Rubber Tiles Made from Secondary Raw Materials with Immobilized Titanium Dioxide as Passive Air Protection
, Marija Tomaš 1, Ivan Brnardić 2, Benjamin Radetić 1, Vedrana Špada 3 and Ivana Grčić 1
Round 1
Reviewer 1 Report
This work reported that TiO2 P25 immobilized on rubber substrates and investigated its photocatalytic activity towards degradation of NH3. The manuscript does not present novel point of view. I don't think this manuscript meets the requirements of Processes, so it is not recommended to be published in Processes. And there are some problems in this manuscript that are unclear or need to be explained.
1. Introduction section did not present clear logic. And the second paper [2] is cited on line38,43,45,46,49,52 and 54, the author should add additional references or quote it at the end of a paragraph.
2. Line 165 “the recycled rubber tiles are mostly composed of 20% granules of size 0.5-2.0 mm and 80% of granules of size 2.0-3.5 mm”. Why is 20% granules of size 0.5-2.0 mm and 80% of granules of size 2.0-3.5 mm?
3. Line 295, the authors need to check the header and table should be on the same page.
4. In part of leaching test analysis, whether the initial concentration (without leaching) of various ions in the sample can be determined by XRF?
5. why did DOC and TSD concentrations rise after immobilization? the author needs to analyze the possible reasons.
6. The authors should check the format of references, the format is not uniform.
7. The diagram on the home page of the article is not clear enough, so it is suggested to make a mechanism diagram or flow chart.
8. Figure.1. A fixed glass instrument is recommended for background comparison.
9. The title of Table 1 should be on the same page as the table.
10.The reaction mechanism of experimental inquiry mentioned on page 8 is not graphically represented.
11.The conversion of ammonia to nitrogen gas is not adequately demonstrated in the article.
12. The EDS mapping in Figure 9 and figure 10 is not processed.
13. It does not show the mechanism and characteristics of material degradation and is not persuasive.
14. Figure 16 only shows the conversion rate of ammonia, not the selectivity of materials.
Author Response
The following text contains responses to your comments, while the revised manuscript is attached.
Response to Reviewer 1 Comments
Comments and Suggestions for Authors:
This work reported that TiO2 P25 immobilized on rubber substrates and investigated its photocatalytic activity towards degradation of NH3. The manuscript does not present novel point of view. I don't think this manuscript meets the requirements of Processes, so it is not recommended to be published in Processes. And there are some problems in this manuscript that are unclear or need to be explained.
Authors are kindly grateful for the suggestions to improve manuscript quality. In the following text, revisions in accordance with the given comments are elaborated. In the manuscript, all changes are visible in track changes, while in the following text changes are correlated with the comments. Therefore, we would be grateful if you would reconsider your first impression.
Point 1: Introduction section did not present clear logic. And the second paper [2] is cited on line38,43,45,46,49,52 and 54, the author should add additional references or quote it at the end of a paragraph.
Response 1: In accordance with the given suggestion introduction section is improved, all changes are visible in track changes, while in the following text changes are correlated with the comments.
Point 2: Line 165 “the recycled rubber tiles are mostly composed of 20% granules of size 0.5-2.0 mm and 80% of granules of size 2.0-3.5 mm”. Why is 20% granules of size 0.5-2.0 mm and 80% of granules of size 2.0-3.5 mm?
Response 2: This ratio is the original recipe for the production of rubber tiles by Gumiimpex d.o.o. from which we get the samples we work with. Since the idea is to have a new product in the future, we have decided to test if the existing recipe is applicable for TiO2 immobilization and therefore product improvement.
Point 3: Line 295, the authors need to check the header and table should be on the same page.
Response 3: Thank you for noticing an omission. According to your comment the stated was corrected.
Point 4: In part of leaching test analysis, whether the initial concentration (without leaching) of various ions in the sample can be determined by XRF?
Response 4: Yes, it could be done, thank you for the suggestion. We will do that in the future, but we have not gone for that option at the moment. In this work, we were only interested in the amount of leaching from the surface of the sample. In the future, we will take this into account and thus improve our experiments.
Point 5: why did DOC and TSD concentrations rise after immobilization? the author needs to analyze the possible reasons.
Response 5: After we have etched the surface of the rubber tile with NaOH solution, the tile is no longer inert, resulting in a pretreated surface. We are currently doing research on the immobilization of TiO2 on untreated rubber tiles, after which we will be able to conclude whether there is a connection between surface etching and an increase in DOC and TDS concentrations. The results are not published here because they will be included in the subject of the next work.
Point 6: The authors should check the format of references, the format is not uniform.
Response 6: Authors are grateful for pointing out the omission. Accordingly, format of references was coreccted.
Point 7: The diagram on the home page of the article is not clear enough, so it is suggested to make a mechanism diagram or flow chart.
Response 7: Authors are kindly grateful for the suggestions to improve manuscript quality. The diagram on the home page represents a graphic abstract that we have improved to make it clearer.
Point 8: Figure.1. A fixed glass instrument is recommended for background comparison.
Response 8: Thank you for the recommendation. Figure 1. is demonstrative, the granulate from the figure was not used for additional research. We do not own the granulate from the figure, it is from the company from which we purchase rubber tiles. During one visit, we took a picture of the granulate, to make it easier to explain the process of obtaining rubber tiles. In the future, we will make sure that the picture look more professional for the purpose of the article.
Point 9: The title of Table 1 should be on the same page as the table.
Response 9: Thank you for noticing. We will pay attention to that and other similar things in the manuscript before sending.
Point 10: The reaction mechanism of experimental inquiry mentioned on page 8 is not graphically represented.
Response 10: Authors are kindly grateful for the suggestions to improve manuscript quality. As recommended, the reaction mechanism of experimental inquiry is graphically shown in Figure 5.
Point 11: The conversion of ammonia to nitrogen gas is not adequately demonstrated in the article.
Response 11: The oxidation of ammonia was elaborated in previous paper that we cited hereby, paper [13]. We rephrased discussion part to sound more adequately in revised version of paper.
Point 12: The EDS mapping in Figure 9 and figure 10 is not processed.
Response 12: In accordance with the comments, information were processed in the manuscript. All changes are visible in track changes.
Point 13: It does not show the mechanism and characteristics of material degradation and is not persuasive.
Response 13: Authors are kindly grateful for the suggestions to improve manuscript quality. Our primary goal was not to investigate the mechanisms of material degradation, but to find the most optimal recipe for the immobilization of TiO2 on rubber substrates. Also, make a characterization of the material after immobilization and achieve photocatalytic degradation using an improved rubber substrate. In further research, we will focus on the aging of materials, which is also the subject of one of our upcoming papers.
Point 14: Figure 16 only shows the conversion rate of ammonia, not the selectivity of materials.
Response 14: The experiment was performed with a reference rubber tile and with a tile made with 2 g of TiO2. As explained in the paper (on pages 9, 10, 11 and 12) a surface coating was observed on samples with 4 and 10 g of TiO2, but the amount of photocatalysts and binders caused the hardening of the surface layer and the formation of crusts which may crack and TiO2 may leach from the surface. Since the tiles are used for different purposes, the surface layer wears out, so it is important that TiO2 is in the deeper layers as well. SEM/EDS analysis of substrates with 4 and 10 g showed that TiO2 particles did not enter into deeper layers of the rubber substrate, while immobilization of TiO2 with the lowest content (2g) was much better, because titanium particles are present in the deepest layer which confirms the successful penetration and immobilization of TiO2. For this reason, the tile made with 2 g of TiO2 was of greatest interest to us for the analysis of photocatalytic degradation.
Author Response File: 
Author Response.docx
Reviewer 2 Report
General] In this work, the authors introduced Rubber tiles immobilized with a P25 catalyst (at different weights of 2, 4, and 10 g) using a sol-gel method. The prepared materials were characterized by different tools, then tested for photocatalytic oxidation of NH3 to N2, as a prospective remediation strategy for polluted air. I recommend publishing this work after a major revision. Below are my comments and suggestion.
1-The abstract must be more informative by including more numerical findings and the importance of the work to attract the scientific reader and audience.
2- The graphical abstract looks very simple and confusing and does not clarify the objectives, idea, and outcomes of this work.
3- The introduction part is too long and does not set the manuscript in an international context to show how it builds based on previous works related to the topic subject. The introduction needs to be further revised to highlight the purpose of the study, what others have studied, and what needs further research. I still also miss the innovation factor that the publication should bring in the view of designing an effective photocatalytic air purifier system for real application.
4-In section 2.1.2, the authors should provide a detailed experimental procedure to ensure the reproducibility of materials, including the accurate weight percentage ratio of P25 to rubber tiles during the immobilization process, the mixing ratios of P25, ethanol, and water, the conc./ volume of acetic acid added, and reaction pH value, etc.
5- In section 2.4, a detailed experimental study should be given, including the light irradiance, NH3 gas flow, and partial pressure, catalyst dosage during the photocatalytic process, reaction time, and how temperature is controlled during the reaction, etc. Also, where are the performance metric equations during photocatalysis?
6- In Table 1, why did the weight of the rubber substrates decrease in some cases after NaOH treatment?
7- There are too many tables and figures in the search, which makes it very difficult for readers to reach and understand the most important results. Therefore, data presentation models must be reduced by effectively integrating some tables and figures to facilitate readers' understanding of the research data. For example, I propose an overlay for the FTIR spectra in one figure and improve the interpretation, taking into account the most important observations after NaOH treatment and TiO2 immobilization. The SEM/EDS figures need also an organization to avoid redundancy and repeat interpretation and observation again over again. Elemental compositions and parameters of rubber substrates (before and after TiO2 incorporation) might be merged in one table, to clearly show the difference.
8-Authors should focus on the discussion of the most important findings during the characterization data rather than the simple presentation of tabulated data. Also, all characterizations and experimental performance should be compared with that of adsorption/ photocatalytic activities of bare rubber tiles (before and after NaOH treatment).
9- As the photocatalytic removal rate of NH3 (as the main performance metric) is sensitively dependent on the operation conditions (e.g., catalyst mass, reaction time, light irradiance, etc.), the authors are asked to compute the actual performance of reported materials by using other proper metrics to avoid a biased judgment on the actual catalytic activity. The suggested performance metrics are quantum yield (QY), Space-time yield (STY), Figure of merits (FoM), turnover frequency (TOF), and turn-over number (TON). Down below are just examples of papers showing the concept of some of these metrics in photocatalytic performance comparison.
Bathla, Aadil, et al. "Recent advances in photocatalytic reduction of CO2 by TiO2-and MOF-based nanocomposites impregnated with metal nanoparticles." Materials Today Chemistry 24 (2022): 100870.
Bathla, Aadil, et al. "Recent progress in bimetallic nanostructure impregnated metal-organic framework for photodegradation of organic pollutants." Applied Materials Today 24 (2021): 101105.
Guo, Zhenguo, et al. "Highly efficient and selective photocatalytic CO2 reduction by iron and cobalt quaterpyridine complexes." Journal of the American Chemical Society 138.30 (2016): 9413-9416.
Ouyang, Ting, et al. "Dinuclear metal synergistic catalysis boosts photochemical CO2‐to‐CO conversion." Angewandte Chemie International Edition 57.50 (2018): 16480-16485.
Tamaki, Yusuke, Kazuhide Koike, and Osamu Ishitani. "Highly efficient, selective, and durable photocatalytic system for CO 2 reduction to formic acid." Chemical science 6.12 (2015): 7213-7221.
10- Based on the above-suggested performance metrics, the authors are asked to compare the performance of designed photocatalysts with published data.
11- the photocatalytic stability of designed materials over multiple reuse cycles and duration time should also be given and discussed. Also, the photocatalytic mechanism should be discussed, considering the potential change in the chemical and electronic structures of the hybrid materials (relative to bare P25-Tio2) via N2-ads/des isotherm, XPS, LSV, UV-Vis DRS, and PL characterization tools.
12- It is highly recommended to check the grammar throughout the article and correct it. Proofread the article as many language errors were identified.
Author Response
The following text contains responses to your comments, while the revised manuscript is attached.
Response to Reviewer 2 Comments
Comments and Suggestions for Authors:
General] In this work, the authors introduced Rubber tiles immobilized with a P25 catalyst (at different weights of 2, 4, and 10 g) using a sol-gel method. The prepared materials were characterized by different tools, then tested for photocatalytic oxidation of NH3 to N2, as a prospective remediation strategy for polluted air. I recommend publishing this work after a major revision. Below are my comments and suggestion.
Authors are kindly grateful for the suggestions to improve manuscript quality. In the following text, revisions in accordance with the given comments are elaborated. In the manuscript, all changes are visible in track changes, while in the following text changes are correlated with the comments.
Point 1: The abstract must be more informative by including more numerical findings and the importance of the work to attract the scientific reader and audience.
Response 1: Thank you for your comment. According to the suggestion, authors improved the abstract.
Point 2: The graphical abstract looks very simple and confusing and does not clarify the objectives, idea, and outcomes of this work.
Response 2: Authors are kindly grateful for the suggestions to improve manuscript quality. The graphic summary has been improved as recommended, the objectives, ideas and outcome of the work have been clarified in more detail.
Point 3: The introduction part is too long and does not set the manuscript in an international context to show how it builds based on previous works related to the topic subject. The introduction needs to be further revised to highlight the purpose of the study, what others have studied, and what needs further research. I still also miss the innovation factor that the publication should bring in the view of designing an effective photocatalytic air purifier system for real application.
Response 3: Authors are kindly grateful for the comment. According to the suggestion, the introduction part was revised and appropriate references were added. At the end of the introduction, the aim of this paper is highlighted, with regard to the reviewed literature [10, 11, 12, 13, 14, 15, 16, 17]. Pure/co-doped TiO2 is used for air protection, and our goal is to apply it to rubber tiles. Also, the rubber tiles are made of recycled rubber, which gives additional value in the framework of the circular economy and environmental protection.
Point 4: In section 2.1.2, the authors should provide a detailed experimental procedure to ensure the reproducibility of materials, including the accurate weight percentage ratio of P25 to rubber tiles during the immobilization process, the mixing ratios of P25, ethanol, and water, the conc./ volume of acetic acid added, and reaction pH value, etc.
Response 4: Thank you for your comments, the information has been provided accordingly.
Point 5: In section 2.4, a detailed experimental study should be given, including the light irradiance, NH3 gas flow, and partial pressure, catalyst dosage during the photocatalytic process, reaction time, and how temperature is controlled during the reaction, etc. Also, where are the performance metric equations during photocatalysis?
Response 5: Experimental study was better formulated in revised paper. However, detailed kinetic study of NH3 photocatalytic oxidation was not the part of current study. The ammonia oxidation was merely used as a marker for evaluation of photocatalytic properties of modified rubber tiles. In revised paper, we give a comparison of experimental results based on basic analysis of NH3 decrease rates.
Point 6: In Table 1, why did the weight of the rubber substrates decrease in some cases after NaOH treatment?
Response 6: A decrease was observed in two samples, which can be explained by the fact that a small piece of rubber separated during leaching, which was visible to us from the residue at the bottom of the bottle after leaching. The increase occurred after the NaOH treatment due to residual Na inside the tiles, which can be seen from EDS analysis, and due to the formation of OH groups, which can be seen from FTIR.
Point 7: There are too many tables and figures in the search, which makes it very difficult for readers to reach and understand the most important results. Therefore, data presentation models must be reduced by effectively integrating some tables and figures to facilitate readers' understanding of the research data. For example, I propose an overlay for the FTIR spectra in one figure and improve the interpretation, taking into account the most important observations after NaOH treatment and TiO2 immobilization. The SEM/EDS figures need also an organization to avoid redundancy and repeat interpretation and observation again over again. Elemental compositions and parameters of rubber substrates (before and after TiO2 incorporation) might be merged in one table, to clearly show the difference.
Response 7: Authors are kindly grateful for the suggestions to improve manuscript quality. The interpretation of FTIR analysis has been improved. Regarding the figures, if we overlay spectra in one figure, the presentation will be unclear and it will be difficult for readers to reach the most important results, because the spectrum range is different for both images. As recommended, the SEM/EDS images have been organized, the table have been merged for clarity, and the text has been improved accordingly.
Point 8: Authors should focus on the discussion of the most important findings during the characterization data rather than the simple presentation of tabulated data. Also, all characterizations and experimental performance should be compared with that of adsorption/ photocatalytic activities of bare rubber tiles (before and after NaOH treatment).
Response 8: Thank you for your comments. According to the suggestion, authors have discussed in more detail the most important findings during the characterization data. In the other hand, our goal was to apply TiO2 as a photocatalyst on the surface of rubber tiles, and considering the need for OH groups, the surface was treated with NaOH. The influence of the surface treated with NaOH was only an intermediate step, and as such was not investigated. In future research, we will pay more attention to this.
Point 9: As the photocatalytic removal rate of NH3 (as the main performance metric) is sensitively dependent on the operation conditions (e.g., catalyst mass, reaction time, light irradiance, etc.), the authors are asked to compute the actual performance of reported materials by using other proper metrics to avoid a biased judgment on the actual catalytic activity. The suggested performance metrics are quantum yield (QY), Space-time yield (STY), Figure of merits (FoM), turnover frequency (TOF), and turn-over number (TON). Down below are just examples of papers showing the concept of some of these metrics in photocatalytic performance comparison.
Response 9: Our work is based on achieving successful immobilization in order to achieve photocatalysis, which was added to the work only as a confirmation that we are going in the right direction. Since photocatalysis has been achieved, future works will be focused on a deeper analysis of photocatalytic research. In revised paper, we introduced basic kinetic analysis based on experimental results. The metrics that reviewer suggested should be a part of single paper whereby authors compare different modified rubber tiles. It is the extensive amount of work, equations and explanation behind those numbers, that would only perplex the audience if given in current paper. It is indeed in preparation and we believe it is better to put in a sequel.
Point 10:
Bathla, Aadil, et al. "Recent advances in photocatalytic reduction of CO2 by TiO2-and MOF-based nanocomposites impregnated with metal nanoparticles." Materials Today Chemistry 24 (2022): 100870.
Bathla, Aadil, et al. "Recent progress in bimetallic nanostructure impregnated metal-organic framework for photodegradation of organic pollutants." Applied Materials Today 24 (2021): 101105.
Guo, Zhenguo, et al. "Highly efficient and selective photocatalytic CO2 reduction by iron and cobalt quaterpyridine complexes." Journal of the American Chemical Society 138.30 (2016): 9413-9416.
Ouyang, Ting, et al. "Dinuclear metal synergistic catalysis boosts photochemical CO2‐to‐CO conversion." Angewandte Chemie International Edition 57.50 (2018): 16480-16485.
Tamaki, Yusuke, Kazuhide Koike, and Osamu Ishitani. "Highly efficient, selective, and durable photocatalytic system for CO 2 reduction to formic acid." Chemical science 6.12 (2015): 7213-7221.
Based on the above-suggested performance metrics, the authors are asked to compare the performance of designed photocatalysts with published data.
Response 10:
Authors are kindly grateful for the suggestions. The basic kinetic analysis was added and performance was compared by the observed rates of NH3 decrease in PWT during experiments. Our future work will present suggested performance metrics.
Point 11: the photocatalytic stability of designed materials over multiple reuse cycles and duration time should also be given and discussed. Also, the photocatalytic mechanism should be discussed, considering the potential change in the chemical and electronic structures of the hybrid materials (relative to bare P25-Tio2) via N2-ads/des isotherm, XPS, LSV, UV-Vis DRS, and PL characterization tools.
Response 11: Authors are kindly grateful for the suggestions to improve manuscript quality. Our primary goal was to find the most optimal recipe for the immobilization of TiO2 on rubber substrates. Also, make a characterization of the material after immobilization and achieve photocatalytic degradation using an improved rubber substrate. In further research, we will focus on the aging of materials, which is also the subject of one of our upcoming papers. For now, we have made 3 measurements using rubber tiles on which TiO2 is immobilized, but we expect that there will be no changes as in the mentioned work [B. Plavac, I. Grčić, I. Brnardić, V. Grozdanić, and S. Papić, “Kinetic study of salicylic acid photocatalytic degradation using sol–gel anatase thin film with enhanced long-term activity,” React. Kinet. Mech. Catal., vol. 120, no. 1, pp. 385–401, 2017, doi: 10.1007/s11144-016-1090-x.].
Point 12: It is highly recommended to check the grammar throughout the article and correct it. Proofread the article as many language errors were identified.
Response 12: Authors are apologizing for the grammatical errors. In accordance with the given suggestion, erros has been revised and improved. Revised paper was thoroughly checked by native English speaker.
Author Response File: Author Response.docx
Reviewer 3 Report
1. It is well known that photocatalysis based on TiO2 has strong oxidation capacity. As an organic base material, the interaction between rubber and active component TiO2 is very important. The author used SEM to characterize the samples, but the magnification was too small, the scale bar was 1 to 2 mm, which basically reached the level of naked eye observation. No further details were available from the photos. The results of EDS and IR spectra are also predictable;
2. The leaching experiment condition adopted by the author is soaked in deionized water for 24 hours, which is too different from the actual application scenario of the material, and cannot show the stability of the sample. This is especially true when TiO2 produces oxidizing species under light;
3. As can be seen from the experimental results of photocatalytic degradation of NH3, there is no significant difference in the transformation of NH3 in the samples under dark and light conditions within 200 minutes.
Although the research content of this work is very meaningful, in my opinion, the conclusion of the manuscript loses its referential value because of the absence of the above key issues.
Author Response
Point 1: It is well known that photocatalysis based on TiO2 has strong oxidation capacity. As an organic base material, the interaction between rubber and active component TiO2 is very important. The author used SEM to characterize the samples, but the magnification was too small, the scale bar was 1 to 2 mm, which basically reached the level of naked eye observation. No further details were available from the photos. The results of EDS and IR spectra are also predictable;
Response 1: Authors are kindly grateful for the suggestions to improve manuscript quality. In the following text, revisions in accordance with the given comments are elaborated. In the manuscript, all changes are visible in track changes, while in the following text changes are correlated with the comments.
Higher magnification of SEM are provided. The results of EDS and IR spectra are predictable for the surface, but not for the layers. The authors agree that if we use TiO2, NaOH and silanes, we will have OH groups and bonds of titanium silicon and oxygen, but we could not predict the same for the interior of the layers. Until we did an EDS analysis by layers, we could not know what to expect in each layer. An example is the sol-gel immobilization of samples with 4 and 10 g of TiO2, where we did not find titanium in the deeper layers because it hardened on the surface. We were not able to predict that. We did not perform FTIR by layers because EDS sufficiently confirmed and indicated that titanium is present in the deeper layers of the sample with 2 g of TiO2, because if we had not achieved binding of titanium, it would have fallen out when cutting the layers.
Point 2: The leaching experiment condition adopted by the author is soaked in deionized water for 24 hours, which is too different from the actual application scenario of the material, and cannot show the stability of the sample. This is especially true when TiO2 produces oxidizing species under light;
Response 2: Leaching test is used to quantify the leaching of hazardous substances from media to groundwater and other water systems. Test is standardized by international agencies such as the International Organization for Standardization (ISO) because the results can provide important information for understanding and addressing human health risks from contaminated soil. None of the laboratory leaching tests can replace the leaching behavior of materials in nature. Nevertheless, when used within the proper framework, the leaching test can ensure helpful information for environmental decision making. Our primary goal was to analyze whether the substrates release and if so, in what concentrations certain potential harmful components. In future research, we plan to conduct tests in acidic and alkaline conditions, as well as to conduct simulation of flow over substrates in cascades. Likewise, photocatalytic properties were tested in a PWT reactor to see which compounds are formed/degraded in the presence of sunlight.
Point 3: As can be seen from the experimental results of photocatalytic degradation of NH3, there is no significant difference in the transformation of NH3 in the samples under dark and light conditions within 200 minutes.
Response 3: Thank you for your comment. For this reason, we made a basic kinetic study and determined decomposition rate constants (Table 6. Experimentally determined rates of NH3 content decrease in PWT). The table introduces in the manuscript shows that the best results were shown in the following order: modified rubber tiles (with TiO2) with irradiation (0.0935) > recycled rubber tiles (referent) with irradiation (0.0826) > recycled rubber tiles (referent) without irradiation (0.0750) > modified rubber tiles (with TiO2) without irradiation (0.0581). The observed results were explained in the text.
Although the research content of this work is very meaningful, in my opinion, the conclusion of the manuscript loses its referential value because of the absence of the above key issues.
The authors hope that the explanations given have justified the value of the manuscript. Therefore, we would be grateful if you would reconsider your first impression.
Author Response File: Author Response.docx
Reviewer 4 Report
The authors report surface modification of recycled rubber tiles with commercial TiO2 samples (P25) and their application as a photocatalyst for NH3 oxidation. Using SEM, EDS mapping, and FTIR techniques, it likely shows the immobilization of TiO2 particles on rubber tiles. Based on stability leaching analysis, it shows the hazardous species including As, Ba, Cd, Cr, etc. are within the allowed concentrations while not affecting the surrounding environment. By introducing TiO2 onto rubber tiles, those materials give out kind of better performance forward photocatalysis, showing photocatalytic extent 1.60 times higher than adsorption with 1.13 times higher than oxidation compared to referent recycled rubber. The results are somehow interesting, particularly combining a recyclable material with photocatalysis. However, this manuscript cannot be recommended for publication with its current shape. Here are some suggestions for authors to be considered for the improvement needed.
1) Here are a couple of writings lack evidence/relative background throughout the manuscript. As shown following:
Page 2, “The application of heterogeneous photocatalysis in air purification has been developed over the last decades.” How the photocatalysts developed? How did they work for air purification?
Page 2. “TiO2 photocatalytic layer acts as a surface modification of such building materials, thus, keeping the building exterior clean by utilizing solar energy.” What is the photocatalytic model reaction and how do the catalysts work?
2) The authors should seriously organize data and figure captions. Here are some examples:
Scale bars for Figure 1, Figure 4 and Figure 6 will be needed. Otherwise, those are not meaningful at all.
Also, SEM images are pretty hard to follow, high-quality ones will be needed.
3) For sample preparation. About the sol-gel method, here should be more details about the preparation process. How is the hydrolysis between TEOS and water? What’s the role of acetic acid added here?
4) For the weighing of samples, why the mass change differently after NaOH treatment? The same after sol-gel?
5) The FTIR data need to be carefully analyzed for the surface-immobilized TiO2. For example, where’s the peak at 950 cm-1 from for reference green samples?
6) For the photocatalytic oxidation of NH3 to N2. A few data points should be provided for N2 concentration evolution for confirming the real oxidation product forming. Also, what about the stability of the photocatalysts?
Author Response
Comments and Suggestions for Authors:
The authors report surface modification of recycled rubber tiles with commercial TiO2 samples (P25) and their application as a photocatalyst for NH3 oxidation. Using SEM, EDS mapping, and FTIR techniques, it likely shows the immobilization of TiO2 particles on rubber tiles. Based on stability leaching analysis, it shows the hazardous species including As, Ba, Cd, Cr, etc. are within the allowed concentrations while not affecting the surrounding environment. By introducing TiO2 onto rubber tiles, those materials give out kind of better performance forward photocatalysis, showing photocatalytic extent 1.60 times higher than adsorption with 1.13 times higher than oxidation compared to referent recycled rubber. The results are somehow interesting, particularly combining a recyclable material with photocatalysis. However, this manuscript cannot be recommended for publication with its current shape. Here are some suggestions for authors to be considered for the improvement needed.
Authors are kindly grateful for the suggestions to improve manuscript quality. In the following text, revisions in accordance with the given comments are elaborated. In the manuscript, all changes are visible in track changes, while in the following text changes are correlated with the comments.
Point 1: Here are a couple of writings lack evidence/relative background throughout the manuscript. As shown following:
Page 2, “The application of heterogeneous photocatalysis in air purification has been developed over the last decades.” How the photocatalysts developed? How did they work for air purification?
Page 2. “TiO2 photocatalytic layer acts as a surface modification of such building materials, thus, keeping the building exterior clean by utilizing solar energy.” What is the photocatalytic model reaction and how do the catalysts work?
Response 1: Thank you for your comment. According to the suggestion, authors improved the manuscript.
Point 2: The authors should seriously organize data and figure captions. Here are some examples: Scale bars for Figure 1, Figure 4 and Figure 6 will be needed. Otherwise, those are not meaningful at all. Also, SEM images are pretty hard to follow, high-quality ones will be needed.
Response 2: Authors are kindly grateful for the suggestions to improve manuscript quality. Scales for Figure 1, Figure 4 and Figure 6 have been added, and figures and figures descriptions for SEM and FTIR analysis have been improved.
Point 3: For sample preparation. About the sol-gel method, here should be more details about the preparation process. How is the hydrolysis between TEOS and water? What’s the role of acetic acid added here?
Response 3: Thank you for your comment. The sol-gel method is explained in more detail. The mechanism of the hydrolysis and condensation reactions of silicon alkoxide is shown in literature; Iler, R.K.: The Chemistry of Silica, Wiley, New York, 1979. It depends on the pH of the medium, because the hydrolysis reaction can be catalyzed by an acid or a base. Furthermore, under acid catalysis, coil structures are formed, on the other hand basic catalysts leading to cage products which could trap TiO2 particles and reduce photocatalytic properties. The point is that in acidic conditions smaller particles are formed what was our goal. Because TEOS is used as a binder of TiO2 and rubber, bigger binder particles formed will lead to the formation of larger particles on the surface of the rubber what can resulted to a weaker connection of TiO2 with the rubber. Also, problem is possibility of the formation of larger agglomerates, with smaller active surface, that could be separated more easily due to mechanical impact on the surface.
Point 4: For the weighing of samples, why the mass change differently after NaOH treatment? The same after sol-gel?
Response 4: The increase in mass occurred after the NaOH treatment due to residual Na inside the tiles, which can be seen from EDS analysis, and due to the formation of OH groups, which can be seen from FTIR. A decrease of mass was observed in two samples after the NaOH treatment, which can be explained by the fact that a small piece of rubber separated during leaching, which was visible to us from the residue at the bottom of the bottle after leaching. Likewise, after sol-gel there was an increase in mass because TiO2 particles were immobilized on the surface of the recycled rubber tiles, which was proven by SEM/EDS and FTIR analysis.
Point 5: The FTIR data need to be carefully analyzed for the surface-immobilized TiO2. For example, where’s the peak at 950 cm-1 from for reference green samples?
Response 5: Authors are kindly grateful for the comment. Thank you for the notice of the omission that was done by authors. FTIR data were carefully analyzed and described more clearly.
Point 6: For the photocatalytic oxidation of NH3 to N2. A few data points should be provided for N2 concentration evolution for confirming the real oxidation product forming. Also, what about the stability of the photocatalysts?
Response 6: Authors are kindly grateful for the suggestions to improve manuscript quality. We observed an increase in nitrogen concentration on the instrument we used (max. 2 %), however, considering that there is a lot of nitrogen in the air, we did not consider it relevant enough to claim that this is evidence of nitrogen formation, since low percentage could be erroneous reading from ballast gases. For this reason, we measured NOx to see that there is no NOx. On the other hand, we measured nitrates and nitrites in the gas-washing bottle to confirm that there are none in the water either. After experiments we rinsed the photocatalysts with distilled water and check for any additional NO3-/NO2- in water as well. Our primary goal was to find the most optimal recipe for the immobilization of TiO2 on rubber substrates. Also, make a characterization of the material after immobilization and achieve photocatalytic degradation using an improved rubber substrate. In further research, we will focus on the aging of materials, which is also the subject of one of our upcoming papers. For now, we have made 3 measurements using rubber tiles on which TiO2 is immobilized, but we expect that there will be no changes as in the mentioned work [B. Plavac, I. Grčić, I. Brnardić, V. Grozdanić, and S. Papić, “Kinetic study of salicylic acid photocatalytic degradation using sol–gel anatase thin film with enhanced long-term activity,” React. Kinet. Mech. Catal., vol. 120, no. 1, pp. 385–401, 2017, doi: 10.1007/s11144-016-1090-x.].
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The author has made some changes in the revised manuscript, but the manuscript still does not meet the requirements of a qualified manuscript in terms of innovation and logic.
Author Response
The author has made some changes in the revised manuscript, but the manuscript still does not meet the requirements of a qualified manuscript in terms of innovation and logic.
Authors are grateful for the suggestions to improve manuscript quality. Manuscript was revised according to the new comments of other reviewers. Hopefully, it now meets the criteria for the acceptance.
Author Response File: Author Response.docx
Reviewer 2 Report
It is important to carefully check the formating and English style, Proofreading.
Author Response
It is important to carefully check the formating and English style, Proofreading.
The authors are grateful for all suggestions given to improve the manuscript quality. The manuscript was revised according to the new comments of other editors. The manuscript was also checked by a native English speaker.
Author Response File: Author Response.docx
