Green Synthesis of A Novel MXene–CS Composite Applied in Treatment of Cr(VI) Contaminated Aqueous Solution

Round 1

Reviewer 1 Report

This manuscript can be published after Major Revision.

The comments are as follows:

1. The English throughout the manuscript needs revisions and corrections.
2. The abstract and conclusion sections should be presented with characterization of the adsorbent and numerical results of the experiments.
3. The introduction is short. The background is not adequate. Please use appropriate literature to improve it for publication.
4. The resolution of SEM images is not appropriate for publication. The information are not clear. They should be changed.
5. A Table must be added for comparing the maximum adsorption capacities of different adsorbents. The following reference should be used for comparing in the Table. You can also use it for the improvement of the introduction.

   Journal of the Taiwan Institute of Chemical Engineers

   Volume 44, Issue 6, November 2013, Pages 977-989

   I look forward to receiving the revised version of this manuscript.

Author Response

This manuscript can be published after Major Revision.

The comments are as follows:

• The English throughout the manuscript needs revisions and corrections.

Response: Thank you very much. We have edited and improved the language writing in the revised manuscript.

 

• The abstract and conclusion sections should be presented with characterization of the adsorbent and numerical results of the experiments.

Response: Thank you very much. We have added the characterization of the adsorbent and numerical results in the abstract and conclusion part.

• The introduction is short. The background is not adequate. Please use appropriate literature to improve it for publication.

Response: Thank you very much. We have added more information and cited appropriate literature in the Introduction part.

 

• The resolution of SEM images is not appropriate for publication. The information are not clear. They should be changed.

Response: Thank you very much. We have rearranged the SEM images in the revised manuscript.

 

• A Table must be added for comparing the maximum adsorption capacities of different adsorbents. The following reference should be used for comparing in the Table. You can also use it for the improvement of the introduction. Journal of the Taiwan Institute of Chemical Engineers, Volume 44, Issue 6, November 2013, Pages 977-989. I look forward to receiving the revised version of this manuscript.

Response: Thank you very much. We have compared with other adsorbents in our revised manuscript as shown in Table 4. What’s more, we have also cited and compared with the mentioned paper (Journal of the Taiwan Institute of Chemical Engineers, Volume 44, Issue 6, November 2013, Pages 977-989)

Reviewer 2 Report

The paper investigates the use of a  MXene-CS composite in the removal of Cr(VI) from aqueous solutions. The topic is of great interest as chromium is a widespread and hazardous contaminant. The authors synthetised a novel reactive material (MXene-CS), a composite of two-dimensional graphene-like nanomaterial and chitosan, that was applied under several operating conditions for Cr(VI) abatement.   

The paper is, generally, well organized and written, however, some improvements are mandatory before considering it for publication. 

• The main weak point of the manuscript regards the discussion of the results. Indeed, only a simple description of the graphs and figures are reported in the text. The detected findings need to be justified more accurately. Moreover, a comparison with the reports of previous works is completely missing. In particular, the results of this paper should be compared with those of studies which exploited other types of reactive materials to understand the benefits/disadvantages of applying MXene-CS (the following are some  papers on the use of different materials https://doi.org/10.3390/ma9080666; https://doi.org/10.1007/s11270-016-3065-y; ttps://doi.org/10.1016/j.chemosphere.2009.01.009; https://doi.org/10.1016/j.watres.2012.11.028; https://doi.org/10.1016/j.chemosphere.2011.09.005; https://doi.org/10.1016/j.watres.2010.09.025).
• The abstract and conclusions are both unsatisfactory. The abstract should better state the main aspects (purpose, results and conclusions) of the manuscript. The conclusions should synthetise the results and affirm the contribution of the work on the topic.
• The acronyms must be specified in the abstract and lines 30-32 must be delated.
• What is the process pH in the experiments reported in the sections 3.2.1-3.2.4 ?
• How many repetitions were conducted for each analysis?

Author Response

The paper investigates the use of a  MXene-CS composite in the removal of Cr(VI) from aqueous solutions. The topic is of great interest as chromium is a widespread and hazardous contaminant. The authors synthetised a novel reactive material (MXene-CS), a composite of two-dimensional graphene-like nanomaterial and chitosan, that was applied under several operating conditions for Cr(VI) abatement.

The paper is, generally, well organized and written, however, some improvements are mandatory before considering it for publication.

• The main weak point of the manuscript regards the discussion of the results. Indeed, only a simple description of the graphs and figures are reported in the text. The detected findings need to be justified more accurately. Moreover, a comparison with the reports of previous works is completely missing. In particular, the results of this paper should be compared with those of studies which exploited other types of reactive materials to understand the benefits/disadvantages of applying MXene-CS (the following are some papers on the use of different materials https://doi.org/10.3390/ma9080666; https://doi.org/10.1007/s11270-016-3065-y; ttps://doi.org/10.1016/j.chemosphere.2009.01.009; https://doi.org/10.1016/j.watres.2012.11.028; https://doi.org/10.1016/j.chemosphere.2011.09.005; https://doi.org/10.1016/j.watres.2010.09.025).

 

Response: Thank you very much. We added the more detailed description and comparison with the  previous studies as the reviewer’s suggestion in the revised manuscript.

 

• The abstract and conclusions are both unsatisfactory. The abstract should better state the main aspects (purpose, results and conclusions) of the manuscript.

Response: Thank you very much. We have improved the abstract part as the reviewer suggested.

 

• The conclusions should synthetise the results and affirm the contribution of the work on the topic.

Response: Thank you very much. We have improved the results part and affirmed the contribution of this work.

 

• The acronyms must be specified in the abstract and lines 30-32 must be delated.

Response: Thank you very much. The acronyms have been specified in the abstract, and the lines 30-32 have also been deleted.

 

• What is the process pH in the experiments reported in the sections 3.2.1-3.2.4 ?

Response: Thank you very much. We have added the data of pH in the Figure captions (pH of 4.3).

 

• How many repetitions were conducted for each analysis?

Response: Thank you very much. Each experiment was repeated three times.

Reviewer 3 Report

The manuscript submitted by H. Wan et al. reports on the green synthesis of a novel inorganic – organic composite and its application in removal of Cr(VI) from aqueous solutions.

The paper reads well, the research design is appropriate (although quite simple), and the methods described to a large degree. The topic of Cr(VI) removal has been studied many times, but still deserves attention since no final solution has been found by now.

The paper can be considered for publication in Processes, after one major and some minor issues have been resolved.

My major concern is the fact, that the authors failed to convince me of the identity of the inorganic part of their composite. MXenes are a novel family of compounds which are not yet known to readers outside a narrow circle of experts in the area, thus I feel that more information should be given in Introduction. The authors write that 'The Transition metal carbide or nitride (Mxene) is a kind of two-dimensional (2D) graphene-like nanomaterial newly developed for recent years', which is true, but they should add two or three sentences about this material, the etching process and preferably add a figure. In 2.2. they describe how Ti3AlC2 was etched with HF, but they fail to characterize their MXene. I assume that Ti3C2 was obtained by etching Al out, but the authors never mention their ‘MXene’ as Ti3C2. Moreover, they did not identify their product by XRD, EDX, etc. Was the XRD pattern (Fig. 2a, lower spectrum) compared either to the pXRD database or to recent publications?

Minor remarks:

The English language should be edited before publishing. Some examples:

• '(…) graphene-like nanomaterial newly developed for recent years' should read: '(…) graphene-like nanomaterial newly developed in recent years'
• 'XRD patterns (…) were shown in Fig. 2' should read: 'XRD patterns (…) are shown in Fig. 2'
• 'adsorption of Cr(VI) was occurred' should read 'adsorption of Cr(VI) has occurred'

Abstract: the authors write that 'The main existing phase of Cr element in aqueous solution were mainly Cr(III) and Cr(VI).' Cr(III) and Cr(VI) are oxidation states of chromium, not phases.

Introduction: the authors write that 'It should be reasonable to expect the complex of Mxene and CS be an ideal choice for treatment of Cr(VI) contaminated water.' In my opinion, the composite of Mxene and CS should not be referred to as complex, since this term is in wide usage for coordination compounds.

Experimental, Paragraph 2.2: 40% HF is a very corrosive and dangerous acid. It would be interesting to know what labware material was used during the experiments. Additionally, a Warning sentence referring to hazards in handling HF should be added, if this is in accordance with the policy of the journal.

Experimental, Paragraph 2.3, eq. 2: The letter C should only be used for molar concentrations (mol/L), while mass concentration (g/L or mg/L) should be denoted with the Greek letter 'gamma' or 'rho' (see IUPAC Gold Book – mass concentration).

Author Response

The manuscript submitted by H. Wan et al. reports on the green synthesis of a novel inorganic – organic composite and its application in removal of Cr(VI) from aqueous solutions.

The paper reads well, the research design is appropriate (although quite simple), and the methods described to a large degree. The topic of Cr(VI) removal has been studied many times, but still deserves attention since no final solution has been found by now.

The paper can be considered for publication in Processes, after one major and some minor issues have been resolved.

• My major concern is the fact, that the authors failed to convince me of the identity of the inorganic part of their composite. MXenes are a novel family of compounds which are not yet known to readers outside a narrow circle of experts in the area, thus I feel that more information should be given in Introduction. The authors write that 'The Transition metal carbide or nitride (Mxene) is a kind of two-dimensional (2D) graphene-like nanomaterial newly developed for recent years', which is true, but they should add two or three sentences about this material, the etching process and preferably add a figure.

Response: Thank you very much. We have given more detailed information for the Mxenes in the Introduction part. The figure has also been added in the revised manuscript (Figure 1).

 

• In 2.2. they describe how Ti3AlC2 was etched with HF, but they fail to characterize their MXene. I assume that Ti3C2 was obtained by etching Al out, but the authors never mention their ‘MXene’ as Ti3C2. Moreover, they did not identify their product by XRD, EDX, etc. Was the XRD pattern (Fig. 2a, lower spectrum) compared either to the pXRD database or to recent publications?

Response: Thank you very much. According to the reviewer’s significant suggestion, we have added the characterization and mechanism diagram from the Ti3C2 to the Mxene as shown in Fig. 1. We have also compared the XPD patterns for the prepared Mxene with other recent publications.

 

Minor remarks:

• The English language should be edited before publishing. Some examples:

 

(…) graphene-like nanomaterial newly developed for recent years' should read: '(…) graphene-like nanomaterial newly developed in recent years'

'XRD patterns (…) were shown in Fig. 2' should read: 'XRD patterns (…) are shown in Fig. 2' 'adsorption of Cr(VI) was occurred' should read 'adsorption of Cr(VI) has occurred'

Abstract: the authors write that 'The main existing phase of Cr element in aqueous solution were mainly Cr(III) and Cr(VI).' Cr(III) and Cr(VI) are oxidation states of chromium, not phases.

Response: Thank you very much for the quite detailed suggestion. We have edited and improved the language writing in the revised manuscript.

 

• Introduction: the authors write that 'It should be reasonable to expect the complex of Mxene and CS be an ideal choice for treatment of Cr(VI) contaminated water.' In my opinion, the composite of Mxene and CS should not be referred to as complex, since this term is in wide usage for coordination compounds.

Response: Thank you very much. It should be composite, but not complex. I have revised in the manuscript.

 

• Experimental, Paragraph 2.2: 40% HF is a very corrosive and dangerous acid. It would be interesting to know what labware material was used during the experiments. Additionally, a Warning sentence referring to hazards in handling HF should be added, if this is in accordance with the policy of the journal.

Response: Thank you very much. We have added in the revised manuscript that the etching experiment was conducted in a PTFE beaker. What’s more, we have also added the warning sentence in the revised manuscript.

 

• Experimental, Paragraph 2.3, eq. 2: The letter C should only be used for molar concentrations (mol/L), while mass concentration (g/L or mg/L) should be denoted with the Greek letter 'gamma' or 'rho' (see IUPAC Gold Book – mass concentration).

Response: Thank you very much. We have replaced the concentration unit from “C” to the “X” in the equations.

Round 2

Reviewer 1 Report

All comments have been performed throughout the manuscript.

I can be published in Processes.

Author Response

All comments have been performed throughout the manuscript.

I can be published in Processes.

 

Reply: Thank you very much.

Reviewer 2 Report

The authors addressed all my suggestions, only some minor errors need to be corrected.

• lines 443-444, Reference 49. Please add the journal's name "Materials".
• lines 216,220,225,226. Change CR to Cr(VI).
• line 184. Correct the reference in the text.  

Author Response

The authors addressed all my suggestions, only some minor errors need to be corrected.

• lines 443-444, Reference 49. Please add the journal's name "Materials".
• lines 216,220,225,226. Change CR to Cr(VI).
• line 184. Correct the reference in the text.  

Reply: Thank you very much. I have corrected the above three erros.