One-Step Carbothermal Synthesis of Super Nanoadsorbents for Rapid and Recyclable Wastewater Treatment
Round 1
Reviewer 1 Report
Manuscript Title: One-Step Carbothermal Synthesis of Super Nanoadsorbents for Rapid and Recyclable Wastewater Treatment.
Manuscript Number: 1037455
In the present work, one-step carbothermal synthesis was introduced to synthesize magnetite nanoparticles with super magnetic and adsorption properties. The synthesized material was investigated for the adsorption of methylene blue dye from aqueous solutions. Different morphological and physicochemical features were investigated, considering several characterization methods.
The writing is well-tailored, and the explanations are often reasonable. However, sometimes, at some points, the submitted research leaves something to be desired Nevertheless, the presented manuscript could be recommended for publication after a major revision and amendments following these next comments:
Comment #1: The novelty aspects and main objectives of this study should be highlighted clearly at the end of the introduction section.
Comment #2: Settlement test is recommended based on the optical absorbance investigation to evaluate the aqueous suspension of the prepared magnetite nanoparticles. In this regard, the following reference should be cited: (Promoting aqueous and transport characteristics of highly reactive nanoscale zero-valent iron via different layered hydroxide coatings. Applied Surface Science 506 (2020): 145018).
Comment #3: Different reaction conditions should be investigated at a range of values in the sorption of methylene blue with magnetite nanoparticles, including pH, temperature, and adsorbent dosage. Moreover, the contribution percentage (POC%) of each condition towards the removal performance should be estimated. In this regard, the following references should be considered: (Investigating the design parameters for a permeable reactive barrier consisting of nanoscale zero-valent iron and bimetallic iron/copper for phosphate removal, Journal of Molecular Liquids 299, 112144 and Multi-objective optimization of permeable reactive barrier design for Cr (VI) removal from groundwater. Ecotoxicology and Environmental Safety 200 (2020): 110773).
Comment #4: Authors should estimate the degree of crystallinity (DOC%) and crystallite size of the synthesized magnetite nanoparticles based on the obtained XRD patterns, as they are important features that could affect the reactive performance and the removal mechanisms.
Comment #5: Coefficient of determination, "R squared" is a low accuracy factor, the authors should use Akaike’s Information Criterion (AIC) which a commonly used statistical approach to check the fitting of adsorption isotherm models to experimental data.
Comment #6: It is recommended that the author use other isotherm models (i.e., Freundlich and Temkin) to compare their fitting for sorption data in addition to the Langmuir model.
Comment #7: The sorption pathways involved in the removal of methylene blue dye by the prepared magnetite nanoparticles should be summarized and discussed in detail (supported with illustrating schematic, if possible).
Comment #8: Kinetic analysis should be conducted to describe the sorption data and assess the reaction rates by different kinetic models.
Comment #9: Conclusions should be supported by more qualitative and quantitative findings.
Comment #10: The authors should consider revising the whole text formatting in the manuscript for any additional spacing, word capitalization, and unnecessary repetitions.
Author Response
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Author Response.docx
Reviewer 2 Report
My main remarks relate to the methylene blue adsorption experiment. And they are as follows:Summary: 23.24. lines, Sentence:
They can quickly and effectively adsorb methylene blue with an
adsorption capacity of 66.67 mg·g-1 , which is much higher than
all other adsorbent materials reported in the literature.
The stated fact that the experiment achieved capacity of 66.67 mg g-1 is
much higher than the capacity of other adsorbents listed in the
literature is not correct. For example in work: Removal of methylene blue
dye from artificially contaminated water using citrus limetta peel waste
as a very low cost adsorbent the adsorption capacity is 227.3 mg g-1
(S. Shakoor,A. Nasar, Journal of the Taiwan Institute of Chemical
Engineers, 2016). Line 86: Sentence: At different time intervals, 5 mL of suspension samples were
taken for external magnetic separation…. It is unclear if this is done
10 times from the same solution how much solution is left in contact
with the adsorbent? Turns out zero for 10 measurements (Figure 5a).
208. and 209. lines: sentence: Methylene blue dye exists in the form of
water-soluble sodium salt, so it is easily soluble in water and
difficult to eliminate. Methylene blue is methylthioninium chloride
not sodium salt.
Lines 212 and 213: sentences: It can be seen from Figure 5a that in the
initial stage of adsorption, the rate is very high.
On reaching equilibrium, the adsorption rate decreases.
The adsorption rate is the time needed for the process to reach
equilibrium. Therefore, to say that the rate of adsorption
decreases after achieving equilibrium adsorption is incorrect.
218. and 219. lines: sentence: After 160 min, the solution was almost
colorless.
The solution is not almost colorless and does not differ significantly
from the solution obtained after 2 seconds. 222 and 223 lines: sentence: When the amount of adsorbent is 40 mg, the
removal effect of MB is the best, and when the amount of adsorbent is
160 mg,the removal effect of MB is weakened. What does the removal
effect mean?
Maybe dye removal efficiency? The sentence is unclear as it can
be seen from Figure 5c that the color removal
increases with increasing mass of adsorbent.
In that same figure, the color removal is from 0.02 to about 0.035
percent, which is too little considering Figure 5a. 223 and 224 lines: Figure 6d is the adsorption isotherm drawn
based on the Langmuir model. Not figure 6d, but 5d. It is not clear
how the authors obtained the Langmuir isotherm, since it can be seen
from Figure 5a that as the dye concentration increases to 80 mg / L,
the adsorption capacity increases and in the 100 mg / L solution
a much smaller capacity is obtained, even smaller than from the 60 mg / L
solution.
Author Response
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Reviewer 3 Report
In this work authors followed a one-step carbothermal synthesis of Fe3O4 crystals to use them as potential agents to adsorb methylene blue in wastewater application. The authors must improve many parts of the whole work to be ready for publication. My specific comments are following:
1) Introduction: Although the reference number starts from 1 the reference numbering does not follow in the right way. Please correct the right numbering.
2) Page 2 line 52: "Here in this work" It is better to say "In this work..."
3) Page 2 line 64: "and can effectively remove MB" change to "that can effectively remove MB"
4) Page 4 Fig 1: Is figure 1c correspond to Sample's 6 diffraction pattern? Authors should be very careful with nomenclature. It is very useful to use samples table to help the reader understand the differences between the samples. It is also recommended to keep the same colors that correspond to the respective samples in every graph presented in the whole study.
5) Page 4 line 138: "the particles are obviously reduced" why is it an obvious claim? The authors should explain.
6) Page 4 line 148: "The difference in the crystallization process will affect the distribution of Fe2+ and Fe3+ in the octahedral sites, thereby affecting the super-exchange between Fe ions." This claim should be given with a respective literature reference.
7) Page 4 line 151: "Therefore, the super-151 exchange between Fe-O-Fe is enhanced, and hence the magnetic properties are improved." Reference is also missing.
8) Page 5 figure 2. Authors should give a clear name in their graphs. SEM images can be given as Figure 2a images with HRTEM images, FT-IR spectra to be figure 2b and c respectively and the enlarged yellow area graph to be the inset of figure 2c graph.
9) Page 5 line 158: "With the decrease of FeO content in the sample" The authors should give in parenthesis which is the correlation between samples numbering and FeO content.
10) Page 5 line 158: "the characteristic peak of Fe3O4 becomes more obvious" which is the characteristic peak of Fe3O4? The authors should explain.
11) Page 5 line 167: "This result is due to a difference in the temperatures of the carbothermal reduction reaction, which deforms the inside of the particles after heating, thereby changing the bond length, and increasing the bond frequency." Is this also a literature finding? The authors should mention that.
12) Page 6 line 173: "The Ms value of Fe3O4 nanoparticles" Give sample's name (S6)
13) Page 6 line 176: "This result can be owed to the different crystal sizes. The following figures provide some useful information about the magnetic response of various samples. These magnetic properties render potential applications in magnetic adsorbents." Explain more by giving reference to literature evidence.
14) Page 6 Figure 3: I don't see any need to give 6 graphs here. The information can be given by one or two graphs. Maybe all hysteresis loops can be presented in one graph. Nevertheless authors should increase the numbers and labels in graphs. Increment value should be decreased also in y axis.
15) Page 7 Figure 4: Again here, name Figure 4a,b,c,d,e,f for S1-S6 samples
16) Page 7 line 216: This is because in the initial stage of adsorption, there are many vacancies on the surface of the adsorbent, and adsorption easily occurs. As the adsorption continues, the vacancies on the surface of the adsorbent lessen, and the adsorption rate significantly declines until an equilibrium is reached." Is this based on any literature report? Support literature evidence.
17) Page 8 line 223: "50ml" mL is the correct unit writing
18) General comment for Langmuir model: Explain more this model by giving more info
19) Page 8 line 244: "due to the high saturation magnetization of Fe3O4 nanoparticles," This is one of my critical questions. Since there are plenty of synthesized methods presented in literature until now that produce pure Fe3O4 magnetic nanoparticles with high saturation magnetization values (more than 90 emu/g) which is the unique property of the presented nanoparticles that make them better than the others to be used in wastewater treatment applications? Authors should emphasize the benefits of these particles compared with those from literature in several points in the article.
20) Page 9 line 248: "has exhibited superior properties" avoid to use such overmuch expressions.
21) Comment on adsorption capacity: In the literature work of {Das, Chanchal, et al. "Green synthesis, characterization and application of natural product coated magnetite nanoparticles for wastewater treatment." Nanomaterials 10.8 (2020): 1615.} authors use magnetite nanoparticles to adsorb MB dye. They report that they reach an adsorption capacity of 466 mg/mg. Similarly there are plenty of works presented in literature with reported adsorption capacity values larger that this works respective values. The authors should clearly emphasize the novelty of this work compared with literature findings.
Author Response
Please see the attachment. The amendment has been submitted by email. I have revised the manuscript as suggested by the reviewers and submitted it on the home page.
Reviewer 4 Report
In this paper, the authors reported a one-step carbothermal method to synthesis purely-stoichiometric, monodisperse and small-sized (~10nm) Fe3O4 nanoparticles for water purification. The crystal structures, morphologies, colloidal stability, as well as adsorption performances of synthesized Fe3O4 nanoparticles are characterized.
The authors failed to clearly describe the experimental designs and the results are not presented in a uniform way (see comments 3, 4, 6). In addition, I doubt the reported saturation magnetization of 90.32 emu/g from ~10 nm Fe3O4 nanoparticles. The saturation magnetization of bulk Fe3O4 is only 92 emu/g. Due to the spin canning effect, as the material size decreases, the saturation magnetization also drops.
Based on these, i cannot recommend its publication at current format. Below are my comments:
- References 1-4 are not cited in the manuscript.
- The quality of English should be improved throughout the manuscript. I just list some of them here:
In the recent years, Fe3O4 nanoparticles have been used as an adsorbent for the purification of wastewater and has gradually attracted great attention from scholars at home and abroad, due to their stable physical and chemical properties, strong magnetism, large specific surface area, and easy dispersion —> In recent years, Fe3O4 nanoparticles have been used as adsorbents for wastewater purification and have gradually attracted great attention from scholars at home and abroad, due to their stable physical and chemical properties, strong magnetism, large specific surface area, and easy of dispersion
a purely-stoichiometric, monodisperse and small-sized (~10nm) Fe3O4 nanoparticles were successfully synthesized by a one-step carbothermal method —> purely-stoichiometric, monodisperse and small-sized (~10nm) Fe3O4 nanoparticles were successfully synthesized by a one-step carbothermal method
- The nanoparticle synthesis conditions (Table 1) should be clearly mentioned in section 2.3. Otherwise, it’s very confusing when it comes to the characterizations of samples S1-S6.
- Why is the XRD pattern of sample S6 not given in Figure 1?
- Correct Figure 1(b) caption. ‘Fe3O NPs’
- Figure 2. Looks like the TEM image of sample S6 is added at a later time. It’s not supportive to provide TEM of sample S6 in comparison with SEM images of S1-S5.
- I doubt the repeatability of nanoparticle preparation. Samples S2 and S3 are prepared under the same condition, but the Fe3O4 wt% as well as magnetic properties are varied.
- Figure 3, either put all the MH curves of samples S1-S6 in one figure for better comparison. Or add figure captions for (a) - (f).
- I doubt the Ms of Fe3O4 nanoparticles from Sample 6. The Ms of bulk Fe3O4 is only 92 emu/g. For nanoparticles, as the size decreases, the Ms drops, due to the spin canting effect. The Fe3O4 nanoparticles in samples 6 are only several nm (from Figure 2), thus, I don’t think authors can get that high Ms of 90.32 emu/g from these nanoparticles.
- In section 3.4, which nanoparticle sample is used for the adsorption experiments? Samples S6?
Author Response
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Round 2
Reviewer 1 Report
The authors did not improve the paper and there wasn't anything new therefore my recommendation for rejection
Author Response
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Reviewer 2 Report
The following need to be corrected:214-216 lines: sentence: It can be
seen from Figure 5a that in the initial stage of adsorption, the adsorption
capacity increased rapidly with the increase of time. Then the
adsorption capacity decreased, and when the adsorption reached
equilibrium, the adsorption capacity tended to be constant. Please,
delete the highlighted part of the sentence. 220- 222 lines: sentences: The color of the MB solution was dark blue in the
beginning, and it became light blue after 2 min of adsorption with the
adsorbent. After 160 min, the solution was almost colorless.
Write the initial concentration of MB solution. After the explanation of Figure 5a, the explanation for Figure 5b
is missing in the text. What does it represents? The explanation of the
figure 5b reads: Equilibrium adsorption curve of Fe3O4 nanoparticles
for methylene blue adsorption; but on the ordinate there are values
for absorbance and not for the equilibrium masses of the adsorbed dye.
There can be no absorbances in the isotherms. It is not stated on the
abscissa whether these are initial dye concentrations in solution or
equilibrium (after adsorption). The sentence (223 line) : 50 ml of 80 mg / L MB solution was taken and different
amounts of Fe3O4 powder was added. No sense here.
Put it in the text with an explanation of Figure 5c.
Written like this it is not clear where it belongs. 224-225 lines: sentence: Figure 5c shows that, as the number of adsorbent
increases, the removal effect of MB gradually slows down.
Instead of the number of adsorbent please write the amount (or mass)
of adsorbent. I emphasize again that the removal efficiencies cannot
be so small if the solutions have discolored as shown in Figure 5a.
Based on the data in Figure 5a, using 50 ml of solution and 40 mg of
adsorbent I obtained that the removal efficiency from the solution of
the initial concentration of 80 mg dm-3 was equal to 20,3%
(Q = 13 mg g-1). 232-233 lines: sentence: Wherein, ƿe is the equilibrium concentration
of the solution of MB dye, qe is the adsorption amount of MB,
qmax is theoretical MB maximum amount of adsorption, b is the adsorption
constant. ƿe -the equilibrium concentration of the solution of MB dye,
this is not in Langmuir's equation. 239 line, sentence: explanation of Figure 5 (d) Fe3O4 adsorption isotherm.
Not true. This Figure would represent the Langmuir isotherm in the form
of a line.
Author Response
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Reviewer 3 Report
The new version, sent by the authors, has been significantly improved. I believe now it is ready to be published.
Author Response
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Reviewer 4 Report
The authors have taken care of my previous comments successfully. However, the following minor issues should be carefully addressed before it’s publication:
- In figure 2, I suggest authors add the size distribution histograms for samples S1-S6. Or, at least add the average diameters of NPs from samples S1-S6. It’s confusing how the authors get the average size of 10 nm from Figure 2-S6 without statistics studies.
- The authors claimed that the synthesized Fe3O4 NPs are spherical and with diameter of 10 nm (at least for sample S6). If so, these NPs should be superparamagnetic at 300 K, however, the MH curves in Figure 3 and Mr, Hc in Table 1 are showing magnetic coercivities at 300 K. Please explain in the revised manuscript.
- The statement “After 160 min, the solution was almost colorless” is not convincing. Since I can still see the light blue color from the photo in Figure 5(a).
- Figure 6(a) inset photos and figure caption. After how many minutes of adsorption did the authors take the photo? The photo of magnetic powder attracted by the magnet after the fifth-cycle is not provided.
- The photo in Figure 5(a) after 160 min is showing light blue color, while the photo in Figure 6(a) after first cycle is almost transparent. Did the authors wait for longer time? It’s not described in section 3.4.
Author Response
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