Enhanced Titania Photocatalyst on Magnesium Oxide Support Doped with Molybdenum
Round 1
Reviewer 1 Report
In this work, Mo-doped MgO supporting TiO2 photocatalysts were synthesized for the degradation of rhodamine B, which reflects the superiority of Mo doping. However, there are still some issues in the article that need to be addressed and it cannot be published in present form. Hence, I recommend it for reject:
1. There are many grammatical problems and mistakes in the article. The authors must check the entire manuscript again and correct the inappropriate phrasing.
E.g., in Lines 49-50, "It should be noted that a large number of original works on the combination of titanium dioxide with other components (carriers) and its doping summarized in a number of reviews"; in Line 66, "It should be noted that in a number of studies have shown"; in Lines 90-91, "mixed oxides with a low MgO content (1–2 mol%) were found to be more UV-active photocatalyst"; in Lines 256-258, "the composite based on the MgO support doped with vanadium ions has the highest photocatalytic activity".
2. It is pointed out in the introduction that the TiO2 photocatalysts are sensitive to both the doping method of Mo and its specific content in the photocatalysts, however, the doping method and doping amount of Mo are not investigated in the study.
3. In Figure 1b, curve 5, what is the ratio of MgO:TiO2? And what is the doping amount of Mo in Figure 1b, curve 1-4? Different doping amounts of Mo need to be analyzed.
4. Some information can be displayed more visually in the figure in the form of a legend.
5. The data of TiO2 should be added when comparing different materials, due to the title and the introduction are based on TiO2 photocatalyst.
6. Some descriptions and data of the figures in the text are wrong.
E.g., in Lines 140-142, "The cumulative pore volume (diameter from 1.7 nm to 300 nm) calculated by the BJH 140 desorption method is 0.45 cm³/g, and the average pore diameter is 5.46 nm. For the Mo doped composite these values are 0.45 cm³/g and 5.46 nm, correspondingly"; in Lines 210-213, "The photocatalytic activity of the prepared composites suspended in an aqueous RhB solution when irradiated with the full UV-spectrum is the highest for the MgO–Mo(VI)–TiO2 photocatalyst doped with molybdenum ions with the ratio of MgO:TiO2=1:0.5 (Figure 6a) and slightly less than for a similar composite with MgO:TiO2=1:0.25".
Comments for author File: 
Comments.pdf
Author Response
Point 1.
There are many grammatical problems and mistakes in the article. The authors must check the entire manuscript again and correct the inappropriate phrasing. E.g., in Lines 49-50, "It should be noted that a large number of original works on the combination of titanium dioxide with other components (carriers) and its doping summarized in a number of reviews"; in Line 66, "It should be noted that in a number of studies have shown"; in Lines 90-91, "mixed oxides with a low MgO content (1–2 mol%) were found to be more UV-active photocatalyst"; in Lines 256-258, "the composite based on the MgO support doped with vanadium ions has the highest photocatalytic activity".
Response 1.
The authors once again checked the grammar of the article and corrected the inappropriate phrasing (Line 49-50, 66, 90-91, 256-258).
Point 2.
It is pointed out in the introduction that the TiO2 photocatalysts are sensitive to both the doping method of Mo and its specific content in the photocatalysts, however, the doping method and doping amount of Mo are not investigated in the study.
Response 2.
Indeed, titania photocatalysts are sensitive to the doping method and specific content of dopants as well as to many other factors (temperature, oxygen or inert atmosphere during sintering, spatial distribution of ions or their associates up to the formation of nanophase inclusions, etc.). To our opinion, it is quite difficult to take into account all possible factors in one article. Therefore, we have limited our consideration to two concentrations of molybdenum: (i) close to optimal one, about 1 wt.%, according to our preliminary experiments, this value corresponds to ion doping. (ii) A higher concentration is 10 wt.%, when MoO3 nanophases and TiO2-MoO3 heterojunctions are formed.
There are known many previously published papers described Mo-doped TiO2, in which the influence of the doping methods and dopant concentration on the structure and physicochemical, including photocatalytic, properties were studied in detail. These works are mainly cited in the introduction. In our paper, we decided to attract attention to a far less studied aspect: to show the possibility of doping TiO2-based photocatalyst using diffusion of Mo ions from doped MgO carrier. The goal of the work was to reduce surface recombination at the levels created by molybdenum ions in the TiO2 layer contacted with the reaction medium. For this reason, we have doped the MgO carrier and then used it as a source of molybdenum ions for modifying TiO2 layer from the carrier side. Thus, we tried to minimize the release of dopant ions directly to the TiO2 interface between the photocatalyst and the reaction medium.
Point 3.
In Figure 1b, curve 5, what is the ratio of MgO:TiO2? And what is the doping amount of Mo in Figure 1b, curve 1-4? Different doping amounts of Mo need to be analyzed.
Response 3.
The content of molybdenum in the MgO substrate is 1 wt.% (curve 1 – 4) and 10 wt.% (curve 5). The MgO:TiO2 ratio for curve 5 is the same as for curve 4. All this information is included in the corrected version of the caption for Figure 1.
Point 4.
Some information can be displayed more visually in the figure in the form of a legend.
Response 4.
To improve visual perception, we have added legends in Figures 1a, 1b, 2a, 2b, 6a, 6b.
Point 5.
The data of TiO2 should be added when comparing different materials, due to the title and the introduction are based on TiO2 photocatalyst.
Response 5.
In our work, we have used the method of TiO2 preparation from titanium alkoxide, and the XRD method unequivocally showed the pure anatase nature of titania. Due to the absence of chemical interaction between TiO2 and the MgO carrier at temperatures used, ca. 500°C, the properties of TiO2 do not differ from those established previously including Eg values. Therefore, we think that inclusion of these data to the text of the manuscript is not reasonable.
Point 6.
Some descriptions and data of the figures in the text are wrong. E.g., in Lines 140-142, "The cumulative pore volume (diameter from 1.7 nm to 300 nm) calculated by the BJH 140 desorption method is 0.45 cm³/g, and the average pore diameter is 5.46 nm. For the Mo doped composite these values are 0.45 cm³/g and 5.46 nm, correspondingly"; in Lines 210-213, "The photocatalytic activity of the prepared composites suspended in an aqueous RhB solution when irradiated with the full UV-spectrum is the highest for the MgO–Mo(VI)–TiO2 photocatalyst doped with molybdenum ions with the ratio of MgO:TiO2=1:0.5 (Figure 6a) and slightly less than for a similar composite with MgO:TiO2=1:0.25".
Response 6.
Indeed, some descriptions and data of the figures in the text were wrong (Lines 140-142, 210-213). Corresponding corrections have been made to the manuscript (highlighted in yellow).
Reviewer 2 Report
Dear Authors:
This is my comment about article 2060066, entitled “Enhanced Titania Photocatalyst on Magnesium Oxide Support Doped with Molybdenum”.
Reviewer: The topic is of interest. However, this manuscript has lots of technical errors so that I could not recommend its publication on Catalysts at this status. Some issues must be corrected which is listed as follows:
· Check the English.
· Please confirm that given names and surnames have been identified correctly and are presented in the desired order.
· Check the maximum number of keywords
· Introduction:
First paragraph is quite well-known and widely reported; therefore, some citations are vital, review references from the last 3 to 5 years and includes them.
In page 2, line 51: References [32,33,34, etc] … please include the references and remove etc., …
In page 2 , lines 52 to 60: Include references in the paragraph.
· Materials and methods: Include all information about the materials (i.e., companies, purity, etc)
· Results and discussion:
The figures, on the X and Y axis, use dots in the decimals and do not use commas. See figure 2 a,b. In addition, Table 1 and 2 appears the same for the decimals. The scientific notation is for example 2.6 x 10n, correct it in Table 2. Check it in the manuscript.
FTIR result, I am sure that the vibrational band at 1485 cm-1 corresponds to Mg-O, reference it. The quality of figure 1 and 3 is not good, improve it.
Page 5, lines 156-159: The paragraph is not clear. Better redaction.
Figure 6b, Y axis, plot from 0.4 to 0.8 to better see the results. Check decimals (use dots)
Figure 7, Y axis, Check decimals (use dots).
· Discussion: rewrite paragraph, … line 263 say: … both in the TiO2 layer and in MoO3 with a slightly narrower band gap … (where is the energy band gap of the doped samples? Please, included the UV-Vis absorption and Eg calculation).
· Where are the conclusions of the work?
· Etc.,
So is required to rewrite the manuscript.
Considering the manuscript is required more analysis and discussion and clarify the study with respect to obtained results.
I recommend rewriting the paper updating the references
I hope you find these comments useful, and we look forward to receiving your new submission of your work.
Author Response
Point 1.
First paragraph is quite well-known and widely reported; therefore, some citations are vital, review references from the last 3 to 5 years and includes them. In page 2, line 51: References [32,33,34, etc] … please include the references and remove etc., …
In page 2 , lines 52 to 60: Include references in the paragraph.
Response 1.
We removed "etc" and added the following references:
Wang, Z.; Lin, Z.; Shen, S.; Zhong, W.; Cao, S. Advances in designing heterojunction photocatalytic materials. Chin. J. Catal. 2021, 42, 710-730.
Liao, G.; Li, C.; Liu, S.Y.; Fang, B.; Yang, H. Emerging frontiers of Z-scheme photocatalytic systems. Trends in Chem. 2022, 4, 111- 127.
Ren, G.; Han, H.; Wang, Y.; Liu, S.; Zhao, J.; Meng, X.; Li, Z. Recent advances of photocatalytic application in water treatment: a review. Nanomater. 2021, 11, 1804.
Wang, H.; Li, X.; Zhao, X.; Li, C.; Song, X.; Zhang, P.; Huo, P. A review on heterogeneous photocatalysis for environmental remediation: From semiconductors to modification strategies. Chin. J. Catal. 2022, 43, 178-214.
Fang, M.; Tan, X.; Liu, Z.; Hu, B.; Wang, X. Recent progress on metal-enhanced photocatalysis: a review on the mechanism. Research 2021, 2021. DOI: 10.34133/2021/9794329
In page 2 , lines 52 to 60: We added the references:
Weng, B.; Qi, M.Y.; Han, C.; Tang, Z.R.; Xu, Y.J. Photocorrosion inhibition of semiconductor-based photocatalysts: basic principle, current development, and future perspective. ACS Catal. 2019, 9, 4642-4687.
Karim, A.V.; Krishnan, S.; Shriwastav, A. An overview of heterogeneous photocatalysis for the degradation of organic compounds: A special emphasis on photocorrosion and reusability. J. Indian Chem. Soc. 2022, 99, 100480.
Point 2.
Materials and methods: Include all information about the materials (i.e., companies, purity, etc)
Response 2.
All information about the materials was included:
MgCl2 (Sigma Aldrich, ACS reagent, 99%)
gelatin (Sigma Aldrich, from bovine skin)
(NH4)6Mo6O24 (Lachema, content of MoO3 67%)
tetrabutoxytitanium [CH3(CH2)3O]4Ti (Merk, reagent grade, 97%)
microcrystalline cellulose (Merk, for column chromatography)
Rhodamine B (RhB) (Sigma Aldrich, Dye content 97 %) and Nigrosin (Solvent black 5; CAS No.: 11099-03-9; Merk)
Point 3.
Results and discussion:
The figures, on the X and Y axis, use dots in the decimals and do not use commas. See figure 2 a,b. In addition, Table 1 and 2 appears the same for the decimals. The scientific notation is for example 2.6 x 10n, correct it in Table 2. Check it in the manuscript.
FTIR result, I am sure that the vibrational band at 1485 cm-1 corresponds to Mg-O, reference it.
The quality of figure 1 and 3 is not good, improve it.
Page 5, lines 156-159: The paragraph is not clear. Better redaction. Figure 6b, Y axis, plot from 0.4 to 0.8 to better see the results. Check decimals (use dots) Figure 7, Y axis, Check decimals (use dots).
Response 3.
In all figures and tables, commas in the decimals have been replaced by dots. Table 2 has also been adjusted.
We have added a reference to an article confirming that the band at 1485 cm-1 corresponds to Mg-O vibrations: Raman, C.V. The vibrations of the MgO crystal structure and its infra-red absorption spectrum / Proc. Indian Acad. Sci. 1961, A54, 205-222.
We have tried to make appropriate corrections to this paragraph.
The Y scale in Figure 6b is rebuilt from 0.4 to 0.8. Commas have been replaced with dots.
Point 4.
Discussion: rewrite paragraph, … line 263 say: … both in the TiO2 layer and in MoO3 with a slightly narrower band gap … (where is the energy band gap of the doped samples? Please, included the UV-Vis absorption and Eg calculation).
Response 4.
We do not present these data because, at such a low doping level, molybdenum ions cannot affect the band gap Eg, but can only create impurity electronic states inside the band gap. Some authors accept impurity absorption with the participation of impurity levels as a long-wavelength shift of the fundamental absorption and believe that even at low doping levels, a decrease in the band gap of titanium dioxide is possible. According to our data, the doping of titania with molybdenum ions in low concentration, which does not affect the crystal lattice parameters, causes only the appearance of impurity absorption, but does not affect the band gap energy. In our opinion, a detailed consideration of this issue could be the subject of a separate work.
Point 5.
Where are the conclusions of the work? - –
Response 5.
We are sorry, by our mistake, this section has been written as a part of Discussion
Reviewer 3 Report
The authors analyzed the photodegradation activities (for Rhodamine B and Nigrosin) in the presence of titania photocatalysts on a mesoporous MgO support doped with Mo(VI) ions. The catalytic materials were characterized by XRD, BET nitrogen adsorption, FT-IR, and EPR methods. The manuscript contains quite interesting results, and before publication, a few points should be changed or addressed.
The analysis of the manuscript led to the remarks presented below.
1. The quality of the figures should be improved. In particular, we suggest that the authors should pay more attention to the colour scheme of the diagram, black and white are too monotonous.
2. The English should be polished before publication.
Author Response
Point 1.
The quality of the figures should be improved. In particular, we suggest that the authors should pay more attention to the colour scheme of the diagram, black and white are too monotonous.
Response 1.
The quality of Fig. 1a, 1b, 2a, 2b, 6b was improved; the legends and color lines were added.
Reviewer 4 Report
Authors showed interesting research results regarding advanced photocatalytic characteristics of MgO-MoO3-TiO2 heterostructure. However, there are some points that need to be improved for publication in this journal.
1) Conclusion section has been omitted.
2) Discussion regarding research results is very weak. Please demonstrate the reason in more detail why the photocatalytic characteristic of MgO-MoO3-TiO2 is superior to other heterostructures. It would be better to add the graphical demonstration for MgO-MoO3-TiO2 to explain the advanced photocatalytic activity.(for example, using a band diagram)
3) Please explain the photocatalytic degradation of Rhodamine B and Nigrosin by using a chemical formula or equation. And what is the role of Mo5+ in the photocatalytic process?
4) Morphological analysis of MgO-MoO3-TiO2 need to be added by using SEM or TEM analysis.
5) In Figure2, why quantity adsorbed and pore volume is decreased when TiO2 is added in the MgO or Mo-doped MgO?
6) In Figure3, please explain the reason why IR spectra of MgO-MoO3-TiO2 is missing.
7) In Figure4 caption, there is a typing error. Mn2+ --> Mg2+
8) In Figure6(b), what is the difference between MgO-Mo(VI)-TiO2 and MgO-MoO3-TiO2?
Author Response
Point 1.
Conclusion section has been omitted.
Response 1.
We are sorry, by our mistake, this section has been written as a part of Discussion.
Point 2. Discussion regarding research results is very weak. Please demonstrate the reason in more detail why the photocatalytic characteristic of MgO-MoO3-TiO2 is superior to other heterostructures. It would be better to add the graphical demonstration for MgO-MoO3-TiO2 to explain the advanced photocatalytic activity.(for example, using a band diagram)
Response 2.
We did not aim to obtain a heterostructure with photocatalytic characteristics superior to those of other heterostructures. The goal of the work was to reduce surface recombination at the levels created by molybdenum ions in the TiO2 layer contacted with the reaction medium. For this reason, we have doped the MgO carrier and then used it as a source of molybdenum ions for modifying TiO2 layer from the carrier side. Thus, we tried to minimize the release of dopant ions directly to the TiO2 interface between the photocatalyst and the reaction medium. In our work, a heterostructure was obtained only at high doping levels (10%) of magnesium oxide, since the dopant formed a MoO3 nanophase and an isotype heterojunction TiO2-MoO3 was formed. Unfortunately, we do not have sufficient information, in particular, about the position of the Fermi level in the components of the heterojunction, to correctly construct the band energy diagram.
Point 3.
Please explain the photocatalytic degradation of Rhodamine B and Nigrosin by using a chemical formula or equation. And what is the role of Mo5+ in the photocatalytic process?
Response 3.
To construct chemical equations for the photocatalytic degradation of dyes, it is necessary to study the chemical composition of the intermediates and determine the quantitative yields of various reaction products. Since, in our case of a very low dopant concentration, the dye photodestruction mechanism hardly differs from that studied earlier for a titanium dioxide photocatalyst, including one doped with molybdenum ions, it seems to us inappropriate to introduce this material into the text of the article.
Point 4.
Morphological analysis of MgO-MoO3-TiO2 need to be added by using SEM or TEM analysis.
Response 4.
We did not present images and SEM or TEM analysis because we did not see fundamental differences between the images of the MgO substrate and the substrate with a thin TiO2 layer deposited on MgO surface at the existing magnification of our equipment.
Point 5.
In Figure2, why quantity adsorbed and pore volume is decreased when TiO2 is added in the MgO or Mo-doped MgO? –
Response 5.
This is the experimental fact. We explain it highly likely as follows: TiO2 films, applied from above, closes mechanically carriers mesopores which are responsible for high specific surface area, thus, we observe mainly interaction with the surface of titanium dioxide.
Point 6.
In Figure3, please explain the reason why IR spectra of MgO-MoO3-TiO2 is missing.
Response 6.
FTIR spectrum of TiO2 contains no additional information, the aim of these spectra is to show the unusual result of the dopant influence on the carrier.
Point 7.
In Figure4 caption, there is a typing error. Mn2+ --> Mg2+
Response 7.
In fact, we used manganese ions Mn2+ as calibration ions when obtaining EPR spectra.
Point 8.
In Figure6(b), what is the difference between MgO-Mo(VI)-TiO2 and MgO-MoO3-TiO2?
Response 8.
The difference can be easily explained: at a low doping level of MgO about 1 wt.%, these ions do not form nanophases and the internal interfaces while at 10 wt.%, the formation of new nanophases occurs as well as of TiO2-MoO3 heterojunction.
Round 2
Reviewer 1 Report
1. The last two sentences of the abstract are repetitive due to their similar meanings.
2. Additional experimental data on other Mo doping are needed as a reference to illustrate the representativeness of 1% and 10% Mo doping.
3. The formation of the heterojunction can be better demonstrated with matching energy band positions of TiO2 and MoO3.
4. In Figure 7, the data of TiO2 can be supplemented for comparison.
Author Response
Point 1: The last two sentences of the abstract are repetitive due to their similar meanings.
Response 1: Unfortunately, the previous version of this sentence has not been removed. We have corrected this omission.
Point 2: Additional experimental data on other Mo doping are needed as a reference to illustrate the representativeness of 1% and 10% Mo doping.
Response 2:
We added experimental data on the effect of Mo(VI) concentration on structure and photocatalytic activity in Supporting Information (Table 1). It follows from the table that, according to the most typical features of the structure and photocatalytic activity, the studied photocatalyst samples can be divided into three groups:
a) undoped MgO-TiO2 samples;
b) lightly doped (0.5-2.0% Mo), in which Mo ions are an impurity that creates point defects, but does not form their own nanophase, therefore we designate them as MgO-Mo(VI)-TiO2;
c) heavily doped (5-20% Mo), in which inclusions of the molybdenum oxide MoO3 nanophase, and correspondingly, the n-n heterojunction MoO3-TiO2 are formed, and therefore, to show the presence of MoO3 phase, we designate these samples as MgO-MoO3-TiO2. Along with the presentation of this information in Table 1, the values of the rate constant under UV and UV-vis irradiation for the pristine (undoped), lightly and heavily doped photocatalyst are added to the manuscript.
Point 3: The formation of the heterojunction can be better demonstrated with matching energy band positions of TiO2 and MoO3.
Response 3: We added an energy band diagram of the heterojunction as an inset to the Figure 6b.
Point 4: In Figure 7, the data of TiO2 can be supplemented for comparison.
Response 4: Unfortunately, we were unable to prepare powdered titanium dioxide identical in its morphology and structural characteristics to that deposited on the surface of MgO carrier. Our method of preparation of MgO-TiO2 photocatalyst is based on the hydrolytic decomposition of adsorbed titanium alkoxide directly on the active surface of MgO carrier containing hydroxyl group and adsorbed water. If the hydrolysis of titanium alkoxide is carried out in the bulk of an aqueous solution, the morphology of hydrated titanium dioxide particles turns out to be completely different. In addition, during the heat treatment of MgO (the final step in the preparation of the catalyst), MgO carrier has a significant effect on the crystallization of titanium dioxide. Considering that the activity of TiO2 photocatalyst strongly depends on its structure, defectiveness, specific surface area, etc., a comparison of the activity of TiO2 formed on MgO surface and the activity of TiO2 obtained in the bulk of the solution, in our opinion, seems to be insufficiently correct.
Reviewer 2 Report
Dear Authors.
Is required to include the UV-Vis measurement (supplementary information) to determine the energy band gap of the photocatalyst. Discuss in the manuscript with respect to the degradation contaminant. kinetic reaction and Energy band gap.
Author Response
Point 1. Is required to include the UV-Vis measurement to determine the energy band gap of the photocatalyst. Discuss in the manuscript with respect to the degradation contaminant. kinetic reaction and Energy band gap.
Response 1. We added UV-Vis spectra (Fig. 8), the energy band diagram (inset in Fig. 6b), and reasoning about the energy band gap to the manuscript. Also we added experimental data on the effect of Mo(VI) concentration on values of pseudo-first-order rate constant for Rhodamine B photodegradation under UV irradiation (Table 1). Along with the presentation of this information in Table 1, the values of the rate constant under UV irradiation for the original, lightly and heavily doped photocatalyst are added to the text of the article.
Reviewer 4 Report
The author responses are not sufficient to address my concerns for the manuscript. It is highly recommended to resubmit the paper after fully revising the manuscript according to my previous review report.
Author Response
Point 1. Conclusion section has been omitted.
Response 1. By our mistake, this section has been written as a part of Discussion. We have corrected this omission.
Point 2. Discussion regarding research results is very weak. Please demonstrate the reason in more detail why the photocatalytic characteristic of MgO-MoO3-TiO2 is superior to other heterostructures. It would be better to add the graphical demonstration for MgO-MoO3-TiO2 to explain the advanced photocatalytic activity. (for example, using a band diagram)
Response 2. We fully revised the discussion of photocatalytic properties of prepared photocatalysts. We added UV-Vis spectra (Fig. 8), the energy band diagram (inset in Fig. 6b), and reasoning about the energy band gap to the manuscript. Also we added experimental data on the effect of Mo(VI) concentration on values of pseudo-first-order rate constant for Rhodamine B photodegradation under UV irradiation (Table 1). We did not aim to obtain a heterostructure with photocatalytic characteristics superior to those of other heterostructures. The main goal of our work was to reduce surface recombination at the impurity centers created by molybdenum ions in the TiO2 layer contacted with the reaction medium. For this reason, we have doped the MgO carrier and then used it as a source of molybdenum ions for modifying the TiO2 layer. Thus, we tried to minimize the release of dopant ions directly to the TiO2 interface between the photocatalyst and the reaction medium.
Point 3. Please explain the photocatalytic degradation of Rhodamine B and Nigrosin by using a chemical formula or equation. And what is the role of Mo5+ in the photocatalytic process?
Response 3. To construct chemical equations for the photocatalytic degradation of dyes, it is necessary to study the chemical composition of the intermediates and determine the quantitative yields of various reaction products. In the case of a very low dopant concentration (1 wt.% in MgO carrier), the mechanism of dye photodestruction is practically the same that has been studied earlier for a titanium dioxide photocatalyst doped with molybdenum ions. Thus, in our opinion, it is inappropriate to introduce this material into the text.
We added experimental data on the effect of Mo(VI) concentration on structure and photocatalytic activity in Table 1. It follows from the table that, according to the most typical features of the structure and photocatalytic activity, the studied photocatalyst samples can be divided into three groups:
a) undoped MgO-TiO2 samples;
b) lightly doped (0.5-2.0% Mo), in which Mo ions are an impurity that creates point defects, but does not form their own nanophase, therefore we designate them as MgO-Mo(VI)-TiO2;
c) heavily doped (5-20% Mo), in which inclusions of the molybdenum oxide MoO3 nanophase, and correspondingly, the n-n heterojunction MoO3-TiO2 are formed, and therefore, to show the presence of MoO3 phase, we designate these samples as MgO-MoO3-TiO2. Along with the presentation of this information in Table 1, the values of the rate constant under UV and UV-vis irradiation for the pristine (undoped), lightly and heavily doped photocatalyst are added to the manuscript (lines 235-241, etc.).
Point 4. Morphological analysis of MgO-MoO3-TiO2 need to be added by using SEM or TEM analysis.
Response 4. We did not present images and SEM or TEM analysis because we did not see fundamental differences between the images of the MgO substrate and the substrate with a thin TiO2 layer deposited on MgO surface at the existing magnification of our equipment.
Point 5. In Figure 2, why quantity adsorbed and pore volume is decreased when TiO2 is added in the MgO or Mo-doped MgO?
Response 5. This is the experimental fact. We explain it as the blocking of mesoporous structure of MgO carrier with titania layer.
Point 6. In Figure3, please explain the reason why IR spectra of MgO-MoO3-TiO2 is missing.
Response 6. We added IR spectrum of MgO-MoO3-TiO2 in Fig.3.
Point 7. In Figure4 caption, there is a typing error. Mn2+ --> Mg2+
Response 7. In fact, we used manganese ions Mn2+ as calibration ions when obtaining EPR spectra. This is commonly use practice in EPR spectroscopy.
Point 8. In Figure6(b), what is the difference between MgO-Mo(VI)-TiO2 and MgO-MoO3-TiO2?
Response 8. Depending on the amount of introduced MoO3, two fundamentally different photocatalysts can be obtained: a) MgO-Mo(VI)-TiO2 based on MgO carrier doped with (0.5–2) wt.% Mo(VI) ions and b) MgO-MoO3-TiO2 heterostructure with a molybdenum content ≥10 wt.%, at which not only doping of TiO2 with Mo(VI) ions takes place but also the formation of MoO3 phase inclusions.
