Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructure (KTiO_xs)/AlO(OH) Composites for Enhanced Photocatalytic Performance

Round 1

Reviewer 1 Report

Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructures (KTiO_xs)/AlO(OH) composites for enhanced Photocatalytic Performance

So Yoon Lee, Tatsuya Matsubara, Daiki Numata and Ai Serizawa

The manuscript deals with the synthesis of K-doped TiOx photocatalyst, supported on AlO(OH), and their photocatalytic evaluation in methylene blue photo-degradation. Steam coating process and wet corrosion process were used for the synthesis of AlO(OH) support and KTiOx photocatalyst, aiming to obtain to obtain a “layered” structure with nanoparticles of TiOx anchored on the support. Although the relevance of the topic, the originality and novelty of the present study it is not evidenced and both photocatalytic and physical-chemical properties of the studied systems are not sufficiently discussed and compared with literature. Moreover, the discussion of results is sometimes vague and a clear definition of structure-activity relationship is missing. Therefore, I recommend to reconsider the manuscript for publication after major revisions. In particular:

1. The abstract is too long and dispersive. As reposted in the “Instruction for Authors”: “The abstract should be a total of about 200 words maximum. The abstract should be a single paragraph and should follow the style of structured abstracts, but without headings: 1) Background: Place the question addressed in a broad context and highlight the purpose of the study; 2) Methods: Describe briefly the main methods or treatments applied. Include any relevant preregistration numbers, and species and strains of any animals used. 3) Results: Summarize the article's main findings; and 4) Conclusion: Indicate the main conclusions or interpretations.”
2. The Introduction is completely centred on the description of the materials and the synthesis methods. A point-to-point analysis of the state-of-the-art of TiOx based semiconductors in similar applications (ex. wastewater photo-purification, CO2 photoreduction, water splitting) should be added. Moreover, the novelty and originality of the work should be better highlighted, considering the vast literature on these systems. Accordingly, the bibliography should be enlarged also considering the following relevant papers:  http://dx.doi.org/10.1016/j.jphotochemrev.2015.06.001; https://doi.org/10.1016/j.jcou.2018.05.010; http://dx.doi.org/10.1016/j.progsolidstchem.2004.08.001; http://dx.doi.org/10.1016/j.enconman.2013.07.046.

3. The style used for Introduction is quite informal. Several expressions are not suitable for a scientific paper. Moreover, AlO(OH) is a SUPPORT not a SUPPORTER.
4. Some sentences are not clear. I suggest to rewrite them, better clarifying the information. Line 40 “Complex high quality of nanostructure…”; line 52 “So far…disadvantage”, lines 69-75, lines 87-89 “Generally…autoclave”.
5. Generally, higher temperatures lead to sintering phenomena in catalysis, thus reducing surface area. In this case, the AlO(OH) support treated at 280°C shows the highest surface area exposure. How can the Author justify this point? Moreover, BET surface area, pore size distribution and pore volume evaluation through N₂-physisorption analysis are more appropriate for the scope of the work and should be reported.
6. Uv-Vis spectra of the studied samples should be reported, along with the determination of band gap energies via extrapolation from Tauc plot.
7. XRD patterns of the final KTiOx photocatalyst could be useful for confirming the structure and properties of the materials.
8. The actual role of K-doping on photocatalytic activity of the studied samples is not sufficiently discussed. From the results reported, it simply appears that the “10mol/L-KOH treated TiO2 at 280°C for 24h” sample exerts the best photocatalytic performance only in reason of its higher surface area exposure. A deeper correlation with chemical-physical and photo-physical properties of the materials is therefore essential to underline the occurrence of structure-activity relationships.
9. The photocatalytic results obtained should be compared with literature data.

Author Response

This is our answer about the comments.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled “Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructures (KTiOxs)/AlO(OH) composites for Enhanced Photocatalytic Performance” fabricates the photocatalysis system which is made from KTiOxs/AlO(OH) composites. Although the characterization is well carried out, the manuscript cannot be accepted in its current form because it has not been well prepared and requires substantial English editing such as:

1. The language and grammar need editing, some nonacademic words, and using third person (We, and our), the passive voice should be used for academic writing.
2. The Introduction section is considerably composed, with a description of the existing literature works. Nevertheless, many leading papers on titanium oxide, TiO₂ (titania) phases, their band gaps, and doping are missing.
3. The XRD of KTiOxs/AlO(OH) composites is not provided, and the details of the obtained AlO(OH) films identification by the XRD diffraction are not provided. What is the software, and the database being used?
4. Poor resolution figures (Images), and some scale bars are not correct (Fig. 1, Fig. 6. and Fig. 7).
5. In page 4, line 154-155, “However, crystalized thick film observed on the surface after subjecting the steam coating process at 280 °C for 24 h (Figure 1(b))” Why? what is the effect of temperature on the film thickness?
6. Several figure captions are cannot be observed clearly by the readers (Such as Fig. 10).
7. The preparation of the samples (AlO(OH), K-incorporated Ti (KTiOxs), and KTiOxs/AlO(OH)) can be put in one section, with the KTiOxs/AlO(OH) composites should be studied mainly and extensively.

Author Response

This is our answer about the comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript reports the synthesis of (KTiOxs)/AlO(OH) composites compounds to be used as possible catalysts for photodegradation processes. The paper reports a complete characterization of the synthesized materials; therefore, the manuscript could be accepted for publication after a minor revision. The following suggestions are proposed:

- A revision of English language and style would be desirable.

- It is advisable to specify that the acronym AA6061 is the Unified Numbering System (UNS) designation of Al-Mg-Si alloy. In addition, the data source of the alloy chemical composition, shown in Table 1, should be mentioned.

- Authors suppose that during the steam coating process the following equation occurs:

2Al + 4H₂O = 2AlO(OH) + 3H₂

However, two other reactions could take place:

2Al + 6H₂O = 2Al(OH)₃ + 3H₂ and  2Al + 3H₂O = Al₂O₃ + 3H₂

It possible to hypothesize that at 180°C aluminum hydroxide Al(OH)₃ is the main stable product formed, while at 280°C the compound AlO(OH) is more stable. The possible presence of Al(OH)₃ should be also considered.

 

- The caption of Figure 3 should be written more clearly.

- In the legend of Figure 10(a), it would be more appropriate to add the complete catalysts names as well as the experimental conditions with which they were obtained. Eventually, the different samples synthetized could be named with acronyms and presented in a summary table.

- In the photocatalytic study it was reported the total degrade of MB by the 10 mol/L-KOH treated Ti catalyst. However, the KTiOxs/AlO(OH) (10 mol/L-KOH, 280 °C, 24 h) composite material demonstrates a lower degradation efficiency (Abs ≈ 0.06 a.u.) than 10 mol/L-KOH treated Ti catalyst. In order to demonstrate the possible enhanced photocatalytic performance of Potassium-Doped Titanium Oxide Nanostructures (KTiOxs)/AlO(OH) composite material, the authors could compare the photodegrade efficiency (%) as a function of the amount of used catalysts?

Author Response

This is our answer about the comments.

Author Response File: Author Response.pdf

Reviewer 4 Report

This work deals with a synthesis of potassium doped titanium oxide nanostructures (KTiOxs)/AlO(OH) composites for enhanced photocatalytic performance.

 

 

The manuscript does not deserve to be publish.

1. Fill in primary particle size of all catalysts. - What is the size of particle? How was it measured and evaluated?
2. Fill in measurement of XRD patterns of all samples.
3. XPS spectroscopy is an effective tool to confirm the chemical and electronic state of the element that exist within a material. Therefore, authors should carry out the XPS characterization.
4. What is the actual loading content of KTiOxs on the AlO(OH)?
5. The high-resolution TEM image of the prepared samples should be provided to investigate the nanostructure of the samples.
6. What was purity of catalyst? What was the amount of carbon?
7. Fill in band gap of all catalysts. - Determine band gap of all catalysts from UV-Vis spectra. Fill in value of band gap to Table 1.
8. Fill in to Table 1the physicochemical properties of all photocatalyst.
9. The active oxidation species should be also investigated by ESR or radical trapping experimental.
10. What was wavelength of UV lamp? Fill in this information to the article. If it is possible, fill in spectrum of this lamp.
11. What was the error of measurement? Fill in this information in the article.
12. Fill in information about irradiation time. - Was the effect of irradiation time on the MB photodegradation over a period? Show the degradation process as the functions of the irradiation.
13. Did you prove blank tests? Information about blank test is necessary. Perform these tests: i) UV-illuminated of MB without the photocatalyst, ii) MB with photocatalysts without of UV-illuminated (in the dark) and fill in to the manuscript.
14. The authors did not study the recyclability and stability of the catalyst.
15. Discussion is poor. Extend it and fill in the article.

Author Response

This is our answer about the comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

ROUND 2

Although the quality of the manuscript was improved, there are some points that were not considered. In particular, Points 2 and 9 were not considered appropriately. (i.e.: "The Introduction is completely centred on the description of the materials and the synthesis methods. A point-to-point analysis of the state-of-the-art of TiOx based semiconductors in similar applications (ex. wastewater photo-purification, CO2 photoreduction, water splitting) should be added. Moreover, the novelty and originality of the work should be better highlighted, considering the vast literature on these systems. Accordingly, the bibliography should be enlarged also considering the following relevant papers:  http://dx.doi.org/10.1016/j.jphotochemrev.2015.06.001; https://doi.org/10.1016/j.jcou.2018.05.010; http://dx.doi.org/10.1016/j.progsolidstchem.2004.08.001; http://dx.doi.org/10.1016/j.enconman.2013.07.046" and “9. The photocatalytic results obtained should be compared with literature data.” ). In particular, the bibliography was not upgraded; considering the huge literature on the topic, it is hard to justify only 36 references for a full-length article. Moreover, a Table for the comparison with literature data could be helpful to highlight the novelty and scientific soundness of the study. Therefore, I will reconsider the manuscript after Major Revision.

Author Response

Thank you for your kind comments and we try to do our best to meet your comments. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript was revised by the authors as suggested.

 

 

Author Response

Thank you for your kind revision.

Reviewer 4 Report

Thank you for resubmission. However, the authors did not answer all comments and recommendations correctly. I still have a lot of comments and I am not satisfied with revision.

 

 

The manuscript does not deserve to be published.

 

1. Fill in measurement of XRD patterns of all samples.

Your answer:

KTiOxs is hard to get the result of XRD because maybe the content of K in the sample does not enough to detect the XRD, so we only presented the XRD pattern of AlO(OH). That is a reason why we carried out the Raman measurement to confirm the existence of KTiOxs.

 

Raman measurement does not include all samples.

 

2. XPS spectroscopy is an effective tool to confirm the chemical and electronic state of the element that exist within a material. Therefore, authors should carry out the XPS characterization.

Your answer:

We add XPS result of the synthesized the KTiOxs.

 

Authors only added the Fig. without any discussion. It is insufficient.

 

3. What is the actual loading content of KTiOxs on the AlO(OH)?

Your answer:

Photocatalysts were taken as 2g of KTiOxs and reacted with AlOOH for 24h. After 24 h, we washed out with H2O to clean up the unattached KTiOXs. Through this, it can be assumed that the actual amount of boned KTiOxs is around 0.5g.

 

It is only your presumption. I tis necessary to confirmed it by measurement.

 

4. The high-resolution TEM image of the prepared samples should be provided to investigate the nanostructure of the samples.

Your answer:

The TEM images of nanowires are presented in the paper.

 

HRTEM was not added.

 

5. What was purity of catalyst? What was the amount of carbon?

 

Your answer:

The purity of KTiOxs can be assumed by the amoreatnt of K content in KTiOxs. The content of K which was treated by 1 M-KOH solution treated Ti was around 1% and while 10 M-KOH solution treated Ti is around 4%.

 

It is only your presumption.   tis necessary to confirm it by measurement.

 

6. Fill in band gap of all catalysts. - Determine band gap of all catalysts from UV-Vis spectra. Fill in value of band gap to Table 1.

 

Your answer:

The band gap of the obtained the KTiOxs is around 2.8~2.9 eV.

 

Was the band gap the same for all samples?

 

7. What was the error of measurement? Fill in this information in the article.

 

Your answer:

There were no error during the process in this strudy.

 

Really? It is almost impossible.

 

8. Fill in information about irradiation time. - Was the effect of irradiation time on the MB photodegradation over a period? Show the degradation process as the functions of the irradiation.

 

Your answer:

The irradiation time already wrote in the paper. UV irradiation was carried out 10, 20 and 30 min.

 

The degradation process as functions of the irradiation is still missing.

 

9. Did you prove blank tests? Information about blank test is necessary. Perform these tests: i) UV-illuminated of MB without the photocatalyst, ii) MB with photocatalysts without of UV-illuminated (in the dark) and fill in to the manuscript.

 

Your answer:

We presented the blank sample in Figure 10 using pure H2O and only MB.

 

The blank test - MB with photocatalyst without of UV-illuminated (in the dark) is still missing.

 

• The authors did not study the recyclability and stability of the catalyst.

Your answer:

.yes we did not study the recyclability and stability of the catalyst, however in near the future we will do.

 

It is necessary to perform it

 

• Discussion is poor. Extend it and fill in the article.

 

The discussion is still very weak.

Author Response

Thank you for your kind comments and we try to do our best to meet your comments. 

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructures (KTiOxs)/AlO(OH) composites for Enhanced Photocatalytic Performance

So Yoon Lee, Tatsuya Matsubara, Daiki Numata and Ai Serizawa

The quality of the paper has been improved: some of the suggestions proposed by this Reviewer have been caught by the Authors and the manuscript has been modified accordingly. However, in my opinion, the bibliography need some other further revisions: in particular, any of the relevant paper suggested by this Reviewer have been considered by the authors and cited in the revised paper. In my opinion, the work suggested are high topics and fundamental in the field of TiO₂ materials.

Accordingly, the bibliography should be enlarged also considering the following relevant papers:  http://dx.doi.org/10.1016/j.jphotochemrev.2015.06.001; https://doi.org/10.1016/j.jcou.2018.05.010; http://dx.doi.org/10.1016/j.progsolidstchem.2004.08.001; http://dx.doi.org/10.1016/j.enconman.2013.07.046.

Author Response

Thank you for your kind comments.

We added more references based on your comments and make the list up to 58 number of references. 

Hopefully our action meets your comments.

Thank you for your time!