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  • Tahani M. Bawazeer

Reviewer 1: Anonymous Reviewer 2: Chi-jung Chang

Round 1

Reviewer 1 Report

The author prepared the Cr-doped ZnO as photocatalysts and carried out a series of characterizations and experiments to investigate its physicochemical and optical properties. It aims to obtain a deeper insight on the photocatalytic degradation of dyes by using the mentioned catalysts. However, some problems also need to be modified properly. Minor revision is required before reconsider whether to publish it.

 1. Line 87. The preparation route of catalyst should be described in detail, to address the novelty of it. Besides, C need to be replaced by oC.

 2. Section 2.3 is needed, more information would be presented about the photocatalytic experiment, like wavelength of UV, experimental system and procedure, etc.

 3. In section 3.1, the peaks, angles and related phases should be marked or mentioned on/in the image or text.

 4. In section 3.4, you’d better to present the bandgaps of each materials on/in the DRS curves (Fig 4c) or the context.

 5. In section 3.5, did you conduct a repeatability test on the decolorization efficiency? If so, please add some data or explain.

Author Response

Comments and Suggestions for Authors

The author prepared the Cr-doped ZnO as photocatalysts and carried out a series of characterizations and experiments to investigate its physicochemical and optical properties. It aims to obtain a deeper insight on the photocatalytic degradation of dyes by using the mentioned catalysts. However, some problems also need to be modified properly. Minor revision is required before reconsider whether to publish it.

Response: I am highly thankful to the reviewer for his kind consideration of the article for publication in Crystals journal.

  1. Line 87. The preparation route of catalyst should be described in detail, to address the novelty of it. Besides, C need to be replaced by oC.

Response: the name of the synthesis procedure and the exact synthesis steps are now added to the synthesis part.

  1. Section 2.3 is needed, more information would be presented about the photocatalytic experiment, like wavelength of UV, experimental system and procedure, etc.

Response: Section 2.3 is added to the experimental section and the required data are added.

  1. In section 3.1, the peaks, angles and related phases should be marked or mentioned on/in the image or text.

Response: We have modified the XRD image and included the indexing to the corresponding peaks and also JCPDS card number has been added

  1. In section 3.4, you’d better to present the bandgaps of each materials on/in the DRS curves (Fig 4c) or the context.

Response: We have added one more figure [Fig. 4(d)] for band gap of each sample separately.

  1. In section 3.5, did you conduct a repeatability test on the decolorization efficiency? If so, please add some data or explain.

Response: Yes, few repeatability experiments were performed, all the obtained results were consistants with an experimental errors not more than 4%.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. Fig.3, 4, 5

All figures should be labeled (a), (b), (c), etc. The details of Figures (a), (b), and (c) should be listed in the figure caption.

 

2. It will be better if the authors can provide the XPS O1s, Zn2p, and Cr2p spectra of Cr-doped ZnO.

 

3. XRD spectra of Cr-doped ZnO and pristine ZnO

It was reported that the diffraction peaks slightly shifted toward higher angles when some Zn2+ (0.74 Å) were replaced with smaller Cr3+ dopants. [Journal of the Taiwan Institute of Chemical Engineers, 45, 1876-1882, 2014]

Please check the close-up images of Figure 1 in this study, and check whether there is any shift after Cr doping.

 

4. Figure 2

The authors mentioned that “In the Cr doped systems, the intensity of all the peaks is diminished macroscopically”.

However, the intensity of almost every peak of Cr-doped ZnO is higher than ZnO. Please recheck them.

 

5. In this study, the bandgap values shift to the lower side upon the insertion of Cr into the host lattice (Figure 4). The incorporation of Cr in the framework significantly improves the photocatalytic performance of ZnO (Figure 5).

 

Similar trends were reported for Cr-doped ZnO nanorod-array photocatalysts [Journal of Solid State Chemistry, 214, 101-107, 2014]. Cr dopant leads to enhanced separation of photogenerated charge carriers, which was confirmed by the results of PEC-SECM. It can be cited in the discussion.

Author Response

Comments and Suggestions for Authors

  1. Fig.3, 4, 5

All figures should be labeled (a), (b), (c), etc. The details of Figures (a), (b), and (c) should be listed in the figure caption.

Response: All figures has been labeled in revised version.

  1. It will be better if the authors can provide the XPS O1s, Zn2p, and Cr2p spectra of Cr-doped ZnO.

Response: I am highly thankful to the reviewer suggestion, however due to non-availability of XPS instrument in our university and even nearby institutions I am unable to include XPS analysis. I apologize for not able to include the suggested analysis. However, in future we will take care as our university is going to purchase such machines.

  1. XRD spectra of Cr-doped ZnO and pristine ZnO

It was reported that the diffraction peaks slightly shifted toward higher angles when some Zn2+ (0.74 Å) were replaced with smaller Cr3+ dopants. [Journal of the Taiwan Institute of Chemical Engineers, 45, 1876-1882, 2014]

Please check the close-up images of Figure 1 in this study, and check whether there is any shift after Cr doping.

Response: Thanks for your kind suggestion, we have included the close image as suggested which clearly shows the shift in peak position after Cr doping.

  1. Figure 2

The authors mentioned that “In the Cr doped systems, the intensity of all the peaks is diminished macroscopically”.

However, the intensity of almost every peak of Cr-doped ZnO is higher than ZnO. Please recheck them.

Response: We have rechecked and found the reduction in peaks intensity with Cr doping, for more clarity please see close view of XRD.

  1. In this study, the bandgap values shift to the lower side upon the insertion of Cr into the host lattice (Figure 4). The incorporation of Cr in the framework significantly improves the photocatalytic performance of ZnO (Figure 5).

 Similar trends were reported for Cr-doped ZnO nanorod-array photocatalysts [Journal of Solid State Chemistry, 214, 101-107, 2014]. Cr dopant leads to enhanced separation of photogenerated charge carriers, which was confirmed by the results of PEC-SECM. It can be cited in the discussion.

Response: Thanks for your kind suggestions, we have added the suggested references in the photocatalysis section.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The revised manuscript can be accepted for publication.