Cu-Doped Porous ZnO-ZnAl₂O₄ Nanocomposites Synthesized by Polymer-Salt Method for Photocatalytic Water Purification

Round 1

Reviewer 1 Report

The authors report the decolorization of Chicago Blue dye in the presence of UV light and ZnO-ZnAl₂O_4-CuO composites. The authors report that the materials are porous, but they do not report surface area from BET isotherms. Without an isotherm it is not possible to conclude if the materials are porous. The authors need to add numerical values to the y-axis of Figure 7 in order to estimate the magnitude of the signal. There are a few small typos: lines 113,191 and 197 a division sign is used when it should be a dash. Finally, the conclusions could be strengthened if the authors could suggest why there is a difference in the photocatalytic activity of the composites. What is the important? Composition, bad gap, morphology?

Overall, this work could be improved with identification of teh degradation products to better understand the mechanism. The authors need BET measurements to support the claim the materials are porous. Overall the work in not very original and with be of low impact to the community.

Author Response

Dear Reviewer!

Thank you for the detailed consideration of our articles and your notes. According to your recommendations we made corresponding changes in our manuscript and added some information. All changes in the text were marked by the green color.

The authors report the decolorization of Chicago Blue dye in the presence of UV light and ZnO-ZnAl₂O_4-CuO composites.

The authors report that the materials are porous, but they do not report surface area from BET isotherms. Without an isotherm it is not possible to conclude if the materials are porous.

     Dear Reviewer, we determined the values of specific surface area of prepared composite using another method.

     In our long-time (7 days) dye (Chicago Sky Blue (CSB; Sigma Aldrich)) adsorption experiments the adsorption/desorption equilibrium was achieved. Based on the obtained results we calculated the values of equilibrium adsorption capacities of prepared powders. These values are 9.71·10^-3 and 8.86·10^-3 mmol/g for powders 1 and 2, correspondingly.

    According to ((PubChem release 2021.05.07) https://pubchem.ncbi.nlm.nih.gov) the surface area of CSB dye molecule is 423 Ǻ². Assuming the monomolecular adsorption we calculated the values of specific surface areas of nanocomposites. These values are 247 and 137 m²/g for powders 1 and 2, correspondingly. Such values are relatively high and are observed often for different porous matrixes.     

    We added this information in the text (page 11).

 The authors need to add numerical values to the y-axis of Figure 7 in order to estimate the magnitude of the signal.

We changed the Figure 7.

 There are a few small typos: lines 113,191 and 197 a division sign is used when it should be a dash.

The corrections have been made.

Finally, the conclusions could be strengthened if the authors could suggest why there is a difference in the photocatalytic activity of the composites. What is the important? Composition, bad gap, morphology?

The chemical composition of Cu-doped ZnO-ZnAl₂O₄ composites and morphology play the most important role in their adsorptive and photocatalytic effectiveness.

We added this information in Conclusions section.

Thank you,

Best regards,

Evstropiev S.K.

Author Response File: Author Response.docx

Reviewer 2 Report

1.     Table 1 contains the results of Chemical composition of powders. It is not proper to put it in the section 2.

2.     In Table 1, the authors use both wt% and mol% to describe the component, which makes it difficult for a clear comparison.

3.     The methods to determine the Chemical composition of powders is missing.

4.     As mentioned in the introduction, the specific area can be important for the materials. However, the surface area data are missing.

5.     Line 39: The sentence is not complete. “synthesized and studied in ?”  

6.     Line 46: “have high a high adsorption…” 

7.     Figure 2 should include the simulated XRD pattern of compared components.

8.     In figure 3, how is the result for powder 1?

9.     The results in figure 4 and 6 were repeatedly present in figure 9.

10.  What is the design of two compositions of initial solutions? How the composition impacts the adsorption and photocatalysis results? 

Author Response

Dear Reviewer!

Thank you for the detailed consideration of our articles and your notes. According to your recommendations we made corresponding changes in our manuscript and added some information. All changes in the text were marked by the green color.

Table 1 contains the results of Chemical composition of powders. It is not proper to put it in the section 2.

Dear Reviewer, Table 1 contains chemical composition as initial solutions so as obtained powders. Therefore, we put this table in the section 2. We added some information about analytical chemical composition of composites (page 2).

2. 2.     In Table 1, the authors use both wt% and mol% to describe the component, which makes it difficult for a clear comparison.

We changed the description of chemical composition of powders (Table 1).

3. The methods to determine the Chemical composition of powders is missing.

The analytical elemental chemical composition of glass was determined by EDS method using setup Advanced Aztec Energy (Oxford Instruments). The differences between nominal and analytical chemical compositions were less than 6%. We added this information into the text (page 2).   

4. As mentioned in the introduction, the specific area can be important for the materials. However, the surface area data are missing.

We determined the surface area data and added this information into the article (page oo).

5. Line 39: The sentence is not complete. “synthesized and studied in ?”  

This sentence was completed (page 1).

6. Line 46: “have high a high adsorption…” 

We made the correction.

7. Figure 2 should include the simulated XRD pattern of compared components.

    You are right that the simulated XRD pattern can be the effective approach of detail study of the crystal structure of multi-component materials. However, in our work prepared materials are consist of only few crystalline phases which XRD pattern are well-known and are observed in Fig.2. The simulated XRD pattern of compared components wouldn’t change the results of our work but will be loading the article additionally.

8. In figure 3, how is the result for powder 1?

The result is similar to that was shown for powder 2. Some difference is that the process rate is higher for powder 1. We think that it is not reasonable to demonstrate two almost similar pictures. The kinetic data are shown in figure 4.

9. The results in figure 4 and 6 were repeatedly present in figure 9.

Figure 9 was removed and the text in the section 3.5 was modified.

10. What is the design of two compositions of initial solutions? How the composition impacts the adsorption and photocatalysis results? 

These two compositions have different Zn/Al molar ratio (Table 1) that provides the variation of the crystal structure, morphology and properties of prepared composites. We added this information into the manuscript (page 2).

Thank you,

Best regards,

Evstropiev S.K.

Author Response File: Author Response.docx

Reviewer 3 Report

1.      The manuscript has numerous flaws.

2.      The experimental procedure was not provided in sufficient detail.

3.      The characterization and analysis were inadequate.

4.      The representation of graphs was poor.

5.      No absorption spectra were recorded.

Author Response

Dear Reviewer!

Thank you for the detailed consideration of our articles and your notes. According to your recommendations we made corresponding changes in our manuscript and added some information. All changes in the text were marked by the green color.

The manuscript has numerous flaws.

1. The experimental procedure was not provided in sufficient detail.

We added the information about experimental procedure.

2. The characterization and analysis were inadequate.

We added some information concerning the characterization and analysis (pages 2,4,11).

3. The representation of graphs was poor.

The representation of graphs was improved.

4. No absorption spectra were recorded.

We have measured absorption spectra and determined band gap values of prepared samples. Additional figure and discussion were added into the article. 

Thank you,

Best regards,

Evstropiev S.K.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Although the authors have estimated the surface area from the saturation adsorption capacity and size of the dye, this does not provide any information about porosity. Since the molecule is rather large it is unlikely the catalyst is micro- or mesoporous. BET is the gold-standard to determine porosity.

The English is acceptable, but could be improved. However, it is not necessary to edit.

Reviewer 3 Report

The revision was done satisfactorily