The Adsorption Performance of Porous Activated Carbons Prepared from Iron (II) Precursors Precipitated on the Porous Carbon Matrix Thermolysis
Round 1
Reviewer 1 Report
This work describes the magnetic adsorbents synthesis with the previously suggested method of iron (II) oxalate deposited on carbonaceous matrix thermolysis and their porous structure and adsorption properties being researched. My comments are as follows,
1. The author should highlight the relationship between the manuscript and the subject of magnetochemistry.
2. The abstract should highlight the research content of the manuscript, and the current formulation does not interest the reader, please revise it.
3. How does pH affect experimental results?
4. It is recommended that the author add characterization to study the morphology and structure of the material.
5. The flowing clay mineral is a good adsorbent for contaminants.
6. How many times can this material be recycled?
Minor editing of English language required
Author Response
- The author should highlight the relationship between the manuscript and the subject of magnetochemistry.
We added to the Introduction section following text:
The development of composite materials combining different properties in one body is one of the most significant trends of contemporary material science. Magnetochemistry aims in creation of new compounds featuring high adsorption [1] and catalytic performance [1,2] with magnetic properties of the material.
- The abstract should highlight the research content of the manuscript, and the current formulation does not interest the reader, please revise it.
We revised the abstract:
Creation of new compounds featuring high adsorption and catalytic performance with magnetic properties of the material is one of the important fields of the Magnetochemistry. The typical synthetic schemes of magnetic carbonaceous adsorbents are rather complicated due to inert atmosphere using and difficult wet ways of magnetite precipitation. The arising experimental is-sues prevent industrial production of the magnetic activated carbons. In order to overcome these obstacles, we suggested a novel approach to porous carbons – magnetite composites synthesis [Russ. J. Appl. Chem. 94(4) 486-490 (2021)] based on iron (II) salt precipitation on the porous carbon and subsequent thermolysis. We facilitated the process at the stage of the material washing. The synthetic route used is simple and can be applied industrially. The present paper is focused on the adsorption performance of the product prepared from commercial activated carbons BAU-A and AG-3. The porous structure was studied with the low-temperature nitrogen adsorption that revealed the surface area decrease by 26% in the case of BAU-A and by 40% in the AG-3 cases with mesopores volume increase. Phenol and nitrobenzene adsorption from water solution was tested with the magnetic carbon prepared from BAU-A. The adsorption isotherms obtained are described well with Langmuir model. The limiting adsorption value in the case of magnetic porous carbon is lower than in the case of pristine carbon. The relative decrease in limiting adsorption value is close to relative decrease in the specific surface area. The adsorption constant remains the same showing that adsorption centers of phenol and nitrobenzene are the same for porous magnetic carbon and its activated carbon precursor. Thus, we showed in the present study that the magnetic activated carbons developed almost retain the adsorption performance of the activated carbons precursors.
- How does pH affect experimental results?
We used distilled water as a solvent both for magnetic adsorbent synthesis and adsorption study without pH control. Thus, the acidity of the medium was close to neutral. The yield of magnetite could depend on pH as it changes the mole fractions of Fe2+ and C2O42- in solution.
The activated carbons used as the magnetic adsorbent precursors were produced via physical activation providing surface almost free of oxygen-containing groups. So the surface of the activated carbon won’t be affected by acids and bases, apart from the mineral part. The phenol is a weak acid, moreover, it is oxidized by dissolved oxygen in basic medium, so its adsorption behavior could be different at pH>10. The nitrobenzene is stable to oxidation and does not show acidic or basic properties, so pH would hardly influence its adsorption.
The following text was added:
The solutions of phenol and nitrobenzene were prepared using distilled water as a solvent.
- It is recommended that the author add characterization to study the morphology and structure of the material.
We added a brief characterization of the products appearance:
The synthesized adsorbent looked like black powder attracted to a stationary magnets. The granulometric distribution of the activated carbon precursor was not affected by the magnetite deposition.
- The flowing clay mineral is a good adsorbent for contaminants.
We agree with this statement. The text was added:
The magnetite-clay minerals composites are another important type of magnetic adsorbents which are useful for both inorganic [18] and organic [19] pollutants. The procedure of magnetite deposition is close to used in the case of activated carbons, so the inertial atmosphere remains essential [19]. In the case of [18] the activation was done by iron oxides leading to rather low specific surface area (172 m2/g).
- How many times can this material be recycled?
We are going to study the material recycling in the following works.
We thank the reviewer for the precious remarks aiming at making the paper better.
Reviewer 2 Report
The paper reports the properties, in terms of porous structure and adsorption, of magnetite compounds synthetized using iron (II) salt precipitated during the porous carbon thermolysis.
The paper reports interesting results and, in my opinion, can be accepted with some minor revisions.
1) In the captions of Figs. 2 and 5 the Authors should explicitly make reference to the numbers "1" and "2" used to identify the different curves/points.
2) Line 10: "obtaining" -> "synthesis" (maybe)
3) Line 19: write better the sentence "while the difference corresponds the surface area decrease"
4) Line 25: "base" -> "based"
5) Line 41: "others, microconcetration" -> "other microconcetration" (maybe)
6) Line 115: "beaked" -> "beaker"
7) Line 140: "desoprtion" -> "desorption"
8) Line 153: "2hours" -> "2 hours"
9) Lines 169-170: write better this sentence "The magnetic adsorbent gives additional increment in the UV range strongly dependent on the wavelength, making contrast to activated carbons."
10) Line 199-200: "the least squares deviations’ of the experimental and calculated optical density minimizations" -> "the minimization of the least squares deviations of the experimental and calculated optical density" (maybe, or something better)
11) Line 221: remove "of"
12) Lines 226-227: write better this sentence (maybe "developed" has to be removed)
13) Lines 229-231: write better this sentence (maybe "used" has to be removed)
14) Lines 231-232: write better this sentence (in particular, replace "are concerned on" with something more proper)
15) Line 241: "solutions’ volumes’ 10 and 15 ml respectively" -> "solution volumes 10 and 15 ml respectively" (more in general there is an abused use of the Saxon Genitive in this paper: generally the Saxon Genitive is used to refer to things owned by people).
Some sentences (specified in the previous field) have to be improved.
Author Response
1) In the captions of Figs. 2 and 5 the Authors should explicitly make reference to the numbers "1" and "2" used to identify the different curves/points.
The figures captions are corrected:
Figure 2. The measured UV light absorption spectra of phenol 1 mM (1) and solution equilibrated with activated carbon BAU-A with stirring (2).
Figure 5. An example of the spectra shown on the figure 3 processing for the adsorbate concentration determination in the solution equilibrated with the magnetic adsorbent with stirring. Circles (1) show the calculated function from the spectrum, line (2) is linear approximation.
2) Line 10: "obtaining" -> "synthesis" (maybe)
We agree and corrected the word.
3) Line 19: write better the sentence "while the difference corresponds the surface area decrease"
We agree with the remark. The sentence was corrected:
The relative decrease in limiting adsorption value is close to relative decrease in the specific surface area.
4) Line 25: "base" -> "based"
The word was corrected.
5) Line 41: "others, microconcetration" -> "other microconcetration" (maybe)
The sentence was corrected in the following way:
An adsorbent containing zinc ferrite for organic pollutants (such as bisphenol A, antibiotics, herbicides, and some others) microconcetration was prepared in [13] via metal-organic framework carbonization.
6) Line 115: "beaked" -> "beaker"
We agree with the misprint found.
7) Line 140: "desoprtion" -> "desorption"
We agree with the misprint found.
8) Line 153: "2hours" -> "2 hours"
We agree with the misprint found.
9) Lines 169-170: write better this sentence "The magnetic adsorbent gives additional increment in the UV range strongly dependent on the wavelength, making contrast to activated carbons."
The sentence was revised:
Comparing figures 3 and 2 one notices that in the case of magnetic adsorbent adsorbates bands are overlapped with continuous light-absorption linked with the magnetic activated carbon.
10) Line 199-200: "the least squares deviations’ of the experimental and calculated optical density minimizations" -> "the minimization of the least squares deviations of the experimental and calculated optical density" (maybe, or something better)
The sentence was rewritten as:
The first one was based on the minimizations of least squares deviations of the experimental and calculated optical density with Neilder-Mead method determining the values Ca and cm.
11) Line 221: remove "of"
It was removed.
12) Lines 226-227: write better this sentence (maybe "developed" has to be removed)
The sentence was revised:
Parameters of AG-3 activated carbon meso- and macroporous structure correlates with its better ability to adsorb methylene blue from concentrated solution.
13) Lines 229-231: write better this sentence (maybe "used" has to be removed)
The word “used” was removed.
14) Lines 231-232: write better this sentence (in particular, replace "are concerned on" with something more proper)
The sentence was rewritten as:
The deviations can be explained taking into account the differences in granulometric composition
15) Line 241: "solutions’ volumes’ 10 and 15 ml respectively" -> "solution volumes 10 and 15 ml respectively" (more in general there is an abused use of the Saxon Genitive in this paper: generally the Saxon Genitive is used to refer to things owned by people).
We got rid of Saxon Genitive.
We also read the paper once more and corrected a couple of grammar mistakes.
We thank the reviewer for his work that made it possible to improve our paper.
