Controllable Preparation of Superparamagnetic Fe₃O₄@La(OH)₃ Inorganic Polymer for Rapid Adsorption and Separation of Phosphate

Round 1

Reviewer 1 Report (New Reviewer)

The paper is devoted for Fe3O4@La(OH)3 synthesis and characterization. The topic is generally interesting, however the paper contain unexplained places (below) and need minor revisions.

 

Corresponding references should be added in the part fabrication procedure of Fe3O4@La(OH)3 (lines 157-169).

Obtained results should be more compared with similar results presented in literature. I find only two references since 180 line.

 

In introduction authors should explain why new materials for phosphate adsorption and separation should by synthesized. Which materials parameters still can be improved for such applications?

Author Response

Reviewer: 1
Comments:

The paper is devoted for Fe3O4@La(OH)3 synthesis and characterization. The topic is generally interesting, however the paper contain unexplained places (below) and need minor revisions.

Corresponding references should be added in the part fabrication procedure of Fe3O4@La(OH)3 (lines 157-169).

Response: We appreciate the reviewer’s suggestion! We have added two references numbered 32 and 33 in the revised manuscript.

Obtained results should be more compared with similar results presented in literature. I find only two references since 180 line.

Response: We have added some references with similar results numbered 38-43 in the revised manuscript.

In introduction authors should explain why new materials for phosphate adsorption and separation should by synthesized. Which materials parameters still can be improved for such applications?

Response: La(OH)₃/Fe₃O₄ nanocomposite has been established to act as an adsorbent for phosphate, with large adsorption capacity and can be separated by external magnetic field. However, Fe₃O₄ used in most literatures are prepared by coprecipitation method. In comparison to coprecipitation method, Fe₃O₄ prepared by solvent method in this study with the characteristic of monodisperse and fast magnetic response, and La(OH)₃ can be directly modified on its surface. Since Fe₃O₄ has no dense protective layer, it is easy to be oxidized, and the corresponding magnetic response is weakened, so magnetic separation recycling cannot be achieved. We can improve the stability of Fe₃O₄ by modifying its surface with a layer of dense silica and then with La(OH)₃. We have made changes in the corresponding part of the introduction, and the major changes are marked with highlight in the revised manuscript (lines of 67-76).

Author Response File: Author Response.docx

Reviewer 2 Report (New Reviewer)

The manuscript entitled "Controllable Preparation of Superparamagnetic Fe3O4@La(OH)3 Inorganic Polymer for Rapid Adsorption and Separation of Phosphate" refers to use  Fe3O4 nanoparticles in indirect way of phosphate separation form water. Basically, La(OH)3 is responsible for phosphate separation Authors made a lot suitable test to prove the structure and properties of  the new inorganic composite.

I have a few doubts.

1. Is it nanocomposite or composite?

Fe3O4  particles are nano particles. Their size is over 100 nm so they are not nanoparticles.

2. What kind of interactions take place between Fe3O4 and La(OH)3?

3. The authors proposed mechanism of phosphate removing by Fe3O4@La(OH)3. Did  they confirm it in any way?

4. Is it any possibility of transfer iron and lanthanum ions to water?

Did the authors checked the presence of these ions in water?

Author Response

Reviewer 2:

The manuscript entitled "Controllable Preparation of Superparamagnetic Fe3O4@La(OH)3 Inorganic Polymer for Rapid Adsorption and Separation of Phosphate" refers to use  Fe3O4 nanoparticles in indirect way of phosphate separation form water. Basically, La(OH)3 is responsible for phosphate separation Authors made a lot suitable test to prove the structure and properties of  the new inorganic composite.

I have a few doubts.

1. Is it nanocomposite or composite?

Fe3O4  particles are nano particles. Their size is over 100 nm so they are not nanoparticles.

Response: Thank you very much for your careful review and kind advice! Strictly speaking, it should not be called nano particles. The particle size of Fe₃O₄ synthesized by solvothermal method is about 400 nm, and the large particle size Fe₃O₄ has fast magnetic response property, which is conducive to rapid separation of adsorbent under the action of magnetic field. We have modified nano particles into particles throughout the manuscript.

2. What kind of interactions take place between Fe3O4 and La(OH)3?

Response: To protect the stability of Fe₃O₄ in long-term storage, a layer of silicon dioxide is first modified on the surface of Fe₃O₄ during the preparation of the material. The surface of Fe₃O₄@SiO₂ contains many silicon hydroxyl groups, lanthanum ions and silicon hydroxyl groups are first adsorbed on the surface of the microsphere through static electricity, and then La(OH)₃ nanoparticles are deposited on the surfaces of Fe₃O₄@SiO₂ generating Fe₃O₄@SiO₂@La(OH)₃ particles under the alkaline.

3. The authors proposed mechanism of phosphate removing by Fe3O4@La(OH)3. Did they confirm it in any way?

Response: To confirm the mechanism of phosphate removal by Fe₃O₄@La(OH)₃, the zeta potential measurements and the test of solution pH before and after phosphate adsorption had been performed. And the detailed discussion had been showed in 3.7. Mechanism of phosphate removing by Fe₃O₄@La(OH)₃. In addition, FTIR spectra of Fe₃O₄@La(OH)₃ before and after phosphate adsorption had been completed, and found no new absorption peak by comparing the spectrograms, which may be due to low content or peak overlap.

4. Is it any possibility of transfer iron and lanthanum ions to water?

Did the authors checked the presence of these ions in water?

Response: In the preparation process of the magnetic composite, fully cleaned has been carried out at each step. Both iron ions and lanthanum ions exist in the form of metal oxides or hydroxides. After the adsorption of phosphate, the two ions will not be transferred to water. To verify whether there are two metal ions in the water after the adsorption, we have used ICP-AES to detect and found no.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report (New Reviewer)

Authors make proper corrections according to

reviewer remarks and I suggest to publish the paper

as it is.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Yao Lu et al. Describe in their manuscript a three step synthesis to obtain defined Fe3O4 nanoparticles equipped with a SiO2 shell on which a layer of La(OH)3 species could be anchored. These particles can be used to remove phosphate from waste water by adsorption and can easily be separated due to the magnetic nature of the Fe3O4 core of the particles.

They give a satisfactory report about the solvothermal and sol-gel synthesis, the used characterization methods, kinetic experiments of the adsorption and a short removal experiment using "real" water.

Despite this, I was not able to identify a property of the material or its performance which shows significant improvements compared to the materials published in the last years. It would therefore be helpful to place the results presented here in the context of the current literature on this topic. In the current version, I can not suggest a publication.

Reviewer 2 Report

The authors presenting their findings on magnetic sorbents based on core-shell systems should carefully consider the following issues for their paper to be of interest.

1) The English language needs to be completely revised, it makes reading the manuscript difficult;

2) The introduction should focus more on phosphate adsorption. Magnetic nanoparticles for other application can be interesting but are not the focus of the manuscript. Please add appropriate references on phosphate removal and proposed mechanisms in the literature. Neither in the abstract nor in the Introduction it is made clear what is the improvement brought by these materials to this application;

3) In the materials and methods the type of reactor used in the solvothermal synthesis should be specified;

4) The characterization of the new materials is quite poor. I don't see the point in reproducing twice the same SEM images (Scheme 1 and Figure 3) and not have a TEM image to show the intimate structure of the magnetic material, of the shell, and the Lanthanum hidroxide;

5) Due to their size, the magnetic cores are probably made of aggregated smaller nanoparticles (which can be superparamagnetic). The term "monodisperse" is abused and quite not right, unless proved by a proper size analysis of the produced materials. The few pictures given (the repeated SEM images) don't give a clear idea on the aggregation/coalescence state of the particles after sol-gel synthesis. The composition should be provided, in particular the amount of La per mass of adsorbent. No porosity data have been provided;

6) The results should be properly discussed compared to the literature.