Enhancing the Photocatalytic Activity of TiO2/Na2Ti6O13 Composites by Gold for the Photodegradation of Phenol
, Atiek Rostika Noviyanti 1, Putri Rizka Lestari 2, Nobuhiro Kumada 2, Diana Rakhmawaty Eddy 1,* and Iman Rahayu 1
Ahmed K. Badawi
Round 1
Reviewer 1 Report
The manuscript by Muhamad Diki Permana et al reports “Gold as a promotor for the catalytic activity of TiO2/Na2Ti6O13 composites in the photodegaradion of phenol”. In this work, composites of Au/TiO2/Na2Ti6O13 are created in an effort to reduce recombination and boost photocatalytic activity. Gold was chosen because of its excellent surface plasmon resonance capabilities and high stability, which allow it to function well in the visible light spectrum. The phase composition, particle size, and bandgap values of the produced composites were determined. The findings revealed that TiO2, which is the rutile phase, made up the majority of the powder, together with Na2Ti6O13. The best composite had bandgap energy of 2.59 eV, good crystallinity, and tiny particle size. Additionally, it was 135 percent more efficient than the industry-standard (P25 TiO2) and 205 percent greater than efficiency without gold.
Overall, this work is interesting. However, some issues deserve clarification and should be carried out, which are not discussed detailed-wise. I recommend a major revision for the manuscript. Some concerns and suggestions are listed below for the author's attention.
Comment 1: The title is hard to read I suggest reformulating it, for example: ‘Enhancing the photocatalytic activity of TiO2/Na2Ti6O13 composites by Gold for the photodegradation of phenol’.
Comment 2: The English language is written in a very careful way, however, there are some minor mistakes. For example line 14: “which makes” remove the “s”.
Comment 3: The introduction part needs to be enhanced by adding and discussing recent references, especially about photocatalysis.
Comment 4: What is the novelty of this work? There is so much literature already available on the use of gold for the enhancement of photodegradation of phenol. So how this work is different from other reported work in literature? Show that in the introduction.
Comment 5: The authors mention in the introduction that “Sodium hexatitanate (Na2Ti6O13), and octatitanate (Na2Ti8O17) have excellent applications such as for ion exchange [22], photocatalysis [23,24], and sensors [25].”. How does this catalyst compare to others in the literature? For example, a review demonstrated that Photocatalysis could remove organic pollutants from wastewater effectively with different types of catalysts (10.1016/j.jwpe.2021.102089); the authors can compare their catalyst with the catalysts explained in this review.
Comment 6: The use of the Rietveld technique to refine the experimental XRD patterns was very significant, as it is hard to measure the lattice parameters and the phase structure directly from XRD. Please add a discussion about the goodness of fit in the manuscript before Table 1, I suggest moving all the sentences about the goodness of fit (GoF) in the supplementary data to the manuscript as it is very important. Authors can also take information from this recent article (10.1016/j.jwpe.2022.102847) about the use Rietveld technique.
Comment 7: There are no discussions about the mineralization which is very important in the removal process, please perform the TOC analysis in order to confirm the mineralization of products, if it is possible and available.
Comment 8: I suggest adding a scavenger study to explore the dominant reactive oxidant species (ROS) responsible for Phenol photodegradation and comprehend its mechanism.
Comment 9: if it is possible and available add GCMS or LCMS analysis in order to determine the by-products of the degradation of phenol.
Comment 10: There are some interesting characterization techniques such as XRD, FTIR, SEM and UV Vis, but some important information and analysis such as XPS and TEM can be very interesting to determine the characteristic of this interesting material before the application if it is possible and available.
Author Response
Response to Reviewer 1 Comments
Point 1: The title is hard to read I suggest reformulating it, for example: ‘Enhancing the photocatalytic activity of TiO2/Na2Ti6O13 composites by Gold for the photodegradation of phenol’.
Response 1: We have changed the title as suggested.
Point 2: The English language is written in a very careful way, however, there are some minor mistakes. For example line 14: “which makes” remove the “s”.
Response 2: We have replaced some errors in English and fixed them.
Point 3: The introduction part needs to be enhanced by adding and discussing recent references, especially about photocatalysis.
Response 3: We have added some recent references to the introduction.
Point 4: What is the novelty of this work? There is so much literature already available on the use of gold for the enhancement of photodegradation of phenol. So how this work is different from other reported work in literature? Show that in the introduction.
Response 4: Gold has been widely used as an enhancement for the photodegradation of phenol. However, no one has combined gold material with TiO2/Na2Ti6O13 composites. In this study, the new composite material was tested, namely Au/ TiO2/Na2Ti6O13 as a photocatalyst for phenol degradation which had not been previously reported. Statements are added to the introduction to Line 95-115.
Point 5: The authors mention in the introduction that “Sodium hexatitanate (Na2Ti6O13), and octatitanate (Na2Ti8O17) have excellent applications such as for ion exchange [22], photocatalysis [23,24], and sensors [25].”. How does this catalyst compare to others in the literature? For example, a review demonstrated that Photocatalysis could remove organic pollutants from wastewater effectively with different types of catalysts (10.1016/j.jwpe.2021.102089); the authors can compare their catalyst with the catalysts explained in this review.
Response 5: We add an explanation that “Photocatalysis is proven to be able to effectively remove organic pollutants from wastewater with various types of metal oxide such as TiO2 and ZnO” in paragraph 2 (Line 42-52) according to the recommended reference, which discusses the advantages of photocatalysis. However, comparisons of catalysts in the literature with those that have been prepared have been discussed in paragraphs 5 and 6 (Line 86-115).
Point 6: The use of the Rietveld technique to refine the experimental XRD patterns was very significant, as it is hard to measure the lattice parameters and the phase structure directly from XRD. Please add a discussion about the goodness of fit in the manuscript before Table 1, I suggest moving all the sentences about the goodness of fit (GoF) in the supplementary data to the manuscript as it is very important. Authors can also take information from this recent article (10.1016/j.jwpe.2022.102847) about the use Rietveld technique.
Response 6: The discussion on the goodness of fit (GoF) has been moved from the supplementary to the manuscript. In addition, information regarding the latest articles on the Rietveld Technique has been included.
Point 7: There are no discussions about the mineralization which is very important in the removal process, please perform the TOC analysis in order to confirm the mineralization of products, if it is possible and available.
Response 7: For now, it is not possible and not available to test the TOC analysis. This analysis will be carried out in our next research.
Point 8: I suggest adding a scavenger study to explore the dominant reactive oxidant species (ROS) responsible for Phenol photodegradation and comprehend its mechanism.
Response 8: For now, it is not possible and not available to test the ROS responsible for Phenol photodegradation. This analysis will be carried out in our next research.
Point 9: If it is possible and available add GCMS or LCMS analysis in order to determine the by-products of the degradation of phenol.
Response 9: At this time, it is not possible and unavailable to test by-products using GCMS or LCMS. This analysis will be carried out in our next research.
Point 10: There are some interesting characterization techniques such as XRD, FTIR, SEM, and UV Vis, but some important information and analysis such as XPS and TEM can be very interesting to determine the characteristic of this interesting material before the application if it is possible and available.
Response 10: For now, it is not possible and not available to perform XPS and TEM analysis. This analysis will be carried out in our next research.
Reviewer 2 Report
1- The abstract needs to be revised. Main methods and findings should be concisely mentioned in the abstract. Authors should consider the following;
a) First, introduce the prepared Au/TiO2/Na2Ti6O13 composites, then highlight the research gap that demonstrates the need to add the Au layer.
b) All material characterizations should be mentioned and the formation of the synthesized composite should also be highlighted.
c) Add some results regarding the optimum affecting conditions/applied kinetic models and highlight novel findings of the study.
2- Regarding the introduction part, the authors should generally highlight the global contamination and environmental pollution problems at the beginning of the introduction part. Then, highlight the significant application of the photocatalysis process rather than adsorption process and highlight its effectiveness in removing diverse contaminants. The authors can follow the following references (https://doi.org/10.1016/j.ceramint.2022.05.151) ; (https://doi.org/10.3390/catal12050500)
3- L76-81 should be revised and more clarified. the authors should indicate a clear gap in knowledge which this study seeks to bridge, and potentially contribute to knowledge.
4- An attractive figure describing the preparation process and how the prepared composites work has to be added to certainly explain material-contaminant interactions for the readers.
5- The released Au and titanium concentrations should be measured and monitored. After that, the authors should compare the results with standards WHO limits.
6- The authors have to add a cost estimation section to highlight the operating cost of applying such composites in diverse applications.
7- Composite recycling is a major concern. The authors have to conduct some experimental work to demonstrate the recycling ability of the Au/Na2Ti6O13 composite.
8- Do the authors recommend using the prepared composite in large scale applications for real water/wastewater treatment? What about the ease of preparation, operation, material recycling and reuse? And how to separate the spent particles in large scale applications? The authors have to highlight this in their work and recommendations.
9- The authors should identify the limitations of this study and the recommended future studies in the conclusion part.
Author Response
Response to Reviewer 2 Comments
Point 1: The abstract needs to be revised. Main methods and findings should be concisely mentioned in the abstract. Authors should consider the following:
- a) First, introduce the prepared Au/TiO2/Na2Ti6O13 composites, then highlight the research gap that demonstrates the need to add the Au layer.
- b) All material characterizations should be mentioned and the formation of the synthesized composite should also be highlighted.
- c) Add some results regarding the optimum affecting conditions/applied kinetic models and highlight novel findings of the study.
Response 1: We have revised the abstract and added it as suggested. However, the abstract that must be submitted is limited to a maximum of 200 words.
Point 2: Regarding the introduction part, the authors should generally highlight the global contamination and environmental pollution problems at the beginning of the introduction part. Then, highlight the significant application of the photocatalysis process rather than adsorption process and highlight its effectiveness in removing diverse contaminants. The authors can follow the following references (https://doi.org/10.1016/j.ceramint.2022.05.151); (https://doi.org/10.3390/catal12050500).
Response 2: We add in the introduction part about generally the global contamination and environmental pollution problems in paragraph 1 (Line 32-41). After that, we highlight the significant application of the photocatalysis process in paragraph 2 (Line 42-52).
Point 3: L76-81 should be revised and more clarified. the authors should indicate a clear gap in knowledge which this study seeks to bridge, and potentially contribute to knowledge.
Response 3: We have added several statements to explain the novelty of this research and also the potential to contribute to knowledge (Line 95-115).
Point 4: An attractive figure describing the preparation process and how the prepared composites work has to be added to certainly explain material-contaminant interactions for the readers.
Response 4: We have added an image that describes the composite preparation process in Figure 1.
Point 5: The released Au and titanium concentrations should be measured and monitored. After that, the authors should compare the results with standards WHO limits.
Response 5: In this study, the release of atoms in the photocatalysis process was not calculated with several considerations. This is because both titanium dioxide and sodium hexatitanate are very difficult to dissolve in water (The National Institute for Occupational Safety and Health (NIOSH), https://www.cdc.gov/niosh/npg/npgd0617.html). In this study also, titanium dioxide and sodium hexatitanate were used as heterogeneous catalysts which could be easily separated using techniques such as filtration or centrifugation (doi.org/10.1371/journal.pone.0164712). In addition, the Safety Data Sheet (Sigma-Aldrich, https://www.sigmaaldrich.com/ID/en/sds/aldrich/718467) shows that the LD50 limit of Oral-Rat- > 10,000 mg/kg, is much higher than that used in the experiment that is equal to 150 mg/L.
Furthermore, in the use of gold, based on the knowledge gained, it is determined that this material is not harmful and will not pose a risk to people or the environment (Safety Data Sheet Gold). According to NIOSH, occupational health risks associated with manufacturing and using nanomaterials are not fully understood. Minimal information is currently available on dominant exposure routes, potential exposure levels, and material toxicity of nanomaterials (https://www-s.nist.gov/m-srmors/msds/8013-MSDS.pdf).
Point 6: The authors have to add a cost estimation section to highlight the operating cost of applying such composites in diverse applications.
Response 6: We have calculated the estimated cost as well as the operating cost. However, other analyzes of design, system and payback analysis have not been carried out in this study, and will be carried out in future studies.
Point 7: Composite recycling is a major concern. The authors have to conduct some experimental work to demonstrate the recycling ability of the Au/Na2Ti6O13 composite.
Response 7: For now, in this study, it is not possible to demonstrate the recycling ability. This analysis will be carried out in our next research.
Point 8: Do the authors recommend using the prepared composite in large scale applications for real water/wastewater treatment? What about the ease of preparation, operation, material recycling and reuse? And how to separate the spent particles in large scale applications? The authors have to highlight this in their work and recommendations.
Response 8: For large-scale applications, the author thinks that this is the first step of research since gold is expensive. Thus, for further research, it is necessary to investigate other materials that can replace gold with a similar ability, which can reduce the band gap and help the hole-electron separation. However, in this study, the preparation of the material used is quite easy and inexpensive (except for gold).
Point 9: The authors should identify the limitations of this study and the recommended future studies in the conclusion part.
Response 9: The limitation of this research is the need for other cheaper materials sources that can reduce the bandgap so that it works in visible light (sunlight). In this study, the use of gold is quite difficult to apply on a large scale because it is expensive.
Round 2
Reviewer 1 Report
The revised manuscript by Muhamad Diki Permana et al reports “Enhancing the photocatalytic activity of TiO2/Na2Ti6O13 composites by Gold for the photodegradation of phenol”.
As already mentioned this work is interesting. However, even after the first revision, some issues deserve clarification and should be carried out. I recommend another major revision. I believe this manuscript requires very serious revision.
It is true that the authors have answered and corrected the first half of the questions, however second half has not been taken seriously.
All suggested analyses and studies have been left for their next investigation, what about this paper? Scavenger study, TOC analysis, GCMS or LCMS as well as XPS and TEM analysis are all very important to improve this research paper. If it is possible and available why not do them in this paper?
The newly added section (Large-Scale Economic Evaluation) is very interesting and has improved this section. However, I find it very similar to reference 65, authors should mention this reference multiple times in this section as they took from it. For example, the equation, mention the reference.
Author Response
Response to Reviewer 1 Comments
Point 1: All suggested analyses and studies have been left for their next investigation, what about this paper? Scavenger study, TOC analysis, GCMS or LCMS as well as XPS and TEM analysis are all very important to improve this research paper. If it is possible and available why not do them in this paper?
Response 1: We have added some data for TEM analysis and identification of the intermediates with GC-MS. However, other characterizations such as TOC analysis and XPS cannot be carried out because NOT possible and NOT available. The instruments are limited, we apologize for this.
Point 2: The newly added section (Large-Scale Economic Evaluation) is very interesting and has improved this section. However, I find it very similar to reference 65, authors should mention this reference multiple times in this section as they took from it. For example, the equation, mention the reference.
Response 2: We have corrected and added some additional references for this section.
Reviewer 2 Report
1. The manuscript must be improved by checking once again English grammar and technical writing.
2. There are identically copied sentences from REF.65 like “In this study, we also evaluate the large-scale economies of this process for industrial applications. Design criteria and a cost evaluation study for phenol removal using Au/TiO2/NTO composites to evaluate the commercial applicability of the proposed photocatalytic treatment system on a large scale” in the introduction part and “After that, cost estimation is proposed as a large-scale application. An integrated economic assessment for treating 1L/min of effluent is presented to examine the commercial potential of the system” in the abstract.
3. The methodology of conducting the cost estimation section is missing and some calculated numbers are incorrect.
4. The break-even analysis and payback analysis are essential and cannot be neglected or not accounted. This confirms the shortcomings of the cost estimation procedure. The authors have to add the break-even analysis and payback analysis.
5. Section 3.6 is incorrect and identically copied from REF.65. The authors have to conduct the cost estimation study on their own and not to copy it or it should be deleted. This explicit plagiarism should be avoided. It was sufficient to refer to the REF.65 and discuss the methodology of conducting the cost estimation study used in it and to comment that the cost in this research will certainly be higher due to the use of gold.
Author Response
Response to Reviewer 2 Comments
Point 1: The manuscript must be improved by checking once again English grammar and technical writing.
Response 1: We decided to correct the manuscript and check English grammar and technical writing to editing services at MDPI (https://www.mdpi.com/authors/english).
Point 2: There are identically copied sentences from REF.65 like “In this study, we also evaluate the large-scale economies of this process for industrial applications. Design criteria and a cost evaluation study for phenol removal using Au/TiO2/NTO composites to evaluate the commercial applicability of the proposed photocatalytic treatment system on a large scale” in the introduction part and “After that, cost estimation is proposed as a large-scale application. An integrated economic assessment for treating 1L/min of effluent is presented to examine the commercial potential of the system” in the abstract.
Response 2: We have changed the sentence.
Point 3: The methodology of conducting the cost estimation section is missing and some calculated numbers are incorrect.
Response 3: We have added a methodology of conducting the cost estimation and improved the calculations.
Point 4: The break-even analysis and payback analysis are essential and cannot be neglected or not accounted. This confirms the shortcomings of the cost estimation procedure. The authors have to add the break-even analysis and payback analysis.
Response 4: We have added break-even analysis and payback analysis.
Point 5: Section 3.6 is incorrect and identically copied from REF.65. The authors have to conduct the cost estimation study on their own and not to copy it or it should be deleted. This explicit plagiarism should be avoided. It was sufficient to refer to the REF.65 and discuss the methodology of conducting the cost estimation study used in it and to comment that the cost in this research will certainly be higher due to the use of gold.
Response 5: We have modified and carried out studies from several references so that the estimates made are considered from various previous studies. However, the estimation by including gold material is considered unprofitable because the gold price is quite high. Thus, break-even analysis and payback analysis, it is calculated by not including gold. Then, in the end, the suggestions and the weaknesses in this study are given that must be completed in the future.
Round 3
Reviewer 1 Report
As mentioned earlier, this work by Muhamad Diki Permana et al is interesting and all comments have been mostly addressed and fulfilled, improving this interesting manuscript. Therefore, it can be accepted in its current state.
Reviewer 2 Report
Accept.
