Microwave-Sample-Preparation-System-Assisted Biogenic Synthesis of Copper Oxide Nanoplates Using Saussurea costus Root Aqueous Extract and Its Environmental Catalytic Activity
Round 1
Reviewer 1 Report
The manuscript describes the preparation of copper oxide nanoplates using a plant extract and the use of these metallic nanoparticles in a catalytic reaction.
Saussurea costus root extract is used to prepare copper oxide CuO nanoparticles. This extract has already been used to synthesize other metallic particles in the literature, but not with copper. The originality of the manuscript is therefore not very high. Nevertheless, the nanoplates are pretty well characterized and the manuscript could interest the readers of Catalysts. This manuscript could be published only after some major revisions:
- English language must be revised in the manuscript
- in the abstract (line 13) and in line 182 (and maybe elsewhere in the text), the author describes the process of nanoparticle formation as "reduction". It is a little surprising because in the starting salt (CuCl2) used in the reaction and in the nanoplates (CuO), the oxidation number of copper stays at +II. No reduction of copper seems to be involved in the formation of the nanoplates. Is there some hypothesis explaining what exactly happen between the extract and the copper salt to produce the nanoplates? In any case, I would remove any mention of a reduction.
- Line 100: I don't understand how the CuO particles are separated using sonication. Does it mean that particles are sonicated in water or ethanol to wash them and then they are separated by filtration or after decantation, by eliminating the supernatant? Can the author precise the procedure a little more?
- Line 130: something is missing in this sentence "decrease in the" ? "at..."
- The author explains that when mixing the copper chloride solution with the plant extract, an immediate change of color is observed which demonstrates the formation of the nanoparticles. In this case, what is the role of microwave heating if the nanoparticles are already formed? If the nanoparticles can be obtained with or without heating, can the author compare the differences between the two types of synthesized particles?
- Line 174: I would remove the word "molecules"
- Page 7: there is no legend below Figure 5.
- For the catalysis experiments, I think some complementary results are needed. Can the author try the reduction of nitrophenol in the presence of only NaBH4 ( without catalyst as a blank experiment)? Can the author repeat the experiment with root extract only (without copper, just to check that only copper catalyzes the reaction)?
- The catalysis results need to be put in perspective. I think some comparison to previous results found in the literature for the same reaction using other copper catalysts is required. Are the presented results comparable or even better than previously reported ones? Is the catalyst more or less performant than others?
- There is no information in the manuscript about the recycling of the catalyst after the reaction. Can the author try to recycle and reuse the catalyst to check whether there is some modification of the activity after the first use? Is it possible to characterize the catalyst (for example, by FTIR and microscopy) to verify whether the structure of the catalyst is modified after the catalytic reaction?
Author Response
The authors thank the reviewer for the positive feedback about the manuscripts and all the suggestions that aim to upgrade the quality of the manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments to Authors
1. In the introduction section authors should discuss the importance of catalytic reduction compare to others methods. For this discussion authors can use the following articles as reference
a) doi.org/10.1002/slct.201900470
b) doi.org/10.1016/j.jece.2020.104596
2. The quality of figure 4 should be improved.
3. There are lots of typos errors such as plane in the XRD. Authors should correct it.
4. Authors should provide a mechanism of catalytic reduction of 4-NP by CuO.
5. In the Figure 6 authors should mention the UV peak corresponding to compounds.
Author Response
The authors thank the reviewer for the positive feedback about the manuscripts and all the suggestions that aim to upgrade the quality of the manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
All my comments and suggested revisions were correctly taken into account by the author. I think that the manuscript can now be published in its present form.
