Tracking the Local Structure Change during the Photoabsorption Processes of Photocatalysts by the Ultrafast Pump-Probe XAFS Method

Round 1

Reviewer 1 Report

This manuscript reports a local crystal structure change analysis of photocatalysts (WO3 and BiVO4) via an ultrafast X-ray absorption fine structure (XAFS) spectroscopy in the femtosecond-to-nanosecond time scale. The authors demonstrated two well-known photocatalysts, WO3 and BiVO4, as model systems. The topic is very interesting and the results are encouraging/helpful for further advanced researches. Further comprehensive researches are expected. Therefore, I recommend this manuscript as acceptable after addressing the following comments.

1) the WO3 and BiVO4 particles are prepared and dispersed. So basic information of microscopy (SEM) and XRD data should be provided to understand the XAFS results correctly.

Author Response

Comments : the WO3 and BiVO4 particles are prepared and dispersed. So basic information of microscopy (SEM) and XRD data should be provided to understand the XAFS results correctly.

Reply:   Thank you for your comments.   The samples were supplied and we should have the complicated problems if we included the XRD and SEM data so that we refer the literatures[28,30,31] that contain the samples details. 

Response:

Line 90 page 2

WO₃ (particle size <200 nm) and BiVO₄ (particle size ca. 200 nm) were prepared as described elsewhere.[28,30,31]

Reviewer 2 Report

The paper is good and scientifically sound. It represents a sucsefull review of investigations previously done and a good presentation of the application of Ultrafast pump-probe XAFS method.

It must be clearly indicated that Figures are not original but reproduced or adapted with permission from....RSC, Springer...or what else. Please specify number of reference/s in each reproduced Figure.

Author Response

Comments : It must be clearly indicated that Figures are not original but reproduced or adapted with permission from....RSC, Springer...or what else. Please specify number of reference/s in each reproduced Figure.

Reply:  we added the permission not only to the acknowledgement but now we also add the permission details in the figure captions.  

Reviewer 3 Report

Uemura et al. reviewed pump-probe XAFS studies on WO3 and BiVO4, part of which are done by the authors in SACLA and PF-AR. Overall, I agree that the review is worthy in that it overviews the valuable time-dependent informations of the two materials.  However, I feel minor improvements are needed before acceptance.

1. It appears necessary to state why the two materials are chosen. In the current version, it is difficult for this reviewer to find a consensus in physical phenomena between the data of WO3 and BiVO4. Adding up a paragraph to conclude the statements for both system in a combinatorial sense in Sec. 4 might be helpful.

2. If the figures are taken from other references, citations must appear in the captions (together with courtesy from the publishers). Also, it should be clarified exactly which works are done by the five authors. For instance, in Line 81, it is stated that ..we have applined the pump-probe XAFS... [28-30], but none of the authors name appeared in the reference.

3. Typo: Some unnecessary underscores are shown in the manuscript.

Author Response

Comments:  It appears necessary to state why the two materials are chosen. In the current version, it is difficult for this reviewer to find a consensus in physical phenomena between the data of WO3 and BiVO4. Adding up a paragraph to conclude the statements for both system in a combinatorial sense in Sec. 4 might be helpful.

Reply:  The reason why we select the WO3 and BiVO4 are followings. 

1. We would like to know the behaviors of photocarriers( electron and holes) after the photoabsorption process. WO3 is suitable to the electron while BiVO4 was expected to follow the hole but not the case.  
2. Secondary reason is that WO3 - BiVO4 nanocomposite forms the Z-scheme photocatalyst. The WO3 and BiVO4 are used for O2 and H2 evolution sites, respectively.  

We added the reasons as follows.  

Line 80 on page 2

WO₃ and BiVO₄, to which we have applied the pump-probe XAFS comprise a Z-scheme photocatalyst system that mimics a photosynthesis system.[28-30]  In the W L₃ edge of WO₃, we mainly followed the excited electron and the local structure of W induced by the excited electron while the Bi L₃ edge of BiVO₄ was expected to provide the behavior of the hole and the related local structure change around Bi.  

Comments : If the figures are taken from other references, citations must appear in the captions (together with courtesy from the publishers). Also, it should be clarified exactly which works are done by the five authors. For instance, in Line 81, it is stated that ..we have applined the pump-probe XAFS... [28-30], but none of the authors name appeared in the reference.

Reply: Thanks we wrote the reuses of figures in acknowledgement but we also added the permission in the figure caption.   

Comments :Typo: Some unnecessary underscores are shown in the manuscript.

Thanks.  We removed it.