Removal of Octinoxate, a UV-filter Compound, from Aquatic Environment Using Polydimethylsiloxane Sponge

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The idea of using floating, easily synthesized sponges as fully regenerable adsorbent materials for emerging contaminants is interesting and worthy of attention. However, substantial revisions are necessary.

In the "Materials and Methods" section, there is no dedicated paragraph describing how the adsorption measurements were carried out. It is unclear under what conditions these measurements were performed. Some information can be found in the "Results and Discussion" section (e.g., lines 145–147) or in the caption of Figure 2, but a clear and comprehensive picture is lacking. Including a graphical abstract-style figure to illustrate the methodology would be very helpful.

Similarly, the synthetic methodology should be represented with a graphical abstract-type image to improve clarity.

In section 2.3 of "Materials and Methods," certain properties of the synthesized sponges, such as density, are reported. These data should instead be presented in the "Results and Discussion"  section. Furthermore, it is not always clear how these properties were determined.

The main issue that raises concern is the use of an octinoxate amount in water that exceeds its solubility. What does it mean that the absorbance signal varies linearly with the amount of compound used up to an absorbance value of 1.25? What is the molar extinction coefficient at 300 nm? If the absorbance measurements were performed using an amount of octinoxate above its solubility limit, how can the absorbance start decreasing immediately from time zero? Maybe time zero is not time zero. The authors state that the surface area of the cuvettes used for the absorbance measurements is relatively large compared to the volume, and therefore the adsorption of octinoxate on the cuvette surfaces had to be considered. How was this accounted for?

Finally, it should be noted that there are no references in the text to Figure S-2 in the Supplementary Information.

In summary, the manuscript has good potential but requires major revisions.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors conducted a study on the removal of Octinoxate, a UV-filter compound, from the aquatic environment using a PDMS sponge. The authors prepared the PDMS sponge using a simple method. The applicability of the developed sponge for the removal of organic UV-filter compounds was thoroughly investigated, and overall, the manuscript is well written. Therefore, I recommend this manuscript for publication in Water after minor revision.

Comments for Revision:

1. Several statements in the introduction are not properly cited, particularly those in lines 58 to 61. The authors need to provide appropriate references for these claims.

2. A scale bar must be added to the optical microscope images in Figures e and f.

3. Error bars must be included in the relevant data plots to indicate variability and statistical significance.

4. It would strengthen the manuscript to include a more in-depth discussion on the adsorption mechanism to provide better insight into the interaction between the PDMS sponge and the UV-filter compound.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article describes a practical, environmentally friendly method of removing the organic UV filter compound octinoxate from aquatic environments using porous polydimethylsiloxane (PDMS) sponges. The study highlights the versatility of PDMS sponges in adsorbing low-solubility organic UV-filter compounds, while also presenting a simple and cost-effective preparation method. By utilizing easily accessible templates such as sugar and salt, the authors achieve tunable porosity, making the approach practical and scalable for large-scale applications.

The study primarily focuses on evaluating the effectiveness of PDMS sponges fabricated using different template materials for octinoxate removal through UV-Vis spectroscopy. Also it is demonstrated excellent recyclability of the PDMS sponges over multiple adsorption/desorption cycles. However, there are several issues that need to be addressed and clarified before the article can be considered for publication.

1. Although octinoxate is representative of many organic UV-filters, the article would benefit from broader testing against other UV-filter compounds with different structures (e.g. camphor derivatives, p-aminobenzoic acid)
2. To better assess the practical applicability of PDMS sponges, I recommend evaluating their adsorption performance in real water samples (river/lake water) with complex matrices (e.g. surfactants, organic matter).
3. The number of references cited in the article is relatively limited. To enhance the scientific context and support the methodology and discussion, additional relevant and recent references should be included.
4. The study assumes that adsorption is the primary mechanism for octinoxate removal, but it lacks a detailed mechanistic investigation. To support this assumption, the authors should include further analysis, such as surface interaction characterization (FTIR, SEM-EDS) and adsorption kinetics or isotherm modeling.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All issues raised and requests for modification have been fully addressed. No further comments from my side.

Author Response

We thank for her/his work and support.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have not addressed the reviewers’ request for additional experimental work. In its current form, the manuscript does not meet the journal's standards. I strongly recommend conducting further experiments, specifically evaluating the adsorption of additional compounds and assessing octinoxate adsorption in a real water matrix. This latter experiment is straightforward and essential—requiring only the spiking of a known concentration of octinoxate into a lake water sample and measuring adsorption under these realistic conditions.

 

Author Response

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