Controlling the Structural Properties and Optical Bandgap of PbO–Al₂O₃ Nanocomposites for Enhanced Photodegradation of Methylene Blue

Round 1

Reviewer 1 Report

In the present work, a PbO-x%Al₂O₃ composites was prepared for enhanced ultraviolet-assistance degradation of methylene blue, and the reaction mechanism was systematically explored. This study has certain meaning for design efficient composite photocatalyst. However, the paper suffers several issues. Therefore, I recommend acceptance of the manuscript after addressing the following issues.

 

1. In page 6,the smaller particle size of PbO-40%Al₂O₃ was proved by TEM, and the author considered that particle size reduction can improve application performance by increasing specific surface area. Therefore, some related characterization results such as BET need to be supplemented to support this conclusion.
2. XPS needs to be conductedto confirm the valence state of Pb in the sample and to study the interaction of PbO and Al₂O₃.
3. Inpage 7, Why does PbO with narrowest energy band gap show weaker visible light absorption than Al₂O₃？The introduction of PbO can effectively reduce the energy band of the catalyst, so is there any results of testing the photocatalytic performance of methylene blue (MB) under visible light?
4. In page 9, the author consideredthat the PbO nanoparticle is a good photoelectron acceptor to reduce photoelectron-hole pair recombination when compared to Al₂O₃. Therefore, some related characterization results such as photoluminescence or electrochemical characterization need to be supplemented to support this conclusion.
5. Inpage 10，what is the reason that the PbO-40%Al₂O₃ composites showed a faster degradation rate of the MB and was reached a constant value after 20 minutes of the UV irradiation?

 

Author Response

First of all, we would like to express our gratefulness for giving us a chance to improve the manuscript entitled “Controlling the Structural Properties and Optical Bandgap of Al₂O₃-PbO Nanocomposite for Enhanced Ultraviolet-assistance Degradation of Methylene Blue", which was submitted to Catalysts. We thank the reviewers for their valuable and insightful comments. We provide our responses to all comments below.

 

Reviewer 1

In the present work, a PbO-x%Al₂O₃ composites was prepared for enhanced ultraviolet-assistance degradation of methylene blue, and the reaction mechanism was systematically explored. This study has certain meaning for design efficient composite photocatalyst. However, the paper suffers several issues. Therefore, I recommend acceptance of the manuscript after addressing the following issues.

 

1. In page 6, the smaller particle size of PbO-40%Al₂O₃was proved by TEM, and the author considered that particle size reduction can improve application performance by increasing specific surface area. Therefore, some related characterization results such as BET need to be supplemented to support this conclusion.

Reply:

The BET device is not currently available at our university for carrying out additional experiments. Instead, we have added the following sentence:

It is widely accepted that a decrease in crystallite size, as well as a decrease in particle size, is followed by an increase in the surface area [39].

 

2. XPS needs to be conducted to confirm the valence state of Pb in the sample and to study the interaction of PbO and Al₂O₃.

Reply:

We are very sorry that the XPS is not available at our university; it is available elsewhere but requires a reservation, which may take more than three months. We'll make plans to do so in the coming work.

 

3. In page 7, Why does PbO with narrowest energy band gap show weaker visible light absorption than Al₂O₃？The introduction of PbO can effectively reduce the energy band of the catalyst, so is there any results of testing the photocatalytic performance of methylene blue (MB) under visible light?

Reply:

Additional experiments are conducted concerning the photocatalytic degradation of MB using such PbO-x%Al₂O₃ nanocomposite under visible light irradiation, and data are shown in Figure 10 and discussed in detail.

 

4. In page 9, the author considered that the PbO nanoparticle is a good photoelectron acceptor to reduce photoelectron-hole pair recombination when compared to Al₂O₃. Therefore, some related characterization results such as photoluminescence or electrochemical characterization need to be supplemented to support this conclusion.

Reply:

Actually, this point is very important, therefore the photoluminescence emission test is provided for various PbO-x% Al₂O₃ nanocomposites and discussed in more detail in the revised version. Moreover, the results of photoluminescence emission are shown in Figure 5.

 

5. In page 10，what is the reason that the PbO-40%Al₂O₃composites showed a faster degradation rate of the MB and was reached a constant value after 20 minutes of the UV irradiation?

Reply:

More explanation is added to the revised version as follow:

As is well known, oxidants increase the number of trapped electrons, preventing recombination and generating oxidizing radicals, which may enhance dye photocatalytic degradation [44]. The increase in the rate of photocatalytic degradation of MB could be attributed to an increase in pH or the MB concentration [44]. As a result, changes in the dye molecule's behavior may be responsible for the change in the percentage degradation of dye at higher MB concentrations. When the substrate concentration was decreased, the degradation rate could be decreased and then decreased. This could be one of the reasons why the degradation rate decreases over time. The photocatalytic activity of different photocatalysts varies due to differences in lattice mismatch, surface area, and impurities on the catalyst's surface, which affect pollutant adsorption and the lifetime and recombination rate of electron-hole pairs. A large surface area can be a deciding factor in certain photodegradation reactions, as a large amount of adsorbed organic molecules accelerates the reaction rate [45]. However, depending on particle size, the dominant mode of electron-hole recombination may differ [46]. As a result, because the PbO-40% Al₂O₃ composite has the smallest crystallite size, higher photocatalytic activity was observed.

 

In the revised version, all changes and edits to the original manuscript are highlighted in red. We hope that all answers and replies satisfy the reviewer's comments.

We look forward to your kind response.

Sincerely Yours,

Alaa M. Abd-Elnaiem

Corresponding author

 

Author Response File: Author Response.pdf

Reviewer 2 Report

This version does not look worthy and cannot be recommended for publication in this form and at least needs major revision.

1. Line 45. The sentence needs general supporting references for each materials.

Moreover, apart from binary simple oxides, more complex ones should be mentioned. See for example:

Porotnikova, N.M.; Eremin, V.A.; Farlenkov, A.S.; Kurumchin, E.K.; Sherstobitova, E.A.; Kochubey, D.I.; Ananyev, M.V. Effect of AO Segregation on Catalytical Activity of La_0.7A_0.3MnO_3±δ (A = Ca, Sr, Ba) Regarding Oxygen Reduction Reaction. Catal. Lett. 2018, 148, 2839–2847.

2. Line 50. The same.
3. “ …by covering with PbO clusters to form …” - the physical meaning is not clear.
4. Lines 57-60. How is the presence of lead consistent with green science area?
5. Line 67. [11-13]. No reference on PbO pure compound !!!
6. Line 93. “… composition of nanocomposite ….” Needs correction.
7. Lines 140-158. It is very advisable to present all peaks in the FTIR spectrum in the form of a Table in order to clearly see all the trends and changes.
8. Interpretation of the absorption spectra in Figure 4 is unproven and inconsistent. The increase in absorption at less than 300 nm is caused not by a change in the band gap, but by absorption associated with point defects in the oxygen sublattice of Al₂O₃, namely oxygen vacancies with trapped electrons. See, as an example: Fig. 1 in the paper

Popov, A. I. et al. Comparison of the F-type center thermal annealing in heavy-ion and neutron irradiated Al₂O₃ single crystals. Nucl. Intstrum. Methods B. 433, 93–97 (2018).

Therefore, subsequent analysis needs correction.

Author Response

First of all, we would like to express our gratefulness for giving us a chance to improve the manuscript entitled “Controlling the Structural Properties and Optical Bandgap of Al₂O₃-PbO Nanocomposite for Enhanced Ultraviolet-assistance Degradation of Methylene Blue", which was submitted to Catalysts. We thank the reviewers for their valuable and insightful comments. We provide our responses to all comments below.

 

Reviewer 2

This version does not look worthy and cannot be recommended for publication in this form and at least needs major revision.

1. Line 45. The sentence needs general supporting references for each materials.

Moreover, apart from binary simple oxides, more complex ones should be mentioned. See for example:

Porotnikova, N.M.; Eremin, V.A.; Farlenkov, A.S.; Kurumchin, E.K.; Sherstobitova, E.A.; Kochubey, D.I.; Ananyev, M.V. Effect of AO Segregation on Catalytical Activity of La_0.7A_0.3MnO_3±δ (A = Ca, Sr, Ba) Regarding Oxygen Reduction Reaction. Catal. Lett. 2018, 148, 2839–2847.

Reply:

We have added suggested references to the mentioned sentence, as well as the reviewer's suggestion about the more complex oxides.

 

2. Line 50. The same.

Reply:

We have added suggested references to the mentioned sentence.

 

3. “ …by covering with PbO clusters to form …” - the physical meaning is not clear.

Reply:

Some sentences to address this concern was added to be clearer for the readers.

 

 

4. Lines 57-60. How is the presence of lead consistent with green science area?

Reply:

The sentence has been edited.

5. Line 67. [11-13]. No reference on PbO pure compound !!!

Reply:

The mentioned references were replaced by three new references concerning the properties PbO are provided in the revised version.

 

6. Line 93. “… composition of nanocomposite ….” Needs correction.

Reply:

The sentence has been edited.

 

7. Lines 140-158. It is very advisable to present all peaks in the FTIR spectrum in the form of a Table in order to clearly see all the trends and changes.

Reply:

For greater clarity, the FTIR peaks are inserted into a new Table (see Table 1) and the text is accordingly edited.

 

8. Interpretation of the absorption spectra in Figure 4 is unproven and inconsistent. The increase in absorption at less than 300 nm is caused not by a change in the band gap, but by absorption associated with point defects in the oxygen sublattice of Al₂O₃, namely oxygen vacancies with trapped electrons. See, as an example: Fig. 1 in the paper

Popov, A. I. et al. Comparison of the F-type center thermal annealing in heavy-ion and neutron irradiated Al₂O₃ single crystals. Nucl. Intstrum. Methods B. 433, 93–97 (2018).

Therefore, subsequent analysis needs correction.

Reply:

The suggested reference and explanation have been incorporated into the revised version.

 

In the revised version, all changes and edits to the original manuscript are highlighted in red. We hope that all answers and replies satisfy the reviewer's comments.

We look forward to your kind response.

Sincerely Yours,

Alaa M. Abd-Elnaiem

Corresponding author

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

none

Reviewer 2 Report

The authors significantly improved the manuscript, accepting constructively all the comments. The manuscript can certainly be recommended for publication.

ACCEPT