Synthesis of Sulfur-Grafted Chitosan Biopolymers and Improvement to Their Sorption of Silver Ions from Different Aqueous Solutions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript, titled “Synthesis and Improvement the Sorption Properties of Silver Ions from Different Aqueous Solutions by Sulfur Grafted Chitosan Biopolymer” describes the development of a chitosan-based biopolymer for the sorption of silver particles from aquatic environment. The authors characterized the sorption properties of produced biopolymers using FTIR, SEM, SEM-EDX, BET, elemental analysis, TGA and so on. The hydroxyl, amine, and thiol groups contributed to the silver binding mechanisms, with optimum sorption achieved around pH 6. The authors successfully used the formulated sorbents for the recovery of Ag (I) from waste spent films.

The experimental design appears sound, and the findings are interesting. However, there are limitations and errors in language detected, and there are opportunities for improvement in the overall writing style. Certain sentences and statements lack adherence to scientific norms. Therefore, I recommend accepting the manuscript after mitigating the following issues:

 

 Some specific comments:

1.      Abstract: The abstract lacking major findings with quantitate values. The authors should improve the abstract section providing the attractive features of results with distinct values.

2.      Introduction: The first 2 paragraphs should be merged together. Please group the information and display in 4-5 paragraphs.

3.      Introduction: Line 63; Solvent extraction techniques from high concentrated solution [19-21]. The sentence in incomplete.

4.      Lines 61-71; There are many studies performed to remove the ions from water. Why do the authors required to undertake the present study? The authors should state the justification of the present study.

5.      Materials and Methods: Synthesis of the adsorbents. Lines 113-120: The authors should state in assertive sentence. The sentences are not completed.

6.      Materials and Methods: Write the elaboration of ICP-AES during first use. Similarly, use the elaboration in first use of others abbreviated forms.

7.      Results and discussion: FTIR spectra: How about evaluating the water by FTIR analysis before and after purification? This may show distinctly the performance in removing Ag particle.

8.      Results and discussion: TGA; The authors should discuss the significance of thermal degradation of sorbents in performing Ag particle removal.

9.      Conclusion: Line 445; Theis should be This….

10.  The authors should provide future directions of this study in conclusion part.

11.  The authors should narrate in past form throughout the manuscript.

12.  References: The authors are suggested to reduce the number of references. They should confine the number in 60 based on the appropriateness.

Comments on the Quality of English Language

There are limitations and errors in language detected, and there are opportunities for improvement in the overall writing style

Author Response

sustainability-3005755

Responses to reviewer#1

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

 Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
(x) Moderate editing of English language required
( ) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are all the cited references relevant to the research?	( )	( )	(x)	( )
Are the research design, questions, hypotheses and methods clearly stated?	(x)	( )	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	( )	(x)	( )	( )
For empirical research, are the results clearly presented?	(x)	( )	( )	( )
Is the article adequately referenced?	( )	(x)	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	( )	(x)	( )	( )

 

Comments and Suggestions for Authors

The manuscript, titled “Synthesis and Improvement the Sorption Properties of Silver Ions from Different Aqueous Solutions by Sulfur Grafted Chitosan Biopolymer” describes the development of a chitosan-based biopolymer for the sorption of silver particles from aquatic environment. The authors characterized the sorption properties of produced biopolymers using FTIR, SEM, SEM-EDX, BET, elemental analysis, TGA and so on. The hydroxyl, amine, and thiol groups contributed to the silver binding mechanisms, with optimum sorption achieved around pH 6. The authors successfully used the formulated sorbents for the recovery of Ag (I) from waste spent films.

The experimental design appears sound, and the findings are interesting. However, there are limitations and errors in language detected, and there are opportunities for improvement in the overall writing style. Certain sentences and statements lack adherence to scientific norms. Therefore, I recommend accepting the manuscript after mitigating the following issues:

We thank the reviewer for his/her globally evaluation and We hope the revised version is meaningful making the manuscript readable.

 Some specific comments:

1. Abstract: The abstract lacking major findings with quantitate values. The authors should improve the abstract section providing the attractive features of results with distinct values.

Thanks for your comment, we try best to improve it and support with data.

2. Introduction: The first 2 paragraphs should be merged together. Please group the information and display in 4-5 paragraphs.

Thanks for alerting, we check and it was revised

3. Introduction: Line 63; Solvent extraction techniques from high concentrated solution [19-21]. The sentence in incomplete.

Thanks for alerting; it was corrected

3. Lines 61-71; There are many studies performed to remove the ions from water. Why do the authors required to undertake the present study? The authors should state the justification of the present study.

Thanks for your comment, this was mentioned through this paragraph, According to the  disadvantages of the most of the recent methods which used for recovering of silver; including consumption of energy, low efficiency and produced toxic by-products. This oriented the authors to develop process with low-cost, effective, and sustainable for recovering of silver with high efficiency.

This was added at the last paragraph of the introduction

This work concerns with developing of manufacturing process with low-cost, effective, and sustainable for recovering of silver with high efficiency by functionalized chitosan composite biopolymer through reaction with thiourea using of formaldehyde as coupling agent in water media (without using solvent). This work was performed due to the disadvantages of most recent methods used for recovering of silver (including high consumption of energy, low efficiency and producing of toxic by-products).

5. Materials and Methods: Synthesis of the adsorbents. Lines 113-120: The authors should state in assertive sentence. The sentences are not completed.

Thanks for alerting, it was revised and improved

6. Materials and Methods: Write the elaboration of ICP-AES during first use. Similarly, use the elaboration in first use of others abbreviated forms.

Thanks for alerting, it was revised as well as the whole manuscript

7. Results and discussion: FTIR spectra: How about evaluating the water by FTIR analysis before and after purification? This may show distinctly the performance in removing Ag particle.

Actually, the spectra shows difference in the spectra before and after purification of solution and after elution this appeared from shifts of some peaks and displacement od others as discussed in the core of the manuscript.

8. Results and discussion: TGA; The authors should discuss the significance of thermal degradation of sorbents in performing Ag particle removal.

We usually perform the TGA analysis for the sorbents to show the thermal degradation of each group and detect the overall stability. On the other hand, it used for comparing the thermal stability of the sorbent before and after modification for verifying the grafting. We thought TGA for eluted samples did not make sense and it is abnormal uses in the researches, we always  did the FTIR after cycling to verify stability and no changes in the chemical formula. But if the reviewer insists to make it, we will try to do.     

9. Conclusion: Line 445; Theis should be This….

Thanks, it was corrected

10. The authors should provide future directions of this study in conclusion part.

Thanks for your comment

This was added

Moreover, the modified biosorbent was synthesized by one pot process with green synthesis method (using water instead of solvent), shows a significant selectivity for Ag(I) over several ions (cations and anions) in a poly-metallic acidic leaching solution. This study provides a novel and eco-friendly sorbent for efficient Ag+ recovery, reflecting its potential application toward environmental monitoring with advantage in conducive to reuse it for long-term of the practical applications.

11. The authors should narrate in past form throughout the manuscript.

Thanks, it was revised  

12. References: The authors are suggested to reduce the number of references. They should confine the number in 60 based on the appropriateness.

Sorry we did not agree with the reviewer in his opinion. We try to support the data we provide in all parts of the manuscript “as much as we can do” by addition of references to be easily and as an evidence for the broad audience of the journal to get it.    

Comments on the Quality of English Language

There are limitations and errors in language detected, and there are opportunities for improvement in the overall writing style

Thanks for your alerting, we try best to improve the language and we hope the revised version is suitable and readable

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

ID: sustainability-3005755

Title: Synthesis and Improvement the Sorption Properties of Silver Ions from Different Aqueous Solutions by Sulfur Grafted Chitosan Biopolymer

 

Overview:

Authors investigate the ion metal sorption from aqueous solutions by modified chitosan-based polymer functionalized by cross-linking. Selectivity and reversibility of the obtained materials are demonstrated. The manuscript is scientifically coherent and convincing. However, there are several minor comments mostly related to wording and presentation issues, as well as two major comments associated with the clarification of conceptual aspects.

 

Major comments:

1) FTIR spectra: for CH-F and CH-TU, please elaborate on the origin of C=O peak at ~1620 cm-1 and its disappearance with sorption-desorption. According to the Schemes 1,2, no C=O bonds are expected in the structure (or Schemes 1 and 2 lack the C=O bonding which should be depicted in the red sites).

2) Although authors provide a brief explanation of the materials' selectivity in Section 3.2.4, they don't discuss the sorption mechanism in the first place. Do authors expect only oxygen and sulfur groups to be absorbance sites? Why =O is supposedly an active site and -OH is not? Do authors expect chelation [10.3390/polym10101090] to be manifested throughout absorption? Have authors investigated the absorption capabilities of pristine chitosan to verify that -OH and -NH2 groups don't play a role in the adsorption?

 

Minor comments:

3) Line 48, what do you mean by "Most of silver production derived as sub-products"?

4) Line 52-53, revise "Many countries were listed the silver" (passive voice not needed).

5) Line 62, revise "The upgrading of the concentration"

6) Scheme 1, should the reaction result in the production of oxygen-containing products? Oxygen from formaldehyde doesn't seem to bind to the resulting structure (or Schemes 1 and 2 lack the C=O bonding which should be depicted in the red sites).

7) Line 119, why do authors call the resulting structure "non-functionalized chitosan particles"? The resulting material is different from pristine chitosan.

8) Section 2.3, what is the resolution of FTIR spectrometer and what accelerating voltage was used for SEM studies?

9) Section 2.4: how was the Ag(I) concentration measured?

10) FTIR spectra: please elaborate on the origin of the spectral feature observed at 2300-2400 cm-1. Is it an instrumental effect?

11) FTIR spectra: as for the 3400 cm-1 peak, do authors attribute its emergence to adsorbed water [10.3390/jcs7070264], or do they expect some hydroxide groups in the structure? To me, it seems like the disappearance of this peak with silver adsorption proves that silver atoms replace adsorbed H2O: I suggest to elaborate on this effect in more detail.

12) FTIR: for untreated CH-TU, please discuss the origin of 1720 cm-1 peak.

13) In the caption of Fig. 1, please denote (a) and (b) subfigures.

14) Line 251, revise "the majority of the particles like sticks" (resemble sticks?).

15) Line 257, revise " is closed to" (is close to?).

16) Line 270, "the electrostatic repulsion" between which substances is implied?

17) Line 275, by "producibility", did you mean "reproducibility"?

18) Line 295, revise "theses".

19) Line 304, revise "The fast kinetics reveals to the easy diffusion" ("to" should be removed).

20) Line 307, define "AIC".

21) Line 310, revise "discussed how it is risky to discuss".

22) Line 323, by "(increased by three time)", did you mean "(increased by three times)"?

23) In the discussion of Table 3, define q_eq,exp.; q_eq,L. b_L.

24) In Table 3, what is MC/MC-PYO/MS-PYS?

25) Line 400, revise "lon pair".

26) Section 3.2.5., in the discussion of Fig. 7, please elaborate on how the elution efficiency was estimated.

27) In the discussion of Table 4, define SE, StD, DE and their measurement units.

Comments on the Quality of English Language

See comments 3, 4, 5, 14, 15, 17, 18, 19, 21, 25.

Author Response

sustainability-3005755

Responses to reviewer#2

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
(x) Moderate editing of English language required
( ) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are all the cited references relevant to the research?	(x)	( )	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	( )	( )	(x)	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	(x)	( )	( )	( )
For empirical research, are the results clearly presented?	( )	( )	( )	(x)
Is the article adequately referenced?	(x)	( )	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	(x)	( )	( )	( )

Comments and Suggestions for Authors

ID: sustainability-3005755

Title: Synthesis and Improvement the Sorption Properties of Silver Ions from Different Aqueous Solutions by Sulfur Grafted Chitosan Biopolymer

 Overview:

Authors investigate the ion metal sorption from aqueous solutions by modified chitosan-based polymer functionalized by cross-linking. Selectivity and reversibility of the obtained materials are demonstrated. The manuscript is scientifically coherent and convincing. However, there are several minor comments mostly related to wording and presentation issues, as well as two major comments associated with the clarification of conceptual aspects.

We thank the reviewer for his/her evaluation and we try best to answer and follow his/her comments and we hope the revised version meet his/her consideration and is readable

 Major comments:

• FTIR spectra: for CH-F and CH-TU, please elaborate on the origin of C=O peak at ~1620 cm-1 and its disappearance with sorption-desorption. According to the Schemes 1,2, no C=O bonds are expected in the structure (or Schemes 1 and 2 lack the C=O bonding which should be depicted in the red sites).

Thanks for alerting, you are right the structure did not have C=O and this peak was assigned for NH. It was corrected, accept our apologize for this error

• Although authors provide a brief explanation of the materials' selectivity in Section 3.2.4, they don't discuss the sorption mechanism in the first place. Do authors expect only oxygen and sulfur groups to be absorbance sites? Why =O is supposedly an active site and -OH is not? Do authors expect chelation [10.3390/polym10101090] to be manifested throughout absorption? Have authors investigated the absorption capabilities of pristine chitosan to verify that -OH and -NH2 groups don't play a role in the adsorption?

Thanks for alerting, you are right but we mention that -OH and -NH (for CH-F and CH-TU) beside =S for CH-TU (which convert to SH by tautomerization) that were involved in the sorption of Ag ions. Both sorbents have OH and NH but the main difference of the presence of C=S in the CH-TU which make the difference. That what we mean during discussion that the Ag(I) was considered as weak acid which favor sorbed by weak base. Any way we thank the reviewer for the alerting us and we improve the discussion in this section.   

This part was added in material section

Figure 3 shows determination of pH_pzc by using the method of pH-drift, the determination was performed using 0.1 M NaCl as background salt. The pH_pzc values was noticed between 6.38 and 5.64 for CH-F and CH-TU respectively. It was concluded that in acidic and slightly acidic solutions the sorbents surface was maintain positively charged (at pH be-low 6.38 and 5.64 for CH-F and CH-TU respectively). The factionalized and non-factionalized sorbents with crossed formaldehyde may obviously change in the properties of acid-base, leading to shift of global pH_pzc.

The sorption mechanism was discussed as follow

The expected sorption mechanisms of Ag (I) and the reactive functional groups was performed through the data collected from the FTIR (through the used functional groups in the sorption, formation of thiol groups through tautomerization of the thion in the composite), pHPZC through concluded the overall charge of the sorbent and the metal speciation of Ag(I) as in Figure S2  (which provide two species at the experimental pH free cationic Ag+ species, and aqua complex (Ag(H2O)4+), which indicating a variable values for both sorbents, the maximum sorption pH was performed below the pHpzc point for CH-TU and over it for CH-F. Mixed mechanisms were predicted through chelating properties (the deprotonated functional groups) on complete negative charged of functionalized sorbent and partially positive for non-functionalized one and with the positively charged metal ions (either free cationic or partially dehydration aqua complex). At this pH (optimum sorption) the electron pairs were available for binding with positively charged metal ions indicating mainly chelation of CH-TU and mixed of chelation and ion exchange for CH-F as shown from Scheme 4.  

 Scheme 4. Expected bending mechanism od Ag(I) on CH-F (a) and CH-TU(b) 

Minor comments:

• Line 48, what do you mean by "Most of silver production derived as sub-products"?

Thanks for your comment; we mean here that the most production of silver is derived as sub-products during other manufactures and this was explained forward from the refining of cadmium, zinc and copper 

• Line 52-53, revise "Many countries were listed the silver" (passive voice not needed).

Thanks for alerting, it was corrected

• Line 62, revise "The upgrading of the concentration"

Thanks for alerting, it was revised  

6) Scheme 1, should the reaction result in the production of oxygen-containing products? Oxygen from formaldehyde doesn't seem to bind to the resulting structure (or Schemes 1 and 2 lack the C=O bonding which should be depicted in the red sites).

Thanks for your comment, actually this reaction is familiar for crosslinking (binding) of two amine groups (through two protons from each one) with oxygen atom from formaldehyde to produce water. Hope it is clear now also please check the below references which clarified these statements.  

https://doi.org/10.1016/j.cej.2019.123635

https://doi.org/10.1016/j.scitotenv.2022.153184

This was added

The expected mechanism was assigned by elimination reaction of oxygen from formaldehyde with two protons from amines of either chitosan and/or thiourea as shown in Scheme 3

   

Scheme 3. Schematic diagram of the coupling mechanism of formaldehyde with thiourea and chitosan

7) Line 119, why do authors call the resulting structure "non-functionalized chitosan particles"? The resulting material is different from pristine chitosan.

Thanks for your comment, this is because we have two moieties in our studies; one without addition of thiourea (only crosslinked chitosan), which considered as non-functionalized because there is no addition of any reactive groups. The other moiety (functionalized one) by grafted of thiourea with crosslinked chitosan. So the referenced material here is the crosslinked chitosan (non-functionalized particles). By the way chitosan itself without crosslinking not used because the amine will be protonated leading to dissolve of the particles. So, it must be crosslinked (this was performed through different moieties as epichlorohydrin, glutaraldehyde, and as in the recent work by formaldehyde).

8) Section 2.3, what is the resolution of FTIR spectrometer and what accelerating voltage was used for SEM studies?

Thanks for alerting; The resolution of FTIR was set to 4 cm-1, while the voltage of SEM was assigned to be 15 Kv. And it was added to discussion

9) Section 2.4: how was the Ag(I) concentration measured?

It was discussed in section 2.3 that the collected samples were measure using ICP-AES

“The collected samples from the experiments (before and after sorption) were filtered (by 1.2 µm- filter membranes) before the inductively coupled plasma atomic emission spectrometer (ICP-AES) measurements. The elements were measured using the ICP through ICPS-7510, Shimadzu-Tokyo (Japan)”.

10) FTIR spectra: please elaborate on the origin of the spectral feature observed at 2300-2400 cm-1. Is it an instrumental effect?

Thanks for alerting, yes, this peak from the instrumental effect mainly caused by carbon dioxide or H₂O from the environment

11) FTIR spectra: as for the 3400 cm-1 peak, do authors attribute its emergence to adsorbed water [10.3390/jcs7070264], or do they expect some hydroxide groups in the structure? To me, it seems like the disappearance of this peak with silver adsorption proves that silver atoms replace adsorbed H2O: I suggest to elaborate on this effect in more detail.

Thanks for your comment, we try to support the discussion and mention these peaks.

12) FTIR: for untreated CH-TU, please discuss the origin of 1720 cm-1 peak.

Thanks, but this peak may be due to the moisture in the sample especially the structure did not involve any of carbonyl or carboxylic groups in its structure.

13) In the caption of Fig. 1, please denote (a) and (b) subfigures.

Thanks, it was corrected

14) Line 251, revise "the majority of the particles like sticks" (resemble sticks?).

Thanks, we revised it and give another expression but we mean it because the particles are unsymmetrical structure and elongated which like sticks, we

15) Line 257, revise " is closed to" (is close to?).

Thanks, it was corrected

16) Line 270, "the electrostatic repulsion" between which substances is implied?

Thanks for alerting, but it was already explained after this between protonated functional groups and positively charged metal ions 

“the electrostatic repulsion was performed of the protonated functional groups and positively charged metal ions”.

17) Line 275, by "producibility", did you mean "reproducibility"?

Thanks, yes, and it was corrected

18) Line 295, revise "theses".

Thanks, it was corrected

19) Line 304, revise "The fast kinetics reveals to the easy diffusion" ("to" should be removed).

Thanks, it was corrected

20) Line 307, define "AIC".

Thanks, we add the definition for it

Akaike Information Criterion (AIC)

22) Line 323, by "(increased by three time)", did you mean "(increased by three times)"?

Thanks, it was corrected

23) In the discussion of Table 3, define q_eq,exp.; q_eq,L. b_L.

Thanks, it was revised

q_eq,exp. (mmol g^-1): experimental sorption capacity, q_eqL, (mmol g^-1): sorption capacity at equilibrium according to Langmuir equation, b_L (L mmol^-1): Affinity coefficient

24) In Table 3, what is MC/MC-PYO/MS-PYS?

Thanks, it was revised and the definition was added

Magnetic chitosan trione-pyrimidine derivative (MC-PYO)

Magnetic chitosan Trithione- pyrimidine derivative (MC-PYS)

Magnetic chitosan (MC)

25) Line 400, revise "lon pair"

Thanks, it was corrected

26) Section 3.2.5., in the discussion of Fig. 7, please elaborate on how the elution efficiency was estimated.

Thanks it was elaborated

This was added

Figure 7 9 shows elution efficiency in nitric acid medium, which estimated by the equation (eq.3)

Elution efficiency= (C_(t)xV)/(q_maxxWt)x100      (eq.3)

Where C_(t) is the concentration of metal ion in the solution at time (t), V volume of the eluent, q_max the maximum loading capacity, Wt; weight of the sorbent

27) In the discussion of Table 4, define SE, StD, DE and their measurement units.

Thanks for alerting, the definition was added

SE: sorption efficiency (%); DE: Desorption efficiency (%); StD: Slandered deviation

 

 

 

 

 

 

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. The authors are asked to redraw the structural formulae for the non-functionalized chitosan particles (CH-F) in Scheme 1 and the functionalized chitosan thiourea particles (CH-TU) in Scheme 2 based on the structure of the substance. The red line alone does not indicate continued grafting and would only be mistaken for a methyl/ethyl.

2. The labels for the axes in Figure 1, Figure 2 and Figure 3 are too small and changes are recommended. The authors are requested to pay attention to the labels of the axes and the size of the legends throughout the text for the reader.

3. The authors need to provide a comprehensive graphic abstract and a schematic diagram of the relevant mechanism.

4. The picture and figure notes are not on one page, it is recommended that the picture be re-spliced and made. Meanwhile, the tables have the same kind of problem.

5. The citation format of references needs to be uniform.

Comments on the Quality of English Language

Moderate editing of English language required.

Author Response

sustainability-3005755

Responses to reviewer#3

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

 

Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
(x) Moderate editing of English language required
( ) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are all the cited references relevant to the research?	(x)	( )	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	( )	(x)	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	( )	(x)	( )	( )
For empirical research, are the results clearly presented?	(x)	( )	( )	( )
Is the article adequately referenced?	( )	(x)	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	( )	(x)	( )	( )

Comments and Suggestions for Authors

1. The authors are asked to redraw the structural formulae for the non-functionalized chitosan particles (CH-F) in Scheme 1 and the functionalized chitosan thiourea particles (CH-TU) in Scheme 2 based on the structure of the substance. The red line alone does not indicate continued grafting and would only be mistaken for a methyl/ethyl.

Thanks for alerting, we think both schemes are right, the mechanism of this reaction focusing on coupling of formaldehyde with two molecules of amine groups and produce water. So the first scheme (CH-F) based on reaction of two molecules of amine from chitosan with one molecules of formaldehyde, the second scheme is little different because we have two different types of amine so the reaction mainly through amine from chitosan and that of thiourea and another one for crosslinking of these chains. We try to modify it accordingly and hope the revised schemes are acceptable  

To be clarified this scheme was added

The expected mechanism was assigned by elimination reaction of oxygen from formaldehyde with two protons from amines of either chitosan and/or thiourea as shown in Scheme 3

   

Scheme 3. Schematic diagram of the coupling mechanism of formaldehyde with thiourea and chitosan

2. The labels for the axes in Figure 1, Figure 2 and Figure 3 are too small and changes are recommended. The authors are requested to pay attention to the labels of the axes and the size of the legends throughout the text for the reader.

Thanks, it was revised and replaced

3. The authors need to provide a comprehensive graphic abstract and a schematic diagram of the relevant mechanism.

Thanks for alerting, we designed graphical abstract and add a schematic diagram as shown below

This was added in the revised version

The expected mechanism was assigned by elimination reaction of oxygen from formaldehyde with two protons from amines of either chitosan and/or thiourea as shown in Scheme 3

   

Scheme 3. Schematic diagram of the coupling mechanism of formaldehyde with thiourea and chitosan

For Binding mechanism this was added

The expected sorption mechanisms of Ag (I) and the reactive functional groups was performed through the data collected from the FTIR (through the used functional groups in the sorption, formation of thiol groups through tautomerization of the thion in the composite), pHPZC through concluded the overall charge of the sorbent and the metal speciation of Ag(I) as in Figure S2  (which provide two species at the experimental pH free cationic Ag+ species, and aqua complex (Ag(H2O)4+), which indicating a variable values for both sorbents, the maximum sorption pH was performed below the pHpzc point for CH-TU and over it for CH-F. Mixed mechanisms were predicted through chelating properties (the deprotonated functional groups) on complete negative charged of functionalized sorbent and partially positive for non-functionalized one and with the positively charged metal ions (either free cationic or partially dehydration aqua complex). At this pH (optimum sorption) the electron pairs were available for binding with positively charged metal ions indicating mainly chelation of CH-TU and mixed of chelation and ion exchange for CH-F as shown from Scheme 4.  

 Scheme 4. Expected bending mechanism od Ag(I) on CH-F (a) and CH-TU(b)   

For the graphical abstract

4.The picture and figure notes are not on one page, it is recommended that the picture be re-spliced and made. Meanwhile, the tables have the same kind of problem.

Thanks for alerting we revised them and designed to be on one page

5. The citation format of references needs to be uniform.

We apologize, it was revised

Comments on the Quality of English Language

Moderate editing of English language required.

We try best for improving language and hope the revised manuscript will be easier to read and understandable.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This article demonstrates the excellent performance of new thiourea functionalized chitosan composite materials in silver ion adsorption, which has high innovation and application value. However, there are still some details and data analysis that can be further improved to enhance the persuasiveness and scientific nature of the paper. It is recommended that the author make modifications and additions based on the following comments:

1. The research progress of silver ion adsorption materials needs to be supplemented.

2. Abbreviations should be avoided in the abstract. The abstract should be more concise.

3. There is a mixed use of adsorption and adsorption in the paper.

4. Writing errors should be avoided, such as line 126 of Table 2.

5. Kinetic fitting can only use data before equilibrium.

6. The pH deviation in Figure 3 is useless. Please check pHpzc.

7. Lines 251-252. How can you get an average size by measuring just one particle?

8. The negative sign (−) and hyphen (-) are used incorrectly for numerical units.

Comments on the Quality of English Language

English needs moderate editing

Author Response

sustainability-3005755

Responses to reviewer#4

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

 Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
(x) Moderate editing of English language required
( ) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	( )	(x)	( )	( )
Are all the cited references relevant to the research?	( )	(x)	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	( )	(x)	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	( )	(x)	( )	( )
For empirical research, are the results clearly presented?	( )	(x)	( )	( )
Is the article adequately referenced?	( )	(x)	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	( )	(x)	( )	( )

Comments and Suggestions for Authors

This article demonstrates the excellent performance of new thiourea functionalized chitosan composite materials in silver ion adsorption, which has high innovation and application value. However, there are still some details and data analysis that can be further improved to enhance the persuasiveness and scientific nature of the paper. It is recommended that the author make modifications and additions based on the following comments:

1. The research progress of silver ion adsorption materials needs to be supplemented.

Thanks for alerting and hope the revised version is readable

2. Abbreviations should be avoided in the abstract. The abstract should be more concise.

Thanks, we revised it and follow your suggestion

3. There is a mixed use of adsorption and adsorption in the paper.

We did not catch what the reviewer mean does you mean adsorption and sorption, any way we revised it and save one definition

4. Writing errors should be avoided, such as line 126 of Table 2.

We apologize, but Table 2 start with line 351 not 126, any way we try best to improve language and avoid such error in the whole manuscript

5. Kinetic fitting can only use data before equilibrium.
6. The pH deviation in Figure 3 is useless. Please check pHpzc.

Thanks for alerting, we transfer the pH deviation to the SI and the pHpzc was added in its section

Figure 3. Effect of pH_pzc of CH-F and CH-TU using 0.1 M NaCl as background salt. 

7. Lines 251-252. How can you get an average size by measuring just one particle?

Thanks for your comment, actually the average size was taken from the data of sieving of sorbents after synthesis and dry, and also measuring different particles by SEM tools, but what added to convince the shape and facilitate the idea to the readers.    

8. The negative sign (−) and hyphen (-) are used incorrectly for numerical units.

Thanks for alerting we try to change it.

Comments on the Quality of English Language

English needs moderate editing

Thanks for alerting. The editing (spelling, typing and grammar) has been carefully checked. We hope the revised version is readable now

 

 

 

 

 

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have improved the manuscript based on the suggestions of the reviewer.

However, the authors should limit the citation of their own articles. Upon checking, I found that the first author has cited 26 of their own papers in this manuscript. I believe this is quite unethical.

Comments on the Quality of English Language

The authors need to thoroughly check for minor grammatical errors.

Author Response

sustainability-3005755R1

Responses to reviewer#1

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

 

Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
( ) Moderate editing of English language required
(x) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	(x)	( )	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	(x)	( )	( )	( )
For empirical research, are the results clearly presented?	(x)	( )	( )	( )
Is the article adequately referenced?	( )	( )	(x)	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	(x)	( )	( )	( )

Comments and Suggestions for Authors

The authors have improved the manuscript based on the suggestions of the reviewer.

However, the authors should limit the citation of their own articles. Upon checking, I found that the first author has cited 26 of their own papers in this manuscript. I believe this is quite unethical.

Thanks for alerting, we try best to remove some references more than half, what appeared to be unimportant, hope the revised version is acceptable for you. 

Comments on the Quality of English Language

The authors need to thoroughly check for minor grammatical errors.

Thanks for your comment we revised the manuscript and fixed errors

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

ID: sustainability-3005755

Title: Synthesis and Improvement the Sorption Properties of Silver Ions from Different Aqueous Solutions by Sulfur Grafted Chitosan Biopolymer

Review 2

 

Authors have provided satisfactory answers to most of my questions. However, there are two comments left. They are related to FTIR interpretation.

 

1) Lines 215-216, “Peaks in the region of 2300-2400 for CH-F were related to carbon dioxide and adsorbed water”: first, they were observed not only for CH-F, but also for CH-TU. Second, no peaks from water are expected in this region [https://mavink.com/explore/Water-Infrared-Spectrum]. Third, the CO2 contribution to the spectra is typically very weak (please see the spectra of CO2-uptaking material in Fig.1(d) of [https://doi.org/10.1016/j.fuel.2021.120466]). I have never seen the contribution of ambient CO2 to the FTIR spectra of porous polymeric structures, and I consider the provided interpretation highly dubious.

2) Question 1 was, unfortunately, answered only partially, as authors haven’t provided any explanation of ~1620 cm-1 N-H peak disappearance with sorption-desorption. Does it mean that Ag adsorption is associated with dehydrogenation?

 

Author Response

sustainability-3005755R1

Responses to reviewer#2

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
( ) Moderate editing of English language required
( ) Minor editing of English language required
(x) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	(x)	( )	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	( )	(x)	( )	( )
For empirical research, are the results clearly presented?	(x)	( )	( )	( )
Is the article adequately referenced?	(x)	( )	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	(x)	( )	( )	( )

Comments and Suggestions for Authors

ID: sustainability-3005755

Title: Synthesis and Improvement the Sorption Properties of Silver Ions from Different Aqueous Solutions by Sulfur Grafted Chitosan Biopolymer

Review 2

 

Authors have provided satisfactory answers to most of my questions. However, there are two comments left. They are related to FTIR interpretation.

• Lines 215-216, “Peaks in the region of 2300-2400 for CH-F were related to carbon dioxide and adsorbed water”: first, they were observed not only for CH-F, but also for CH-TU. Second, no peaks from water are expected in this region [https://mavink.com/explore/Water-Infrared-Spectrum]. Third, the CO2 contribution to the spectra is typically very weak (please see the spectra of CO2-uptaking material in Fig.1(d) of [https://doi.org/10.1016/j.fuel.2021.120466]). I have never seen the contribution of ambient CO2 to the FTIR spectra of porous polymeric structures, and I consider the provided interpretation highly dubious.

We return to the instrument lab and this is peak is as standard error from the equipment and can be noticed with different degree intensities depends on the pressure on the machine, I make a notice for this in the manuscript.  

2) Question 1 was, unfortunately, answered only partially, as authors haven’t provided any explanation of ~1620 cm-1 N-H peak disappearance with sorption-desorption. Does it mean that Ag adsorption is associated with dehydrogenation?

Thanks for your comment, you are right but as appeared from expected binding mechanism that N-H and O-H sharing in binding with silver ions by chelating mechanism (through the available lone pair of electrons), and also by cation exchange (through replacement of protons by silver cations) and this give us high evidence for the dehydrogenation and cause decreasing in the intensity of this band

We thank the reviewer for his time in review of our paper and improve the it, and we hope the revised version is meaningful making the manuscript readable.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

It can be accepted after minor editing of English language.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

sustainability-3005755R1

Responses to reviewer#3

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
( ) Moderate editing of English language required
(x) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	(x)	( )	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	(x)	( )	( )	( )
For empirical research, are the results clearly presented?	(x)	( )	( )	( )
Is the article adequately referenced?	(x)	( )	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	(x)	( )	( )	( )

Comments and Suggestions for Authors

It can be accepted after minor editing of English language.
Comments on the Quality of English Language

Minor editing of English language required

We thank the reviewer for his/her globally evaluation and We hope the revised version is meaningful making the manuscript readable.

 

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

1. In Table 2, there is a mix of mmol and Mmol, which one should be correct? Please check the whole manuscript carefully to avoid these writing mistakes.

2. In Figure 6, please use the data of the first 90 minutes for fitting. 

Comments on the Quality of English Language

Moderate editing of English language required.

Author Response

sustainability-3005755R1

Responses to reviewer#4

Red: Specific response to Reviewer comment.

Blue: New statement added to the revised manuscript

Open Review

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

Quality of English Language

( ) I am not qualified to assess the quality of English in this paper
( ) English very difficult to understand/incomprehensible
( ) Extensive editing of English language required
(x) Moderate editing of English language required
( ) Minor editing of English language required
( ) English language fine. No issues detected

 

	Yes	Can be improved	Must be improved	Not applicable
Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?	(x)	( )	( )	( )
Are the research design, questions, hypotheses and methods clearly stated?	(x)	( )	( )	( )
Are the arguments and discussion of findings coherent, balanced and compelling?	( )	(x)	( )	( )
For empirical research, are the results clearly presented?	( )	(x)	( )	( )
Is the article adequately referenced?	( )	(x)	( )	( )
Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?	( )	(x)	( )	( )

Comments and Suggestions for Authors

1. In Table 2, there is a mix of mmol and Mmol, which one should be correct? Please check the whole manuscript carefully to avoid these writing mistakes.

Thanks for alerting, it was corrected and being symmetry

2. In Figure 6, please use the data of the first 90 minutes for fitting. 

Thanks, it was revised

Comments on the Quality of English Language

Moderate editing of English language required.

Thanks for your alerting, we try best to improve the language and we hope the revised version is suitable and readable

 

 

Author Response File: Author Response.docx