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  • Mats Ahmadi Götelid1,*,
  • Sareh Ahmadi Götelid2 and
  • Saman Hosseinpour3
  • et al.

Reviewer 1: Anonymous Reviewer 2: Anonymous Reviewer 3: Anonymous

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In manuscript ID cmd-3856262 the authors studied the co-absorption of formic acid and selenol hexane on a Cu surface, using X-ray photoelectron spectroscopy (XPS).

In the introductory part of the paper, the authors presented types of corrosion and the factors that trigger their formation. Thus, it is known that at low concentrations of formic acid (organic acid) in the presence of humidity and oxygen, localized corrosion occurs, called ant nest corrosion, corrosion that causes leaks and failures in installations containing copper tubes, such as air conditioning installations. In the documentary study, the authors presented the fact that the selective diffusion of O2 H2O and formic acid through the alkane chain modifies the corrosion reaction pathway and delays the formation of certain corrosion products. Also, from the documentary studies of researchers in the field, it was shown that protective self-assembled monolayers (SAMs), due to their nanometric thickness, ease of application and spontaneous formation, constitute protective layers against corrosion. These SAMs can form a well-ordered layer on the substrate, with a dense carpet of carbon chains protruding from the surface, which can prevent or at least slow down the penetration of hostile corrosion promoters.

It was found that selenol with hexane was more easily removed from the surface, presenting a weaker corrosion protection capacity compared to its counterpart with hexane thiol, during exposure to a simulated corrosive environment.

 In the second part of the study, the experimental one, the used a polycrystalline disc of Cu (2 mm thick, 8 mm radius) polished by SiC paper and diamond paste, using ethanol as lubricant. The sample was cleaned in a vacuum by Ar-ion bombardment (1 kV). The cooling of sample was done with liquid nitrogen, and heating was done by electron bombardment. Hexane selenole was deposited on the Cu surface, from the gas phase and formic acid and oxygen were also introduced into the UHV chamber (for their controlled absorption). To distinguish the elements and their chemical environment, such as chemical bonds and electron density, X-ray photoelectron spectroscopy (XPS) was used.

After analyses, the authors concluded that: ( i) the adsorption of hexane selenole at room temperature breaks the Se-C bond, leaving a monolayer of Se on the surface; (ii) by exposing Cu-selenole to formic acid, the formic acid is absorbed into the alkane network, and the formate binds to the unprotected areas. After heating to room temperature, the formate remains intact, the formic acid desorbs, and the Se-C bond breaks; (iii)the  formic acid alone does not affect the Se-C bond, but its presence creates disorder and opens up the  alkane carpet for other species (iv) selenol removes formate and oxide from the surface at room temperature. And (v) the Se-C bond breaks, and the alkane chain reacts with surface oxygen to form carbon oxides and volatile hydrocarbons.

In my opinion, the paper is well written, and the results are of interest to researchers in materials science engineering , especial in environmental degradation of materials.

As a result , I agree to publish the paper in this form.

Author Response

We thank the reviewer for the positive comments. 

Reviewer 2 Report

Comments and Suggestions for Authors

In this work, the authors investigated the XPS method for the co-adsorption of formic acid and hexane selenol on the copper surface. This study is an integral part of the authors' systematic investigations of how the components of organic molecules can be used as protective layers against metal corrosion. I believe that the job can be accepted after minor remarks have been corrected.

  1. The abstract should preferably be given in one paragraph, as is usually the case. It is also advisable to take into account the instructions for the authors when writing it.
  2. Introduction. The description is based mainly on sources older than the last five years, with the possible exception of individual citations (for example, ref.18). At the same time, the research topic is quite interesting and relevant: it is recommended to supplement the Introduction with a brief description of 2-3 more modern works for 2024-2025.
  3. In the Materials and Methods section, it is advisable to specify the purity of the initial reagents.
  4. Before the Conclusion section, it is recommended to provide a visual scheme of the processes studied. I think this will be even more clearer for readers and will complement the discussion in the text of the manuscript.
  5. All references should be formatted according to the MDPI standard, and it is highly desirable to provide DOI indexes.

Author Response

In this work, the authors investigated the XPS method for the co-adsorption of formic acid and hexane selenol on the copper surface. This study is an integral part of the authors' systematic investigations of how the components of organic molecules can be used as protective layers against metal corrosion. I believe that the job can be accepted after minor remarks have been corrected.

  1. The abstract should preferably be given in one paragraph, as is usually the case. It is also advisable to take into account the instructions for the authors when writing it. Response: The abstract has been put in one paragraph.
  2. The description is based mainly on sources older than the last five years, with the possible exception of individual citations (for example, ref.18). At the same time, the research topic is quite interesting and relevant: it is recommended to supplement the Introduction with a brief description of 2-3 more modern works for 2024-2025. Response: We have added a few modern and relevant papers. We have also removed some self citations. All changes are marked red in the manuscript.
  3. In the Materials and Methods section, it is advisable to specify the purity of the initial reagents. Response: We have added this information and also the name of the producer.
  4. Before the Conclusion section, it is recommended to provide a visual scheme of the processes studied. I think this will be even more clearer for readers and will complement the discussion in the text of the manuscript. Response: This would probably be helpful, but given the short time to respond we do not see the possibility to include this.
  5. All references should be formatted according to the MDPI standard, and it is highly desirable to provide DOI indexes. We followed the formatting given in the template. Response: We used the template, and we have added DOI for all references.

We thank the reviewer for the constructive comments. 

Reviewer 3 Report

Comments and Suggestions for Authors

This article reports the adsorption of hexane selenol and formic acid molecules on a polycrystalline copper surface. The obtained XPS results are well-organized, and significant to the surface science and engineering of copper. I recommend to publish after elucidating some following points.

1. At the Experimental Details section, line 90: 
If possible, please add some information of hexane selenol molecules. Did authors purchase or synthesize this? If authors reported previously, citing a paper can be better.

2. At line 130, it seems that the description of “[21 Anneli]” can be something wrong. Please modify.

3. About Figure 1, I recommend to add some information at the spectra of desorption stages. I think that the “160 K” data corresponds to the “10 L” formic acid adsorption, right? I think that addition at caption or in the Figure can be better.

4. About Figure 2, I recommend to add the deposition condition of hexane selenol (5 L) and the adsorption temperature of formic acid (140 K) at caption, if possible.

5. At Figure 3, I recommend to add the information of temperature at captions and/or related main text. I think that after O2 exposure, formic acid and selenol were adsorbed at room temperature. However, this temperature information is described only at conclusion. Please confirm.

Author Response

This article reports the adsorption of hexane selenol and formic acid molecules on a polycrystalline copper surface. The obtained XPS results are well-organized, and significant to the surface science and engineering of copper. I recommend to publish after elucidating some following points.

1. At the Experimental Details section, line 90: If possible, please add some information of hexane selenol molecules. Did authors purchase or synthesize this? If authors reported previously, citing a paper can be better. Response: we have added this information.

2. At line 130, it seems that the description of “[21 Anneli]” can be something wrong. Please modify. Thank you for pointing this out. We have corrected.

3. About Figure 1, I recommend to add some information at the spectra of desorption stages. I think that the “160 K” data corresponds to the “10 L” formic acid adsorption, right? No, the 160 K spectrum was recorded after heating the adsorbed layer to 160 K. I think that addition at caption or in the Figure can be better. We have revised the figure caption.

4. About Figure 2, I recommend to add the deposition condition of hexane selenol (5 L) and the adsorption temperature of formic acid (140 K) at caption, if possible. We have revised the figure caption and also revised the text in connection to this figure to be more clear.

5. At Figure 3, I recommend to add the information of temperature at captions and/or related main text. I think that after O2 exposure, formic acid and selenol were adsorbed at room temperature. However, this temperature information is described only at conclusion. Please confirm. We have added this information both in the figure caption and in the text.

We thank the reviewer for the constructive comments