Sunlight-Driven Photodegradation of RB49 Dye Using TiO2-P25 and TiO2-UV100: Performance Comparison
, Moisés Canle 2, Chaimaa Haoufazane 3, Juan Arturo Santaballa 2, Belkheir Hammouti 4, Khalil Azzaoui 4,5, Shehdeh Joedh 6,*, Aomar Hadjadj 7 and Abderrahim El Hourch 1
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe work entitled: “Sunlight-driven photodegradation of RB49 dye using TiO2-P25 and TiO2-UV100: Performance comparison” by Zaaboul and co-workers describes the systematic evaluation of two commercial catalysts devoted to the degradation of a model dye such as RB49. This manuscript covers on the topic of water remediation and the potential pollution generated by the textile sector. The authors have made a systematic evaluation of adsorption kinetics, photocatalytic degradation and evaluation of total organic degradation. The work is systematic and well executed. The conclusions are solid and consistent with the experimental outcome. I can recommend the acceptance after some minor questions are addressed:
1) The authors should better justify the selection of this specific dye and make some additional discussion about other candidates that could be selected (both in the intro and discussion sections).
2) The authors should include a detail description accompanied by schemes and pictures of the experimental setup to perform the photocatalytic experiments in order to ensure reproducibility and replicability elsewhere.
3) Statitics and error bars corresponding to the experiments should be included in the revised version of the manuscript.
4) Authors should make a better effort to better justify the novelty of this study in comparison with other reports available in the literature.
Author Response
Reviewer 1
The authors are grateful to the reviewer for his careful reading of their manuscript and for his pertinent comments to improve the manuscript.
Comments and Suggestions for Authors
1°/ The authors should better justify the selection of this specific dye and make some additional discussion about other candidates that could be selected (both in the intro and discussion sections).
We have added the following two sentences to the Introduction: “Reactive blue 49 (RB49) dye was chosen because it is one of the most widely used and environmentally harmful dyes in the textile industry. In addition, its degradation can be easily monitored by the discoloration of the solution over time.”
2°/ The authors should include a detail description accompanied by schemes and pictures of the experimental setup to perform the photocatalytic experiments in order to ensure reproducibility and replicability elsewhere.
In the revised version of the manuscript, we have detailed the measurement protocol in the Experimental section and added Figure 1 for this purpose. The decision to study RB49 is explained in the Introduction. We apologize for this omission in the original version of the manuscript.
3°/ Statitics and error bars corresponding to the experiments should be included in the revised version of the manuscript.
In the revised version of the manuscript, we have indicated that the calibration curve that allows us to determine the concentration during photodegradation gives a measurement uncertainty not exceeding ± 2 mg/L. We have also provided the parameters determined by fitting with their uncertainties.
4°/ Authors should make a better effort to better justify the novelty of this study in comparison with other reports available in the literature.
As stated in the abstract, we emphasized in the introduction that, to our knowledge, no other RB 49 elimination study has combined UV-visible absorption measurements with total carbon measurements during the photodegradation of RB 49 under solar radiation.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
TiO2-P25 and TiO2-UV100 commercial photo-19 catalysts were tested within a photocatalyst concentration ranging from 0.5 to 4 g/L. TiO2-UV100 proved to be more active in adsorbing RB49 23 dye than TiO2-P25. The manuscript contains significant results, but certain additional information and consideration should be made prior publication.
1. The TiO2 in different morphology was studied previously in photocatalysis. At least two important reviews should be mention in the manuscript: Surface. Science.Reports. 66 (2011) 185–297and Surface Science Reports, 71 (2016) 473-546.
2. What is the difference in band gaps in the two titanate?
3. Is the OH radical formation the first step in photocatalysis?
4. The discussion of FTIR results should be in more details. What is the origin of the bands at ~1640 and 1068 cm-1? OH or adsorbed water?
Author Response
Reviewer 2
The authors are grateful to the reviewer for his careful reading of their manuscript and for his pertinent comments to improve the manuscript.
1°/ The TiO2 in different morphology was studied previously in photocatalysis. At least two important reviews should be mention in the manuscript: Surface. Science.Reports. 66 (2011) 185–297and Surface Science Reports, 71 (2016) 473-546.
The authors thank the reviewer for suggesting two interesting papers. One of them has been cited as reference 10.
2°/ What is the difference in band gaps in the two titanate?
The two photocatalysts have a fairly close bandgap around 3.3-3.4 eV (see reference 22). For this reason, we did not find it necessary to repeat the bandgap measurement.
3°/ Is the OH radical formation the first step in photocatalysis?
The photogenerated conduction band electron reacts with O2 to form the •O2- radical, which then reacts with the water molecule to form the OH• radical. This does not preclude the photogenerated hole from reacting with the water molecule to form the OH• radical.
4°/ The discussion of FTIR results should be in more details. What is the origin of the bands at ~1640 and 1068 cm-1? OH or adsorbed water?
We have enriched the discussion on the FTIR part. We have given the possible origins of these two bands.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsZaaboul et al. have studied the photocatalytic degradation efficiency of two types of TiO2 based NPs. Authors need to perform detailed measurements and analysis before publishing in this journal. My comments are as follows.
1. Authors should include the optical absorbance spectra of the two NPs and calculate their band gap, which will clearly show their photon absorbance capacity.
2. The FTIR analysis is not conclusive. Please try to add some meaningful analysis.
3. FTIR could also be done to understand the adsorption kinetics of RB49 by the two types of NPs.
4. Authors should discuss and perform a few experiments to demonstrate the nature of the photocatalytic degradation, whether it is surface-mediated or reactive oxygen species (ROS) mediated. Authors can refer and cite this article 10.1021/acsanm.0c00090.
5. The reusability and repeatability of the catalyst should also be discussed the manuscript.
6. Authors should also emphasize their motivation part in the introduction and justify properly the importance of a UV active NPs in photocatalysis when UV is only 4% in the solar spectrum. It is also advised to cite and discuss some important papers in this field a10.1021/acs.chemrev.7b00161.
Author Response
Reviewer 3
The authors are grateful to the reviewer for his careful reading of their manuscript and for his pertinent comments with a view to improving the manuscript.
My comments are as follows.
1°/ Authors should include the optical absorbance spectra of the two NPs and calculate their band gap, which will clearly show their photon absorbance capacity.
The two photocatalysts have a fairly close bandgap around 3.3-3.4 eV (see reference 22). For this reason, we did not find it necessary to repeat the bandgap measurement.
2°/ The FTIR analysis is not conclusive. Please try to add some meaningful analysis.
We have expanded and enriched the discussion on the FTIR part.
3°/ FTIR could also be done to understand the adsorption kinetics of RB49 by the two types of NPs.
We performed FTIR measurements before and after adsorption of RB49. These measurements do not seem to add any value to the paper's objective and we have decided not to include them.
4°/ Authors should discuss and perform a few experiments to demonstrate the nature of the photocatalytic degradation, whether it is surface-mediated or reactive oxygen species (ROS) mediated. Authors can refer and cite this article 10.1021/acsanm.0c00090.
The main aim of this study is to compare the photocatalytic performance of the two photocatalysts. The study of photodegradation mechanisms is certainly interesting, but will be the subject of another study. The very interesting article proposed by the reviewer does not, unfortunately, seem appropriate for this study.
5°/ The reusability and repeatability of the catalyst should also be discussed the manuscript.
As recommended by the reviewer, we have added this section on the reuse of photocatalysts (Figure 13).
6°/ Authors should also emphasize their motivation part in the introduction and justify properly the importance of a UV active NPs in photocatalysis when UV is only 4% in the solar spectrum. It is also advised to cite and discuss some important papers in this field a10.1021/acs.chemrev.7b00161.
The use of solar radiation is mainly driven by environmental and cost considerations, although photocatalysts have a band gap of about 3.3-3.4 eV. The aim is to compare their photocatalytic performance, not to make them active in the visible range. The interesting paper suggested by the reviewer and cited as reference 6.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe manuscript presents experimental research on the degradation of the dye RB49 with TiO2-P25 and TiO2-UV100 under solar irradiation. The authors present a comprehensive characterisation of the commercially available TiO2 nanoparticles and provide the results for adsorption kinetics, photocatalysis under solar radiation and TOC determination. They use the term “solar radiation” extensively, but never clearly define what is meant by it. In fact, the sentence in lines 115-116, with which they describe the radiation source: “This solution is then exposed to sunlight with an energy of about 200 W [21]”, is scientifically incorrect. Watt (W) is a unit for power, not energy. The reference only describes the use of a 300 W Xe lamp, which is very different from solar radiation. Its not clear what is the source of radiation used by the author to conduct the experiments.
This is an article on photodegradation. The optical source must be described in detail in all its optical properties. Without this information, all results presented in connection with photodegradation are not meaningful.
Author Response
Reviewer 4:
The manuscript presents experimental research on the degradation of the dye RB49 with TiO2-P25 and TiO2-UV100 under solar irradiation. The authors present a comprehensive characterisation of the commercially available TiO2 nanoparticles and provide the results for adsorption kinetics, photocatalysis under solar radiation and TOC determination. They use the term “solar radiation” extensively, but never clearly define what is meant by it. In fact, the sentence in lines 115-116, with which they describe the radiation source: “This solution is then exposed to sunlight with an energy of about 200 W [21]”, is scientifically incorrect. Watt (W) is a unit for power, not energy. The reference only describes the use of a 300 W Xe lamp, which is very different from solar radiation. Its not clear what is the source of radiation used by the author to conduct the experiments.
This is an article on photodegradation. The optical source must be described in detail in all its optical properties. Without this information, all results presented in connection with photodegradation are not meaningful.
The authors apologize to the reviewer for this inconvenience. The version sent is not the final version. The various typos have not been rectified. We are submitting a clean version in which the experimental conditions are properly described and the correct references given.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe revised version is suitble for publication.
Reviewer 3 Report
Comments and Suggestions for AuthorsAuthors addressed all the comments. Thus, could be accepted.
Reviewer 4 Report
Comments and Suggestions for AuthorsAfter careful reading of the revised manuscript, the authors have made the recommended changes that improve the overall quality of the article. It is now clear how the photodegradation experiments were carried out with the clarification of the sun exposure conditions. My recommendation is to accept.
