Adsorption Capability and Mechanism of Pb(II) Using MgO Nanomaterials Synthesized by Ultrasonic Electrodeposition
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript examines the process of synthesizing magnesia nanomaterials via the so-called ultrasonic electrodeposition technique. The obtained material is characterized as an adsorbent for the removal of Pb(II) ions. I have several comments that the authors need to address before their work can be recommended for publication.
1. The title of the manuscript is formulated ambiguously and confusingly. It might give the impression that the final words "for Pb(II)" pertain to "electrodeposition." However, this is not the case. Thus, the title needs to be significantly revised.
2. It is necessary to unambiguously explain the electrochemical and/or chemical processes occurring at the cathode during the deposition of magnesia. What is the chemistry and mechanism of these processes? How does ultrasonic treatment affect the kinetics of these processes? All of this should be analyzed in detail, as these are key questions regarding the scientific foundations of the nanomaterial synthesis discussed in the manuscript.
3. It is unclear why lead salt (0.1 g/L, Table 1) is added to the plating solution. What happens if it is not added? Presumably, electrodeposition will still occur? Metallic lead should co-deposit at the cathode if Pb(II) ions are present in the aqueous solution.
4. The properties of the coatings deposited at different ultrasonic powers should be compared with those of coatings deposited without the use of ultrasound. Otherwise, it is difficult to correctly assess the impact of ultrasonic treatment.
5. Can BET adsorption isotherms be provided in their linear form? What is the influence of ultrasound on the parameters of the BET equation?
6. The authors analyze adsorption kinetics data using pseudo-second-order and pseudo-first-order kinetics models. Which model is appropriate in this case? This should be clearly stated in the paper. Both models cannot be valid simultaneously, as this would contradict the physical meaning of kinetic equations of different orders.
7. It is necessary to specify the dimensions of the rate constants in the table; otherwise, these data lose their meaning.
8. When characterizing the effect of temperature on adsorption, the impact on thermodynamic parameters and the kinetics of the process should be considered separately.
9. Fitting adsorption isotherms should be checked and conducted in the linear coordinates of the respective equations.
10. The dimension of the Langmuir equilibrium adsorption constant should be specified in the Langmuir adsorption equation.
Author Response
Dear Professors,
Thank you for your useful comments. We would like to thank the referees for their kind suggestions regarding our article. The changes in the revised paper have been done in blue color.
Below you can find our point-by-point response to the referees’ comments.
Yours sincerely,
Dr Dan Tang
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article mentioned the adsorption study of Pb using MgO prepared by ultrasonic electrodeposition. There is no significant novelty along with a small discussion of the adsorption behaviour of the MgO nanomaterials prepared at different ultrasonic power electrodeposition. The study needs to be redesigned to be published in a scientific journal. Here are some points of view to improve the study.
1. The authors mentioned the mechanical polishing of 304 stainless steel before electrodeposition. How do the authors do the polishing? Is it automatic or manual? The author mentioned this polishing is important for coating. So it is important to reproduce similar roughness to optimize the roughness factor for the coating. The author should provide evidence about this in the manuscript.
2. What is the thickness of the MgO coating? Does it change with the different ultrasonic power electrodeposition?
3. What is the current profile for the electrodeposition? What is faradic efficiency for different ultrasonic power deposition?
4. From XRD it seems there are still MgO peaks after Pd adsorption. The authors should mention the MgO peak and Mg(OH)2 peak in both XRD figures.
5. What is the mechanism to change the grain size of MgO at 150 W ultrasonic power electrodeposition? The authors need to mention this in the manuscript along with the grain size value for each sample.
6. The author also needs to add the EDX elemental mapping before claiming uniform magnesia dispersion in Fig 4a. Please mention the correct line for each plane detected in the SAED image (fig. 4d). Surprisingly, there is no figure caption for Fig 4.
7. Although the authors claimed that increasing the ultrasonic power improved the BET-specific surface area, there is no discussion of lowering the surface area from 150 W to 200 W ultrasonic power.
8. Data from the fitting curve have a lower correlation coefficient, R2 value for the 100 W sample (Table 2). There is no trend for K1 in the PFOK model. The authors should discuss these points in the manuscript.
9. The authors use pH 4.5 for the temperature-dependent study (Fig 7) whereas pH 6.0 for the adsorption kinetics study (Fig 6) and isothermal adsorption study (Fig 8). Later the pH study (Fig 9) showed that pH 7 had the highest adsorption capacity. Why is there inconsistency in the solution pH for different studies? As solution pH is very important for the adsorption of Pb using MgO, it is better to discuss the pH effect at the beginning of the discussion and then follow the rest discussion to conclude the adsorption mechanism.
10. The error bar in all the figures looks the same. How many times did the authors check for each point for each experiment?
11. The authors mentioned the FTIR in the abstract and conclusion. However, there is no FTIR discussion in the main manuscript.
Author Response
Dear Professors,
Thank you for your useful comments. We would like to thank the referees for their kind suggestions regarding our article. The changes in the revised paper have been done in blue color.
Below you can find our point-by-point response to the referees’ comments.
Yours sincerely,
Dr Dan Tang
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis manuscript can be accepted for publication after the authors provide sufficient responses to the following comments:
1. In Section 2.3, the authors added small amounts of organic matter and clay minerals. What kind of organic matter and clay minerals did they use in the study? How many grams of each were added to the system?
2. The addition of clay mineral will influence the adsorption of Pb.
3. In Figure 5(b), the legend of the y-axis is not correct.
4. The mathematical expression of the kinetic as well as isotherm models should be given in the manuscript.
5. The legend of y-axis in Figures 6–8 should be amount adsorbed (mg/g)
Author Response
Dear Professors,
Thank you for your useful comments. We would like to thank the referees for their kind suggestions regarding our article. The changes in the revised paper have been done in blue color.
Below you can find our point-by-point response to the referees’ comments.
Yours sincerely,
Dr Dan Tang
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors updated the articles according to the comments. However, there is some information missing. I suggest the authors include this information in the manuscript.
1. The author did not mention how they do the polishing. Is it manual or any specific instrument is used? What is the roughness value in a quantitative manner? Because it is essential to get a similar result every time.
2. Write the equations of MgO formation separately with the equation number in line 157 for better readability.
3. The author did not change the XRD figures. The authors should add the MgO and Mg(OH)2 reference peaks according to the JCPDS card in both Figure 3a and 3b. And If Mg(OH)2 peaks are shifted compared to the standard value then write the discussion. Also, calculate the lattice constant value and compare it with the standard value for MgO and Mg(OH)2.
Author Response
Dear Prof.,
Thank you for your useful comments.
We have corrected the paper according to the reviewer's comments.
Thank you very much!
Dr. Tan
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have provided sufficient responses to my comments, this manuscript can be accepted and published in journal.
Author Response
Dear Reviewer and editor,
Thank you for your useful comments.
Have a good day!
