Chitosan Beads Incorporated with Graphene Oxide/Titanium Dioxide Nanoparticles for Removing an Anionic Dye

Round 1

Reviewer 1 Report

Dear authors,

This research addresses the problem of removing anionic contaminants from wastewater using chitosan beads cross-linked with glutaraldehyde, incorporated with graphene oxide and titanium dioxide nanoparticles.

It is an interesting idea of using graphene oxide and titanium dioxide nanoparticles to improve the adsorption properties of chitosan.

Although chitosan is an intensively studied biopolymer, combining it with both graphene oxide and titanium dioxide is exciting and original. These additives act as new adsorption active sites within the synthesized beads. The addressed topic is of great interest.

The manuscript is well written and easy to read.

Conclusions are supported by the presented results, with the amendment that the first paragraph should be reconsidered.

1. The introduction could be improved, for example, by adding more information on other composite materials used for such applications.
2. Sections 3.1 and 3.2 are a summary of already published results. Figure 1 and Figure 2 are optical and SEM images of the same materials (different as images, but on the same "object"). The author's intentions are to present a clear image of the relevant sample properties. As a suggestion, you could shorten that part.
3. The first paragraph in the Conclusions section, lines 419-425, contains conclusions already presented in previous work. Please refer only to the present study. 

Author Response

We want to submit our corrected version of the paper entitled " Chitosan Beads Incorporated with Graphene Oxide/Titanium Dioxide Nanoparticles for Removing an Anionic Dye" by Moises A. Solano, Johanna Galan, William Vallejo, Victoria A. Arana, and Carlos David Grande Tovar, who agreed with all the corrections. All the modifications are available in the attached document.

 

Reviewer 1

1. The introduction could be improved, for example, by adding more information on other composite materials used for such applications.

R// We appreciate the reviewer's comment. The introduction has improved; we have added information about other composite materials used for adsorption processes between lines 39 and 46.

2. Sections 3.1 and 3.2 are a summary of already published results. Figure 1 and Figure 2 are optical and SEM images of the same materials (different as images, but on the same "object"). The author's intentions are to present a clear image of the relevant sample properties. As a suggestion, you could shorten that part.

R// We appreciate the reviewer's comment. We have decided to unify sections 3.1 and 3.2. The new section was named "Characterization of the cross-linked chitosan beads," and the 168-172 were edited. The section was left as a summary of the reader's location. We have also decided to eliminate figure 1 and the discussion of the TGA, which is available in the previously published work.

3. The first paragraph in the Conclusions section, lines 419-425, contains conclusions already presented in previous work. Please refer only to the present study.

R// We appreciate the reviewer's comment. We have deleted the first paragraph.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. What' the purpose for the swelling test? Is there any correlation between the degree of swelling and the dye adsorption capacity?Please make a specific discussion and show a explicit result.
2. What is the mechanism of the action of the incorporation of graphene oxide on dye adsorption? If it is related to the formation of cross-linked structures, please provide more detailed discussion.
3. Figure 1 shows TiO₂ nanoparticles were added to the beads, decreasing the orange intensity due to their white color. But in your previous work, the color ranged from yellow to light-red, which showed conversely according to Figure 6 in the reference 16. Which one is right?
4. Please pay more attention to the writing format, such as the abbreviations of proper nouns. For example, the CDD in line 85 and the DCC in line 133 should be indicated in full for the first time they appeared, and the analysis of variance (ANOVA) in line 207, which appeared for the second time should be abbreviated.

Author Response

We want to submit our corrected version of the paper entitled " Chitosan Beads Incorporated with Graphene Oxide/Titanium Dioxide Nanoparticles for Removing an Anionic Dye" by Moises A. Solano, Johanna Galan, William Vallejo, Victoria A. Arana, and Carlos David Grande Tovar, who agreed with all the corrections. All the modifications are in the attached document.

Reviewer 2

1. What' the purpose of the swelling test? Is there any correlation between the degree of swelling and the dye adsorption capacity? Please make a specific discussion and show an explicit result.

R// We appreciate the reviewer's comment. The swelling test gives us an idea of the porous expansion of the synthesized beads, and although it is related to the adsorption capacity, it is not the variable that affects it to a greater extent. The swelling test results for GO beads show a low decrease in swelling concerning the TiO₂ beads, but these beads were the ones that showed the best adsorption (those with GO), demonstrating the potential of the GO for the uptake of molecules of the dye. The specific discussion was highlighted in lines 320-322 and 342-347.

2. What is the mechanism of the action of the incorporation of graphene oxide on dye adsorption? If it is related to the formation of cross-linked structures, please provide a more detailed discussion.

R// We appreciate the reviewer's comment. The modification of GO with CS is possible due to the existence of oxygenated groups through the nanosheet, which can interact with the polymeric matrix through supramolecular interactions. In this way, the GO aligns itself between the CS chains, where it establishes an interlocking interaction that clings to the CS chains through hydrogen bonds. GO molecules play a role within the synthesized beads as new adsorption active sites where three possible types of interactions with the dye can occur (electrostatic, hydrogen bonds, and π-π interactions). The specific discussion was highlighted in lines 302-310.

3. Figure 1 shows TiO₂ nanoparticles were added to the beads, decreasing the orange intensity due to their white color. But in your previous work, the color ranged from yellow to light-red, which showed conversely according to Figure 6 in reference 16. Which one is right?

R// We appreciate the reviewer's comment. You are right, and the correct images are those of the previously published work. In addition, taking into account the corrections of reviewer 1, we have decided to altogether remove the image to summarize the section. We have decided to unify sections 3.1 and 3.2 so that the new section was named "Characterization of the cross-linked chitosan beads," and the lines 168-172 were edited.

4. Please pay more attention to the writing format, such as the abbreviations of proper nouns. For example, the CDD in line 85 and the DCC in line 133 should be indicated in full for the first time they appeared, and the analysis of variance (ANOVA) in line 207, which appeared for the second time, should be abbreviated.

R// We appreciate the reviewer's comment. The acronyms were appropriately modified.

 

 

Author Response File: Author Response.pdf