Enhanced Photocatalytic Degradation of the Antidepressant Sertraline in Aqueous Solutions by Zinc Oxide Nanoparticles

Round 1

Reviewer 1 Report

Z.H. Mohamed et.al, reports photocatalytic degradation of the antidepressant sertraline in aqueous solutions by zinc oxide nanoparticles. The results are acceptable and the way of the research work, execution is good. The stated results are interesting and the manuscript is also well organized/written, which will likely to attract attention in photocatalytic degradation applications. However, the novelty and some characterization techniques are necessary to address the concept of this work. As such this reviewer believes that this work is suitable for the publication with a minor revision and here are some of the comments.

1)      What is the elemental (weight and atomic) percentage of ZnO nanoparticles?

2)      Authors have compared the ZnO nanoparticle with bulk ZnO, however, also please provide the detailed difference between bulk and NP of ZnO and their electronic/optical characteristics for enriching your research results.

3)      Provide UV-visible absorption spectra and its corresponding bandgap analysis with respective to the FTIR analysis.

4)      Please provide the corresponding indexes to XRD peak for Ex; (002) or something to recognize the peaks. It would give time to readers to easily understand the phenomena.

5)      What is the power density of UV-illumination in your study and area of illumination over the ZnO NP samples.

6)      In the TEM image, it seems that the structure of ZnO NP depicts a nanorod-like structure along with nanosized particles, what may be the reason for the rod-like (~200 nm) structure that could be better if authors can add it in the revised manuscript.

7)      Please add the PL spectra of bulk and ZnO NP, in the revised manuscript.

8)      In addition, I believe that as compared to the NP, 1D-based nanorods are having high specific surface area and excellent optoelectrical properties, which can be more beneficial to the light-assisted photocatalytic degradations. Please emphasize and justify your research concept in the introduction section.

 

9)      In recent times, 2D materials also been widely used in photocatalytic dye degradation. In that hot research perspective why authors choose ZnO NP? Please compare your research material with the other 2D, polymer-based materials and enrich your research novelty. Here are some of the references I suggest to authors that could be helpful. 10.1039/D2NJ04862K, 10.1016/j.jece.2023.109440, 10.1007/s12274-023-5472-x, 10.1140/epjp/s13360-023-03667-1, 10.1039/D2NJ04117K

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In the presented work, the authors report the sol-gel synthesis of ZnO NPs and report its photocatalytic activity in the process of degradation of the antidepersant sertalin. However, some points require attention and more detailed explanation.

1. In the «Analytical Procedures» section, the authors calculated the SERT removal efficiency using the formula:

C_t/C_0 *100%

However, the removal efficiency is calculated using the formula:

(C_0-C_t)/C_0 *100%

Where С0 is the initial concentration, Сt is the concentration at time t.

Please check your calculations.

2. In Figure 2b, the diffraction results are presented in the 2 theta angle range of 10º-60º and show a total of 5 X-ray reflections. However, in the text, the authors describe 7 X-ray reflections located in the range 30º -68º 2 theta.

3. The authors write that they used XRD analysis to “determine the size of the crystals”, but do not give any numerical values for the size of the crystallites. So what is the size of the crystallites?

4. According to the results of SEM analysis, the sample has a porous structure. What is the reason for the formation of a porous structure?

5. When describing diffraction, the authors wrote about the presence of impurity reflections (paragraph 2, lines 189-190, section 3.1), however, according to the results of elemental analysis (Fig. 2d), the authors speak of the highest degree of purity of the obtained material. But at energies around 2 keV and 8 keV, low-intensity signals are observed. Is this a background or is it just impurity elements? If this is a background, then what is the presence of impurity reflections on diffraction pattern connected with?

6. Why does the ZnO NPs/UV sample show higher photocatalytic activity than ZnO NPs/UV/H2O2?

7. When comparing the catalytic activity of ZnO NPs and ZnO bulk, as well as the COD study, the authors write that the highest activity of ZnO NPs is associated with a larger surface area than that of ZnO bulk. What is the surface area and porosity for ZnO NPs and ZnO bulk?

Author Response

Response to Reviewer 2

Dear Editor,

On behalf of all authors, I would like to thank you for your feedback and kind coordination. My thanks are also extended to the reviewers for their insightful comments and suggestions to improve the quality of the manuscript. We have addressed almost suggestions and comments as given below (all corrections and/or changes are highlighted in red).

 

1. In the «Analytical Procedures» section, the authors calculated the SERT removal efficiency using the formula: C_t/C_0 *100%

However, the removal efficiency is calculated using the formula: (C_0-C_t)/C_0 *100%

Where С₀ is the initial concentration, Сt is the concentration at time t. Please check your calculations. Done

 

2. In Figure 2b, the diffraction results are presented in the 2 theta angle range of 10º-60º and show a total of 5 X-ray reflections. However, in the text, the authors describe 7 X-ray reflections located in the range 30º -68º 2 theta. It has been corrected

The XRD analysis was used to identify the sample's shape and crystalline size. Figure 2b indicates the XRD pattern of the synthesized ZnO-NPs calcined at 600◦C. As shown from the spectra, there are characteristic peaks at 2Ɵ values of 31.7^o, 34.3^o, 36.2^o, 47.6^o, and 56.6^o for reflections at 100, 002, 101, 102 and 110 planes respectively. All peaks could be indexed as the zinc oxide wurtzite structure (JCPDS Data Card No: 36-1451). These peaks can be indexed to ZnO's hexagonal zincite-type crystallite [25]. Moreover, the crystallite size of the synthesized ZnO-NP was calculated by the Scherrer equation was used to determine the crystallite size of ZnO-NP of 53.88 nm.

 

3. The authors write that they used XRD analysis to “determine the size of the crystals”, but do not give any numerical values for the size of the crystallites. So what is the size of the crystallites?

The crystallite size of the synthesized ZnO-NP was calculated by the Scherrer equation was used to determine the crystallite size of ZnO-NP of 53.88 nm.

 

4. According to the results of SEM analysis, the sample has a porous structure. What is the reason for the formation of a porous structure?

Synthesis method and applied temperature  

 

5. When describing diffraction, the authors wrote about the presence of impurity reflections (paragraph 2, lines 189-190, section 3.1), however, according to the results of elemental analysis (Fig. 2d), the authors speak of the highest degree of purity of the obtained material. But at energies around 2 keV and 8 keV, low-intensity signals are observed. Is this a background or is it just impurity elements? If this is a background, then what is the presence of impurity reflections on diffraction pattern connected with?

The elemental analysis of the synthesized ZnO-NP yielded 82.49% of zinc, 11.65% of oxygen, and 5.84% of carbon. Our results agree with the data published in the literature [26]. 

 

6. Why does the ZnO NPs/UV sample show higher photocatalytic activity than ZnO NPs/UV/H2O2?

The removal of SERT by the ZnO-NPs/H₂O₂/UV process was 75% after 40 minutes which is slightly higher than that recorded for H₂O₂/UV process by 3% but less than that recorded for the ZnO-NPs/UV process as shown in Figure 6. This result is because hydrogen peroxide can act as a scavenger for holes or ^●OH radicals and, consequently, no enhancement in the removal of SERT by the ZnO-NPs/H₂O₂/UV process [31]. 

 

7. When comparing the catalytic activity of ZnO NPs and ZnO bulk, as well as the COD study, the authors write that the highest activity of ZnO NPs is associated with a larger surface area than that of ZnO bulk. What is the surface area and porosity for ZnO NPs and ZnO bulk?

The surface area and porosity of ZnO-NPs was calculated by nitrogen adsorption–desorption analysis at 77. The specific surface area of the sample was determined by BET method and the pore size and pore volume distribution was assessed by the Barrett–Joyner–Halenda (BJH) method.

The textural properties of ZnO-NPs and Bulk ZnO are presented in Table 1. This includes specific surface area, average pore diameter and total pore volume.

Sincerely yours,

Dr. Yasser M. Riyad

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have synthesized ZnO-NPs using sol-gel method and used it for the degradation of  Sertraline hydrochloride from aqueous solution.

-Equation 1 is not well-equilibrated

-The study of the optical features would enrich the discussion part

-The removal equation is wrong

-The FTIR and XRD spectra should be indexed

-Add the standard XRD pattern of ZnO

-Provide the JCPDS number 

-Authors can calcultae the crystallite size from the XRD data

- One SEM image is not enough, the one provided is not clear enough

-Authors have mentioned highly porous structure of ZnO, no adsorption/desorption of gaz was done.

-The given % in EDX was in atomic? please precise

-The adsorption experiments were not carried out

-Authors have mentioned the mineralisation to CO2 and H2O. This was not confirmed

-To explain the pH effect, the authors can caculate the surface charge of their catalyst

 

Author Response

Response to Reviewer 3

Dear Editor,

On behalf of all authors, I would like to thank you for your feedback and kind coordination. My thanks are also extended to the reviewers for their insightful comments and suggestions to improve the quality of the manuscript. We have addressed almost suggestions and comments as given below (all corrections and/or changes are highlighted in red).

1. Equation 1 is not well-equilibrated. Corrected

 

2. The study of the optical features would enrich the discussion part UV & PL

We have sent our samples to another lab in order to study the optical properties (UV and PL data). We expect to get data within a couple of days.

 

3. The removal equation is wrong. Corrected

Where C_o is the initial SERT drug concentration and C_t is the drug concentration at time t.

4. The FTIR and XRD spectra should be indexed. Done

 

5. Add the standard XRD pattern of ZnO. Done

The XRD analysis was used to identify the sample's shape and crystalline size. Figure 2b indicates the XRD pattern of the synthesized ZnO-NPs calcined at 600◦C. As shown from the spectra, there are characteristic peaks at 2Ɵ values of 31.7^o, 34.3^o, 36.2^o, 47.6^o, and 56.6^o for reflections at 100, 002, 101, 102 and 110 planes respectively. All peaks could be indexed as the zinc oxide wurtzite structure (JCPDS Data Card No: 36-1451).

 

6. Provide the JCPDS number Done

 

7. Authors can calculate the crystallite size from the XRD data.

The crystallite size of the synthesized ZnO-NP was calculated by the Scherrer equation was used to determine the crystallite size of ZnO-NP of 53.88 nm.

 

8. One SEM image is not enough, the one provided is not clear enough

I provided a second image.

 

9. Authors have mentioned highly porous structure of ZnO, no adsorption/desorption of gaz was done. N2 Adsorption-desorption experiment was done.

The surface area and porosity of ZnO-NPs was calculated by nitrogen adsorption–desorption analysis at 77. The specific surface area of the sample was determined by BET method and the pore size and pore volume distribution was assessed by the Barrett–Joyner–Halenda (BJH) method.

The textural properties of ZnO-NPs and Bulk ZnO are presented in Table 1. This includes specific surface area, average pore diameter and total pore volume.

 

 

10-The given % in EDX was in atomic? please precise.

 

11. The adsorption experiments were not carried out.

The adsorption experiments were carried out (please see Figure 6@ZnO-NP in the dark as an example) and 12% removal of SERT was determined.  

 

12. Authors have mentioned the mineralisation to CO₂ and H₂ This was not confirmed The reduction in the oxygen chemical demand (COD) is a clear indication of mineralization of SERT pollutant.

 

 

 

13. To explain the pH effect, the authors can calculate the surface charge of their catalyst.

Zeta potential was used to measure the surface charges of ZnO-NPs. Figure 2d showed that ZnO-NPs has a positive surface charge of +13.0 mV.

 

Sincerely yours,

Dr. Yasser M. Riyad

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors took into account all the comments, now the work can be recommended for publication.

 

Reviewer 3 Report

The revised manuscript can be accepted for publication