A Study of the Inhibition Capacity of a Novel Ilex guayusa Green Extract for Preventing Corrosion in Mild Steel Exposed to Different Conditions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

(1) In this manuscript, a novel green inhibitor was extracted from Guayusa leaf. But there is no results about the composition, structure and inhibition mechanism of this novel green inhibitor.

(2) In the abstract, discussion and conclusion, it’s said that the inhibition efficiency was depended on the pH value of corrosive solutions. But there is no results about the pH value of four corrosive solutions with different inhibitor additions.

(3) In the section of 3.3 Analysis of the effect of the environment in the corrosion resistance, the inhibition efficiency of this green inhibitor on mild steel in different corrosive solutions and different inhibitor addition was assessed by using ANOVA method. What’s the meaning of this section? For the suitable corrosive solution of this green inhibitor or the optimum addition in the corrosive solution?

Comments on the Quality of English Language

Good

Author Response

(1) a novel green inhibitor was extracted from Guayusa leaf in this manuscript. However, there are no results about this novel green inhibitor's composition, structure, and inhibition mechanism. 
Chemical characterization of the extract. The chemical characterization of the obtained extract was necessary to determine which are the main components to protect the metal against corrosion. In these senses, the chemical characteristics of the obtained extract were evaluated by using FT-IR measurements, in which it was used a spectrometer (type Vector 22, from Bruker). Moreover, it was evaluated what are the main components of the extract by using Wagner, Drage Dorff, and Mayer reactive to determine if the extract content alkaloids (the main anticorrosive component of the present inhibitor). Finally, it was evaluated if the inhibitor had polyphenols (another anticorrosive component) by using ferric chloride (FeCl3) reactive.
Corrosion Inhibition mechanism
To determine the inhibition mechanism of the prepared inhibitor it was evaluated to be linear polarization and interpreted by Tafel curves. In these senses, the voltage position allowed to determine if the protection is anodic or cationic. The potentiodynamic polarization measurements were carried out over a potential range of±200 mV vs. OCP with a scan rate of 0.5 mV s−1. The recorded measurements were plotted and analyzed as Tafel plots. These plots allowed the estimation of the corrosion kinetic parameters such as corrosion potential (Ecorr), corrosion current density (icorr), anodic (ba), and cathodic (bc) Tafel slopes (Hidalgo Viteri, J., Cotolan, N., Lupan, A. et al. A poly (methyl methacrylate)–ibuprofen composite film as anticorrosive coating of Ti–6Al–4 V surface. J Solid State Electrochem 28, 479–494 (2024). https://doi.org/10.1007/s10008-023-05681-w)

(2) In the abstract, discussion and conclusion, it’s said that the inhibition efficiency was depended on the pH value of corrosive solutions. But there are no results about the pH value of four corrosive solutions with different inhibitor additions. 

Section 2.6.
Additionally, to study the behavior of the inhibitor in greater depth, the influence of the corrosive environment (specifically, the pH) on the efficiency of the inhibitor was evaluated, as in the various studies available on the behavior of inhibitors, their efficiency has been quantified in a single corrosive medium (mainly saline and acidic), without evaluating a single inhibitor together in corrosive media of different oxidative capacities.
Table 1. pH values for the different corrosion mediums
Corrosion Medium    pH
5% NaCl
Without Inhibitor
5% NaCl    5,72
With Inhibitor
200ppm    4,63
400ppm    4,21
600ppm    3,92
800ppm    3,71
1000ppm    3,53
5% NaCl + Acetic Acid
Without Inhibitor
5% NaCl + Ác. acético    2,55
With Inhibitor
200ppm    2,59
400ppm    2,62
600ppm    2,63
800ppm    2,64
1000ppm    2,66
1% HNO3
Without Inhibitor
1% HNO3    0,54
With Inhibitor
200ppm    0,61
400ppm    0,61
600ppm    0,78
800ppm    0,79
1000ppm    0,81
10% HNO3
Without Inhibitor
10% HNO3    0,044
With Inhibitor
200ppm    0,018
400ppm    0,072
600ppm    0,080
800ppm    0,108
1000ppm    0,176

(3) In the section of 3.3 Analysis of the effect of the environment in corrosion resistance, the inhibition efficiency of this green inhibitor on mild steel in different corrosive solutions and different inhibitor addition was assessed by using ANOVA method. What’s the meaning of this section? For the suitable corrosive solution of this green inhibitor or the optimum addition in the corrosive solution? 

The measurements were taken in triplicate for each trial, to improve the statistical treatment of the data. The results obtained allowed for the determination of the variation in inhibitor efficiency with respect to the pH of the corrosive medium, for which the ANOVA test was applied to the efficiency results in each treatment, enabling the identification of statistical differences between the data groups and the generation of statistically supported conclusions. The statistical tests allowed us to conclude that the inhibitor does not behave the same way in different corrosive environments, as significant statistical differences were recorded between the means of the evaluated concentrations with respect to the Tukey comparator value. (16,27). The inhibitor shows the best performance in purely saline media (5% NaCl) with an average percentage of 64.95% across all concentrations, while the efficiency of the inhibitor decreases as the pH of the corrosive medium decreases, having an average percentage of 12.97% across all concentrations in the most strongly acidic environment (10% HNO3).

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript concerns the use of Ilex Guayusa extract as a corrosion inhibitor.

The topic is interesting, especially due to their application potential.

 

1. The introduction is well prepared and provides a sufficient introduction to the discussed topics.

2. Materials and Methods:

There is no short description of Ilex guayusa. Why was this particular plant chosen? What compounds extracted from it interest us (as corrosion inhibitors)? Have the extracts been checked for their content of active compounds?

There is no brief description of ASTM A36 steel, its chemical composition.

I understand that the steel samples were first immersed in corrosive solutions, then in corrosive solutions with added inhibitors. Why is that? Why weren't fresh steel samples used?

3. Results, I propose combining chapters 3 and 4. When presenting the results, the Authors already partially comment on them. Additionally, chapter 4 is relatively short.

Figure 3; please correct the descriptions under the chart.

4. Discussion.

The authors write about the influence of the pH of the environment, it was not measured anywhere. We only have the saline and acid environment (it is known that they differ in pH). In order to analyze the influence of pH, it would be necessary to conduct tests in different concentrations of corrosive agents and correlate the obtained results with the pH values..

Why was nitric acid chosen for testing? Why not hydrochloric and/or sulfuric acid?

What is the point of discussing the literature in detail on the stability of various plant extracts in aggressive environments? Since no such studies were conducted in this case.

 

The conclusions regarding the study of the pH influence are too far-fetched, there are no pH measurements, tests in different concentrations of corrosive agents. Only the corrosion inhibition properties in saline and acid environments can be compared.

The manuscript should be rewritten or supplemented with additional research..

 

Of the minor errors, in tables, numerical values ​​are given with commas instead of dots. Please verify and correct.

 

Author Response

Second reviewer There is no short description of Ilex guayusa. Why were this particular plant chosen? What compounds extracted from it interest us (as corrosion inhibitors)? Have the extracts been checked for their content of active compounds?  Moreover, the plant Ilex guayusa (Loes) was selected for this study due to its richness in bioactive compounds and its origin in the Ecuadorian Amazon region, where it holds significant cultural and medicinal relevance. In particular, the focus has been on flavonoids, as these, along with other compounds such as tannins, polyphenols, phenolic acids, and glycosides, have demonstrated a high potential as corrosion inhibitors (Sharma, Solanki and Sharma, 2024). The effectiveness of the active compounds in guayusa extracts has been proven in previous pharmaceutical studies. For example, Armijos et al. (2021) highlight in their research on Ecuadorian medicinal plants that guayusa leaves contain polyphenols and alkaloids, phytochemical compounds capable of inhibiting corrosion on metal surfaces, as evidenced in recent studies of (C.N. Njoku et al., 2024).  Also, in the section Chemical characterization of the extract it is evaluated the principal active compounds of the Guayusa extract. The chemical characterization of the obtained extract was necessary to determine which are the main components to protect the metal against the corrosion. In these senses, the chemical characteristics of the obtained extract were evaluated by using FT-IR measurements, in which it was used a spectrometer (type Vector 22, from Bruker). Moreover, it was evaluated what are the main components of the extract by using Wagner, Drage Dorff, and Mayer reactive to determinate if the extract content alkaloids (the main anticorrosive component of the present inhibitor). Finally, it was evaluated if the inhibitor had polyphenols (another anticorrosive component) by using ferric chloride (FeCl3) reactive. The chemical groups were characterized by FT-IR measurements of the extract as indicated in figure 3. The spectrum shows the presence of alkaloids in the green extract. As it is indicated in figure, the O-H stretching of alcohol, phenol, and carbohydrate and the N-H stretching of amine are responsible for the 3282.25 cm−1 bandwidth. A band at 2923 cm−1 depicts alkane C-H stretching, whereas a band at 1550 cm−1 symbolizes C=C stretching and C=N stretching, as well as imine or oxime, amide, or δ-lactum C=O stretching and amine N-H bending, which are the principal functional groups of the alkaloids [https://doi.org/10.1016/j.arabjc.2021.103423]. Moreover, aromatic C=C bending and the N-H bending of amine are denoted by a sharp band at 1550 cm−1. Likewise, the absorption band at 1450 cm−1 is due to carboxylic acid O-H bending and the strong peak at 1336 cm−1 is owed to alcohol, phenol and gem dimethyl, or aldehyde C-H bending. A band at 1238 cm−1 is attributed to aromatic amine C-N stretching, which is corroborated by a strong peak at 1029 cm−1. The absorption band at 1164 cm−1 is caused by the C-O stretching of aromatic ether and the 3rd alcohols, ester and C-N stretching of amine, whereas the band at 1164 cm−1 is caused by the C-O stretching of secondary alcohols, ether, and the C-N stretching of amine. Because of the alkene’s C=C bending, there is another band at 860 cm−1 [https://doi.org/10.3390/electrochem3020013, https://doi.org/10.3390/electrochem3030029]     Figure 3. FT-IR analysis of the Guayusa Soxhlet extract.   Also, it was analysis the alkaloids content of the green extract (as it is indicated at Table 3). The results for all the determination were positive which confirms the presences of the alkaloids in the extract, which is a clear response of the quality of the extraction and the potential uses of the extract. This is in accordance with the author [https://doi.org:10.3126/jncs.v40i0.27274], who indicates that the corrosion inhibition efficacy of such phytochemicals is largely influenced by the presence of such heteroatoms and follows a general trend of O < N < S < P, and due to the high presences of =O groups in the prepared extract as it is indicated at the FT-IR analysis, the Guayusa extract is going to serve as a corrosion inhibitor as it is indicated in the following sections.   Table 3. Alkaloids content analysis of the Guayusa Ile green inhibitor extract. Reactive Composition Use Results Wagner Iodide (I2) and Potassium Iodide (KI) Detection of Alkaloids + Dragendorff Bismuth (Bi) and Chloride acid (HCl) Detection of Alkaloids + Mayer Chloride acid (HCl) and cupper chloride (CuCl2) Detection of Alkaloids +     (2) There is no brief description of ASTM A36 steel, its chemical composition.  Also, ASTM A36 steel, also known as black iron. It is a material that is not heat-treated be-cause it is part of the structure, with an alloy composed mainly of iron (98%), with a car-bon content of less than 1%, and with traces of minerals such as manganese, which helps improve its strength, as well as phosphorus, sulfur, and copper, which contribute to enhancing its weldability and resistance to atmospheric corrosion. Presenting advantages such as: High resistance, Uniformity, Ductility, Durability, Toughness, and Fatigue resistance (Wang, 2023).   Table 1: Chemical Composition of the ASTM A36 mild steel  Element C Cu Fe Mn P S % 0,25 0,02 98 0,8-1,2 Max. 0,04 Max. 0,05   I understand that the steel samples were first immersed in corrosive solutions, then in corrosive solutions with added inhibitors. Why is that? Why weren't fresh steel samples used? As it is described in section 2.3 fresh metallic samples were immersed in the different corrosive medium. Therefore, each cleaned sample was weighed before and after immersion for the analysis.   3. Results, I propose combining chapters 3 and 4. When presenting the results, the Authors already partially comment on them. Additionally, chapter 4 is relatively short.   Now it is combined at the reviewer suggested.   4. The authors write about the influence of the pH of the environment, it was not measured anywhere. We only have saline and acid environment (it is known that they differ in pH). In order to analyze the influence of pH, it would be necessary to conduct tests in different concentrations of corrosive agents and correlate the obtained results with the pH values. Section 2.6, additionally, to study the behavior of the inhibitor in greater depth, the influence of the corrosive environment (specifically, the pH) on the efficiency of the inhibitor was evaluated, as in the various studies available on the behavior of inhibitors, their efficiency has been quantified in a single corrosive medium (mainly saline and acidic), without evaluating a single inhibitor together in corrosive media of different oxidative capacities, as it is indicated at the table 1.   Table 1. pH values for the different corrosion mediums Corrosion Medium pH 5% NaCl Without Inhibitor 5% NaCl 5.72 With Inhibitor 200ppm 4.63 400ppm 4.21 600ppm 3.92 800ppm 3.71 1000ppm 3.53 5% NaCl + Acetic Acid Without Inhibitor 5% NaCl + Acetic Acid 2.55 With Inhibitor 200ppm 2.59 400ppm 2.62 600ppm 2.63 800ppm 2.64 1000ppm 2.66 1% HNO3 Without Inhibitor 1% HNO3 0.54 With Inhibitor 200ppm 0.61 400ppm 0.61 600ppm 0.78 800ppm 0.79 1000ppm 0.81 10% HNO3 Without Inhibitor 10% HNO3 0.044 With Inhibitor 200ppm 0.018 400ppm 0.072 600ppm 0.080 800ppm 0.108 1000ppm 0.176     Why was nitric acid chosen for testing? Why not hydrochloric and/or sulfuric acid? The studies were carried out at Ecuador, where it is difficult to use chloric acid and sulfuric acid, because of they are used as precursor of the production of cocaine. Therefore, some authors such as (Polish Journal of Chemical Technology, 15, 1, 61 — 67, 10.2478/pjct-2013-0011), https://doi.org/10.1016/j.cscee.2024.100836, https://www.jmaterenvironsci.com/Document/vol5/vol5_N2/54-JMES-536-2014-Barouni.pdf, studies the corrosion inhibition of different extract in nitic acid, and they indicated that this medium is as similar as the other strong acids.   What is the point of discussing the literature in detail on the stability of various plant extracts in aggressive environments? Since no such studies were conducted in this case. It was studied in an acid aggressive environment that is why in the discussion it is compared with different research. Therefore, it was omitted to avoid these kinds of errors.   The conclusions regarding the study of the pH influence are too far-fetched, there are no pH measurements, tests in different concentrations of corrosive agents. Only the corrosion inhibition properties in saline and acid environments can be compared.   Section 2.6, additionally, to study the behavior of the inhibitor in greater depth, the influence of the corrosive environment (specifically, the pH) on the efficiency of the inhibitor was evaluated, as in the various studies available on the behavior of inhibitors, their efficiency has been quantified in a single corrosive medium (mainly saline and acidic), without evaluating a single inhibitor together in corrosive media of different oxidative capacities.   The manuscript should be rewritten or supplemented with additional research. Now the article is rewritten because of the addition of different analysis which were not added in the previous version of the paper.   Of the minor errors, in tables, numerical values are given with commas instead of dots. Please verify and correct.   Corrected

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Hidalgo et al. did a work about the inhibition capacity of a novel Ilex Guayusa green extract for preventing corrosion in mild steel exposed to different conditions. The synergistic inhibition efficiency can be up to 84.78% with the addition of a minimal quantity of inhibitor. Before accept, some content needs to be modified:

1. The abstract section is too long and lacks innovative data analysis.

2. Compared with other inhibitor such as carbon dots in Journal of Materials Research and Technology 28 (2024) 3865-3881; Journal of Materials Research and Technology 32 (2024) 2149-2159; Journal of Cleaner Production 264 (2020) 121682; Corrosion Sci 2019;161:108197, what are the advantages of your inhibitor? Please discuss in the Introduction section.

3. What method is used to calculate the corrosion protection efficiency?

4. The Tafel curve should be added.

5. Some sentences have grammar issues and need to be carefully revised.

6. The analysis of corrosion was not thorough enough, please refer to Tungsten. 2024;6(2):342-354. https://doi.org/10.1007/s42864-023-00228-y.

Comments on the Quality of English Language

revision

Author Response

1. The abstract section is too long and lacks innovative data analysis.  The abstract was rewritten to improve the quality of it and to reduce the size of it. Moreover, it was added that in conclusion, this study provides a detailed understanding of how the corrosive environment in-fluences the effectiveness of the guayusa inhibitor which is for the first time used as green inhibitor, allowing its viability and performance to be assessed under various conditions, to highlight the novelty of the research. 2. Compared with other inhibitors such as carbon dots in Journal of Materials Research and Technology 28 (2024) 3865-3881; Journal of Materials Research and Technology 32 (2024) 2149-2159; Journal of Cleaner Production 264 (2020) 121682; Corrosion Sci 2019;161:108197, what are the advantages of your inhibitor? Please discuss it in the Introduction section.   In this senses, some authors such as [https://doi.org/10.1016/j.jmrt.2023.12.250, https://doi.org/10.1016/j.jmrt.2024.08.048,https://doi.org/10.1016/j.jclepro.2020.121682] reported a corrosion protection efficiencies above 90%, when different green inhibitors such as carbon dots were used. In comparison with the present research, these methods are more sophisticated but difficult to produce under our laboratory conditions. So, it is necessary to obtain green inhibitors which can be obtained by simple methods available in Ecuador which can be comparable with the previous reports. 3. What method is used to calculate corrosion protection efficiency? It was calculated by the equation IE_p  (%)=(〖i^0〗_corr- i_corr)/〖i^0〗_corr ×100, which it is indicated at section 2.7. 4. The Tafel curve should be added. It is added to section 2.7 and discussed in section 3.4. Corrosion Inhibition mechanism. In a fast view the type of inhibition was anodic and in a saline environment the corrosion efficiency was equal to 88.15. 5. Some sentences have grammar issues and need to be carefully revised.  Now the typo is corrected all over the manuscript. 6. The analysis of corrosion was not thorough enough, please refer to Tungsten. 2024;6(2):342-354. https://doi.org/10.1007/s42864-023-00228-y.  The taffel curves are added to the manuscript and the discussion is elongated. Moreover, the references were introduced.   English typos and errors were checked and now the text looks better.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

accept

Comments on the Quality of English Language

accept