NiO-NiFe2O4-rGO Magnetic Nanomaterials for Activated Peroxymonosulfate Degradation of Rhodamine B
Round 1
Reviewer 1 Report
The manuscript deals with the activation of peroxymonosulfate by NiO-NiOFe2O4-rGO Magnetic Nanomaterials and presented good degradation performance of Rhodamine B. However, major revisions are needed in this manuscript for its publication. For such purpose, refer to attached file.
Comments for author File: 
Comments.pdf
Author Response
Reviewers' comments 1:
The manuscript deals with the activation of peroxymonosulfate by nio-NioFe204-rGo Magnetic Nanomaterials and presented good degradation performance of Rhodamine B. However, major revisions are needed in this manuscript for its publication these include:
Broad comments
(1) Background knowledge and interpretations of results are missing in the abstract. Need to include!
Responses：Thanks a lot for this valuable suggestion. According to the suggestion from reviewer, we have rewritten the abstract, which is as followings:
Magnetic spinel ferrites, as heterogeneous catalysts to generate powerful radicals from peroxymono-sulfate (PMS) for the degradation of organic pollutants, have received much attention in recent years due to the characteristic of environmental benefits. In this study, NiO-NiFe2O4-rGO magnetic nanomaterials were synthesized by calcinated Ni-Fe-LDH-rGO precursor. The morphology, structure and chemical constitution were characterized by XRD, SEM, EDS, TEM, N2 adsorption-desorption isotherms, XPS and VSM. The catalytic performance of NiO-NiFe2O4-rGO nanoparticles was thoroughly evaluated for peroxymonosulfate (PMS) activation for removal of rhodamine B (RhB) from water. The influence of different process parameters on the RhB degradation efficiency was examined and the catalytic stability was evaluated. Under optimized conditions, the NiO-NiFe2O4-rGO/PMS system was very efficient with a full degradation of RhB in 40 min at room temperature. Quenching experiments and EPR results suggested that SO4-‧ and OH‧ were the main active species in the degradation process. Moreover, NiO-NiFe2O4-rGO catalyst was stable without any apparent activity loss after 3 cycling runs.
(2) The introduction is too small to explain the background knowledge and doesn't provide readers sufficient background. Therefore, it is suggested to include the proper background knowledge that why it is important? Include the related literature regarding degradation of organic matter? Why do you select Rhodamine B? Moreover, define the problem statement properly! In general, the authors need to rewrite introduction and avoid long sentences
Responses：Thanks for reviewer’s kind question. Rhodamine B, which is a xanthene zwitterionic dye and is the most common dyes around the world, is always chosen as the targeted contaminant in the AOPs study process. Therefore, we also select it.
According to the suggestion from reviewer, we have rewritten introduction, which is as followings:
Currently, in industrial production processes, sustainable development is a major issue. The most contaminated textile wastewater stream, dyeing discharge, was selected for dedicated treatment by advanced oxidation processes (AOPs) [1]. The basic principle of the AOPs is to generate highly active intermediate species (i.e. OH‧, O2-‧, SO4-‧) for mineralization of refractory organic pollutants, water pathogens and disinfection by-products. Due to the high oxidative potential of hydroxyl radicals (OH‧), which appear in AOPs, many organic compounds, including dyes, can be decomposed, and OH‧ have high second-order reaction rate constants with most organic molecules, including both bulk organic matter and micropollutants [2]. The bulk organic matter being abundantly present in secondary effluent acts, however, as an important scavenger for OH‧ that become much less available for reaction with the organic micropollutants [3,4]. Therefore, the interest in sulfate radical (SO4-‧) based AOPs has recently grown. Because of the higher selectivity of SO4-‧ reacting mainly through an electron transfer mechanism, the scavenging rate of SO4-‧ by bulk organic matter is 35–75 times lower compared to that of OH‧ [5,6]. Other advantages of SO4-‧ are the high oxidation reduction potential (2.5~3.1 v), could oxidize and degrade refractory organic pollutants in wastewater. At the same time, it has long half-life and wide using range of pH [7]. Therefore, it has more potential in the field of pollutant removal.
Usually sulfate radicals can be obtained through persulfate (PMS) and sulfates activation by heat, light, radiation, or chemical activation, with which, the oxidative properties can be significantly enhanced to form the free radicals [8], while PMS and sulfates also have certain oxidation properties without activation. Therefore, many scholars have paid attention to how to activate PMS, sulfates, and produce more sulfate radicals. Spinel oxides are widely used in catalysis, energy storage, environmental restoration and other fields due to its good catalytic activity and magnetic characteristics [9]. For example, Boukherroub et al. demonstrated that spinel Co2SnO4/PMS system was very efficient with a full degradation of rhodamine B (RhB) and pentachlorophenol (PCP) in less than 10 min at room temperature[10]; Ren et al. evaluated the performance of CoFe2O4,CuFe2O4, MnFe2O4, and ZnFe2O4 in PMS oxidation, and concluded that CoFe2O4 possessed superior catalytic activity towards PMS for the degradation of dibutyl phthalate and all catalysts presented favorable recycling and stability in the repeated batch experiment [11]. However, spinel ferrite is easy to reunite in the synthesis process, and its catalytic properties would be affected significantly [12], while composited with reductive graphene (rGO) with high conductivity and high specific surface area, the effect could be overcome. Yao et al. and Xu et al. deposited MnFe2O4 and CoFe2O4 nanoparticles on reduced graphene oxide (rGO), respectively, and they found that both PMS activation and organic pollutants degradation by the obtained hybrid catalysts could be substantially enhanced [13,14].
To the best of our knowledge, there is no investigation of NiO-NiFe2O4-rGO for peroxymonosulfate (PMS) activation reported so far in the literature. In this study, we focused on the synthesis of NiO-NiFe2O4-rGO magnetic nanomaterials using a hydrothermal route and their ability to activate PMS for efficient degradation of RhB at room temperature. The as-prepared hybrid catalyst was characterized by XRD, SEM, EDS, TEM, N2 N2 adsorption-desorption isotherms, XPS and VSM. Its catalytic activity in PMS solution was evaluated by the oxidation of a xanthene zwitterionic dye rhodamine B (RhB). The influence of various parameters related to the operational procedure was investigated. Finally, the degradation mechanism was tentatively proposed and the recyclability of magnetic hybrid catalyst was studied.
(3) The paper requires careful check for typo and grammar, some sentence structures need to be checked. However, it will be appreciated if English editing is done by native english speaker or professional English editing service.
Responses：Thanking for your helpful opinion.
According to the suggestion from reviewer, we have checked the grammar and sentence structures again. In addition, we have asked several colleagues who are skilled authors of English language papers to check the English. We believe that the language is now acceptable for published.
(4) The manuscript has not been prepared as per guidelines of this journal. For example, in the Experimental Section the subheadings are not set according to journal guidelines. Similarly, Section 3. 3. subheadings of Influence factors are not set as per guidelines. Moreover, references are not set according to "Water”.
Responses：Thanks for reviewer’s suggestion.
According to the suggestion from reviewer, we have prepared the manuscript according to guidelines of this journal, including references, which is as follows.
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Spectic comments
(1) Line 88! Have the authors checked that UV/Vis detect RhB at 555 nm. If there is some reference cite it.
Responses：Thank you very much to point out this problem. We decided to detected RhB at 555 nm according to the UV/Vis spectrum in the range from 190nm to 800nm, which was shown as follows, and Boukherroub et al[10] also detected RhB at 555 nm.
(2) Line 169! Is it compassion or camparison? Kindly correct it.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have changed “compassion” to “comparison”.
(3) Line 173-175! "Compared with Nio-NiFe2O4/PMS system, Nio-NiFe2O4-rGO/PMS system exhibited a better removal effect and nearly 100% RhB was removed after 40 min while only 83.6% RhB was removed in the same condition The sentence is confusing! Make sure the clarity of sentence.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have rewritten this sentence, which is as followings.
NiO-NiFe2O4-rGO/PMS system exhibited a better removal effect, and nearly 100% RhB was removed after 40 min, while for NiO-NiFe2O4/PMS system, only 83.6% RhB was removed in the same condition.
(4) Line 176! Correct spelling activate.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have amended this error.
(5) Figure 6 The scale should be similar in both figures. For clarity Line 182 and 184! Cite figure.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have redrawn this figure.
(6) Figure 7! Confusing Since 0-60 min, rhb degradation is insignificantly affected by pms dosage! How authors decide the optimium pms dose as 1g/L.
Responses：Thank you very much to point out this problem. The removal rate of RhB increased from 80.0% to 90.7% with the PMS dosage increasing from 0.5 to 1.0 g·L-1 in 30 min, respectively, and then kept almost unchanged with initial PMS dosage further increasing to 2.5 g·L-1 at the catalyst dosage of 1.5 g·L-1. Therefore, we decided the optimum PMS dose as 1g/L, and we have rewritten this section in the manuscript.
(7) Line 204-205! Sentence structure need improvement.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have rewritten this section, which is as follows:
Fig. 7b showed the impact of initial PMS dosage on the removal of RhB at initial pH 7.00. The increase of PMS concentration could accelerate RhB degradation. The removal rate of RhB increased from 80.0% to 90.7% with the PMS dosage increasing from 0.5 to 1.0 g·L-1 in 30 min, respectively, and then kept almost unchanged with initial PMS dosage further increasing to 2.5 g·L-1 at the catalyst dosage of 1.5 g·L-1.
(8) Section 3. 3. What was the pH when author conduct experiments on rh b degradation in the presence of 1)NiO-NiFe2O4-rGO and 2)PMs dosage.
Responses：Thank you very much to point out this problem. PH was 7.0 when the influence of 1) NiO-NiFe2O4-rGO and 2) PMs dosage on the RhB degradation was investigated. We have amended relevant content in the manuscript.
(9) Section 3.3 What about at ph 9, do the authors observe similar phenomena as in the case of pH 11, where authors mentioned decrease in pH from 11 to 8.3?
Responses：Thank you very much to point out this problem. In this study, the reaction was under the pH of 8.3 actually when the initial pH value was 11.0, which decreased from 11.0 to 8.3 after the addition of the PMS. Therefore, a relatively high degradation efficiency was maintained at initial pH 11.
(10) Line 238-239! What make HPO42- to reduce degradation rate of RhB?
Responses：Thank you very much to point out this problem.
As reported in literature [24], phosphate ions demonstrated a scavenging effect for sulfate radical as well as hydroxyl radical. Moreover, phosphate ions have a more apparently abominable effect on the catalysts through chelating reactions, which decreases the active species on the catalyst surface. We have amended the related content in the manuscript.
(11) Line 273! Is it 270 or 555 nm. Since, in Methods section the authors mentioned 555 nm while in line 273, it is mentioned as 270 nm. Clarify it!
Responses：Thank you very much to point out this problem. The concentration of RhB was analyzed by a UV-Vis spectrophotometer (Shimadzu UV1700, Japan) at 555 nm. Identification of transformation products were detected by LC-MS at 270 nm.
(12) Line 310-316! Author contributions are not mentioned/ edited.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have rewritten this section as follows.
Author Contributions: Conceptualization, X.X. and F.L.; Methodology, X.X. and F.L.; Formal Analysis, X.X.; Investigation, F.L.; Resources, F.L.; Data Curation, F.L.; Writing-Original Draft Preparation, X.X.; Writing-Review & Editing, Q.Z.; Visualization, P.H.; Supervision, Q.Z. and F.Y.; Project Administration, F.Y.
(13) Remove Line 317-319.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have changed this section to “Funding: This research was funded by the National Key Scientific and Technological Project for Water Pollution Control and Management (2012ZX07202-002).”
(14) Line 323-329! Conflicts of Interest section is not edited.
Responses：Thank you very much to point out this problem. According to the suggestion from reviewer, we have filled in Conflicts of Interest section- Conflicts of Interest: The authors declare no conflict of interest.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Fig.2 with SEM images shall be modified.
It is better just to present to pictures with different magnifications, elements mapping is meaningless in this case.
Author Response
Reviewers' comments 2:
Fig.2 with SEM images shall be modified.
It is better just to present to pictures with different magnifications, elements mapping is meaningless in this case.
Response: Thanking for your helpful opinions. According to the suggestion from reviewer, we have replaced Figure 2b with a new picture with magnification of 40000, as shown in followings.
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript entitled “Nio-NiFe2O4-rGO magnetic nanomaterials for activated peroxymonsulfate Degradation of Rhodamine” describes the effect RhB in water and its removal due to the nanomaterials they have synthesis. XRD, TEM, SEM, etc are used to characterize the sample. Though there are some points the author need to address before being accepted for publication.
1. The paper title "Nio-NiFe2O4-rGO magnetic nanomaterials..." but the author didn't mention the magnetic properties of Nio-NiFe2O4-rGO and didn't talk the effect of its magnetic properties into RhB removal contribution. Only morphological discussion using XRD, TEM and SEM are not sufficient.
2. Introduction part is short compare to the body of the content and doesn’t have sufficient information to support the work.
3. There are several mis-print ([ ]) types of symbols. It might be due to the change from word to pdf but it should be corrected.
4. Figure 6 need to be well drawn.
5. Topics and sub-topics need to be rearranged according to the journal guidelines.
6. Conclusion part need to be supported by the main result and discussion section. It should be organize before being accepted for publication.
Author Response
Reviewers' comments 3:
The manuscript entitled “Nio-NiFe2O4-rGO magnetic nanomaterials for activated peroxymonsulfate Degradation of Rhodamine” describes the effect RhB in water and its removal due to the nanomaterials they have synthesis. XRD, TEM, SEM, etc are used to characterize the sample. Though there are some points the author need to address before being accepted for publication.
(1) The paper title "Nio-NiFe2O4-rGO magnetic nanomaterials..." but the author didn't mention the magnetic properties of Nio-NiFe2O4-rGO and didn't talk the effect of its magnetic properties into RhB removal contribution. Only morphological discussion using XRD, TEM and SEM are not sufficient.
Response: Thanks for reviewer’s kind question. According to the suggestion from reviewer, we have carried out VSM test to measure the magnetic properties of NiO-NiFe2O4-rGO magnetic nanomaterials and amended the related content in the manuscript.
Vibrating sample magnetometer MPMS-XL-7 (Quantum Design, USA) was used to measure the magnetic properties of NiO-NiFe2O4-rGO magnetic nanomaterials.
Figure 12b showed the hysteresis loop of NiO-NiFe2O4-rGO, which was measured at room temperature with a maximum applied field from −20 to 20 kOe. The saturation magnetization of NiO-NiFe2O4-rGO was determined to be 25.17 emu/g, which was strong enough to separate from the solution via external magnet (the inset of Figure 12a). Since NiO-NiFe2O4-rGO catalyst was a highly magnetic material, recovery of NiO-NiFe2O4-rGO catalyst from water could be easily implemented by placing an external magnet (neodymium) to keep NiO-NiFe2O4-rGO catalyst within the beaker and then the aqueous solutions were removed from the beaker. the weight changes before and after a recycle test was measured and it was found that the weight change (dry basis) was less than 1 wt%. Thus, no additional NiO-NiFe2O4-rGO catalyst was required for subsequent cyclic tests.
(2) Introduction part is short compare to the body of the content and doesn’t have sufficient information to support the work.
Response: Thanks for reviewer’s suggestion. According to the suggestion from reviewer, we have rewritten introduction, which is as shown in the manuscript.
(3) There are several mis-print ([ ]) types of symbols. It might be due to the change from word to pdf but it should be corrected.
Response: Thanking for your helpful opinions. According to the suggestion from reviewer, we have amended these errors.
(4) Figure 6 need to be well drawn.
Response: Thanks a lot for these valuable suggestions. According to the suggestion from reviewer, we have redrawn this figure as follows.
(5) Topics and sub-topics need to be rearranged according to the journal guidelines.
Response: Thanks a lot for this question. According to the suggestion from reviewer, we have rearranged according to the journal guidelines in the manuscript.
(6) Conclusion part need to be supported by the main result and discussion section. It should be organized before being accepted for publication.
Response: Thanks a lot for this valuable suggestion. According to the suggestion from reviewer, we have rewritten the Conclusion as follows.
In this study, we have demonstrated that NiO-NiFe2O4-rGO was an effective catalyst for the activation of peroxymonosulfate (PMS) to efficiently degrade RhB in aqueous solution. Elevated temperature and pH could improve RhB degradation efficiency by NiO-NiFe2O4-rGO activated PMS. The presence of HCO3- and Cl- were found to facilitate the removal of RhB. However, the addition of HPO42- noticeably hindered degradation process. Through quenching experiments and EPR spectroscopic analyses, NiO-NiFe2O4-rGO was proven to activate PMS to generate SO4-‧ and OH‧. The facile synthesis of the catalyst along with its stability and the simple experimental procedure hold promise for the investigation of NiO-NiFe2O4-rGO/PMS system for the decomposition of persistent organic chemicals. We believe these results may open up a new avenue for the design and preparation of various novel heterogeneous catalysts for PMS activation in advanced oxidation processes.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have answered all my questions and made proper revisions, thus I recommend its publication as its current form.
