Hydroxypropyl-β-Cyclodextrin Improves Removal of Polycyclic Aromatic Hydrocarbons by Fe3O4 Nanocomposites
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this study “Hydroxypropyl-β-Cyclodextrin Improves the Removal of Polycyclic Aromatic Hydrocarbons by Fe₃O₄ Nanocomposites.” The author modified Fe3O4 based magnetic absorbents with hydroxypropyl-β-cyclodextrin polymer to enhance their absorption capacity for PAHs. As these nanomaterials are low cost and the author showed an improvement in the absorption capacity this work is worthful in the field of water treatment.
This study can be subjected to publication after some important revisions:
1. How does the author consider hydroxypropyl-β-cyclodextrin polymer as a low-cost material and is the modification method also cheap? i.e. chemical requirements. Please add some statements about it in the manuscript.
2. Since you have done absorption experiments, some of the important investigations are missing here. i.e. application of isotherms like Langmuir, Freundlich, or Temkin isotherm fitting to evaluate adsorption capacity and mechanism. These methods are important to relate your work with other studies in literature. I am sure you don’t need to perform additional experiments for it.
3. A comparison of the absorption performance of your modified material with the commonly applied material is missing here. i.e. GAC (as mentioned in this study). If you cannot perform additional experiments a comparison with the literature is necessary.
4. Reviewer is not satisfied with the adsorption mechanism described by the author because some of the important characterizations are missing in the study i.e. what was the surface area of the modified material compared to the Fe3O4 (BET analysis). Zeta potential analysis is also missing to explain the mechanism.
5. Were the experiments performed in triplicate? How to authenticate the results without them.
6. How will this material work with the presence of organics in the real water system. Please mention this via literature support.
7. Please mention the magnetic power required for this material to be separated from the treated water. Large scale system uses electric magnets to operate this task. Energy requirement analysis is compulsory.
Author Response
- How does the author consider hydroxypropyl-β-cyclodextrin polymer as a low-cost material and is the modification method also cheap? i.e. chemical requirements. Please add some statements about it in the manuscript.
Thank you for pointing this out. we agree with this comment. The hydroxypropyl-β-cyclodextrin polymer was synthesized through cross-linking of hydroxypropyl-β-cyclodextrin with epichlorohydrin. The HP-β-CDCP/Fe₃O₄ nanocomposites were prepared using reagents of analytical grade, including hydroxypropyl-β-cyclodextrin, methanol, ethanol, epichlorohydrin, acetone, sodium chloroacetate, ferrous sulfate, and ferric chloride, all of which were relatively low in cost. The detailed information could be found in 2.1 and 2.2.
- Since you have done absorption experiments, some of the important investigations are missing here. i.e. application of isotherms like Langmuir, Freundlich, or Temkin isotherm fitting to evaluate adsorption capacity and mechanism. These methods are important to relate your work with other studies in literature. I am sure you don’t need to perform additional experiments for it.
Agree. The study of adsorption isotherms and adsorption thermodynamics have been added on page 13-14, in section 3.3, 3.4.
- A comparison of the absorption performance of your modified material with the commonly applied material is missing here. i.e. GAC (as mentioned in this study). If you cannot perform additional experiments a comparison with the literature is necessary.
Agree. The absorption performance of this modified material was compared with other literatures in section 3.7.
- Reviewer is not satisfied with the adsorption mechanism described by the author because some of the important characterizations are missing in the study i.e. what was the surface area of the modified material compared to the Fe3O4 (BET analysis). Zeta potential analysis is also missing to explain the mechanism.
Agree. BET characterization can provide insights extending beyond surface area and pore size analysis. Although the analysis has been initiated and remains ongoing, full results are not yet available for inclusion in the present work due to time constraints. We plan to report the complete dataset in a subsequent publication, accompanied by a more detailed examination of the underlying mechanisms.
- Were the experiments performed in triplicate? How to authenticate the results without them.
The error bars have been added to support reproducibility.
- How will this material work with the presence of organics in the real water system. Please mention this via literature support.
Cyclodextrin exhibits a dual selective mechanism based on "hydrophobic matching–size matching." As reported in the literature (e.g., Hua et al., Environmental Pollution, 2007), the cyclodextrin cavity shows a preferential affinity for hydrophobic PAH molecules. Consequently, the HP-β-CD/Fe₃O₄ composite material is expected to retain a degree of targeted removal capability in practical applications. We will focus on studying the specific impacts of coexisting organic substances as the key research content in the future.
- Please mention the magnetic power required for this material to be separated from the treated water. Large scale system uses electric magnets to operate this task. Energy requirement analysis is compulsory.
On the sixth page of the paper, we added the VSM characterization, and the results showed that the HP-β-CDCP/Fe₃O₄ nanocomposites still maintained strong magnetic properties, enabling effective magnetic separation under an external magnetic field.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. Abstract: Please summarize this part and add important results to this section, not details. Select keywords from MeSH.
2. Introduction: Please provide more description about PAHs and the selected PAHs for this study with attention to human and environmental exposure and WHO and EPA standards. Better explain your novelty and aims of the study.
3. Methods: Cite the adsorbent synthesis references. How to determine pHpzc? How did you study adsorption isotherms? I suggest using the appropriate and high quality papers for improve your work.
4. Results: Your results were presented very briefly and need more description and scientific and strong discussion. With details, explain functional groups in FTIR and cite the related references. In the elemental analysis, what are the element percentages and elemental distribution? Where is the XRD analysis? Where is VSM analysis based on the magnetic feature? Where is the BET analysis for determining surface area?
5. Effective parameters need scientific discussion. The increasing or decreasing removal efficiency affect parameters? Why did not study adsorption isotherms for determining the type of adsorption? I suggest investigating the removal efficiency on real samples.
6. Conclusion: This section needs to improve the quantitative and qualitative aspects of your results and description.
7. There are many typos and grammatical errors.
8. Use newer references, like suggested papers or other papers in the databases.
Author Response
- Abstract: Please summarize this part and add important results to this section, not details. Select keywords from MeSH.
Thank you for pointing this out. we agree with this comment. The abstract and keywords in the paper have been revised.
- Introduction: Please provide more description about PAHs and the selected PAHs for this study with attention to human and environmental exposure and WHO and EPA standards. Better explain your novelty and aims of the study.
The introduction has been revised as per the requirements.
- Methods: Cite the adsorbent synthesis references. How to determine pHpzc? How did you study adsorption isotherms? I suggest using the appropriate and high quality papers for improve your work.
The study of adsorption isotherms and adsorption thermodynamics have been added on page 13-14, in section 3.3, 3.4.. And the references have been replaced.
- Results: Your results were presented very briefly and need more description and scientific and strong discussion. With details, explain functional groups in FTIR and cite the related references. In the elemental analysis, what are the element percentages and elemental distribution? Where is the XRD analysis? Where is VSM analysis based on the magnetic feature? Where is the BET analysis for determining surface area?
The analysis of the HP-β-CDCP/Fe3O4 nanocomposite material has been revised. XRD and VSM analysis have been added. BET characterization can provide insights extending beyond surface area and pore size analysis. Although the analysis has been initiated and remains ongoing, full results are not yet available for inclusion in the present work due to time constraints. We plan to report the complete dataset in a subsequent publication, accompanied by a more detailed examination of the underlying mechanisms.
- Effective parameters need scientific discussion. The increasing or decreasing removal efficiency affect parameters? Why did not study adsorption isotherms for determining the type of adsorption? I suggest investigating the removal efficiency on real samples.
The study of adsorption isotherms has been added. At 298.15 K, the maximum adsorption capacity of HP-β-CDCP/Fe₃O₄ nanocomposites was evaluated by varying the initial concentrations of Ant and Bap. The experimental data were fitted using the Langmuir equation and the Freundlich equation. Comparative analysis of the linear correlation coefficients revealed that the R² values for PAHs in the Freundlich isothermal model (Ant: 0.9838; Bap: 0.9903) were higher than those in the Langmuir model (Ant: 0.9747; Bap: 0.9838), suggesting a heterogeneous adsorption surface and the occurrence of multilayer adsorption. Furthermore, all 1/nF values were less than 1, indicating a nonlinear relationship between analyte concentration and adsorption ca-pacity. This implies that while analyte concentration influences adsorption, other factors—such as chemical interactions—also contribute significantly, thereby enhancing the overall adsorption potential.
- Conclusion: This section needs to improve the quantitative and qualitative aspects of your results and description.
The conclusion section of this paper has already been revised.
- There are many typos and grammatical errors.
These errors have already been corrected.
- Use newer references, like suggested papers or other papers in the databases.
The literatures have been replaced.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsManuscript ID: magnetochemistry-3996325
Manuscript Title: Hydroxypropyl-β-Cyclodextrin Improves the Removal of Poly- 2 cyclic Aromatic Hydrocarbons by Fe3O4 Nanocomposites
The manuscript addresses the synthesis and application of hydroxypropyl-β-cyclodextrin polymer-modified Fe₃O₄ nanocomposites for removal of PAHs from aqueous solution. While the study has potential environmental relevance, the current version lacks sufficient material characterization and in-depth mechanistic insight. Major experimental gaps and insufficient data interpretation limit the scientific rigor and reproducibility of the work. Detailed comments are provided below.
- The characterization of the Fe₃O₄ and Fe₃O₄/HP-β-CDCP composites relies mainly on FTIR, elemental analysis, and a single TEM image. This is inadequate to confirm successful surface modification and structure-property correlation; XPS must be performed.
- For a magnetic nanocomposite study, Vibrating Sample Magnetometry (VSM) or magnetization curve analysis is essential to demonstrate the magnetic strength, coercivity, and remanence, which determine separability and reusability. This omission weakens the “magnetic” claims.
- BET surface area and pore size distribution analyses are crucial to understand adsorption performance. The absence of BET data prevents assessment of how polymer coating influences surface characteristics and adsorption efficiency.
- XRD analysis is missing. X-ray diffraction should be performed to confirm the crystalline nature and phase purity of Fe₃O₄ after modification.
- The band gap or optical absorption characteristics (UV–Vis DRS) were not studied. This could provide insights into possible electronic changes upon modification.
- The TEM image (Figure 5) is superficially discussed. No scale bar measurements, particle size distribution, or morphological consistency are provided. High-resolution TEM or SAED pattern should be added to confirm structural homogeneity.
- The “effect of operation parameters” section presents very basic optimization (pH, temperature, time, dose, and volume) with limited interpretation. No mechanistic explanation or adsorption thermodynamics (ΔH, ΔG, ΔS) are provided.
- Common adsorption models such as Langmuir and Freundlich should be applied to determine maximum adsorption capacity and surface heterogeneity. Their absence limits quantitative comparison with literature.
- Only pseudo-first and pseudo-second-order models were tested. Intraparticle diffusion or Elovich models could further clarify rate-controlling mechanisms.
- The manuscript lacks comparison with other Fe₃O₄-based or cyclodextrin-based adsorbents reported in recent literature to justify performance claims.
- The study uses “simulated wastewater,” but no real environmental samples were tested. Validation with real wastewater would enhance application credibility.
- The link between HP-β-CDCP coating thickness, surface functionality, and PAH adsorption efficiency is not quantified.
- The authors mention higher adsorption efficiency for modified Fe₃O₄, but do not discuss possible trade-offs in magnetic recovery efficiency due to polymer coating.
- Some formulas and units (e.g., mg g⁻¹, μg L⁻¹) are inconsistently formatted. Standard SI unit presentation should be ensured.
- The abstract and conclusion repeat the same data without analytical or predictive insight.
- Revise figures for clarity and add error bars to support reproducibility.
- The possibility of π–π stacking, hydrophobic interactions, van der Waals forces, and hydrogen bonding should be explored, especially since PAHs are aromatic and cyclodextrin derivatives often adsorb via multi-mode interactions.
- The authors should provide a schematic diagram of the proposed adsorption mechanism showing host–guest inclusion and surface binding sites on Fe₃O₄.
- Thermodynamic parameters such as ΔH, ΔS, and ΔG were not determined. These values are critical to clarify whether the adsorption process is endothermic or exothermic and to differentiate between physisorption and chemisorption.
Comments for author File: Comments.pdf
Author Response
1.The characterization of the Fe₃O₄ and Fe₃O₄/HP-β-CDCP composites relies mainly on FTIR, elemental analysis, and a single TEM image. This is inadequate to confirm successful surface modification and structure-property correlation; XPS must be performed.
Thank you for pointing this out. we agree with this comment. Due to the tight schedule for revising the manuscript, no research has been conducted on XPS, we will give it more attention in our subsequent research work. The analysis of the HP-β-CDCP/Fe3O4 nanocomposite material has been revised and XRD, VSM analysis were added.
2. For a magnetic nanocomposite study, Vibrating Sample Magnetometry (VSM) or magnetization curve analysis is essential to demonstrate the magnetic strength, coercivity, and remanence, which determine separability and reusability. This omission weakens the “magnetic” claims.
VSM analysis has been added on page 6, in section 3.1.
3. BET surface area and pore size distribution analyses are crucial to understand adsorption performance. The absence of BET data prevents assessment of how polymer coating influences surface characteristics and adsorption efficiency.
Agree. BET characterization can provide insights extending beyond surface area and pore size analysis. Although the analysis has been initiated and remains ongoing, full results are not yet available for inclusion in the present work due to time constraints. We plan to report the complete dataset in a subsequent publication, accompanied by a more detailed examination of the underlying mechanisms.
4. XRD analysis is missing. X-ray diffraction should be performed to confirm the crystalline nature and phase purity of Fe₃O₄ after modification.
XRD analysis has been added on page 6, in section 3.1.
5. The band gap or optical absorption characteristics (UV–Vis DRS) were not studied. This could provide insights into possible electronic changes upon modification.
Due to the tight schedule for revising the manuscript, we will give this study more attention in our subsequent research work.
6. The TEM image (Figure 5) is superficially discussed. No scale bar measurements, particle size distribution, or morphological consistency are provided. High-resolution TEM or SAED pattern should be added to confirm structural homogeneity.
Due to the tight deadline for revising the manuscript, I'm very sorry that I was unable to provide more detailed information.
7. The “effect of operation parameters” section presents very basic optimization (pH, temperature, time, dose, and volume) with limited interpretation. No mechanistic explanation or adsorption thermodynamics (ΔH, ΔG, ΔS) are provided.
The study of adsorption thermodynamics have been added on page 16, in section 3.5.
8. Common adsorption models such as Langmuir and Freundlich should be applied to determine maximum adsorption capacity and surface heterogeneity. Their absence limits quantitative comparison with literature.
The study of adsorption isotherms have been added on page 16, in section 3.4.
9. Only pseudo-first and pseudo-second-order models were tested. Intraparticle diffusion or Elovich models could further clarify rate-controlling mechanisms.
The study of Elovich models have been added on page 13, in section 3.3.
10. The manuscript lacks comparison with other Fe₃O₄-based or cyclodextrin-based adsorbents reported in recent literature to justify performance claims.
The comparison with other cyclodextrin-based adsorbents was listed on page 19, in section 3.7.
11. The study uses “simulated wastewater,” but no real environmental samples were tested. Validation with real wastewater would enhance application credibility.
Cyclodextrin exhibits a dual selective mechanism based on "hydrophobic matching–size matching." As reported in the literature (e.g., Hua et al., Environmental Pollution, 2007), the cyclodextrin cavity shows a preferential affinity for hydrophobic PAH molecules. Consequently, the HP-β-CD/Fe₃O₄ composite material is expected to retain a degree of targeted removal capability in practical applications.
12. The link between HP-β-CDCP coating thickness, surface functionality, and PAH adsorption efficiency is not quantified.
Our characterization (such as FTIR, XRD, VSM) and adsorption performance studies have basically qualitatively demonstrated the existence of the coating, the success of functionalization, and the resulting performance improvement.
13. The authors mention higher adsorption efficiency for modified Fe₃O₄, but do not discuss possible trade-offs in magnetic recovery efficiency due to polymer coating.
VSM analysis has been added on page 6, in section 3.1. The HP-β-CDCP/Fe₃O₄ nano-composites still maintained strong magnetic properties, enabling effective magnetic separation under an external magnetic field.
14. Some formulas and units (e.g., mg g⁻¹, μg L⁻¹) are inconsistently formatted. Standard SI unit presentation should be ensured.
These errors have already been corrected.
15. The abstract and conclusion repeat the same data without analytical or predictive insight.
The abstract and conclusion have both been revised.
16. Revise figures for clarity and add error bars to support reproducibility.
The figures have been revised.
17. The possibility of π–π stacking, hydrophobic interactions, van der Waals forces, and hydrogen bonding should be explored, especially since PAHs are aromatic and cyclodextrin derivatives often adsorb via multi-mode interactions.
The adsorption mechanism of polycyclic aromatic hydrocarbons (PAHs) onto the modified cyclodextrin-Fe₃O₄ composite appears to be governed by a combination of multiple interactions, as supported by kinetic, isotherm, and thermodynamic analyses. The Freundlich model provided an excellent fit to the experimental data, while the spontaneous and exothermic adsorption process, accompanied by a positive entropy change (ΔS), suggests that hydrophobic interactions and physisorption—such as van der Waals forces—play a dominant role. These interactions facilitate the transfer of hydrophobic PAHs from the aqueous phase to the non-polar regions of the adsorbent. Additionally, π–π stacking is likely enabled by the presence of aromatic rings in both the PAH molecules and the phenyl-functionalized cyclodextrin derivative. Consequently, the high adsorption efficiency can be ascribed to this synergistic multi-mode interaction mechanism—a distinguishing feature of cyclodextrin-based adsorbents.
18. The authors should provide a schematic diagram of the proposed adsorption mechanism showing host–guest inclusion and surface binding sites on Fe₃O₄.
Due to the tight schedule for revising the manuscript, If necessary, we will add the schematic diagram of the adsorption mechanism later.
19. Thermodynamic parameters such as ΔH, ΔS, and ΔG were not determined. These values are critical to clarify whether the adsorption process is endothermic or exothermic and to differentiate between physisorption and chemisorption
The adsorption thermodynamics have been studied on page 16, in section 3.5..
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThis work is ready to be published
Author Response
We sincerely appreciate the reviewer for the positive evaluation and constructive feedback on our manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear authors,
In the revised manuscript, some concerns were not addressed. There are many issues with the results and discussion. Please accurately and rigorously check the following concerns. I suggest a major revision:
1. The presented results for characterization analysis are very cursory. Please pay attention to the details of these analyses and discuss scientifically for them.
2. The effective factors are very poorly written and discussed. Why does a pH change affect adsorption? Why does the adsorbent dose affect adsorption? etc... I suggest investigating at least 4 isotherms and 4 kinetics for your adsorption.
3. Please investigate your optimum process on real samples.
4. There are a few details for the regeneration and reusability of the adsorbent. Please mention the whole results with details, and investigate the characterization analyses for the regenerated adsorbent.
5. The comparative table needs more study investigation, and more details of the studies.
Author Response
Comments 1.The presented results for characterization analysis are very cursory. Please pay attention to the details of these analyses and discuss scientifically for them.
Response 1: Thank you for pointing this out. we agree with this comment. To address the concern about the cursory characterization results, we have revised and expanded the details of all characterization analyses (including TEM, FT-IR, etc.) in the revised manuscript. Additionally, we have added a new BET characterization to further reveal the porous structure of the nanocomposites.
Comments 2. The effective factors are very poorly written and discussed. Why does a pH change affect adsorption? Why does the adsorbent dose affect adsorption? etc... I suggest investigating at least 4 isotherms and 4 kinetics for your adsorption.
Response 2: Agree. We are grateful to the reviewer for pointing out this critical deficiency, which has guided us to substantially improve the scientific rigor of our manuscript. To address this comment, we have comprehensively revised and expanded the section on influencing factors (pH and adsorbent dosage).
In our study, we employed 3 kinetic models (pseudo-first-order, pseudo-second-order, Elovich) and 2 isotherm models (Langmuir, Freundlich) to analyze PAHs adsorption onto HP-β-CDCP/Fe3O4 nanocomposites, along with thermodynamic analysis at three temperatures.The kinetic models adequately distinguished physisorption/chemisorption contributions and verified the heterogeneous surface interaction mechanism. The Langmuir and Freundlich models clearly revealed the heterogeneous and multilayer adsorption characteristics of the system.Additionally, thermodynamic parameters further elucidated the spontaneous and exothermic nature of adsorption. We consider the current model set sufficient to comprehensively clarify the adsorption mechanism.We hope this explanation can address the reviewer’s concern and are willing to provide further data if needed.
Comments 3. Please investigate your optimum process on real samples.
Response 3: We sincerely appreciate the reviewer for this insightful suggestion. Due to the limitations of sample collection and the difficulties in obtaining water samples containing 15 types of polycyclic aromatic hydrocarbons, we were unable to conduct experiments on actual wastewater samples in this current study. To partially verify the practical potential of the HP-β-CDCP/Fe3O4 nanocomposites, we instead evaluated their PAHs removal performance in simulated wastewater (Section 3.6.2 of the manuscript).This outcome preliminarily confirms the feasibility of the adsorbent for treating PAHs-polluted water matrices. According to previous studies, cyclodextrin exhibits a dual selective mechanism based on "hydrophobic matching–size matching." As reported in the literature (e.g., Xie et al., Analyst, DOI:10.1039/c0an00076k), the cyclodextrin cavity shows a preferential affinity for hydrophobic PAHs molecules. Consequently, the HP-β-CD/Fe₃O₄ composite material is expected to retain a degree of targeted removal capability in practical applications. We fully agree that testing on real samples is essential for further validating the practical value of this material, and we will incorporate it as an important part of our future work.
Comments 4. There are a few details for the regeneration and reusability of the adsorbent. Please mention the whole results with details, and investigate the characterization analyses for the regenerated adsorbent.
Response 4: We sincerely appreciate the reviewer’s insightful suggestion to supplement the details of adsorbent regeneration and reusability, to address this concern, we have made comprehensive revisions on page 12, in section 3.6.1.
Comments 5. The comparative table needs more study investigation, and more details of the studies.
Response 5: Agree. we have supplemented the analysis content and the comparison table ( Table 7; page 14).
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have thoroughly addressed all the concerns raised in the previous round of review. The revisions have been completed satisfactorily, and the manuscript has been significantly improved. I recommend the acceptance of the manuscript in its present form.
Author Response
We sincerely appreciate the reviewer for the positive evaluation and constructive feedback on our manuscript.
