Review Reports - Ultraviolet Radiation-Assisted Preparation of a Novel Biomass Fiber to Remove Cadmium from Wastewater

Round 1

Reviewer 1 Report

-Include a more detailed comment about the improvement reached with the uv treatment of loofah fiber .A comparative table would help.

- In tables with results of regression fits include the errors in the parameters in addition to regression coefficient.

Author Response

Point 1: Include a more detailed comment about the improvement reached with the uv treatment of loofah fiber .A comparative table would help.

Response 1: We are very sorry for our negligence of the errors in the parameters,we added the adsorption capacity data of loofah fiber before and after the uv treatment in “3.2. Effect of pH”. “Under strong acidic conditions (pH=2.0), the adsorption capacity of LF and LF@AA for Cd2+ was at a low level, which were 24.1 mg/g and 143.7 mg/g, respectively. With the increase of pH, the adsorption capacity of LF@AA increased significantly, while that of LF did not increase significantly. In the pH range of 4-7, the adsorption capacity of LF@AA for Cd2+ can be maintained at about 315.0 mg/g, which is about 9 times of that of LF.”

Point 2: In tables with results of regression fits include the errors in the parameters in addition to regression coefficient.

Response 2: We are very sorry for our negligence of the errors in the parameters,we added the sum of squared errors (SSE) in Table 1.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript reports on the production of carboxyl functioned loofah fiber (LF@AA) by UV-induced surface-initiated polymerization. The material has been structurally characterized by different analytical techniques and its heavy metal adsorption properties evaluated by batch experiments. The adsorbent reusability was also evaluated.

The manuscript is well arranged scientifically and contains much new information. The quality of the data reporting (figures and tables) is good. The paper is surely interesting and the obtained results are valid but an improvement of different sections should be provided. I consider the paper suitable for publication, but before this, some major revisions should be done.

Entire manuscript:

- The manuscript is nicely written and it is easy to follow, but a linguistic check should be performed (check verbs and plurals).

Introduction:

- The authors should report previous attempts to produce loofah-based materials for heavy metal adsorption.

Experimental section:

- Photos of the loofah before and after the UV-based treatment should be provided.

- What do the Authors mean with “situated sorptional capacity”?

Results and discussion section:

- Please rewrite the sentences at line 19 of the Abstract, at lines 51-52 of introduction, at lines 314-315 of conclusions.

- More details about the textural properties of the material (also of the starting one) should be provided.

- How do the authors evaluate the degree of aggregation/disaggregation of fiber bundles?

- The description of the FTIR data is not very clear, please revise it properly.

- SEM images of the adsorbent surface morphology after different adsorption cycles should be reported.

- A comparison with the previously published adsorption results obtained by using similar materials is kindly suggested. Data regards loofah-based materials as well as carboxyl enriched biomass-derived materials can be used for the comparison.

Author Response

Thank you for your comments concerning our manuscript,those comments are all valuable and very helpful for revising improving our paper, as well as the important guiding significance to our researches. We have studied the comments carefully and have made correction which we hope meet with your approval. Revised portion are marked in red in the paper. The responds to your comments are as follows.

Point 1: The authors should report previous attempts to produce loofah-based materials for heavy metal adsorption.

Response 1: We have added about ten reports on the use of loofah-based materials for heavy metal adsorption.

Point 2: Photos of the loofah before and after the UV-based treatment should be provided.

Response 2: Thank you for your valuable comments, due to the limitation of the length of the article, and we have conducted SEM analysis, photos of the loofah before and after the UV-based treatment was not provided in the manuscript. Optical photos of loofah original (a, a1) and LF@AA (b, b1, b2) are below.

Point 3: What do the Authors mean with “situated sorptional capacity”?

Response 3: “situated sorptional capacity” was modified to “adsorption capacity”.

Point 4: Please rewrite the sentences at line 19 of the Abstract, at lines 51-52 of introduction, at lines 314-315 of conclusions.

Response 4: We have modified the above three sentences (in red).

Point 5: More details about the textural properties of the material (also of the starting one) should be provided.

Response 5: We have added more details about the textural properties of the material in “3.1. Characterization”. “After modification, the fiber of LF@AA was uniformly thickened, and after drying, it could be found that LF@AA still maintained the natural three-dimensional spongy structure of Luffa, which indicated that the ultraviolet photocatalytic grafting technol-ogy could be used to uniformly graft polyacrylic acid on the Luffa fiber skeleton.”

Point 6: How do the authors evaluate the degree of aggregation/disaggregation of fiber bundles?

Response 6: Through direct observation and SEM results of natural loofah and LF@AA, we believe that the fiber bundles of LF@AA are looser than natural loofah.

Point 7: The description of the FTIR data is not very clear, please revise it properly.

Response 7: Thank you for your valuable comment, we have enriched the description of FTIR data.

Point 8: SEM images of the adsorbent surface morphology after different adsorption cycles should be reported.

Response 8: We are very sorry for our negligence of SEM analysis during the adsorption cycle test. Thank you for your valuable comments, and we will pay attention to this issue in future research.

Point 9: A comparison with the previously published adsorption results obtained by using similar materials is kindly suggested. Data regards loofah-based materials as well as carboxyl enriched biomass-derived materials can be used for the comparison.

Response 9: We added related literature and compared the results of this study with two reports on the use of luffa fibers for cadmium removal.

Author Response File: Author Response.pdf

Reviewer 3 Report

The purpose of the work was the synthesis of adsorbent by UV initiated grafting of acrylic acid (AA) to the surface of loofah fibre (LF). The absorbent was used for the removal of cadmium ions from wastewater. It was proved by SEM/EDS and FTIR analysis of the samples synthesized that AA was really grafted to the surface of LF. The effect of pH, ionic strength, cadmium ion concentration and temperature on the adsorption properties of the functionalized loofah fibre (LF@AA) for Cd²⁺ ions were studied. Adsorption mechanism was suggested. The reusability of LF@AA was verified by 8 consecutive adsorption cycles.

The topic of the manuscript is of practical importance. Heavy ions are toxic for human beings, plants and animals. Therefore, it is necessary to remove them from the wastewater.

The manuscript is clearly presented in a well-structured manner.

The tables and figures are appropriate. The figures are clear and easy to understand.

The conclusions are supported by the data presented in the manuscript.

I have a few problems with the manuscript.

I do not understand why do the authors mention UV-induced surface-initiated polymerization. The polymerization is initiated by UV (using benzophenone initiator) and AA was grafted to the surface of loofah fibre. However, I do not think that it was surface initiated the grafting. I suggest correcting the manuscript by removing the term surface-initiated polymerization.

The cited papers were published between 1998 and 2016. Among the cited references there are no recent publications (within the last 6 years). It seems as if the manuscript was written earlier (5-6 years ago). I recommend the authors to fill this gap. Make a fresh literature search and include the results obtained in the field of the manuscript.

A paper has been published with topic very similar to the topic of this manuscript: Chen Liu; Chunjie Yan; Sen Zhou; Wen Ge, Fabrication of sponge biomass adsorbent through UV-induced surface-initiated polymerization for the adsorption of Ce(III) from wastewater. Water Sci Technol (2017) 75 (12): 2755–2764. https://doi.org/10.2166/wst.2017.144

This paper must be cited.

English language needs some improvement. Not the proper terms are used at some places.

Fig. 2 shows the FTIR spectrum of the base material, LF, the spectrum of AA grafted LF. I suggest the authors to include to this Fig. the spectrum of AA as well.

Line 104: DI water – what does it mean? Please explain.

Line 270: 3.5. Adsorption isotherms I do not agree with the conclusion of the authors in this chapter. The effect of temperature on the adsorption capacity is not significant.

Author Response

Dear Reviewer:

Point 1: I do not understand why do the authors mention UV-induced surface-initiated polymerization. The polymerization is initiated by UV (using benzophenone initiator) and AA was grafted to the surface of loofah fibre. However, I do not think that it was surface initiated the grafting. I suggest correcting the manuscript by removing the term surface-initiated polymerization.

Response 1: We have made correction according to the reviewer’s comment, “UV-induced surface-initiated polymerization” was modified to “UV-induced polymerization”.

Point 2: The cited papers were published between 1998 and 2016. Among the cited references there are no recent publications (within the last 6 years). I recommend the authors to fill this gap. Make a fresh literature search and include the results obtained in the field of the manuscript.

Response 2: We have added about ten fresh papers (2016~2021) on the use of loofah-based materials for heavy metal adsorption.

Point 3: A paper has been published with topic very similar to the topic of this manuscript: https://doi.org/10.2166/wst.2017.144. This paper must be cited.

Response 3: We cited this paper in the latest revision.

Point 4: Fig. 2 shows the FTIR spectrum of the base material, LF, the spectrum of AA grafted LF. I suggest the authors to include to this Fig. the spectrum of AA as well.

Response 4: Since Acrylic acid (AA) does not participate in the adsorption of Cd²⁺, the FTIR spectrum of AA was not analyzed during our study. Thank you for your valuable comments, and we will pay attention to this issue in future research.

Point 5: Line 104: DI water – what does it mean? Please explain.

Response 5: “DI water” was modified to “deionized water”.

Point 6: Line 270: 3.5. Adsorption isotherms I do not agree with the conclusion of the authors in this chapter. The effect of temperature on the adsorption capacity is not significant.

Response 6: Thank you for your valuable comment, we have added the corresponding conclusion, “The adsorption capacity increased with the increase of temperature, but the effect was not significant”.

Reviewer 4 Report

I find that the Article entitled: "Ultraviolet radiation-assisted preparation of a novel biomass fiber to remove cadmium from wastewater" is very interesting.

In this paper, the authors reported the research of the heavy metal adsorbents on material developed based on biomass.

However, the Latin name and origin of biomass is not clearly stated in the Abstract and Introduction. I believe that the authors should define it clearly.

In addition, in the Abstract, the abbreviation PAA appears, which was not previously defined, nor is it used in the rest of the paper. I ask the authors to clarify this and provide the complete name of the abbreviation.
Furthermore, the Authors state the name of the material carboxyl functioned loofah fiber (LF@AA), which they define as a novel biomass fiber. However, it is not entirely clear whether it is biomass, carbon material, active carbon material or some composite obtained by combining of loofah fiber template and PAA? I ask the authors that this also be clearly defined and that the characterization of the obtained material be presented accordingly.
The authors report the results of the adsorption kinetics and isotherm parameters revealed that the adsorption characteristics of cadmium was conformed to the Weber-Morris and pseudo-second-order kinetics equations, and the adsorption process of cadmium conformed to Redlich-Peterson and Langmuir models, which is usually in works and does not represent a special scientific contribution.

However, the authors state that the material in general has the potential for eight cycles of regeneration. However, the authors did not clearly state the regeneration process, as well as the methodology and the mechanism of separation of Cd2+ ions from the adsorbent. Apart from rough calculations, nothing concrete is presented by way of measurement and interpretation of regeneration results. I ask the authors to supplement it, because the process of the regeneration mechanism in this work is an innovation and has a scientific contribution.

The list of references is short and needs to be supplemented with newer references.

Accordingly, I recommend reconsider after minor revision (corrections to minor methodological errors and text editing).

Author Response

Dear Reviewer:

Point 1: The Latin name and origin of biomass is not clearly stated in the Abstract and Introduction. I believe that the authors should define it clearly.

Response 1: We are very sorry for our negligence of the Latin name and origin of biomass, we added the Latin name in Introduction, and the new content is as follows: “which is the vascular bundle of dried ripe fruit of Luffa cylindrica (L.) Roem”.

Point 2: In the Abstract, the abbreviation PAA appears, which was not previously defined, nor is it used in the rest of the paper. I ask the authors to clarify this and provide the complete name of the abbreviation.

Response 2: We are very sorry for our negligence of the complete name of PAA, we added the complete name of PAA (polyacrylic acid) in Abstract.

Point 3: The Authors state the name of the material carboxyl functioned loofah fiber (LF@AA), which they define as a novel biomass fiber. However, it is not entirely clear whether it is biomass, carbon material, active carbon material or some composite obtained by combining of loofah fiber template and PAA? I ask the authors that this also be clearly defined and that the characterization of the obtained material be presented accordingly.

Response 3: After modification, the surface characteristics of LF@AA have changed, but it still maintains the natural three-dimensional spongy structure of Luffa without carbonization, so we think it is still a kind of biomass fiber.

Point 4: The authors state that the material in general has the potential for eight cycles of regeneration. However, the authors did not clearly state the regeneration process, as well as the methodology and the mechanism of separation of Cd2+ ions from the adsorbent. Apart from rough calculations, nothing concrete is presented by way of measurement and interpretation of regeneration results. I ask the authors to supplement it, because the process of the regeneration mechanism in this work is an innovation and has a scientific contribution.

Response 4: The regeneration process, and the methodology of separation of Cd²⁺ ions from the adsorbent were described in “2.5. Regeneration” (in red), and we have added more detailed descriptions of the regeneration process and the calculation of adsorption capacity.

Point 5: The list of references is short and needs to be supplemented with newer references.

Response 5: We have added about ten reports on the use of loofah-based materials for heavy metal adsorption.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I read the revised manuscript and also the answers provided by the Authors to my comments and to those of the other Reviewers and I come to the conclusion that the manuscript is not ready for publication to me. Some improvements are still needed and minor revisions are still requested. A revision of the entire manuscript has to be performed to remove grammar and typo errors. I suggest to provide the photos of the starting loofah and the synthetized materials as supporting information.

Author Response

Thank you for your comments concerning our manuscript,those comments are all valuable and very helpful for revising improving our paper. We have corrected some grammatical and spelling errors in the manuscript and hope to meet with your approval. Revised portion are marked in red in the paper.

Reviewer 3 Report

The authors have made all the corrections I suggested. They inserted several citations, these papers were published not long ago. They also cited the paper written by Chen et al. (Water Sci Technol, 2017)

Author Response

Thank you for your comments concerning our manuscript,those comments are all valuable and very helpful for revising improving our paper.