Novel Fenton-like Catalyst HKUST-1(Cu)/MoS₂-3-C with Non-Equilibrium-State Surface for Selective Degradation of Phenolic Contaminants: Synergistic Effects of σ-Cu-Ligand and ≡Mo–OOSO₃⁻ Complex

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I received this article for review today and due to free time on weekend, I studied it in my first convenience. The article is a nice piece of work in the degradation of phenolic compounds. The authors presented the results in a good way to catch the readers attention. However, I have few challenging doubts in my mind about the applicability of your prepared materials. 

1. In heterogeneous Fenton systems, the leaching of ions from surface into the reaction medium is a big problem. How could this issue be tackled? Have you observed it in your case? Give your answer with reference to recent reports.

2. Most of the studies are focused on specific contaminants, however the industrial and pharmaceutical wastewaters contains mixture of several compounds. How could your prepared materials be applicable in that real time applications.

3. If you want to increase the impact of your research work, I suggest to add BET and DRS measurements of your prepared samples to validate your research. Specific surface area and band gap energy play major role in such complex mechanisms.

4. The mineralization products are mentioned in supplementary data. I suggest to add it in the main file because they are of more importance in such studies. 

5. What would be the cost estimation of your prepared materials on commercial scale? Is it a viable or not? 

6. Colored compounds are largely used in textile industry. What would be the feasiblilty of your prepared materials in the degradation of colored compounds.

Comments on the Quality of English Language

Minor corrections needed

Author Response

Replies to Referee: 1

I received this article for review today and due to free time on weekend, I studied it in my first convenience. The article is a nice piece of work in the degradation of phenolic compounds. The authors presented the results in a good way to catch the readers attention. However, I have few challenging doubts in my mind about the applicability of your prepared materials. 

1. In heterogeneous Fenton systems, the leaching of ions from surface into the reaction medium is a big problem. How could this issue be tackled? Have you observed it in your case? Give your answer with reference to recent reports.

Reply as: Thank you for your comment. Due to the dual reaction centre not only avoided the accumulation of high valence Mo and Cu but also prevented the invalid decomposition of PMS, we could conclude that the catalyst synthesized in this paper does not have metal ions leaching problems. Besides, the leached concentration of Mo and Cu ions after BPA degradation have been presented in the main file, as shown in section 3.2. The results show that the concentration of leached ions is lower than the limitations specified by the EU and US (< 2 ppm).

Reusability and stability of catalyst are important factors that related to the practical application. As expected, HKUST-1(Cu)-C/MoS₂-3-C exhibit satisfied stability. Even after five cycles, HKUST-1(Cu)-C/MoS₂-3-C could still maintain more than 80% degradation rate of BPA within 60 min (Figure 4a). The concentrations of Mo and Cu leached after reaction are detected, which are much lower than the limitation of standard proposed by EPA (Table S6). Besides, morphology and structure of HKUST-1(Cu)/MoS₂-3-C are not destroyed after successive experiments (Figure 4b), exhibiting the superior stability. In addition, an obvious increase proportion of Cu(I) from 35.09% to 55.53% and Mo(IV) from 93.22% to 95.40% are observed after reaction (Figure 4c-f), which suggests that PMS activation over HKUST-1(Cu)/MoS₂-3-C did not follow the electron transfer behavior of the classic Fenton reaction involving transition metal oxidized by oxidants. Thus the catalytic process is dominated by the synergistic effect of non-equilibrium-state surface, σ-Cu-ligand and ≡Mo-OOSO₃⁻ that directly capture electrons from phenolic compounds for PMS activation.

Figure 4. (a) Catalytic stability tests in five consecutive runs of HKUST-1(Cu)/MoS₂-3-C for BPA degradation; (b) SEM imagine of HKUST-1(Cu)/MoS₂-3-C before and after reaction; High-resolution XPS spectra of (c) and (d) Cu LMM; (e) and (f) Mo 3d for before and after reaction.

Table.S6 The leached concentration of Mo and Cu ions after BPA degradation

Metal ions	Mo	Cu
Concentration (mg/L)	0.7196	0.1565

 

2. Most of the studies are focused on specific contaminants, however the industrial and pharmaceutical wastewaters contains mixture of several compounds. How could your prepared materials be applicable in that real time applications.

Reply as: Thank you for your comment. Although industrial and pharmaceutical wastewater contain mixture of several compounds, phenolic contaminants are the most important pollutants in the wastewater of some specific industries, such as plastics, resins and insulating materials, so selective treatment of phenolic pollutants has good application prospects. In addition, the catalyst synthesized in this paper can also degrade pollutants by generating a variety of reactive oxygen species, so it could also play a good purification effect for multi-pollutant wastewater. Then, we are trying to conduct continuous operation research with actual wastewater, but the regulation of many process parameters of wastewater treatment, such as pH, oxidizer dosage, and hydraulic residence time, is not the focus of this paper due to space constraints, so it will be elaborated in the subsequent research papers.

 

3. If you want to increase the impact of your research work, I suggest to add BET and DRS measurements of your prepared samples to validate your research. Specific surface area and band gap energy play major role in such complex mechanisms.

Reply as: Already revised. Thank you for your comment. The specific surface area of a material is often used to prove that it has more active sites to further support the high catalytic activity of the material. The synthesized materials in this paper focus on the synergistic effect for selective removal of phenolic pollutants, and BET test results show that the catalyst has high specific surface area (208.9509 m²/g). In addition, band gap energy is only used to evaluate the performance of photocatalysts, thus it is not considered as the important characterization of Fenton-like catalysts.

Fig. S 5 BET surface area and pore distribution

 

4. The mineralization products are mentioned in supplementary data. I suggest to add it in the main file because they are of more importance in such studies. 

Reply as: Thank you for your comment. The degradation path map of BPA and its possible degradation products have been presented in the main file, as shown in section    3.3. The section in the supplementary is only specific measurement data.

The degradation intermediates of BPA over HKUST-1(Cu)/MoS₂-3-C are identified by ESI-MS analysis (Table S2-3, Figure S5-7), and the possible degradation pathways are proposed (Figure 5). On one hand, BPA was transformed to monohydroxylated BPA (m/z = 243.9) and 2,2-diphenylpropane (m/z = 195.1). Followed by the attack to alkyl carbon, these intermediates were decomposed to 4-hydroxyacetophenone (m/z = 135.0) and acetophenone (m/z = 117.9) respectively. On the other hand, the aromatic ring which was at the para-position of the phenolic hydroxyl group was initially hydroxylated to form 4-isopropylphenol (m/z = 135.1), hydroquinone (m/z = 109.0), and phenol (m/z = 93.0). With the proceeding of ring-rupturing reaction, the above phenolic compounds were decomposed to maleic acid (m/z = 116.9), glycerol (m/z = 92.0), glycolic acid (m/z = 77.0) and carbonic acid (m/z = 62.0), and finally mineralized into CO₂ and H₂O.

 

Figure 5. Possible degradation pathways of BPA in HKUST-1(Cu)/MoS₂-3-C+PMS system.

 

5. What would be the cost estimation of your prepared materials on commercial scale? Is it a viable or not?

Reply as: Thank you for your comment. The reagents used in the synthetic materials can be purchased in the market (not expensive), and the dosage of catalyst used in wastewater treatment is low. Thus it can be prepared on commercial scale and viable. 

 

6. Colored compounds are largely used in textile industry. What would be the feasiblilty of your prepared materials in the degradation of colored compounds.

Reply as: Thank you for your comment. The catalyst synthesized in this paper can degrade pollutants by generating a variety of reactive oxygen species, so it could also play a good purification effect for colored compounds. We added the degradation of RhB results (Fig. S6) in Supplementary Materials.

Fig. S6 Degradation of RhB

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The publication authored by Wang and colleagues provides research conducted on PMS activation using the novel catalyst HKUST-1(Cu)/MoS2-3-C represents a significant advancement in understanding the synergistic mechanisms involved in the selective degradation of phenolic compounds. The authors emphasize the synergistic effect of the σ-Cu-ligand and ≡Mo-OOSO3− complex in achieving a high degradation rate of phenolic contaminants and efficient utilization of PMS. Furthermore, it emphasizes the specific adsorption of phenolic compounds and PMS on the electron-poor Cu center and electron-rich Mo center, respectively, facilitating electron transfer for PMS activation.

Based on the following remarks, the manuscript holds the potential for acceptance in the context of publication:

1.      The manuscript could be further improved by refining the language to enhance its quality.

2.     In the abstract, please use the full name of PMS instead of the abbreviation.

Comments on the Quality of English Language

   The manuscript could be further improved by refining the language to enhance its quality.

Author Response

Replies to Referee: 2

The publication authored by Wang and colleagues provides research conducted on PMS activation using the novel catalyst HKUST-1(Cu)/MoS₂-3-C represents a significant advancement in understanding the synergistic mechanisms involved in the selective degradation of phenolic compounds. The authors emphasize the synergistic effect of the σ-Cu-ligand and ≡Mo-OOSO₃⁻ complex in achieving a high degradation rate of phenolic contaminants and efficient utilization of PMS. Furthermore, it emphasizes the specific adsorption of phenolic compounds and PMS on the electron-poor Cu center and electron-rich Mo center, respectively, facilitating electron transfer for PMS activation.

Based on the following remarks, the manuscript holds the potential for acceptance in the context of publication:

1. The manuscript could be further improved by refining the language to enhance its quality.

Reply as: Thank you for your comment. We have optimized the English writing in the revised manuscript.

2. In the abstract, please use the full name of PMS instead of the abbreviation.

Reply as: Thank you for your comment. We have revised the abstract and used the full name of PMS instead of the abbreviation.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors I have evaluated this MS carefully. This Ms could be considered for publication after response to the following comments. 1. The drawing and quality of figures and curves are very weak. Data on the curves and figures can be observed hardly. Please redraw all figure and tables and graphs. 2. Re-usability of this material as catalyst should be done. 3. Make sure all abbreviations are written out in full the first time used. This is particularly important in the abstract and the conclusions but work through the entire ms carefully from this perspective. 4. The advantages of these materials over similar reported photocatalysts should be added.

5. There are grammatical, syntax, or word usage errors in the manuscript. Please improve the English of this manuscript.

6. A schematic diagram for phocatalytic degradaion should be drawn together with cb and vb potential bands.

7. Some related references should be added and may be also used for comparison of the photocatalytic systems: ACS Appl. Mater. Interfaces., 2021, 13, 12463−12471; Molecules 2023, 28, 6848; J. Alloy. Compd, 2022, 897, 163178 and Mater. Today. Commum., 2022, 31,103514.

8. All the PXRD patterns of all compounds before and after degradation should be provided.

9. The possible mechanism is not explained clearly, and should further explain.

10. The number of repeated experiments should be mentioned in the legend of Figures.

11. Please add the mass yields of the products (in mg or g scale).

12. The wavelength of used UV-irradiation should be mentioned in the main text.

13. The relationship between structures and photocatalytic activity should be described. I think this theme is very interesting, but it is not clear why author use the catalyst.

Comments on the Quality of English Language

revise carefully

Author Response

Replies to Referee: 3

I have evaluated this MS carefully. This Ms could be considered for publication after response to the following comments. 

1. The drawing and quality of figures and curves are very weak. Data on the curves and figures can be observed hardly. Please redraw all figure and tables and graphs. 

Reply as: The quality of figures and curves are improved and can be observed easily in revised manuscript.

2. Re-usability of this material as catalyst should be done. 

Reply as: Re-usability of catalyst have been performed and show satisfied stability.

In section 3.2:

Reusability and stability of catalyst are important factors that related to the practical application. As expected, HKUST-1(Cu)-C/MoS₂-3-C exhibit satisfied stability. Even after five cycles, HKUST-1(Cu)-C/MoS₂-3-C could still maintain more than 80% degradation rate of BPA within 60 min (Figure 4a). The concentrations of Mo and Cu leached after reaction are detected, which are much lower than the limitation of standard proposed by EPA (Table S6). Besides, morphology and structure of HKUST-1(Cu)/MoS₂-3-C are not destroyed after successive experiments (Figure 4b), exhibiting the superior stability. In addition, an obvious increase proportion of Cu(I) from 35.09% to 55.53% and Mo(IV) from 93.22% to 95.40% are observed after reaction (Figure 4c-f), which suggests that PMS activation over HKUST-1(Cu)/MoS₂-3-C did not follow the electron transfer behavior of the classic Fenton reaction involving transition metal oxidized by oxidants. Thus the catalytic process is dominated by the synergistic effect of non-equilibrium-state surface, σ-Cu-ligand and ≡Mo-OOSO₃⁻ that directly capture electrons from phenolic compounds for PMS activation.

Figure 4. (a) Catalytic stability tests in five consecutive runs of HKUST-1(Cu)/MoS₂-3-C for BPA degradation; (b) SEM imagine of HKUST-1(Cu)/MoS₂-3-C before and after reaction; High-resolution XPS spectra of (c) and (d) Cu LMM; (e) and (f) Mo 3d for before and after reaction.

 

Table.S6 The leached concentration of Mo and Cu ions after BPA degradation

Metal ions	Mo	Cu
Concentration (mg/L)	0.7196	0.1565

 

 

3. Make sure all abbreviations are written out in full the first time used. This is particularly important in the abstract and the conclusions but work through the entire ms carefully from this perspective. 

Reply as: Thank you for your comment. We have revised the abstract and used the full name of PMS instead of the abbreviation.

 

4. The advantages of these materials over similar reported photocatalysts should be added.

Reply as: In fact, this manuscript reported a novel Fenton-like catalyst, not a photocatalyst.

 

5. There are grammatical, syntax, or word usage errors in the manuscript. Please improve the English of this manuscript.

Reply as: Thank you for your suggestion. We have revised the manuscript carefully including grammatical and other errors.

 

6. A schematic diagram for phocatalytic degradation should be drawn together with cb and vb potential bands.

Reply as: In fact, this manuscript studied on the Fenton-like degradation of BPA, not photodegradation reaction. Please review the manuscript and confirm the comments.

 

7. Some related references should be added and may be also used for comparison of the photocatalytic systems: ACS Appl. Mater. Interfaces., 2021, 13, 12463−12471; Molecules 2023, 28, 6848; J. Alloy. Compd, 2022, 897, 163178 and Mater. Today. Commum., 2022, 31,103514.
8. All the PXRD patterns of all compounds before and after degradation should be provided.
9. The possible mechanism is not explained clearly, and should further explain.
10. The number of repeated experiments should be mentioned in the legend of Figures.
11. Please add the mass yields of the products (in mg or g scale).
12. The wavelength of used UV-irradiation should be mentioned in the main text.

13.The relationship between structures and photocatalytic activity should be described.  think this theme is very interesting, but it is not clear why author use the catalyst.

 

Reply as（Q7-13）: In fact, this manuscript studied on the Fenton-like catalyst, not photocatalst. Please review the manuscript and confirm the comments. Our paper studies Fenton-like reactions, but most comments listed by reviewer 3 relative to photocatalytic reactions. Please confirm whether the wrong comment has been uploaded.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I accept authors responses and recommend acceptance

Comments on the Quality of English Language

Minor corrections needed

Reviewer 3 Report

Comments and Suggestions for Authors

accept