A Highly Efficient Tribocatalysis of La/ZnO Powders for Degradation of Rhodamine B
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this work, the annealing dependence on the tribocatalysis of La-doped ZnO has been investigated. This is novel and interesting. Some comments are list here.
1. On basis of the XRD in Fig.2, the La are well doped ito ZnO. However, " La-modified powder has a higher BET surface area (32.34 m2/g) compared to the the ZnO sample (10.30 m2/g) " What's the reason for the high surface area after doping?
2. Is the decreasing after anealing due to the change of particles's size or the triboelectric performance of La-doped ZnO?
3. The ZnO is aso a well-known piezoctalysis. The references cited in this manuscript should be strengthened. How to distinguish piezocatalysis and tribocatalysis in this work? It's better to give a comprehensive discussion on basis of references report or experiment result.
Author Response
The manuscript: “A highly efficient tribocatalysis of La/ZnO powders for degra-dation of Rhodamine B”
by Dobrina Ivanova, Bozhidar Stefanov and Nina Kaneva.
Manuscript ID: catalysts-3123162
Dear Editors,
Thank you very much for the fast review process as well as the Reviewers comments and recommendations. Taking in mind all advices and suggestions we made the necessary corrections in order to improve the manuscript.
The new changes in the paper text are pointed out in blue color. Please, see our comments below.
Reviewer #1
In this work, the annealing dependence on the tribocatalysis of La-doped ZnO has been investigated. This is novel and interesting. Some comments are list here.
- On basis of the XRD in Fig.2, the La are well doped ito ZnO. However, " La-modified powder has a higher BET surface area (32.34 m2/g) compared to the the ZnO sample (10.30 m2/g) " What's the reason for the high surface area after doping?
The addition of the commercial La2O3 powder leads to a finely-dispersed secondary phase in the La/ZnO case. Additionally, even though we do not see much evidence of La-penetration inside the ZnO starting phase, it could be assumed that due to the different atomic size of the dopant some alteration of the starting ZnO crystals, could occur leading to surface roughening and imperfection. Such imperfections cause more surface roughness and disorder (Line defects, and dislocations, may cause surface texture), which may increase the specific surface area. In the revised version we have added TEM evidence to demonstrate the finely dispersed lanthanum oxide phase, however, a more in-depth BET investigation on the surface area effects in the La/ZnO samples will be conducted in future studies.
- Is the decreasing after anealing due to the change of particles's size or the triboelectric performance of La-doped ZnO?
In the revised version, as suggested by one of the other reviewers we have added XRD data for La/ZnO materials annealed not only at 100, but also at the extreme case of 500 °C and the intermediate 300 °C. A Rietveld and Scherrer analysis confirmed that the annealing leads to a growth of the ZnO crystals, which could be associated both with a decrease in the surface area and also more volume in which the tribogenerated charges could recombine, as well as lower amounts of surface defects which are often crucial catalytic centers. Hence, we can assume that the poorer performance of the annealed samples is possibly linked to an increase in crystallite size, and also re-structuring of the ZnO surface, however, this assumption is only based on the available evidence we have.
- The ZnO is aso a well-known piezoctalysis. The references cited in this manuscript should be strengthened. How to distinguish piezocatalysis and tribocatalysis in this work? It's better to give a comprehensive discussion on basis of references report or experiment result.
Indeed – the known piezoelectric properties of ZnO were one of the reasons that we decided to work on it as a base system for these tribocatalytic studies, which are new to our groups. As know, piezoelectric catalysis is based on the polarization characteristics of the material, which generate a polarization electric field under the action of ultrasound or mechanical action drive charges to its surface and trigger redox reactions. However, piezocatalysis depends on particular crystal orientations or texturing of the crystal to allow them (e.g., needle particles that could orient themselves between the stirring bar and the glass beaker surface). We have attempted to measure the d33 value for the ZnO and La/ZnO (dry) powders and the result came as nil, possibly because they are spherical and lack orientation when pressed in the d33 meter. Hence, this option was not discussed in the manuscript. For the second question – typically piezo- and tribocatalysis could be distinguished by performing experiments with a glass rod / glass surface of the reactor and comparing them to the PTFE/glass case (since a driving force for the tribo-activity is the charge transfer between the PTFE bar and the ZnO catalyst). We are really are hoping to continue the work on the tribocatalysts and follow up with an investigation of the crystal-shape effects on both mechanisms.
Apart from this discussion:
We strengthened the references in the introduction for the piezocatalysis, as you recommended.
We gave a few literature experiment data in the introduction, as you recommended.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript discusses a modified catalyst based on La/ZnO, showcasing its catalytic activity in the degradation of Rhodamine.
The manuscript could be considered for publication after addressing the following comments:
1. Complete the introduction by including the necessary references.
2. Determine the amount of hydroxyl radical produced by the new catalyst.
3. Include the reaction pathway for the degradation of Rhodamine.
4. Make improvements in grammar and language usage.
Make improvements in grammar and language usage.
Author Response
The manuscript: “A highly efficient tribocatalysis of La/ZnO powders for degra-dation of Rhodamine B”
by Dobrina Ivanova, Bozhidar Stefanov and Nina Kaneva.
Manuscript ID: catalysts-3123162
Dear Editors,
Thank you very much for the fast review process as well as the Reviewers comments and recommendations. Taking in mind all advices and suggestions we made the necessary corrections in order to improve the manuscript.
The new changes in the paper text are pointed out in blue color. Please, see our comments below.
Reviewer #2
The manuscript discusses a modified catalyst based on La/ZnO, showcasing its catalytic activity in the degradation of Rhodamine.
The manuscript could be considered for publication after addressing the following comments:
- Complete the introduction by including the necessary references.
We strengthened the references in the introduction, as you recommended
- Determine the amount of hydroxyl radical produced by the new catalyst.
In the revised version we conducted some additional experiments with scavengers to determine the contributions of both types of radicals. We also added a new figure related to the scavengers – Figure 5.
- Include the reaction pathway for the degradation of Rhodamine.
We included plausible reaction tribocatalytic degradation pathway for Rhodamine B, based on literature evidence, as you recommended. We added a new figure – Figure 9.
- Make improvements in grammar and language usage.
The revised version has been thoroughly read by a proficient English speaker and corrected accordingly. All of the revisions are marked in blue.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this study, the authors synthesized La/ZnO catalysts by mixing commercial ZnO and La2O3 followed by annealing. The materials were characterized and evaluated for tribocatalytic degradation of RhB. The work is meaningful, but several concerns need to be addressed before publication.
1. In the discussion of the XRD characterization, Scherrer's equation should be provided, and the crystallite size should be calculated and presented in a table.
2. In lines 109-111, the authors mentioned that the particle size and crystallite size of pure ZnO are 40 nm and 36.68 nm. The authors should explain where this information comes from.
3. Direct evidence of the La-O-Zn bond formation is missing from the manuscript. I recommend either FT-IR or XPS characterization.
4. The RhB concentration vs. time profile without catalyst should be provided in the manuscript.
5. Radical trapping experiments should be conducted to support the discussion in lines 144-166. Please refer to and cite these manuscripts for details about the hydroxyl radical scavenger, superoxide radical scavenger, and hole scavenger: https://doi.org/10.1016/j.cej.2022.137735; https://doi.org/10.3390/nano13010046
6. The titles of Sections 2.3 and 2.4 seem to be the same. Please revise.
7. There are some grammar errors in the manuscript. For example, in lines 20-22, it should be “Ultimately, it is demonstrated that by utilizing La/ZnO powders, contaminated wastewater can be efficiently treated employing tribocatalysis.” The English of the article should be thoroughly polished by a native English speaker or a professional service provider.
Comments on the Quality of English LanguageModerate editing of English language required
Author Response
The manuscript: “A highly efficient tribocatalysis of La/ZnO powders for degra-dation of Rhodamine B”
by Dobrina Ivanova, Bozhidar Stefanov and Nina Kaneva.
Manuscript ID: catalysts-3123162
Dear Editors,
Thank you very much for the fast review process as well as the Reviewers comments and recommendations. Taking in mind all advices and suggestions we made the necessary corrections in order to improve the manuscript.
The new changes in the paper text are pointed out in blue color. Please, see our comments below.
Reviewer #3
In this study, the authors synthesized La/ZnO catalysts by mixing commercial ZnO and La2O3 followed by annealing. The materials were characterized and evaluated for tribocatalytic degradation of RhB. The work is meaningful, but several concerns need to be addressed before publication.
- In the discussion of the XRD characterization, Scherrer's equation should be provided, and the crystallite size should be calculated and presented in a table.
We provided the Scherer equation in the paper, calculated the crystallite size, and presented them in the table (Table 1), as you recommended. Additionally, a Rietveld analysis was conducted.
- In lines 109-111, the authors mentioned that the particle size and crystallite size of pure ZnO are 40 nm and 36.68 nm. The authors should explain where this information comes from.
We agree with the reviewer about lines 109-111 in the article - we changed the sentences. Crystallite size was determined by Scherrer’s equation (in this case automatically during Rietveld refinement, based on all available peaks).
- Direct evidence of the La-O-Zn bond formation is missing from the manuscript. I recommend either FT-IR or XPS characterization.
We thank the reviewer for pointing out this sentence. The article presents FT-IR characterization on La/ZnO samples, but as seen from the figure, the Zn-O and La-O vibrations are outside our setup's possibilities. Because the characteristic virations of La–O are found at 860-850, 670, and 430 cm-1. Currently, the XPS apparatus is also unavailable during the summer months.
In order to best answer the reviewer's question, we used TEM analysis, shown in Figure 3, which demonstrates the distribution of the La2O3 particles on the ZnO surface and the formation of La-oxide / Zn-oxide interface.
We have deleted the indicated lanthanum-oxygen-zinc bonds in the text.
- The RhB concentration vs. time profile without catalyst should be provided in the manuscript.
We have added the data from the experiment without catalyst in Figure 3, as you recommended.
- Radical trapping experiments should be conducted to support the discussion in lines 144-166. Please refer to and cite these manuscripts for details about the hydroxyl radical scavenger, superoxide radical scavenger, and hole scavenger: https://doi.org/10.1016/j.cej.2022.137735; https://doi.org/10.3390/nano13010046
In the revised version we added additional experimental data for the contributions of hydroxyl and superoxide radicals to the overall tribodegradation activity using pure and lanthanum modified zinc oxide (annealed at 100oC – the most active composition). We also added a new figure related to the scavengers. We have added two references required by the reviewer:
[42] Duan, L.; Wang, B.; Heck, K.; Clark, C.; Wei, J.; Wang, M.; Metz, J.; Wu, G.; Tsai, A.; Guo, S.; Arredondo, J.; Mohite, A.; Senftle, T.; Westerhoff, P.; Alvarez, P.; Wen, X.; Song, Y.; Wong, M. Titanium oxide improves boron nitride photocatalytic degradation of perfluorooctanoic acid. Chem. Eng. J. 2022, 448, 137735.
[44] Lei, H.; Cui, X.; Jia, X.; Qi, J.; Wang, Z.; Chen, W. Enhanced Tribocatalytic Degradation of Organic Pollutants by ZnO Nanoparticles of High Crystallinity. Nanomaterials 2023, 13, 46.
- The titles of Sections 2.3 and 2.4 seem to be the same. Please revise.
We appreciate the repeatability shown. We have corrected the section titles.
- There are some grammar errors in the manuscript. For example, in lines 20-22, it should be “Ultimately, it is demonstrated that by utilizing La/ZnO powders, contaminated wastewater can be efficiently treated employing tribocatalysis.” The English of the article should be thoroughly polished by a native English speaker or a professional service provider.
We apologize for the deficiencies in the English presentation in the original submission and the text was thoroughly revised by a proficient English speaker with all the changes marked in blue.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsIn the present work, Kaneva et al. report the preparation of La/ZnO powders for the degradation of Rhodamine B. The effect of annealing temperature on RhB degradation is investigated. There is a lack in the characterization of the different catalysts prepared that could explain the differences on the performance of the different materials. It would be suggested to perform at least N2 porosimetry and XRD to all the samples prior to the publication of this work.
How it is explained that a small La loading lead to a increase in surface area from 10.3 to 32.3 m2/g . It should be considered alto to revise the decimal figures (to much accuracy in the measurements)
Authors stated that "...when the annealing temperature rises at modified samples, the grain size of La/ZnO powders decreases..." it is hard to believe if particle size is not properly measured further than showing SEM images.
Isotherm plots used in the determination of surface area should be shown at least in the supporting ingo.
On line 112, what Ln stand for?
With the La loading on the sample it is not logical to expect any change in ZnO crystallite. The mentioned increase is negligible.
In section 2.3 it is stated that " as annealing temperatures rise, the efficiency of all catalysts decreases" as consequence of aggregation of nanostructures. The data corresponding to the materials annealed at different temperatures must be provided. It would be also interesting if there is any change in textural properties that could explain the differences found.
Author Response
The manuscript: “A highly efficient tribocatalysis of La/ZnO powders for degra-dation of Rhodamine B”
by Dobrina Ivanova, Bozhidar Stefanov and Nina Kaneva.
Manuscript ID: catalysts-3123162
Dear Editors,
Thank you very much for the fast review process as well as the Reviewers comments and recommendations. Taking in mind all advices and suggestions we made the necessary corrections in order to improve the manuscript.
The new changes in the paper text are pointed out in blue color. Please, see our comments below.
Reviewer #4
In the present work, Kaneva et al. report the preparation of La/ZnO powders for the degradation of Rhodamine B. The effect of annealing temperature on RhB degradation is investigated.
There is a lack in the characterization of the different catalysts prepared that could explain the differences on the performance of the different materials. It would be suggested to perform at least N2 porosimetry and XRD to all the samples prior to the publication of this work.
We agree with the reviewer's recommendation. We therefore performed an X-ray analysis of the samples to trace the trend at the crystallite sizes and parameters of crystal lattice (Table 1), as you recommended. A detailed characterization and a Rietveld analysis of the two extreme cases (100 and 500 degrees) and also the intermediate annealing temperature (300 degres) was added. Unfortunately, we don't have the option to make the N2 porosimetry, due to the summer period and hope that the reviewer will understand.
How it is explained that a small La loading lead to a increase in surface area from 10.3 to 32.3 m2/g . It should be considered alto to revise the decimal figures (to much accuracy in the measurements)
The addition of the commercial La2O3 powder leads to a finely-dispersed secondary phase in the La/ZnO case. Additionally, even though we do not see much evidence of La-penetration inside the ZnO starting phase, it could be assumed that due to the different atomic size of the dopant some alteration of the starting ZnO crystals, could occur leading to surface roughening and imperfection. Such imperfections cause more surface roughness and disorder (Line defects, and dislocations, may cause surface texture), which may increase the specific surface area. In the revised version we have added TEM evidence to demonstrate the finely dispersed lanthanum oxide phase, however, a more in-depth BET investigation on the surface area effects in the La/ZnO samples will be conducted in future studies.
Authors stated that "...when the annealing temperature rises at modified samples, the grain size of La/ZnO powders decreases..." it is hard to believe if particle size is not properly measured further than showing SEM images.
The indicated part of the sentence is related to the SEM images and have removed it to avoid confusion (we would like to apologize for the confusing use of the term “grain”, as here it was meant to state that the particle (agglomerate) size is decreasing, purely based on the visual evidence by the SEM. In the revised version any comments on the effects of temperature on the catalysts grain size was made only based on the XRD data, and only referring to the crystallite average size (which is more logical indicator for the relationship to the activity of the samples).
Isotherm plots used in the determination of surface area should be shown at least in the supporting ingo.
We thank the reviewer for the recommendation regarding the specific surface and musk acknowledge that this analysis is an external service for us and we are not familiar with the way that the BET area is obtained from the physical measurement itself, thus, being honest, have not been asked to include isotherm plots in previous publications, since we only get the area itself reported by the colleagues who perform the measurement. Acknowledging that this answer is sadly demonstrating some ignorance, we will do our best to require the raw BET data and include it as figures in future works.
On line 112, what Ln stand for?
The abbreviation is derived from lanthanides (Ln), and is sometimes used as a placeholder in studies where more than one element is used. We removed it to avoid confusion and also – logically it was not needed, since the paper only deals with a single rare-earth element – La.
With the La loading on the sample it is not logical to expect any change in ZnO crystallite. The mentioned increase is negligible.
We agree with the reviewer that the increase is minor. There is no change in the zinc oxide structure, as it was confirmed by the Rietveld analysis + additional XRD work + TEM in the revised version.
In section 2.3 it is stated that " as annealing temperatures rise, the efficiency of all catalysts decreases" as consequence of aggregation of nanostructures. The data corresponding to the materials annealed at different temperatures must be provided. It would be also interesting if there is any change in textural properties that could explain the differences found.
We would like to thank the reviewer for this recommendation and have included a more detailed XRD analysis representing the entire temperature treatment range (the two extreme cases + the intermediate). Based on it is shown that the ZnO structure increases the crystallite size proportionally to the treatment temperature, which could be linked to the drop in catalyst activity.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript was substantially improved. Therefore, the manuscript can be considered as publishable.
Author Response
We greatly appreciate the reviewer's comment.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have addressed my concerns and greatly improved the manuscript. It can be accepted for publication now.
Author Response
We greatly appreciate the reviewer's comment.
