“Sea Anemone”-like CeFe Oxides for High-Efficient Phosphate Removal

Round 1

Reviewer 1 Report

The authors synthesized a recyclable CeFe-based oxides with high adsorption capacity and selectivity for inorganic phosphate removal (or recovery) from water. Although Ce oxides loading had been reported with priority for phosphate removal, the construction of “sea anemone”-like 3D porous structure is a valuable try in term of phosphate adsorbent design for the paper. Moreover, ample data of structural characterization, phosphate adsorption property and adsorption mechanism is another merit of the paper. The main defect of this paper is that there are some improper format and confusing expression. Therefore, I suggested that a minor revision is essential for being published in Water.

 Specific comments are listed as follows.

1) Line 141-143: Whether the qe, C0 and Ce are based on phosphate molecule or phosphorus atom is not clear.   

 2) Formats need revision: CeO2 on Line 198, Ce3+ and Ce4+ on Line 231, N2 on Line245.

 3) Figure 8. Note the pH values.

 4) The assignment of 990.6eV and 882.5eV in Figure 3b is not consistent with the presentation of Line 228-229.

 5) Line 319-321. Provide reference literature.

 6) Line 332-323. Since the higher pH at equilibrium than in the initial may also be caused by the buffering of solution by adsorbent, the conclusion “originating from the exchanged hydroxyls” is not reasonable. Another expression, for example “probably originating from the exchanged hydroxyls” may be better.

 7) Why air atmosphere was employed in CeFe-CM-T synthesis? In view that Ce³⁺ is more effective than Ce⁴⁺ in phosphate adsorption and Ce³⁺ was partially oxidized to Ce⁴⁺ in heating treatment, oxygen-limited or oxygen-avoided atmosphere seemed better (in preserving Ce³⁺).

Author Response

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Reviewer 2 Report

In this work, CeFe-based oxides were prepared with CeFe CMs as precursor and used to remove phosphate from water. The micromorphology of adsorbents was characterized, various operating conditions were optimized, the adsorption capacity was conducted and compared with the commercial oxides and the adsorption mechanism was discussed. As a general comment, the manuscript is well structured and written. Therefore, I recommend that the paper can be considered for publication after the authors have considered the questions/comments that arise from my reading of the manuscript, as detailed below.

1.     Recently, the research on phosphorus removal with MOF materials has made great progress. It is suggested to discuss it in the introduction.

2.     Please discuss in the introduction why Fe element is selected to prepare adsorbents.

3.     On page 3, is there an oxidative digestion step in the determination of phosphate? Please clarify.

4.     It is very attractive for this “Sea Anemone” structure. Except for its amazing shape, is it helpful for the phosphate removal on practical?

5.     Phosphate adsorption mechanism: The authors claim the ligand exchange mechanism. If the mechanism were true, why uncalcined CMs possessing more CN ligands on the surfaces could not adsorb phosphate? Did the authors detect liberated CN anion?

Author Response

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Reviewer 3 Report

Manuscript Number: water -1819460

“Sea Anemone”-like CeFe Oxides for High-efficient Phosphate Removal.

GENERAL COMMENTS

The present work shows an extensive study on the synthesis of an adsorbent based on a compound of cerium and iron oxide for the elimination of phosphates. It has seemed to me a very interesting work, since it is a topic very in trend, the work carries out a wide characterization of the synthesized adsorbent and something that seems to me of great interest, a study on the useful life of the adsorbent. This is an aspect that other authors who carry out similar essays do not delve into and for which I would like to congratulate the authors.

I think the work is interesting and it should be accepted after minor revision.

 I only have some recommendation for the authors:

In figure 1, the SEM scales must be clear to facilitate their understanding and comparison.

In figure 2, perhaps it would be more convenient to indicate with arrows the axes that correspond to each of the curves, instead of colors.

Finally, I have missed some citations that support what the authors indicated in some of the results presented, specifically in lines 191, 209, 226, 260, 295 and 321.

Author Response

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Reviewer 4 Report

Presented manuscript entitled “”Sea-Anemone”-like CeFe Oxides for High-efficient Phosphate Removal” by X. Tang et al. greatly presents the possible of phosphate removal from wastewaters by CeFe-based oxides constructed from highly porous cyanometallates. The manuscript is written with a good English level, and I did not find any blatant grammar mistakes.

Below, please find my minor comments to the text:

-  Did Authors find similar researches about phosphate removal by MOF’s based metal oxides?

- In 2.1. subchapter: Fe₃O₄ is “ferrous ferric oxide” not “ferric oxide”.

- FT-IR proper name is “Fourier transform infrared spectra” not “[…] transformation”

- Please check the whole manuscript in order to add missing superscripts and subscripts.

- Did Authors check the exact value of CeFe-CM’s magnetization?

Concluding, I suggest acceptance of presented manuscript after minor revision.  

Author Response

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