Ability of Deep Eutectic Solvent Modified Oat Straw for Cu(II), Zn(II), and Se(IV) Ions Removal

Round 1

Reviewer 1 Report

The paper described the adsorption of heavy metal ions by modified biomass materials, but the adsorption capacity was small, the adsorption experimental data was less, and there were many unreasonable aspects.

（1）The unit in Fig.4 are wrong.

（2）The time in Fig. 5 directly ranges from 400 minutes to 1500 minutes, which is not reasonable.

（3）There is no significant difference before and after scanning electron microscopy.

（4）Insufficient adsorption experimental data and insufficient research depth.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The work deals with the characterization of oat straw (OS) and treated oat straw (IOS) by deep eutectic solvent through selected analytical techniques (SEM, FTIR, TG, DCS). IOS is further subjected to a set of adsorption tests, where the effect of pH, kinetics and sorption capacities are studied and the description of adsorption by four different types of isotherms for adsorbates Cu(II), Zn(II) and Se(IV) is monitored.

The text is concise, clearly designed, brings interesting insights, the results are clearly described and analyzed, the results achieved are straightforwardly interpreted. The text range of the manuscript corresponds to the acquired knowledge.

I think a minor revision is needed and adequate addition should be made, while the authors should take an opinion to the following comments:

-          Due to the type of adsorbent and adsorbates (Cu, Zn, Se), combustion is certainly assumed after use/lifespan. It could be mentioned in the introduction as part of the issue of waste management compared to, for example, other sorbents whose matrix is not combustible.

-          Fig. 4 – the indicated pH values on the x-axis are input. Shouldn't the graph show the output (equilibrium) pH values, which may deviate from the input values due to the contact of phases (s) + (l) and ongoing processes?

-          As part of the discussion, I would welcome some comparison for other types of adsorbents (commercial or newly developed described in publications) and their achieved reported adsorption capacity compared to the achieved capacity of IOS in the presented work, for example in the form of a short table.

-          Is the fact of lifetime (not in terms of capacity) and mechanical resistance of the adsorption material in a watery/moist environment somehow overlooked? From the point of view of practical applicability, this is a relatively important parameter.

-          In the introduction and conclusion, the authors declare ambitions towards the advantages of the described biosorbent (new, effective, low-cost, sustainable,...). In the study, the tests were carried out on the particle size fraction of 63-125 µm. What form of material do the authors envisage in practice? Will it be a flow of wastewater through a granular bed or a suspension of fine particles in the water with subsequent separation? And is it possible to easily modify material with a coarser fraction in this way using DES?

-          In the same light - application perspectives: is it possible to modify the OS→IOS material on an industrial scale in the given ratio of contacted components? Is the process economically viable?

-          Propose the costs for 1 kg of IOS sorbent, because then it is clear whether the treatment process is not financially disqualifying in terms of costs compared to other established sorbents and their adsorption capacities and prices, despite the advantages of the nature of the biosorbent.

-          Line 425: typo - missing Freundlich "constant"

-          Fig 5: typo – in the legend IOC → IOS

-          Occasionally inappropriate prepositions are chosen, e.g. line 255, line 349: on diagrams, on Figure → in the Fig., picture, diagram,...

I suggest a minor revision.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled "Enhanced Adsorption Ability of Agro-waste Biomaterial by Deep Eutectic Solvent", is an interesting work. However, the main problem is the lack of an adequate optimization system, characterization process, application, and crucial information. In my opinion, the present work should be improved before being considered for publication. 

Some critical points in the paper are: 

·         The title of the paper is not adequate for the manuscript's content, I recommend changing it.

·         The analytical parameters are not presented.

·         The inclusion of this information in a table (not figures) and the discussion in terms of analytical sensitivity will be more attractive.

·         The paper suffers from a lack of clarity on several points that need to be better written and discussed.

·         The volume used biomass amount, and experimental condition are not clearly stated. This parameter is necessary for the results and discussion sections.

·         The paper doesn’t establish the evaluation of the DES proportion employed.

·         Is it necessary to evaluate the biomass before and after modification and discuss.

·         I suggest adding a table with the results obtained and comparing them with those reported for the use of adsorbents similar to these.

·         The authors did not include real sample analysis.

·         Other validation parameters, such as discussion about matrix effect, interference analysis, simultaneous adsorption, quantification mode, and accuracy, are not presented.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The stability of materials does not simply refer to physical stability, so the paper uses ultrasonic experiments to demonstrate the strength of the material. For the material, to consider the treatment of the adsorbed material, whether to prepare for desorption and reuse for adsorption, or conduct multiple repeated adsorption experiments to demonstrate the stability of the material's continuous adsorption.

Author Response

We thank the reviewer for the comment. The manuscript is supplemented with an adsorption/desorption study.

Reviewer 3 Report

The authors show the modification made in the function of each suggestion. My recommendation is "Accept in present form."

Author Response

We thank the reviewer for accepting our manuscript.