Facile Preparation of Fe3O4@SiO2 Derived from Iron-Rich Sludge as Magnetic Catalyst for the Degradation of Organic Contaminants by Peroxymonosulfate Activation
Round 1
Reviewer 1 Report
In general, the article is well written, and the difference between the article and other studies should be written in the introduction.
Spelling errors in the article should be corrected
Line 102-104: font needs to be corrected
Line 100: ((CIP, ≥ 99.9%),) comma should be removed
This article can be acceptable after minor revision.
Author Response
Comments and Suggestions for Authors
- In general, the article is well written, and the difference between the article and other studies should be written in the introduction.
Response: Thanks for this comment.
The difference between this article and other studies has been written and added in the revised manuscript in the introduction, seen at third paragraph in the introduction section.
Some research reported that biochar derived by pyrolyzing biomass under oxygen limited conditions can behave as an effective carrier for transition metals, and this type of biochar-loaded iron oxides composites exhibit higher catalytic activity [1]. However, the sewage sludge-derived biochar has to be developed by external additional Fe sources and high pyrolysis temperature (>800 °C) which inhibited the practical application. In comparison, drinking water treatment iron-rich sludge was used as precursor and iron source to prepare Fe3O4@SiO2 catalyst via low energy input process (hydrothermal treatment, 200 °C) without additional Fe sources in this study.
- Spelling errors in the article should be corrected
Response: Thanks for this comment.
We have checked this Manuscript again and corrected the spelling errors carefully.
- Line 102-104: font needs to be corrected
Response: Thanks for this comment.
The font in Line 100-106 has been corrected as Palatino Linotype.
- Line 100: ((CIP, ≥ 99.9%),) comma should be removed
Response: Thanks for this comment.
This comma has been deleted. “CIP ≥ 99.9%”.
This article can be acceptable after minor revision.
References:
[1] J. Liang, X. Xu, Q. Zhong, Z. Xu, L. Zhao, H. Qiu, and X. Cao, Roles of the mineral constituents in sludge-derived biochar in persulfate activation for phenol degradation. J. Hazard. Mater. 398 (2020) 122861.
Reviewer 2 Report
The manuscript deals with the Facile preparation of Fe3O4@SiO2 derived from iron-rich sludge as a magnetic catalyst for the degradation of organic contaminants by peroxymonosulfate activation But publication point of view some major changes are necessary.
1) There are a few grammatical mistakes. Please check the manuscript for grammar and English.
2) What is the novelty of the present work? Rewrite it at the end of the introduction section.
3) Literature survey is very poor in the introduction section. To enrich it add some references.
i) Catalysts 12 (10), (2022) 1290, ii) Materials 15 (17), (2022) 6133, iii) Catalysts 11 (4), (2021) 460, iv) Journal of Photochemistry and Photobiology A: Chemistry 434, (2023) 114250
4) Compare your photocatalytic experimental results with other researcher work in tabular form.
5) Calculate the conduction and valence band potential of prepared materials.
6) Recycling experiments should be provided, and XRD or XPS should characterize after the photocatalytic reaction to check the stability of the catalyst.
7) The photocatalytic reaction mechanism should be further explored by the necessary experiments, such as the trapping experiments for hydroxide radical and the ESR experiments for the O2.
8) Add XPS study of prepared materials in order to confirm their oxidation states.
9) While studying photocatalytic properties optical study is most important so add absorbance spectra, bandgap plot and PL study of all prepared materials.
10) Add photocatalytic stability study of prepared material.
11) Add LC-MS study of CIP with possible intermediate products.
Author Response
Response to Reviewer 2’s Comments
Thank you for your comments and suggestions.
We discussed the comments and suggestions about our study with some senior experts related to “persulfate activation” and some relevant professors or researchers in terms of catalytic oxidation. However, we have some different opinions on the Reviewer 2’s comments.
Our study used iron-rich sludge as raw material to prepare PMS catalyst for the degradation of organic contaminants by only chemical oxidation process without any addition input (i.e. ultraviolet or visible light) rather than “Photocatalytic reaction”. However, we all think that the expert (Reviewer 2) misunderstood our study and made the comments on Photocatalyst or photocatalytic oxidation which were uncorrelated to our work.
For example,
Comment 3: To enrich literature survey add some references: i) Catalysts 12 (10), (2022) 1290, ii) Materials 15 (17), (2022) 6133, iii) Catalysts 11 (4), (2021) 460, iv) Journal of Photochemistry and Photobiology A: Chemistry 434, (2023) 114250.
Response: We have checked all the references but those literature are about Photocatalysis that were not relevant to the contents of the manuscript at all.
Comment 4: “Compare your photocatalytic experimental results with other researcher work…”
Response: Our study is about chemical catalytic oxidation by PMS activation but not photocatalytic experiments.
Comment 5: “Calculate the conduction and valence band potential of prepared materials”.
Response: The “conduction and valence band potential” is the characterization parameter of Photocatalyst. But our Fe3O4@SiO2 catalyst is just heterogeneous chemical compounds that were not relevant to Photocatalysis.
Comment 6: “…after the photocatalytic reaction to check the stability…”
Comment 7: “The photocatalytic reaction mechanism should be…”
Comment 9: “While studying photocatalytic properties optical study is…”
Comment 10: “Add photocatalytic stability study of…”
Response: The description about the novelty (Comments 2) of this study has been rewritten at last paragraph in the introduction section. XPS analysis (Comments 8) was employed to investigate the Fe species about the materials.
However, our experiment is not photocatalytic reaction. Therefore, we think these comments provided by Reviewer 2 might be good or valuable but were not relevant to our work. For these reasons, we apologize that we cannot make changes based on these uncorrelated comments.
Reviewer 3 Report
This paper deals with the synthesis of a magnetic heterogeneous catalyst (Fe3O4@SiO2) via hydrothermal reduction treatment using drinking water iron-rich sludge and utilized as peroxymonosulfate activator for ciprofloxacin removal.
I thinks that the manuscript can be accepted but it needs to be minor revised before publication.
Comments:
1- Some of the Keywords should be revised. For example; Catalytic Oxidation and Hydrothermal reduction treatment
2- The Advantages and disadvantages of the Fe3O4@SiO2 as a magnetic catalyst
should be present in the introduction section.
3- The novelty of the menuscript should be present very clearly in the introduction section.
3- Effect of SiO2 in the magnetic catalyst should be present in manuscript.
4- The characterization of the iron-rich sludge (Fe2+ and Fe3+ concentration, non soluble materials, Free acid based on the HCl and heavy metals) should be provide in the manuscript.
Author Response
This paper deals with the synthesis of a magnetic heterogeneous catalyst (Fe3O4@SiO2) via hydrothermal reduction treatment using drinking water iron-rich sludge and utilized as peroxymonosulfate activator for ciprofloxacin removal.
I think that the manuscript can be accepted but it needs to be minor revised before publication.
Comments:
1- Some of the Keywords should be revised. For example; Catalytic Oxidation and Hydrothermal reduction treatment
Response: Thanks for this comment.
The Keywords have been revised as:
“Iron-rich sludge; Fe3O4@SiO2 catalyst; Peroxymonosulfate activation; Ciprofloxacin; Waste recycling”
2- The Advantages and disadvantages of the Fe3O4@SiO2 as a magnetic catalyst should be present in the introduction section.
Response: Thanks for this comment.
The advantages and disadvantages of the Fe3O4 as a magnetic catalyst have been added in the introduction section of revised manuscript. Seen as follows:
“Considering several disadvantages of homogeneous iron-activated PMS system including strict pH restriction, large input of iron ion dosage, and the introduction of anions related to iron salts like SO42- or Cl-. Considerable efforts have been made to develop various transition metal-based heterogeneous catalysts for PS activation.” (line 62-65)
“For example, numerous research focused on the synthesis of heterogeneous Fe-based catalysts such as Fe3O4 due to the fact that non-toxic and abundant Fe(II) could induce the decomposition of PMS to produce SO4•− and •OH. Moreover, the Fe3O4 with magnetic property could be easily separated from aqueous solution in the presence of external magnetic field.” (line 69-73)
3- The novelty of the manuscript should be present very clearly in the introduction section.
Response: Thanks for this comment.
The description about the novelty of this study has been rewritten at last paragraph in the introduction section, seen as follows:
Some research reported that “Biochar derived by pyrolyzing biomass under oxygen limited conditions can behave as an effective carrier for transition metals, and this type of biochar-loaded iron oxides composites exhibit higher catalytic activity [2]. However, the sewage sludge-derived biochar has to be developed by external additional Fe sources and high pyrolysis temperature (>800 °C) which inhibited the practical application.” In comparison, drinking water treatment iron-rich sludge was used as precursor and iron source to prepare Fe3O4@SiO2 catalyst via low energy input process (hydrothermal treatment, 200 °C) without additional Fe sources in this study.
“Powdered solid iron-rich sludge might act as the precursor and support to synthesize a green and economic PMS catalyst without high energy input and massive addition of transition metals. Therefore, exploring its additional value (as iron source and catalyst support) while dealing with this iron-rich sludge may be a process of waste resource utilization. Herein, in this work, a facile hydrothermal treatment was attempted to use to convert partial Fe(III) species in raw iron-rich sludge into Fe(II) through this reduction process. The as-prepared magnetic nanocomposite (Fe3O4@SiO2), possibly with superior catalytic activity, porous structure and large specific surface area, could be utilized as PMS activator for the oxidation of refractory organic pollutants in wastewater.”
4- Effect of SiO2 in the magnetic catalyst should be present in manuscript.
Response: Thanks for this comment.
The relevant descriptions about effect of SiO2 have been presented in section 3.1, shown as follows:
“The SiO2 in magnetic catalyst derived from iron-rich sludge has been extensively investigated as the support for the transition metal-based catalyst (i.e., Fe3O4, Fe2O3) due to the Fe-O-Si interactions, which could improve the stability and reduce iron ion leaching [1].”
5- The characterization of the iron-rich sludge (Fe2+ and Fe3+ concentration, non soluble materials, Free acid based on the HCl and heavy metals) should be provide in the manuscript.
Response: Thanks for this comment.
The characterization of the iron-rich sludge has been added in the revised manuscript. The relevant descriptions have been displayed at first paragraph in 3.1 section. Seen as follows:
“Before the solvothermal treatment, iron-rich sludge was pretreated and analyzed. The content of compositions was measured by ICP-AES and XPS analysis. The content of Fe in the ferric sludge was found to be 188.6±3.50 mg/g. The main characteristics of the iron-rich sludge are shown in Table S1. XPS was employed to investigate the percentage of Fe in different valence states in the catalyst. As displayed in Fig. S1, the peaks situated at around 710.0 and 723.6 eV were corresponding to Fe (II) species (19.1 atom%), while the binding energies of 712.1 and 725.7 eV were assigned to Fe (III) species (80.9 atom%), suggesting the coexistence of Fe(II)/Fe(III) on the surface of catalyst. Thus, the Fe(II) and Fe(III) concentration could be calculated as 36.0±0.67 mg/g and 152.6 ± 2.83 mg/g, respectively.”
References:
[1] A. Nadar, A.M. Banerjee, M.R. Pai, S.S. Meena, R.V. Pai, R. Tewari, S.M. Yusuf, A.K. Tripathi, and S.R. Bharadwaj, Nanostructured Fe2O3 dispersed on SiO2 as catalyst for high temperature sulfuric acid decomposition—Structural and morphological modifications on catalytic use and relevance of Fe2O3-SiO2 interactions. Applied Catalysis B: Environmental 217 (2017) 154-168.
[2] J. Liang, X. Xu, Q. Zhong, Z. Xu, L. Zhao, H. Qiu, and X. Cao, Roles of the mineral constituents in sludge-derived biochar in persulfate activation for phenol degradation. J. Hazard. Mater. 398 (2020) 122861.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Necessary corrections have been made in the article. The article is acceptable in this present form
Reviewer 3 Report
The authors have addressed my concerns appropriately, and I recommend the manuscript be now accepted for publication in its current form.
