Enhancement of the Activity of Electrochemical Oxidation of BPS by Nd-Doped PbO2 Electrodes: Performance and Mechanism
Round 1
Reviewer 1 Report
Zhang and coauthors report electrochemical oxidation of bisphenol S (BPS) using Nd doped PbO2 electrodes produced by pulse electrodeposition. Morphologies and structures of the electrodes were studied by EDS, SEM, and XRD. They attribute increased activity for BPS oxidation to smaller crystallite size which increases the potential required to oxidize water.
The authors show impressive results for the electrochemical removal of BPS as compared to PbO2 electrodes without Nd, but I am not sure their data adequately supports their conclusions. One would expect the increased surface area to facilitate oxygen evolution as well.
There may be more complex phenomena occurring at the surface during catalysis. Several studies have shown that the surface of lead anodes changes drastically under oxidative conditions under similar electrolyte conditions (see refs: M. Xu, et al, Electrochim. Acta, 2016, 201, 240-250; J.F.K. Kotyk, et al, Coatings, 2018, 8, 246)
The authors should perform experiments to investigate their anodes post-electrolysis more thoroughly (both electrochemically and using SEM, EDX, and XPS) to determine whether or not there are structural changes that could better support their hypothesis.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
- What is the role of NaF in the deposition solution for preparing Ti/PbO2-Nd electrode?
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We recommend reviewing the sentence shown in lines from 138 to 142 because there is some confusion between the chromatographic apparatus and the mass detector. It is suggested that an HPLC-MS system is an ifenate system consisting of a chromatographic apparatus (HPLC) and a mass detector (MS). Furthermore, it would be appropriate to express the chromatographic and mass parameters: solvents, flow rate, gradient, type of source (experimental ionization conditions) and type of detector (quadrupole, TOF ...).
- In figures from 1 to 4 it is necessary to indicate which image is a, b, c ...
- It is recommended to improve the caption of the figures, especially in the "electrochemical" figures it is recommended to report the experimental conditions used.
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In SEM figure, is it possible to report the voltage, spot and
magnification used for each image? -
Section 3.6 has been referred to as "Mechanism of the electrochemical oxidation of BPS by Ti/PbO2-Nd". However, no reference is made in the paragraph to the role of Nd in the mechanism. Is it possible to say something else about it?
- In table 2 the structures c and d are the same molecule obtained simply with a rotation of the phenol by 180° along the S-phenol bond. Furthermore, different chemical structures are reported for the same m/z values. Have you thought of carrying out an MS/MS analysis to try to uniquely identify the structure?
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have done a good job addressing my comments. They need to do one final check of their reference numbering to ensure that the numbers correspond to the appropriate place in the manuscript (there are a couple instances where there are numbering errors) and perform minor grammatical corrections, then the paper is appropriate for publication.
Author Response
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Author Response File: Author Response.docx
Reviewer 2 Report
- In the paragraph “Analytic method” it isn’t clear if you have used two different methods to analyze the concentration of BPS and intermediate products. It would be appropriate to clarify if the analyzes of the concentrations of the BPS were carried out with an HPLC-UV, while those of the intermediate products with HPLC-MS. If this were not the case, then the insertion, at line 150, of a UV wavelength and then, at line 154, the sentence “The other parameters are the same as HPLC” are not justified. Clarify this aspect.
- In the paragraph “Analytic method” on line 148 you still refer to an "Agilent 1200 high performance liquid chromatography spectrometry (HPLC)", this review repeat that or the word spectrometry is superfluous or you should use for instance high performance liquid chromatography mass spectrometry (HPLC-MS) or high performance liquid chromatography coupled with UV detector (HPLC-UV), if you use UV to detect the concentration of BPS .
- You have not answered to my previous comment. Have you thought about performing an MS/MS analysis to try to uniquely identify the structure? Having used a triple quadrupole, it would be feasible.
Author Response
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Author Response File: Author Response.docx
Round 3
Reviewer 2 Report
This referee feels obliged to make a clarification. To my question "Have you thought about performing an MS/MS analysis to try to uniquely identify the structure? Having used a triple quadrupole, it would be feasible.", you replied "We have not performed MS/MS analysis to try to uniquely identify the structure because of the limitation of instruments."
Consider that it is not a correct answer to give because a triple quadrupole can safely perform MS/MS analysis.
