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Analysis of a Mixture of Banana Peel and Rice Straw Extracts for Inhibiting Corrosion of Carbon Steel in Hydrochloric Acid Solution

Appl. Sci. 2025, 15(9), 5026; https://doi.org/10.3390/app15095026

by Maral Dazdari¹, Azizollah Khormali^1,*

and Akram Taleghani²

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Appl. Sci. 2025, 15(9), 5026; https://doi.org/10.3390/app15095026

Submission received: 24 March 2025 / Revised: 29 April 2025 / Accepted: 29 April 2025 / Published: 30 April 2025

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

(1) In Figs.4, 5, 6, Nyquist diagram of EIS spectrum of carbon steel in HCl solution with and without the addition of BPE, RSE and their mixture was presented. It’s better that Bode diagram are also provided, and the EIS spectrum are analyzed by using electrochemical equivalent circuit.

(2) In Fig.7, the surface morphology of carbon steel after corrosion was observed. It’s better that the element composition of corroded surface or the corrosion products on steel surface are also determined.

(3) In the section of 3.4, it’s said that “In this study, different isotherms were used to evaluate the adsorption of the inhibitor. The results showed that the Langmuir model could better describe the adsorption of the used extracts as green corrosion inhibitors”. What’s about other adsorption isotherms apart from Langmuir model?

Author Response

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Comment 1: In Figs.4, 5, 6, Nyquist diagram of EIS spectrum of carbon steel in HCl solution with and without the addition of BPE, RSE and their mixture was presented. It’s better that Bode diagram are also provided, and the EIS spectrum are analyzed by using electrochemical equivalent circuit.

Response: Thank you for this comment. The Bode plot and equivalent circuit results were added in the revised manuscript:

The Bode plot of the EIS tests is shown in Figure 7. As depicted in this figure, the loop size in the presence of green corrosion inhibitors was larger than in their absence in the acidic environment. This indicates corrosion protection in the presence of the inhibitors used. This effect was enhanced by increasing the inhibitor concentration. These figures show that 750 ppm is the optimal value for banana peel and rice straw extracts. In addition, the best mixing ratio is 40:60 banana peel and rice straw. These results are completely consistent with the weight loss results.

Figure 7. Bode plots of EIS tests for steel specimens in HCl solution in the absence and presence of green corrosion inhibitors: banana peel extract (a), rice straw extract (b), mixture of extracts at different mixing ratios at 750 ppm (c), single and mixture of extracts at 750 ppm.

The electrochemical equivalent circuit was also used to analyze the impedance characteristics, as shown in Figure 8. The system used consists of R_s (HCl solution resistance), R_CT (charge transfer resistance) and CPE (constant phase element). This test was carried out in the absence (blank case) and in the presence of green corrosion inhibitors under static conditions. The results obtained from this analysis are presented in Table 1. It should be noted that the inhibition efficiency was determined using the following formula:

(6)

Where R_CT1 and R_CT0 are related to the bank case (o ppm) and the solution with the inhibitor (ohm.cm²). As shown in Table 1, the R_CT values increased with the increase of inhibitor concentration, and as a result, the inhibition efficiency increased. For the extracts, the optimum concentration of steel corrosion protection was 750 ppm. In addition, rice straw extract showed better results than banana peel extract. These results are consistent with those obtained in the weight loss tests. In addition, the best inhibition performance was obtained by mixing banana peel and rice straw in a ratio of 40:60. The inhibition efficiencies of banana peel, rice straw and their mixture (40:60) were 78.18, 95.19 and 96.34% at 750 ppm, respectively.

Figure 8. The equivalent circuit used for fitting data obtained in EIS.

Table 1. Charge transfer resistance and inhibition efficiency results for the fitted EIS data using the equivalent circuit.

Inhibition efficiency (%)	R_CT (ohm.cm²)	Concentration (ppm)	Inhibitor type
---	46.15	0	blank
30.13	66.05	250	banana peel
59.96	115.26	500
78.18	211.48	750
81.50	249.45	1000
50.34	92.94	250	rice straw
90.56	488.62	500
95.19	958.57	750
95.52	1029.47	1000
96.34	1259.48	750	40/60	banana peel/rice straw
94.67	865.07	750	50/50
93.41	700.18	750	60/40

=====================================================================

Comment 2: In Fig.7, the surface morphology of carbon steel after corrosion was observed. It’s better that the element composition of corroded surface or the corrosion products on steel surface are also determined.

Response: Thank you for this comment. The corrosion products of steel samples in the presence and absence of green corrosion inhibitors were analyzed by Raman spectroscopy. The results showed that the main corrosion products in the uninhibited surface and in the inhibited surface at low inhibitors concentrations were oxide and chlorides materials. The details of peaks in this spectroscopy and XPS analysis will be presented in our future work. In addition, the corrosion equations, which produce the corrosion products were added. The following statement was added in the revised manuscript.

The corrosion products of steel samples in the presence and absence of green corrosion inhibitors were analyzed by Raman spectroscopy. The results showed that the main corrosion products in the uninhibited surface and in the inhibited surface at low inhibitors concentrations were in the form of oxide and chlorides due to appearance of oxygen and chlorine peaks.

It should be noted that the corrosion process of steel samples in an HCl solution without an inhibitor or at low inhibitor concentrations occurs through anodic and cathodic reactions and leads to the formation of chloride products as follows:

Fe Fe²⁺ + 2e^-

2H⁺ + 2e^- H₂

Fe + 2HCl FeCl₂+ H₂

Other side reactions also occur due to the presence of dissolved oxygen (1 ppm) and produce oxide products as follows:

O₂+ 4H⁺+4e^- 2H₂O

2Fe+O₂+ 2H₂O 2Fe(OH)₂

2Fe(OH)₂+ 0.5O₂+ H₂O 2Fe(OH)₃

2Fe(OH)₃ Fe₂O₃+ 3H₂O

At a sufficient concentration of the inhibitor, the above reactions do not occur due to the prevention of contact of the metal with the acidic environment and the inhibition of the formation of electrons.

=====================================================================

Comment 3: In the section of 3.4, it’s said that “In this study, different isotherms were used to evaluate the adsorption of the inhibitor. The results showed that the Langmuir model could better describe the adsorption of the used extracts as green corrosion inhibitors”. What’s about other adsorption isotherms apart from Langmuir model?

Response: Thank you for this comment. As mentioned in section 2.5, the obtained data showed the best agreement with the Langmuir adsorption model. The adoption results for the were better than the results of Temkin and Freundlich models. This fining was added as follows in the revised manuscript:

In this study, Temkin, Freundlich and Langmuir models were used for adsorption analysis of inhibition data of banana peel, rice straw and their mixture at three immersion periods. The average value of coefficient of determination (R²) for the linear fitting of experimental data for Temkin, Freundlich and Langmuir was 0.832, 0.891, and 0.955, respectively. Thus, Langmuir model was selected for the adsorption analysis since it could better describe the adsorption of the used extracts as green corrosion inhibitors.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments for applsci-3575178

The manuscript investigated the inhibit effects of banana peel and rice straw extracts on the corrosion behavior of carbon steel in hydrochloric acid environments. The results showed that results showed that the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors. In general, this paper is well written. The results are interesting, but the manuscript in the current version cannot be accepted for publication. I recommend that this article be major revised. Some comments are as follows:

About the electrochemistry test condition, what’s the dissolved oxygen in the test environment? The dissolved oxygen has a significant effect on the corrosion behavior of materials.
About the EIS data, Fig. 4 to Fig. 6, It is better to show the Bode plots in additional. The Bode plots can give us more information about the phase angle vs. the frequency, how many time exponents exist? The analysis of EIS data is not in-depth enough. It is best to use the equivalent circuit fitting method to conduct in-depth analysis of EIS data.
Were all the obtained EIS data validated using the Kramer-Kroning relationship in the whole measured frequency range? Some evidence related to Kramer-Kroning relationship should be added.
Fig. 8, the adsorption data, it is better to add some error bars to each data point.
The mechanism for the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors was not fully clarified. Some comprehensive discussions and additional evidence should be provided to support the statements.
The conclusion part, it should be much more concise and not just repeat the previous data.

Considering all the problems mentioned here above, some parts of this manuscript should be revised, and some additional data should be added to support the statement in the manuscript. This paper may not be considered to be accepted for publication in the current version. I recommend that the manuscript be major revised.

Comments on the Quality of English Language

The manuscript needs some significant general editing to modify sentence structures and correct grammatical errors.

Author Response

General comment: The manuscript investigated the inhibit effects of banana peel and rice straw extracts on the corrosion behavior of carbon steel in hydrochloric acid environments. The results showed that results showed that the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors. In general, this paper is well written. The results are interesting, but the manuscript in the current version cannot be accepted for publication. I recommend that this article be major revised. Some comments are as follows:

Response: Thank you for your thorough review of our manuscript. Your insightful comments have substantially improved the quality of our work. We have carefully considered each point raised and have systematically addressed them in the revised version, as detailed below.

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Comment 1: About the electrochemistry test condition, what’s the dissolved oxygen in the test environment? The dissolved oxygen has a significant effect on the corrosion behavior of materials.

Response: Thank you for this comment. The dissolved oxygen in the test environment was 1 ppm. The invention on the effect of dissolved oxygen is a purpose for our future work. This statement was added in the revised manuscript.

The value of dissolved oxygen in the test environment was 1 ppm.

Other side reactions also occur due to the presence of dissolved oxygen (1 ppm) and produce oxide products as follows:

O₂+ 4H⁺+4e^- 2H₂O

2Fe+O₂+ 2H₂O 2Fe(OH)₂

2Fe(OH)₂+ 0.5O₂+ H₂O 2Fe(OH)₃

2Fe(OH)₃ Fe₂O₃+ 3H₂O

=====================================================================

Comment 2: About the EIS data, Fig. 4 to Fig. 6, It is better to show the Bode plots in additional. The Bode plots can give us more information about the phase angle vs. the frequency, how many time exponents exist? The analysis of EIS data is not in-depth enough. It is best to use the equivalent circuit fitting method to conduct in-depth analysis of EIS data.

Response: Thank you for this comment. The Bode plot and equivalent circuit results were added in the revised manuscript:

(6)

Figure 8. The equivalent circuit used for fitting data obtained in EIS.

Table 1. Charge transfer resistance and inhibition efficiency results for the fitted EIS data using the equivalent circuit.

Inhibition efficiency (%)	R_CT (ohm.cm²)	Concentration (ppm)	Inhibitor type
---	46.15	0	blank
30.13	66.05	250	banana peel
59.96	115.26	500
78.18	211.48	750
81.50	249.45	1000
50.34	92.94	250	rice straw
90.56	488.62	500
95.19	958.57	750
95.52	1029.47	1000
96.34	1259.48	750	40/60	banana peel/rice straw
94.67	865.07	750	50/50
93.41	700.18	750	60/40

=====================================================================

Comment 3: Were all the obtained EIS data validated using the Kramer-Kroning relationship in the whole measured frequency range? Some evidence related to Kramer-Kroning relationship should be added.

Response: Thank you for this comment. Validation of EIS data by Kramers–Kronig transformation (KKT) is a topic for our future work. The following statement was added:

Validation of EIS data using Kramers-Kronig Transformation (KKT) can ensure the accuracy of testing and help in the correct selection of corrosion inhibitors. Validation of EIS data in KKT is a topic for our future work.

=====================================================================

Comment 4: Fig. 8, the adsorption data, it is better to add some error bars to each data point.

Response: Thank you for this comment. The error bars were added for the mentioned figure as follows:

=====================================================================

Comment 5: The mechanism for the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors was not fully clarified. Some comprehensive discussions and additional evidence should be provided to support the statements.

Response: Thank you for this comment. Various experiments conducted have shown better efficiency of the proposed mixture in inhibiting corrosion than individual inhibitors. This is due to the manifestation of a positive synergistic effect of inhibition due to the chemical compounds of banana peel and rice straw. Moreover, the higher efficiency of the mixture is explained by the formation of a denser and more uniform protective film on the metal surface than in the case of individual extraction. This behavior is associated with chemical adsorption of extracts on the metal surface through the formation of coordination bonds due to the presence of heteroatoms in the structure of inhibitors and physical adsorption through pi-electrons of banana peel and rice straw in the form of a mixture. The high strength of chemical adsorption of the mixture compared to the extract alone is explained by the co-adsorption of heteroatoms in both green inhibitors, which simultaneously participate in surface bonds. Moreover, heteroatoms and pi electrons can cause easier electron donation to the d-orbital of steel atoms (Fe), which leads to strong adsorption of extract molecules on the sample surface, thereby improving the corrosion protection efficiency. In addition, the formation of a compact and stable layer is associated with electrostatic interactions between protonated particles in the structure of green inhibitors and negatively charged particles on the metal surface.

The determination of chemical compounds (phytochemical analysis) of the used extracts will be carried out by gas chromatography-mass spectrometry (GC-MS) in the future work. Despite the discussed experiments, our future work will study additional tests on the studied extracts such as FTIR, GC-MS, EDS, AFM, polarization analysis and molecular dynamics simulation.

The above statements were added in the revised manuscript.

=====================================================================

Comment 6: The conclusion part, it should be much more concise and not just repeat the previous data.

Response: Thank you for this comment. The conclusion section was revised to be much more concise as follows:

In this work, banana peel extract, rice straw extract and their mixture were used as green corrosion inhibitors for carbon steel in the acidic environment. The following findings were drawn:

The inhibition efficiency of the mixture at a ratio of 40:60 (banana peel to rice straw) was higher than that of the individual extracts at all concentrations and immersion times based on weight loss method.
The inhibition efficiency was increased by increasing the concentration of the green corrosion inhibitors. Weight loss and electrochemical experiments showed that the optimum concentration of individual inhibitors and their mixture was 750 ppm, and the performance did not change significantly with further increase of the extract content in the HCl solution. Moreover, increasing the immersion time increased the corrosion inhibition efficiency, but this effect was weaker than the effect of inhibitor concentration.
For all immersion times and inhibitor concentrations, a positive synergistic effect was observed at a mixing ratio of banana peel and rice straw of 40:60. The highest synergistic value was 1.65, indicating an average increase of 65% in inhibition efficiency for the mixture compared to the extract alone.
The electrochemical tests confirmed the higher efficiency of the mixture (40:60 banana peel and rice straw) compared to 100% banana peel and 100% rice straw. When extracts were added to the corrosive environment, the resistance of the solution increased and it became more difficult for ions to reach the metal surface, which led to an increase in the effectiveness of corrosion inhibition.
Scanning electron microscope images clearly showed the formation of a stable film on the metal surface. The film formed in the presence of the banana peel and rice straw mixture was more stable and uniform than that in the presence of the individual extract.
The Langmuir isotherm model most accurately describes the adsorption characteristics of the used extracts and their mixture. Both physical and chemical adsorption occurred for the banana peel and rice straw extracts, as well as for their mixture.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

-the introduction needs to be shortened because the introduction went into too much detail about new related research

- the introduction also contains a lot of things that are generally known

- the preparation of the extracts is not written clearly enough

-no device is specified nor are recording conditions specified

- the results (IE values) for mass loss measurements are impossible to verify

-some very important things are not even mentioned (mechanism, corrosion equations, tabular measurement results) while the same things are repeated several times

-it is necessary to present the EIS results in a table and compare the experimental and theoretical values as well as the EEC used so that some conclusions can be proven

-experimental results are generally missing because the whole discussion of EIS results looks like an impedance book

-lacks surface analysis such as FTIR, AFM and SEM lacks EDS

-how did you convert ppm to M ie. with which molar mass did you divide

Comments for author File: Comments.pdf

Author Response

Comment 1: the introduction needs to be shortened because the introduction went into too much detail about new related research

Response: Thank you for this comment. The introduction section was shortened in the revised manuscript.

=====================================================================

Comment 2: the introduction also contains a lot of things that are generally known

Response: Thank you for this comment. The introduction section was shortened in the revised manuscript and well-known statements were removed. Please see the revised manuscript.

=====================================================================

Comment 3: the preparation of the extracts is not written clearly enough

Response: Thank you for this comment. The preparation of the used extracts was explained in more desilts in the revised manuscript as follows:

The collected samples of rice straw and banana peel were washed, dried, crushed to a smaller size using an industrial grinder and powdered separately. 200 g of powdered banana peel and rice straw which extracted separately by soaking in 70% ethanol (400 cc) for 72 h at 25 °C. Then, the solutions were stirred at 65°C on a hot plate for 2 hours. The extracted solutions were filtered under a vacuum pump. The alcohol was then removed from the mixture using a centrifuge, after which the extracts were obtained.

=====================================================================

Comment 4: no device is specified nor are recording conditions specified

Response: Thank you for this comment. The name of the used devices for EIS and SEM was added in the revised manuscript. And the conditions of each test (time, concentration, temperature, ....) were added and highlighted in the revised manuscript (material and method section). Please see the revised manuscript.

=====================================================================

Comment 5: the results (IE values) for mass loss measurements are impossible to verify

Response: Thank you for this comment. The table of mass loss measurements was added in the revised manuscript to verify and see the details of inhibition efficiency by this method. Please see the revised manuscript.

=====================================================================

Comment 6: some very important things are not even mentioned (mechanism, corrosion equations, tabular measurement results) while the same things are repeated several times

Response: Thank you for this comment. The inhibition mechanism, corrosion equations and table of inhibition efficiency determination were added in the revised manuscript. Please see the revised manuscript.

3.5. Inhibition mechanism

Various experiments conducted have shown better efficiency of the proposed mixture in inhibiting corrosion than individual inhibitors. This is due to the manifestation of a positive synergistic effect of inhibition due to the chemical compounds of banana peel and rice straw. Moreover, the higher efficiency of the mixture is explained by the formation of a denser and more uniform protective film on the metal surface than in the case of individual extraction. This behavior is associated with chemical adsorption of extracts on the metal surface through the formation of coordination bonds due to the presence of heteroatoms in the structure of inhibitors and physical adsorption through pi-electrons of banana peel and rice straw in the form of a mixture. The high strength of chemical adsorption of the mixture compared to the extract alone is explained by the co-adsorption of heteroatoms in both green inhibitors, which simultaneously participate in surface bonds. Moreover, heteroatoms and pi-electrons can cause easier electron donation to the d-orbital of steel atoms (Fe), which leads to strong adsorption of extract molecules on the sample surface, thereby improving the corrosion protection efficiency. In addition, the formation of a compact and stable layer is associated with electrostatic interactions between protonated particles in the structure of green inhibitors and negatively charged particles on the metal surface.

Fe Fe²⁺ + 2e^-

2H⁺ + 2e^- H₂

Fe + 2HCl FeCl₂+ H₂

Other side reactions also occur due to the presence of dissolved oxygen (1 ppm) and produce oxide products as follows:

O₂+ 4H⁺+4e^- 2H₂O

2Fe+O₂+ 2H₂O 2Fe(OH)₂

2Fe(OH)₂+ 0.5O₂+ H₂O 2Fe(OH)₃

2Fe(OH)₃ Fe₂O₃+ 3H₂O

Table 1. The detail of data obtained by weight loss method (mass reduction, corrosion rate and inhibition efficiency).

Time (h)	Inhibitor	Concentration (ppm)	Δm (g)	CR (mm.y^-1)	IE (%)
6	blank	0	0.024	18.718	-
	100% rice straw	250	0.014	10.685	42.917
		500	0.004	2.808	85.000
		750	0.003	2.574	86.250
		1000	0.003	2.340	87.500
	100% banana peel	250	0.019	14.506	22.500
		500	0.010	7.409	60.417
		750	0.006	4.913	73.750
		1000	0.006	4.835	74.167
	40/60 banana/straw	250	0.010	7.799	58.333
		500	0.003	1.950	89.583
		750	0.002	1.482	92.083
		1000	0.002	1.404	92.500
	50/50 banana/straw	250	0.012	9.047	51.667
		500	0.003	2.028	89.167
		750	0.002	1.638	91.250
		1000	0.002	1.560	91.667
	60/40 banana/straw	250	0.011	8.735	53.333
		500	0.003	2.496	86.667
		750	0.002	1.560	91.667
		1000	0.002	1.560	91.667
24	blank	0	0.135	26.264	-
	100%starw	250	0.064	12.537	52.264
		500	0.011	2.227	91.522
		750	0.007	1.306	95.026
		1000	0.005	1.014	96.140
	100%banana	250	0.094	18.347	30.141
		500	0.051	10.002	61.915
		750	0.030	5.810	77.877
		1000	0.023	4.563	82.628
	40/60	250	0.049	9.554	63.623
		500	0.011	2.184	91.685
		750	0.005	0.955	96.362
		1000	0.004	0.858	96.733
	50/50	250	0.056	10.919	58.426
		500	0.011	2.164	91.759
		750	0.007	1.443	94.506
		1000	0.007	1.384	94.729
	60/40	250	0.062	12.069	54.046
		500	0.018	3.432	86.934
		750	0.009	1.696	93.541
		1000	0.007	1.365	94.803
48	blank		0.197	19.196	-
	100%starw	250	0.092	8.969	53.276
		500	0.016	1.511	92.128
		750	0.009	0.848	95.582
		1000	0.007	0.692	96.394
	100%banana	250	0.133	12.986	32.351
		500	0.071	6.951	63.789
		750	0.043	4.221	78.009
		1000	0.034	3.305	82.783
	40/60	250	0.071	6.922	63.941
		500	0.015	1.472	92.331
		750	0.006	0.536	97.207
		1000	0.004	0.409	97.867
	50/50	250	0.081	7.887	58.913
		500	0.015	1.423	92.585
		750	0.009	0.916	95.226
		1000	0.010	0.955	95.023
	60/40	250	0.089	8.677	54.799
		500	0.025	2.437	87.303
		750	0.012	1.131	94.109
		1000	0.009	0.858	95.531

=====================================================================

Comment 7: it is necessary to present the EIS results in a table and compare the experimental and theoretical values as well as the EEC used so that some conclusions can be proven

Response: Thank you for this comment. The mentioned statements were added as follows:

(6)

Figure 8. The equivalent circuit used for fitting data obtained in EIS.

Table 1. Charge transfer resistance and inhibition efficiency results for the fitted EIS data using the equivalent circuit.

Inhibition efficiency (%)	R_CT (ohm.cm²)	Concentration (ppm)	Inhibitor type
---	46.15	0	blank
30.13	66.05	250	banana peel
59.96	115.26	500
78.18	211.48	750
81.50	249.45	1000
50.34	92.94	250	rice straw
90.56	488.62	500
95.19	958.57	750
95.52	1029.47	1000
96.34	1259.48	750	40/60	banana peel/rice straw
94.67	865.07	750	50/50
93.41	700.18	750	60/40

=====================================================================

Comment 8: experimental results are generally missing because the whole discussion of EIS results looks like an impedance book

Response: Thank you for this comment. EIS results were revised as mentioned in the above comments (comment 7)

=====================================================================

Comment 9: lacks surface analysis such as FTIR, AFM and SEM lacks EDS

Response: Thank you for this comment. The following statement was added in the revised manuscript:

The determination of chemical compounds (phytochemical analysis) of the used ex-tracts will be carried out by gas chromatography-mass spectrometry (GC-MS) in the future work. Despite the discussed experiments, our future work will study additional tests on the studied extracts such as FTIR, GC-MS, EDS, AFM, polarization analysis and molecular dynamics simulation.

=====================================================================

Comment 10: how did you convert ppm to M ie. with which molar mass did you divide

Response: Thank you for this comment. Ppm to molar was converted by molecular weight. It as added in the revised manuscript:

In this table, the values of Kads in molar were obtained by dividing Kads in ppm by 1000×MW (molecular weight). According to the literature [25, 30], gallocatechin (306 g/mol) and glycosides (584 g/mol) were the main components for banana peel and rice straw, respectively. For the mixture, the average molecular weight of gallocatechin (306 g/mol) and glycosides (472.8=0.4×306+0.6×584) was used.

=====================================================================

Comment: comments in the pdf file:

Response: Thank you. All comments in the pdf file were responded in the revised manuscript. Please see the revised manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript investigated the inhibit effects of banana peel and rice straw extracts on the corrosion behavior of carbon steel in hydrochloric acid environments. The results showed that results showed that the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors. In general, this revised paper is well-organized and comprehensively modified. Some of the comments of the reviewer were considered in the revised manuscript, but the manuscript in the current version cannot be accepted for publication. I recommend that this article be major revised. Some comments are as follows:

The mechanism for the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors was not fully clarified. The authors mentioned that “the higher efficiency of the mixture is explained by the formation of a denser and more uniform protective film on the metal surface than in the case of individual extraction.” But there’s no evidence in the present manuscript (such as the cross section morphology of the uniform protective film on the metal surface or other solid evidence) to support the above statement.
“This behavior is associated with chemical adsorption of extracts on the metal surface through the formation of coordination bonds due to the presence of heteroatoms in the structure of inhibitors and physical adsorption through pi-electrons of banana peel and rice straw in the form of a mixture.” Were the extracts analyzed in details? Some references and additional evidence should be provided to support the statements.
“heteroatoms and pi electrons can cause easier electron donation to the d-orbital of steel atoms (Fe), which leads to strong adsorption of extract molecules on the sample surface, thereby improving the corrosion protection efficiency.” Some references and additional evidence should be provided to support the statements.
“the formation of a compact and stable layer is associated with electrostatic interactions between protonated particles in the structure of green inhibitors and negatively charged particles on the metal surface.” Did the authors analyze the structure of the extracts inhibitors? What kind of negatively charged particles will be adsorbed on the metal surface? Why protonated particles can be formed in the inhibitors? Some references and additional evidence should be provided to support the above statements.

Author Response

Response to Reviewer 2

Many thanks to the reviewer for his/her helpful comments. We have revised our present research paper in his/her useful suggestions and comments. These comments could improve the quality of the work. We hope our revision has improved the paper to a level of satisfaction.

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General comment: The revised manuscript investigated the inhibit effects of banana peel and rice straw extracts on the corrosion behavior of carbon steel in hydrochloric acid environments. The results showed that results showed that the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors. In general, this revised paper is well-organized and comprehensively modified. Some of the comments of the reviewer were considered in the revised manuscript, but the manuscript in the current version cannot be accepted for publication. I recommend that this article be major revised. Some comments are as follows:

=====================================================================

Comment 1: The mechanism for the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors was not fully clarified. The authors mentioned that “the higher efficiency of the mixture is explained by the formation of a denser and more uniform protective film on the metal surface than in the case of individual extraction.” But there’s no evidence in the present manuscript (such as the cross section morphology of the uniform protective film on the metal surface or other solid evidence) to support the above statement.

Response: Thank you for this comment. “a denser” was removed The SEM analysis in Figure 10 showed that the film formed in the presence of the mixture was more uniform than in the presence of banana peel extract or rice straw extract. The response was added in the revised manuscript as follows:

=====================================================================

Comment 2: “This behavior is associated with chemical adsorption of extracts on the metal surface through the formation of coordination bonds due to the presence of heteroatoms in the structure of inhibitors and physical adsorption through pi-electrons of banana peel and rice straw in the form of a mixture.” Were the extracts analyzed in details? Some references and additional evidence should be provided to support the statements.

Response: Thank you for this comment. The following analysis of extracts and references were added in the revised manuscript:

This behavior is associated with chemical adsorption of extracts on the metal surface through the formation of coordination bonds due to the presence of heteroatoms and pi-electrons in the structure of inhibitors and physical adsorption in the form of a mixture. This mechanism has been mentioned in previous studies of banana peel and rice straw by researchers [25, 29, 31]. In this study, FTIR and phytochemical analysis of the extracts were also completed to confirm this finding. FTIR results were obtained after immersing the metal samples in HCl solution in the presence and absence of banana peel and rice straw extracts. The results for the blank showed the absence of peaks (a constant transmittance value at all wavenumbers). Figure 12 shows the FTIR analysis in the presence of extracts at 750 ppm. The figure demonstrates that in the presence of banana peel and rice straw extracts, the spectrum was characterized by the presence of several peaks, confirming the existence of corrosion inhibiting molecules. The results show that both extracts used were adsorbed on the surface of the steel samples, forming a protective layer. In addition, phytochemical analysis of banana peel and rice straw extracts was carried out to deter-mine their compounds. The results showed that the existence of many chemical com-pounds, among which gallocatechin and glycosides were the main components of banana peel extract and rice straw extract, respectively. The chemical structure of these materials is shown in Figure 13. These findings are consistent with the results of previous studies [25, 29, 43, 44].

Ji, G., Anjum, S., Sundaram, S., & Prakash, R. (2015). Musa paradisica peel extract as green corrosion inhibitor for mild steel in HCl solution. Corrosion Science, 90, 107-117.
Fouda, A. S., Gadow, H. S., Abd Elal, E. G., & El-Tantawy, M. I. (2021). Corrosion inhibition of aluminium by rice straw extract in 2 M hydrochloric acid solution. Journal of Bio-and Tribo-Corrosion, 7(3), 102.
Yahya, S., Othman, N. K., & Ismail, M. C. (2019). Corrosion inhibition of steel in multiple flow loop under 3.5% NaCl in the presence of rice straw extracts, lignin and ethylene glycol. Engineering Failure Analysis, 100, 365-380.
González-Montelongo, R., Lobo, M. G., & González, M. (2010). Antioxidant activity in banana peel extracts: Testing extraction conditions and related bioactive compounds. Food Chemistry, 119(3), 1030-1039.
Utami, S. P., Fermi, M. I., Aziz, Y., & Irianti, R. S. (2018). Corrosion control of carbon steel using inhibitor of banana peel extract in acid diluted solutions. Materials Science and Engineering, 345(1), 012030.

Banana peel

Rice straw

Figure 12. FTIR analysis after addition of banana peel and rice straw extracts.

Figure 13. Structure of gallocatechin and glycoside molecules that were identified as major components of banana peel and rice straw extracts, respectively.

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Comment 3: “heteroatoms and pi electrons can cause easier electron donation to the d-orbital of steel atoms (Fe), which leads to strong adsorption of extract molecules on the sample surface, thereby improving the corrosion protection efficiency.” Some references and additional evidence should be provided to support the statements.

Response: Thank you for this comment. The following sentences and references were added:

Moreover, as shown in Figure 13, heteroatoms (pairs of free electrons in oxygen) and pi-electrons (in the aromatic rings) in the structure of gallocatechin and glycosides (as the main components of banana peel and rice straw for corrosion inhibition) can cause easier electron donation to the d-orbital of steel atoms (Fe), which leads to strong adsorption of extract molecules on the sample surface, thereby improving the corrosion protection efficiency [25, 29, 34, 45].

Ji, G., Anjum, S., Sundaram, S., & Prakash, R. (2015). Musa paradisica peel extract as green corrosion inhibitor for mild steel in HCl solution. Corrosion Science, 90, 107-117.
Fouda, A. S., Gadow, H. S., Abd Elal, E. G., & El-Tantawy, M. I. (2021). Corrosion inhibition of aluminium by rice straw extract in 2 M hydrochloric acid solution. Journal of Bio-and Tribo-Corrosion, 7(3), 102.
Khormali, A., & Ahmadi, S. (2023). Synergistic effect between oleic imidazoline and 2-mercaptobenzimidazole for increasing the corrosion inhibition performance in carbon steel samples. Iranian Journal of Chemistry and Chemical Engineering, 42(1), 321-336.
Verma, D. K., Dewangan, Y., Dewangan, A. K., & Asatkar, A. (2021). Heteroatom-based compounds as sustainable corrosion inhibitors: an overview. Journal of Bio-and Tribo-Corrosion, 7(1), 15.

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Comment 4: “the formation of a compact and stable layer is associated with electrostatic interactions between protonated particles in the structure of green inhibitors and negatively charged particles on the metal surface.” Did the authors analyze the structure of the extracts inhibitors? What kind of negatively charged particles will be adsorbed on the metal surface? Why protonated particles can be formed in the inhibitors? Some references and additional evidence should be provided to support the above statements.

Response: Thank you for this comment. the extracts were analyzed. The following sentences and are references were added:

In addition, the formation of a compact and stable layer is associated with electrostatic interactions (physical adsorption) between protonated particles (charged inhibitor molecules INH–H+) and negatively charged surface [12, 29, 46, 47]. Protonated molecules are adsorbed on the metal surface, which is charged with chlorine anions. It should be noted that the oxidation of iron in a hydrochloric acid environment, which makes the metal surface positively charged, which attracts negative Cl-1, causing the surface to be negatively charged [12]. Moreover, as shown in Figure 13, the main components of the extracts under study have heteroatoms in their structure. Chemical reagents containing heteroatoms can be protonated in an aggressive acidic solution according to the following relationship [29]:

[gallocatechin/glycoside moldecules] + xH⁺ [ gallocatechin/glycoside moldecules -H_x ]^x+

Chen, L., Lu, D., & Zhang, Y. (2022). Organic compounds as corrosion inhibitors for carbon steel in HCl solution: a comprehensive review. Materials, 15(6), 2023.
Fouda, A. S., Gadow, H. S., Abd Elal, E. G., & El-Tantawy, M. I. (2021). Corrosion inhibition of aluminium by rice straw extract in 2 M hydrochloric acid solution. Journal of Bio-and Tribo-Corrosion, 7(3), 102.
Mohd, N. K., Kian, Y. S., Ibrahim, N. A., Nor, S. M. M., Wan Yunus, W. M. Z., Ghazali, M. J., & Huei, L. W. (2021). Corrosion inhibition, adsorption and thermodynamic properties of hydrophobic-tailed imines on carbon steel in hydrochloric acid solution: a comparative study. Journal of Adhesion Science and Technology, 35(23), 2558-2579.
Olasunkanmi, L. O., Obot, I. B., Kabanda, M. M., & Ebenso, E. E. (2015). Some quinoxalin-6-yl derivatives as corrosion inhibitors for mild steel in hydrochloric acid: experimental and theoretical studies. The Journal of Physical Chemistry C, 119(28), 16004-16019.

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Comment 5: Considering all the problems mentioned here above, some parts of this manuscript should be revised, and some additional data should be added to support the statement in the manuscript. This paper may not be considered to be accepted for publication in the current version. I recommend that the manuscript be major revised.

Response: Thank you for this comment. The above comments were responded. Also, the results of additional tests were added to support the inhibition efficiency of the used extracts and their mixture, including: EDS, FTIR, potentiodynamic polarization, phase angle plots and phytochemical analysis. Please see the results of these additional tests in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The table of mass loss measurements should be transferred to supplementary materials
Equations must be written in ionic form, and solid and gaseous reactants/products must indicate their aggregate state - references and evidence are missing for the inhibition mechanism
All the above analyzes (FTIR, GC-MS, EDS, AFM, polarization analysis and molecular dynamics simulation) must be done for this work. It is simply unacceptable to work without one of the aforementioned analyses.
All physical quantities are still not written in italics
Why the dependence of the phase angle on the frequency was not shown, which would confirm the suitability of the selected EEC, since the Nyquist diagram does not really indicate that it is a single time constant
A comparison of the experimental and theoretical values is still missing
Response to comment no. 9 is unacceptable
Kads-1 is not in ppm-1 but in ppm?!
The citation of references is not harmonized

Author Response

Response to Reviewer 3

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Comment 1: The table of mass loss measurements should be transferred to supplementary materials

Response: Thank you for this comment. It was done in the revised manuscript.

=====================================================================

Comment 2: Equations must be written in ionic form, and solid and gaseous reactants/products must indicate their aggregate state - references and evidence are missing for the inhibition mechanism

Response: Thank you for this comment. The equations were written in the ionic form and the phases of the materials were added. The inhibition mechanism section was revised by adding references and FTIR and phytochemical analyses.

Fe (s) Fe²⁺ (aq) + 2e^-

2HCl (aq) 2H⁺ (aq)+ 2Cl^1- (aq)

2H⁺ (aq) + 2e^- H₂(g)

Fe (s) + 2HCl (aq) Fe²⁺ (aq) + H₂ (g)+ 2Cl^1- (aq) FeCl₂(aq)+ H₂(g)

O₂ + 4H⁺ + 4e^- 2H₂O (l)

2Fe (s) + O₂(g) + 2H₂O (l) 2Fe²⁺ (aq) + 4(OH)^1-(aq) 2Fe(OH)₂(s)

2Fe(OH)₂(s)+ 0.5O₂(g) + H₂O (l) 2Fe(OH)₃ (s)

2Fe(OH)₃ (s) Fe₂O₃(s)+ 3H₂O (l)

Moreover, the higher efficiency of the mixture can be related to the formation of a more uniform protective film on the metal surface than in the case of individual extraction. The SEM analysis in Figure 10 showed that the film formed in the presence of the mixture was more uniform than in the presence of banana peel extract or rice straw extract. This behavior is associated with chemical adsorption of extracts on the metal surface through the formation of coordination bonds due to the presence of heteroatoms and pi-electrons in the structure of inhibitors and physical adsorption in the form of a mixture. This mechanism has been mentioned in previous studies of banana peel and rice straw by researchers [25, 29, 31]. In this study, FTIR and phytochemical analysis of the extracts were also completed to confirm this finding. FTIR results were obtained after immersing the metal samples in HCl solution in the presence and absence of banana peel and rice straw extracts. The results for the blank showed the absence of peaks (a constant transmittance value at all wavenumbers). Figure 12 shows the FTIR analysis in the presence of extracts at 750 ppm. The figure demonstrates that in the presence of banana peel and rice straw extracts, the spectrum was characterized by the presence of several peaks, confirming the existence of corrosion inhibiting molecules. The results show that both extracts used were adsorbed on the surface of the steel samples, forming a protective layer. In addition, phytochemical analysis of banana peel and rice straw extracts was carried out to determine their compounds. The results showed that the existence of many chemical compounds, among which gallocatechin and glycosides were the main components of banana peel extract and rice straw extract, respectively. The chemical structure of these materials is shown in Figure 13. These findings are consistent with the results of previous studies [25, 29, 43, 44].

The high strength of chemical adsorption of the mixture compared to the extract alone is explained by the co-adsorption of heteroatoms in both green inhibitors, which simultaneously participate in surface bonds. Moreover, as shown in Figure 13, heteroatoms (pairs of free electrons in oxygen) and pi-electrons (in the aromatic rings) in the structure of gallocatechin and glycosides (as the main components of banana peel and rice straw for corrosion inhibition) can cause easier electron donation to the d-orbital of steel atoms (Fe), which leads to strong adsorption of extract molecules on the sample surface, thereby improving the corrosion protection efficiency [25, 29, 34, 45].

In addition, the formation of a compact and stable layer is associated with electrostatic interactions (physical adsorption) between protonated particles (charged inhibitor molecules INH–H⁺) and negatively charged surface [12, 29, 46, 47]. Protonated molecules are adsorbed on the metal surface, which is charged with chlorine anions. It should be noted that the oxidation of iron in a hydrochloric acid environment, which makes the metal surface positively charged, which attracts negative Cl^-1, causing the surface to be negatively charged [12]. Moreover, as shown in Figure 13, the main components of the extracts under study have heteroatoms in their structure. Chemical reagents containing heteroatoms can be protonated in an aggressive acidic solution according to the following relationship [29]:

[gallocatechin/glycoside moldecules] + xH⁺ [ gallocatechin/glycoside moldecules -H_x ]^x+

=====================================================================

Comment 3: All the above analyzes (FTIR, GC-MS, EDS, AFM, polarization analysis and molecular dynamics simulation) must be done for this work. It is simply unacceptable to work without one of the aforementioned analyses.

Response: Thank you for this comment. The results of FTIR, phytochemical analysis, phase angle plots, EDS, and polarization tests were added. Please see the revised manuscript.

=====================================================================

Comment 4: All physical quantities are still not written in italics

Response: Thank you for this comment. it was done and highlighted in the revised manuscript.

=====================================================================

Comment 5: Why the dependence of the phase angle on the frequency was not shown, which would confirm the suitability of the selected EEC, since the Nyquist diagram does not really indicate that it is a single time constant

Response: Thank you for this comment. Phase angle plots were added in the revised manuscript.

=====================================================================

Comment 6: A comparison of the experimental and theoretical values is still missing

Response: Thank you for this comment. It was done and following table was added:

In order to verify the accuracy of used data, a comparison of experimental and theoretical values was performed by electrochemical frequency modulation technique using a capacity of 10 mV by defining two causal factors. These factors corresponded to the standard values 2 and 3. The obtained results are presented in Table 2. The table shows that the deviation of experimental and theoretical values is not significant at both standard values. In this case, the maximum deviation values for causal factors 2 and 3 were 9% and 7%, respectively. Moreover, the current density was significantly reduced by increasing the extract concentration. These results confirmed the previous findings regarding the optimal inhibitor concentration (750 ppm) and the extract mixing ratio (40:60 BPE:RSE). It should be noted that the inhibition efficiency in potentiodynamic polarization tests was determined using the following formula:

(7)

Where i_corr0 and i_corr1 are the corrosion current densities, which are related to the blank case (o ppm) and the solution with inhibitor (μ/cm²).

Table 2. Inhibition efficiency results obtained from potentiodynamic polarization tests and comparison of experimental and theoretical values in determining causal factors (according to standard values 2 and 3).

Inhibition efficiency (%)	Deviation (comparison of experimental and theoretical values) (%)	Causal factor according to 3	Deviation (comparison of experimental and theoretical values) (%)	Causal factor according to 2	i_corr (μ/cm²)	Concentration (ppm)	Inhibitor type
---	4.67	3.14	9.00	2.18	1065	0	blank
30.70	1.67	3.05	2.50	1.95	738	250	banana peel
61.03	4.00	2.88	1.00	2.02	415	500
78.40	1.00	2.97	4.00	2.08	230	750
80.19	3.33	3.10	2.00	2.04	211	1000
51.27	1.33	2.96	7.00	2.14	519	250	rice straw
88.92	4.33	2.87	2.00	2.04	118	500
94.55	3.00	3.09	2.50	1.95	58	750
95.02	7.00	3.21	5.50	1.89	53	1000
95.59	5.33	3.16	8.50	2.17	47	750	40/60	banana peel/rice straw
95.87	1.67	3.05	6.50	2.13	44	750	50/50
92.86	3.67	3.11	8.50	2.17	76	750	60/40

=====================================================================

Comment 7: Response to comment no. 9 is unacceptable

Response: Thank you for this comment. The following results of EDS and FTIR were added:

EDS analysis of metal samples was performed in order to determine the mass percentage of elements in the used steel after immersion in the HCl solution in the absence and presence of banana peel extract, rice straw extract and their mixture (40:60 BPE:RSE) at 750 ppm. The analysis indicated that there was a large difference in the mass percentage of iron (the main element of steel) between the inhibited and uninhibited metal samples. The results showed the following mass percentage for the blank case, banana peel, rice straw and their mixture: 70.12%, 88.94%, 90.07% and 92.13%, respectively. The low iron percentage in the blank case shows the metal consumption due to corrosion. The higher iron percentage value in the steel in the presence of green inhibitors confirms their effectiveness in inhibiting corrosion. The highest iron percentage was for the case of the extract mixture, which demonstrates its higher inhibitory capacity compared to individual extracts.

In this study, FTIR and phytochemical analysis of the extracts were also completed to confirm this finding. FTIR results were obtained after immersing the metal samples in HCl solution in the presence and absence of banana peel and rice straw extracts. The results for the blank showed the absence of peaks (a constant transmittance value at all wavenumbers). Figure 12 shows the FTIR analysis in the presence of extracts at 750 ppm. The figure demonstrates that in the presence of banana peel and rice straw extracts, the spectrum was characterized by the presence of several peaks, confirming the existence of corrosion inhibiting molecules. The results show that both extracts used were adsorbed on the surface of the steel samples, forming a protective layer. In addition, phytochemical analysis of banana peel and rice straw extracts was carried out to determine their compounds. The results showed that the existence of many chemical compounds, among which gallocatechin and glycosides were the main components of banana peel extract and rice straw extract, respectively. The chemical structure of these materials is shown in Figure 13. These findings are consistent with the results of previous studies [25, 29, 43, 44].

Rice straw

Figure 12. FTIR analysis after addition of banana peel and rice straw extracts.

Figure 13. Structure of gallocatechin and glycoside molecules that were identified as major components of banana peel and rice straw extracts, respectively.

=====================================================================

Comment 8: Kads-1 is not in ppm-1 but in ppm?!

Response: Thank you for this comment. K_das in ppm^-1 (K_das^-1 in ppm) according to the adsorption formula. It was corrected in the revised manuscript in Table 3.

=====================================================================

Comment 9: The citation of references is not harmonized.

Response: Thank you for this comment. all references in a same style in the revised manuscript.

=====================================================================

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript investigated the inhibit effects of banana peel and rice straw extracts on the corrosion behavior of carbon steel in hydrochloric acid environments. The results showed that results showed that the mixture of extracts banana peel and rice straw had a higher inhibitory capacity than the individual inhibitors. In general, this revised paper is well-organized and comprehensively modified. The comments of the reviewer were considered in the revised manuscript very well. I recommend the paper be accepted for publication.

Author Response

many thanks.

Reviewer 3 Report

Comments and Suggestions for Authors

Protonated molecules are adsorbed on the metal surface, which is charged with chlorine anions. It should be noted that the oxidation of iron in a hydrochloric acid environment, which makes the metal surface positively charged, which att racts negative Cl-1, causing the surface to be negatively charged [12]. - this is rather contradictory because chloride ions would rather cause pitting corrosion than attract protonated molecules of green inhibitors. - proof is needed to support the above statement - it is necessary to study reference 12 in more detail and not just paste what fits in the hope that it will hold water until the review passes

- instead of ordinary structural formulas, formulas optimized by some semi-empirical method should be presented

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 3

=====================================================================

Comment 1: Protonated molecules are adsorbed on the metal surface, which is charged with chlorine anions. It should be noted that the oxidation of iron in a hydrochloric acid environment, which makes the metal surface positively charged, which attracts negative Cl-1, causing the surface to be negatively charged [12]. - this is rather contradictory because chloride ions would rather cause pitting corrosion than attract protonated molecules of green inhibitors. - proof is needed to support the above statement - it is necessary to study reference 12 in more detail and not just paste what fits in the hope that it will hold water until the review passes

Response: Thank you for this comment. As you can see (and we studied this reference very well) in reference 12, the following paragraph is about physical adsorption:

Physisorption mechanism: excessive oxidation of Fe elements in the HCl solution makes the carbon steel surface positively charged, which attracts negatively charged chloride ions, causing the surface to be negatively charged and forming a so-called inner Helmholtz plane (IHP) (as shown in Equation (20)), while the attractive forces between the positively charged inhibitor molecules INH–H⁺ (because heteroatoms become protonated in aggressive acidic media) and the carbon steel surface increased as a result of a bridge created by the adsorption of chlorides (Cl⁻), which formed the outer Helmholtz plane (OHP) [32]. It has been reported that such physical interactions between the inhibitor and the iron surface would behave loosely with increasing temperature [43].

Fe(H2O)nads+2Cl−⇔Fe[(H2O)n(Cl)−2]adsFe(H2O)nads+2Cl−⇔Fe(H2O)n(Cl)2−ads (20)

In the above paragraph, it was mentioned how Cl causes a negative surface. However, to confirm your opinion, we removed the following sentence:

=====================================================================

Comment 2: - instead of ordinary structural formulas, formulas optimized by some semi-empirical method should be presented

Response: Thank you for this comment. Dear reviewer, many papers about rice straw and banana peel were published, in which these compounds were mentioned as the main component for corrosion inhibition. Our tests also showed these results. We have previously used RSM methods for optimization and published many papers about corrosion optimization. The aim of this paper is not formula optimization. Please see for detailed information some our recent papers about optimization:

https://doi.org/10.1016/j.rineng.2025.104671

https://doi.org/10.1016/j.fuel.2023.129783

https://doi.org/10.1080/10916466.2023.2253269

https://doi.org/10.1016/j.rineng.2024.103094

https://doi.org/10.1016/j.fuel.2022.124270

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Comment in pdf file:

- Lines 261 and 266, the charge of Cl and OH is "-1", otherwise the charge balance may not be satisfied.

Author Response File: Author Response.pdf

Round 4

Reviewer 3 Report

Comments and Suggestions for Authors

-Fe(H2O)nads+2Cl−⇔Fe[(H2O)n(Cl)−2]adsFe(H2O)nads+2Cl−⇔Fe(H2O)n(Cl)2−ads (20) why is this equation written twice and which one is correct

-I can't access most of the works. The formula should definitely show the unshared electron pair and the positive charge you are talking about

-unit is not written in charges, only the sign

Author Response

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Comment 1: -Fe(H2O)nads+2Cl−⇔Fe[(H2O)n(Cl)−2]adsFe(H2O)nads+2Cl−⇔Fe(H2O)n(Cl)2−ads (20) why is this equation written twice and which one is correct

Response: Thank you for this comment. Sorry for writing this equation twice. The correct form of this equation is as follows in the reference 12:

Fe(H2O)n_ads+2Cl⁻⇔Fe[(H₂O)n(Cl)−₂]ads

Chen, L., Lu, D., & Zhang, Y. (2022). Organic compounds as corrosion inhibitors for carbon steel in HCl solution: a comprehensive review. Materials, 15(6), 2023.

=====================================================================

Comment 2: -I can't access most of the works. The formula should definitely show the unshared electron pair and the positive charge you are talking about

Response: Thank you for this comment. Unshared electrons (lone pair) are for heteroatoms (all oxygen atoms in the structure of molecules in Figure 13). Also, the positive charge is due to inhibitor molecule protonation through H⁺ ions of HCl solution. The following sentences were added in the revised manuscript:

It should be noted that lone pairs of electrons are present in all oxygen atoms in the structure of the molecules in Figure 13.

The positive charge is due to the protonation of the inhibitor molecule by H⁺ ions in the HCl solution.

=====================================================================

Comment 3: -unit is not written in charges, only the sign.

Response: Thank you for this comment. It was done. Please see lines 261 and 266 in the revised manuscript.

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Analysis of a Mixture of Banana Peel and Rice Straw Extracts for Inhibiting Corrosion of Carbon Steel in Hydrochloric Acid Solution

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