Biochar Derived from Palm Waste Supported Greenly Synthesized MnO2 Nanoparticles as a Novel Adsorbent for Wastewater Treatment
Round 1
Reviewer 1 Report
The following report is based on my review of the manuscript entitled “Biochar derived from palm waste supported greenly synthesized MnO2 nanoparticles as a novel adsorbent for wastewater treatment.” The manuscript catalysts-2208873 suits the scope of “Catalysts” and is also interesting. However, the following minor comments have been pointed out and need to be addressed properly for further improvement of the manuscript. They are as follows:
1. The present work is highly appreciable. The abstract needs a bit of improvement by adding novelty to the study.
2. The introduction is well written. However, improvements can be made to enrich the manuscript to attract readers across the globe. The authors may include the following studies to enrich this section;
· https://0-doi-org.brum.beds.ac.uk/10.3390/su14116484
· https://0-doi-org.brum.beds.ac.uk/10.1007/978-981-16-5932-4_8
3. The problem statement should be clearly stated.
4. Methodology is well written. However, the authors are suggested to add the flow chart of the study conducted.
5. The results are stated very well in every subheading. However, Line numbers 235, 309, and 315 contain equations that should be moved to the methodology section under appropriate subheadings.
6. The discussions lack support from previous studies. The authors should improve the discussions by supporting them with previous studies.
7. The results of kinetic studies should be compared with previous studies in tabular form.
8. The conclusion section is also well written. However, the authors should mention facts and figures related to the study conducted.
9. Authors should avoid citations of non-index articles. Kindly, update the reference list with valid indexed citations. Authors should cite only recent 5 years' published articles. The journal referencing style should be followed throughout the manuscript.
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. The manuscript has been revised accordingly. Our item-wise responses to the comments are given in blue.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Summary and general comments
In this work, the authors infused MnO2 onto biochar derived from date palm frond and tested its performance in the removal of methyl orange from an aqueous solution.
The overall work seems alright. The methodology is suitable and relevant to adsorption science. The results and discussion support the conclusion. However, there are a lot of minor errors. Please see the specific comments below for details.
Specific comments
1. Abstract “acacia” needs to be in capital letter.
2. Keywords: to improve article discovery, I suggest the authors include green MnO2 nanoparticle synthesis instead of MnO2. Instead of palm fronds, I suggest “Date palm fronds”.
3. Introduction: I suggest authors to add a sentence to describe the nature of azo-anionic dyes, and a sentence to give a few examples of industrial uses.
4. In the introduction, the authors should discuss other prominent choices of adsorbents other than biochar. Here are some of my recommendations:
doi.org/10.1007/s13201-018-0714-x
doi.org/10.1007/s13201-017-0537-1
5. Line 80 “acacia nilotica” should be corrected as “Acacia nilotica”. Following the biological rule of naming species. “Acacia nilotica” is to be mentioned in full at first appearance in the main text, and as “A. nilotica” thereafter.
6. Line 82, 84, 103, etc : spelling error “Nilotic”
7. Line 95, I suggested authors correct as “date palm fronds”
8. Line 104. Please mention the centrifugation speed and time. This is to ensure the experimental procedure is clear and can be reproduced. The instrument manufacturer and model should also be mentioned.
9. Line 107, Abbreviation PF should be assigned at the first appearance of the word “Palm fronds” which is in the introduction section.
10. Line 125-126: is there any sputtering of gold or Pt to the sample prior to the SEM image being taken? The authors should mention the procedure briefly.
11. Line 129 is the FTIR using ATR crystal method or pellet pressed?
12. Line 137 HCL to be corrected as HCl.
13. Line 136. Is there any change of colour to MO at extreme pH?
14. Line 137-140: Is the shaker used for mixing the adsorbent with the adsorbate? How was the mixture shaken? Stirrer?
15. Line 142. Please mention the filter paper number.
16. Line 149 eq 1. Do remove the word percentage from “% removal percentage”.
17. Line 150 equation 2. “Adsorbant” to be corrected as “adsorbent”. “amount adsorbed (qe)” should be corrected as “adsorption capacity at equilibrium (qe)”.
18. The unit expression should be consistent and unified to one form. Both mg/L and mg/l are observed.
19. Table 1. As the methods section expressed unit in form of mg/L, I suggest authors avoid using another format in Table 1 e.g. m2.g-1.
20. Fig 6 was there any previous expt to compare PF biochar performance with those of MnO2/PF?
21. Fig 6,7, should use “% removal” instead of RE (%)
22. Line 272 missing letter with unit “mg/”
23. Line 280. It is not explained and confusing why 10 mg/l Cr (VI) is added. Or perhaps an error.
24. Section 3.3.3. Authors should use the data from the effect of MO initial concentration to fit into Langmuir and Fruendlich isotherm models because qmax is often used as a performance indicator of biomass.
25. Error bars should be added to the figure wherever applicable
26. For symbols used in scientific writing, K1 and k1 can mean a different variable. Authors need to unify and keep all the symbols consistent.
27. Fig 9 is not necessary as all the important data is summarised in the table. Authors may move fig 9 to the supplementary section.
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. The manuscript has been revised accordingly. Our item-wise responses to the comments are given in blue.
Author Response File: Author Response.pdf
Reviewer 3 Report
Reviewer: 1
Comments:
In this paper the authors have presented an interesting work on MnO2-loaded biochar for enhanced methyl orange adsorption. Different materials were optimized for higher adsorption activity. After reading the manuscript, it can be accepted for publication after revision.
1. Missing references in some paragraphs in the introduction such as:
• Furthermore, due to their abundant functional groups, and large chemical and electrical stability biochar can serves as an in retesting support for metal nanoparticles
2. It is important for the authors to add a paragraph in the introduction about the advantage of this materials compared to the other solid adsorbent.
3. Fig. 2(c) showed the distinguishing peaks of 166 Mn nanoparticles in MnO2/PF biochar nanocomposite at 2θ1= 18.48 °, 29.04°, 37.04°, 167 50.44° and 65.08 °indexed to (200), (310) , (301), (411) and (002) crystal planes, respectively. This is confusing, can you revise this better and add some references.
4. The authors study the effect of MO initial concentration on the adsrioption capacity “From Fig.7 it clears that with the increase in MO initial concentration the removal efficiency decreased. The higher removal efficiency was 91.5 % for 10 mg/L, and with further increased in initial concentration the removal percentage decreased from 61.9 % to 50 mg/L. This is owing to the limitation of active site on the MnO2/PF surface, since the amount of adsorbent was kept constant while the initial concentration was increased from (10-50 mg/L).” The date of biochar without MO, and concentration lower than 10 mg/L should give in Figure 7.
What about the MO concentration decrease to 5mg/L.
5. Any evidence that the materials are stabilized? The stability and reusability of adsorbents after several cycles should be performed. In this context, XRD OR XPS or other characterizing of adsorbent after adsorption should be given.
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. The manuscript has been revised accordingly. Our item-wise responses to the comments are given in blue.
Author Response File: Author Response.pdf
Reviewer 4 Report
The paper presents an interesting study of the preparation of biochar from waste materials, and testing as a novel adsorbent for wastewater treatment. Although the topic of adsorbents is related to catalysis, the paper does not actually report a catalytic reaction. Therefore, it may be peripheral to the scope of the journal ‘Catalysts’. However, the preparation and characterisation of the adsorbents have been clearly described. The editor will need to decide if this article fits within the scope, in which case it could be suitable for publication after revision. The following points would need to be addressed:
11. The presentation and English is of a fair standard, but the grammar could be improved. Some examples include but are not limited to: Line 201 should be ‘it is noticed’, rather than ‘it notices’. Line 203 ‘The same results’ rather than ‘Same results’, Line 262 ‘it is clear’ rather than ‘it clears’.
22. On Figure 3 the scale bars on the SEM and the element names on the EDX are unclear, and the figure quality could be improved.
33. There are a few spelling errors, e.g. line 313 ‘linear’, not ‘liner’, line 250 ‘weak’, not ‘week’.
44. Section 3.3.3. presents the effect of initial MO (dye) concentration at constant adsorbent dose, whilst 3.3.4 presents the effect of biochar dose at constant dye concentration. These effects would seem to be related as just the dye/adsorbent loading ratio, rather than two independent effects.
55. Error bars should ideally be added to figures 6-8.
66. The removal efficiency (blue) line in Figure 8 looks quite wavy. Is this a real effect, or could be a result of outliers?
77. Could the equilibrium isotherm be represented by a model, such as the Freundlich equation? Although the kinetics have been analysed, it could also be useful to analyse the equilibrium behaviour quantitatively.
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. The manuscript has been revised accordingly. Our item-wise responses to the comments are given in blue.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
After the revision, the quality of the manuscript improved. Previously raised issues/ errors were clarified/ corrected. I recommend this manuscript for publication in this journal.
Reviewer 3 Report
Accept in present form
