Photocatalytic Efficacy of Heterocyclic Base Grafted Chitosan Magnetite Nanoparticles on Sorption of Pb(II); Application on Mining Effluent

Round 1

Reviewer 1 Report

1. What are the particles presented in Fig.1A TEM image, if the average size of the sorbent is around 10 μ Moreover, the SEM image is very poor in quality and charged. Kindly provide a clear image at different magnifications and indicate the sorbent morphology size.
2. The sentence is unclear; kindly reframe it to make it clear and precise. “The broadness peak at 3427 cm^-1 for MCc, 3447 cm^-1 for MCa-ATA, at 3425 as Pb sorption, and 3412 cm^-1 after 5 cycles of sorption”. The authors are suggested to replot the image Fig.3 in a stacked form for the clear identification of bands without overlapping.
3. Why are the sorption properties stabilized at pH 5? Provide the studies at neutral and higher pH.
4. What is the reason for stable performance from kinetics study after 2 hours in light and UV?
5. Why its 0.2 M HCl for desorption studies? What is the parameter playing a role in desorption time?
6. List out the advantage of using MCa-ATA over the MCc in absorption and desorption studies.
7. Kindly check the grammatical errors in the entire manuscript.

Author Response

Response to Reviewer#1

Red: Response to reviewer’s comments

Blue: New information/comment added to the manuscript

First, we would like to thank you for your interest in our contribution, for your general positive evaluation and for your fruitful comments.

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

We would like to thank the reviewer for the positive evaluation of the work. This is appreciated.

The manuscript was carefully checked.

Comments and Suggestions for Authors

1. What are the particles presented in Fig.1A TEM image, if the average size of the sorbent is around 10 μ Moreover, the SEM image is very poor in quality and charged. Kindly provide a clear image at different magnifications and indicate the sorbent morphology size.

Thanks for the notification, Actually the size in the TEM image (Fig. 1A) is 50 nm, while the Sem image (Fig. 1B) is 10 μm. We try best for increasing the image quality and hope it is clear now in the revised version. Also, we provide the XRD analysis to this figure for supporting the sorbent characterization.

1. The sentence is unclear; kindly reframe it to make it clear and precise. “The broadness peak at 3427 cm^-1 for MCc, 3447 cm^-1 for MCa-ATA, at 3425 as Pb sorption, and 3412 cm^-1 after 5 cycles of sorption”. The authors are suggested to replot the image Fig.3 in a stacked form for the clear identification of bands without overlapping.

Thanks, it was reframed as follow:

The broadness peak at 3427, 3447, 3425, 3412 cm^-1  for MCc, MCa-ATA, MCa-ATA+Pb, and after 5 cycles of sorption desorption respectively are related to OH and NH stretching bands

Also figure 3 was rearranged for decreasing the overlapping of peaks

1. Why are the sorption properties stabilized at pH 5? Provide the studies at neutral and higher pH.

Thanks for the comment

As discussed in the result section; the higher pH values cause protonation for the functional groups (to  be positive charge), which cause a repulsion effect with the cationic metal ions (Pb²⁺), this also leads for making unavailable electrons on the functional groups for binding which considered the main reason that decreasing the sorption at higher pH values. It is noteworthy that as the pH increased the positively charged density on the function groups decreased with increasing the ability for binding with metal ions (decreasing the repulsion effect). After pH 5 and as reported from figure 4 of the data collected from the pH_pzc of the MCc and MCa-ATA sorbents, that the sorbents being completely negatively charged at around pH 6 and 5 respectively, which indicating that the functional groups of the sorbents are available completely for binding. This is parallel to our results that pH 5 is the optimum for loading and the sorption is slightly increased comparing to the acidic and mild acidic pH conditions.  

1. What is the reason for stable performance from kinetics study after 2 hours in light and UV?

It seems there is a typing error from the reviewer in which the maximum saturation was achieved during 15 min for MCa-ATA and 30 min for MCc. From the kinetic results (report in figure 6), the kinetic sorption was performed for 48h with two profiles; firstly, a steep increasing (related to sorption of metal ions from the functional groups on the sorbent surface), followed by slightly increasing, which related to sorption via functional groups in the pores of sorbents. From TEM analysis, the organic materials are represented as a thin layer, this limit the intraparticle diffusion effects of metal ions and make the sorption of the first stage is the main profile at either light or UV. The completely sorption were performed after 15 min of contact for MCa-ATA comparing to 30 min for MCc, the first 10 min of contacts achieved 85% of Pb sorption for MCa-ATA comparing to 60% for the MCc (this is the first stage of the profile), then the second stage seems to be also much faster in MCa-ATA (5 min) than MCc (20 min) as reported in the text.  

1. Why its 0.2 M HCl for desorption studies? What is the parameter playing a role in desorption time?

From the previous studies on the magnetite chitosan particles the most effective eluent is the 0.2M HCl, beside a limitation of loss of magnetite after recycling for more than 5 cycles, which making such reagent as one of the most effective desorbing agents

1. List out the advantage of using MCa-ATA over the MCc in absorption and desorption studies.

Thanks for this notification this was added in the conclusion section

From the sorption profiles of both MCa-ATA and MCc, it was shown that, the high performance of MCa-ATA over MCc (0.251 and 0.346 mmol Pb g^–1 in visible light and under UV respectively for the MCc comparing to 0.7814 and 1.014 mmol Pb g^-1 respectively for the MCa-ATA at the same condition. The sorption profiles of both sorbents show a highly kinetics of MCa-ATA (15 min) over MCc (20 min sufficient for complete sorption). The 85% of Pb sorption was achieved in the first 10 min for MCa-ATA comparing to 60% for the MCc. The MCa-ATA is a highly efficient for treatment of contaminated solution (including water). From the sorption/desorption experiments, it was shown that the sorbent is chemically stable with fast desorption profile. The sorbent shows a preference for Pb over representative elements, while less selectivity is obtained compared to Fe and U. It is a promising sorbent for recovering of heavy metal ions as well as removal of contaminants in polymetallic solution at high pH values under UV emission and used in a wide range of pH.

1. Kindly check the grammatical errors in the entire manuscript.

We carefully revised the manuscript and made corrections of typing mistakes and try best for correction the grammatical errors. We hope the revised version is now more understandable by the readers.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors present  the synthesis of nano magnetite chitosan particles functionalized with thiazole carboxylic acid derivative with full physically and chemically characterization by FT-IR spectroscopy, TEM , SEM-EDX, and TGA . The synthesized sorbent was used for the sorption of Pb(II) from synthetic solution through pH, sorption kinetics, and sorption isotherms followed by studying the sorption from synthetic simulated nature solution.

The work is well presented and clearly outlined, supported by the evidence and appropriate conclusions. Before accepting the manuscript, I would like to propose some minor changes and suggestions:

In the introduction part, the authors mention XRD as a method used in the research. With all dues respect, the XRD was not used.

The elemental analysis does not need to include three decimal points.

Could you please comment on how come the water release in the TH curve is happening at such a high temperature (above 200 °C), since it is known that water release usually occurs around 100-150 °C?

Fig 7 and  8, could you please simply connect the points and not draw the ideal curve? Or leave the points without a curve.

Please include the number of mole and not only mass in the experimental part.

Please include the TGA setup, the instrument data, and the type of crucible in which the same was analyzed.

Please include the future perspectives of the research in the conclusion part.

Author Response

Response to Reviewer

Red: Response to reviewer’s comments

Blue: New information/comment added to the manuscript

First, we would like to thank you for your carful revision, evaluation and your valuable comments. We try best answering the comments and made the corrections, we hope it will meet with your approval.

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

The authors present  the synthesis of nano magnetite chitosan particles functionalized with thiazole carboxylic acid derivative with full physically and chemically characterization by FT-IR spectroscopy, TEM , SEM-EDX, and TGA . The synthesized sorbent was used for the sorption of Pb(II) from synthetic solution through pH, sorption kinetics, and sorption isotherms followed by studying the sorption from synthetic simulated nature solution.

The work is well presented and clearly outlined, supported by the evidence and appropriate conclusions. Before accepting the manuscript, I would like to propose some minor changes and suggestions:

In the introduction part, the authors mention XRD as a method used in the research. With all dues respect, the XRD was not used.

Thanks for notification it was added as figure 1C for increasing the sorbent characterization

And this was added

Figure 1C represents the XRD diffraction pattern analysis of the MCa-ATA sorbent. The magnetite was characterized by matched through nine peaks reported at 2θ = 18.2700, 30.2500, 35.5474, 37.3469, 43.1967, 57.0873, 62.6265, 81.4031 and 82.2235 degrees. These peak signals are corresponding to the magnetite (JCPDS: 01-077-1545). Table S1 shows the diffraction patterns positions of the XRD peaks with comparing to the reference file.

The elemental analysis does not need to include three decimal points.

Thanks, it was corrected

Could you please comment on how come the water release in the TH curve is happening at such a high temperature (above 200 °C), since it is known that water release usually occurs around 100-150 °C?

Thanks, the reviewer is correct, but in some modified crosslinking materials, some peaks were shifted toward higher temperature values. According to the literature survey, the crosslinked or modified materials are realizing water at high temperature than the low thermally stable or volatile one.  Reddy et al [1], assigned the water release of alginate based on silver nanocomposite hydrogels at 230°C, while Lee et al [2] reports the water release from neat cellulose acetate (CA) and CA/ Ni(NO₃)₂·6H₂O matrix polymers ranged from 200°C to 300°C depending on the process used. Others assigned the absorbed water release from volatile compounds below 200°C [3] 

[1] Reddy, P., K. Madhusudana Rao, K. S. V. Rao, Yury Shchipunov, and Chang-Sik Ha. "Synthesis of alginate based silver nanocomposite hydrogels for biomedical applications." Macromolecular Research 22, no. 8 (2014): 832-842.

[2] Lee, Woong Gi, Do Hyeong Kim, Woo Cheol Jeon, Sang Kyu Kwak, Seok Ju Kang, and Sang Wook Kang. "Facile control of nanoporosity in Cellulose Acetate using Nickel (II) nitrate additive and water pressure treatment for highly efficient battery gel separators." Scientific reports 7, no. 1 (2017): 1-9.

[3] Ismail, N. H., W. N. W. Salleh, N. Sazali, and A. F. Ismail. "Effect of intermediate layer on gas separation performance of disk supported carbon membrane." Separation Science and Technology 52, no. 13 (2017): 2137-2149.

Fig 7 and  8, could you please simply connect the points and not draw the ideal curve? Or leave the points without a curve.

Thanks for notifications, we not agree with the reviewer, we usually draw the ideal curves to avoid confusion of the readers, we would like to thank the reviewer for understanding, but if you insist, we can modify it.

Please include the number of mole and not only mass in the experimental part.

Thanks, it was added in the revised version.

Please include the TGA setup, the instrument data, and the type of crucible in which the same was analyzed.

Thanks for comment. We modify it and this sentence was added

the sample weight is around ~1.978 and 2.64 mg for MCc and MCa-ATA respectively, it is occurred in aluminum crucibles at temperature around 30 to 800 °C, under nitrogen atmosphere for temp. ramp 10 °C min^-1.

Please include the future perspectives of the research in the conclusion part.

Thanks for comment. This sentence was added

The MCa-ATA is a highly efficient for treatment of contaminated solution (including water). From the sorption/desorption experiments, it was shown that the sorbent is chemically stable with fast desorption profile. The sorbent shows a preference for Pb over representative elements, while less selectivity is obtained compared to Fe and U. It is a promising sorbent for recovering of heavy metal ions as well as removal of contaminants in polymetallic solution at high pH values under UV emission and used in a wide range of pH.

Author Response File: Author Response.docx

Reviewer 3 Report

The said paper can be accepted for publication after minor corrections. 

Author Response

Response to Reviewer#3

Red: Response to reviewer’s comments

Blue: New information/comment added to the manuscript

We would like to thank you for reviewing our manuscript and your global recommendation.

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

The said paper can be accepted for publication after minor corrections. 

Thanks for the global recommendation, we check the manuscript and hope the  revised version will be suitable for publication now.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The manuscript is suitable for publication.