Quaternization of Porous Cellulose Beads and Their Use for Removal of Humic Acid from Aqueous Medium
Round 1
Reviewer 1 Report
A new adsorbent obtained from porous cellulose beads through quaternization was successfully used as adsorbent of humic acid. The beads were quaternized with glycidyltrimethylammonium chloride to introduce quaternary ammonium groups. The adsorption capacity was higher than those of other articles.
Some minor mistakes should be corrected and questions should be answered:
p2 line 79 ‘….and the porosity of 87% in nominal value’
What does the above expression means? What types of pores were present in the material before and after quaternization? How did the porosity change after quaternization?
p4 line 159 where Ceg in the Cr(VI) ion concentration…
Please correct this phrase.
p5 lines 186-7 Have you determined the highest possible concentration of GTMAC on the Surface of cellulose beads? This strategy would help the reader understand limits of the experiment. If yes, have you examined at the highest concentrtion of GTMAC the highest concentration of quaternary ammonium groups? Did those conditions provide the maximum adsorption capacity?
p5 line 192 Instead of ‘addition’ should be ‘additional’;
p9 lines 270-1 The amount of OH- groups at both pH 3 and pH 6 is negligible, and can be omitted in discussion.
p9 line 279 ‘The adsorption capacity at pH 3.0 was higher than that at pH 6.0 irrespective of the content of quaternary ammonium groups.’ The authors described various types of intereactions. How about the OH groups created during epoxy ring degradation? Were they active in the adsorption of HA?
p10 line 291 sharply
p13 line 367 As far as desorption is considered, have you tried immersion in the HA solution at pH 3 again after the treatment with HCl solution of pH=3?
Author Response
We received e-mail and greatly thanked the reviewers in giving valuable comments for our manuscript. Here, we accepted many of the reviewer’s comments and revised the manuscript to publish in Journal, physchem. Our responses to the reviewer comments are described as follows.
Answers to Reviewer 1
Comment #1 on nominal value
Reply: The description on the data obtained from the manufacturer of the used cellulose beads is revised (See Line 82-83).
Comment #2 on explanation of symbols
Reply: We have used the description like this on other articles. However, the term of “Cr(VI) ion concentration” was revised to “HA concentration” (See Line 163-166). This is our careless mistake.
Comment #3 on quaternization with GTMAC
Reply: Some descriptions on quaternization with GTMAC were revised (See Line 188-190). The maximum content of quaternary ammonium groups of 0.524 mmol/g was obtained for the reaction time of 2 h at the GTMAC concentration of 1.0 M at 65°C in this study as shown in Figure 1. In addition, the maximum adsorption capacity of 0.430 g/g was obtained at pH 3.0 for the quaternized cellulose beads with 0.524 mmol/g as shown in Figure 7.
Comment #3 on addition reaction
Reply: The term of “addition reaction” is correct. This refers to the reaction of an epoxy compound with a hydroxy group. Therefore, this description was not revised (See Line 201).
Comment #4 on the concentration of the hydroxide ions
Reply: The hydroxide ion concentration should be taken into account at pH values higher than 7. On the other hand, the hydroxide ion concentration can be omitted in the acidic range. Some descriptions on the hydroxide ion concentration were added (See Line 282-285).
Comment #5 on the involvement of hydroxide groups in HA adsorption
Reply: Hydroxy groups generated by the addition reaction with GTMAC would be also involved in the adsorption of HA through hydrogen bonding. A short description on the hydroxide ions was added (See Line 296-299).
Comment #6 on desorption
Reply: We are aware that the experiments of the adsorption at pH 3.0 and desorption cycle are required. HA was adsorbed on the quaternized cellulose beads at pH 6 after desorption in NaOH solution in this study. On the other hand, the adsorption (at pH 3.0) and desorption cycle was not performed. We will perform the repetitive adsorption and desorption cycle experiments under other conditions, such as adsorption at pH 3, desorption in NaCl or NH4Cl to write a next manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors reported the development of a quaternized cellulose adsorbent to remove humic acid from water. The characterization aspect of the prepared adsorbent was sufficient, and the practical aspect (humic acid removal) was reasonably and sufficiently studied. The study is not that novel and lacks proper justification. Also, the results are not properly discussed. This manuscript needs major revision and I have listed these issues and recommendations in chronological order.
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. The similar studies, particularly those based on cellulose adsorbent should be cited and discussed to highlight the importance and novelty of the developed system.
3. What was the molecular weight of the starting cellulose material and what was the molecular weight of the modified cellulose?
4. The developed adsorbent should be more characterized, including: zeta potential measurements, FTIR and specific surface area.
5. Please compare the adsorption capacity of current work with other cellulose adsorbents for removal of humic acid in a separate table.
6. What is the reason to study the adsorption of humic acid? Is this pollutant more abundant in wastewater as compared to other persistent contaminants, like dyes, pesticides or pharmaceutic pollutants?
7. 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.
8. Can this work be feasible to be done in industrial scale, and can it be scaled up?
9. Can the same experiments be done using continuous adsorption column?
Author Response
We received e-mail and greatly thanked the reviewers in giving valuable comments for our manuscript. Here, we accepted many of the reviewer’s comments and revised the manuscript to publish in Journal, physchem. Our responses to the reviewer comments are described as follows.
Answers to Reviewer 2
Comment #1 on purpose of this manuscript
Reply: We described some disadvantages of adsorbents for removal of HA in Line 50-51. In addition, we explained the usability of cellulose to develop a novel adsorbent for removal of HA in Line 60-65. There are a few articles for cellulose-based adsorbents for removal of HA. Many of the adsorbents for removal of HA have been prepared from materials, such as zeolite, biomass, Fe3O4, silica, and so on. We systematically organized the Introduction section on natural organic pollutants, removal methods, advantage of adsorption, removal of humic acid, advantage of cellulose, and purpose of this study. Since we have received no comments on our introduction from other reviewers on revision of Introduction, we believe that our introduction is successfully organized. However, Some sentences were revised and added for readers to understand the purpose of this study (See Line 72-77).
Comment #2 on molecular weight of the cellulose beads used
Reply: We used the commercial porous cellulose beads in this study. I purchased them from Rengo Co., Ltd. The values of some physical properties are listed as nominal value in Line 83-85. The molecular weight of the used cellulose beads is not clear. As the cellulose beads are insoluble in water, I think it is not such a big issue.
Comment #3 on characterization of quaternized cellulose beads
Reply: The difference in the FT-IR spectrum between untreated cellulose beads and quaternized cellulose beads was small. Therefore, we didn’t show their spectra in our first draft. However, the FT-IR spectra was shown as one of the supplementary materials and add some sentences on FT-IR spectra (See Line 105-107 and 204-208). The specific surface area of the used cellulose beads was described in Line 79. The zeta potential measurements aren’t measured for following reasons: we don’t own a zeta potential analyzer in our campus. As a quaternary ammonium group is a strong base functional group, the charge density on the surfaces of the quaternized cellulose beads keeps unchanged even when the pH value of HA solutions is varied. Instead, the content of quaternary ammonium groups is determined. This is a distinctive procedure and result because the content of functional groups involved in HA adsorption is not determined in other articles.
Comment #4 on HA adsorption capacity of other cellulose-based adsorbents
Reply: We carefully reviewed articles on the HA adsorption capacity of other adsorbents before publishing the first draft and after receiving the review letter. Some of the experimental conditions are lacked (or insufficient) in some of the articles. For example, the adsorption capacity is shown in a graph but numerical value is not shown, the maximum adsorption capacity determined from Langmuir isotherm equation is shown but the experimental adsorption capacity is not shown, and some experimental conditions of the adsorption experiment are not clear. However, some values of the adsorption capacity for some cellulose-based adsorbents are added in Table 4 (See Table 4).
Comment #5 on removal of HA in this article
Reply: We fully understand your suggestion. Removal of pollutants except for HA has been required. So far, we have published many papers on removal of pollutants, such as metal ions (Journal of Applied Polymer Science, 102, 5965-5976 (2006), and 133, article 43360 (2016), Environmental Technology, 40, 855-869 (2019) and 43, 1885-1898 (2021), and 43, 2033-2046 (2022)), organic dyes (Journal of Applied Polymer Science, 99, 381-391 (2006) and 104, 3301-3308 (2007)), alkyl phenols (Journal of Applied Polymer Science, 115, 137-145 (2010), Bioscience Biotechnology, and Biochemistry, 70, 2467-2475 (2006)), chlorophenols (Bioscience Biotechnology, and Biochemistry, 71, 2503-2510 (2007)), and bisphenol A and its derivatives (Environmental Technology, 31, 243-256 (2010) and 37, 1733-1744 (2016), Journal of Applied Polymer Science, 124, 796-804 (2012)) from aqueous medium through the adsorption process and the enzymatic reaction-adsorption process. Based on these investigations, we tried to remove HA from aqueous medium through the adsorption process. The our above efforts are not described in this manuscript, because the content becomes unnecessarily long. Finally, we hope that the reviewer understand our opinion.
Comment #5 on use of linearized analysis
Reply: We fully understand your suggestion. We have analyzed the adsorption and desorption data mainly using pseudo-second order model and Langmuir isotherm and have published articles (Journal of Applied Polymer Science, 102, 5965-5976 (2006), and 133, article 43360 (2016), Environmental Technology, 40, 855-869 (2019) and 43, 1885-1898 (2021), and 43, 2033-2046 (2022)). In addition, the linearized analysis have been used and their results have been published recently by other researchers. Since we are of the experimental scientists, we hope that the reviewer understands our opinion.
Comment #6 on practical use of this study and the fixed bed column experiments
Reply: Thank you for your suggestion. Since we obtained the experimental results by the batch adsorption system. In the next step, we will perform the experiments on removal of HA by the fixed bed column system. We added some explanations on practical use and future outlook of this study in the Conclusions section (See Line 419-423).
Additional revision
#1: We carefully checked the references and rearranged the reference number.
#2: FT-IR spectra were added in Supplementary materials.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The manuscript still contains some unclear details as mentioned in the last report. The reviewer can only see minor improvments. Thus, I cannot recommend that the manuscript is published, in this form.
Author Response
Thank you for your advice. We extensively revised the introduction section according to reviewer's comment. The revised or modified sentences are in red.
Round 3
Reviewer 2 Report
Authors have revised the manuscript according the recommendations, and answered the questioned points.
