Innovative Magnetite Based Polymeric Nanocomposite for Simultaneous Removal of Methyl Orange and Hexavalent Chromium from Water
, Faouzi Ben Rebah 4,5,* and Mohamed A. Tahoon 4,6
Round 1
Reviewer 1 Report
The authors present a study on synthesis of magnetic chitosan-polypyrrole hybrids for methyl orange and chromium (VI) removal from aqueous solutions. The study investigates contact time, initial concentration and pH effects. The following issues need to be clarified before further consideration of the manuscript:
1. Please rework English – e.g. L37 -use ‘have’, L71-73, L82-83, L90, L142 –use ‘polypyrrole’, L194
2. Please present clearly section 2.2 L155-158 : 100 mL aq solution of? Please present the role of reactants in the preparation of magnetic hybrids. What is the solvent for chitosan?
3. Please describe the parameters used for each characterization in section 2.3.
4. Fig 1b shows the nanoparticles wrapped up in polymer matrix with no clear identification of the nanoparticles. Please support better the discussion L214-220 with images. What is ‘low Fe3O4 nanoparticles on the surface’?
5. Please correct caption in fig 3. Please show Raman of Fe3O4 nanoparticles as well in order to support the discussion.
6. Please show chitosan and polypyrrole only in TGA curves in order to support the discussion
7. Why the co-ions concentration was selected as 200 mg/L?
8. Please clarify L185.
9. Please present L330-333 clearer.
10. Please show images of the hybrids in between cycles to support the claims in section 3.5
11. Please complete table 2 with relevant infos such as adsorbent dosage etc. in order to have an overall view on the comparison with other adsorbent performance.
Author Response
1. Please rework English – e.g. L37 -use ‘have’, L71-73, L82-83, L90, L142 –use ‘polypyrrole’, L194
All the statements were corrected
2. Please present clearly section 2.2 L155-158 : 100 mL aq solution of? Please present the role of reactants in the preparation of magnetic hybrids. What is the solvent for chitosan?
The statement was corrected" 100 mL of water"
The role of reactants: ammonium persulfate is the initiator and pyrrole is the monomer.
chitosan was dissolved in acetic acid solution
3. Please describe the parameters used for each characterization in section 2.3.
The requested information was added in the text (section 2.3)
4. Fig 1b shows the nanoparticles wrapped up in polymer matrix with no clear identification of the nanoparticles. Please support better the discussion L214-220 with images. What is ‘low Fe3O4 nanoparticles on the surface’?
The statement was corrected in the text" Polypyrrole was successfully loaded over the magnetic chitosan, which is clearly indicated the presence of coated Fe3O4 nanoparticles" (Line 222)
Fig.1b, showed uniform smoother surface (the the nanoparticles is coated with chitosan)
We provide clear picture
5. Please correct caption in fig 3. Please show Raman of Fe3O4 nanoparticles as well in order to support the discussion.
Raman of Fe3O4 nanoparticles was added in the figure 3a
Fig 3 capitation was corrected: (a) Raman spectrum, (a) Thermogravimetric analysis, and (c) room temperature magnetization curve of polypyrrole@magnetic chitosan nanocomposite
6. Please show chitosan and polypyrrole only in TGA curves in order to support the discussion
TGA of chitosan and polypyrrole were added in Fig 3b.
7. Why the co-ions concentration was selected as 200 mg/L?
In the literature, the study of the effect of competing anions (chloride, nitrate, carbonate, sulfate and phosphate) was conducted generally with initial competing anion concentrations of 20–200 mg/L for various adsorbents. So, on the basis of a preliminary study, we chose to work at high concentration (200 mg/L).
8. Please clarify L185.
The paragraph was clarified (Line 185)
9. Please present L330-333 clearer.
The statement was clarified (Line 333)
10. Please show images of the hybrids in between cycles to support the claims in section 3.5
We thank the reviewer for this remark. In this section, we have highlighted the reusability of the polypyrrole@magnetic chitosan nanocomposite after 5 regeneration cycles. Now, we are planning to study the nanocomposite reusability using various methods with different eluents and we will arrange to take images after each process to illustrate and confirm the efficiencies.
11. Please complete table 2 with relevant infos such as adsorbent dosage etc. in order to have an overall view on the comparison with other adsorbent performance.
The operating conditions were added in table 2.
Reviewer 2 Report
This paper presents the removal of methyl orange (MO, dye) and chromium (VI) from wastewaters. There seems to be high novelty in the used adsorbent, ppy@CS/magnetite.
The novelty seems to be in the simultaneous reduction of Cr(VI) and removal of MO and Cr(IV) over this adsorbent.
Otherwise, paper seems to follow the structure of typical adsorption papers. My comments related to this paper:
-Fig 1 .... it seems that SEM and TEM are mixing, at least if You look at the scale given in the figures. But on the other hand, figs 1c and 1d looks more like TEM images. Can you confirm this?
-In the text, it is said that uniform distribution of Fe3O4 nanoparticles on the sample. Any experimental evidence for this?
-Fig 2 and related XRD or FTIR data --- it would be good to present the peaks sites in the figure (at least the most dominant ones) Maybe as asterix in the figure, and separate label for these. It seems that chitosan eg has two dominant XRD peaks in the pattern.
-Again in Fig 3, it seems that a and b are mixed together in the figure label. 3b is TGA curve and 3a Raman spectrum. In the body text, this seems to be correct.
-pH dependent of adsorbent is significant … how limited is the use of this adsorbent material if you take into account the precipitation of MO (at lower pH) and poor adsorption capacity at high pH values?
-Similarly, for Cr(VI) different species are present at different pH values. How this affects the adsorption capacity?
-Cr(VI) is an anionic species in water solution, what is the surface charge of the surface?
-Contact time is evaluated in the batch type reactor with mixing. Adsorbent in industrial scale are used in columns with the optimized residence time. How reliable are these measurements related to column experiments which are not performed?
-There are some spelling mistakes in the paper (eg. in abstract)
-Spent and contaminated adsorbent is the challenge, what to do with the spent sorbent?
-Fig 5 presents the role of competitive ions. In the case of anions it is clear, but why also capacity decrease in the case of MO? What is surface charge and is adsorption based on electrostatic forces in that case ? "MO adsorption was not significantly affected by the existence of bicarbonate ions. " Why? Is that in line with earlier observations?
-Fig5b, reusability of sorbents is shown in the batch conditions. These are not equal to column adsorption. Would these sorbents be reusable in column experiments as well? Are they mechanically strong enough to be used in colums? What to do with spent regeneration solution?
-Fig 6 and Table 1 are not in line. Based on Fig 6, there is better fitting of Langmuir model (Fig 6b) but in the table it seems to be vice versa. This cannot be true. Spelling mistakes also in word Freundlich .
-Given adsorption capacities are here much higher than given in literature. Could it be possible that there is other mechanisms of removal as well? Very important parameter to evaluate this would be the specific surface area of adsorbent, and comparison with SSAs of other sorbents in table 2. If adsorption is only based on electrostatic forces, the amount of functional groups could be evaluated, and surface acidity/basidity to measured.
Author Response
-Fig 1 .... it seems that SEM and TEM are mixing, at least if You look at the scale given in the figures. But on the other hand, figs 1c and 1d looks more like TEM images. Can you confirm this?
The Fig 1a and 1b are SEM images; Fig 1c and 1d are TEM images.
-In the text, it is said that uniform distribution of Fe3O4 nanoparticles on the sample. Any experimental evidence for this?
The uniform distribution of coated Fe3O4 nanoparticles was reported based on the SEM image. This agree with that reported in the literature
-Fig 2 and related XRD or FTIR data --- it would be good to present the peaks sites in the figure (at least the most dominant ones) Maybe as asterix in the figure, and separate label for these. It seems that chitosan eg has two dominant XRD peaks in the pattern.
dominant peaks were emphasized in the figure with their corresponding values.
The two peaks of chitosan at 2θ= 20.35 and 9.95 are characteristics of the biopolymer chitosan.
-Again in Fig 3, it seems that a and b are mixed together in the figure label. 3b is TGA curve and 3a Raman spectrum. In the body text, this seems to be correct.
Fig 3 capitation was corrected: (a) Raman spectrum, (a) Thermogravimetric analysis, and (c) room temperature magnetization curve of polypyrrole@magnetic chitosan nanocomposite
-pH dependent of adsorbent is significant … how limited is the use of this adsorbent material if you take into account the precipitation of MO (at lower pH) and poor adsorption capacity at high pH values?
In the present work, we tried to remove simultaneously MO and Cr(VI). Based on the experiment data, the adsorption capacity for Cr was high (for low pH). However, at pH <4.5, MO could precipitate. This may limit the use of this absorbent. Therefore, is very important to determine the quantity of MO that precipitate at the operating pH. An optimization experiment should be conducted in order to determine the optimum pH at which MO precipitation is minimized, and the removal efficiency of both pollutants was maximized. Is also interesting to conduct the water treatment in two stage at different pH to eliminate MO and Cr(VI) separately.
-Similarly, for Cr(VI) different species are present at different pH values. How this affects the adsorption capacity? -Cr(VI) is an anionic species in water solution, what is the surface charge of the surface?
The surface of adsorbent contains positive charges (NH4+ groups in both polymers chitosan and ppy). This fact is well discussed in the manuscrit
-Contact time is evaluated in the batch type reactor with mixing. Adsorbent in industrial scale are used in columns with the optimized residence time. How reliable are these measurements related to column experiments which are not performed?
First, is very important to indicate that the use of batch experiment in the present study is motivated by the advantage offered by the magnetic NPs, that allowed the fast and ease separation of adsorbent by commercial magnet.
Generally, before using an adsorbent at large scale, experiments are generally conducted in batch and column reactors. At the beginning of a study of a potential adsorbent material, batch experiments should be conducted. This help to determine the possible use of the adsorbent for pollutant removals. Based on the obtained results, more investigated should be conducted including the column experiments and operating parameters optimization.
-There are some spelling mistakes in the paper (eg. in abstract)
The manuscript was revised and mistakes were corrected
-Spent and contaminated adsorbent is the challenge, what to do with the spent sorbent?
Various management approaches were conducted such as incineration, regeneration and landfilling.
-Fig 5 presents the role of competitive ions. In the case of anions it is clear, but why also capacity decrease in the case of MO? What is surface charge and is adsorption based on electrostatic forces in that case ? "MO adsorption was not significantly affected by the existence of bicarbonate ions. " Why? Is that in line with earlier observations?
This fact can be explained by the affinity of adsorbent against MO and bicarbonate. The adsorbent has higher affinity to MO than bicarbonate ions. This explanation was reported by Li et al (2016)
-Fig5b, reusability of sorbents is shown in the batch conditions. These are not equal to column adsorption. Would these sorbents be reusable in column experiments as well? Are they mechanically strong enough to be used in colums? What to do with spent regeneration solution?
As indicated above, more investigations are needed to conclude about the use of the material as adsorbent in column reactors. Also, results should be verified at large scale with real wastewater.
The regeneration solution will be treated as wastewater.
-Fig 6 and Table 1 are not in line. Based on Fig 6, there is better fitting of Langmuir model (Fig 6b) but in the table it seems to be vice versa. This cannot be true. Spelling mistakes also in word Freundlich .
Table 2 was corrected. The kinetic study illustrated that the adsorption fit well with Langmuir isotherm as indicated in Fig 6
-Given adsorption capacities are here much higher than given in literature. Could it be possible that there is other mechanisms of removal as well? Very important parameter to evaluate this would be the specific surface area of adsorbent, and comparison with SSAs of other sorbents in table 2. If adsorption is only based on electrostatic forces, the amount of functional groups could be evaluated, and surface acidity/basidity to measured.
Generally, the variability of the adsorption capacities could be explained by various factors including the material nature (material origin, polymerization process, characteristics, etc.) and the operating conditions (dosage, pollutants, pH, temperature, contact time, etc.). I agree that the Specific surface areas and pore volumes help to understand the differences between the efficiency of adsorbents. Now, we are planning researches to deepen the knowledge regarding the adsorption behaviour of the present adsorbent and will be compared to other materials.
Round 2
Reviewer 1 Report
The authors have addressed the comments and reworked the manuscript accordingly. Overall, the paper can be accepted for publication.
Reviewer 2 Report
Authors have carefully commented/answered the questions, and mostly also updated the manuscript to support these findings. There are some issues presented which are not supported by the given data. Anyhow, I see that corrections are sufficient and this paper can be accepted.
