Cellulose nanocrystals/graphene oxide composite for the adsorption and removal of levofloxacin hydrochloride antibiotic from aqueous solution

Residual antibiotics in water are often persistent organic pollutants. The purpose of this study was to prepare a cellulose nanocrystals/graphene oxide composite (CNCs-GO) with a three-dimensional structure for the removal of the antibiotic levofloxacin hydrochloride (Levo-HCl) in water by adsorption. The scanning electron microscope, Fourier transform infrared (FT-IR), energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and other characterization methods were used to study the physical structure and chemical properties of the CNCs-GO. The three-dimensional structure of the composite material rendered a high surface area and electrostatic attraction, resulting in increased adsorption capacity of the CNCs-GO for Levo-HCl. Based on the Box–Behnken design, the effects of different factors on the removal of Levo-HCl by the CNCs-GO were explored. The composite material exhibited good antibiotic adsorption capacity, with a removal percentage exceeding 80.1% at an optimal pH of 4, the adsorbent dosage of 1.0 g l−1, initial pollutant concentration of 10.0 mg l−1 and contact time of 4 h. The adsorption isotherm was well fitted by the Sips model, and kinetics studies demonstrated that the adsorption process conformed to a quasi-second-order kinetics model. Consequently, the as-synthesized CNCs-GO demonstrates good potential for the effective removal of antibiotics such as levofloxacin hydrochloride from aqueous media.

Junhong et.al, reported that cellulose nanocrystals/graphene oxide composite is used to remove levofloxacin hydrochloride antibiotic from aqueous solution. The materials reported in the manuscript were analyzed by SEM, XPS and FT-IR. In my view, there are some questions need to be solved before it can be accepted for publication. Here is the detail of necessary revision, 1.
Please add the reagent grade of "levofloxacin hydrochloride, cellulose nanocrystals, and graphite powder" in the 2.1 materials section.

2.
Compared with HPLC, UV detection method, it is more convenient and fast ,and can also achieve a certain degree of accuracy. Please explain why UV is not selected to detect the concentration of levofloxacin. 3.
The coordinates of the pictures in figure 8 of the manuscript are not clear and cannot be seen clearly. 4.
Page 21 line 44-48: "The influence of the adsorbent concentration and initial solution pH on the removal rate under the center point conditions of the pollutant concentration (10.0 mg•L⁻1) and contact time (4 h) is shown in Error! Reference source not found. a." There are many similar mistakes in this article, please check and correct them. 5.
Page 30 line 53-59: "The equilibrium experimental data was fitted using the Sips adsorption isotherm model. The correlation coefficient of the fitted results was R2> 0.98, and the non-uniformity coefficient γ = 0.3852, indicating that the adsorption type of antibiotics on CNCs-GO was non-homogeneous monolayer chemisorption." Please explain this sentence. 6.
It is suggested that the author should supplement the comparative diagram of SEM and XPS before and after adsorption.

Decision letter (RSOS-200857.R0)
We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.
Dear Dr LI: Title: Cellulose nanocrystals/graphene oxide composite for the adsorption and removal of levofloxacin hydrochloride antibiotic from aqueous solution Manuscript ID: RSOS-200857 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
The editor assigned to your manuscript has now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Subject Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
Please submit your revised paper before 15-Jul-2020. Please note that the revision deadline will expire at 00.00am on this date. If we do not hear from you within this time then it will be assumed that the paper has been withdrawn. In exceptional circumstances, extensions may be possible if agreed with the Editorial Office in advance. We do not allow multiple rounds of revision so we urge you to make every effort to fully address all of the comments at this stage. If deemed necessary by the Editors, your manuscript will be sent back to one or more of the original reviewers for assessment. If the original reviewers are not available we may invite new reviewers.
To revise your manuscript, log into http://mc.manuscriptcentral.com/rsos and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision. Revise your manuscript and upload a new version through your Author Centre.
When submitting your revised manuscript, you must respond to the comments made by the referees and upload a file "Response to Referees" in "Section 6 -File Upload". Please use this to document how you have responded to the comments, and the adjustments you have made. In order to expedite the processing of the revised manuscript, please be as specific as possible in your response.
Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. ********************************************** RSC Associate Editor: Comments to the Author: (There are no comments.) RSC Subject Editor: Comments to the Author: (There are no comments.) ********************************************** Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) Manuscript Number: RSOS-200857 Journal: Royal Society Open Science Title : Cellulose nanocrystals/graphene oxide composite for the adsorption and removal of levofloxacin hydrochloride antibiotic from aqueous solution Comments and Recommendation: It is very important to obtain good view study the physical structure and chemical 7 properties of the CNCs-GO. The three-dimensional structure of the composite material rendered a 8 high surface area and electrostatic attraction, resulting in an increased adsorption capacity of the 9 CNCs-GO for Levo-HCl. Based on the Box-Behnken design, the effects of different factors on the 10 removal of Levo-HCl by the CNCs-GO were explored.I have some comments as following: 1. In introduction , Authors must be reduce the general parts and focus on aim of the work 2. Author should add more reference in introduction part in adsorption part and Central composite statistical analysis part as Melamine grafted chitosan-montmorillonite nanocomposite for ferric ions adsorption: Central composite design optimization study, Journal of Cleaner Production,Volume 241, 20 December 2019, 118189 3. Authors should make more characterization as GPC, TEM , DLS , Elemental analysis , mass spectroscopy for composites . 4. Authors should rescan of SEM because magnification powers to are different.

Recommendation: minor revision Best regards
Reviewer: 2 Comments to the Author(s) The manuscript entitled " Cellulose nanocrystals/graphene oxide composite for the adsorption and removal of levofloxacin hydrochloride antibiotic from aqueous solution " written by Tao, Junhong et.al, reported that cellulose nanocrystals/graphene oxide composite is used to remove levofloxacin hydrochloride antibiotic from aqueous solution. The materials reported in the manuscript were analyzed by SEM, XPS and FT-IR. In my view, there are some questions need to be solved before it can be accepted for publication. Here is the detail of necessary revision, 1. Please add the reagent grade of "levofloxacin hydrochloride, cellulose nanocrystals, and graphite powder" in the 2.1 materials section. 2. Compared with HPLC, UV detection method, it is more convenient and fast ,and can also achieve a certain degree of accuracy. Please explain why UV is not selected to detect the concentration of levofloxacin.  (4 h) is shown in Error! Reference source not found. a." There are many similar mistakes in this article, please check and correct them. 5. Page 30 line 53-59: "The equilibrium experimental data was fitted using the Sips adsorption isotherm model. The correlation coefficient of the fitted results was R2> 0.98, and the nonuniformity coefficient γ = 0.3852, indicating that the adsorption type of antibiotics on CNCs-GO was non-homogeneous monolayer chemisorption." Please explain this sentence. 6. It is suggested that the author should supplement the comparative diagram of SEM and XPS before and after adsorption. It is a pleasure to accept your manuscript in its current form for publication in Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry. I apologise it has taken longer than usual to send you this decision.
The comments of the reviewer(s) who reviewed your manuscript are included at the end of this email. Thanks for your letter and the reviewer's comments concerning our manuscript "Cellulose nanocrystals/graphene oxide composite for the adsorption and removal of levofloxacin hydrochloride antibiotic from aqueous solution". These comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to us.
We have studied the comments very carefully and tried our best to revise our manuscript according to the comments. The related changes in the revised manuscript are in blue color. The detailed modifications in the article and the responses to the Editorial Board Member's and the reviewer's comments are as following:

Reviewer #1
Comments: It is very important to obtain good view study the physical structure and chemical 7 properties of the CNCs-GO. The three-dimensional structure of the composite material rendered a 8 high surface area and electrostatic attraction, resulting in an increased adsorption capacity of the 9 CNCs-GO for Levo-HCl. Based on the Box-Behnken design, the effects of different factors on the 10 removal of Levo-HCl by the CNCs-GO were explored. I have some comments as following: 1. In introduction, Authors must be reduce the general parts and focus on aim of the work.

Author reply:
Thank you very much for the precious suggestion. Under the reviewer's suggestion, in the introduction, the general part is reduced, the sentence for the purpose of the work is added, and the last paragraph of the introduction is rewritten.
The following sentence has been added on Line 48-49:

"Hence, nanocellulose nanocomposites have been used as sorbents for heavy metals and organic pollutants removal from aqueous solution. [1] "
The following sentence has been added on Line 58-60:

"In recent, GO has attracted increasing attention as new adsorbent owing to its distinguished properties of high surface area as well as easy to functionalize ability. [2] "
We have rewritten the last paragraph of the introduction, and the last paragraph of the introduction is as follows：

Author reply:
Thanks for your valuable comments and kind suggestion. The above literature is very relevant to the contents of this manuscript. According to your suggestion, we have add the literature, and this document is cited in the introduction, adsorption, and response surface analysis.
The document number is [32].

3.
Authors should make more characterization as GPC, TEM, DLS, Elemental analysis, mass spectroscopy for composites.

Author reply:
We are grateful for the pertinent comment of the reviewer. According to the reviewer's comments, we supplemented the TEM and DLS characterization of CNCs-GO composites.
The following sentence has been added on Line 148-152: " Fig. 2

Fig. 2 TEM images of CNCs-GO
The following sentence has been added on Line 173-182:

4.
Authors should rescan of SEM because magnification powers to are different.

Author reply:
According to the reviewer's comments, we re-selected the appropriate and clear SEM images.
As shown below. The SEM image contains photos of CNCs, GO and CNCs-GO at 5000× and 30,000× magnifications respectively.

Author reply:
Thanks for your valuable suggestion. We have rewritten the 2.1 materials section based on your suggestion, and the 2.1 materials section is as follows.

Materials
Levofloxacin hydrochloride 98%, cellulose nanocrystals, and graphite powder 99.95% (for the preparation of graphene oxide) were purchased from Shanghai Macklin Biochemical Co., Ltd.
Deionized water was used for all experiments. Otherwise specified chemicals were of reagent grade and utilized without further purification. Deionized water was used throughout the experiments.

2.
Compared with HPLC, UV detection method, it is more convenient and fast, and can also achieve a certain degree of accuracy. Please explain why UV is not selected to detect the concentration of levofloxacin.

Author reply:
We really appreciate the reviewer's precious comments, which is very important for us to improve our work. High performance liquid chromatography (HPLC) and ultraviolet-visible spectrophotometry (UV-Vis) are two commonly used methods for detecting Levofloxacin. Wang investigated the high-performance liquid chromatography and ultraviolet-visible spectrophotometry to determine the concentration of levofloxacin hydrochloride on a new synthetic scaffold, and compared the characteristics of the two detection methods. The findings demonstrated that although UV-Vis is simple to operate, and the expenses are low, it is not accurate to measure the concentration of drugs loaded on the composite composites. The HPLC method could be used to separate Levofloxacin from various impurities in the chromatographic column, which eliminated the interference of impurities with Levofloxacin. As a method, HPLC exhibited the advantages of high precision and high recovery. [1] In addition, some of the literature on the removal of antibiotics also uses high-performance liquid chromatography to determine the concentration of antibiotics, [2][3][4][5][6] and our laboratory has the conditions to use high performance liquid chromatography, so in this study, high performance liquid chromatography was used to determine antibiotics. isotherm model. The correlation coefficient of the fitted results was R 2 > 0.98, and the non-uniformity coefficient γ = 0.3852, indicating that the adsorption type of antibiotics on CNCs-GO was non-homogeneous monolayer chemisorption." Please explain this sentence.

Author reply:
We are grateful for the pertinent comment of the reviewer. Under the reviewer's suggestion, we found the wrong conclusion in this paragraph. According to the reviewer's suggestion, we have explained the sentence. Sips model is a hybrid model based on Langmuir and Freundlich models.
Sips model is often used to represent the adsorption of non-uniform surfaces. In the Sips equation, γ is a heterogeneous coefficient, which is often used to indicate the heterogeneity of adsorption. If the γ value approaches zero, indicating that the surface adsorption is more uneven, the Sips isotherm equation follows the Freundlich isotherm model; when the γ value is equal to or close to 1, indicating that the surface adsorption is more uniform, the Sips isotherm equation is simplified to Langmuir isotherm model [1][2] . Among the three isothermal models, the Sips isothermal model has the largest correlation coefficient (R 2 >0.98), indicating that the Sips isothermal model can describe the adsorption process well. The heterogeneity coefficient γ = 0.3852, approaching zero, that is, the adsorption process in the low concentration antibiotic solution is the multilayer adsorption of the heterogeneous surface of the Frendlich model.
The erroneous conclusion we found is " the non-uniformity coefficient γ = 0.3852, indicating that the adsorption type of antibiotics on CNCs-GO was non-homogeneous monolayer chemisorption". The correct conclusion should be "multimolecular layer chemisorption on heterogeneous surface".
We have partially rewritten the paragraph, and the paragraph is as follows：

6.
It is suggested that the author should supplement the comparative diagram of SEM and XPS before and after adsorption.

Author reply:
Thanks for your valuable comments and kind suggestion. According to the reviewer's comments, we supplemented the SEM-EDS and XPS characterization of the CNCs-GO composite after adsorption of Levo-HCl.
The following sentence has been added on Line 583-590: (Fig. 15b, c). The ratio of Leco-HCl was estimated at about 1.90% and is evenly dispersed on the surface of the material."