Eco-friendly synthesis of VO2 with stripped pentavalent vanadium solution extracted from vanadium-bearing shale by hydrothermal process in high conversion rate

VO2(B) has shown excellent cathode performance in lithium batteries and become a hot research topic in recent years. A stripped vanadium solution extracted from vanadium-bearing shale containing a high concentration of vanadium and certain amounts of impurities was used as a vanadium source to synthesize VO2(B) by hydrothermal process. The VO2 conversion rate can reach as high as 99.47% in a reaction time of 8 h, and this is the highest result reported. The crystalline structure and morphology of the synthesized products were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Furthermore, the electrochemical properties of VO2(B) in lithium-ion batteries were investigated. The results indicated that the VO2(B) has the initial specific discharge capacity of 192.0 mAh g−1. Stripped vanadium solution is a raw material for producing V2O5 and NH4VO3, which are indispensable vanadium sources in VO2 synthesis. Therefore, synthesis of VO2 via hydrothermal reduction by oxalic acid using stripped vanadium solution extracted from vanadium-bearing shale as a direct vanadium source is an eco-friendly, innovative and efficient method, and will have a great impact on VO2 synthesis.

manuscript publishable. 4. The author had prepared their electrode material using 20 % acetylene black which will have a massive impact on the electrochemical measurement, So, we can't able to justify the true nature of the VO2(B) as the cathode material. 5. The author needs to elaborate on the electrochemical method in the revised manuscript. 6. The mass loading of the electrode needs to be provided in the revised manuscript. 7. Surface area and pore size analysis plays a vital role in the electrochemical properties of any material. Authors need to provide the BET analysis of the VO2 in the revised manuscript. 8. Long-term cyclic stability is one of the main aspects of electrode material to implement in the practical applications.so author needs to perform cyclic stability in the revised manuscript. 9. The charge transfer kinetics and to evaluate the capacitive nature of the VO2 electrode material EIS analysis need to be performed in the revised manuscript. 10. Some literature about novel energy storage devices should be cited in suitable places. Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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Reviewer: 2
Comments to the Author(s) Eco-friendly synthesis of VO2 with stripped pentavalent vanadium solution extracted from vanadium-bearing shale by hydrothermal in high yield Manuscript ID: RSOS-181116 After careful reading this manuscript, I cannot recommend this to be published in Royal society open science at the current form. However, it can be published after major revision if the authors addressed all the issues raised. Major Revision: 1. The experimental methodologies and material preparation are not new. Hence, a clear statement to the novelty of the work presented is necessary. Further, how did you choose 1073K for 1 h (stripped vanadium) and 220° C for 8h (VO2)? Are it's optimized conditions? 2. The quality of fig. 3 (SEM pictures) is not sufficient for the publication 3. The electrode materials are characterized using a half-cell test configuration which is quite routine. Hence, authors need to provide the full device characterization for making the manuscript publishable. 4. The author had prepared their electrode material using 20 % acetylene black which will have a massive impact on the electrochemical measurement, So, we can't able to justify the true nature of the VO2(B) as the cathode material. 5. The author needs to elaborate on the electrochemical method in the revised manuscript. 6. The mass loading of the electrode needs to be provided in the revised manuscript. 7. Surface area and pore size analysis plays a vital role in the electrochemical properties of any material. Authors need to provide the BET analysis of the VO2 in the revised manuscript. 8. Long-term cyclic stability is one of the main aspects of electrode material to implement in the practical applications.so author needs to perform cyclic stability in the revised manuscript. 9. The charge transfer kinetics and to evaluate the capacitive nature of the VO2 electrode material EIS analysis need to be performed in the revised manuscript.

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? No

Recommendation?
Accept as is

Comments to the Author(s)
Authors have addressed all the comments and now paper is suitable to accept as is.

Recommendation?
Accept as is

Comments on # RSOS-181116
Authors synthesized the VO2(B) nanorods by an efficient and eco-friendly hydrothermal process with stripped vanadium solution. Various characterization technique were used in order to find the structure, morphology of the sample such as XRD, Raman spectrum, SEM to show the as-synthesized VO2 is a pure phase. Further materials were tested for cathode electrode in Li-ion batteries, which exhibit an initial specific capacity of 192.3 mAh/g and its capacity decreased to 95 mAh/g after 20 cycles.
[1] Authors should add clear TEM, HRTEM, SAED analysis of there nanorod samples. [2] What is the long term cyclic stability of the materials ? [3] Detail analysis of XPS needed in order to support the supercapacitor performance results. [4] Have authors fabricated coin cell device or actual practical device?
Authors can add this data.

Point-by-point responses to the referees' comments
Dear Editor and Reviewers, Thank you for your letter and for the reviewers' comments concerning our manuscript. The authors thank cordially the editor and two anonymous reviewers for giving us an opportunity to improve the manuscript. These comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We studied your comments carefully and have made revisions thoroughly which we hope meet with your approval. The specific corrections in the manuscript and the responds to the reviewer's comments are as follows: Responses to Reviewer's comments: Reviewer #1: Authors synthesized the VO2(B) nanorods by an efficient and eco-friendly hydrothermal process with stripped vanadium solution. Various characterization technique were used in order to find the structure, morphology of the sample such as XRD, Raman spectrum, SEM to show the as-synthesized VO2 is a pure phase. Further materials were tested for cathode electrode in Li-ion batteries, which exhibit an initial specific capacity of 192.3 mAh/g and its capacity decreased to 95 mAh/g after 20 cycles.
1. Authors should add clear TEM, HRTEM, SAED analysis of these nanorod samples.
Response: Thank you very much for your suggestions. According to your advice, TEM, HRTEM, SAED have been applied to analyze the microscopic morphology, electron diffraction, orientation of the crystal plane and the direction of growth of the material (shown in Fig. 7).

What is the long term cyclic stability of the materials ?
Response: Thanks for your suggestion. We have added the long term cyclic stability test of the materials and analyzed its performance (shown in Fig. 8a) in the revised manuscript.
3. Detail analysis of XPS needed in order to support the supercapacitor performance results.

Response:
We agree with you that XPS could support the supercapacitor performance results.  Response: Thank you very much for your careful review. Hydrothermal synthesis is commonly used to synthesize VO2, but it is indeed that this method is the first time to be used to prepare VO2 (B) with stripped pentavalent vanadium solution. Besides, stripped pentavalent vanadium solution is different from pure V2O5 as vanadium source because the former contains certain amounts of impurities such as Fe, Al, P, Si. The synthesized VO2(B) obtained in this experiment is pure phase material, indicating that stripped pentavalent solution with a certain amounts of impurities also can be used to synthesize VO2, which has never been reported before.
The vanadium-bearing shale for the preparation of stripped pentavalent vanadium solution is calcined at a temperature of 800 °C for 1 hour. Under this condition, vanadium can be effectively leached from the ore, which have been intensively studied by our group. The synthesis condition of 220 °C and 8 hours is obtained after the temperature and time exploration tests, which have been sorted and added in the revised manuscript.
2. The quality of fig. 3 (SEM pictures) is not sufficient for the publication.
Response: Thank you very much for your careful review. We have replaced Fig. 6 by a new one which is sufficient for the publication in the revised manuscript.
3. The electrode materials are characterized using a half-cell test configuration which is quite routine. Hence, authors need to provide the full device characterization for making the manuscript publishable.
Response: In the early literature review stage, we found that the half-cell is used to characterize the electrode material, and the full battery is used to study the overall system properties of the battery. What we want to investigate is the nature of the prepared VO2 (B) as an electrode material, so the authors chose half-cell characterization. 4. The author had prepared their electrode material using 20 % acetylene black which will have a massive impact on the electrochemical measurement, So, we can't able to justify the true nature of the VO2(B) as the cathode material.
Response: Because of acetylene black has the advantages of higher electronic conductivity, small particle size, and isotropy, the migration rate of electrons in the battery can be increased. Therefore, acetylene black is often used as a conductive agent for electrode materials. The choice of adding 20% acetylene black in this experiment is the result of reference to a large amount of relevant literatures. 5. The author needs to elaborate on the electrochemical method in the revised manuscript.
Response: Thanks for your suggestion. We have elaborated on the electrochemical method in the revised manuscript.
6. The mass loading of the electrode needs to be provided in the revised manuscript.
Response: Thank you very much for your careful review. The mass loading of the electrode has been provided in the revised manuscript. 7. Surface area and pore size analysis plays a vital role in the electrochemical properties of any material. Authors need to provide the BET analysis of the VO2 in the revised manuscript.
Response: Thanks for your suggestion. We added BET test of the material and analyzed effect of surface area in the revised manuscript.
8. Long-term cyclic stability is one of the main aspects of electrode material to implement in the practical applications.so author needs to perform cyclic stability in the revised manuscript.