This work describes the application of Fe-Mn oxides composite for p-chloroaniline (PCA) degradation under persulfate. Different perspectives on the impact on degradation of for p-chloroaniline, such as material systems, calcining temperatures, pH, temperature have been investigated. Additionally, the reaction mechanism of the Fe-Mn oxides composite for p-chloroaniline degradation with persulfate was investigated via trapping experiments, GC-MS measurement of intermediate. XPS was performed to characterized the catalytic materials before/after the catalysis. The quality of this work is poor. On both material and catalysis perspectives, I have major concerns about the scientific soundness and certain conclusion. I would recommend rejecting this work.

1. The authors should provide more characterization of Fe-Mn oxides composites, such as SEM, elemental mapping, XRD, etc. Now, there is basically no information of this Fe-Mn oxides composites, for example size.

2. The authors claimed that the Fe-Mn oxides composite was used as catalyst. What is the catalyst loading for the catalytic process? In the Figure, the concentration of PCA is 20 mg/L.

However, the concentration of MnFe2O4 is 1.3 g/L. How come this is a catalytic process?

3. What is the final product of p-chloroaniline degradation? Based on Figure 6, there are eight peaks on the LC spectra. Clearly, this is unacceptable and ridiculous being define as a catalytic degradation.

4. The quality of scientific language is also poor and the manuscript is missing necessary and enough reference, basically in every paragraph of introduction.

5. For example, in Figure 1, after 4 hours, the conversion is approaching to ~90 %. Why doesn’t the conversion go higher, in another word, to go completion?

6. I am not convinced by any conclusion in the section of 3.5 Mechanism of PCA degradation by MnFe2O4/PDS systems. The authors performed GC-MS measurement to identify intermediate. Compound P1 and P2 were proposed based on GC-MS result. P1 and P2 are oxidated intermediates in the system, which unnecessarily proves that there are two mechanistic pathways. Furthermore, in figure 6, there are more than 8 species in this system and 6 of them are not identified. And I have no idea how the authors propose the steps such as ring cleavage, simple organic acid. Figure 8 and Figure 10 are not acceptable for a catalytic mechanism study.

Author Response

Dear Reviewer,

All changes (point by point) in the revised manuscript can be found

according to the following Response to the Reviewers' Comments.

Black words are comments from Reviewers and red words are response to

the comments.

3.Because of the modification of manuscript, the order of the references has

been updated in the revised manuscript.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the framework of the paper.

We appreciate for Reviewers’ work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

Best regards,

Bingtao Liu

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and suggestions:

1. Abstract- “…. reaction temperature and pH on the degradation of PCA were studied. In addition, the reaction mechanism of the MnFe2O4catalyzed oxidative degradation of PCA by PDSwas investigated by free radical quenching experiments, and the reactants leading to PCA degradation were identified using different scavengers. The results showed that singlet.” -The author should be clear in their writing whether it is removal or degradation of of p-chloroaniline.

2. “Therefore, direct discharge of wastewater containing PCA can cause environmental pollution, and it is crucial to find an efficient wastewater treatment method.”--- I suggest the author, to discuss a paragraph related to water pollution due to the presence of different contaminants and applications of different adsorbents for the treatment techniques. The authors are recommended to check the below related references, which will improve the supporting information.

Journal of Cleaner Production 241, 2019, 118263

Environmental research 2019, 170, 389-397

Journal of Molecular Liquids 317, 2020, 113916

Journal of environmental management 219, 2018, 285-293

Materials 5 (12), 2012 2874-2902

Desalination and Water Treatment 57 (46), 2016, 21863-21869

Nanomaterials 9 (5), 2019, 776

3. “The catalytic methods of PDSincludetransition metal activation[5], electrochemical activation [6], photo-activation [7], thermal activation [8] and microwave activation [9] ,etc..” – Delete etc.

4. “When the pH value is increased to 11, the efficiency of PCA was reduced by 43.88% compared with that of pH 7.”- Explain the possible reason. Separation Science and Technology 55 (10), 2020, 1766-1775

5. “To further investigate thedegradation mechanism of PCA in the MnFe2O4/PDSsystem, the intermediates during the oxidative degradation of PCA were identified by HPLC-MS.” – Various hyphenated HPLC methods should be defined in brief including their advantages.

International Journal of Environmental Analytical Chemistry 98 (2), 2018, 171-181

Arabian Journal of Chemistry 12 (5), 2019, 633-651

Journal of King Saud University-Science 32 (4), 2020, 2414-2418

6. “…-xahydrate (FeCl3•6H2O) and manganese sulphate monohydrate (MnSO4•H2O)were supplied by Tianjin Comio Chemical Reagent Co. Provide the details of the supplier and also do same for all chemical used including city and country in experimental section.

7. “For the preparation process and properties of the catalyst (MnFe2O4), please refer to the previous experimental results of their group ” – Change to “The preparation process and properties of the catalyst (MnFe2O4), were carried out based on the previous experimental results.”

8. “A liquid chromatograph (Waters W2489-QDa, USA) with a reversed-phase C-18 column (4.7 ×250 mm), the m”- Provide the details of the manufacturer including city and country and also do same for all instruments used.

9. “Figure6. Liquid chromatogram of PCA at 0 h and after 4 h of reaction”—Add the optimal conditions in each caption.

10. “Figure7.LC-MS identification of PCA degradation intermediates” – It was better to provide the separation peaks and mass spectrum in same figure to identify them in better way.

11. The English quality not up to the mark. All the typos and grammar need to check thoroughly in the manuscript, especially the uses of spaces must be corrected.

Author Response

Dear reviewer,

Thank you for your decision and constructive comments on my manuscript. We have carefully considered the suggestion of Reviewer and make some changes. We have tried our best to improve and made some changes in the manuscript.Please see the attachment.Please note:

All changes (point by point) in the revised manuscript can be found

according to the following Response to the Reviewers' Comments.

Black words are comments from Reviewers and red words are response to

the comments.

3.Because of the modification of manuscript, the order of the references has

been updated in the revised manuscript.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the framework of the paper.

We appreciate for Reviewers’ work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

Best regards,

Bingtao Liu

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled “The removal efficiencies and mechanism of p-chloroaniline degradation by persulfate activated with Fe-Mn oxides composite”, by Yu Shi, Lin Qiao, Panfeng Ma, and Bingtao Liu,has been reviewed.

This manuscript investigates the removal of p-chloroaniline (PCA) using Fe and Mn oxide composite (MnFe₂O₄) catalysts prepared by chemical co-precipitation method. The MnFe₂O₄catalyst and its activation on the decomposition of PCA was studied using X-ray Photo Electron Spectroscopy (XPS).The experiments showed that the decomposition of PCA by MnFe₂O₄/PDS system depended on several reaction conditions (initial pH, reaction temperature and the calcination temperature) of the catalyst. According to the quenching experiments, SO₄^•−, •OH and ¹O₂ dispensed from MnFe₂O₄/PDS system act as the primary reactive oxygen species for PCA degradation in solutions. Additionally, the TOC removal efficiency as a function of various amounts of oxidants is also investigated. The degradation intermediates of PCA were identified with HPLC-MS. It is concluded that MnFe₂O₄ is an efficient heterogeneous catalyst for the degradation of PCA by PDS.

The paper reports an efficient and advanced oxidation technology for waste water (water containing p-chloroaniline) treatment to eliminate or reduce the environmental pollution, which is definitely a burning issue of the century and hence worth publishable. The experimental analysis, such as synthesis, characterization and testing of the catalyst are very good. However, the presentation (writing) of the work especially the discussion part of the manuscript is very poor. The manuscript required a thorough revision, needs lot of corrections in English Grammar, sentence structure and flow of language. Please do the corrections described below before publication.

Q1. P1, L09, “The results showed that singlet oxygen (¹O₂), sulfate radicals (SO₄· – ) and hydroxyl radicals (•OH) may all be involved”.

Please correct the “SO₄ ^._” as (SO₄^•−) in the Abstract. Also please correct this on Page 2, L-21 as well.

Q2. P2, L16-17, “The metal oxides are easily separated from the reacting liquid in subsequent processing.”

Please correct the English grammar of the sentence.

Q3. P1, L22-23, “In recent years, spinel ferrites (e.g. CuFe₂O₄, CoFe₂O₄, MnFe₂O₄, etc.) have been widely concerned by researchers.”

Explain briefly why researchers are concerned about spinel ferrites?

Q4. P3, L7-P8, “For the preparation process and properties of the catalyst (MnFe2O4), please refer to the previous experimental results of their group [5, 16]”.

The authors mentioned that “the preparation process and properties of the catalyst (MnFe₂O₄)” are given in detail on references [5-16]. However for this context, please explain the synthesis process briefly (in two or three sentences).

Q5. P3, L-9-11, “20mg/L PCA was adjusted to the desired pH value with 0.1mol/L sulfuric acid or sodium hydroxide. Then a certain amount of catalyst and 50mL 20mg/L PCA were added to six 150mL conical bottles, respectively”.

Please correct the sentence structure

Q6. P3, L 24-25, “The concentration of PCA was analyzed by N-(1-naphthyl) ethylenediamine azo spectrophotometric method”

Please give a reference to this method.

Q7. P3, L29-34, “A liquid chromatograph (Waters W2489-QDa, USA) with a reversed-phase C-18 column (4.7 ×250 mm), the mobile phase of acetonetrile/ultrapure water (V/V= 55/45), the column temperature of 40 °C, the flow rate of 0.50 mL/min, the fragment ion scan range: 50-1050 amu, the mass spectrometer operated under positive ionization with electrospray at fragmenter voltage of 600V”

Check the spelling. It seems to be the author is listed all the testing parameters used/required to conduct the liquid chromatography experiment. Please write it into a meaningful sentence.

Q8. P4, L-3-6, “When MnFe₂O₄ and PDS exist in the reaction system, the removal efficiency of PCA gradually increased to 94% at 240 min. Further- more, the degradation efficiency of PDS/Fe³⁺and PDS/Mn²⁺ systems for PCA in 240 minutes was 5.45% and 13.30%, respectively.”

Correct the sentence structure and English grammar.

Q9. P4, L-6-11, “The results showed that the oxidation mode of the MnFe₂O₄/PDS system is dominated by heterogeneous activation. And MnFe₂O₄ can be activated by PDS. Similarly, Jing et al [14] found that the removal of bisphenol A by homogeneous systems (PMS/Fe³⁺, PMS/Mn²⁺) waseless than 10%, which was much lower than the 90% removal by heterogeneous activation systems (MnFe₂O₄/PMS).”

Please correct the sentence structure and grammar.

How do you reach to a conclusion that the degradation of PCA was due to the oxidation of MnFe₂O₄/PDS system is dominated by heterogeneous activation? Is there any characterization results such as HPLC or FTIR that you can present to support your findings?

Q10. P4, L-15-16, “Relevant studies showed that the calcining temperature may affect the structure of the material itself, thus affecting its catalytic activity”.

Please correct the “calcining temperature” as “calcination temperature”

Q11. P4, L-16-18, “In this work, the catalytic performance at different temperatures was compared, and the result was shown in Figure 2.”

Please correct the English grammar and the sentence structure.

Q12. P4, L-23-26, “These results showed that the removal rate decreases when the calcining temperature reached 600°C. This may be due to decomposition of the MnFe₂O₄ material to other oxidizing substances [17] (e.g. Fe₂O₃ and Mn₂O₃) at 600℃, which reduces the decomposition point and effective contact area for the oxidative degradation of PCA. It is not conducive to further effective removal of PCA.”

This part of the discussion is not clear. What is the decomposition temperature of PCA? Please elaborate your argument and correct the sentence structure.

Q13. P5, L10-11, “The maximum yield of PCA decomposition was achieved at pH 7, K_obswas 0.013 min^-1 at pH 7”

Please define “K_obs”

Q14. P5, L19-20, “The results might be cause by three reasons. First of all, with the initial pH increasing from 3.0 to 11.0, the leaching concentration of Fe³⁺after 4h re- action were detected to be 0.12, 0.18, 0.14, 0.16 and 0.52 mg/L .”