Efficient Removal of Cr(VI) by Protonated Amino-Bamboo Char Prepared via Radiation Grafting: Behavior and Mechanism

Round 1

Reviewer 1 Report

In this work, a cation functionalized bamboo char was proposed and used for removal of Cr(Ⅵ). The work was completed and the manuscript was well organized. However, the presented work was similar to the one that already published (named: Enhanced removal of Cr(VI) by cation functionalized bamboo hydrochar).  The structure of the adsorbents in the two articles is almost the same, and the only difference is the grafting method of GMA. In addition, as a kind of  Cr(VI) adsorbent, the maximum adsorption capacity is 169.13 mg/g, which is much lower than 424.09 mg/g in the published article. Therefore, the paper is not suitable for publication in this journal due to its current innovation and academic value.

The language of the article is smooth on the whole, but there are still some defective expression in the introduction, which need to be further improved. Therefore, moderate editing of English language is required.

Author Response

Response to Reviewers' Comments

Dear reviewer,

Thanks very much for your time and efforts spent in editing my manuscript (Manuscript ID: Sustainability-2496381). Your suggestions and queries have greatly improved the quality of this manuscript. We have revised our manuscript carefully following your comments and highlighted all alteration to the original submission in Yellow.

We sincerely hope that our revision have met the expectation of the editor and reviewers. Please don’t hesitate to let us know if the manuscript is found to contain any mistakes.

Response to the Reviewer 2 

Reviewer Comments:

In this work, a cation functionalized bamboo char was proposed and used for removal of Cr(Ⅵ). The work was completed and the manuscript was well organized. However, the presented work was similar to the one that already published (named: Enhanced removal of Cr(VI) by cation functionalized bamboo hydrochar). The structure of the adsorbents in the two articles is almost the same, and the only difference is the grafting method of GMA. In addition, as a kind of  Cr(VI) adsorbent, the maximum adsorption capacity is 169.13 mg/g, which is much lower than 424.09 mg/g in the published article. Therefore, the paper is not suitable for publication in this journal due to its current innovation and academic value.

Answer: Thanks a lot for your kind and careful review. I'm so sorry for not showing the innovation of the paper clearly. However, despite the presented work was similar to the one that already published, but there are improvements and innovations in our work. These are summarized as follows:

1. Bamboo char (BC), because of its large surface area and stable physicochemical properties been widely employed to remove hazardous contaminations. In this study, the structurally stable and environmentally friendly bamboo char was used as the substrate of adsorbent. However, the bamboo char uesd in the published (named: Enhanced removal of Cr(VI) by cation functionalized bamboo hydrochar)was hydrothermal bamboo char, which needs to be produced with high temperature and high pressure hydrothermal reactor, and a large amount of hydrochloric acid was required for the preparation process. So it is not suitable for large-scale industrial applications. However, in this study the commercially available bamboo char was used, it was obtained by a lower cost and simpler preparation method, which is also the result for the lower adsorption capacity compared with the previous work.
2. Modification of bamboo char can significantly improve the removal rate of toxic ions from wastewater, however, there are few reports focused on radiation grafting modification. The electron beam radiation carries advantages over conventional techniques, such as high efficiency, environmentally friendly, simplicity, low cost, easy control of process and material composition, pure products, no any catalyst or initiators required, operation at ambient and sub-ambient temperatures[1,2]. Ionizing radiation can obtain higher grafting yield when the same monomer was grafted to polymers[3].In this research, A biosorbent cation-functionalized BC was fabricated via electron beam irradiation grafting method followed by chemical modification, and the fabricated CDGBC was determined by FTIR, SEM, TG, and Zeta potential. After the grafting of GMA and chemical modification, the thermostability of BC has been reduced, but the adsorption capacity has been significant improvement. This work shows that the electron beam radiation is an efficient and environmental friendly approach for BC modification, which will benefit the industrial application of BC based bio-absorbent. Compared with the previous work, the preparation method of the material in this study is also innovative, and the electron beam radiation grafting method is more suitable for large-scale industrial production.

In summary, compared with previous studies, our work still have improvements and innovations. The purpose of this study is to reduce the cost of preparation of adsorbent on the basis of previous work, in order to apply in the large-scale industrial production.

[1] Chen, J.C., Zhang, M.X., Zhang, S.T., et al. Metal-Organic Framework@Metal Oxide Heterostructures Induced by Electron-Beam Radiation. Angewandte Chemie International Edition. 2022, e202212532. https://doi.org/10.1002/anie.202212532

[2] Zhao, Y., Yang, J.Y., et al. Controlled preparation of a MCC-g-AM/EDA/PA loaded Fe(iii) adsorbent by the pre-radiation grafting method and its application for the adsorption removal of phosphate. RSC Advances, 2021, 11:6173-6181. DOI: 10.1039/d0ra09389k

[3] Dong, Z., Wang, Y., Wen, D., et al. Recent Progress in Environmental Applications of Functional Adsorbent Prepared by Radiation techniques: A review. Journal of Hazardous Materials, 2021, 424:126887. https://doi.org/10.1016/j.jhazmat.2021.126887

 

Comment 2: The language of the article is smooth on the whole, but there are still some defective expression in the introduction, which need to be further improved. Therefore, moderate editing of English language is required.

Answer: Thanks a lot for the reviewer’s valuable suggestions, and some defective expression in the introduction has been clearly addressed and revised according to your suggestions.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments on the manuscript

 

 Zhao, J., Gao, J., Liang, T., Chen, T., Han, X., Hu, G., Li, B.:

Fabrication of cation functionalized bamboo char via electron beam irradiation grafting for removal of Cr(VI)

The study is focused on the enhancement of adsorbents of plant origin that can be used for the elimination of toxic Cr(VI). The manuscript contains valuable results of experiments, but it is processed carelessly, it contains several incorrect facts and the wording should be improved. Several errors in English begin already in the abstract and continue throughout the rest of the text.

My recommendations for improving the manuscript are as follows:

·         The title does not match the content. The content is focused on investigating the properties of the modified adsorbent and not the process of its preparation. The actual preparation of CDGBC is described only in Section 2. Materials and Methods. The title should be adapted to the content.

·         Facts about the health effects of Cr(VI) are unnecessarily repeated in the Introduction, including irrelevant and redundant references; for the allowed Cr(VI) limit, the reference to the relevant WHO document should be given directly, not indirectly.

·         Link [6] is meaningless. The entire Introduction should be focused on the facts known so far regarding the studied problem without unnecessary digressions.

·         The reference to [19] mentions the adsorption mechanism for Pb(II) surprisingly also via reduction. But that one concerns Fe.

·         Reference [23] wrongly states that the highest adsorption capacity for Pb(II) was 1036 mg/g. This value refers to methylene blue, while for Pb(II) it is 291.8 mg/g.

·         At the first use of each abbreviation in the text, it is necessary to explain it, independently of the Abstract, and in the following text only use the explained abbreviation, not alternately.

·         The last sentence in the Introduction sounds a bit pompous in mentioning a new strategy using radiation-initiated grafting, which replaces initiation by radical decomposition of benzoyl peroxide.

·         In addition, the authors already mention cases of radiation modification in [25-27] and the application of an electron beam as an initiator, although for a different biomaterial, is also mentioned in another publication (E. Fatarella, I. Ciabatti , J. Cortez: Plasma and electron-beam processes as pretreatments for enzymatic processes. Enzyme and Microbial Technology  Volume 46, Issue 2, 5 February 2010, Pages 100-106). It would be more appropriate to state that the work extends the application of radiation initiation of the grafting reaction.

·         The statement that the modification is environmentally friendly must be worded carefully, because operations requiring chemicals also produce waste water. There are more such operations in this modification. The only indisputable environmentally friendly fact is the use of renewable raw material - waste bamboo. Radiation initiation is also partially environmentally friendly, it does not require an auxiliary chemical, but it does need electricity. A detailed analysis must decide “for and against”.

·         In section 2.1., give the names of the chemicals uniformly, i.e. also HCl and NaOH by name.

·         In section 2.3., specify the country of manufacture of the spectrometer as USA.

·         Line 137: replace “... performed” ... with “observed” or “evaluated”.

·         Section 2.4. - specify the amount of CDGBC taken into the experiment and also the temperature. The meaning of the data “an initial concentration of 300 mg/L” is unclear.

·         Line 182: replace the term “conductive” with a more suitable one.

·         Line 190:  should be “differential” ... instead of “different” and “is” instead of “were”.

·         Line 194 - no clear referencing [37, 38]. Are these taken over or matched results?

·         When interpreting TG and DTG results, always specify the relevant part of Figure 3 in the text.

·         Line 199 - no clear referencing [28, 29]. Are these taken over or matched results?

·         Line 205: specify the abbreviation GMC.

·         Line 212: replace “period” with range or segment.

·         Lines 215, 219: add ... after the contact with Cr(VI) ...

·         Line 222 - ... considered to be positive ...

·         Lines 323-325, 358, 367: rephrase the sentences to make them complete.

·         Equation (10) is wrong, what is DFBC? Where is R?

·         Please provide evidence by which you believe that conversion of Cr(VI) to Cr(III) is taking place, otherwise it is just speculation.

·         Equations (12, 13) are wrong.

·         Section 2 does not mention Na₂SO₄, but sulfuric acid, although it is not used.

·         Line 350: how does Fig. 2b relate to competitive adsorption? In my opinion, none.

·         Figure 9: On the y axis, specify that it is the adsorbed amount of Cr(VI) so as not to be confused with sulfate (Na₂SO₄).

·         Table 5: How can you claim that CDGBC outperformed other presented adsorbents, when the already next item Q_max is of 2.5 x higher value?

·         You state that the adsorbent has a macroporous structure. Therefore, it must be assumed that part of Cr(VI) adsorption also takes place through a physical mechanism. In the presence of sulfate with a smaller molecule, this can be physically adsorbed in the pores in preference to dichromate and thus suppress the physical component of Cr(VI) adsorption. I think this should be taken into account and not limit the interpretation of reduced adsorption of Cr(VI) only to competition in electrostatic attraction.  The last sentence in the Conclusion should be revised, because the central topic of the work was not the initiation of the grafting reaction by the electron beam. The inclusion of radiation grafting is already mentioned sufficiently in the first sentence of the Conclusions.

The manuscript really needs a major revision.

 

Comments for author File: Comments.pdf

English needs improvement. See my comments.

Author Response

Response to Reviewers' Comments

 

Dear reviewer,

Thanks very much for your time and efforts spent in editing my manuscript (Manuscript ID: Sustainability-2496381). Your suggestions and queries have greatly improved the quality of this manuscript. We have revised our manuscript carefully following your comments and highlighted all alteration to the original submission in Yellow.

We sincerely hope that our revision have met the expectation of the editor and reviewers. Please don’t hesitate to let us know if the manuscript is found to contain any mistakes.

Response to the Reviewer 1 

Reviewer Comments:

The study is focused on the enhancement of adsorbents of plant origin that can be used for the elimination of toxic Cr(VI). The manuscript contains valuable results of experiments, but it is processed carelessly, it contains several incorrect facts and the wording should be improved. Several errors in English begin already in the abstract and continue throughout the rest of the text.

Comment 1: The title does not match the content. The content is focused on investigating the properties of the modified adsorbent and not the process of its preparation. The actual preparation of CDGBC is described only in Section 2. Materials and Methods. The title should be adapted to the content.

Answer: Thanks a lot for your kind and careful review. The title of the manuscript has been revised according to your advice. Thank you very much for your valuable suggestion.

In the revised manuscript: 

Efficient removal of Cr(VI) by protonated amino-bamboo char prepared via radiation grafting: Behavior and mechanism

 

Comment 2: Facts about the health effects of Cr(VI) are unnecessarily repeated in the Introduction, including irrelevant and redundant references; for the allowed Cr(VI) limit, the reference to the relevant WHO document should be given directly, not indirectly.

Answer: Thanks for your valuable suggestions. We are very sorry for our improper organization of the introduction part and the irrelevant and redundant references has been cited. We have carefully checked the introduction part, the health effects of Cr(VI) that were unnecessarily repeated in the introduction as well as the irrelevant and redundant references have been deleted, and the introduction part has been revised to our best. Thanks again to the reviewers for your valuable advice.

In the revised manuscript: 

1. Introduction

In recent years, heavy metal pollution caused by industrial and agricultural has attracted extensive attention. Compared with organic pollutants, inorganic pollutants are easy to enrich and difficult to eliminate, because inorganic pollutants can not be decomposed naturally and can exist in other forms in the environment [1]. Among these toxic heavy metals, chromium is considered to be one of the most toxic metals due to its extensive used in the field of painting and leather. Chromium ions not only cause huge pollution to the eco-environment but also cause irreversible damage to the human body [2].Chromium usually exist in the form of Cr(VI) and Cr(III). However, Cr(VI) is generally more toxic than Cr(III), even a very small amount of Cr(VI) can cause serious harm to human body[3]. Therefore, in order to minimize the risks of contamination caused by excessive Cr(VI), it is urgent to reduce the concentration of Cr(VI) from industrial wastewater before discharge [4].

At present, varieties of Cr(VI) wastewater treatment methods have been employed to eliminate Cr(VI) from the wastewater, including the chemical precipitation , reduction , ion exchange , membrane separation, and adsorption method[5,6]. Among these approaches, adsorption has been widely concerned for its advantages such as simplicity, efficiency, and environmental protection [7]. Over the past decades, a series of Cr(VI) adsorption materials, including activated carbon, biomass, synthetic polymer resin, clay minerals have been developed. For the environmentally sustainability and low cost, biomass originating from low-cost agricultural and forestry wastes has attracted wide attention in the removal of contaminants in wastewater [8-10].

 

Comment 3: Link [6] is meaningless. The entire Introduction should be focused on the facts known so far regarding the studied problem without unnecessary digressions.

Answer: Thanks a lot for the reviewer’s valuable suggestion. The link 6 has been removed according to your suggestion, we have carefully examined and revised the introduction part. Thanks again for your kind and careful review.

 

Comment 4: The reference to [19] mentions the adsorption mechanism for Pb(II) surprisingly also via reduction. But that one concerns Fe.

Answer: Thanks a lot for your kind and careful review. As described in the reference [19], the Ca-MBHC could achieve Pb(II) binding owing to complexation, reduction, ion exchange and electrostatic attraction. In this research, zero-valent iron reduced the Pb(II) to Pb, and the Pb was insoluble, could be removed by sedimentation. Thanks again for your kind and careful review.

[19]

[19] Qu, J.; Lin, X.; Liu, Z.;  Liu, Y.; Wang, Z.; Liu, S.;Meng, Q.; Tao, Y.; Hu, Q.; Zhang, Y. One-pot synthesis of Ca-based magnetic hydrochar derived from consecutive hydrothermal and pyrolysis processing of bamboo for high-performance scavenging of Pb(Ⅱ) and tetracycline from water. Bioresour Technol., 2022, 343, 126046. DOI: 10.1016/j.biortech.2021.126046.

 

Comment 5: Reference [23] wrongly states that the highest adsorption capacity for Pb(II) was 1036 mg/g. This value refers to methylene blue, while for Pb(II) it is 291.8 mg/g.

Answer: Thanks a lot for your kind and careful review. It was our negligence that led to such a mistake. We have corrected it in the manuscript and carefully checked the whole manuscript. Thanks again to the reviewer for your patient and careful review, so that we could find the mistake and correct it in time.

In the revised manuscript: 

In addition, polyitaconate functionalized BC was fabricated through free radical polymerization, and used for Pb(II) adsorption [23]. The highest adsorption capacity for Pb(II) was 291.8 mg/g, and the kinetics can be explained by pseudo second order kinetics equations.

 

Comment 6: At the first use of each abbreviation in the text, it is necessary to explain it, independently of the Abstract, and in the following text only use the explained abbreviation, not alternately.

Answer: Thanks for the reviewer’s valuable suggestions. According to your suggestion, all the abbreviations that first appeared in the manuscript have been explained, and in the following text all the materials used have been changed to abbreviations. Thank you for your suggestion

In the revised manuscript: 

Therefore, a novel cation-functionalized Bamboo char (BC) was fabricated via electron beam irradiation grafting method in this work, and the successful grafting of glycidyl methacrylate (GMA) onto BC (GBC) through electron beam irradiation then followed by chemical modification with diethylenetriamine (DGBC), and finally treated with hydrochloric acid to obtain protonated diethyltriamine functionalized BC (CDGBC). The modification of the BC could significantly improve the ability to remove Cr(VI) in wastewater.

 

Comment 7: The last sentence in the Introduction sounds a bit pompous in mentioning a new strategy using radiation-initiated grafting, which replaces initiation by radical decomposition of benzoyl peroxide.

Answer: Thanks a lot for your kind and careful review. According to your suggestion, we have revised the last sentence in the introduction part, radiation-initiated grafting method without the use of initiators, free radicals can be generated under electron beam radiation, avoiding secondary pollution in the grafting process[1-3], so it have certain advantages over BPO initiators, but each each method has its own scope of application. However, it is not appropriate to overstate the advantages of electron beam radiation grafting. Thanks again for your valuable advice.

In the revised manuscript: 

This work revealed that the electron beam radiation grafting method is an efficient and environmental friendly approach for BC modification, which can be used for enhanced trapping of toxic metal ions in industrial wastewater.

[1] Chen, J.C., Zhang, M.X., Zhang, S.T., et al. Metal-Organic Framework@Metal Oxide Heterostructures Induced by Electron-Beam Radiation. Angewandte Chemie International Edition. 2022, e202212532. https://doi.org/10.1002/anie.202212532

[2] Zhao, Y., Yang, J.Y., et al. Controlled preparation of a MCC-g-AM/EDA/PA loaded Fe(iii) adsorbent by the pre-radiation grafting method and its application for the adsorption removal of phosphate[J]. RSC Advances, 2021, 11:6173-6181. DOI: 10.1039/d0ra09389k

[3] Dong, Z., Wang, Y., Wen, D., et al. Recent Progress in Environmental Applications of Functional Adsorbent Prepared by Radiation techniques: A review[J]. Journal of Hazardous Materials, 2021, 424:126887. https://doi.org/10.1016/j.jhazmat.2021.126887

 

Comment 8: In addition, the authors already mention cases of radiation modification in [25-27] and the application of an electron beam as an initiator, although for a different biomaterial, is also mentioned in another publication (E. Fatarella, I. Ciabatti , J. Cortez: Plasma and electron-beam processes as pretreatments for enzymatic processes. Enzyme and Microbial Technology  Volume 46, Issue 2, 5 February 2010, Pages 100-106). It would be more appropriate to state that the work extends the application of radiation initiation of the grafting reaction.

Answer: Thanks a lot for your kind and careful review. Electron beam irradiation technology has gained more attention as it appears to be a promising economically and environmentally sustainable alternative to traditional chemical processing. Electron beam irradiationis was considered as a new non-thermal technology due to is it low price, non-pollution, and good antibacterial effect. Electron beam radiation method has been widely used in many fields, such as, material modification, new material production, environmental protection, processing and production, sterilization and disinfection of medical health supplies, food sterilization and preservation[1-3].

The applications of electron-beam irradiation in this field mentioned by reviewers also expands its application in the field of pretreatments of enzymatic process with transglutaminase (TGase). In fact, electron-beam irradiation could promoted the cleavage of high-energy bond, and enhancing the depolymerization reaction.

[1]Qi Wei, Jun Mei, Jing Xie. Application of electron beam irradiation as a non-thermal technology in seafood preservation. LWT-Food Science and Technology 169 (2022) 113994.

[2]Tarek Abou Elmaaty, Satoko Okubayashi, Hanan Elsisi, Shahinaz Abouelenin. Electron beam irradiation treatment of textiles materials: a review. Journal of Polymer Research (2022) 29: 117.

[3]Adrian Barylski, Krzysztof Aniołek, Andrzej S. Swinarew, et al. Novel Organic Material Induced by Electron Beam Irradiation for Medical Application. Polymers 2020, 12, 306.

Comment 9: The statement that the modification is environmentally friendly must be worded carefully, because operations requiring chemicals also produce waste water. There are more such operations in this modification. The only indisputable environmentally friendly fact is the use of renewable raw material - waste bamboo. Radiation initiation is also partially environmentally friendly, it does not require an auxiliary chemical, but it does need electricity. A detailed analysis must decide “for and against”.

Answer: Thanks a lot for the reviewer’s valuable suggestions. Your suggestion is very meaningful. Chemical reactions inevitably lead to pollution. The purpose of our work is to use the less pollution substances to remove serious pollutions. The modification is environmentally friendly was just relative to the chemical modification method, because the high energy electron accelerator will produce β rays could trigger grafting polymerization reaction, no initiator, compared to chemical methods, which is less pollutionto the environment. Ionizing radiation carries many other advantages over conventional techniques, such as high efficiency, simplicity, easy control of process and material composition, pure products, no any catalyst or initiators required, operation at ambient and sub-ambient temperatures. Ionizing radiation can obtain higher grafting yield when the same monomer was grafted to polymers[1]. The advantages of irradiation grafting are introduced in the introduction part. Thanks again for your valuable comments.

[1] Dong, Z., Wang, Y., Wen, D., et al. Recent Progress in Environmental Applications of Functional Adsorbent Prepared by Radiation techniques: A review[J]. Journal of Hazardous Materials, 2021, 424:126887. https://doi.org/10.1016/j.jhazmat.2021.126887

In the revised manuscript: 

Electron beam irradiation technology has received increasing attention as an economical and environmentally sustainable alternative to traditional chemical treatment methods. It is an advanced method that is clean, solvent-free, time-saving, eco-friendly and has acceptable operation performance.

 

Comment 10: In section 2.1., give the names of the chemicals uniformly, i.e. also HCl and NaOH by name.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We are so sorry for our negligence of giving the names of the chemicals uniformly. This is the mistakes of our work, and the names of chemical reagents have been modified to be uniformed.

In the revised manuscript: 

hydrochloric acid, sodium hydroxide, 

 

Comment 11: In section 2.3., specify the country of manufacture of the spectrometer as USA.

Answer: Thanks a lot for the reviewer’s valuable suggestions. The country of manufacture of the spectrometer as USA has been added according to your comments.

In the revised manuscript:

2.3.Characterization

FT-IR was measured via a NICOLET 5700 spectrometer (Thermo Fisher Nicolet, USA). The thermal stability of the sample was characterized on a TG 209 F3 thermogravimetric analyzer under an N₂ atmosphere, with a heating rate of 10 °C/min between ambient temperature to 700 °C (NETZSCH, Germany). The morphology and microstructure were evaluated by a VEGA-3 SBH scanning electron microscopy (Tescan, Czech Republic). Surface charges of DFBC were observed on a Zetasizer Nano ZS90 device (Malvern, UK). X-ray powder diffraction (XRD) was observed by a LabX XRD6100 (Shimadzu, Japan). The samples were irradiated by a electron accelerator (1 MeV, Wasik Associates, USA)

 

Comment 12: Line 137: replace “... performed” ... with “observed” or “evaluated”.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised the manuscript according to your suggestion, and the “... performed” has been replaced by “observed” or “evaluated”. Thans again for your kindful advice.

In the revised manuscript:

2.3.Characterization

The morphology and microstructure were evaluated by a VEGA-3 SBH scanning electron microscopy (Tescan, Czech Republic). Surface charges of DFBC were observed on a Zetasizer Nano ZS90 device (Malvern, UK).

 

Comment 13: Section 2.4. - specify the amount of CDGBC taken into the experiment and also the temperature. The meaning of the data “an initial concentration of 300 mg/L” is unclear.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have carefully examined and revised the Section 2.4 according to your suggestion, and the amount of CDGBC taken into the experiment and also the temperature has been added. This unclear sentences “an initial concentration of 300 mg/L” also has been revised.

In the revised manuscript:

2.4. Batch adsorption of Cr(VI)

The adsorption performance of CDGBC was evaluated by batch experiments in duplicate. At each run, 20mg of the prepared CDGBC was added to 20 mL of solution in a 50 mL transparent glass bottle and then agitated on a thermostatic oscillator shaking at a rate of 180 rpm at a certain temperature, for kinetics study the temperature is 298.15K, for isothermal study the temperature is 298.15K, 308.15K, 318.15K.  

The pH value of the Cr(VI) solution was adjusted by 0.1M NaOH or 0.1M HCl, when exploring the effect of pH value on the adsorption performance of CDGBC, with an initial Cr(VI) concentration of 300mg/L at 298.15K.

 

Comment 14: Line 182: replace the term “conductive” with a more suitable one.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised the manuscript according to your suggestion, and the “conductive” has been replaced by “favorable for” . Thans again for your kindful advice.

In the revised manuscript:

which will be more favorable for the Cr(VI) adsorption process [24,31].

 

Comment 15: Line 190:  should be “differential” ... instead of “different” and “is” instead of “were”.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised the manuscript according to your suggestion, and the “different” has been replaced by “differential” and“is”has been replaced by“were”. Other similar errors were also corrected. Thans again for your kindful advice.

In the revised manuscript:

3.3 TGA Analysis

The differential thermal stability of BC, GBC, DGBC, and CDGBC were showed in Figure 3. The pure BC shows the greatest thermal stability, only 1.7% weight loss was observed before 100 °C, which can be ascribed to the release of absorbed water. During this stage, the highest mass loss rate appeared at 58.5 °C. Before the temperature of 700 °C, only 8.2 wt% weight loss was found for the pure BC [37,38]. In this stage, the highest mass loss rate appeared at 371.6 °C, 503.8 °C, 619.3 °C. The decomposition of GBC was divided into three stages, namely before 210 °C, 210~420 °C, and after 420 °C. For the first and third stages, there was no obvious difference for the GBC and BC was observed. The weight loss of GBC at the second stage was mainly ascribed to the decomposition of grafted GMA, thus the grafting yield of GMA was calculated to be 3.5 wt% [28,29]. Besides, the highest mass loss rate during this stage was took place at 128.9 °C, higher than the counterpart for BC, indicating that thermostability increased after the irradiation grafting method.

The decomposition of DGBC and CDGBC were more complete to that of GMC, the much weight loss not only reveals the low thermal stability of DGBC and CDGBC, but also demonstrated the successful amination and protonation [28,29]. A sharp weight loss was observed between 210 to 480 °C, which is mainly assigned to the grafted GMA and DETA, with a percentage of 12.8%. According to the grafting yield of GMA, the weight ratio of reacted DETA was calculated to be 9.3%. The decomposition of DGBC was similar to that of CDGBC, while more weight loss (15.4%) was observed between 210 to 480 °C for CDGBC. At this period, the highest weight loss was revealed at 293.9 °C and 412.8 °C, which may be ascribed to the salinization of amine and hydrochloric acid [24,31].

 

Comment 16: Line 194 - no clear referencing [37, 38]. Are these taken over or matched results?

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have consulted a large number of literatures when analyzing the thermogravimetric test results, and referred to these two literatures during the analysis. However, due to our negligence, the position of the quotation was inappropriate, and we have corrected it. Thank you again for your valuable advice.

 

Comment 17: When interpreting TG and DTG results, always specify the relevant part of Figure 3 in the text.

Answer: Thanks a lot for the reviewer’s valuable suggestions. It was our negligence that we did not specify the TG & DTG curves and analysis results of different samples, which caused the misunderstanding of readersWe have revised the part of TG and DTG analysis according to your suggestion, different samples of the TG and DTG were clearly pointed out in the text.

In the revised manuscript:

3.3 TGA Analysis

The differential thermal stability of BC, GBC, DGBC, and CDGBC were showed in Figure 3. As represent in figure 3a, the pure BC shows the greatest thermal stability, only 1.7% weight loss was observed before 100 °C, which can be ascribed to the release of absorbed water. During this stage, the highest mass loss rate appeared at 58.5 °C. Before the temperature of 700 °C, only 8.2 wt% weight loss was found for the pure BC, which was due to the volatilization of water and volatile compounds [37]. In this stage, the highest mass loss rate appeared at 371.6 °C, 503.8 °C, 619.3 °C. The thermal degradation of GBC was showed in figure 3b, the decomposition of GBC was divided into three stages, namely before 210 °C, 210~420 °C, and after 420 °C. For the first and third stages, there was no obvious difference for the GBC and BC was observed. The weight loss of GBC at the second stage was mainly ascribed to the decomposition of grafted GMA, thus the grafting yield of GMA was calculated to be 3.5 wt% [28,29]. Besides, the highest mass loss rate during this stage was took place at 128.9 °C, higher than the counterpart for BC, indicating that thermostability increased after the irradiation grafting method.

The decomposition of DGBC and CDGBC were more complete to that of GBC, the much weight loss not only reveals the low thermal stability of DGBC and CDGBC, but also demonstrated the successful amination and protonation. A sharp weight loss was observed between 210 to 480 °C in figure 3c, which is mainly assigned to the grafted GMA and DETA, with a percentage of 12.8%. According to the grafting yield of GMA, the weight ratio of reacted DETA was calculated to be 9.3%. The decomposition of DGBC was similar to that of CDGBC, while more weight loss (15.4%) was observed between 210 to 480 °C for CDGBC (figure 3d). At this segment, the highest weight loss was revealed at 293.9 °C and 412.8 °C, which may be ascribed to the salinization of amine and hydrochloric acid [24,31].

 

Comment 18: Line 199 - no clear referencing [28, 29]. Are these taken over or matched results?

Answer: Thanks a lot for the reviewer’s valuable suggestions. The referencing [28, 29] were about the radiation grafting of PGMA, the grafting rate of PGMA can be calculated by thermogravimetric results. And we mainly referred to these two references in TG analysis.

 

Comment 19: Line 205: specify the abbreviation GMC.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We are very sorry that we wrote the wrong sample name of GMC due to our negligence. We have revised it to GBC and carefully checked the whole manuscript. Thank you for your careful review.

In the revised manuscript:

The decomposition of DGBC and CDGBC were more complete to that of GBC, the much weight loss not only reveals the low thermal stability of DGBC and CDGBC,

 

Comment 20: Line 212: replace “period” with range or segment.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised the it according to your suggestion, and the “period” has been replaced by “segment”. Thans again for your kindful advice.

In the revised manuscript:

At this segment, the highest weight loss was revealed at 293.9 °C and 412.8 °C, which may be ascribed to the salinization of amine and hydrochloric acid [24,31].

 

Comment 21: Lines 215, 219: add ... after the contact with Cr(VI) ...

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised the it according to your suggestion, and the “CDGBC after Cr(VI)” has been replaced by “after the contact with Cr(VI)”. Thans again for your kindful advice.

In the revised manuscript:

3.4 XRD Analysis

XRD patterns for pure BC, CDGBC and after the contact with Cr(VI) were presented in Figure 4. Each sample exhibited wide peaks, which represented the features of amorphous substances[38] .Peaks were observed at approximately 24° and 43°. The wide diffraction peak of the adsorbent at approximately 24° belongs to the (002) of graphite carbon.

For CDGBC and CDGBC after the contact with Cr(VI), the diffraction peaks of BC overlapped with others while the intensity was slightly weakened. The results indicated that the crystal structure of the CDGBC did not change after Cr(VI) adsorption. Generally speaking, the disorder arrangement of amorphous materials were considered to be positive for the adsorption process[39].

 

Figure 4. XRD of pure BC, CDGBC and CDGBC after the contact with Cr(VI).

Comment 22: Line 222 - ... considered to be positive ...

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised it according to your suggestion, and the “considered positive” has been replaced by “considered to be positive”. Thans again for your kindful advice.

In the revised manuscript:

Generally speaking, the disorder arrangement of amorphous materials were considered to be positive for the adsorption process[39].

 

Comment 23: Lines 323-325, 358, 367: rephrase the sentences to make them complete.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have rephrased the sentences according to your suggestion, and thans again for your kindful advice.

In the revised manuscript:

3.6 Possible mechanism of Cr(VI) uptake on CDGBC  

The changes of functional groups before and after CGDBC adsorption of Cr(VI) play an important role in the understanding of the adsorption mechanism, the FT-IR of CDGBC and CDGBC after uptake of Cr(VI) were presented in figure 8. The broad adsorption peaks at 2987 and 3276 cm^-1 were ascribed to the stretching vibration of C-H and N-H/O-H, respectively. After Cr(VI) adsorption, the peaks slightly shifted to 2918 and 3416 cm^-1. While the peaks at 2900-3000 cm^-1 were weakened evidently, which was proved that the amine and hydroxyl groups were participated in the Cr(VI) uptake.  Obviously, the new bands appeared at 915 and 693 cm^-1, which could be ascribed to Cr=O and Cr-O stretching vibrations, respectively [24]. The migration of some characteristic peaks and the appearance of new characteristic peaks confirmed that Cr(VI) was successfully uptaked by CDGBC.

 

Comment 24: Equation (10) is wrong, what is DFBC? Where is R?

Answer: Thanks a lot for the reviewer’s valuable suggestions. we are very sorry that we wrote the wrong sample name due to our negligence. We have revised it to DGBC and carefully checked the whole manuscript. Thank you for your careful review.

In the revised manuscript:

CDGBC-N+H2- + HCrO4- →DGBC-NH3+····HCrO4-

(10)

 

Comment 25: Please provide evidence by which you believe that conversion of Cr(VI) to Cr(III) is taking place, otherwise it is just speculation.

Answer: Thanks a lot for the reviewer’s valuable suggestions. To further explore the remove mechanisms of Cr(VI) and certificate that conversion of Cr(VI) to Cr(III) is taking place, XPS analysis after Cr(VI) adsorption was carried out.

In the revised manuscript:

In order to further explore the adsorption mechanism, High-resolution XPS spectra of Cr2p for CDGBC after uptake of Cr(VI) was displayed in figure 9. The results showed that two peaks were obsearved at 587.12 and 577.69 eV, which ascribed to Cr2p1/2 and Cr2p3/2, respectively. In addition, both Cr2p3/2 and Cr2p1/2 could be deconvoluted into two peaks. The peaks at 577.35 and 587.08 eV were corresponded to Cr(III), while the peaks detected at 579.27 and 588.59 eV were assigned to Cr(VI)[24]. According to the XPS results, the coexistence of Cr(III) and Cr(VI) indicates that the removal of Cr(VI) by CDGBC includes both adsorption and reduction processes.

 

Figure 9. High-resolution of Cr 2p specturm of CDGBC-Cr(VI).

 

Comment 26: Equations (12, 13) are wrong.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have revised the equations (12) and (13), please pay attention to “3.6 Possible mechanism of Cr(VI) uptake on CDGBC”.

In the revised manuscript:

In addition, the groups of -N⁺H₃, -N⁺H₂-, and -OH could donate electrons to convert a part of adsorbed Cr(VI) to Cr(III) [51]. Due to the repulsion of electrostatic charge between CDGBC and Cr(III), the cationic Cr(III) escaped from CDGBC to the solution and it can be fixed onto the surface of CDGBC through the complexation with -NH and -OH. As shown in the following equations:

HCrO4- + 3e- + 7H+ →Cr(III) + 4H2O	(11)
Cr(III) + − NH→ − NH····Cr(III)	(12)
Cr(III) + -OH→ - OH···· Cr(III)	(13)

 

Therefore, besides the electrostatic interaction, specific interaction such as complexation was also involved in the Cr(VI) capture of CDGBC, which is consistent with the experiment result and previous studies [24,49].

 

Comment 27: Section 2 does not mention Na2SO4, but sulfuric acid, although it is not used.

Answer: Thanks a lot for the reviewer’s valuable suggestions. It was our mistake that sodium sulfate was written as sulfuric acid, and we have changed sulfuric acid to sodium sulfate. Thanks to the reviewer's careful review, we corrected this mistake in time.

In the revised manuscript:

2.1. Materials and Chemicals

Bamboo char was purchased from a local reagent company (Xianning, China). Glycidyl methacrylate (GMA), and diphenylcarbazide were supplied by Aladdin Reagent (Shanghai, China). Potassium dichromate, diethylenetriamine (DETA), ethanol, sodium sulfate, hydrochloric acid, sodium hydroxide, and acetone were supported by Sinopharm Chemical Reagent Co. Ltd. Chemicals used were of analytical grade, and ultra-pure water (18.25 MΩ) was used throughout the study.

 

Comment 28: Line 350: how does Fig. 2b relate to competitive adsorption? In my opinion, none.

Answer: Thanks a lot for the reviewer’s valuable suggestions. We are very sorry that we mistakenly wrote figure 2b instead of Figure 10. We have corrected it according to your suggestion. Thank you for your careful review.

In the revised manuscript:

3.7 The effect of competing ions for Cr (VI) uptake.

The coexisting ions impacting on the Cr(VI) uptaking of CDGBC was investigated in Figure 10. The SO₄^2- solutions with different concentrations were studied. The uptake capacity of CDGBC decreased dramatically from 110.87 to 37.62 mg/g as the concentration of SO₄^2- increased from 0 to 2.0 mol/L (Fig.10). Obviously, with the addition of sulfate, it has a strong effect on chromium adsorption, its due to the competitive electrostatic attraction between sulfate and Cr₂O₇^2-.

 

Comment 29: Figure 9: On the y axis, specify that it is the adsorbed amount of Cr(VI) so as not to be confused with sulfate (Na₂SO₄).

Answer: Thanks a lot for the reviewer’s valuable suggestions. We have corrected it according to your suggestion. Thank you for your careful review.

In the revised manuscript:

3.7 The effect of competing ions for Cr (VI) uptake.

The coexisting ions impacting on the Cr(VI) uptaking of CDGBC was investigated in Figure 10. The SO₄^2- solutions with different concentrations were studied. The uptake capacity of CDGBC decreased dramatically from 110.87 to 37.62 mg/g as the concentration of SO₄^2- increased from 0 to 2.0 mol/L (Fig.10). Obviously, with the addition of sulfate, it has a strong effect on chromium adsorption, its due to the competitive electrostatic attraction between sulfate and Cr₂O₇^2-.

 

Figure 10. Effect of competing ions concentration on adsorption capacities of Cr(VI) by CDGBC. (C₀ = 200 mg/L, CDGBC dosage =20 mg; pH = 2, t = 24 h, T = 298 K).

 

Comment 30: Table 5: How can you claim that CDGBC outperformed other presented adsorbents, when the already next item Qmax is of 2.5 x higher value?

Answer: Thanks a lot for your kind and careful review. Compared with the original bamboo char, the adsorption capacity of modified bamboo charcoal increased significantly. In addition, compared with other bamboo char based adsorbent, CGDBC is innovative in its preparation for the irradiation grafting method. Although the adsorption capacity is better than some of bamboo char-based sorbents. However, there is still a big gap compared with the adsorption capacity of reference [24]. In our later work, we will summarize the shortcomings and continue to explore new modification methods, looking forward to prepare more bamboo char based biosorbent with better uptake capacity. According to your suggestion, we have revised the expression of the “3.9 Comparison of CGDBC with other adsorbents for Cr (VI)”. Thank you so much for your valuable suggestions.

In the revised manuscript:

3.9 Comparison of CGDBC with other adsorbents for Cr (VI).  

Table 5 compares Cr(VI) removal capacity of maximal adsorption capacity (Qmax), experimental conditions and adsorption equilibriums time of CDGBC for Cr(VI) with other bamboo based adsorbents in references. According to the experimental results and a good adsorption capacity compared with other low-cost bamboo based adsorbents which revealed that CDGBC is an excellent adsorbent, it also provides a new method for Cr(VI) removal from contaminated water.

 

Comment 31: You state that the adsorbent has a macroporous structure. Therefore, it must be assumed that part of Cr(VI) adsorption also takes place through a physical mechanism. In the presence of sulfate with a smaller molecule, this can be physically adsorbed in the pores in preference to dichromate and thus suppress the physical component of Cr(VI) adsorption. I think this should be taken into account and not limit the interpretation of reduced adsorption of Cr(VI) only to competition in electrostatic attraction. The last sentence in the Conclusion should be revised, because the central topic of the work was not the initiation of the grafting reaction by the electron beam. The inclusion of radiation grafting is already mentioned sufficiently in the first sentence of the Conclusions.

Answer: Thanks a lot for the reviewer’s valuable suggestions. Your suggestion is of great value in improving the quality of our manuscript. Thank you again for your careful review. According to the SEM characterization result, bamboo char based adsorbent does have a large numbers of pore structures, which has a physical adsorption effect on the target pollutants. Activated carbon material usually has a physical adsorption process for pollutants, but after the graft modification, there is not only exist physical adsorption, but also have the chemical adsorption process. While the two adsorption mechanisms promote synergism for the Cr(VI) uptake, besides the electrostatic interaction, pore adsorption and complexation was also involved in the Cr(VI) capture of CDGBC. In addition, the last sentence of the conclusion part has been modified according to your suggestions. Thanks again to the reviewer for spending a lot of time and energy reviewing our manuscript, which gave a lot of valuable suggestions for the improvement of the quality of the paper.

In the revised manuscript:

4.Conclusions

 In summary, cation-functionalized bio-based CDGBC was successfully fabricated through electron beam radiation grafting and applied for the Cr(VI) removal. SEM results indicated the reserved rougher surface and macro-porous structure of the obtained CDGBC, XRD results showed that the adsorbent owns amorphous structure, and TG results revealed that the grafting yield of GMA was 3.5 wt%. The results of the pH effect and zeta potential demonstrated that the adsorption of Cr(VI) onto CDGBC was mainly relied on electrostatic attraction. The kinetic results revealed that the adsorption process obeys the pseudo-second order model, indicating that chemisorption is the main adsorption process. The isotherm results shown that the highest adsorption capacity of CDGBC was 169.13 mg/g, and the process of Cr(VI) adsorption is a multi-layer process. This study provides some insights for the design of biosorbent derived from bamboo char with good performance for heavy metals uptake, which will benefit the industrial application of BC based bio-absorbent. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Accept

Author Response

Many thanks for reviewer’s kindness. Thank you for your considering my article for publication in sustainability. I am grateful to  the reviewers for the valuable suggestions provided.

Reviewer 2 Report

Comments on the manuscript

 Zhao, J., Gao, J., Liang, T., Chen, T., Han, X., Hu, G., Li, B.:

Efficient removal of Cr(VI) by protonated amino-bamboo char prepared via radiation grafting: Behavior and mechanism

The authors carried out many changes to the original text and I agree with most of them. However, I still have the following comments on the revised text:

•Be correct when using was and were when stating stability or decomposition; it is a single property,  even if it is for several substances.

•Equation (10) is fundamentally wrong. How should the term „CDGBC-N⁺H_2- “ be understood? In addition, the left side is not equal to the right. I consider the comment on equation 10 to be important. It must be corrected.

• In section 3.7. (line 356) The expression „...was investigated in Figure 9“ is not suitable. If, then „...was investigated and is displayed in Figure 9.“

Comments for author File: Comments.pdf

Author Response

Response to Reviewers' Comments

 

Dear reviewer,

Thanks again for your time and efforts spent in editing our manuscript. Your suggestions and queries have greatly improved the quality of this manuscript. We have revised our manuscript carefully following your comments and highlighted all alteration to the original submission in Red.

We sincerely hope that our revision have met the expectation of reviewer. The point-by-point responses to the reviewer comments are listed as follows.

 

Response to the Reviewer 2-2 

Reviewer Comments:

The authors carried out many changes to the original text and I agree with most of them. However, I still have the following comments on the revised text:

Comment 1: Be correct when using was and were when stating stability or decomposition; it is a single property, even if it is for several substances.

Response: Thanks a lot for your kind and careful review. We are so sorry for the improper using was and weere in our manuscript. According to your suggestion, we have revised them. At the same time, we have checked the manuscript thoroughly, and all the similar errors have been checked, revised and highlighted in yellow color.

In the revised manuscript:

3.3 TGA Analysis

In order to explore the composition and thermal stability of the BC, GBC, DGBC, and CDGBC, TG analysis was conducted (Figure 3). As represent in figure 3a, the pure BC showed the greatest thermal stability, only 1.7% weight loss was observed before 100 °C, which can be ascribed to the release of absorbed water. During this stage, the highest mass loss rate appeared at 58.5 °C. Before the temperature of 700 °C, only 8.2 wt% weight loss was found for the pure BC, which was due to the volatilization of water and volatile compounds [29]. In this stage, the highest mass loss rate appeared at 371.6 °C, 503.8 °C, 619.3 °C. The thermal degradation of GBC was showed in figure 3b, the decomposition of GBC was divided into three stages, namely before 210 °C, 210~420 °C, and after 420 °C. For the first and third stages, there was no obvious difference for the GBC and BC was observed. The weight loss of GBC at the second stage was mainly ascribed to the decomposition of grafted GMA, thus the grafting yield of GMA was calculated to be 3.5 wt% [22,23]. Besides, the highest mass loss rate during this stage was took place at 128.9 °C, higher than the counterpart for BC, indicating that thermostability increased after the irradiation grafting method.

The decomposition of DGBC and CDGBC was more complete to that of GBC, the much weight loss not only reveals the low thermal stability of DGBC and CDGBC, but also demonstrated the successful amination and protonation. A sharp weight loss was observed between 210 to 480 °C in figure 3c, which is mainly assigned to the grafted GMA and DETA, with a percentage of 12.8%. According to the grafting yield of GMA, the weight ratio of reacted DETA was calculated to be 9.3%. The decomposition of DGBC was similar to that of CDGBC, while more weight loss (15.4%) was observed between 210 to 480 °C for CDGBC (figure 3d). At this segment, the highest weight loss was revealed at 293.9 °C and 412.8 °C, which may be ascribed to the salinization of amine and hydrochloric acid [20,25].

 

Comment 2: Equation (10) is fundamentally wrong. How should the term „CDGBC-N+H2- “ be understood? In addition, the left side is not equal to the right.

Response: Thanks for the reviewer’s valuable suggestions. We are so sorry for our negligence of not examining the equation carefully and we have revised it according to your suggestion. Thank you very much for your careful review, so that we could find the error and correct it in time.

In the revised manuscript:

According to the above obtained results, possible adsorption mechanisms of Cr(VI) adsorbed on CDGBC were proposed. Based on the adsorption performance at the pH range of 2-10 and the surface zeta potential analysis of CDGBC, it proves that electrostatic interaction plays an important role in the process of Cr(VI) adsorption. Because the cationic groups of -NH₂R⁺ (-NH₂⁺- or -NH₃⁺) on the CDGBC could capture Cr(VI) through electrostatic interaction under strong acidic conditions [20]. As shown in the following equations:

CDGBC-N+H2R + HCrO4- →CDGBC-NH2R+····HCrO4-

(10)

 

Comment 3: In section 3.7. (line 356) The expression „...was investigated in Figure 9“ is not suitable. If, then „...was investigated and is displayed in Figure 9.“

Response: Thanks a lot for your kind and careful review. I am so sorry for our negligence of proper expression this sentence and we have re-written it according to the reviewer’s suggestion and the modified parts are highlighted in yellow in the revised manuscript. We will be happy to edit the text further, based on the helpful comments from the reviewers.

In the revised manuscript:

3.7 The effect of competing ions for Cr (VI) uptake.

The coexisting ions impacting on the Cr(VI) uptaking of CDGBC was investigated and is displayed in Figure 9. 

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Dear authors,

There is probably no chemist in the author's team with experience in writing chemical equations, which surprises me. Equation (10) should be written using tool Insert-Equation-Insert new equation and select the current superscript and subscript option. Equations 11-13 also need such an approach. We never use Cr(III) in the equation, but Cr with charge as Cr³⁺ (use the same procedure as above, but select the relevant superscript).

Basic problems like this greatly reduce the quality of the manuscript in my eyes.

 .

Author Response

Response to Reviewers' Comments

 

Dear reviewer,

 Thanks very much for your kind and careful review. Your suggestions and queries have greatly improved the quality of this manuscript. We have revised our manuscript carefully following your comments and highlighted all alteration to the original submission in Green. Thanks again for your time and efforts spent in editing our manuscript.

Response to the Reviewer 2-3 

Reviewer Comments:

Comment 1: There is probably no chemist in the author's team with experience in writing chemical equations, which surprises me. Equation (10) should be written using tool Insert-Equation-Insert new equation and select the current superscript and subscript option. Equations 11-13 also need such an approach. We never use Cr(III) in the equation, but Cr with charge as Cr³⁺ (use the same procedure as above, but select the relevant superscript).

Response: Thanks a lot for your kind and careful review. We are so sorry for the improper writing of the chemical equations in our manuscript. According to your suggestion, we have revised them and all the similar errors have been checked, revised and highlighted in green color.

In the revised manuscript:

(10)

 

	(11)
	(12)
	(13)

 

Author Response File: Author Response.pdf