Round 1

Reviewer 1 Report

This manuscript "Fabrication of a TiO₂-MoO₃ nanocomposite with high surface area photocatalyst for the removal of organic pollutants from water bodies" authors Fatima Abla, Yehya El-Sayed, Khaled Obaideen, Nedal Abu-Farha, Ahmed A. Mohamed, Haesung Lee, Changseok Han , Mehmet Egilmez and Sofian Kanan report the synthesis of Ti-Mo NC with high surface area due to the synergistic effect of combining Ti-Mo into a single composite product resulting in more active sites on the surface.

The catalytic efficiency of the synthesized materials was tested in the adsorption and photocatalytic degradation of MB and two carbamate insecticides (carbaryl and fenoxycarb),

The conclusions of this work are relevant and supported by the results, being of interest for the readership .

This manuscript is suitable for publication in the Catalysts journal , special issue Special Issue "Advances in Photocatalysis for the Degradation of Organic Pollutants" after major revision.

Concerning my main remarks, corrections and suggestions about your work are:

1.     1.  Can you provide more information about the synthesis of the material used for the
removal of NaCl? What method did you use to confirm the total removal of NaCl?

The existence of Na+ cation can influence adsorption and catalytic properties.

2.    2.  Figure 3 shows the X-ray diffraction pattern of Ti-Mo NC compared to TiO2 and MoO3. The characteristic diffraction lines of TiO₂ at 2ϴ=53.99 can also be found in the X-ray diffraction pattern of Ti-Mo NC spectra. In this figure, the presence of TiO2 is not marked as crystalline phase.

The x axis does not have units - respectively 2 ϴ (degrees)

3.    3.   Figure 4A shows XPS spectra for Ti-Mo NC. For a better understanding, individual spectra for Mo and Ti should be presented. The surface composition from XPS analysis can also be calculated. The quality of the figure 4 should be improved,

4.     4.  The acidic character of the Ti-Mo NC surface is associated with the presence of active hydroxyl surface modes from fig 4C with Bronsted and Lewis acid sites.  The basic nature of carbamates causes them to be adsorbed on acidic materials

In order to demonstrate the acidic character (Bronsted and Lewis acid sites  ) of Ti-Mo NC, it is necessary to carry out additional measurements  of NH₃-TPD .

5.     5.  “Interestingly, the adsorbed  carbamates irradiated with 75 W LEDs visible light for 60 min produced the expected oxidized products as presented in scheme 1.”

 Where is Scheme 1?

6.     6.  What are the degradation products of carbaryl and Fenoxycarb.

The authors state that they monitored the photocatalytic degradation products by GC–MS analysis using a GC–MS (QP 2010 ultra, Shimadzu-Japan).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this manuscript the authors report the preparation of a nanocomposite (NC) of titanium (IV) oxide (TiO2) and molybdenum (VI) oxide (MoO3) using a hydrothermal route, its characterization and photocatalytic tests in the degradation of  carbaryl and fenoxycarb pesticides and methylene blue.

The authors try to give a full picture of the properties of the nanocomposite and explain the results. However, some points need to be clarified:

1.      Abstract: “ While 20% of the MB is adsorbed 30 on the Ti-Mo NC, compared to the irradiated MB alone, the photocatalytic degradation of MB in the presence of the catalyst enhanced by 2.9 folds and 5.5 folds upon irradiation with white Leed and 302 nm UV light source, respectively, was found to be enhanced by two-fold.”. So, the activity was enhanced by 2.9 and 5.5 folds, or by 2 fold?

2.       The mention that the pure oxides were prepared by the same procedure as the nanocomposite should be put in the experimental section.

3.       The DR-UV-Vis spectra of the nanocomposite and the pure oxides should be provided, especially to see how they fit with the emission spectra of the light sources.

4.       Does the XPS analysis confirm the EDS Ti/Mo/O ratios?

5.       Which is the concentration of the MB solution used for the photocatalytic tests?

6.       How long were the reaction mixtures allowed to stir in dark for the adsorption-desorption equilibrium to be established? Which were the concentrations of the solutions after that time?

7.       Photocatalytic tests were performed also for the pure oxides?

8.       The results for the photocatalytic results of pesticide degradation under visible LED irradiation are missing from the manuscript. Also, Scheme 1 is missing from the manuscript.

9.       The photocatalytic degradation of MB in the presence of the nanocomposite was enhanced by 2.9 folds and 5.5 folds upon irradiation with white LED or 302 nm UV light source, respectively, compared with the reaction in the absence of the catalyst. How many times was this enhanced compared with the pure oxides?

10.   There are some issues related to the writing of the manuscript:

-          In many instances we can see “Leed” instead of LED;

-          In some cases the authors use “EDS”, in other “EDX”;

-          Pages 7/8 there are some paragraphs with a different font size;

-          Some figures are noted as A,B etc, others as I, II etc;

-          Some sentences need to be more clear.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

In this work, the authors have prepared TiO2-MoO3 nanocomposite by a hydrothermal method, and the TiO2-MoO3 nanocomposite was applied as a photocatalyst for degradation of pesticides and dye pollutants from water. The TiO2-MoO3 nanocomposite has shown significantly enhanced activity than that of the single TiO2 or MoO3. This manuscript could be published after addressing the following issues.

1. TiO2-MoO3 nanocomposite for photocatalytic pollutants degradation and hydrogen evolution have been published previously. What’s the advantages of this work as compared to the existing literatures?

2. There are many expressions and grammatical errors. For example: “A nanocomposite (NC) of titanium (IV) oxide (TiO2) and molybdenum (VI) oxide (MoO3)” should be “A nanocomposite (NC) consisting of titanium (IV) oxide (TiO2) and molybdenum (VI) oxide (MoO3)”. “concluded the successful formation of TiO2-MoO3 (Ti-Mo) NC was confirmed” should be “concluded that the successful formation of TiO2-MoO3 (Ti-Mo) NC was confirmed”. There are many similar questions in the paper. It is recommended that the author meticulously review the entire manuscript and enhance the proficiency in the English language.

3. It is suggested that the author optimize the keywords.

4. There is a format error in this article. For example, in lines 37-39, the sentence is incoherent. In lines 212-232, the font is different. It is suggested that the author carefully check the errors in the text.

5. The author's statement in lines 43-45 is incorrect. First of all, the two materials should be combined to improve the photocatalytic activity of a single material, not mixed. Second, it is well known that the position of valence band is crucial in degradation. Therefore, the band gap of the composite should be increased rather than decreased. In addition, the authors should state that TiO2 is a UV light excited material and needs to be combined with a visible light  excited material (MoO3), thus changing the inherent light absorption characteristics of TiO2.

6. Authors should unify the writing of EDS and EDX in lines 154-162. In addition, I believe that the morphology of the composites is not spherical, but irregular polyhedra.

7. First, the lattice fringes in HRTEM are not clear and it is suggested that the authors strengthen the clarity. Second, the interplanar spacing should be the distance between two lattice fringes, not the distance between lattice fringes voids. Finally, the authors should search for lattice fringes and heterojunctions of the two single material materials in the HRTEM of the composites, proving the existence of the composites.

8. The presence of characteristic peaks of both catalysts in XRD does not prove the existence of composites. Because, a mixture of the two also has the same properties.

9. In line 213, “Figure 4B” in the text should be changed to “Figure 4b”. The author's “2p Ti” in line 202 was written incorrectly and should be changed to “Ti 2p”. In addition, Figure 4 the font and format of the three figures are not the same. And, there are redundant spots of contamination in the figure. So, authors should unify the formatting and font of all figures in the text.

10. In the description, the authors do not mention Figure 5. In addition, please authors explain why the sorption of water isotherms for Ti Mo oxide in Figure 7 are not merged.

11. The band gap is one of the effective demonstrations to show whether a material can theoretically degrade. Authors should add band gap diagrams to the text. In addition, the authors should also add a mechanistic diagram, thus further illustrating the underlying reasons why composites effectively enhance the photocatalytic activity of single materials.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been improved, can be published in present form. 

Reviewer 2 Report

The authors answered to all concerns. The manuscript can be published in present form.

Reviewer 3 Report

Necessary changes have been made to the paper, this paper can be accepted for publication in its present form.