Oxygen Vacancy Enhanced Photoreduction Cr(VI) on Few-Layers BiOBr Nanosheets
Round 1
Reviewer 1 Report
Comments:
The authors have synthesized few-layer nanosheets of BiOBr with oxygen vacancies (BiOBr-Ov) by solvothermal method using ethylene glycol as solvent. This system presents improved catalytic properties for Cr(VI) photoreduction. The manuscript demonstrates that the enhanced photocatalytic performance is ascribed to the existence of oxygen vacancies which trap the electrons (involve in photoreducing Cr(VI) reaction). and inhibit the recombination of photogenerated electrons and holes. Materials and catalysis results seem interesting, but English is very poor. In order to improve the message delivery of the paper, the authors should have to revise the English. Here are additional comments that need to be addressed for accepting the manuscript.
Recommendation: Publish after major revisions noted.
Comments
1. There are too much grammar/syntax errors. I recommend the authors to check the throughout the complete manuscript. Here are just a few of the errors.
- line 55: “oxygen vacancies is not been reported” should be changed to “oxygen vacancies has not been reported”
- Line 74 sits should be sites
- line 131 that the main diffraction peaks the obtained BiOBr samples are should be changed to the main diffraction peaks of the obtained BiOBr samples are
- line 140: there is a stronger EPR signalà that there is a strong EPR signal
- line 160: BiOBr and BiOBr-Ov was taken for XPS analysis à BiOBr and BiOBr-Ov were taken for XPS analysis
(These are few examples from an extend list)
2. Errors in the figure label references:
_In line 147 and 148, it is not 2d, it is 1d.
- In line 161, it is not 2b, it is 2d
- in figure 6: a) and b) captions are interchanged
- In table 1, Catalyst mass and volume for BiOBr-OV are 50 mg and 50 mL respectively, when 40 and 40 are always cited throughout the text.
3. Abbreviations must be accompanied of the complete name the first time. For instance, I guess these are:
- CTAB: Cetrimonium bromide
-ITO: Indium tin oxide.
- MO: methyl orange
4. in line 133: “The intensity of (001) peaks in BiOBr synthesized from water solvent is the strongest among all the diffraction peaks, which indicates the obtained BiOBr sample exposes (001) crystal facets.”. I do not agree with this. A variation of the relative intensity of the diffraction peaks compared to the reference indicates morphology differences. In this case, an increased intensity of the (001) peak (and related ones) respect to the other peaks suggests that the piling along the crystallographic c axis is favored, which does not mean that the plane (001) is exposed in greater proportion. in fact, they would be opposite consequences. However, in the case of in BiOBr-Ov, all the (00L) related planes (L=1, 2, 3 and 4) present relative intensities very similar to the reference (JCPDS NO. 09-0393). Therefore, suggesting that the lower intensity is due to the presence of vacancies is not clear and straightforward. Thus, from XRD data, it is not clear that the authors can ensured that the two materials preferably exhibit (001) face. In fact, my interpretation is that BiOBr and BiOBr-OV have different morphologies.
5. They should provide TEM images for BiOBr as well to clarify previous statement.
6. Line 139: “(EPR) is considered to be direct evidence of oxygen vacancies. Figure 1b gives out the EPR spectra of the obtained BiOBr. It can be found that there is a stronger EPR signal at about g =2.004 for BiOBr-Ov sample, indicating oxygen vacancies existence.” Normally, EPR studies of oxygen vacancies are carried out by indirect measurement of a probe molecule adsorbed on those centers (EPR active) that allows to quantify the Vo concentration. In this case, they have acquired EPR spectra directaly from the bare samples, without any teartment. So the observed feature at 2.004 is due to F centers, thus is trap electrons in the vacancies. The authors should provide references about it.
7. In line 145, they say obtained. “TEM image (Fig.1c) of BiOBr-Ov obviously shows the thickness of each nanosheet is about 15 nm.” It is not so obvious. How did they measure it? How many entities were measured? Can they show thickness measurement for BiOBr as well?
8. In line 187, “High concentration Cr(VI) (30 mg/L) can be photoreduced by BiOBr-Ov in 2 min under solar light irradiation at acid condition” Maybe I am missing something but I cannot see how 20 mg/L of Cr(VI) can be completely photoreduced by BiOBr-Ov within 12 min at acid condition, and higher concentration (39mg/L) is reduced in lower time (2 min).
8. Line 193: “The photocatalytic performances of the as-prepared samples were also evaluated by degradation of MO under visible/solar”. Please, including details in experimental section.
Comments for author File: 
Comments.pdf
Author Response
Comments:
The authors have synthesized few-layer nanosheets of BiOBr with oxygen vacancies (BiOBr-Ov) by solvothermal method using ethylene glycol as solvent. This system presents improved catalytic properties for Cr(VI) photoreduction. The manuscript demonstrates that the enhanced photocatalytic performance is ascribed to the existence of oxygen vacancies which trap the electrons (involve in photoreducing Cr(VI) reaction). and inhibit the recombination of photogenerated electrons and holes. Materials and catalysis results seem interesting, but English is very poor. In order to improve the message delivery of the paper, the authors should have to revise the English. Here are additional comments that need to be addressed for accepting the manuscript.
Recommendation: Publish after major revisions noted. Comments
1. There are too much grammar/syntax errors. I recommend the authors to check the throughout the complete manuscript. Here are just a few of the errors.
Response: We have checked the manuscript and corrected them carefully.
- line 55: “oxygen vacancies is not been reported” should be changed to “oxygen vacancies has not been reported”
Response: We have corrected it in our revised manuscript.
- Line 74 sits should be sites
- Response: We have corrected it in our revised manuscript.
- line 131 that the main diffraction peaks the obtained BiOBr samples are should be changed to the main diffraction peaks of the obtained BiOBr samples are
- Response: We have corrected it in our revised manuscript.
- line 140: there is a stronger EPR signal that there is a strong EPR signal
- Response: We have corrected it in our manuscript.
- line 160: BiOBr and BiOBr-Ov was taken for XPS analysis BiOBr and BiOBr-Ov were taken for XPS analysis
- Response: We have corrected it in our revised manuscript.
(These are few examples from an extend list)
2. Errors in the figure label references:
_In line 147 and 148, it is not 2d, it is 1d.
- Response: We have corrected it in our revised manuscript.
- In line 161, it is not 2b, it is 2d
- in figure 6: a) and b) captions are interchanged
- Response: We have corrected it in our revised manuscript.
- In table 1, Catalyst mass and volume for BiOBr-OV are 50 mg and 50 mL respectively, when 40 and 40 are always cited throughout the text.
- Response: Thanks for the reviewer. We have corrected it in our revised manuscript.
3. Abbreviations must be accompanied of the complete name the first time. For instance, I guess these are:
Response: Thanks for the reviewer. We have corrected them in our revised manuscript.
- CTAB: Cetrimonium bromide
-ITO: Indium tin oxide.
- MO: methyl orange
4. in line 133: “The intensity of (001) peaks in BiOBr synthesized from water solvent is the strongest among all the diffraction peaks, which indicates the obtained BiOBr sample exposes (001) crystal facets.”. I do not agree with this. A variation of the relative intensity of the diffraction peaks compared to the reference indicates morphology differences. In this case, an increased intensity of the (001) peak (and related ones) respect to the other peaks suggests that the piling along the crystallographic c axis is favored, which does not mean that the plane (001) is exposed in greater proportion. in fact, they would be opposite consequences. However, in the case of in BiOBr-Ov, all the (00L) related planes (L=1, 2, 3 and 4) present relative intensities very similar to the reference (JCPDS NO. 09-0393). Therefore, suggesting that the lower intensity is due to the presence of vacancies is not clear and straightforward. Thus, from XRD data, it is not clear that the authors can ensured that the two materials preferably exhibit (001) face. In fact, my interpretation is that BiOBr and BiOBr-OV have different morphologies.
5. They should provide TEM images for BiOBr as well to clarify previous statement.
Response (4-5 questions): The TEM image of BiOBr has been provided in our revised manuscript. The BiOBr is still sheet-like structure, and HRTEM images prove the BiOBr nanosheets expose (001) crystal facets. In the processing of XRD test, amounts of (001) facets of BiOBr nanosheets are exposed in the range of X-ray irradiation, and then the intensities of the diffraction peaks of (001) facets will be strong.
6. Line 139: “(EPR) is considered to be direct evidence of oxygen vacancies. Figure 1b gives out the EPR spectra of the obtained BiOBr. It can be found that there is a stronger EPR signal at about g =2.004 for BiOBr-Ov sample, indicating oxygen vacancies existence.” Normally, EPR studies of oxygen vacancies are carried out by indirect measurement of a probe molecule adsorbed on those centers (EPR active) that allows to quantify the Vo concentration. In this case, they have acquired EPR spectra directaly from the bare samples, without any teartment. So the observed feature at 2.004 is due to F centers, thus is trap electrons in the vacancies. The authors should provide references about it.
Response: one reference is provided in revised manuscript.
7. In line 145, they say obtained. “TEM image (Fig.1c) of BiOBr-Ov obviously shows the thickness of each nanosheet is about 15 nm.” It is not so obvious. How did they measure it? How many entities were measured? Can they show thickness measurement for BiOBr as well?
Response: We have provided the AFM images in order to measure the thickness of the obtained BiOBr and BiOBr-Ov nanosheets. And the accurate data are given in our revised manuscript.
8. In line 187, “High concentration Cr(VI) (30 mg/L) can be photoreduced by BiOBr-Ov in 2 min under solar light irradiation at acid condition” Maybe I am missing something but I cannot see how 20 mg/L of Cr(VI) can be completely photoreduced by BiOBr-Ov within 12 min at acid condition, and higher concentration (39mg/L) is reduced in lower time (2 min).
Response: 20 mg/L of Cr(VI) can be completely photoreduced by BiOBr-Ov within 12 min at acid condition under visible light irradiation. High concentration Cr(VI) (30 mg/L) can be photoreduced by BiOBr-Ov in 2 min under solar light irradiation at acid condition (Fig. S2a). The light source is different.
8. Line 193: “The photocatalytic performances of the as-prepared samples were also evaluated by degradation of MO under visible/solar”. Please, including details in experimental section.
Response: the information about photodegrading MO is added in experimental section in revised manuscript.
Reviewer 2 Report
Please see the attachment.
Comments for author File: Comments.pdf
Author Response
Review of Manuscript ID: Catalysts-501738
Title: Oxygen vacancy engineering enhanced photoreduction Cr(VI) on few-layers two- dimensional BiOBr nanosheets
Summary: In this work, authors synthesized BiOBr nanosheets with oxygen vacancies (BiOBr-Ov) via solvo thermal method using ethylene glycol as solvent. They characterized the morphology, structure, optical properties and surface oxygen vacancy in these materials. The BiOBr-Ov displayed higher photoreduction of Cr(VI) with complete reduction under visible light. The enhanced photocatalytic performance is ascribed to the existence of oxygen vacancies which can narrow bang gap, and inhibit recombination of photogenerated electrons and holes as justified via electrochemical impedance and photocurrent experiements. The work appears interesting and falls within the scope of the journal. Authors presented their research idea supported with original data& results. Although, some more results and scientific arguments are needed in support of the manuscript to be considered for publication. The current manuscript doesn’t meet the publication quality as there are many shortcomings,(Some of the comments are listed below). Also, the manuscript would require careful English and technical editing as there are numerous confusing sentences, clauses, etc… The reviewer suggest a major revision for further assessment. Authors should take care of the reviewer’s comments as shown below-
Comment 1: ‘Title’ needs to be more clear and direct. Please change it to a better one.
Response: “Title” has been changed to “Oxygen vacancy enhanced photoreduction Cr(VI) on few-layers BiOBr nanosheets”.
Comment 2: Authors need to improve the quality of the abstract. These are some specific comments -
- L-13-15: “…completely reduced within 12 min under visible light 13 irradiation. However, Cr(VI) with high concentration (such as 30 mg/L) only requires 2 min to be 14 photoreduced completely under solar light irradiation. ..” The experiment Using of words- 'visible light' and 'solar light' are confusing. Did they carry out the expt. under different conditions?
- L-15 “…completely under solar light irradiation. The experiment of trapping of electrons and 15 holes, and the results..”- specify the name of experiment.
- L-15-18: Please rewrite this paragraph in a concise and clear way.
- Response: The abstract has been rewritten in our revised manuscript. “visible light” and “solar light” are different experimental conditions. Xe lamp light is the simulated solar light, we also call it “solar light”. Xe lamp with a cut-off filter at 400 nm can be served as visible light source, we call it “visible light”.
Comment 3: Introduction part can be improved. It does not cover enough on all aspects of the proposed research work. Authors need to include more important literature on past work highlighting their accomplishment and lack of existing research in the current field to justify their research objective and motivation clearly. Overall, authors should work on the introduction to improve its quality. Some recent important reference as mentioned below should be added. Also, authors can elaborate these reference and specify some examples-
Catal. Sci. Technol., 2018,8, 2588-2597
ChemCatChem 2016, 8, 2525.
J. Am. Chem. Soc. 2018, 140, 5, 1760-1766
L-21-30: “……… In order to improve the photocatalytic 26 performance, a number of strategies such as heterostructure, crystal facet exposure, doping, the engineered defects, dimension tuning and so on.6-11 Among which, the dimension tuning has been regarded as an effective strategy to boost charge separation, the light absorption and ….” Authors are recommended to refer the below important articles in support of discussion on heterostructutre and 1-D nanostructure, examples for photocatalysis under visible light and include a brief discussion on them-
ChemCatChem 2018, 10, 3305
ACS Appl. Mater. Interfaces, 2012, 4 (8), pp 4024–4030
Catalysts 2017, 7(5), 153
More reference(s) needed throughout the manuscript e.g., L-42-45: Reference is needed
Response: Some refs have been cited in the revised manusicript, and Introduction Section has been revised.
Comment 4: Following points need to be taken care of (some points are highlighted with yellow)–
- Herein, few-layer BiOBr nanosheets with oxygen vacancies have been synthesized by simple 68 solvothermal method- Can authors provide the number of layers in BiOBr nanosheets?
Response: We provide the AFM images and accuracy data are given in the revised manuscript.
- Experimental section L-80: space between number and unit english correction
Response: We have corrected it.
- L-84: The products were washed with distilled…”- Please specify it in terms of color, form etc.. Which product did authors refer here? L-130: cite appropriate reference.
Response: the products are BiOBr and BiOBr-Ov. BiOBr is white powder, and BiOBr-Ov is gray powder. One ref has been cited.
L 235: “According to above analysis, the schematic photocatalytic mechanism for reduction of Cr(VI) is 235 shown in Fig. 5. 236”- English correction ..” – Name of analysis? Confusing line.
- Fig. 6: Please use consistent color to refer sample- such as red for BiOBr-OV should be in both
Fig 6(a-b).
Response: above questions are answered in revised manuscript.
- Please include the title of the reference(s)
Response: the title of the refs has been provided.
- L 134: “peaks in BiOBr synthesized from water solvent is the strongest among all the 134 ..”- What is water solvent – elaborate it.
Response: BiOBr was synthesized using H2O as solvent, we corrected in revised manuscript.
- Fig. 2b shows the high-resolution XPS spectra for the O1s- Fig. 2b- Bi4f XPS ? check.
Response: We have checked and corrected it.
- L-204: Please include ref and put equation number.
- Response: We have added equation number and one ref is cited.
- L-213: define VB-XPS..
- Response: We have defined VB-XPS in revised manuscript.
Comment 5: Some degree of english and technical correction are needed. There are many incorrect lines and requires correction e.g.,
- L-139-140: “facets.54 Electron paramagnetic resonance (EPR) is considered to be direct evidence of oxygen vacancies. Figure 1b 139 gives out the EPR 140…” - incorrect sentence- meaning is not clear. Should be like EPR characterization or results
- “BiOBr and BiOBr-Ov was taken for XPS analysis. It can be seen..”- check English
- L-225: To further investigate the photocatalytic mechanism and to statistics the roles of different reactive species (h+ and e-), different ….”
Response: We check our manuscript and corrected them.
Comment 6: Fig. 1: Authors can put XRD and EPR results in a separate Figure. TEM and HR TEM results are can be represented in another figure.
Response: We have separated EPR spectrum from the Figure 1. And TEM and HRTEM results are put in one Figure in revised manuscript.
Comment 7: L-186: “..XRD pattern (Fig. 3f), it can be found that the BiOBr-Ov structure has no change after recycled photocatalysis ..” XRD can conclude the crystallinity or crystalline form integrity. However, authors should provide the SEM/TEM micrographs to conclude the morphological and mechanical integrity of the catalyst samples after photo-catalytic experiments. How is the morphological robustness of these material?
Response: SEM image of the BiOBr-Ov after recycled photocatalysis is provided.
Comment 8: Some of the data and results can be rearranged in order to maintain the flow of the work. E.g., UV data and Band gap results can be included before the photo-catalysis discussion part.
Response: the reviewer’s suggestion is very good. As we know, UV-Vis band-edge absorption, band gap, VB-XPS and active species, play the important roles in discussing the photocatalytic mechanism of BiOBr-Ov. Therefore, they were put in one Figure.
Comment 9: Role of surface area and porosity are important parameters considering the photocatalytic performance and application of the nanostructure materials. This important point is missing in the manuscript. Can authors comment on the surface area of their systhesized materials? Authors are suggested to carry out BET surface analysis of the synthesized materials and provide a brief discussion on surface area of the materials. They can refer some of the recommended articles as indicated in Comment 3.
Response: BET surface analysis of the obtained BiOBr and BiOBr-Ov is carried out, and the data and a brief discussion on surface areas are provided in revised manuscript.
Round 2
Reviewer 1 Report
Accept in present form
Author Response
Thanks very much
Reviewer 2 Report
Please see the attachment.
Comments for author File: Comments.pdf
Author Response
Review of Manuscript ID: Catalysts-501738
Title: Oxygen vacancy enhanced photoreduction Cr(VI) on few-layers BiOBr nanosheets
Authors answered majority of the queries and included them in the revised version. The quality of the manuscript improved. However, some comments were not properly answered in the revised manuscript. Also, some degree of English/technical correction is still needed. Hence, another round of revision is necessary to take care of the below comments:
Please take care of the highlighted part: “…. which makes it beneficial to obtain few or atom layers. BiOX photocatalysts- define X
Response: One ref is cited, and X is defined
L- 82: “To solution A was added solution B with vigorous magnetically 82 stirring for 1 h.”
– correct the sentence.
Response: Sentence is corrected.
L- 91: In a typical experiment, 40 mL K2Cr2O7 solution (or methyl orange (MO) ) was added
the photocatalyst (40 mg). Please correct this - “….TEM image (Fig.3a) of BiOBr obviously shows…” – Fig. 3: BiOBr-Ov(a,b); refers oxygen vacancy BiOBr.
Response: Above contents are corrected.
L-276: “As we know, many factors can influence the photocatalytic activity of a photocatalyst, such as 276 BET surface area 277”- can be written in a better way.
Response: This part has been rewritten
L-133: tetragonal crystal phase (JCPDS NO. 09-0393).- provide ref.
Response: One ref has been cited.
SEM image of BiOBr-Ov after five recycles should be added separately.
Response: SEM image has been separated from the XRD pattern.
The quality of Figure 2. AFM images of BiOBr-Ov(a) and BiOBr is poor.
Comment#4: Can authors provide the number of layers in BiOBr nanosheets?
Response: AFM images are not re-provided because it will take long time to measure AFM data. The number of layers is given in the revised manuscript.
Authors need to take care of the reviewer comment#3. Some suggested references were not highlighted.
Response: We highlight ref 13, and more refs are cited.
“The larger BET surface area of BiOBr-Ov maybe is a reason to enhance the photocatalytic activity” are they porous? what sort of porosity-meso/micro etc.? Please include BET adsorption- desorption isotherm in the manuscript.
Response: BET adsorption- desorption isotherm is provided in manuscript.
L-285-287: “…..This enhancement on the photocatalytic performance could be contributed to the existence of oxygen vacancies which..”- Surface area of the material also increased as evident by BET study. Hence, the role of surface area must be taken into account in enhancement of photo performance. Conclusion needs to be corrected.
Response: Conclusion is corrected.
