Electrochemical and thermodynamic properties of 1-phenyl-3-(phenylamino)propan-1-one with Na2WO4 on N80 steel

The corrosion inhibition effect and adsorption behaviour of 1-phenyl-3-(phenylamino)propan-1-one (PPAPO) on N80 steel in hydrochloric acid solution have been investigated by Fourier transform infrared (FTIR), electrochemical method and scanning electron microscopy. The corrosion inhibition mechanism of PPAPO mixed with Na2WO4 was interpreted from the thermodynamic point of view. The results indicated that PPAPO mixed with Na2WO4 acted as a mixed-type inhibitor. The inhibition film formed on N80 steel surface can increase the charge transfer resistance and prevent the occurrence of corrosion reaction, thereby reducing the corrosion rate of metal surface. The inhibition efficiency was up to 96.65%; the inhibitor PPAPO with Na2WO4 showed good synergistic effect on N80 corrosion behaviour in HCl solution. The adsorption behaviour of inhibitors on N80 steel surface was in accordance with the Langmuir adsorption model and mainly belonged to chemisorption. The adsorption process of PPAPO on N80 surface was spontaneous and irreversible endothermic reaction.

I would like to see the English significantly improved throughout the manuscript. Sometimes it can be hard to understand the points the authors wish to make.
Decision letter (RSOS-191692.R0) 28-Feb-2020 Dear Professor Lei: Title: Electrochemical and thermodynamic properties of 1-phenyl-3-(phenylamino)propan-1-one with Na2WO4 on N80 Steel Manuscript ID: RSOS-191692 Thank you for submitting the above manuscript to Royal Society Open Science. On behalf of the Editors and the Royal Society of Chemistry, I am pleased to inform you that your manuscript will be accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the reviewers' comments at the end of this email. I apologise that this has taken longer than usual.
The reviewers and handling editors have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
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Once again, thank you for submitting your manuscript to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry. I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. ********************************************** RSC Associate Editor: Comments to the Author: (There are no comments.) RSC Subject Editor: Comments to the Author: (There are no comments.) ********************************************** Reviewer comments to Author: Reviewer: 1 Comments to the Author(s) This article choses 1-phenyl-3-(phenylamino) propan-1-one (PPAPO) as the research object, and explores the corrosion inhibition effect and adsorption behavior of PPAPO on N80 steel in hydrochloric solution. This is a very innovative work, and it is an interesting and quite important for the inhibition behavior of N80 steel in hydrochloric solution. My opinion is the minor revision. However, several issues in the paper should be addressed before the manuscript could be considered for publication. 1. The detailed steps for PPAPO synthesis are unclear. 2. In page 3, for IR spectrum of synthesized PPAPO corrosion inhibitor, some characteristic peaks are discussed in the text, but they are not marked in the figure 2.
3. In the corrosion morphology of N80 in presence inhibitors, why choose the 0.5 M HCl solution containing 2 mM PPAPO？ 4. In Equations 2 and 3, the ion subscript needs to be taken seriously, which is inconsistent with the text. 5. In Fig. 6, the meaning of "R.E" and "W.E" needs to be explained in detail. 6. In figure 7 and 8, the equation of fitting curve needs to be added in the figures. 7. There are some grammar issues in the text. They all should be identified and corrected.

Reviewer: 2
Comments to the Author(s) The manuscript by Zhang and co-workers reports the anti-corrosion and surface adsorption properties of 1-Phenyl-3-(phenylamino)propan-1-one and Na2WO4. The study is well done and contains some significant analytical chemistry. I'm happy to recommend publication subject to the following points being addressed.
I would like to see section 3.3 re-written a little bit. The section starting "As can be seen in Fig.  4…" is unclear. It doesn't appear to be a simple case of 'different concentration of PPAPO' leading to decreases in the corrosion current density. This should be clarified and rewritten.
It may be a question of resolution in the file I received, but Figure 9 is not clear.
On page 8, the English is not clear at all. On the bottom line of the left column ' the organic functional groups in the presence of a pair of electrons…' is confusing and unclear. The reference to the dsp3 hybrid is hard to understand. This could be simplified with a standard explanation of the coordination chemistry.
I would like to see the English significantly improved throughout the manuscript. Sometimes it can be hard to understand the points the authors wish to make. Thank you very much for your letter and for the reviewer's comments concerning our manuscript entitled "Electrochemical and thermodynamic properties of 1-phenyl-3-(phenylamino)propan-1-one with Na2WO4 on N80 Steel" ID: RSOS-191692. Those comments are very valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied the comments carefully and tried our best to revise the manuscript. Now we want to resubmit for possible publication in Royal Society Open Science. The main corrections in the manuscript and the responds to the reviewer's comments are as following: Responds to the reviewer's comments:

Reviewer: 1
Comments: 1. The detailed steps for PPAPO synthesis are unclear.

Reply:
We have re-edited the pictures in the manuscript as follows: When preparing the PPAPO corrosion inhibitor, 2mmol of acetophenone, 3mmol of formaldehyde and 2.6mmol of aniline were dissolved in 200 ml ethanol solution. The pH value of the solution was adjusted to 3 with HCl aqueous solution. Finally, a red brown liquid was obtained after refluxed for 6 h by heating at 60 °C.
2. In page 3, for IR spectrum of synthesized PPAPO corrosion inhibitor, some characteristic peaks are discussed in the text, but they are not marked in the figure 2.

Reply:
We have re-edited the Figure 2 in the manuscript as follows:  4. In Equations 2 and 3, the ion subscript needs to be taken seriously, which is inconsistent with the text. Reply: we have revised the ion subscript of Equations 2 and 3 in manuscript as follows:

5.
In Fig. 6, the meaning of "R.E" and "W.E" needs to be explained in detail. Reply: The meaning of "R.E" and "W.E" have been added in manuscript as follows: "W.E and R.E represent the working electrode and reference electrode respectively." 6. In figure 7 and 8, the equation of fitting curve needs to be added in the figures. Reply: The fitting equation have been added in Figure 7 and 8 as follows:  "which consists of the admittance magnitude (Y0) and the exponent (n)." "And that is the sample is corroded" "The surface coverage is an important parameter to study the adsorption behavior of PPAPO and Na2WO4 at the metal/solution interface and further analysis the inhibition mechanism." "The equilibrium constant is related with the standard free energy of adsorption as follows" "where ΔH is the heat of adsorption, K0 is the adsorption equilibrium constant, R is the gas constant (8.314 J·k -1 ), and T is the absolute temperature (K)." "The thermodynamic activation parameter, Gibbs energy change (ΔG), was used to investigate the thermodynamic change in the adsorption reaction." "According to the previous experimental results, the corrosion rate of N80 steel in HCl medium was inhibited by adding PPAPO alone or mixed with Na2WO4, but there is difference for corrosion inhibition mechanism (Fig. 9)." ". Further more, it prevents the diffusion of electrons from the metal surface to the corrosion solution." "The adsorption process belongs to endothermic reaction (ΔH>0) according to the corrosion thermodynamics analysis of PPAPO and Na2WO4 with strong coherence to the metal surface."

Reviewer: 2
Comments: 1. I would like to see section 3.3 re-written a little bit. The section starting "As can be seen in Fig. 4…" is unclear. It doesn't appear to be a simple case of 'different concentration of PPAPO' leading to decreases in the corrosion current density. This should be clarified and rewritten.
Reply: In section 3.3, we have modified in manuscript as follows: "As can be seen from Fig. 4(a), the polarization curves after the addition of PPAPO corrosion inhibitor in HCl solution move to the left, which indicates that the corrosion current density has decreased. In addition, the value of icorr gradually reduced with the increase of the PPAPO concentration, which indicates that the corrosion of carbon steel is inhibited when adding PPAPO. Compared with the results of polarization curve when PPAPO is added alone, the corrosion current density of the mixed PPAPO and Na2WO4 inhibitors ( Fig. 4(b)) is obviously lower than that of PPAPO alone." "Comparing with icorr of N80 steel in 0.5 M HCl solution without PPAPO, the icorr decreased markedly in the presence of PPAPO. That may due to the adsorption of PPAPO on carbon steel surface prevents the anodic metal dissolution and cathodic hydrogen evolution and then decreases the metal surface activation points [15] . The adsorption of inhibitor molecules may include physical and chemical adsorption and generate an energy barrier to block electron transfer." 2. It may be a question of resolution in the file I received, but Figure 9 is not clear.

Reply:
We have re-edited the picture in the manuscript as follows:  Sometimes it can be hard to understand the points the authors wish to make.
Reply: Thanks for your review, we have checked carefully and modified in manuscript as follows: "The corrosion inhibition mechanism of PPAPO mixed with Na2WO4 was interpreted from the point of view of the thermodynamic. The results indicated that PPAPO mixed with Na2WO4 acted as a mixed type inhibitor." "The inhibition efficiency was up to 96.65%; and the inhibitor PPAPO with Na2WO4 showed good synergistic effect on N80 corrosion behavior in HCl solution." "developing a large amount of corrosion pits and causing serious corrosion of equipment and piping components." "In the present work, the inhibition and synergistic effect of PPAPO mixed with Na2WO4 on N80 steel corrosion were investigated in 0.5 M HCl solution using Fourier transform infrared, potentiodynamic polarization curve, electrochemical impedance spectroscopy, scanning electron microscopy. Based on corrosion thermodynamics. the corrosion inhibition mechanism was also analyzed." "The Fe atoms on surface of N80 steel may lose two electrons, and generating Fe 2+ when N80 steel corrodes in 0.5 M HCl solution." "which consists of the admittance magnitude (Y0) and the exponent (n)." "And that is the sample is corroded" "The surface coverage is an important parameter to study the adsorption behavior of PPAPO and Na2WO4 at the metal/solution interface and further analysis the inhibition mechanism." "The equilibrium constant is related with the standard free energy of adsorption as follows" "where ΔH is the heat of adsorption, K0 is the adsorption equilibrium constant, R is the gas constant (8.314 J·k -1 ), and T is the absolute temperature (K)." "The thermodynamic activation parameter, Gibbs energy change (ΔG), was used to investigate the thermodynamic change in the adsorption reaction." "According to the previous experimental results, the corrosion rate of N80 steel in HCl medium was inhibited by adding PPAPO alone or mixed with Na2WO4, but there is difference for corrosion inhibition mechanism (Fig. 9)." "Furthermore, it prevents the diffusion of electrons from the metal surface to the corrosion solution." "The adsorption process belongs to endothermic reaction (ΔH>0) according to the corrosion thermodynamics analysis of PPAPO and Na2WO4 with strong coherence to the metal surface."