Enhanced Photocatalytic Degradation of Amoxicillin with Mn-Doped Cu₂O under Sunlight Irradiation

Round 1

Reviewer 1 Report

In this work, the authors report the synthesis of Mn-doped Cu₂O nanoparticles through aloe vera leaves extract. The surface morphology and photocatalytic activity of Mn-doped Cu₂O nanoparticles were investigated in detail. The work is well designed and written. I recommended the acceptance of this article for publication after minor revision.

1.      The author should provide relevant characterization, such as HR-TEM or XPS, to identify the successful doping of Mn and its chemical state in Mn-doped Cu₂O.

2.      Can Cu₂O be synthesized without using aloe vera leaves extract? If yes, the differences in physical and chemical properties of Cu₂O synthesized with and without using aloe vera leaves extract should be compared, such as morphology and photocatalytic performance, to show the advantages of aloe vera leaves extract.

In Fig. 7, the position of the conduction/valence band of Mn-doped Cu₂O should be supplemented. Additionally, for the sake of completeness, I would suggest adding the following references, which concern the energy band configuration of photocatalysts. Chem. Eng. J. 2022, 439, 135787; ACS Appl. Energy Mater. 2022, 5 (5), 6228-6237; ACS Appl. Nano Mater. 2022, 5 (8), 11150-11159.

Author Response

Dear Ms. Emily Gui,

Thank you for giving me the opportunity to submit a revised draft of our manuscript titled “Enhanced Photocatalytic Degradation of Amoxicillin with Mn-doped Cu₂O under Sunlight Irradiation” to journal of Composites Science. We appreciate the time and effort that you and the reviewers have dedicated to provide your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. We have highlighted the changes within the manuscript.

Here is a point-by-point response to the reviewers’ comments and concerns

Response to Reviewer 1 Comments

Point 1: The author should provide relevant characterization, such as HR-TEM or XPS, to identify the successful doping of Mn and its chemical state in Mn-doped Cu₂O.

Response 1: The instruments are not available in our country, Ethiopia. Thank you for this suggestion. It would have been interesting to characterize the Mn-doped Cu₂O using HR-TEM or XPS. However, we didn’t find out the instruments in our country. Thus, we used the available instruments such as XRD,  SEM and UV for characterization of the material.

Point 2: Can Cu₂O be synthesized without using aloe vera leaves extract? If yes, the differences in physical and chemical properties of Cu₂O synthesized with and without using aloe vera leaves extract should be compared, such as morphology and photocatalytic performance, to show the advantages of aloe vera leaves extract.

Response 2: We don’t have financial support for chemicals and sample characterization charge at current situation. Thank you for this suggestion. It would have been interesting to prepare Cu₂O without using aloe vera leaves extract, characterize and test its catalytic performance. However, we haven’t chemicals, laboratory access and sample characterization fee.

Point 3: In Fig. 7, the position of the conduction/valence band of Mn-doped Cu₂O should be supplemented. Additionally, for the sake of completeness, I would suggest adding the following references, which concern the energy band configuration of photocatalysts. Chem. Eng. J. 2022, 439, 135787; ACS Appl. Energy Mater. 2022, 5 (5), 6228-6237; ACS Appl. Nano Mater. 2022, 5 (8), 11150-11159.

Response 3: We agree with this and have incorporated your suggestion in the manuscript. We supplemented the position of the conduction/valence band of Mn-doped Cu₂O in the revised version of the manuscript in page number 10. Besides, We added the three references (Chem. Eng. J. 2022, 439, 135787; ACS Appl. Energy Mater. 2022, 5 (5), 6228-6237; ACS Appl. Nano Mater. 2022, 5 (8), 11150-11159) to the revised manuscript.

In addition to the above comments, all spelling and grammatical errors pointed out by the reviewers have been corrected.

We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

 Sincerely,

Yohannes Teklemariam

Submission Date: 26 September 2022

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, the authors synthesized Mn-doped Cu₂O nanoparticles through Aloe vera leaves extract and investigated the factors affecting the photocatalytic degradation efficiency of Cu₂O nanoparticles. This manuscript is a little rough and simple , and it still needs to be further improved according to the following comments before the acceptance.

1.       Please provide more characterization results to prove the existence of Mn²⁺ on Cu₂O nanoparticles，such as XPS, TEM, FTIR and so on.

2.       Please give more evidences to illustrate the role of Mn²⁺ on the improved photocatalytic degradation efficiency of Cu₂O nanoparticles. For example, the author explained the introduction of Mn²⁺ accelerate the separation of photogenerated electron-hole pairs, but is not able to give the PL and EIS results for further authenticated.

3.       How about the different concentration of Mn²⁺ influence the photocatalytic degradation efficiency of Cu₂O nanoparticles?

4.       Why Mn²⁺ was selected as dopant? What about the photocatalytic degradation efficiency of Cu₂O nanoparticles when doping with other ions?

5.       How about the comparison of this work with other similar works on the photocatalytic degradation efficiency?

Author Response

Dear Ms. Emily Gui,

Thank you for giving me the opportunity to submit a revised draft of our manuscript titled “Enhanced Photocatalytic Degradation of Amoxicillin with Mn-doped Cu₂O under Sunlight Irradiation” to journal of Composites Science. We appreciate the time and effort that you and the reviewers have dedicated to provide your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. We have highlighted the changes within the manuscript.

Here is a point-by-point response to the reviewers’ comments and concerns.

Response to Reviewer 2 Comments

Point 1: Please provide more characterization results to prove the existence of Mn²⁺ on Cu₂O nanoparticles， such as XPS, TEM, FTIR and so on.

Response 1: The instruments such as  XPS, TEM and EDX are not available in our country, Ethiopia. You have raised an important point here. It would have been interesting to characterize the Mn-doped Cu₂O using HR-TEM or XPS. However, we didn’t find out the instruments in our country. Thus, we used the available instruments such as XRD,  SEM and UV to indicate the presence of Mn²⁺ on Cu₂O.

Point 2: Please give more evidences to illustrate the role of Mn²⁺ on the improved photocatalytic degradation efficiency of Cu₂O nanoparticles. For example, the author explained the introduction of Mn accelerate the separation of photogenerated electron-hole pairs, but is not able to give the PL and EIS results for further authenticated.

Response 2: The introduction of Mn²⁺ enhanced absorption in the visible light range, reduced the band gap, increased charge separation and most importantly enhanced the photocatalytic activity of Cu₂O. At high light intensity (900 W/m² in our experiment, a high intensity), the impruvement is considerably higher because the electron–hole formation is predominant, and hence , electron–hole recombination is negligible Thank you for pointing this out. The absorption of Mn-doped Cu₂O in the visible light range is notably enhanced as compared to the pristine Cu₂O. The band gap energies are ~2.3 and 2.2 eV for pristine Cu₂O and the Mn-doped Cu₂O respectively. The red shift in absorption edge and the decrease in the band gap energy are mainly attributed to the existence of crystal defects in Cu₂O from the presence of Mn²⁺. The defects create certain states in the energy gap which can absorb sub-bandgap photons, thus causes artifacts and features that can interpret as a lesser bandgap related to the real bandgap. Moreover, The Mn²⁺ traps electron from conduction band of the Cu₂O and hindering the recombination of electron/hole pair. As the Mn²⁺ traps large number of electrons, large number of superoxide radical anions (O₂^{. –}) are formed. The generation of large number of superoxide radical anions is important for attacking the organic pollutant which in turn enhanced degradation efficiency. At higher intensity of light irradiation, the enhancement was considerably higher because the electron–hole formation is predominant, and hence , electron–hole recombination is negligible [1]. In our study, the average intensity of the sunlight during the degradation experiments was 900 W/m² (high light intensity). Consequently, the role of Mn²⁺ on the improved photocatalytic degradation efficiency of Cu₂O is predominantly inhibiting electron-hole recombination as reported by Reza et al., 2017.

Point 3: How about the different concentration of Mn²⁺ influence the photocatalytic degradation efficiency of Cu₂O nanoparticles?

Response 3: We didn’t investigate the effect of dopant concentration (concentration of Mn²⁺) in this research. Thank you for your suggestion. We synthesized the Mn-doped Cu₂O with 5% of manganese. It would be great if there was XPS or EDX and we could use it for investigating the effect of different Mn²⁺ concentrations on photocatalytic degradation efficiency of Cu₂O. However, XPS or EDX are not available in our country as explained in the above. Thus, we synthesized the Mn:Cu2O to be 5%:95% as different researchers investigate different metal doped metal oxides.

Point 4: Why Mn²⁺ was selected as dopant? What about the photocatalytic degradation efficiency of Cu₂O nanoparticles when doping with other ions?

Response 4: Mn²⁺ has never been investigated as dopant to Cu₂O. Thank you for pointing this out. There are reports related to the Cu₂O and Mn-doped CuO. However, to the best of our knowledge, Mn-doped Cu₂O has never been investigated for photocatalytic degradation of antibiotics under sunlight irradiation. Hence we selected Mn²⁺ as dopant in our study. In addition to the above, we have studied only one dopant because our budget is limited (insufficient to investigate other additional ions).

Point 5: How about the comparison of this work with other similar works on the photocatalytic
degradation efficiency?

Response 5: We agree with this and have incorporated your suggestion in the revised manuscript on page number 9 highlighted with orange color. The photocatalytic degradation of MB blue using Cu₂O, a green photocatalyst prepared using plant extract has been reported by Kerour et al [2]. The average size of these particles ranged between 24 and 61 nm proved by XRD analysis, while 37-40 nm in our present study. The band gap of Cu₂O reported by Kerour was in the range of 2.50 eV to 2.62 eV which is higher than the band gap of the present study, 2.2 to 2.3. Tamam et al [3] reported photocatalytic degradation of Rh–B dye using Mn-doped CuO nanostructured material under visible light irradiation. According to the authors, Mn-doped CuO material has much better photocatalytic activity for the mineralization of Rh–B dye than pristine CuO, with 93.8% dye mineralization compared to 56.52% for pristine CuO. The Mn-doped CuO material has negligible electron-hole recombination aptitude but quicker charge transport characteristics than the un-doped. In our study, 65% and 92% of amoxicillin was removed using pristine Cu₂O and Mn-doped Cu₂O nanoparticles respectively, which is comparable with the previous work reported by Tamam et al (2022).

Photocatalytic degradation of amoxicillin was studied by [4] using TiO₂ photocatalyst under UV irradiation. According to the authors, 60 % of amoxicillin was degraded within 300 min of irradiation. Rani et al (2021) examined the photocatalytic degradation of amoxicillin using TiO₂-SiO₂ composites. 88% of amoxicillin was degraded in 150 min under UV light illumination [5]. Photocatalytic decomposition of amoxicillin has been explored by Mohammadi et al (2012) using Sn/TiO₂. According to the authors, Sn/TiO₂ nanoparticles showed good activity in the mineralization of amoxicillin under UV light [6]. Olama et al (2018) investigated the removal of amoxicillin from aqueous solution using TiO₂/UV-C doped with trivalent iron. 99% of amoxicillin was removed by the catalyst under UV irradiation. Percentage degradation of amoxicillin in the presint study was found to be 92% which is comparable with the other reports.

In addition to the above comments, all spelling and grammatical errors pointed out by the reviewers have been corrected.

We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

Sincerely,

Yohannes Teklemariam

Submission Date: 26 September 2022

Reference

1. Reza, K.M., A.S.W. Kurny, and F. Gulshan, Parameters affecting the photocatalytic degradation of dyes using TiO2: a review. Applied Water Science, 2017. 7(4): p. 1569-1578.
2. Kerour, A., et al., Eco-friendly synthesis of cuprous oxide (Cu2O) nanoparticles and improvement of their solar photocatalytic activities. Journal of Solid State Chemistry, 2018. 263: p. 79-83.
3. Tamam, N., et al., Surfactant assisted synthesis of nanostructured Mn-doped CuO: An efficient photocatalyst for environmental remediation. Ceramics International, 2022. 48(20): p. 29589-29600.
4. Elmolla, E.S. and M. Chaudhuri, Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution using UV/TiO2 and UV/H2O2/TiO2 photocatalysis. Desalination, 2010. 252(1-3): p. 46-52.
5. Rani, S., A. Garg, and N. Singh, Photocatalytic degradation and mineralization of amoxicillin and ofloxacin using TiO2-SiO2 composites. Toxicological & Environmental Chemistry, 2021. 103(2): p. 137-153.
6. Mohammadi, R., B. Massoumi, and M. Rabani, Photocatalytic decomposition of amoxicillin trihydrate antibiotic in aqueous solutions under UV irradiation using Sn/TiO2 nanoparticles. International Journal of Photoenergy, 2012. 2012.

Author Response File: Author Response.docx

Reviewer 3 Report

I have carefully read the article entitled “Enhanced photocatalytic Degradation of Amoxicillin with Mn-doped Cu2O under Sunlight irradiation”. The authors carry out a systematic and well-conducted study of the catalytic activity of the manganese-doped copper oxide nanoparticle system on amoxicillin degradation. The effect of pH, the concentration of amoxicillin, and the catalyst concentration on photocatalytic degradation of amoxicillin are evaluated in the work. The results are relevant because the optimal parameters for the adequate photodegradation of this antibiotic in solution are determined. It is established that the presence of manganese enhances the photocatalytic capacity of the doped CuO2 nanoparticles. However, the authors do not discuss throughout the work the effect of the concentration of Manganese ions on the catalytic potential of these nanomaterials. Before accepting the article, the following points must be addressed: 1)the authors must establish the final concentration of manganese incorporated in the CuO2 nanoparticles. For this, it is crucial to quantify the manganese content in the nanoparticles by atomic absorption and to estimate the efficiency of manganese incorporation in the synthesis. 2)On the other hand, synthesis with plant extracts forms a cover on the synthesized nanoparticles that act as stabilizers. How does this coating affect the catalytic activity where the process is required to take place on the nanoparticle's surface?  The authors should clarify the point.

 Other comments to consider:

1. In line 130, change “nanoparticle” to “nanoparticles”
2. In methods, section 2.4 "Photocatalysis experiments," the authors must include the average value of the solar irradiance of the locality where the photodegradation experiments were carried out.
3. At line 150, specify the value of temperature or range of temperatures in the experiments.
4. At line 184 change “Scherer” by “Scherrer” 
5. Review the results obtained for the crystallite size by the Scherrer equation. The reported results are at least twice the expected value.
6. In line 230, change “Fig. 1” to “Fig. 3”
7. In line 247, change “Fig,2” to “Fig. 4”
8. In line 260, change “Fig. 3” to “Fig. 5”
9. In line 282, change “Fig. 4” to “Fig.6”
10. In line 305, change “Fig. 5” to “Fig. 7”
11. In line 326, change “Fig. 6” to “Fig. 8”
12. In line 343, change “Fig. 7” to “Fig.9”

Author Response

Dear Ms. Emily Gui,

Thank you for giving me the opportunity to submit a revised draft of our manuscript titled “Enhanced Photocatalytic Degradation of Amoxicillin with Mn-doped Cu₂O under Sunlight Irradiation” to journal of Composites Science. We appreciate the time and effort that you and the reviewers have dedicated to provide your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. We have highlighted the changes within the manuscript.

Here is a point-by-point response to the reviewers’ comments and concerns.

Response to Reviewer 3 Comments

Point 1: The authors must establish the final concentration of manganese incorporated in the Cu₂O
nanoparticles. For this, it is crucial to quantify the manganese content in the nanoparticles
by atomic absorption and to estimate the efficiency of manganese incorporation in the
synthesis.

Response 1: At current situation , the atomic absorbtion spectrometry is not easily available in a nearby place and may be difficult to get it. Thank you for this suggestion. It would have been
interesting to quantify the manganese content in the nanoparticles by atomic absorption. However the instrument is found in insecured regional state far from our current region. If you give us enough time (not less than 3 months), we can quantify the contet of Mn in the prepared nanoparticles because the security of the place may be returned.

Point 2: On the other hand, synthesis with plant extracts forms a cover on the synthesized nanoparticles that act as stabilizers. How does this coating affect the catalytic activity where the process is required to take place on the nanoparticle's surface? The authors should clarify the point

Response 2: In our study, Aloe vera leaves extract was used as reducing agent (reducing Cu²⁺ in CuSO₄.5H₂O precursor into Cu⁺  in the Cu₂O) in addition to the stabilizing agent . Thank you for pointing this out. Instead of using chemical based reducing agents such as ascorbic acid, hydrazine, sodium borohydride, hydroquinone and gallic acid, plant extract was used as an eco-friendly approach in our study. The specifi surface area of photocatalyst prepared by plant extract is reported to be higher than that of conventional nanoparticles that account for the increased catalyst and reactant interaction (enhanced adsorption capability ability). The utilization of plant extract in the synthesis of photocatalyst reduces the optical band gap of the synthesized nanoparticles which increases the excitation potential of electrons from the valence band. The chances of recombination of electron and hole pairs can be reduced by stabilizing the nanoparticles. In this aspect, using plant extract as stabilizer reported being excellent in the separation of holes and electrons which causes effective photodegradation. Stabilization of nanoparticles by plant extract assist in the immobilization of organic pollutants on the surface of the catalyst, which further advances the photocatalytic degradation of pollutants.

The plant extract concentrations have an effect on the morphological, structural and optical properties of the synthesized nanoparticles [1], which inturn affects the catalytic activity of the nanoparticles. The  green synthesis is attributed to the increase in the surface area of TiO₂ NPs that enhances the adsorption of hexavalent chromium [2]. The utilization of plant extract in the synthesis of photocatalyst reduces the optical band gap of the synthesized NPs which increases the excitation potential of electrons from the valence band [3]. The specifi surface area of photocatalyst prepared by plant extract is reported to be higher than that of conventional NPs that account for the increased catalyst and reactant interaction. Even though photocatalytic degradation increases with the surface area of the catalyst, it should be well noted that a high concentration of plant extract may increase turbidity and reduces light penetration, and results in decreased photodegradation processes. Prior research suggested that the optimization of the concentration of plant extract is an important parameter to achieve maximum degradation potential [4].

The chances of recombination of electron and hole pairs can be reduced by stabilizing the NPs. In this aspect, plant extract having plant biomolecules as the stabilizing agent reported being excellent in the separation of holes and electrons which causes effective photodegradation of hexavalent chromium [5]. Capping agents such as saponins and tannins present in the C. lanceolata extract were found to be the main factor behind the restriction in the recombination of electrons and holes that causes furtherance in reactive species formation and improved photodegradation effiiency of ZnO NPs [6]. Enhancement in the migration effiiency of electrons and holes has also been achieved, when normal metal oxide form is replaced with iron oxide NPs synthesized using K. alvarezii plant [7]. Due to the supplement of Aegle marmelos leaf extract in the synthesis of NiO NPs, intrinsic and surface defects have been naturally produced without the addition of any impurities that make the synthesized NiO NPs effiacious in the photocatalytic activities [8].

Stabilization of iron NPs by Hibiscus sabdariffa plant extract assist in the immobilization of organic pollutants on the surface of the catalyst, which further advances the photocatalytic degradation of pollutants. It is reported that plant extract (panax species) can cause inherent morphological variations in the ZnO NPs structure which additionally provide more active sites for the reactive species interaction with organic pollutants under UV irradiation [9]. Photoluminescence studies inferred that rapid recombination of electron and hole has been observed for bismuth oxychloride (BiOCl) photocatalyst synthesized without plant extract, whereas plant extract (Azadirachta indica) incorporated BiOCl shows signifiant improvement in photocurrent response, accelerate surface charge transfer, and inhibited recombination to some extent [10].

Other comments to consider:
1 . In line 130, change “nanoparticle” to “nanoparticles”
2. In methods, section 2.4 "Photocatalysis experiments," the authors must include the average value of the solar irradiance of the locality where the photodegradation experiments were carried out.
3. At line 150, specify the value of temperature or range of temperatures in the experiments.
4. At line 184 change “Scherer” by “Scherrer”
5. Review the results obtained for the crystallite size by the Scherrer equation. The reported results are at least twice the expected value

6. In line 230 change “Fig 1” to “Fig 3”
7. In line 247, change “Fig,2” to “Fig. 4”
   8. In line 260, change “Fig. 3” to “Fig. 5”
   9. In line 282, change “Fig. 4” to “Fig.6”
   10. In line 305, change “Fig. 5” to “Fig. 7”
   11 . In line 326, change “Fig. 6” to “Fig. 8”
   12. In line 343, change “Fig. 7” to “Fig.9”

Response: The above comments (1-12) are corrected and included in the revised version of the manuscript .

In addition to the above comments, all spelling and grammatical errors pointed out by the reviewers have been corrected.

We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

Sincerely,

Yohannes Teklemariam

Submission Date: 26 September 2022

References

1. Kerour, A., et al., Eco-friendly synthesis of cuprous oxide (Cu2O) nanoparticles and improvement of their solar photocatalytic activities. Journal of Solid State Chemistry, 2018. 263: p. 79-83.
2. Goutam, S.P., et al., Green synthesis of TiO2 nanoparticles using leaf extract of Jatropha curcas L. for photocatalytic degradation of tannery wastewater. Chemical Engineering Journal, 2018. 336: p. 386-396.
3. Stan, M., et al., Enhanced photocatalytic degradation properties of zinc oxide nanoparticles synthesized by using plant extracts. Materials Science in Semiconductor Processing, 2015. 39: p. 23-29.
4. Sharma, S., et al., The effect of shape and size of ZnO nanoparticles on their antimicrobial and photocatalytic activities: a green approach. Bulletin of Materials Science, 2019. 43(1): p. 20.
5. Abinaya, M., et al., Synthesis and Characterization of 1D-MoO3 Nanorods Using Abutilon indicum Extract for the Photoreduction of Hexavalent Chromium. Journal of Inorganic and Organometallic Polymers and Materials, 2019. 29(1): p. 101-110.
6. Lu, J., et al., The assessment of photocatalytic activity of zinc oxide nanoparticles from the roots of Codonopsis lanceolata synthesized by one-pot green synthesis method. Optik, 2019. 184: p. 82-89.
7. Arularasu, M.V., J. Devakumar, and T.V. Rajendran, An innovative approach for green synthesis of iron oxide nanoparticles: Characterization and its photocatalytic activity. Polyhedron, 2018. 156: p. 279-290.
8. Angel Ezhilarasi, A., et al., Green synthesis of NiO nanoparticles using Aegle marmelos leaf extract for the evaluation of in-vitro cytotoxicity, antibacterial and photocatalytic properties. Journal of Photochemistry and Photobiology B: Biology, 2018. 180: p. 39-50.
9. Kaliraj, L., et al., Synthesis of panos extract mediated ZnO nano-flowers as photocatalyst for industrial dye degradation by UV illumination. Journal of Photochemistry and Photobiology B: Biology, 2019. 199: p. 111588.
10. Garg, S., et al., Plant leaf extracts as photocatalytic activity tailoring agents for BiOCl towards environmental remediation. Ecotoxicology and Environmental Safety, 2018. 165: p. 357-366.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Our problems have been addressed mostly, therefore we recommend this manuscript for publication.

Reviewer 2 Report

The authors almost did not providing any additional experimental evidence  raised by our previous comments and suggestions. 

Moreover, we don't think that reasons like "The instruments such as XPS, TEM and EDX are not available" or "budget is limited" are not good excuses for missing important information of results to be publication. If the conclusion of experimental work can not be supported by sufficient experimental evidence, the manuscript should not be published anywhere.

Therefore, according to the author's reply, I have to recommend rejection of this manuscript, and I think the authors should think over their attitude on doing research and publishing their ideas/results.

Reviewer 3 Report

The arguments provided by the authors are well structured. Although it is relevant to know the final content of Mn in the system, the absence of this data does not diminish the importance of the work as a whole. The authors expose the limitations that arise in carrying out atomic absorption experiments. The modifications requested in the manuscript were made, so I recommend proceeding with its publication.