentration (1,000 ppm).

Table 6

Thermodynamic parameters obtained by weight-loss method

Parameters R 2 E a (kJ/mol) ∆H ads (kJ/mol) ∆S ads (kJ/mol)
Blank (1 M of HCl) 0.9238 16.412 13.994 −146.960
1,000 ppm 0.9999 70.015 67.617 −26.182

The values of apparent enthalpy of activation ∆H ads and entropy of activation ∆S ads were obtained by the linearized transition state theory. As shown in Figure 8, the values of ∆H ads and ∆S ads listed in Table 6 were calculated using the slope and the intercept of the straight line of ln CR/T versus 1/T, respectively. The positive values of ∆H show that the P. oceanica/PVP adsorption on the steel surface is endothermic. This means that the dissolution of steel is difficult. However, the negative values of ∆S ads in the presence of the inhibitor imply that the activated complex in the rate-determining step is an association rather than a dissociation step. The increase in entropy in the presence of P. oceanica/PVP indicates that the increase in the disorder takes place in going from reactants to the film formed on the metal/solution interface.

Figure 8 A plot of ln C.R./T versus 1/T for mild steel in 1 M of HCl solutions in the absence and presence of the best P. oceanica/PVP concentration (1,000 ppm).
Figure 8

A plot of ln C.R./T versus 1/T for mild steel in 1 M of HCl solutions in the absence and presence of the best P. oceanica/PVP concentration (1,000 ppm).

3.8 Mechanism inhibition process

The physical adsorption of P. oceanica/PVP molecules on the surface of the metal steel sample increased with the increase in the P. oceanica/PVP concentration. It was suggested that the high lipid content of P. oceanica/PVP (Figure 1) arises from the existence of C═O at 1,727 and 1,634 cm−1 and the additional peaks correspond to carbonyl moiety in lipids molecules. The C−O groups also show an IR peak at 1,170 cm−1. These IR peaks confirmed the existence of long-chain (C22−C34) fatty acids, such as palmitoleic, palmitic, linoleic, and oleic acids, which correspond to the general concept of traditional corrosion inhibitors. The non-fortified oxygen electrons are protonated in acidic media. Due to the electrostatic interactions, the protonated P. oceanica/PVP particles are adsorbed physically. The erosion hindrance happens because of the adsorption of natural atoms at the interface of metal/solution. The adsorption process itself relies on the particle’s composition, temperature, and the electrochemical potential at the interface of metal/solution. The H2O molecules are adsorbed on the metal surface to form the interface of metal/solution. In addition, some adsorbed molecules of H2O may occur on the metal surface by the P. oceanica/PVP inhibitor.

The mechanism of steel sample corrosion in corrosive media of 1 M of HCl is shown in Eq. 15:

(15) Fe → Fe 2 + + 2 e −

There are different cathodic reactions that are the most common reactions in acidic media [10]:

(16) 2 H + + 2 e − → H 2

(17) O 2 + 4 H + + 4 e − → 2 H 2 O

When iron corrodes, the rate is usually controlled by the cathodic reaction.

(18) Fe + HCl → FeCl 2 + H 2

Fe is oxidized to Fe2+ by H+; the Cl− ion was not strong enough to act as an oxidizing agent so it plays no role in the reaction according to Le Chatelier’s principle. In the reduction reaction, the hydrogen gas evolution is as follows:

(19) 2 H + + 2 e − → H ads + 2 H 2

where H ads is the adsorbed hydrogen ions on the surface of the steel sample which acts as a catalyst to enhance the generation of the new bubble of hydrogen gas in the surface of the cathode [39,40,41]. The percent of P. oceanica/PVP can prevent hydrogen gas generation and stop the corrosion process.

3.9 Spectroscopic analysis of mild steel

Figure 9 represents the SEM micrographs of the steel samples in the corrosive media of 1 M of HCl after 120 h in the existence and absence of P. oceanica/PVP. In addition, this figure collects the macrostructure of the polished samples before cathodic corrosion, the corroded samples of blank samples, and at the concentrations of 100, 300, and 1,000 ppm in the investigated inhibitors. The scanning electron micrographs show the protective film formed on the surface of the steel sample by P. oceanica/PVP. Figure 9b shows that the specimen surface of the mild steel is extensively oxidized and rougher. Additionally, it strongly damaged the blank sample. On the other hand, Figure 6c–e shows that forming a protective layer on the surfaces of the steel samples results in a safer and clearer surface for the examined inhibitors. This protective sheet of P. oceanica/PVP could act as an isolate and barrier to the vulnerable surface of the steel in corrosive environments. The extent of damage on the surface of the steel sample and the rate of steel sample corrosion is considerably lower in the existence of inhibitors, especially at high concentration of 1,000 ppm. This revealed that there was a good defensive film adsorbed on the metal surface that acted as a physical and charged barrier and which was responsible for the inhibition of erosion. The SEM micrographs show an adherence of the inhibitors on the metallic surfaces which are in acceptable concurrence with the results of the electrochemical estimation. While the metallic surfaces were coated with 1,000 ppm of PVP, they were strongly damaged. They also showed big voids on the steel surface (Figure 9f).

Figure 9 SEM micrographs of blank polished steel samples (a), after an immersion in corrosive media of 1 M of HCl in the absence of P. oceanica/PVP (b), after a soak in corrosive media of 1 M of HCl in the existence of 100 ppm of P. oceanica/PVP (c), after a soak in corrosive media of 1 M of HCl in the existence of 300 ppm of P. oceanica/PVP (d), after a soak in corrosive media of 1 M of HCl in the existence of 1,000 ppm of P. oceanica/PVP (e), and after a soak in corrosive media of 1 M of HCl in the existence of 1,000 ppm of PVP (f).
Figure 9

SEM micrographs of blank polished steel samples (a), after an immersion in corrosive media of 1 M of HCl in the absence of P. oceanica/PVP (b), after a soak in corrosive media of 1 M of HCl in the existence of 100 ppm of P. oceanica/PVP (c), after a soak in corrosive media of 1 M of HCl in the existence of 300 ppm of P. oceanica/PVP (d), after a soak in corrosive media of 1 M of HCl in the existence of 1,000 ppm of P. oceanica/PVP (e), and after a soak in corrosive media of 1 M of HCl in the existence of 1,000 ppm of PVP (f).

4 Conclusion

The accompanying ends might be drawn from the examination: ethanolic extract concentrates of P. oceanica/PVP in the hydrochloric corrosion have been discovered to be a solid inhibitor of mild steel erosion. The restraint effectiveness increments with an inhibitor focused on achieving an estimation of 81% at 1,000 ppm. Polarization measurements show that the ethanolic extracts of P. oceanica/PVP act as a cathodic inhibitor. The model of adsorption mechanism of P. oceanica/PVP on steel surface fitted the equation of Langmuir adsorption isotherm and was physisorption. The inhibitor efficiency determined by the electrochemical polarization and the gravimetric method is in good agreement.

  1. Funding information: Authors state no funding involved.

  2. Author contributions: Ghalia A. Gaber: writing – original draft, methodology, formal analysis; Mohamed Mohamady Ghobashy: writing – original draft, formal analysis, visualization; Mohamed Madani: methodology, writing – review and editing; Dalal Mohamed Alshangiti: methodology, formal analysis, writing; Sheikha A. Alkhursani: methodology, formal analysis, writing; Samera Ali Al-Gahtany: methodology, formal analysis, writing – review and editing; Norhan Nady: methodology, formal analysis, resources, supervision, writing – review and editing. All authors have read and agreed to the published version of the manuscript.

  3. Conflict of interest: Authors state no conflict of interest.

  4. Data availability statement: All data generated or analyzed during this study are included in this published article.

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Received: 2021-04-09
Revised: 2021-07-09
Accepted: 2021-07-28
Published Online: 2021-09-13

© 2021 Ghalia A. Gaber et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/gps-2021-0055
Schlagwörter für diesen Artikel
polyvinylpyrrolidone; corrosion; Posidonia oceanica; ethanolic extract
Creative Commons
BY 4.0

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  28. Silver nanoparticles elicited physiological, biochemical, and antioxidant modifications in rice plants to control Aspergillus flavus
  29. Mixed gel electrolytes: Synthesis, characterization, and gas release on PbSb electrode
  30. Supported on mesoporous silica nanospheres, molecularly imprinted polymer for selective adsorption of dichlorophen
  31. Synthesis of zeolite from fly ash and its adsorption of phosphorus in wastewater
  32. Development of a continuous PET depolymerization process as a basis for a back-to-monomer recycling method
  33. Green synthesis of ZnS nanoparticles and fabrication of ZnS–chitosan nanocomposites for the removal of Cr(vi) ion from wastewater
  34. Synthesis, surface modification, and characterization of Fe3O4@SiO2 core@shell nanostructure
  35. Antioxidant potential of bulk and nanoparticles of naringenin against cadmium-induced oxidative stress in Nile tilapia, Oreochromis niloticus
  36. Variability and improvement of optical and antimicrobial performances for CQDs/mesoporous SiO2/Ag NPs composites via in situ synthesis
  37. Green synthesis of silver nanoparticles: Characterization and its potential biomedical applications
  38. Green synthesis, characterization, and antimicrobial activity of silver nanoparticles prepared using Trigonella foenum-graecum L. leaves grown in Saudi Arabia
  39. Intensification process in thyme essential oil nanoemulsion preparation based on subcritical water as green solvent and six different emulsifiers
  40. Synthesis and biological activities of alcohol extract of black cumin seeds (Bunium persicum)-based gold nanoparticles and their catalytic applications
  41. Digera muricata (L.) Mart. mediated synthesis of antimicrobial and enzymatic inhibitory zinc oxide bionanoparticles
  42. Aqueous synthesis of Nb-modified SnO2 quantum dots for efficient photocatalytic degradation of polyethylene for in situ agricultural waste treatment
  43. Study on the effect of microwave roasting pretreatment on nickel extraction from nickel-containing residue using sulfuric acid
  44. Green nanotechnology synthesized silver nanoparticles: Characterization and testing its antibacterial activity
  45. Phyto-fabrication of selenium nanorods using extract of pomegranate rind wastes and their potentialities for inhibiting fish-borne pathogens
  46. Hydrophilic modification of PVDF membranes by in situ synthesis of nano-Ag with nano-ZrO2
  47. Paracrine study of adipose tissue-derived mesenchymal stem cells (ADMSCs) in a self-assembling nano-polypeptide hydrogel environment
  48. Study of the corrosion-inhibiting activity of the green materials of the Posidonia oceanica leaves’ ethanolic extract based on PVP in corrosive media (1 M of HCl)
  49. Callus-mediated biosynthesis of Ag and ZnO nanoparticles using aqueous callus extract of Cannabis sativa: Their cytotoxic potential and clinical potential against human pathogenic bacteria and fungi
  50. Ionic liquids as capping agents of silver nanoparticles. Part II: Antimicrobial and cytotoxic study
  51. CO2 hydrogenation to dimethyl ether over In2O3 catalysts supported on aluminosilicate halloysite nanotubes
  52. Corylus avellana leaf extract-mediated green synthesis of antifungal silver nanoparticles using microwave irradiation and assessment of their properties
  53. Novel design and combination strategy of minocycline and OECs-loaded CeO2 nanoparticles with SF for the treatment of spinal cord injury: In vitro and in vivo evaluations
  54. Fe3+ and Ce3+ modified nano-TiO2 for degradation of exhaust gas in tunnels
  55. Analysis of enzyme activity and microbial community structure changes in the anaerobic digestion process of cattle manure at sub-mesophilic temperatures
  56. Synthesis of greener silver nanoparticle-based chitosan nanocomposites and their potential antimicrobial activity against oral pathogens
  57. Baeyer–Villiger co-oxidation of cyclohexanone with Fe–Sn–O catalysts in an O2/benzaldehyde system
  58. Increased flexibility to improve the catalytic performance of carbon-based solid acid catalysts
  59. Study on titanium dioxide nanoparticles as MALDI MS matrix for the determination of lipids in the brain
  60. Green-synthesized silver nanoparticles with aqueous extract of green algae Chaetomorpha ligustica and its anticancer potential
  61. Curcumin-removed turmeric oleoresin nano-emulsion as a novel botanical fungicide to control anthracnose (Colletotrichum gloeosporioides) in litchi
  62. Antibacterial greener silver nanoparticles synthesized using Marsilea quadrifolia extract and their eco-friendly evaluation against Zika virus vector, Aedes aegypti
  63. Optimization for simultaneous removal of NH3-N and COD from coking wastewater via a three-dimensional electrode system with coal-based electrode materials by RSM method
  64. Effect of Cu doping on the optical property of green synthesised l-cystein-capped CdSe quantum dots
  65. Anticandidal potentiality of biosynthesized and decorated nanometals with fucoidan
  66. Biosynthesis of silver nanoparticles using leaves of Mentha pulegium, their characterization, and antifungal properties
  67. A study on the coordination of cyclohexanocucurbit[6]uril with copper, zinc, and magnesium ions
  68. Ultrasound-assisted l-cysteine whole-cell bioconversion by recombinant Escherichia coli with tryptophan synthase
  69. Green synthesis of silver nanoparticles using aqueous extract of Citrus sinensis peels and evaluation of their antibacterial efficacy
  70. Preparation and characterization of sodium alginate/acrylic acid composite hydrogels conjugated to silver nanoparticles as an antibiotic delivery system
  71. Synthesis of tert-amylbenzene for side-chain alkylation of cumene catalyzed by a solid superbase
  72. Punica granatum peel extracts mediated the green synthesis of gold nanoparticles and their detailed in vivo biological activities
  73. Simulation and improvement of the separation process of synthesizing vinyl acetate by acetylene gas-phase method
  74. Review Articles
  75. Carbon dots: Discovery, structure, fluorescent properties, and applications
  76. Potential applications of biogenic selenium nanoparticles in alleviating biotic and abiotic stresses in plants: A comprehensive insight on the mechanistic approach and future perspectives
  77. Review on functionalized magnetic nanoparticles for the pretreatment of organophosphorus pesticides
  78. Extraction and modification of hemicellulose from lignocellulosic biomass: A review
  79. Topical Issue: Recent advances in deep eutectic solvents: Fundamentals and applications (Guest Editors: Santiago Aparicio and Mert Atilhan)
  80. Delignification of unbleached pulp by ternary deep eutectic solvents
  81. Removal of thiophene from model oil by polyethylene glycol via forming deep eutectic solvents
  82. Valorization of birch bark using a low transition temperature mixture composed of choline chloride and lactic acid
  83. Topical Issue: Flow chemistry and microreaction technologies for circular processes (Guest Editor: Gianvito Vilé)
  84. Stille, Heck, and Sonogashira coupling and hydrogenation catalyzed by porous-silica-gel-supported palladium in batch and flow
  85. In-flow enantioselective homogeneous organic synthesis
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Heruntergeladen am 2.2.2026 von https://www.degruyterbrill.com/document/doi/10.1515/gps-2021-0055/html?lang=de
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