The three-dimensional flower-like Bi2WO6 assisted by ethanolamine through a microwave method for efficient photocatalytic activity

The three-dimensional flower-like Bi2WO6 was synthesized through a one-step microwave method (the reaction temperature was 434 K and the reaction took 10 min) with the assistance of ethanolamine (EA). The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, PL, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analysis. Methyl orange was used as target pollutant to evaluate the photocatalysis property of samples. Furthermore, the influence of the mechanism of EA on the structure and catalytic performance of Bi2WO6 was discussed. The detailed characterizations revealed that the three-dimensional flower-like Bi2WO6 was successfully synthesized with the assistance of EA. The results confirmed that EA significantly influenced the morphology of Bi2WO6 products. The addition of EA can effectively alter the pressure of the reaction and improve the crystal phase and structure of Bi2WO6 photocatalysts, enhancing the photocatalytic activity of samples and improving the photocatalytic efficiency. EA can serve as an assembling agent and structure-directing agent resulting in the formation of flower-like architectures. With the increase of the amount of EA, the as-prepared Bi2WO6 sample gradually forms a flower-like structure, leading to a shorter time of light holes migrating to the surface of the catalyst. It makes the compound rate significantly decreased, and improves the photocatalytic efficiency of the sample.

Major comments (1) The recycling ability of the photocatalyst may be discussed.

Abstract
(1) Indicate the reaction temperature and time within the parenthesis after the sentence (microwave method) and specify concentration of ethanolamine for clarity. (2) The role of ethanolamine in altering the pressure of the reaction and on the crystallization of Bi2WO6 must be highlighted. (3) The results derived from materials characterization should be briefly emphasized. Section 1.0 (1) Modify the starting phrase 'In recently, …. pollution'! (avoid using pollution twice in the same phrase).
(3) The samples may be abbreviated as 'EA:X' instead of 'EA X'. Section 2.3 (1) The details of excitation source including its intensity, wavelength maxima and distance between light source and solution surface must be provided.
(2) Specify the solution pH at which degradation reaction were carried out. Section 3.1 (1) The effect on pressure on the reaction speed as referenced from literature [15,16] may be briefly explained. (2) The viscosity of the ethanolamine-water mixture (EA 1-1 to EA 7-1) may be supplemented for more understanding. Section 3.2 (1) The XRD studies requires few clarifications: (i) is it possible to observe crystallized Bi2O3 if only Bi precursor are used in the similar experimental condition?; (ii) reflections of Bi2O3 and Bi2WO6 in the XRD patterns may be distinguished using symbols (like, asterisk '*' for Bi2O3); (iii) can pure Bi2WO6 formation is feasible if reaction time is prolonged for EA 1-1?.

Conclusion
(1) The significant results obtained highlighting the role of ethanolamine may be presented.

Recommendation?
Major revision is needed (please make suggestions in comments)

Comments to the Author(s)
In this manuscript, the 3D flower-like Bi2WO6 was synthesized with the assist of ethanolamine through one-step microwave method and evaluated the photocatalytic property of samples. The results showed that the ethanolamine significantly influenced the morphology of Bi2WO6 products and improved the photocatalytic efficiency. Overall this topic is interesting, and the results were presented satisfactorily. However, some parts of the manuscript were not presented well, and revisions are needed prior to a possible publication in Royal Society Open Science. Detailed comments are listed as follows: 1. on Abstract: the authors should provide the detailed results and conclusions, and describe briefly if and how the structure and catalytic performance of Bi2WO6 change with the assist of ethanolamine.
2. On 1st paragraph: Better background information on microwave applications and organic pollutant removal by other methods including advanced oxidation and biological processes should be presented to the prospective audiences, and these following recent articles in this field could serve this purpose in some aspects: Scientific Reports, 2017, 7 (1)  6. In section 2.1, the symbol for temperature should be presented in an accepted style. 7. Line 30-41 in Page 6: Viscosity of EA is much higher than that of water, which could affect the mass transfer rate for ions in the system. This claim needs more reliable explanations and experimental evidences or data.
8. Line 25-27 in Page 7: More explanations and evidences including literature citation for "the high dispersion of EA makes the precursor sodium tungstate and bismuth nitrate to be fully in contact, thus contributing to the formation of Bi2WO6" are needed. The following literature could be referred for the dispersion: Influences of anion concentration and valence on dispersion and aggregation of titanium dioxide nanoparticles in aqueous solutions. Journal of Environmental Sciences, 2017, 54: 135-141.
9. Fig.2 shows that the EA 2-1 sample has the highest purity and crystallinity, but the authors only compared EA 7-1 to EA 5-1, indicated that the EA 7-1 sample has a higher purity and crystallinity. That comparison and explanation is incomplete and cannot support the following conclusion. In addition, the XRD spectra of ethanolamine should be provided to eliminate its effects for the crystal phase and structure of Bi2WO6.
10. Line 47-56 in Page 7: The authors should edit this manuscript more carefully. Such as Line 52-53 in Page 7, the clerical error in the sentence "This result proves that EA 2-1 is a mixture of two substances, which is consistent with the XRD result". it should be EA 1-1, not EA 2-1.
11. Line 55 in Page 8: The sentence "The surface area of all the samples is similar, shown in Table  1, which can indicate that the difference in adsorption capacity is not caused by the BET difference" should be placed in section 3.7 to explain the difference in adsorption capacity.
12. Line 3-19 in Page 11: the amount of EA could promote the increased atomic ratio of OS in Bi2WO6, the authors should explain it.
13. Line 55 in Page 9: in the paper, the values of band gaps of EA 0, EA 1-1, EA 2-1, EA 5-1 and EA 7-1 were calculated in the Fig.5, and the variation of energy band positions were observed from the XPS valence band spectra in the Fig.9. It's better to write out the calculation. In order to further confirm the energy band positions and its variation, other means, such as Mott-Schottky calculation process should be also provided. The literature mentioned in Comment 3 could provide such information.
14. On Conclusions: The results show that the addition of EA can improve the photocatalytic activity of materials and the increase of the amount of EA, the photocatalytic activity gradually increases. The author only compared the performances of EA 0, EA1-1, EA 2-1, EA 5-1 and EA 7-1, while did not conclude how the photocatalytic activity change when EA was increased further. Data on more higher proportion should be supplemented to find the optimal proportion, so as to make the conclusion and research more valuable. The editor assigned to your manuscript has now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Subject Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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Major comments (1) The recycling ability of the photocatalyst may be discussed. (2) Remove 'more than 10 hours' and generalize as 'longer time', while discussing hydrothermal method. Section 2.1 (1) The preparative method should be detailed out completely to ensure reproducibility: (i) volume of Bi precursors and tungstate precursors taken should be indicated; (ii) concentration of ethanolamine must be specified.
(2) The apparatus in which these solutions were mixed must be indicated.
(3) The samples may be abbreviated as 'EA:X' instead of 'EA X'. Section 2.3 (1) The details of excitation source including its intensity, wavelength maxima and distance between light source and solution surface must be provided.
(2) Specify the solution pH at which degradation reaction were carried out. Section 3.1 (1) The effect on pressure on the reaction speed as referenced from literature [15,16] may be briefly explained.
(2) The viscosity of the ethanolamine-water mixture (EA 1-1 to EA 7-1) may be supplemented for more understanding. Comments to the Author(s) In this manuscript, the 3D flower-like Bi2WO6 was synthesized with the assist of ethanolamine through one-step microwave method and evaluated the photocatalytic property of samples. The results showed that the ethanolamine significantly influenced the morphology of Bi2WO6 products and improved the photocatalytic efficiency. Overall this topic is interesting, and the results were presented satisfactorily. However, some parts of the manuscript were not presented well, and revisions are needed prior to a possible publication in Royal Society Open Science. Detailed comments are listed as follows: 6. In section 2.1, the symbol for temperature should be presented in an accepted style. 7. Line 30-41 in Page 6: Viscosity of EA is much higher than that of water, which could affect the mass transfer rate for ions in the system. This claim needs more reliable explanations and experimental evidences or data. 9. Fig.2 shows that the EA 2-1 sample has the highest purity and crystallinity, but the authors only compared EA 7-1 to EA 5-1, indicated that the EA 7-1 sample has a higher purity and crystallinity. That comparison and explanation is incomplete and cannot support the following conclusion. In addition, the XRD spectra of ethanolamine should be provided to eliminate its effects for the crystal phase and structure of Bi2WO6.
10. Line 47-56 in Page 7: The authors should edit this manuscript more carefully. Such as Line 52-53 in Page 7, the clerical error in the sentence "This result proves that EA 2-1 is a mixture of two substances, which is consistent with the XRD result". it should be EA 1-1, not EA 2-1.
11. Line 55 in Page 8: The sentence "The surface area of all the samples is similar, shown in Table  1, which can indicate that the difference in adsorption capacity is not caused by the BET difference" should be placed in section 3.7 to explain the difference in adsorption capacity. 12. Line 3-19 in Page 11: the amount of EA could promote the increased atomic ratio of OS in Bi2WO6, the authors should explain it.
13. Line 55 in Page 9: in the paper, the values of band gaps of EA 0, EA 1-1, EA 2-1, EA 5-1 and EA 7-1 were calculated in the Fig.5, and the variation of energy band positions were observed from the XPS valence band spectra in the Fig.9. It's better to write out the calculation. In order to further confirm the energy band positions and its variation, other means, such as Mott-Schottky calculation process should be also provided. The literature mentioned in Comment 3 could provide such information.
14. On Conclusions: The results show that the addition of EA can improve the photocatalytic activity of materials and the increase of the amount of EA, the photocatalytic activity gradually increases. The author only compared the performances of EA 0, EA1-1, EA 2-1, EA 5-1 and EA 7-1, while did not conclude how the photocatalytic activity change when EA was increased further. Data on more higher proportion should be supplemented to find the optimal proportion, so as to make the conclusion and research more valuable.
Author's Response to Decision Letter for (RSOS-181422.R0) See Appendix A.

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? I do not feel qualified to assess the statistics

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s) Dear authors,
The point-to-point response for all the comments deserves appreciation and revised manuscript provides more insight into the work. The listed comments may be considered for better readability.

Minor comments
Title: Replace 'efficiency' by 'efficient'! Abstract (1) Remove the phrase 'The whole process took only ten minutes'!

Introduction
(1) The ethanolamine should be abbreviated as 'EA' in its first appearance in the text.

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
The authors have either revised this submission according to the comments and suggestions from the reviewers satisfactorily, or responded to the concerns from the reviewers well. I suggest this manuscript be accepted for publication in Royal Society Open Science after the authors correct the following problems. 1. There are many spelling or style problems in the reference list. For example, some journals were presented with whole names (such as References 1 and 2), and some with abbreviated ones (such as References 3 and 4). 2. Some of whole journal titles were listed in upper case (such as References 3 and 4), and some not (such as References 5 and 6). 3. Some bibliographic information are lost, such as Reference 12 whose volume and page numbers of (Chem Eng J, 2018, 353: 533-541) were not provided. The authors should correct these minor mistakes to meet the standard of publication. Thank you for submitting the above manuscript to Royal Society Open Science. On behalf of the Editors and the Royal Society of Chemistry, I am pleased to inform you that your manuscript will be accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the reviewers' comments at the end of this email.
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Introduction
(1) The ethanolamine should be abbreviated as 'EA' in its first appearance in the text.  Comments to the Author(s) The authors have either revised this submission according to the comments and suggestions from the reviewers satisfactorily, or responded to the concerns from the reviewers well. I suggest this manuscript be accepted for publication in Royal Society Open Science after the authors correct the following problems. 1. There are many spelling or style problems in the reference list. For example, some journals were presented with whole names (such as References 1 and 2), and some with abbreviated ones (such as References 3 and 4). 2. Some of whole journal titles were listed in upper case (such as References 3 and 4), and some not (such as References 5 and 6). 3. Some bibliographic information are lost, such as Reference 12 whose volume and page numbers of (Chem Eng J, 2018, 353: 533-541) were not provided. The authors should correct these minor mistakes to meet the standard of publication.