Improved Adsorption and Photocatalytic Degradation of Methyl Orange by Onion-like Nanocarbon/TiO2 Nanocomposites
, Ludwe L. Sikeyi 2, Faria Dziike 3, Neil J. Coville 1,2, Edward N. Nxumalo 4 and Manoko S. Maubane-Nkadimeng 1,2,5,*Round 1
Reviewer 1 Report
Authors have described an interesting study. Although study is well planned and results are properly discussed, however, there are few concerns which must be addressed before publishing this research in this journal.
1. Abstract must be improved by adding quantitative values of degradation efficiencies of each catalyst.
2. Introduction is weak, some of the recent literature is not cited. To strengthen the literature overview, following papers should be cited. https://link.springer.com/article/10.1007/s10853-020-05721-0
https://pubs.acs.org/doi/10.1021/acsomega.9b02040
https://www.sciencedirect.com/science/article/abs/pii/S0959652620347120
https://www.sciencedirect.com/science/article/abs/pii/S2213343722012027
3. Details of chemicals and their purity is not provided in experimental section.
4. In Results and Discussion section, XRD Peaks are not properly discussed.
5. SEM images of same magnification are not provided, so it is difficult to compare each catalyst morphology.
6. There is a clear difference in TEM images of four catalyst. Authors didn't clearly state why there is such drastic change in morphology among these catalysts.
7. Schematic representation of MO degradation using OLNCs/TiO2 photocatalyst should be improved.
8. Comparison table should be more strengthened by adding few more examples of similar catalysts.
Author Response
Thank you for your decision letter dated 18 March 2023 and for affording us the opportunity to revise and improve the manuscript. Please find enclosed, a revised copy of our manuscript entitled “Improved adsorption and photocatalytic degradation of methyl orange by onion-like nanocarbon/TiO2 nanocomposites” for your consideration for publication in Applied Sciences.
We appreciate the comments from the referees which have led to a tightening of the paper. We have responded to all comments from the reviewers point-by point. We hope that our responses have provided additional information and the clarity required. The corrections and changes made are tracked in the revised manuscript.
We thank you and the reviewers for your time and effort in reviewing our manuscript. All authors have read and approved the changes made to the manuscript. We hope that the revised manuscript is now suitable for inclusion and publication in Applied Sciences, and we look forward to hearing from you.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Report on the manuscript applsci-2301677 entitled “Improved adsorption and photocatalytic degradation of methyl orange by onion-like nanocarbon/TiO2 nanocomposites”.
The submitted manuscript should be revised. The following points should be addressed:
1. The submitted manuscript should be revised to be free from editing or grammar errors. For example: there is big distance in the second line of 2.1 paragraph.
2. Could the authors indicate the role of 5 M NaOH during the synthesis of the studied composite?
3. Why pH 7 was used in this study without study the effect of pH?
4. Could the authors suggest the reason of formation of anatase structure and estimate the lattice parameters a, b and c in addition to cell volume as reported in Applied Surface Science
volume 400, 1 April 2017, Page 355?
5. XRD discussion should be supported by the formation of (002) phase of carbon in the case of TC-50 sample.
6. FTIR spectra of TiO2 and its composite to study the effect of OLNCs over the function groups of TiO2?
7. X-ray photoelectron spectroscopy (XPS) should be studied to investigate the chemical and bonding environment of the prepared OLNCs/TiO2 composites?
8. HRTEM is required and its relation to d-spacing from XRD analysis.
9. [Important] Study the adsorption isotherm is very important for any photocatalysis study?
Author Response
Thank you for your decision letter dated 18 March 2023 and for affording us the opportunity to revise and improve the manuscript. Please find enclosed, a revised copy of our manuscript entitled “Improved adsorption and photocatalytic degradation of methyl orange by onion-like nanocarbon/TiO2 nanocomposites” for your consideration for publication in Applied Sciences.
We appreciate the comments from the referees which have led to a tightening of the paper. We have responded to all comments from the reviewers point-by point. We hope that our responses have provided additional information and the clarity required. The corrections and changes made are tracked in the revised manuscript.
We thank you and the reviewers for your time and effort in reviewing our manuscript. All authors have read and approved the changes made to the manuscript. We hope that the revised manuscript is now suitable for inclusion and publication in Applied Sciences, and we look forward to hearing from you.
Author Response File: Author Response.pdf
Reviewer 3 Report
The article submitted for review is founded on the interesting idea of employing used oil to produce carbon nanoparticles and then forming carbon-TiO2 composites for photocatalytic decomposition of organic pollutants. However, the work bears numerous errors and shortcomings. The paper lacks morphological and structural analysis of TiO2 and OLNCs. Nothing is also known about the method of synthesis of TiO2. Only from the section on TEM images does it appear that TiO2 was synthesized and not purchased. However, it is not known whether it was synthesized each time the composites were made or whether the previously synthesized powder was added to the OLNCs and NaOH. Substantive errors were made in the analysis of the spectral dependence of absorbance, in the determination of the energy of the refractive interval of the materials studied, the methodology of photocatalytic measurements and the interpretation of their results. At this stage, the article requires solid correction and refinement of the methodology and, in the reviewer's opinion, is not suitable for publication. Below are some comments and questions that may point the authors in the direction of necessary changes.
1. Why was NaOH used to prepare the nanocomposites?
2. What is the chemical composition and morphology of OLNCs? Does the synthesis method used give reproducible results? By what method was TiO2 obtained? What is the morphology of TiO2? What is the particle size distribution? Please provide pictures showing the morphology of TiO2.
3. The paper reported that there was 10 mg, 20 mg, 30 mg, or 50 mg of OLNCs per 100 mg of TiO2. It was reported that this was a molar ratio of 1:2, 1:4, 1:6, and 1:10, respectively. What molar mass of OLMCs was assumed by the authors because the reviewer's calculations show that this is not a molar ratio. Nor is it a weight ratio.
4. Figure 1: What is the result of the non-monotonic change in the intensity of the reflex coming from anatase? The order according to decreasing intensity is 10>30> 20=50 and one would expect 10>20>30>50.
5. Figure 1. The following details are ommited in the text:
- TC-10 - low-intensity reflections before and after the anatase-derived main reflex,
- TC-20 - widening of the anatase main reflex and its asymmetrical shape along with a shift in position toward lower 2-theta values,
- TC-30 - Shift towards lower 2-theta values of the main anatase reflex and analogous to TC-10 reflections of low intensity,
- TC-50 - additional reflections at least at 2-theta values around 14, 24, 35 and a shift towards lower 2-theta values although minimally smaller than at TC-30.
6. Figure 2: The use of black/dark line color for TC-10 and TC-20 samples makes it impossible to analyze.
7. The spectral dependence of absorbance was incorrectly interpreted. The shifting of the absorbance range described in the paper does not occur. It can only be seen that the absorbance decreases as the contribution of OLNCs to the nanocomposites increases. The energy of the band gap was incorrectly determined. The correct method can be found, for example, in the works of 10.1039/D0RA06866G, 10.1021/acs.jpclett.8b02892, 10.1039/C6TA03376H. When the correct method is applied, it can be seen that the energy of the TiO2 band gap is about 3.6 eV and practically does not change regardless of the content of OLNCs in the nanocomposite.
8. Figure 7. The fitted straight lines should have their origin at 0,0 which is due to the fact that at time 0 the photocatalytic decomposition is also 0. It can also be seen that TiO2 and at least both TC-10 results require a different method of analysis - considering two ranges due to a change in the mechanism of photocatalytic decomposition or using a different kinetic model, such as pseudo-second order kinetics. Also missing from the graph are the results for TC-10 using H2O2.
9. Figure 9.Each time before measuring the spectral absorbance characteristics of a dye, the spectrophotometer should be brought to zero so that all curves have their starting point at the same point (see eg. 10.1007/s11051-014-2473-4).
Author Response
Thank you for your decision letter dated 18 March 2023 and for affording us the opportunity to revise and improve the manuscript. Please find enclosed, a revised copy of our manuscript entitled “Improved adsorption and photocatalytic degradation of methyl orange by onion-like nanocarbon/TiO2 nanocomposites” for your consideration for publication in Applied Sciences.
We appreciate the comments from the referees which have led to a tightening of the paper. We have responded to all comments from the reviewers point-by point. We hope that our responses have provided additional information and the clarity required. The corrections and changes made are tracked in the revised manuscript.
We thank you and the reviewers for your time and effort in reviewing our manuscript. All authors have read and approved the changes made to the manuscript. We hope that the revised manuscript is now suitable for inclusion and publication in Applied Sciences, and we look forward to hearing from you.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Report on the manuscript applsci-2301677 entitled “Improved adsorption and photocatalytic degradation of methyl orange by onion-like nanocarbon/TiO2 nanocomposites”.
The revised manuscript should be revised. The following points should be addressed:
1. XPS discussion should be improved and tables S1 and S2 couldn’t be found in Supplementary Material!
2. [Important comment from previous revision] Study the adsorption isotherm is very important for any photocatalysis study?
Author Response
We thank the reviewer for the comments and we have provided a response to the best of our knowledge. The XPS discussion has been improved by adding the discussion on the deconvoluted peaks. Tables S1 and S2 have been included in the supplementary section. The adsorption isotherms have been studied and the data is presented in Figures S3 and S4. Its discussion is included in the main text.
Author Response File: Author Response.pdf
Reviewer 3 Report
Despite the answers to part of my questions, the authors did not make the necessary changes to the manuscript.
They addressed my doubts about the molar composition of nanocomposites, however the necessary changes in the the manuscript were not made. Readers wishing to repeat the synthesis will be denied the opportunity to do so. Additionally, according to the authors' response, the authors relied on XPS analysis for molar composition determination. Detailed XPS spectra of the elements should therefore be included, along with the corresponding fitting and analysis.
The authors did not address the comments regarding the lack of analysis of broadened XRD peaks (composed of two peaks) and additional peaks on the roentgenogram. I found no corresponding analysis in the manuscript.
The authors, despite assurances in their response to the review about the changes made in Figure 7, did not make such changes in the text of the manuscript. They also did not address the possible change in the mechanism of the photocatalytic process and the associated need to fit kinetic models on two separate time scales.
Therefore, in the reviewer's opinion, the article requires further work and cannot be recommended for publication at this stage.
Author Response
We are appreciative of the reviewer's comments and have responded to the best of our knowledge. As discussed previously the XPS data was used to calculate the C: TiO2 molar ratio and have corrected the information in the main text
Author Response File: Author Response.pdf
