Comparing the Photocatalytic Oxidation Efficiencies of Elemental Mercury Using Metal-Oxide-Modified Titanium Dioxide under the Irradiation of Ultra-Violet Light

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors of the article performed a study on the topic: Comparison of Metal Oxide Doped TiO2 under the Irradiation of UVA for Photocatalytic Oxidation of Elemental Mercury. They obtained a large amount of experimental data using a variety of research methods. The topic of the work is certainly relevant and interesting for readers. However, there are some comments regarding the work that need to be corrected.

1. It is better to exclude abbreviations from the title of the article and abstract. In addition, there are also too many abbreviations in the introduction, some of them are not explained (for example, SCR).

2. It is impossible to read the scale marks on SEM images (they are too small!), as well as the conditions for obtaining images: a mode, a detector, an accelerating voltage, WD, etc.). It is very desirable to present images obtained at approximately the same magnification for comparison of structures.

3. The TEM images show the dimensions of only one crystal! It is necessary to provide the crystal size distribution for each sample. For this purpose, you can use, for example, the dark-field imaging mode.

4. STEM and EDX-mapping  can be used to visualize the location, distribution, and sizes of areas containing metal oxides relative to anatase crystals.

5. It is better to use the same colors for every metal oxide for Figures 1,3, 4 in order to facilitate the perception of experimental results.

6. It is necessary to highlight the novelty of the results in conclusion.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, Dear Editor,

I carefully read your manuscript and it seems to me that you mixed few terms all over it. First of all in the title you wrote „metal oxide doped TiO2”- later in the text you used modification as name for your material. These terms are not the same. In my opinion you synthesized nanocomposites of two oxides. It would be easier to name your materials if you presented quantities of different oxides you used in synthesis, but you didnt do it. It is necessary to present your experimental part as detailed as possible.

Than you mixed terms thermal and photo catalysis randomly, without idea to separate those processes. That is why I suggested additional experiments regarding what you called „photocatalysis”, this time without light. This should give you the clue is this really photocatalysis as well as it is thermocatalysis.

I made several comments in the text as well. Please follow my instructions when you rewrite your article.

I do not recommend publication of this manuscript at this stage. Everything should be improved: English (strange sentences, sometimes impossible to understand), experiments, discussion.

Best regards

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript deals with the characterization of titanium oxide modified with other metal oxides (copper, cerium, bismuth) and the photocatalytic performances in the oxidation of elemental mercury in gas phase. The aim of the work is interesting and the catalytic results appear promising, anyway there are several issues, lacks and shortcomings that make it not recommendable for publication. The main points are listed below.

1. The authors write in the whole text about “doping with metal oxides”, which seems a contradiction: doping is the modification obtained by the insertion of atoms into the lattice of the semiconductor, while coupling TiO2 with another metal oxide can produce a variety of heterostructures or composite oxides, which should not be defined as doping. The goal of the study is therefore unclear, as well as the nature of the resulting materials.  

2. The state of the art of relevant literature reports on Hg oxidation on TiO2-based photocatalysts is not illustrated.

3. Regarding the synthesis of the materials, there is no motivation for the choice of the preparation procedure and no details about the amounts of reagents used.

4. No information about the nominal and actual stoichiometry of the materials is given.

5. The effect of the modification on TiO2, including the XPS data, is not commented in detail, and some of the discussion appears inconsistent, e.g. “After modifying with metal oxides, the electron cloud around Ti decreased and the oxidation state increased, leading to the peaks shifting to lower binding energy” (p. 7, lined 232-233): how is the oxidation state of Ti⁴⁺ increased? An opposite trend would be expected.  

6. Although a kinetic modelling is provided, the relationship between the different catalytic performances of the materials and their composition is not explained.

 

 

 

Comments on the Quality of English Language

The language is insufficient and there are several mistakes throughout the text. 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

In my opinion this manuscript still needs improvements.

The title has word "COMPARISON" at the very beginning and it is not clear that authors compare different titania based nanocomposites- the doping is still in the title. The removal of doping from the manuscript was one of my comments.

Also the very title (Comparison of Metal Oxide Doped TiO2 under the Irradiation of UVA for Photocatalytic Oxidation of Elemental Mercury)  has PHOTOCATALYTIC in it and if authors decided not to exclude light from experiment it is not possible to decide is this catalytic or photocatalytic reaction. Authors decided to ignore my comment regarding performing additional experiment without illumination of the reaction mixture- so it is not possible to have clear answer to this question. 

Comments on the Quality of English Language

There are still a lot of mistakes in speling and grammar.

Author Response

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Author Response File: Author Response.pdf