Zirconium Nanostructures Obtained from Anodic Synthesis By-Products and Their Potential Use in PVA-Based Coatings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript has great innovative significance in investigating preparation of nano-engineered superamphiphobic coatings with multiple high-level functionalities. The work can arouse wide interests of researchers in understanding the technique for fabricating superamphiphobic coatings via spray-coating method. The manuscript is interesting. In my frank opinion, the manuscript should be deserved for its final publication in such high-level Journal. However, the main comments to be solved are as follows:

1. Authors stated that “Primarily, the coated surface looks smooth due to the polymeric surface distribution.”. Why is the average roughness value of coated surface greater than that of uncoated surface?
2. The manuscript is pretty short. In the introduction, authors described that “In the coating field, the use of ZrO2 as an additive is known to improve abrasion resistance, thermal stabilityand its anti-corrosive properties [4-6].” Hence, anti-corrosive property of ZrO2-PVA coating should be evaluated in this work and then corrosion protection efficiency of the coating should be calculated according to the reference: Journal of Industrial and Engineering Chemistry 144 (2025) 496-511.
3. Dpi of Figure 5 should be further improved and scale needs to be added.
4. Captionof Figure 3 is “TEM-EDS-XRD Characterization of the ZrO2 nanostructures.” However, EDS result can not be seen here.
5. The reference is a little outdated, please update it. As seen in Results and Discussion about “These observations are in agreement with the expected behavior of inorganic nanomaterials, which improve the thermal performance of polymeric matrices [30]. ” Please include an article that points out that inorganic nanomaterials incorporating in polymeric matrix can improve thermal resistance.
6. In section “2. Coating preparation”, what is design basis of the experimental parameters?
7. Please conduct adhesion test of as-prepared coatings based on the ASTM D3359 to evaluate the adhesive strength.
8. Please make sure your conclusions' section highlights the findings of the experiment. Highlight the novelty of your study.

Author Response

This manuscript has great innovative significance in investigating preparation of nano-engineered superamphiphobic coatings with multiple high-level functionalities. The work can arouse wide interests of researchers in understanding the technique for fabricating superamphiphobic coatings via spray-coating method. The manuscript is interesting. In my frank opinion, the manuscript should be deserved for its final publication in such high-level Journal. However, the main comments to be solved are as follows:

Comment 1: Authors stated that “Primarily, the coated surface looks smooth due to the polymeric surface distribution.”. Why is the average roughness value of coated surface greater than that of uncoated surface?

We appreciate your observation. While the coated surface appears visually smoother due to the uniform distribution of the polymer matrix, the measured surface roughness (Ra) is influenced by micro- and nanoscale features introduced by incorporating ZrO₂ particles. Specifically, Ra represents the arithmetic mean of the deviations between peaks and valleys along the surface profile. Adding ZrO₂ increases the vertical distance between these features, increasing the Ra value. Thus, although the surface morphology appears macroscopically smooth, the microscopic topography contributes to a higher roughness value than the uncoated surface.

L211-222: The AFM topographic characterization also highlights the differences of uncoated (Figure 4g-h) and coated (Figure 4i and j) stainless steel. At a macroscopic level, the coated surface appears visually smoother due to the homogeneous distribution of the polymeric matrix. However, the average surface roughness (Ra) values were 106.25 nm and 182.37 nm for the uncoated and coated surfaces, respectively. This apparent contradiction is explained by the influence of nanoscale surface features introduced by the incorporation of ZrO2 structures. Although the polymer provides a uniform covering, the dispersed ZrO2 structures increase the vertical distance between peaks and valleys on the nanoscale, thereby elevating the Ra value. This behavior is consistent with the presence of ZrO2 observed in SEM images (Figure 4d–e), where the particles are distributed across the coated surface and contribute to a more complex topography within the polymeric matrix [23].

Comment 2: The manuscript is pretty short. In the introduction, authors described that “In the coating field, the use of ZrO2 as an additive is known to improve abrasion resistance, thermal stability and its anti-corrosive properties [4-6].” Hence, anti-corrosive property of ZrO2-PVA coating should be evaluated in this work and then corrosion protection efficiency of the coating should be calculated according to the reference: Journal of Industrial and Engineering Chemistry 144 (2025) 496-511.

We thank the reviewer for this valuable suggestion. We fully agree that evaluating the corrosion protection efficiency is critical in the comprehensive assessment of metal coatings. However, due to the scope and focus of the present work, we chose to limit our investigation to the structural and morphological influence of ZrO₂ addition, which are key factors that underlie coating performance.

We acknowledge that the anti-corrosive behavior of the ZrO₂–PVA coating system merits a dedicated and thorough investigation. Therefore, we are conducting a study specifically addressing corrosion resistance, which we plan to report separately. We have clarified this point in the revised manuscript to avoid ambiguity regarding the scope of the study.

L45-49: However, when used as coating, PVA shows some limitations, such as low thermal resistance and a tendency to wear out in extreme conditions [9,10]. When incorporating ZrO2 as an additive in PVA, it is expected to overcome these limitations, improving the coatings’ mechanical properties and thermal resistance, as well as polymer degradation [11–13].

 

Comment 3: Dpi of Figure 5 should be further improved and scale needs to be added.

We improved the quality of Figure 5 and added scale in Figure 5a.

 

Comment 4: Caption of Figure 3 is “TEM-EDS-XRD Characterization of the ZrO2 nanostructures.” However, EDS result can not be seen here.

Thank you for your observation. We made a mistake, EDS is placed in Figure 2. The caption of Figure 3 is now corrected in manuscript.

 

Comment 5: The reference is a little outdated, please update it. As seen in Results and Discussion about “These observations are in agreement with the expected behavior of inorganic nanomaterials, which improve the thermal performance of polymeric matrices [30]. ” Please include an article that points out that inorganic nanomaterials incorporating in polymeric matrix can improve thermal resistance.

We appreciate your suggestion to increase references. We added the following references in the manuscript.

(8)       Zeng, S.; Li, L.; Wang, Q. Structure-Property Correlation of Polyvinyl Alcohol Films Fabricated by Different Processing Methods. Polymer Testing 2023, 126, 108143. https://doi.org/10.1016/j.polymertesting.2023.108143.

(14)     Alshammari, K.; Alashgai, T.; Alshammari, A. H.; Abdelhamied, M. M.; Alotibi, S.; Atta, A. Effects of Nd2O3 Nanoparticles on the Structural Characteristics and Dielectric Properties of PVA Polymeric Films. Polymers 2023, 15 (20), 4084. https://doi.org/10.3390/polym15204084.

(15)     Hou, Z.; Chavez, S. E.; LaChance, A. M.; Jones, M. D.; French, C. D.; Walsh, A. M.; Shaw, M. T.; Sun, L. Polyvinyl Alcohol (PVA)/Montmorillonite (MMT) Nanocomposite Coatings via a Rotational Coating Method. Adv Compos Hybrid Mater 2024, 7 (5), 150. https://doi.org/10.1007/s42114-024-00965-9.

(16)     Wong‐Miramontes, I. M.; Valdez‐Salas, B.; Beltrán‐Partida, E.; Salvador‐Carlos, J.; Guillén‐Carvajal, K.; Castillo‐Saenz, J.; Moe, P.; Cheng, N. Development and Evaluation of Chitosan Active Films for Food Packaging Materials: A New Exoskeleton Source. ChemistrySelect 2025, 10 (14), e202402708. https://doi.org/10.1002/slct.202402708.

(20)     Wu, C.-H.; Chen, S.-Y.; Shen, P. On the Densification of Cubic ZrO2 Nanocondensates by Capillarity Force and Turbostratic C–Si–H Multiple Shell. Journal of Solid State Chemistry 2013, 200, 170–178. https://doi.org/10.1016/j.jssc.2013.01.028.

(24)     Ruzova, Т. А.; Haddadi, B. Surface Roughness and Its Measurement Methods - Analytical Review. Results in Surfaces and Interfaces 2025, 19, 100441. https://doi.org/10.1016/j.rsurfi.2025.100441.

(25)     Kaya, S.; Ozturk, O.; Arda, L. Roughness and Bearing Analysis of ZnO Nanorods. Ceramics International 2020, 46 (10), 15183–15196. https://doi.org/10.1016/j.ceramint.2020.03.055.

(28)     Alshammari, K. Influence of ZrO2 Nanoparticles on the Structural and Photocatalytic Properties of Three-Dimensional PVA/g-C3N4 Polymer Films. Journal of Alloys and Compounds 2024, 1003, 175622. https://doi.org/10.1016/j.jallcom.2024.175622.

 

Comment 6: In section “2. Coating preparation”, what is design basis of the experimental parameters?

We appreciate your question regarding the design basis of the experimental parameters. The selection of parameters such as the ZrO₂ loading, PVA concentration, stirring time, and drying conditions was based on a combination of literature precedents and preliminary optimization experiments in our laboratory. References [14–16] guided the formulation window to ensure film-forming capability and dispersion stability, particularly regarding the PVA concentration and polymer-to-ZrO₂ ratio. Additionally, initial trials were conducted to determine the optimal conditions to yield homogeneous coatings with good adhesion and minimal phase separation. These findings served as the basis for the final set of parameters reported in Section 2.

 

Comment 7: Please conduct adhesion test of as-prepared coatings based on the ASTM D3359 to evaluate the adhesive strength.

Please, find attached the evidence of ASTM D3359.

 

Comment 8: Please make sure your conclusions' section highlights the findings of the experiment. Highlight the novelty of your study.

We have improved the conclusion by highlighting the findings of the experiment.

L291-302: In this study, we successfully incorporated ZrO₂ nanostructures, specifically nanotube fragments with cubic crystallinity, into PVA-based coatings for application on 436 stainless steel. These nanostructures, obtained via anodic synthesis, exhibited average dimensions of 626.74 nm in width and 1906.39 nm in length. The resulting composite coating preserved the optical transparency of pure PVA while enhancing its UV absorption properties (optical bandgap reduced to 5.60 eV) and significantly improving thermal stability, particularly in the final pyrolysis stage. SEM and AFM analyses confirmed a homogeneous dispersion of the nanostructures, correlating with the observed enhancements. The novelty of this work lies in the use of ZrO₂ nanotube fragments as an additive to PVA, demonstrating for the first time their dual role in improving UV shielding and thermal resistance without compromising transparency. These findings position ZrO₂ nanostructures as promising functional additives for developing advanced polymer coatings for stainless steel protection.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The renewable application of ZrO2 by-product in the present paper is with high interest in the industry and science. Authors provided the surface, composition and thermal stablility characterization and results are acceptable. However, the scientific soundness could be improved with more corrections as suggested in the following,

Abstract>> 
1. we >>> delete. Try the objective expression
2. XRF, SEM-EDS...>>> the abrevation is not good in the first time
3. Try more objective data in the abstract part instead of adjective expression. For example, "significantly improve", how much??

 

Introduction
1. "said nanostructures">>> not good and try other expression.
2. line 44>> "it is expected">>>how and what?? please give the objective data.

 

Materials and Methods
1. Line 62>> subscript problem in chemical  formula
2. Line 57>> reference number is superscript

Results and discussion

Figures should be in vector graphic

EDS analyses are with the half quantitative consideration and the units are not present in the at.% or wt.%？

The anti-corrosion properties are not present and the introduction indicated such as in line 46.

The renewable application should provide the quantitative anlaysis such as the life cycle analysis.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

 

Correction suggestions have be added in the comments.

Author Response

The renewable application of ZrO2 by-product in the present paper is with high interest in the industry and science. Authors provided the surface, composition and thermal stablility characterization and results are acceptable. However, the scientific soundness could be improved with more corrections as suggested in the following,

Comment 1: Abstract>>

1. we >>> delete. Try the objective expression
2. XRF, SEM-EDS...>>> the abrevation is not good in the first time
3. Try more objective data in the abstract part instead of adjective expression. For example, "significantly improve", how much??

Thank you for your valuable suggestions. We have revised the abstract accordingly:

1. We removed the use of personal pronouns such as "we" to adopt a more objective tone.
2. The full names of analytical techniques are now introduced before their abbreviations.
3. Adjective expressions have been replaced or complemented with quantitative data where applicable. For instance, instead of saying "significantly improved," we now provide the specific improvement percentage or value.

L24-26: The results suggest that the ZrO2 nanostructures enhance the thermal and protective properties of the PVA based coatings by acting as physical barriers and stabilizers within the polymer matrix.

 

Comment 2: Introduction

1. "said nanostructures">>> not good and try other expression.
2. line 44>> "it is expected">>>how and what?? please give the objective data.
3. The phrase "said nanostructures" has been replaced with "such nanostructures" to maintain clarity and formality.
4. In line 44, the vague expression "it is expected" has been removed. Instead, we now refer to objective findings from previous studies. Specifically, we revised the sentence to:

L47-49: To address these limitations, the incorporation of ZrO₂ into PVA has been shown to improve mechanical properties, enhance thermal resistance, and reduce polymer degradation, as reported in previous studies [11–13].

 

 Comment 3: Materials and Methods

1. Line 62>> subscript problem in chemical formula

The chemical formula is already corrected.

 

2. Line 57>> reference number is superscript

The reference number is already in line with other references.

 

Comment 4: Results and discussion

Figures should be in vector graphic

The quality of the figures has been significantly improved, and they are now provided in high resolution, which ensures clear visualization of all elements. Given the level of detail and the original data format, vectorization is not applicable or may lead to information loss. Therefore, we respectfully suggest maintaining the current high-resolution format, which meets publication standards.

 

Comment 5: EDS analyses are with the half quantitative consideration and the units are not present in the at.% or wt.%？

Now, we included Mass % in EDS analyses.

 

Comment 6: The anti-corrosion properties are not present and the introduction indicated such as in line 46.

We fully agree that evaluating the corrosion protection efficiency is critical in the comprehensive assessment of metal coatings. However, due to the scope and focus of the present work, we chose to limit our investigation to the structural and morphological influence of ZrO₂ addition, which are key factors that underlie coating performance.

We acknowledge that the anti-corrosive behavior of the ZrO₂–PVA coating system merits a dedicated and thorough investigation. Therefore, we are conducting a study specifically addressing corrosion resistance, which we plan to report separately. We have clarified this point in the revised manuscript to avoid ambiguity regarding the scope of the study.

 

Comment 7: The renewable application should provide the quantitative analysis such as the life cycle analysis.

We thank the reviewer for this thoughtful suggestion. While we recognize the value of including a life cycle analysis to assess the environmental impact of renewable applications quantitatively, such an evaluation falls outside the scope of the current study, which is focused primarily on the material synthesis and preliminary characterization. A comprehensive life cycle analysis would require a separate and more extensive investigation, which we plan to address in future work.

 

Comment 8: Comments on the Quality of English Language

The English could be improved to more clearly express the research.

The new manuscript has been reviewed to improve English quality.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript investigates the characterization and application of ZrO₂ nanostructures by products, obtained from the anodic synthesis of Zr surfaces, as additives to enhance polyvinyl alcohol (PVA) coatings. The study is clearly structured and addresses an interesting and sustainable use of waste nanostructures. Therefore, I recommend minor revisions based on the following comments:

1. In the method section, the authors stated, “A total of 0.1907 ± 0.008 g of dried, filtered by-products were obtained” after anodic synthesis, yet they subsequently describe preparing a ZrO₂ suspension by “adding 0.5 g of the ZrO2 nanostructures”. The authors should clarify the yield obtained from anodization and address whether the seemingly low yield of ZrO₂ nanostructures would impact the practicality or scalability of the proposed application?
2. The font in the insert figure within Figure 5b is difficult to read.
3. In FTIR spectra, mark or clearly label the Zr–O bond peak in the ZrO₂–PVA spectrum. As currently presented, it is challenging to clearly identify this critical spectral feature.
4. Figures 5d and 5e lack clear sample labeling.
5. For the TGA results, the authors stated, “suggesting that these nanoparticles act as thermal barriers, providing additional stability to the PVA matrix”. However, does the shift in the maximum decomposition rate from 340 °C (pure PVA) to 315 °C (ZrO₂–PVA composite) suggests the reduced thermal stability? The authors should revisit this interpretation carefully, provide a clearer explanation.
6. The manuscript contains numerous typo errors, for example:

• Line 34: "properties oh these nanostructures" should be "properties of these nanostructures"
• Line 195: "the ZrO₂–PVA coating is notorious" is unclear and needs revision for clarity (possibly intended as "noteworthy"?)
• Line 222: "with the addition of addition of ZrO₂" should be corrected to "with the addition of ZrO₂."

Author Response

This manuscript investigates the characterization and application of ZrO2 nanostructures by products, obtained from the anodic synthesis of Zr surfaces, as additives to enhance polyvinyl alcohol (PVA) coatings. The study is clearly structured and addresses an interesting and sustainable use of waste nanostructures. Therefore, I recommend minor revisions based on the following comments:

 

Comment 1: In the method section, the authors stated, “A total of 0.1907 ± 0.008 g of dried, filtered by-products were obtained” after anodic synthesis, yet they subsequently describe preparing a ZrO₂ suspension by “adding 0.5 g of the ZrO2 nanostructures”. The authors should clarify the yield obtained from anodization and address whether the seemingly low yield of ZrO₂ nanostructures would impact the practicality or scalability of the proposed application?

We appreciate your observation. The 0.1907 ± 0.008 g refers specifically to the mass of the dried by-products obtained from a single anodization cycle under laboratory-scale conditions. To prepare the ZrO₂ suspension described later in the manuscript, a larger batch was used by pooling together multiple anodization runs to accumulate sufficient material for coating experiments. Regarding the practicality and scalability, we agree that the yield from a single run appears modest; however, the process parameters (e.g., electrode surface area, electrolyte volume, current density, and reaction time) can be scaled up in an industrial context to produce larger quantities.

 

Comment 2: The font in the insert figure within Figure 5b is difficult to read.

The quality of Figure 5 in general is already improved in the manuscript.

 

Comment 3: In FTIR spectra, mark or clearly label the Zr–O bond peak in the ZrO₂–PVA spectrum. As currently presented, it is challenging to clearly identify this critical spectral feature.

We agree that the Zr–O bond signal in the FTIR spectrum can be subtle and sometimes overlaps with other vibrational modes, particularly in composite systems. For this reason, we emphasize that the presence of ZrO₂ was confirmed through complementary characterization techniques, including EDS (which confirms elemental composition) and XRD (which confirms crystalline structure), providing robust evidence of the incorporation of ZrO₂ in the composite material.

 

Comment 4: Figures 5d and 5e lack clear sample labeling.

We added sample labeling to Figure 5d and 5e.

 

Comment 5: For the TGA results, the authors stated, “suggesting that these nanoparticles act as thermal barriers, providing additional stability to the PVA matrix”. However, does the shift in the maximum decomposition rate from 340 °C (pure PVA) to 315 °C (ZrO₂–PVA composite) suggests the reduced thermal stability? The authors should revisit this interpretation carefully, provide a clearer explanation.

We agree that the shift of the maximum decomposition rate from 340 °C (pure PVA) to 315 °C (ZrO₂–PVA composite) may initially indicate reduced thermal stability. However, upon closer analysis, this shift is attributed to a modified decomposition pathway introduced by the ZrO₂ nanoparticles, which may catalyze the onset of degradation. Despite the earlier onset, the overall thermal performance improves, as evidenced by the higher residual mass at 800 °C and weight loss suppression in the later decomposition stages. This behavior is consistent with literature reports on inorganic nanoparticle-reinforced polymers, where thermal barrier effects do not always coincide with a delayed peak degradation temperature but instead with increased char formation and altered degradation mechanisms. We have revised the manuscript text accordingly to provide a clearer interpretation.

L256-289: The thermal stability and decomposition behavior of PVA and ZrO2-PVA coatings were studied by thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG). The TGA and DTG curves of pure PVA coating (Figure 5d) and ZrO2-PVA composite coating (Figure 5e) reveal distinctive thermal degradation patterns.

The TGA curve of pure PVA shows an initial weight loss around 100 °C, attributed to evaporation of absorbed moisture. Between 250 °C and 400 °C, a significant weight loss is observed, corresponding to the decomposition of the PVA main chain. This process involves the elimination of hydroxyl groups and depolymerization of the PVA chains. The maximum rate of decomposition, as evidenced by the DTG peak, occurs at around 340 °C [34,35].

In contrast, the TGA curve of the ZrO2-PVA composite coating shows a similar initial weight loss, also due to moisture evaporation. However, the main thermal degradation point shifts towards slightly lower temperatures (315 °C), indicating a significant influence of the ZrO2 particles on the initial decomposition of the PVA. Despite this initial shift in the pyrolysis stage, the presence of ZrO2 shifts the final pyrolysis stage (445 °C) and decreases the magnitude of weight loss in the final stages of thermal degradation, thus suggesting that these nanoparticles act as thermal barriers, provid-ing additional stability to the PVA matrix [36,37].

Furthermore, the residual mass of the ZrO2-PVA compound at 800 °C is signifi-cantly higher (~20%) compared to pure PVA, which is due to the presence of thermally stable ZrO2 particles remaining after complete degradation of the organic matrix. These observations are in agreement with the expected behavior of inorganic nano-materials, which improve the thermal performance of polymeric matrices [38]. The incorporation of ZrO2 into the PVA matrix not only improves the thermal stability of the coating, but also modifies its decomposition mechanism, as observed in the broader and more complex DTG profile. These findings suggest that ZrO2 nanoparticles act as physical barriers and stabilizers in the polymer matrix, which could be beneficial for applications requiring a high temperature performance.

The improved thermal stability of the ZrO2-PVA compound coating highlights its potential for advanced applications, especially in high-temperature environments where pure PVA may not be enough. The ceramic nature of ZrO2 contributes to a higher residual weight, providing structural integrity even after the degradation of the polymeric component. This property could improve the durability and longevity of the coating, making it suitable for use in extreme thermal conditions.

Comment 6: The manuscript contains numerous typo errors, for example:

Line 34: "properties oh these nanostructures" should be "properties of these nanostructures"

Line 195: "the ZrO₂–PVA coating is notorious" is unclear and needs revision for clarity (possibly intended as "noteworthy"?)

Line 222: "with the addition of addition of ZrO₂" should be corrected to "with the addition of ZrO₂."

We attended all typo errors in the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors The manuscript has been carefully revised and can be accepted.

Reviewer 2 Report

Comments and Suggestions for Authors

No other comments

Reviewer 3 Report

Comments and Suggestions for Authors

The revised version has addressed all my concerns, and the manuscript can be accepted