Grafting of Polyethyleneimines on Porous Silica Beads and Their Use for Adsorptive Removal of Cr(VI) from Aqueous Medium
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe framework of this manuscript has promising results however some changes are required. Please find my comments below:
*Abstract, line 16: Do not use abbreviations at the first appearance. Replace “Cr(VI)” with “hexavalent chromium (Cr(VI))”.
*Mention in the Abstract the characterization that has been conducted (NMR and XPS analysis).
* Add references for the following:
- Lines 42-44.
- Lines 46-48.
- Lines 64-67.
*In the Introduction section, you need to talk about the previous studies in more detail to link previous research with the current research. You have referred only to your previous research, which is not sufficient. Please explain at least the recent 5 papers' methodologies and main findings. And, then you can link with your research.
-Please mention previous studies that have used different adsorbents for Cr(VI) removal.
-Please also mention previous studies that have used “Polyethyleneimines on Porous Silica Beads” for adsorption of other contaminants.
*Lines 157-160: should be part of “Materials and Methods” section.
*Replace “Scheme 1.” with “Figure 2”
*Line 179: replace “are prepared according to a proposed reaction scheme 1 [20,33,34].” With “are prepared according to a proposed reaction scheme shown in Figure 2 [20,33,34].”
*Lines 216-219: Explain the reason why the maximum adsorption capacity of 1.06 mmol/g was obtained at the content of amino groups of 2.17 mmol/g. What is the scientific reason behind such behavior? Support your explanation with references.
*Explain the abbreviations in Equations 3 and 4 below each equation.
*Line 333: Please check this statement “The adsorption capacity increased with an increase in the Cr(VI) ion concentration.” Because normally the reverse happens.
*Mention the optimum condition of your study in the Abstract and Conclusion section.
pH 3, Temp. 30oC, dose 0.1 g/L, Cr(VI) conc. 10.4 mg/L, and mention the Qmax 58.7 mg/g
*Please create a new section after the conclusion to state the limitations of your study or you can add the limitations of your study at the end of the conclusion section.
Comments on the Quality of English Language
Moderate editing of English language required.
Author Response
We received e-mail and greatly thanked the reviewers in giving valuable comments and suggestions for our manuscript. We accepted many of the comments and suggestions from the reviewers and revised our manuscript to publish in Journal, physchem. Our replies to the reviewers and revisions are described as follows. The corrections are in red in the revised manuscript.
Answers to Reviewer 1
Comment #1 on abbreviation of Cr(VI)
Reply: In Abstract, Cr(VI) was defined as hexavalent chromium (L16).
Comment #2 on characterization obtained by XPS and NMR
Reply: The characterization of the grafting of BPEI and LPEI, preparation of LPEI were described in Abstract. See L18-20.
Comment #3 on addition of references
Reply: Some references were transferred and added on Cr(III) and Cr(VI) (refs [1,2]), toxicity of Cr(VI) (refs [2,3]), viability of adsorption (refs [16,17]). The reference numbers were rearranged. See L47-51 and L72.
Comment #4 on methodologies of other studies
Reply: The preparation of adsorbents for Cr(VI) ion adsorption prepared through the modification of silica particles with amino-group containing silane coupling agents and through the subsequent functionalization of BPEI was described and explained in detail (L75-83). In addition, the application of these adsorbents to removal of other metals and contaminants was also described. Here, we used the term “particles” in place of “beads” with respect to the originality (L88-93). Some related references were added. In these paragraphs, we cited 8 references according to the reviewer’s comment. The reference number was rearranged throughout the manuscript.
Comment #5 on the sentence (L157-160) in the first manuscript
Reply: I think that it is a little sudden to start with a sentence on the experimental results. In order to lead readers to understand, the sentence on the conditions of the adsorption experiments is left as it is without revisions (L175-178). We hope that the reviewer accepts our opinion.
Comment #6 on replacement of Scheme 1 with Figure 2
Reply: We replaced Scheme 1 with Figure 2. In the revised manuscript, the term of “Figure” was used and the figure number was rearranged (L197 and 223-224).
Comment #7 on the maximum value of adsorption capacity
Reply: In many articles on Cr(VI) ion adsorption, the amount (content) of functional groups are not shown or determined. For these articles, the maximum value of the adsorption capacity cannot be discussed. It is difficult for us to deeply or correctly answer this suggestion. However, the maximum value was briefly described and discussed. In our revised manuscript, some discussions with the hydration radius of CrO2- 4 ions were added (L236-243) and related references were added.
Comments #8 on the abbreviation in Equations 3 and 4
Reply: All symbols used in this manuscript are listed in Nomenclature on page 16. The symbol of “t” in Equations 3 and 4 was added and defined. Therefore, the sentences related are not changed (L261).
Comment #9 on the concentration dependence of adsorption capacity
Reply: It is general that the Cr(VI) ion adsorption capacity increases with an increase in the Cr(VI) ion concentration of the outer solution. In our previous papers on Cr(VI) ion adsorption (for example, refs. 18, 35, 36, and 71). Therefore, the description is left as it is (L359).
Comment #10 on the description of optimum and maximum conditions of Cr(VI) adsorption
Reply: As the Cr(VI) ion adsorption capacity was already described in Abstract (L24-26), we didn’t describe an additional explanation in Abstract. However, according to the comment from reviewer, we added some descriptions and explanations in the conclusion section (L487-490).
Comment #11 on Limitations of our study
Reply: According to the comment, some sentences were added at the end of the conclusion section. Although we have some concrete or specific solutions (L514-519), they cannot be described in the conclusion section to keep them. We hope that the reviewer accepts our opinion.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe conclusions of the manuscript completely repeat the abstract. It should be rewritten to recommendations for practical use or the importance of the results for general ideas.
Figures can be presented in colors.
What chemical reaction, according to the authors, occurs between the adsorbent and chromium ions Cr(VI) ?
It is necessary to sign the figures (a), (b), (c) and (d) on the corresponding graphs.
Author Response
We received e-mail and greatly thanked the reviewers in giving valuable comments and suggestions for our manuscript. We accepted many of the comments and suggestions from the reviewers and revised our manuscript to publish in Journal, physchem. Our replies to the reviewers and revisions are described as follows. The corrections are in red in the revised manuscript.
Answers to Reviewer 2
Comment #1 on conclusion section
Reply: We revised Abstract and added some sentences in Abstract section according to the reviewer 1. The corrections are in red in the revised manuscript (L16-20). In addition, we revised the conclusion section according to your and the other reviewer’s comments (L488-497, 504-509, and 514-519). The findings obtained in this study, limitations of this study, and our future efforts were described and explained.
Comment #2 on color presentation of figures
Reply: We have drawn all figures in black-and-white in our publications. Therefore, all figures are drawn in black-and-white and not in color in this manuscript. We hope that the reviewer accepts our opinion.
Comment #3 on symbols (a)-(d)
Reply: We must apologize the unclear representation. In the captions of Figures 3, 4, 6, 10, the sign of (a), (b), (c), and (d) were deleted. See the titles of each Figures (L226-227,for Figure 3, L256-258 for Figure 4, L300-302 for Figure 6, and L445-448 for Figure 10). On the other hand, The sign of (a), (b), (c), and (d) is left as it is in Figure 1.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsLines 45-47 – cited literature need to be added
Lines 52-52 -needs reformulation
Lines 61-67 -point out why the “adsorption is regarded as the most viable approach”
Line 98 characteristics of the material and not characters
Line 116 missing abbreviation explanation for LPEI
Line 150 missing the name of the spectrophotometer used for absorbance measurement
Increase the size of all figures in the manuscript (not in the supplementary file) because they difficult to read
Figure 3 it contains only experimental data. From the representation it seems that are points below the line or above the line giving the impression that the line is representing calculated data. The same for Figure 6, Figure S2 …. Usually if there is only experimental data this is represented by dots only.
Table 4 – it would be interesting if you could add a column with the BET values for comparison purposes
Also it would be interesting to add the determination of pH point of zero charge of the adsorbents. This is a characteristic that is presented in performing the evaluation of the adsorption capacity of materials.
How do you foreseen the subsequent recovery of Cr (VI) from your material, or you just simply dispose off the saturated adsorbents?
Have you noticed any material degradation of the adsorbents during your experiments?
Regarding the measuring units, in order to make comparisons it is used the same for instance you have used for time, h , min
Comments on the Quality of English Language
Minor English revision
Author Response
We received e-mail and greatly thanked the reviewers in giving valuable comments and suggestions for our manuscript. We accepted many of the comments and suggestions from the reviewers and revised our manuscript to publish in Journal, physchem. Our replies to the reviewers and revisions are described as follows. The corrections are in red in the revised manuscript.
Answers to Reviewer 3
Comment #1 on addition of references
Reply: We added new references on toxicity of Cr(VI) ions. See L51.
Comment #2 on representation on chromium discharge limits
Reply: We revised this representation to “limitation of chromium discharge to the aquatic environments” according to the reviewer’s comment. See L55.
Comment #3 on viable approach of adsorption process
Reply: Additional descriptions or explanations on the main reasons for the viable approach. See L67-68.
Comment #4 on representation of characters
Reply: We appreciate your comment. This is our careless error and revised to the term of “characteristics”. See L114.
Comment #5 on the definition of LPEI
Reply: We appreciate your comment. This is our careless error and defined the abbreviation of LPEI See L135-136.
Comment #6 on the model of spectrophotometer
Reply: We appreciate your comment. This is our careless error and described the model of the used spectrophotometer and its manufacturer. See L165-166.
Comment #7 on the size of figures
Reply: According to reviewer’s comment, the size of all figures was expanded from the reduced scale of 65% to 70%. See each figure in the revised manuscript.
Comment #8 on the lines in the figures
Reply: We have drawn all figures with plots with lines like the figures shown in this manuscript. In addition, I received such comment first time. Therefore, we show the all figures with plots and lines. We hope that the reviewer accepts our opinion.
Comment #9 on the use of BET isotherm
Reply: We can understand the reviewer’s comment and it is a useful suggestion. Since the adsorption process in this study well followed Langmuir isotherm and the adsorption behavior was discussed using the analytical results obtained by Langmuir isotherm in the sections 3.6 and 3.7. Therefore, analysis of adsorption process by BET isotherm is not performed in this study. However, we will plan to use BET isotherm in the next submission on adsorption. We hope that the reviewer accepts our opinion.
Comment #10 on the determination of zero charge of the adsorbents
Reply: This comment is useful for our study. Unfortunately, we don’t have a zeta potential instrument in our campus. As the results on zeta potential on the particle surface are of great use, we have to purchase it.
Comment #11 on the recovery of Cr(VI)
Reply: The recovery of Cr(VI) is an important assignment for this study. In the next submission of a manuscript on Cr(VI) ion adsorption of silica beads functionalized with LPEI and BPEI and other amino-group containing polymer (for example, polyallylamines) with different molecular weights, we will discuss the desorption of Cr(VI) and regeneration of the functionalized silica beads. On the basis of the experimental results obtained in this study and in our previous studies, desorption of Cr(VI) is expected through the deprotonation with NaOH and/or the ion-exchange with NaCl.
Desorption of Cr(VI) ions was explained at the end of the conclusion section as a future prospect (L514-516).
Comment #12 on the degradation of BPEI-silica beads
Reply: In appearance, no or little degradation of the BPEI-silica beads is observed during the adsorption experiments. In the next manuscript, we will perform the desorption experiments. At that time, if the adsorption performance, such as the adsorption capacity, adsorption rate, and desorption % are kept constant for the repetitive adsorption-desorption cycles, the stability of the BPEI-silica beads can be experimentally explained and discussed.
Comment #13 on the unit of the time.
Reply: We used “min” and “h” as the unit of the time on purpose. For example, under some experimental conditions, the half-time is very short. Some of the half-times are within 1 h, or 60 min. In this case, it is comprehensible to use the unit of min. In addition, for the explanation of the intra-particle diffusion rate constant, the use of the min unit is common. On the other hand, when the initial late is represented in the min unit, the numerical is too small. Therefore, the initial rate was shown in the h unit. We consciously and properly use the unit of time, min and h in this manuscript. We hope that the reviewer accepts our opinion.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsLine 55 – 56 “Its own legislation on chromium emissions as follows [10,11]. “ this sentence needs a verb -english revision. Also this is repetitive, the previous sentence states the same thing.
Line 57-58 , You state that the limit for Cr6+ in USA is 0.05mg/L, by citing an article. When giving the limits of some contaminant in water, air, soil, etc you should always cite the directive or the authority that regulates that limit
In this case according to the link below the limit is 0.1 mg/L for TOTAl chromium
https://www.epa.gov/sdwa/chromium-drinking-water#:~:text=Agency%20will%20follow%3F-,What%20are%20EPA%27s%20drinking%20water%20regulations%20for%20chromium%3F,chromium%2C%20including%20chromium%2D6.
Please change accordingly the value and citation.
The same for citations 10-14 you should update them with the directive in force and not articles that are maybe citing some old directives that are no longer valid.
Line 67-68 , you have added a very short enumeration of advantages without citing publications in support of that. Please change it.
Comment # 12
You should add a short sentence about the stability of the tested adsorbents.
Comments on the Quality of English Language
Minor editing of English language required
Author Response
We received e-mail and greatly thanked the reviewers in giving valuable comments and suggestions for our manuscript. We accepted many of the comments and suggestions from the reviewers and revised our manuscript to publish in Journal, physchem. Our replies to the reviewers and revisions are described as follows. The corrections are in red in the revised manuscript.
Answers to Reviewer 2
Comment #1 on directive or reference on Cr(VI) and total Cr
Reply: We revised and added some sentences on maximum contaminant level and the limit of Cr(III) and Cr(VI). A related reference was cited. In addition, the reference numbers were rearranged.
See L57-62
Commenet #2 on regulation of Cr(VI)
Reply: regulations or guidelines were published as mentioned in L62-66. The reference was shortly explained. Therefore, as we revised these sentences in the past tense to represent the past facts. See L62-
Commenet #3 on citation of references on advantage of adsorption
Reply: We cited some references to explain the advantage of the adsorption process. Following this, the references numbers were rearranged. See L71. Unfortunately, the revision of guideline by Ministry of the Environment in Japan is released only in Japanese. There is no release in English. Therefore, the reference of 15 was cited. I hope that the reviewer accept our engagement.
Author Response File: Author Response.pdf
