Preparation of pod-shaped TiO2 and Ag@TiO2 nano burst tubes and their photocatalytic activity

The pod-shaped TiO2 nano burst tubes (TiO2 NBTs) were prepared by the combination of electrospinning and impregnation calcination with oxalic acid (H2C2O4), polystyrene (PS) and tetrabutyl titanate. The silver nanoparticles (AgNPs) were loaded onto the surface of TiO2 NBTs by ultraviolet light reduction method to prepare pod-shaped Ag@TiO2 NBTs. In this work, we analysed the effect of the amount of oxalic acid on the cracking degree of TiO2 NBTs; the effect of the concentration of AgNO3 solution on the particle size and loading of AgNPs on the surface of TiO2 NBTs. Scanning electron microscopy and transmission electron microscopy investigated the surface morphology of samples. X-ray diffraction and X-ray photoelectron spectroscopy characterized the structure and composition of samples. Rhodamine B (RhB) solution was used to evaluate the photocatalytic activity of pod-shaped TiO2 NBTs and Ag@TiO2 NBTs. The results showed that TiO2 NBTs degraded 91.0% of RhB under ultraviolet light, Ag@TiO2 NBTs degraded 95.5% under visible light for 75 and 60 min, respectively. The degradation process of both samples was consistent with the Langmuir–Hinshelwood first-order kinetic equation. Therefore, the catalytic performance of the sample is: Ag@TiO2 NBTs > TiO2 NBTs > TiO2 nanotubes.


Are the interpretations and conclusions justified by the results? Yes
Is the language acceptable? Yes

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

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

Comments to the Author(s) Dear authors,
The fabrication of TiO2 nanotubular structures assisted with polystyrene template and oxalic acid is excellently presented and further decorated with Ag metal via photodeposition to form metal-semiconductor heterostructure. The reasonable characterization and appreciable discussion throughout on the structure-electronic and photocatalytic properties offers some insights into the work. However, morphological evolution of TiO2 with relevance to varied reaction parameters needs to be discussed for better visibility of the work.
Major comments (1) The influence of annealing temperature on the morphology and photocatalytic activity must be discussed.
(2) The band alignment and Fermi-level equilibration of Ag-TiO2 indicating the charge carrier dynamics may be presented.

Introduction
(1) The starting phrase 'TiO2 has very….international research' may be either removed or condensed as it is too general in its content.
Section 3 (1) The 'materials characterization' must appear before 'photocatalytic activity measurement' to synchronize with 'Results and discussion' part! Section 4 (1) The ripening process leading to tubular structure and further cracking associated with oxalic acid should be properly addressed for more understanding.
(2) Is it possible to provide TGA/DTA analysis which might provide more information on the decomposition of additives?
(3) Comment on the amount of Ag metal leaching (if any) from the catalyst surface at the end of the reaction.
Decision letter (RSOS-191019.R0) 24-Jun-2019 Dear Dr Cheng: Title: Preparation of novel mature pod-shaped TiO2 and Ag@TiO2 nano burst tubes and their photocatalytic activity Manuscript ID: RSOS-191019 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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RSC Subject Editor:
Comments to the Author: (There are no comments.) ********************************************** Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) The manuscript entitled "Preparation of novel mature pod-shaped TiO2 and Ag@TiO2 nano burst tubes and their photocatalytic activity" reports the fabrication of TiO2 fibers using electrospinning method and deposited with Ag via impregnation and finally calcination towards the phase formation. H2C2O4 was used to crack down the fibers from tubular shape to near-sheet shape. The objective and experimental design of the work is good. The developed method and obtained results are promising in the field. However, the manuscript lacks in providing substantial evidences and appropriate discussions on the obtained results. Therefore, I recommend for a major revision of the manuscript as per the following comments.
1. What is mechanism behind the cracking of TiO2 fibers using H2C2O4? Discuss the interaction between H2C2O4 and TBOT 2. Authors should also discuss at which stage the cracking is happening? Is it during the electrospinning or calcination at 550 °C?
3. The discussion on XRD should be improved by discussing the observed intensity changes of the rutile phase with increasing concentration of H2C2O4. 4. It is suggested to discuss whether the morphological changes influenced the crystal structural changes in TiO2. (the change of tubular morphology to sheet may induce lattice stress in the TiO2 crystals) 5. It is mentioned that the large surface area of TiO2(0.3%) is due to the presence of 0.3% H2C2O4. But it is mentioned that H2C2O4 decomposes after the calcination. This should be clarified.
6. The decomposition of H2C2O4 is true with other concentrations also (0.5 and 1%) during the calcination. However, why the decomposition of more H2C2O4 (0.5 and 1%) didn't lead to have the TiO2 with highly reduced wall thickness and more pores? 7. Provide the pore size distribution curves of the various samples 8. Discuss the mechanism of photodeposition of Ag onto the surface of TiO2 fibers 9. The discussion on the UV-visible spectra should be improved 10. Estimate the band gap energy of bare TiO2(0%), TiO2(0.3%) and Ag-TiO2 using Tauc plot 11. It is mentioned that "the morphology of mature podshaped TiO2 NBTs changes as the degradation experiment proceeds". This needs to be supported by experimental evidences such as SEM or TEM. Both for TiO2 and Ag-TiO2 samples 12. The photocatalytic efficiency of the system should be studied some colorless pollutants as well (e.g. phenol) 13. The degradation products should be analyzed using TOC 14. Fig. S1 given in the supporting information should be cited (and discussed) in the main manuscript 15. English of the manuscript should be improved Reviewer: 2 Comments to the Author(s) This paper "Preparation of novel mature pod-shaped TiO2 and Ag@TiO2 nano burst tubes and their photocatalytic activity" reports the preparation of TiO2 and Ag@TiO by using electrospinning, which has been used extensively. The idea on the materials design is not clear. The sample preparation was not explained clearly and the products characterization was not enough to conclude the mechanism of the photocatalytic reaction. The reviewer does not recommend publication of this paper. Comments 1. The introduction (especially the first paragraph) is too general. 2. Why the mass fraction of H2C2O4 is 0%, 0.1%, 0.3%, 0.5% and 1.0% were used? The expected effects of the mass fraction of H2C2O4 on the photocatalyst performances should be clearly explained. 3. Why the samples were calcined at 550 °C, though the products are mixture of rutile and anatase.
4. Experimental section, alpha is missing after K (line 16) and Ka (line 19) should be K alpha. 5. Figure 1 is not clear, especially Figure 1 f (TEM) is not appropriate to discuss the crystallite. 6. P 5, line 18 "Ag@TiO2 nanocomposites are capable of absorbing RhB molecules" what does this statement mean? 7. In conclusion, the authors claimed "The current work provides a new form of carrier for metal and metal oxide particles, which has a high potential value for future photocatalytic research". The reviewer does not find "new" aspect of the present results and discussion. And there are no experimental data reported for the discussion on the reaction mechanisms.
Reviewer: 3 Comments to the Author(s) Dear authors, The fabrication of TiO2 nanotubular structures assisted with polystyrene template and oxalic acid is excellently presented and further decorated with Ag metal via photodeposition to form metal-semiconductor heterostructure. The reasonable characterization and appreciable discussion throughout on the structure-electronic and photocatalytic properties offers some insights into the work. However, morphological evolution of TiO2 with relevance to varied reaction parameters needs to be discussed for better visibility of the work.
Major comments (1) The influence of annealing temperature on the morphology and photocatalytic activity must be discussed.
(2) The band alignment and Fermi-level equilibration of Ag-TiO2 indicating the charge carrier dynamics may be presented.

Minor comments
Title: Remove the term 'novel mature' for readability!

Summary
(1) Remove the term 'mature' in the starting phrase.
(2) Indicate the optimum content of Ag NPs and its size to attain maximum activity.
(3) Specify the band gap response of Ag-TiO2 achieved.

Introduction
(1) The starting phrase 'TiO2 has very….international research' may be either removed or condensed as it is too general in its content.
Section 3 (1) The 'materials characterization' must appear before 'photocatalytic activity measurement' to synchronize with 'Results and discussion' part! Section 4 (1) The ripening process leading to tubular structure and further cracking associated with oxalic acid should be properly addressed for more understanding.

RSOS-191019.R1 (Revision)
Review form: Reviewer 1 Is the manuscript scientifically sound in its present form? Yes

Recommendation?
Accept as is

Comments to the Author(s)
Authors have revised the manuscript satisfactorily and it can be accepted for the publication.

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

Dear authors,
The patience to consider all the comments and point-to-point valid response for each of the queries raised complimented with significant corrections in the article deserves appreciation and revised article deserves to be published. It is a pleasure to accept your manuscript in its current form for publication in Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
The comments of the reviewer(s) who reviewed your manuscript are included at the end of this email.
Thank you for your fine contribution. On behalf of the Editors of Royal Society Open Science and the Royal Society of Chemistry, I look forward to your continued contributions to the Journal. The patience to consider all the comments and point-to-point valid response for each of the queries raised complimented with significant corrections in the article deserves appreciation and revised article deserves to be published.

Reviewer: 1
Comments to the Author(s) Authors have revised the manuscript satisfactorily and it can be accepted for the publication.

Dear Editor and Reviewers:
Many thanks for your letter and the reviewers' comments and suggestions concerning our manuscript entitled Preparation of pod-shaped TiO2 and Ag@TiO2 nano burst tubes and their photocatalytic activity. Those comments and suggestions are all valuable and helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The following is the answers and revisions I have made in response to the reviewers' questions and suggestions on an item by item basis:

Coments:
Editor: We added Acknowledgements in the manuscript. The content is as follows: This paper was made better thanks to helpful comments from Shengzhe Zhao, Mingxu Chu, Chaoyue Zhao, Caijiao Ying and Yafeng Yuan.

Reviewer1:
1. What is mechanism behind the cracking of TiO2 fibers using H2C2O4? Discuss the interaction between H2C2O4 and TBOT.
2. Authors should also discuss at which stage the cracking is happening? Is it during the electrospinning or calcination at 550 °C?
3. The discussion on XRD should be improved by discussing the observed intensity changes of the rutile phase with increasing concentration of H2C2O4.
4. It is suggested to discuss whether the morphological changes influenced the crystal structural changes in TiO2. (the change of tubular morphology to sheet may induce lattice stress in the TiO2 crystals).
5. It is mentioned that the large surface area of TiO2(0.3%) is due to the presence of 0.3% H2C2O4. But it is mentioned that H2C2O4 decomposes after the calcination. This Appendix A should be clarified.
6. The decomposition of H2C2O4 is true with other concentrations also (0.5 and 1%) during the calcination. However, why the decomposition of more H2C2O4 (0.5 and 1%) didn't lead to have the TiO2 with highly reduced wall thickness and more pores? 7. Provide the pore size distribution curves of the various samples.
8. Discuss the mechanism of photodeposition of Ag onto the surface of TiO2 fibers.
9. The discussion on the UV-visible spectra should be improved.
11. It is mentioned that "the morphology of mature podshaped TiO2 NBTs changes as the degradation experiment proceeds". This needs to be supported by experimental evidences such as SEM or TEM. Both for TiO2 and Ag-TiO2 samples.
12. The photocatalytic efficiency of the system should be studied some colorless pollutants as well (e.g. phenol).
13. The degradation products should be analyzed using TOC.
14. Fig. S1 given in the supporting information should be cited (and discussed) in the main manuscript.
15. English of the manuscript should be improved.

Reviewer2:
1. The introduction (especially the first paragraph) is too general.
The expected effects of the mass fraction of H2C2O4 on the photocatalyst performances should be clearly explained. 7. In conclusion, the authors claimed "The current work provides a new form of carrier for metal and metal oxide particles, which has a high potential value for future photocatalytic research". The reviewer does not find "new" aspect of the present results and discussion. And there are no experimental data reported for the discussion on the reaction mechanisms.

Reviewer3:
Major comments (1) The influence of annealing temperature on the morphology and photocatalytic activity must be discussed.
(2) The band alignment and Fermi-level equilibration of Ag-TiO2 indicating the charge carrier dynamics may be presented.

Minor comments
Title: Remove the term 'novel mature' for readability!

Summary
(1) Remove the term 'mature' in the starting phrase.
(2) Indicate the optimum content of Ag NPs and its size to attain maximum activity.
(3) Specify the band gap response of Ag-TiO2 achieved.

Introduction
(1) The starting phrase 'TiO2 has very….international research' may be either removed or condensed as it is too general in its content.

Section 3
(1) The 'materials characterization' must appear before 'photocatalytic activity measurement' to synchronize with 'Results and discussion' part! Section 4 (1) The ripening process leading to tubular structure and further cracking associated with oxalic acid should be properly addressed for more understanding.
(2) Is it possible to provide TGA/DTA analysis which might provide more information on the decomposition of additives?
(3) Comment on the amount of Ag metal leaching (if any) from the catalyst surface at the end of the reaction.
1. What is mechanism behind the cracking of TiO2 fibers using H2C2O4? Discuss the interaction between H2C2O4 and TBOT.
(1) What is mechanism behind the cracking of TiO2 fibers using H2C2O4?
The mechanism of H2C2O4 cracking TiO2 fiber is very simple. First, H2C2O4 is added to the electrospinning solution. Polystyrene (PS) nanofibers with H2C2O4 were prepared by electrospinning, and PS nanofibers were used as a sacrificial template for the preparation of TiO2 nanotubes. During the heating and calcination process, the PS nanofibers and H2C2O4 will completely decompose. In particular, H2C2O4 releases gas during the decomposition process. The decomposition temperature of H2C2O4 (250 °C) is lower than the decomposition temperature of PS, so under the same calcination conditions, H2C2O4 will preferentially decompose. And the presence of a large amount of gas causes the PS fiber structure to be looser, thereby accelerating the decomposition of PS. At the same time, 350~450 °C is the key period for the fixed shape of TiO2 nanotubes. When TiO2 nanotubes are subjected to a large amount of gas (H2O and CO2 produced by decomposition of PS) during this critical period, the TiO2 nanotubes will be cracked to form a pod-shaped TiO2 NBTs, and the surface of the TiO2 NBTs will be have a lot of gas overflows the hole.
There is no interaction between H2C2O4 and TBOT. Since the complete decomposition temperature of H2C2O4 is 250 °C, tetrabutyl titanate (TBOT) is subjected to aerobic calcination to form TiO2 at 350 °C. Therefore, H2C2O4 is preferentially decomposed into H2O and CO2 gases. Because 350~450 °C is the key period for TiO2 NBTs shaping.
Therefore, the presence of H2C2O4 indirectly leads to a thinner and more brittle wall of the TiO2 nanotubes, and cracking occurs during the heating and calcination process to form a pod-shaped TiO2 NBTs.
2. Authors should also discuss at which stage the cracking is happening? Is it during the electrospinning or calcination at 550 °C?
The cracking of TiO2 nanotubes is carried out during the calcination process at a temperature of 550 °C. First, we added H2C2O4 to the electrospinning solution. PS nanofibers with H2C2O4 were prepared by electrospinning, and PS nanofibers were used as a sacrificial template for the preparation of TiO2 nanotubes. Secondly, in the aerobic calcination process, the PS nanofibers and H2C2O4 will completely decompose, leaving only the TiO2 NBTs. Therefore, the crack generated by TiO2 is during the calcination at 550 °C.
3. The discussion on XRD should be improved by discussing the observed intensity changes of the rutile phase with increasing concentration of H2C2O4.  (110) and (101) directions and are characterized by rutile TiO2 (JCPDS 21-1276). The peak of the XRD pattern corresponding to the TiO2 anatase structure is very sharp and has a plurality of corresponding peaks, and thus these peaks serve as main product peaks. The peak of the XRD pattern of the TiO2 rutile structure is very small and can only be used as a by-product peak. As the concentration of H2C2O4 increased, the strength of the rutile phase did not change. Therefore, we have not improved the discussion of sample XRD.
4. It is suggested to discuss whether the morphological changes influenced the crystal structural changes in TiO2. (the change of tubular morphology to sheet may induce lattice stress in the TiO2 crystals).
The main diffraction peaks of TiO2 at 27.45° and 36.09° point in the (110) and (101) directions and are characterized by rutile TiO2 (JCPDS 21-1276). The peak of the XRD pattern corresponding to the TiO2 anatase structure is very sharp and has a plurality of corresponding peaks, and thus these peaks serve as main product peaks. The peak corresponding to the TiO2 rutile structure serves as a by-product peak. The change of the TiO2 from the tubular shape to the sheet does not affect the crystal structure change of TiO2.
5. It is mentioned that the large surface area of TiO2(0.3%) is due to the presence of 0.3% H2C2O4. But it is mentioned that H2C2O4 decomposes after the calcination. This should be clarified. As can be seen from Fig. 2(a), the complete decomposition temperature of H2C2O4 was 250 °C. Fig. 2(b) shows the picture of weight loss when pyrolysis of TiO2(0.3%) precursor fiber soaked with TBOT. There was no significant change in the weight loss of the sample before 250 °C. The mass fraction of H2C2O4 in the TiO2(0.3%) precursor fiber soaked in TBOT was only 0.3%. Therefore, during the heating and calcination process, the PS nanofibers and H2C2O4 are completely decomposed. In particular, H2C2O4 releases gas during the decomposition process. The decomposition temperature of H2C2O4 (250 °C) is lower than the decomposition temperature of PS, so under the same calcination conditions, H2C2O4 will preferentially decompose. And the presence of a large amount of gas causes the PS fiber structure to be looser, thereby accelerating the decomposition of PS. At the same time, 350~450 °C is the key period for the fixed shape of TiO2 NBTs. When TiO2 NBTs are impacted by a large amount of gas (the gas source is H2O and CO2 generated by PS decomposition) in this critical period, TiO2 NBTs will crack and form pod-shaped TiO2 NBTs, and there will be a lot of gas overflow holes on the surface of TiO2 NBTs. Therefore, the specific surface area of TiO2 NBTs is increased.
6. The decomposition of H2C2O4 is true with other concentrations also (0.5 and 1%) during the calcination. However, why the decomposition of more H2C2O4 (0.5 and 1%) didn't lead to have the TiO2 with highly reduced wall thickness and more pores?  NBTs (TiO2(0.3%)) is well-defined, the tubes and tubes will maintain a suitable distance. However, the degree of cracking of the TiO2 NBTs is increased, which directly causes an increase in the overlap between the TiO2 tubes and the tubes, and multiple nano burst tubes or a plurality of nanobelts are stuck together, thereby affecting the BET test result of the sample, resulting in The specific surface area of the sample becomes smaller and the pores are less. 7. Provide the pore size distribution curves of the various samples.  respectively. The TiO2(0.3%) NBTs (Fig. 5c) has the largest total pore volume and average pore size while having the largest specific surface area. It also showed excellent performance in photocatalytic performance testing.
8. Discuss the mechanism of photodeposition of Ag onto the surface of TiO2 fibers.
The deposition of AgNPs on the surface of the pod-shaped TiO2 NBTs is very simple.
Mainly by the irradiation of ultraviolet light, glucose is used to reduce silver nitrate to prepare AgNPs. It is particularly important that the silver nitrate aqueous glucose solution be mixed with the pod-shaped TiO2 NBTs before mixing the AgNPs. The reason is that the AgNPs produced by the reduction of ultraviolet light can be effectively grown in the pod-shaped TiO2 NBTs.
9. The discussion on the UV-visible spectra should be improved.   shows that the addition of H2C2O4 did not change the band gap energy of the TiO2 NBTs.
According to the Tauc plot method, the band gap energy of TiO2(0.3%) is 2.92 eV and the (0.05M)Ag@TiO2(0.3%) band gap energy of deposited AgNPs is 2.73 eV. Therefore, the band gap energy is reduced after the sample is loaded with the AgNPs, and the utilization efficiency of light is improved.
11. It is mentioned that "the morphology of mature podshaped TiO2 NBTs changes as the degradation experiment proceeds". This needs to be supported by experimental evidences such as SEM or TEM. Both for TiO2 and Ag-TiO2 samples. The sample is transformed from a uniformly cracked nano burst tubes into a broken nano burst tubes. Therefore, the morphology of the of pod-shaped TiO2(0.3%) NBTs changes with the degradation experiment.
12. The photocatalytic efficiency of the system should be studied some colorless pollutants as well (e.g. phenol).
Reviewers have suggested that it is very meaningful to degrade colorless pollutants. We are very sorry, there is no degradation of colorless contaminants such as phenol in manuscript. Because our work is mainly to propose that we have successfully prepared a shape-controllable pod-shaped TiO2 NBTs, and compared the catalytic performance of TiO2 NBTs and ordinary TiO2 nanotubes. Therefore, we only used a simple colored RhB solution to discuss the catalytic performance of the prepared samples. We plan to complete the catalytic degradation of colorless pollutants (such as phenol) by podshaped TiO2 NBTs in the next step. I look forward to further communication with you.
13. The degradation products should be analyzed using TOC.
Thanks to the reviewer for his suggestions. When degrading organic pollutants, we can determine the degradation of pollutants by measuring the absorbance of the solution and the total organic carbon (TOC). However, for colored organic pollutants (RhB), it is simpler and more convenient to directly measure the absorbance of the solution.
Therefore, only the content of the solution absorbance is measured in our manuscript.
The reviewer's suggestion to determine the TOC in the solution is very meaningful. We plan to degrade the colorless pollutants in the next step and determine the contents of the TOC solution to enrich the experimental content.
14. Fig. S1 given in the supporting information should be cited (and discussed) in the main manuscript.
Thanks for your suggestion, we decided to add the content of the support information to the body of the manuscript for your reading and understanding. We added the H2C2O4 decomposition curve to enrich the experimental content. Add content in a red font in the manuscript. TG-DTA analysis of pure H2C2O4 and PS/TBOT composite fiber samples with H2C2O4 content of 0.3%, the result was shown in Fig. 9. As can be seen from Fig. 9(a), the complete decomposition temperature of pure H2C2O4is 250 °C and H2C2O4 has been completely decomposed when PS has not been decomposed. Fig. 9(b) shows that the thermal decomposition process of the sample was divided into three stages. The first stage occurred between 70°C~350°C. The sample lost water and H2C2O4decomposed to release CO2 gas. The second stage is 350~450°C, which represents the decomposition of PS organic components and some of the organics produced by TBOT hydrolysis. The third stage is 450°C~700°C, mainly including PS main chain degradation and amorphous TiO2 to anatase phase two processes.
15. English of the manuscript should be improved.
Thanks to the reviewer's suggestion, we used a professional language editing service to improve the English of the manuscript.
Although notable advances have been made, but the high recombination rate of the photogenerated electron/hole pairs and the low utilization rate of ultraviolet hinders its further application in industry.
The expected effects of the mass fraction of H2C2O4 on the photocatalyst performances should be clearly explained.
(1) First, the use of H2C2O4 in experiments to cause changes in the morphology of TiO2 nanotubes is an unexpected finding. We do not know that the addition of H2C2O4 will affect the morphology of TiO2 nanotubes. Moreover, we do not know how much H2C2O4 will be added to produce this pod-shaped TiO2 NBTs. Therefore, the five H2C2O4 mass fractions of 0%, 0.1%, 0.3%, 0.5% and 1.0% were used to determine whether the amount of H2C2O4 added would affect the morphology of TiO2 nanotubes.
(2) The expected result of our experiment is that as the amount of H2C2O4 added increases, the catalytic performance of the sample after calcination will be better.
Because H2C2O4 can be completely decomposed at 250 °C, H2O and CO2 gases are released. When the amount of H2C2O4 added is increased, it means that more gas is generated, resulting in a looser structure of the PS fiber, which leads to rapid decomposition of PS. 350~450 °C is the key period for the formation of TiO2 nanotubes.
When TiO2 nanotubes are subjected to a large amount of gas (H2O and CO2 produced by decomposition of PS) during this critical period, TiO2 nanotubes are cracked, and there are many gas overflow holes on the surface of TiO2 nanotubes. At the same time, the specific surface area and photocatalytic ability of the sample are improved.
In fact, the results of the degradation experiment are not exactly the same as our expected results. The specific result is that the specific surface area and catalytic ability of the sample increase when the mass fraction of H2C2O4 is 0%, 0.1% and 0.3%.
However, when the H2C2O4 mass fraction is 0.5% and 1.0%, the specific surface area decreases and the catalytic ability also decreases a lot. This shows that only the appropriate mass fraction (0.3%) of H2C2O4 can increase the specific surface area and catalytic ability of TiO2 nanotubes.
3. Why the samples were calcined at 550 °C, though the products are mixture of rutile and anatase.  (110) and (101) directions and are characterized by rutile TiO2 (JCPDS 21-1276). The peak of the XRD pattern corresponding to the TiO2 anatase structure is very sharp and has a plurality of corresponding peaks, and thus these peaks serve as main product peaks. The peak of the XRD pattern of the TiO2 rutile structure is very small and can only be used as a byproduct peak. Therefore, the product is a mixture of rutile and anatase, and anatase TiO2 is the main product.

Experimental section, alpha is missing after K (line 16) and Ka (line 19) should be K alpha.
We are very sorry for the confusion for editors and reviewers caused by our negligence in the writing process. We have already checked the manuscript and corrected the above mistakes.
The crystal structure properties of pod-shaped TiO2 NBTs and Ag@TiO2 NBTs were studied by X-ray diffractometry (XRD, XRD-7000, Shimadzu) with Cu K alpha (λ = 0.15418 nm) as radiation source and the scanning range from 20° to 80°. Measure the specific surface area of the sample by Specific surface & pore size analysis instrument (3H-2000PS1, BeiShiDe Instrument). X-ray photoelectron spectroscopy (XPS) was performed on a VG ESCALAB LKII instrument with Mg-K alpha-ADES (hv = 1253.6 eV) source at a residual gas pressure of below 1028 Pa.
5. Figure 1 is not clear, especially Figure 1 f (TEM) is not appropriate to discuss the crystallite. is the addition of H2C2O4during the electrospinning process. It can be clearly seen from Fig. 2 (a-e) that as the amount of H2C2O4 added increases, the degree of cracking of the TiO2 nanotubes also changes greatly. It can be obtained by observing the Fig. 2(c) that the surface morphology of TiO2(0.3%) is the best, the cracking is uniform, and the crack is maintained at 200 nm to 400 nm. It also has good catalytic ability in the subsequent photocatalytic performance test. Therefore, a sample of TiO2(0.3%) was selected for TEM ( Fig. 2(f)). It can be clearly seen in Fig. 2(f) that there are small white spots on the surface of the sample. In fact, these are the pores on the surface of the sample, which increase the specific surface area of the sample. Fig. 2(g) is an HRTEM image of TiO2 (0.3%), and the lattice spacing d of the sample was measured to be 0.351 nm.
The description of the added portion of Figure 1 in the manuscript is indicated in red.
6. P 5, line 18 "Ag@TiO2 nanocomposites are capable of absorbing RhB molecules" what does this statement mean? Fig. 3 Nitrogen sorption-desorption isotherms of the samples Sorry, our language is not rigorous enough to cause problems for reviewers. The meaning of "Ag@TiO2 nanocomposites are capable of absorbing RhB molecules" is that the Ag@TiO2 nanocomposites we prepared have the ability to adsorb dye molecules. It can be seen from Fig. 3 that the prepared pod-shaped TiO2 NBTs has the same type of hysteresis loop as ordinary TiO2 nanotubes, which proves that there is a similar pore structure between these samples. Moreover, the specific surface area of the pod-shaped TiO2 NBTs increases, which also indicates that the sample with H2C2O4 added has a stronger adsorption capacity. At the same time, Ag@TiO2 NBTs are Ag@TiO2 NBTs prepared by photoreduction based on pod-shaped TiO2 NBTs.
Therefore, Ag@TiO2 NBTs also have a larger specific surface area and can adsorb more RhB molecules.
7. In conclusion, the authors claimed "The current work provides a new form of carrier for metal and metal oxide particles, which has a high potential value for future photocatalytic research". The reviewer does not find "new" aspect of the present results and discussion. And there are no experimental data reported for the discussion on the reaction mechanisms.
Dear reviewer, "new" in "The current work provides a new form of carrier for metal and metal oxide particles, which has a high potential value for future photocatalytic research" means that we successfully prepared the pod-shaped TiO2 NBTs, and the degree of cracking of this tube is completely controlled by humans. This is a new form that has not appeared in the research of TiO2 nanotubes. Moreover, because of the addition of oxalic acid, the pod-shaped TiO2 NBTs has a larger specific surface area, which is more favorable for the catalyst to adsorb dye molecules. It can be seen from the catalytic degradation experiments that the degradation performance of the podshaped TiO2 NBTs is better than that of the ordinary TiO2 nanotubes (the same illumination time, the degradation efficiency of the pod-shaped TiO2 NBTs is 91%, ordinary TiO2 nanotubes is 68%). These experimental data and results show that the work we do is valuable. At the same time, in the next study, the pod-shaped TiO2 NBTs can be used as a base material, and different metals and metal oxide particles are loaded to improve the ability of TiO2 to catalytically degrade organic pollutants. Catalytic research has positive implications. Therefore, it can be said that our work provides a new form of carrier for metal and metal oxide particles.

Response to reviewer3:
Major comments (1) The influence of annealing temperature on the morphology and photocatalytic activity must be discussed.
In fact, during the experiment we also explored the effects of different calcination temperatures on the catalytic ability of the pod-shaped TiO2 NBTs. However, when the calcination temperature was 350 °C and 750 °C, the sample had almost no catalytic ability. Therefore, the experimental contents when the calcination temperatures are 350 °C and 750 °C are not described in the manuscript. Here are our additional content: When the calcination temperature is 350 °C, Fig. 1(a) shows that only a small portion of the TiO2 nanotubes is cracked. The reason is that H2O and CO2 produced by the decomposition of H2C2O4 and PS are very slow at low temperature calcination.
Therefore, the gas gently escapes from the surface of the TiO2 NBTs, resulting in TiO2 not being well cracked. However, when the temperature rises to 550 °C ( Fig. 1(b)) and 750 °C (Fig. 1(c)), H2C2O4 and PS will rapidly decompose the H2O and CO2 gases generated. The impact of a large amount of gas will cause the surface of the TiO2 nanotube to crack and form a pod-shaped TiO2 NBTs. Therefore, there is almost no difference in the SEM pattern formed by calcination at 550 °C and 750 °C. The catalytic degradation experiments were carried out on three samples. The experimental results in Fig. 1(d) show that the degradation efficiency of the TiO2 NBTs calcined at 550 °C is 94.0%, while the degradation efficiency at 550 °C and 750 °C is 30.7. % and 20.1%, so only the catalytic performance of the 550 °C sample was analyzed in the manuscript.
(2) The band alignment and Fermi-level equilibration of Ag-TiO2 indicating the charge carrier dynamics may be presented.
Thanks to the reviewer for his suggestions. We give the band alignment of the Ag@TiO2 and the Fermi level balance to show the charge carrier dynamics, which can improve the academic level of the article. The following is the modification:

Summary
(1) Remove the term 'mature' in the starting phrase.
Thanks for the reviewer's suggestion. We removed the 'mature' from the summary section. We have put the revised content into the manuscript. In order to maintain the consistency of phrases in the manuscript, we deleted all the "mature" in the body so as to facilitate reviewers to read.
(2) Indicate the optimum content of AgNPs and its size to attain maximum activity. To further understand the chemical composition of the obtained Ag@TiO2 NBTs, energy dispersive X-ray (EDX) analysis was carried out. From the Fig. 3  leads to an increase in particle size, resulting in a decrease in the specific surface area of the particles and the surface active sites. Therefore, when the atomic percentage of the peaks of Ti, O and Ag is 74:25:0.12, the sample has the strongest catalytic ability.
(3) Specify the band gap response of Ag-TiO2 achieved. There are two ways to get the semiconductor bandwidth from the UV-vis DRS spectrum.
One is to use the intercept method to easily determine the semiconductor forbidden band width. The basic principle is that the band edge wavelength of the semiconductor (also called the absorption threshold, λg) is determined by the forbidden band width Eg, and there is a quantitative relationship between Eg(eV)=1240/λg (nm). Therefore, Eg can be obtained by obtaining λg. The other is to determine the forbidden band width of the semiconductor by the Tauc plot method. Mainly based on the formula proposed by Tauc, Davis and Mott et al: Where α is the absorption coefficient, h is the Planck constant, v is the frequency, A is a constant, Eg is the semiconductor forbidden band width, and the index n is directly related to the semiconductor type (anatase TiO2 is an indirect bandgap semiconductor, n is 2).  We modified the content of Fig. 7 in the manuscript. Expressed in red font.

Introduction
(1) The starting phrase 'TiO2 has very….international research' may be either removed or condensed as it is too general in its content.
'TiO2 has very....international research' is indeed too general, and we decided to concentrate and modify this part. The modified content is indicated in red font in the body of the manuscript. The changes are as follows: consists of a valence band (VB) filled with electron orbits, an empty orbital conduction band (CB) without electrons, and a band gap (Eg) between the valence band and the conduction band. When TiO2 is not excited, electrons in the valence band do not automatically transition to the conduction band. Only when the energy excited by the photons is greater than Eg, the electrons in the valence band absorb the energy of the photon transition into the conduction band, and holes are generated in the valence band, "electron-hole pairs" (e --h + ) are formed [13][14][15][16]. As the research groups continue to explore, the morphological structure of TiO2 is also constantly changing. Nanorods, nanotubes, nanoflowers, nanoparticles and nanofibers have been studied and prepared.
Although notable advances have been made, but the high recombination rate of the photogenerated electron/hole pairs and the low utilization rate of ultraviolet hinders its further application in industry.
Section 3 (1) The 'materials characterization' must appear before 'photocatalytic activity measurement' to synchronize with 'Results and discussion' part! Sorry, we misplaced the two parts of "material characterization" and "photocatalytic activity measurement". Thank you for your suggestion, we have completed the exchange of these two parts in the manuscript. For your convenience, the title 'Materials characterization' and 'Photocatalytic activity measurement' are indicated in red.
Section 4 (1) The ripening process leading to tubular structure and further cracking associated with oxalic acid should be properly addressed for more understanding. First, H2C2O4 is added to the electrospinning solution. PS nanofibers with H2C2O4 were prepared by electrospinning, and PS nanofibers were used as a sacrificial template for the preparation of TiO2 nanotubes. During the heating and calcination process, the PS nanofibers and H2C2O4 will completely decompose. In particular, H2C2O4 releases a large amount of gas during the decomposition process. Fig. 5 shows that the complete decomposition temperature of H2C2O4 (250 °C) is lower than the decomposition temperature of PS, so under the same calcination conditions, H2C2O4 will preferentially decompose. The presence of a large amount of gas causes the PS fiber to loosen and accelerate the decomposition of PS. At the same time, 350~450 °C is the key period for the fixed shape of TiO2 nanotubes. The impact of a large amount of gas (H2O and CO2 produced by the decomposition of PS) during the critical period of TiO2 nanotubes will cause the TiO2 nanotubes to crack, forming a pod-shaped TiO2 NBTs. Moreover, the surface of TiO2 NBTs will have a large number of gas overflow holes.
(2) Is it possible to provide TGA/DTA analysis which might provide more information on the decomposition of additives?
Thanks to the reviewer for this suggestion. In fact, we have already done this part of the work, but it is not in the body of the manuscript, which affects your understanding and reading of the content of the article. Therefore, we decided to put this part of the work in the body. The following is a TG/DTA analysis of pure H2C2O4 and sample TiO2(0.3%): TG-DTA analysis of pure H2C2O4 and PS/TBOT composite fiber samples with H2C2O4 content of 0.3%, the result was shown in Fig. 6. As can be seen from Fig. 6(a), the complete decomposition temperature of pure H2C2O4 is 250 °C, and H2C2O4 has been completely decomposed when PS has not been decomposed. Fig. 6(b) shows that the thermal decomposition process of the sample was divided into three stages. The first stage occurred between 70°C~350°C. The sample lost water and H2C2O4 decomposed to release CO2 gas. The second stage is 350~450°C, which represents the decomposition of PS organic components and some of the organics produced by TBOT hydrolysis. The third stage is 450°C~700°C, mainly including PS main chain degradation and amorphous TiO2 to anatase phase two processes.
(3) Comment on the amount of Ag metal leaching (if any) from the catalyst surface at the end of the reaction. Sorry, we did not discuss the amount of Ag metal leaching on the catalyst surface at the end of the reaction. Because it is difficult to separate the Ag metal from the Ag@TiO2 catalyst. In the catalytic degradation experiment, in order to allow the Ag@TiO2 catalyst to be in full contact with the RhB solution, we chose to stir the Ag@TiO2 catalyst and the RhB mixture at high rotation speed. However, during the high-speed agitation, a small amount of AgNPs will fall off the surface of the TiO2 NBTs. Fig. 7(a) is a photograph after the end of the reaction, the Ag metal and the Ag@TiO2 catalyst are thoroughly mixed. It can also be observed from Fig. 7(b) that the recovered Ag metal and Ag@TiO2 catalyst have been completely mixed and cannot be separated.
Therefore, it is difficult to determine the amount of Ag metal leaching on the surface of the catalyst at the end of the reaction.
Thanks again to the reviewers for their constructive comments and suggestions. We have reworked the content of the electronic supplementary material to make up for the deficiencies in the manuscript.
Finally, we sincerely appreciate your insightful and constructive comments and suggestions. We appreciate for Editor/Reviewers' warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for taking the time to review this paper.