Adsorption of Sunscreen Compounds from Wastewater Using Commercial Activated Carbon: Detailed Kinetic and Thermodynamic Analyses

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work by Gheorghe et al. reported the adsorption of several sunscreen compounds with activated carbon. The following issues should be addressed:

(1)    Please provide more information for the wastewater samples. For example, where were the samples obtained? Did the authors measure their proprieties, such as pH, COD, etc.?

(2)    Please discuss the adsorption mechanisms in detail by additional experimental results. For example, FTIR spectra of the carbon samples after adsorption may provide some information.

(3)    Please pay more attention to the format of the manuscript. For example, the unit for enthalpy change was wrong in Table 4.

(4)    Please provide a comparison of the adsorption results with those in previous works.

Author Response

Please see the attachment!

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this manuscript, Gheorghe et al reported the detail investigation of the the removal several compounds which are found in cosmetics especially sunscreen using commercially available activated carbon (AC). The study includes the detail thermodynamic and kinetic analysis of the adsorption, which was performed by using batch adsorption experiments. Adsorption materials play a crucial role in the environmental remediation processes, particularly, for the removal of some of the hazardous organic compounds from waste water. The study on the removal of targeted compounds such as the substances found in sunscreen using readily available material is desirable. The concept and approach of the study is executed well, however, the characterization, explanation and language of the manuscript has to be significantly improved. Therefore, it is only suggested for publication after the authors consider the following major revisions.

The reviewer suggests to change the title of the manuscript, such as,

·       “Adsorption of sunscreen compounds from wastewater using commercial activated carbon: Detailed kinetic and thermodynamic analyses”

·       First sentence of the abstract is unclear, indeed there are several other mistakes in the abstract such as, high chromatography (line 22)?

·        The quality of figure 2 is not good should be replaced, the authors have claimed that the IR peaks represents some functional groups, should provide more details about these functional groups.

·       Together with SEM, EDX will shed some light on the presence of other elements in the AC.

·       Heterogeneous pores? Line 220

·       Introduction should be improved, the flow of information is not in order

·       What about the nature of the sample, is it crystalline or amorphous?

·       Schemes of the preparation of catalysts and also for the organic transformation are necessary.

·       Compare the efficiency of AC in this study with other studies where it was used to remove similar hazardous organic substances

·       How did the identity of organic waste compounds confirmed, no data is provided? It is mentioned in the experimental section about the LC-MS but results are not given

·       Extensive English changes are required (Authors must carefully read the manuscript and work on sentence construction and use of prepositions and tenses. The composition of the manuscript should also be improved, as several paragraphs are very short which should be merge with other to enhance readability.

·       Cite some recent references about the application of nanomaterials for environmental remediation such as,

“Saif, Sadia, et al. "Adsorption studies of arsenic (V) by CuO nanoparticles synthesized by phyllanthus emblica leaf-extract-fueled solution combustion synthesis." Sustainability 13.4 (2021): 2017.”

Sabzehmeidani, Mohammad Mehdi, et al. "Carbon based materials: A review of adsorbents for inorganic and organic compounds." Materials Advances 2.2 (2021): 598-627.

 

Comments on the Quality of English Language

extensive language corrections are required

Author Response

Please see the attachment!

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. Lines 83-87 begin with the phrase “Although the literature abounds with studies on the removal of organic contaminants ...” and then they are listed, not a single reference to the literature is given, although in this case, this is more than necessary.

2. The experimental part (line 143) states that the studies were carried out at pH 3, 5, 7, 9, and 11, but the results obtained are also given for pH 1. Correct the experimental part.

Also, add an explanation as to why studies at pH greater than 11 were not included.

3. In addition to %R and g_e, the distribution coefficient is generally accepted to describe the results of sorption experiments. The authors can easily calculate it based on the data they have. This will allow readers to compare their results with a large number of results from other researchers.

4. The drawings are unclear and difficult to perceive. The labels and display should be made larger and clearer, especially in Figure 2.

5.  In lines 401-404 authors talk about the correspondence of kinetic models to the process being studied, but the authors only state the results obtained and do not draw absolutely any conclusions from them.

Unfortunately, a similar presentation of the kinetics results is repeated in the conclusions.

6. In the entire manuscript, the format of the links provided needs to be reconsidered. Avoid lumping links together. Instead, summarize the main contribution of each referenced article in a separate sentence. This will make the article more informative and useful for readers.

Author Response

Please see the attachment!

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed all the comments, it can now be accepted for the publication

Comments on the Quality of English Language

minor changes are still required

Author Response

Dear Reviewer 2

Thank you for reading the article carefully and for your time. The manuscript has been revised and corrected according to your suggestion.

Gheorghe Stefania

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have significantly improved the manuscript.

However, after the improvement, two new observations appeared:

1. The formula for calculating the distribution coefficient used by the authors is very different from the generally accepted one [1 - 3]:

K_d = [(C₀ - C_e)*V]/(C_e*m) = Q_e/C_e.

It is not possible to derive the generally accepted formula from your formula. I ask you to correct the formula and recalculate the distribution coefficients using the generally accepted formula.

 

2. The authors concluded that the pseudo-second order kinetic model describes adsorption processes caused by chemisorption.

However, Khamizov [1] showed that the applicability of the pseudo-second order model does not depend on the sorption mechanisms. It is impossible to draw conclusions about the mechanism of the sorption process without studying its physicochemical features.

 

[1] Sarı, A., Tuzen, M., & Soylak, M.  Adsorption of Pb(II) and Cr(III) from aqueous solution on Celtek clay. Journal of Hazardous Materials, 144(1-2), 41–46 (2007). https://doi.org/10.1016/j.jhazmat.2006.09.080 

[2] Rafferty, P., Shiao, S.-Y., Binz, C. M., & Meyer, R. E. . Adsorption of Sr(II) on clay minerals: Effects of salt concentration, loading, and pH. Journal of Inorganic and Nuclear Chemistry, 43(4), 797–805 (1981). https://doi.org/10.1016/0022-1902(81)80224-2 

[3] Hai Nguyen Tran. Improper Estimation of Thermodynamic Parameters in Adsorption Studies with Distribution Coefficient KD (qe/Ce) or Freundlich Constant (KF): Considerations from the Derivation of Dimensionless Thermodynamic Equilibrium Constant and Suggestions // Adsorption Science & Technology/, 2022, 5553212 (2022). https://doi.org/10.1155/2022/5553212

[4] Khamizov, R.K. A Pseudo-Second Order Kinetic Equation for Sorption Processes. Russ. J. Phys. Chem. 94, 171–176 (2020). https://doi.org/10.1134/S0036024420010148

Author Response

Dear Reviewer 3

Thank you for your suggestion and for your time. 

The manuscript has been revised and corrected according to your suggestion:

 

Q1 However, after the improvement, two new observations appeared:

The formula for calculating the distribution coefficient used by the authors is very different from the generally accepted one [1 - 3]:

Kd = [(C0 - Ce)*V]/(Ce*m) = Qe/Ce.

It is not possible to derive the generally accepted formula from your formula. I ask you to correct the formula and recalculate the distribution coefficients using the generally accepted formula.

R: We modify the formula accordingly, but the result remains identical.

 

Q2: The authors concluded that the pseudo-second order kinetic model describes adsorption processes caused by chemisorption.

However, Khamizov [1] showed that the applicability of the pseudo-second order model does not depend on the sorption mechanisms. It is impossible to draw conclusions about the mechanism of the sorption process without studying its physicochemical features.

R: We modify the explication as: ‘The pseudo-second-order kinetic model provides a better description of the adsorption process of BP-3 and BP-1 onto activated carbon. This model assumes that the rate-limiting step in the adsorption process is chemisorption, involving the exchange or sharing of electrons between the activated carbon and BP-3/BP-1. The model considers that the adsorption rate is directly related to the product of the concentrations of the activated carbon and BP-3/BP-1 [9]. However, the pseudo-second-order kinetic model provides important information about the rate of adsorption and can be used to determine the equilibrium adsorption capacity, it does not provide direct insights into the underlying mechanism of the ad-sorption process.’

Thank you,

Gheorghe Stefania