Synthesis of a Novel Catalyst MnO/CNTs for Microwave-Induced Degradation of Tetracycline

Round 1

Reviewer 1 Report

This work is correctly performed and the subject it treats is of substantial interest. Therefore I suggest acceptance subject to revisions:

What makes the authors choose carbon nanotubes as support of MnO? As a reader, I would expect that simple carbon nanoparticles, which are cheaper anyway,  may do the job or even be better than nanotubes.  The authors must provide sufficient justification of their choice, other than carbon nanotube popularity.

In section 2.1 it is not necessary to repeat "Beijing Chemical Industry Corporation". Please, combine it in one sentence.

Are there any data for dye removal without any sonication at all?

In Fg.9, it is not clear which material has the HOMO-LUMO structure?  Apparently carbon nanotubes. However, not all carbon nanotubes posses such well separated levels. How do the the authors know that this corresponds to the present case? 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript describes the synthesis of a novel catalyst composed of MnO nanoparticles supported onto CNTs. This material is applied as catalyst for the mocrowave-induced degradation of a specific antibiotic, tetracycline, reported as one of the most common antibiotics detected in wastewater. In the paper the authors used a vey clear presentation of their approach and their results. Moreover, they further developed the possible use of MnO/CNTs as catalysts for the wastewater remediation, and for this reasons I suggest to consider this manuscript for publication.

However, I'd also suggest to perform some modifications to the paper:

line 37: you say that photocatalysis can be used as remediation treatment, but you limit the method only to TiO2. As this technique can be applied to other semiconductor materials, I'd ask the authors to add the following references: 1) Environ Sci Pollut Res (2017) 24:8287–8296 2) Catalysis Today (2009) 144 100-105 3) Materials Letters (2015) 161 45-48. line 58: here you first suggest the use of Mn(II)-based materials for microwave assisted degradation of pollutants. Even if I'm not an expert of this particular technology, I think you could provide some more references and explanation regarding its possible use and why it should be used. line 68: why do you suggest that a strong interaction should exist between MnO and CNTs? At the beginning it's just an electrostatic interaction between Mn(II) centers and CNTs surface. Do you think that a stronger bond is formed after calcination? What kind of bonds are involved? line 146: I'd suggest to substitute the word "effectiveness" with "stability". You say that MnO/CNTs can resist to the degradation process of TC because you don't detect any Mn in the TC solution. That means that this material is stable during the process. The effectiveness is evaluated through other measurements line 158: I'd substitute as follow: "MnO nanoparticles are supported on the CNTs" line 169: as a support of the results, I'd suggest to add also the reference XPS spectra of the CNTs before any treatments line 174: again I would say that the results indicate the stability of the materials instead of its robust catalytic activity in the manuscript, the authors claim that a complete mineralization of the tetracycline occurs thanks to the combined use of MnO/CNTs. However, one possible complementary pathway could involve the adsorption of tetracycline molecules on the surface of MnO/CNTs. In this case, the total disappearance of the tetracycline from the solution would be connected to a different phenomena compared to its decomposition. For this reason I'd suggest to analyze also the surface of MnO/CNTs after the catalytic process, to assess whether the organic molecules may be absorbed by the porous catalyst and the extent of the absorption phenomena in these experimental conditions. In this sense, it's interesting to further understand if the total mineralization occurs or if some other intermediate species can be also formed and subsequently adsorbed onto CNTs support instead of being destroyed. I also have a general curiosity: what happens to the tetracycline when it comes into an acidic solution? Is the pH able to influence its solubility or worse, its structure? I was wondering if the better results obtained in the acidic conditions could be due to a change in the TC concentration inside the analyzed sample and not connected to the experimental removal of TC.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Please, publish this revised version

Reviewer 2 Report

I think the manuscript can be now considered for publication in the present form. I thank the authors for all their answers and for their explanations to my questions.