Novel Synthesis of Carbon Dots from Coconut Wastes and Its Potential as Water Disinfectant

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript reports a facile and effective method for large-scale production of carbon dots (CDs) from diverse coconut wastes using several doping agents to obtain surface modified CDs to enhance their anti-bacterial properties.

With the aim of improving the yield in CDs, a novel two sequential processes (pyrolysis followed by sonication) were explored.

The potential of coconut wastes for the synthesis of CDs with water disinfection property was attained.

The CDs structures were extensively characterized by several analytical techniques, e.g., High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscope (SEM). Their crystal structure was determined by Selected Area Electron Diffraction (SAED) of HR-TEM and corroborated using an X-ray diffractometer. The UV-Vis and FTIR spectroscopies were also used, and Zeta-potential determined.

The manuscript is clear, the introduction and discussion are adequate. The references are exhaustive for article content. The paper has good quality to be published with minor revisions.

 In the following, some comments and questions are listed:

1)  Pag. 3 in 2.1.2. Two sequential synthesis processes (line 108):

“To separate the supernatant liquid from the carbon precipitate, the solution was centrifuged at 10,000 rpm for 10 min.”

Haven't you attempted membrane filtering instead of centrifuging?

2)  Pag. 3 in 2.2. Synthesis of surface modified CDs: the different dopant agents were adding after CDs had been synthesized. Why the different dopants were not introduced when the CDs were prepared?

3)  Pag. 6,7,8 in Figures 1, 2 and 4: the UV-Vis and FTIR spectra don´t have good resolution and should be improved. The UV-Vis spectrum profile is not adjusted to the baseline and the FTIR spectra show higher background noise and are not corrected. Some important absorption bands are not identified, specifically hydroxyl and carbonyl groups. Are not present in theses CDs? Should be confirmed.

4)  Pag. 8 in 3.2. Optical studies (line 263/264): “… strong absorption peak was observed at 226 nm and 263 nm another shoulder peak at 330 nm.” Which the CDs (UV-Vis) that showed these bands? Is not clear.

5)  Pag. 8 in 3.2. Optical studies (line 271): “…the formation of O-H stretching vibration as denoted by the intense broad peak at 3440 cm⁻¹.” This absorption band value is only attributed in Figure 3e) but is not broad!

6)  Pag. 10 in Table 4: in column %Cytotoxicity, the meaning superscript font is missing (must be at the bottom of the table).

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article presents the results of an experimental study in obtaining non-traditional sorbents for the purification and disinfection of wastewater from waste. The work is interesting, well-presented, and illustrated. The only remark to the authors may be extending the conclusion to the article. In addition to a general conclusion about the best option for modifying waste during the production of CD, briefly explain the mechanism of action of the selected reagent on the mechanism of wastewater disinfection.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

I consider the contribution to be of high quality and suitable for publication in Sustainability. I particularly appreciate the incisive characterization of carbon dots. I have no reservations about the scientific concept and processing of the publication. Perhaps the preparation of doped CCDs and especially their cleaning and isolation would deserve a more detailed description ensuring more reliable reproducibility.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript deals with the preparation of carbon dots by a combination of pyrolysis and sonification. The yield of carbon dots was higher in this case than when using only one procedure. The authors state that the paper presents an effective method for the production of carbon dots for large scale production. In the paper, the preparation is at the laboratory scale level and it is not clear from what the authors conclude that the results can be transferred to large scale production. For none of the experiments is it stated how many times it was repeated. Information about the conditions of individual experiments is also missing. For example, at what pH was the zeta potential measured. There is no more detailed justification in the values of the zeta potential, or in the values of the specific surface between individual types of carbon dots. In chapter 3.7 it is stated that the antibacterial activity is mainly caused by the interaction between the positive surface of the carbon dots and the negative surface of the bacteria. However, the zeta potential of carbon dots is negative. The text states that in this case the cause may be the generation of reactive oxygen species. Do the authors have any evidence for this claim? This is an interesting article, for possible publication it is necessary to add information about individual experiments, information about standard deviations. It is necessary to expand the discussion about the mechanisms of action of carbon dots on microorganisms and also to justify the differences in the properties of individual carbon dots.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 5 Report

Introduction

- Please add more literature review on a related studies and how does their carbon dots performed?

- What makes your study different than the previous ones? Please highlight the novelty of your study

Minor English editing required.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Very good revision. At this moment I recommend publish the article.