Coffee Husk and Lignin Revalorization: Modification with Ag Nanoparticles for Heavy Metals Removal and Antifungal Assays

Round 1

Reviewer 1 Report

I had already revised the manuscript. The authors have greatly improved the manuscript which was previously poorly organized and clear. At the moment I have no further suggestions to send to the authors and therefore I believe that in the current version the manuscript can be considered for its publication.

Author Response

Thank you for your acceptance!

Reviewer 2 Report

The authors of the Manuscript did not respond in an exhaustive way to the comments of the first review process. Following are reviewer concerns:

1- SEM images. The authors did not provided a revised version of all the SEM micrographs. They affirmed "The changes to the images with similar magnification were made" . However, images b and c are the same of the first version;

2- At question 6 authors affirm: "With the inclusion of the error bars in the figures, we could infer that there are probably no significant differences between the maximum and the value at equilibrium". This is absolutely wrong. As an example, but this is not the only case, check graph in figure 1a. The 4th square point is higher than mostly of the successive points also if we consider error bar. This is only an example but other are present in the figure.

3-The authors did not provided experimental evidences of what is affirmed in the answer of the question number 4 (pH studies)

4-Negative value in pseudo-second-order kinetiks has no sense (the authors did not provide any explaination). Therefore, cannot be affirm that the model well describe the process. Consequently all the paragraph about kinetic modelling should be rediscussed

Author Response

Dear Reviewer

I appreciate the comments given to improve the quality of the manuscript. Below we give you the answer to the different suggestions:

Reviewer 2 

1. SEM imagesThe authors did not provide a revised version of all the SEM micrographs. They affirmed "The changes to the images with similar magnification were made". However, images b and c are the same of the first version; 

Reply: Dear reviewer, we appreciate your observation. To respond, we made the following changes to the micrographs.  (See Figure 1- attached Manuscript)

2. At question 6 authors affirm: "With the inclusion of the error bars in the figures, we could infer that there are probably no significant differences between the maximum and the value at equilibrium". This is absolutely wrong. As an example, but this is not the only case, check graph in figure 1a. The 4th square point is higher than mostly of the successive points also if we consider error bar. This is only an example but other are present in the figure.

Reply: We appreciate this observation that allows us to further clarify some details and information. As the referee indicates, error bars are different form point to point, because each point is a result of 2-3 replicates of the same experiment. When working with biomass systems errors around 20% can be expected, even they can be also lower. So, in figure 3 all a, b, c and d have points with small error bars and other points with bigger error bars. Even such errors, the tendency of the lines will not change so much, and in this case, with kinetics study, the time to get the equilibria is not affected. Furthermore, for experimental facility, following experiments where run at 24 hours. As can be seen, this decision is not affected by error bars, different for each experimental point of the adsorption vs. time. It is also important to mention that the lines are a guide for the eye. The Following sentence has been added in all the corresponding figures: “Line is a guide for the eye”. 

3. The authors did not provide experimental evidences of what is affirmed in the answer of the question number 4 (pH studies).

Reply: The pH selected is motivated on previous works of the authors were this parameter was checked. In addition, as FTIR published earlier shows typical carboxylic and hydroxyl functional groups, they are here expected as main responsible of the adsorption process. Furthermore, the addition of silver nanoparticles will not change this expected behaviour.  

The references associated to this study are: 

Zhang, L.; Webster, T.J. Nanotechnology and Nanomaterials: Promises for Improved Tissue Regeneration. Nano Today 2009, 4, 66–80, doi:https://doi.org/10.1016/j.nantod.2008.10.014.

Zhang, H.; Carrillo-Navarrete, F.; Palet-Ballús, C. Human Hair Biogenic Fiber as a Biosorbent of Multiple Heavy Metals from Aqueous Solutions. Journal of Natural Fibers 2020, 1–16, doi:10.1080/15440478.2020.1798841.

Zhao, J.; Shen, X.-J.; Domene, X.; Alcañiz, J.-M.; Liao, X.; Palet, C. Comparison of Biochars Derived from Different Types of Feedstock and Their Potential for Heavy Metal Removal in Multiple-Metal Solutions. Scientific Reports 2019, 9, 9869, doi:10.1038/s41598-019-46234-4.

Zhao, J.; Boada, R.; Cibin, G.; Palet, C. Enhancement of Selective Adsorption of Cr Species via Modification of Pine Biomass. Science of The Total Environment 2021, 756, 143816, doi:10.1016/j.scitotenv.2020.143816.

Zhang, H. Biosorption of Heavy Metals from Aqueous Solutions Using Keratin Biomaterials, Universitat Autònoma de Barcelona, 2014.

4. Negative value in pseudo-second-order kinetics has no sense (the authors did not provide any explanation). Therefore, cannot be affirmed that the model well describes the process. Consequently, all the paragraph about kinetic modelling should be rediscussed.

Reply: Again, I thank the reviewer for such an important observation.  

In this case in the article explain: * The negative values ​​shown in the table are considered non-relevant values. In this sense, the negative coefficients do not explain the sorption kinetics of the system shown. 

Although such negative values (Table 2) are not usually observed, other study reported previously, this may be associated with the electrostatic nature of the adsorption process. (Reference: 65. Kul, A.R.; Caliskan, N. Equilibrium and Kinetic Studies of the Adsorption of Zn(II) Ions onto Natural and Activated Kaolinites: Adsorption Science & Technology 2009, 27, 85–105.

Additionally, I included these values in the table with a (*) as shown below: 

Table 2: 

We attach the manuscript (pdf version) with the highlighted changes.

We appreciate the valuable input you, as a reviewer, have given us in this process.

Sincerely,

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript is interesting and well prepared; I suggest publishing this manuscript with slight modifications. Please rewrite the last paragraph in the introduction. The author should clearly indicate the aim & scope of the paper; it is to be mentioned how the study is useful for the theoretical and practical purposes.

Author Response

Dear Reviewer

I appreciate the comments given to improve the quality of the manuscript. Below we give you the answer to the different suggestions:

Reviewer 3  

1. This manuscript is interesting and well prepared; I suggest publishing this manuscript with slight modifications. Please rewrite the last paragraph in the introduction. The author should clearly indicate the aim & scope of the paper; it is to be mentioned how the study is useful for the theoretical and practical purposes. 

Replay: The last paragraph of the introduction was modified to clarify the aim and importance of this study. 

In this study, we present the preparation and characterization of nanocomposite based on revalorized materials: coffee husk, coffee lignin, and coffee husk and lignin modified with silver nanoparticles (AgNPs). In addition, suitability for the sorption capacity towards different metal ions of Pb (II), Cd (II), Cr (III), and Cu (II) and antifungal activity with Candida fungi species were properly evaluated, including metal concentration and contact time experiments [20–28]. The results obtained contribute with the revalorization of these Colombian agroindustrial waste due to their modification with silver nanoparticles. The improvement of tradition waste materials in the extraction of heavy metal ions in an aqueous solution and antifungal activity as an alternative to their disposal. 

We attach the manuscript (pdf version) with the highlighted changes.

We appreciate the valuable input you, as a reviewer, have given us in this process.

Sincerely,

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors answered to all the questions and the manuscripts can be accepted in the present form

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The manuscript entitled “Coffee Husk and Lignin Revalorization: Modification with Ag Nanoparticles for Heavy Metals Removal and Antifungal As- says” reports a research on the adsorbing and antifungal action of biomasses, such as coffe husk and lignin, modified with silver nanoparticles. The subject matter is consistent with the purpose of the journal.

The manuscript, however, is very lacking in clarity and organization. The figures are reported in a confused way and do not follow a numerical order in the manuscript. For example, after figure 2 follows figure 4 and figure 3 is after figure 5. The comments of the figures are also very confused.

There are also errors in the numbering of paragraphs a as for paragraph 3.4 repeated 2 times.

Paragraph 2.2 does not seem to refer to the preparation of nano composites but to biomasses.

It is not clear what the sentences repeated several times in the text "Error! Reference source not found" mean.

In light of the above, I believe that in the current version the manuscript cannot be considered for its publication but needs a major revision.

Reviewer 2 Report

The authors reported the development of of modified coffee husk and coffee lignin as sorbents in the heavy metal ions sorption of Pb(II), Cd(II), Cr(III), and Cu(II) in an aqueous solution. The characterization aspect of the prepared composites was insufficient, and the practical aspect (arsenic removal) was not reasonably and sufficiently studied. This manuscript needs major revision and I have listed these issues and recommendations in chronological order. Following is a summary of the major corrections and revisions:

1. The authors may need to briefly address the difference(s) between the current manuscript and other similar published review articles in the Introduction section.
2. In general, the references in the introduction are poorly chosen, when compared to the sentences they serve as confirmation for.
3. In adsorption experiments, the surface area plays an important role, the authors should calculate the BET-specific surface areas of the nanoparticles that are used in this work. What about the pore volume and surface area of the adsorbent? BET analysis is important.
4. Overall, the materials used should be more characterized.
5. Please compare the adsorption capacity of current work with other adsorbents for removal of Pb(II), Cd(II), Cr(III), and Cu(II) in a separate table.
6. Please do not use linearization of the equations. Nowadays, most computer programs can perform non-linear regression and should be used in preference of linearization to determine adsorption parameters.
7. Can this work be feasible to be done in industrial scale, and can it be scaled up?
8. Can the same experiments be done using continuous adsorption column?
9. Possible adsorption mechanism should be proposed.
10. In order to make the adsorption process more feasible, the adsorbent is usually regenerated. Data regarding the recycling performance of the material should be added in the manuscript. Moreover, please provide the XRD and TEM, results of the adsorbent after the five times of regeneration.
11. Conclusions: Conclusions need to be improved by specifying the discussed important points within this work. In the conclusions, the authors should also provide an outlook of the challenges and potential future directions.

Reviewer 3 Report

The manuscript titled “Coffee Husk and Lignin Revalorization: Modification with Ag Nanoparticles for Heavy Metals Removal and Antifungal Assays” aims to describe the synthesis of lignin-based sorbents for the removal of heavy metals from aqueous solutions. Also, antifungal activity of the material was observed.  The discussion in the text and the results are poor and should be deeply implemented in order to be published in Water. Following are reviewer concerns:

• 3 line 129 the authors say: “All the results are expressed as the mean value of minimum duplicate measurements, and the standard deviation (SD) is used to analyze data errors.” Therefore, error bars should be reported in the graph relative to sorption experiments.
• SEM images in figure 1 are not clear. Images at higher magnification should be provided to demonstrate the presence of Ag nanoparticles. Moreover, in figure 1c the smoother surface could be an artifact due to the wrong setup in acquiring images. Otherwise, the surface could be smoother for two reasons: 1) metallization of the surface with adsorbed metal (highly improbable); 2) etching of the surface at pH=4, but this means that the system is instable and cannot be used for real applications. Probably more detailed studies should be performed to clarify these aspects.
• It is really strange that the presence of AgNPs on sorbent surface cause an increment on the amount of heavy metals that can be adsorbed. In fact, the authors affirm that chemisorption occurs on material surface. Therefore, the amount of free chemical groups is really important to adsorb higher amount of pollutants. However, the adsorption of AgNP should hinder these chemical groups thus decreasing the sites of interactions with heavy metals…
• To better clarify which groups are important for the adsorption of heavy metals, studies at different pH should be performed;
• The figures and references should be corrected in the whole text;
• In the graphs relative to sorption experiments some curves evidenced a higher adsorption (%) at short time with respect to that observed at equilibrium. Please provide an explanations;
• Heavy metals adsorption experiments for kinetic studies should be performed on a single metal and not on a mixture;
• Isotherms (at least Langmuir and Freundlich models) should be provided to better understand the adsorption characteristics of all the materials;
• In table 2 some pseudo-second-order kinetics values are negative. A comment on this aspect should be provided.