Garcinia mangostana L. Leaf-Extract-Assisted Green Synthesis of CuO, ZnO and CuO-ZnO Nanomaterials for the Photocatalytic Degradation of Palm Oil Mill Effluent (POME)
, Mohammod Aminuzzaman 1,2, Yip Foo Win 1, Sinouvassane Djearamane 3,4, Ling Shing Wong 5,*, Samar Kumar Guha 6, Hamad Almohammadi 7, Md. Akhtaruzzaman 8,9,* and Lai-Hock Tey 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe presented work is novel and interesting. The authors prepared and well characterized a nanocomposite with potential practical application. I recommend the acceptance of the manuscript after minor revisions.
1. The author should provide valid references to the following statement “While many studies have investigated conventional methods for synthesizing nanomaterials for POME treatment under polychromatic light sources”.
2. The plant extract consists of many other components, did the authors check the effect of pure plant extract on the reaction?
3. In Figure 2, many apparent peaks are not labelled and explained. Are there any impurities?
4. Figure 4, TEM image – It is insufficient for confirmation. The author should add more images.
5. The catalyst's long-term stability is also important for practical applications.
6. There are some typological errors, so authors need to correct them properly
Comments for author File: 
Comments.pdf
Author Response
The amended parts in the manuscript have been highlighted in yellow.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article is devoted to the synthesis of nano-sized composites of CuO, ZnO, CuO-ZnO and the study of their photocatalytic properties in relation to organic pollutants in wastewater from an oil manufacturing plant. The article contains new scientific data and may be of interest to a wide range of readers, because it describes a method for the synthesis of oxides from metal complexes obtained by reacting salts with plant extracts. Meanwhile, the article has many shortcomings that can be corrected.
1. It is not clear from the text of the article what CuO-ZnO was ultimately synthesized. Is this a mixture of phases? Then in what proportion are these phases present in the final product? The authors can estimate the phase relationships from the X-ray diffraction pattern in Figure 2.
2 .Figure 2 shows X-ray diffraction patterns of CuO and ZnO. What is the phase purity of the resulting oxides? X-ray diffraction patterns of CuO and ZnO contain reflections not identified by the authors. What are these impurities?
3.What are the advantages of using plant extract for the synthesis of composites compared to traditional synthesis methods? What is the nature of the complex compound that could be formed by the interaction of the plant extract and copper and nickel salts.
4. Table 1 shows the zone width for the synthesized oxides. How will the authors explain the differences in the zone width of the experimental samples from the theoretical values? For example, for CuO a value of 3.23 was obtained versus the theoretical value of 1.2-2.00? The same question arises in relation to ZnO.
5. In the interpretation of Figure 1, the type of vibrations of functional groups is not indicated. How do the authors of the work explain the shift in vibration at 540 cm-1 for CuO-ZnO compared to CuO, ZnO?
6. In the experimental part, the concentration of the plant extract is indicated. How was a solution with a concentration of 0.03 g/ml obtained? The mass of what substance is used for the calculation? Why was this extract concentration chosen?
7. Figure 6 incorrectly estimates the band gap. Absorption curves are shown here, discuss them, what are the maxima on the curves associated with?
8. What chemical interaction causes the results shown in Figure 7. Write the chemical reactions. What do the authors mean by COD?
9. How will the authors of the article explain the migration of electrons from CuO to ZnO (Scheme 2)?
10. Based on what data do the authors accept χ = ​​Absolute electronegativity of semiconductor (CuO = 5.80, ZnO = 5.79) and Ee = Free electron energy in the hydrogen scale (4.50 eV)?
Author Response
The amended parts in the manuscript have been highlighted in yellow.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAll my comments were adequately answered. The corrected article may be published.
