Efficient Degradation of Printing and Dyeing Wastewater by Lotus Leaf-Based Nitrogen Self-Doped Mesoporous Biochar Activated Persulfate: Synergistic Mechanism of Adsorption and Catalysis

Round 1

Reviewer 1 Report

The manuscript titled " Efficient Degradation of Printing and Dyeing Wastewater by Lotus Leaf-Based Nitrogen Self-Doped Mesoporous Biochar Activated Persulfate: Synergistic Mechanism of Adsorption and Catalysis"

In this manuscript, authors reported synthesis of N-self-doped mesoporous lotus leaf biochar (LLC800) from lotus leaves as raw material for the activation of Persulfate (PS) to degrade printing and dyeing wastewater. The prepared catalyst was fully characterized by different characterization techniques such as X-ray diffraction, Raman spectra, BET, XPS, FTIR and SEM. The accomplished samples performance is impressive. Therefore, I would like to recommend published this work after addressing the following points:

1. There are many abbreviations in the text that are not explained when they first appear such as AO7, LLC800 (800 means what), ....etc.

2. Introduction is well-organized and well-written, but the importance and novelty of the research should be highlighted and more clearly stated. The authors give some examples of works in the bibliography, but which is the advantage of their work in comparison with those works.

3. what about cycle stability of the prepared catalysts, and after cycle stability of adsorption reaction, whether morphology and crystal structure of the catalysts were changes?

4. The comparison on catalytic activity of as-prepared samples with some typical mesoporous silica-based catalysts ever reported should be added.

5. The authors are responsible for the English, which should be polished throughout the manuscript to clear some minor typo/grammar errors.

6. In the introduction part, Some publications on adsorption techniques and photocatalysis are suggested to refer to improve the quality of the manuscript, such as: https://doi.org/10.1007/s10904-022-02389-8 , https://doi.org/10.1016/j.heliyon.2022.e09652 , https://doi.org/10.1016/j.jobe.2022.104869, https://doi.org/10.1016/j.catcom.2022.106479.

7. All equation should be revised, which contain some typo error.

8. The author should better improve the beauty and quality of the figures in the manuscript.

Comments for author File: Comments.pdf

Author Response

Reviewer #1:

 

Comment 1: There are many abbreviations in the text that are not explained when they first appear such as AO7, LLC800 (800 means what), ....etc.

 

As suggested, we have made corrections in the manuscript.

 

Comment 2: Introduction is well-organized and well-written, but the importance and novelty of the research should be highlighted and more clearly stated. The authors give some examples of works in the bibliography, but which is the advantage of their work in comparison with those works.

 

As suggested, we have modified the introduction section. In fact, modification methods including acid-base modification, loaded metal modification, and heteroatomic modification are listed in the introduction. The purpose of modification is to further improve the performance of biochar materials, but modification not only increases the production cost of catalytic materials, but also generates a large amount of secondary waste during the modification process, which is likely to cause secondary pollution to the environment. N-doping is one of the methods of heteroatom modification, and an increase in the proportion of appropriate N elements can significantly improve the catalytic performance of the material. Therefore, we consider whether we can find a high N content biomass to prepare biochar, and it is a new research idea to improve the catalytic performance spontaneously by "N self-doping" instead of N atom modification.

 

Comment 3: what about cycle stability of the prepared catalysts, and after cycle stability of adsorption reaction, whether morphology and crystal structure of the catalysts were changes?

 

The initial removal rate of AO7 by LLC800 is 99.46%, and the removal rate decreases significantly as the number of cycles increases (Figue S1). The decrease in degradation efficiency was attributed to the depletion of active sites such as oxygen-containing functional groups, pyridine nitrogen and pyrrole nitrogen on the surface of LLC800, and the decrease in adsorption efficiency was attributed to the clogging and collapse of voids on the surface of LLC800. The shortcoming of LLC800 is that it cannot achieve slow release of activation capacity resulting in poor circulation capacity, but proper utilization can be used as an advantage to achieve fast and efficient treatment of high concentration of organic pollutants using LLC800. The morphology and crystal structure of LLC800 were changed after cyclic use. The FT-IR spectra was compared before and after catalyst use, and the vibrational peaks of functional groups on the surface of LLC800 did not change significantly before and after the reaction, but the peak area changed decayingly.

 

Figure S1. Cycle number of LLC800 for AO7 removal

 

 

Comment 4: The comparison on catalytic activity of as-prepared samples with some typical mesoporous silica-based catalysts ever reported should be added.

 

To further illustrate that LLC800 has both excellent adsorption performance and efficient catalytic performance, a comparison with other modified and unmodified biochars was made here (Table 2). It is easy to find that LLC800 has the excellent performance in terms of the amount of biochar applied, the concentration of degraded AO7 and the degradation rate.

Table 2. Comparison of AO7 removal effect with other biochar

Samples	Biochar raw  materials	Modification method	Specific  Surface  area (m2/g)	Dosing amount（g/L）	AO7 Concentration (mg/L)	Degradation rate %	Ref
LSB-800	luffa sponge	/	304.49	0.20	20	96.00	［1］
B-nZVI	bush branch	FeSO4·7H2O	52.21	2.00	20	98.30	［2］
Fe-N-BC	straw	FeSO4·7H2O/urea	362.5	0.20	20	98.20	［3］
NRSBC800	rice straw	urea	471.10	0.10	50	100.00	［4］
SBC-700	sawdust	/	208.59	1.5	50	90.00	［5］
LLC800	Lotus leaf	/	676.34	0.25	200	99.81	work

 

［1］https://doi.org/10.1016/j.seppur.2022.120650

［2］https://doi.org/10.1007/s11270-014-2195-3

［3］https://doi.org/10.1016/j.jhazmat.2020.122764

［4］https://doi.org/10.3390/nano11092288

［5］https://doi.org/10.1016/j.scitotenv.2019.07.043

 

 

 

Comment 5: The authors are responsible for the English, which should be polished throughout the manuscript to clear some minor typo/grammar errors.

 

As suggested, we have invited native English-speaking experts to revise the manuscript.

 

Comment 6: In the introduction part, Some publications on adsorption techniques and photocatalysis are suggested to refer to improve the quality of the manuscript, such as: https://doi.org/10.1007/s10904-022-02389-8 , https://doi.org/10.1016/j.heliyon.2022.e09652 , https://doi.org/10.1016/j.jobe.2022.104869, https://doi.org/10.1016/j.catcom.2022.106479.

 

As suggested, we have cited some relevant references in the introduction.

 

Comment 7: All equation should be revised, which contain some typo error.

 

As suggested, we have revised all equation in the manuscript.

 

 

Comment 8: The author should better improve the beauty and quality of the figures in the manuscript.

 

As suggested, we have embellished the figures in the manuscript.

 

Reviewer 2 Report

Comments:

1. Page No:3, Line 106, what is the intial PH value ?

2. Line : 109, If any Particular reason to set RPM at 175 range?

 

Author Response

Reviewer #2:

 Comment 1: Page No:3, Line 106, what is the intial PH value ?

 pH=6.4±0.1 for 200 mg/L AO7 initial solution pH.

 Comment 2: Line : 109, If any Particular reason to set RPM at 175 range?

The RPM is set based on the following:

• Many references set the RPM at 175 https://doi.org/10.1016/j.chemosphere.2019.124454, https://doi.org/10.1016/j.jece.2020.104808

https://doi.org/10.1016/j.cej.2022.135947

https://doi.org/10.1016/j.jwpe.2022.102681

https://doi.org/10.1016/j.chemosphere.2022.133665

https://doi.org/10.1016/j.chemosphere.2022.133665

• The RPM is set according to the ratio of the reaction solution in the reaction vessel and the specific operating conditions.

Reviewer 3 Report

The present manuscript of Huo and co-workers summarized very interesting information for scientific community based on nitrogen doped mesoporous biochar for remediation of water contaminated with dyes. However, after a careful review of the manuscript, I do not find it fit for publication in the current form. My specific comments are as follows:

 

1)     The introduction of the manuscript is poor, does not illustrate the background correctly with particular reference to removal of dyes from water by other modified biochar based approaches, novelty of this adopted method and materials as compared to other reported in literature.

2)     In fact, there are many similar examples in the preparation of modified biochar (https://doi.org/10.1016/j.jclepro.2021.130069; https://doi.org/10.1016/j.chemosphere.2021.132788; https://doi.org/10.1016/j.chemosphere.2022.134034; https://doi.org/10.1016/j.molliq.2022.118623 ) for remediation of water contaminated with dyes. What is the novelty in this developed biochar and significant advantages as compared to other modified biochar in real field application?

3)     Author should mention every peaks in the images of XPS, XRD, EPR and FTIR analysis in before and after removal process.

4)     Authors should examine the pH of the point of zero charge of the developed biochar and correlate the observation of removal efficacy.

5)     Sub-Section 3.2 and 3.5: Explanation about removal mechanisms effect of operating process variables and experimental conditions are very poor. Just repeating common trend. The both sub-section 3.2 and 3.5 should be revised with scientific analytical proof and mechanistic aspects.

6)     It will be better for readers and researchers if efficacy of the developed biochar will be examine in removal of dyes from real samples of printing and dyeing wastewater which is contaminated with dyes.

7)     Desorption studies help to elucidate the mechanism behind of adsorption and recovery of the adsorbates and adsorbent. So desorption study of dyes should be provided in the revised form of manuscript.

 

Therefore, my recommendation is resubmission of the manuscript with a major revision in the suggested points, before being considered for publication in this Journal.

 

Author Response

Reviewer #3:

Comment 1: The introduction of the manuscript is poor, does not illustrate the background correctly with particular reference to removal of dyes from water by other modified biochar based approaches, novelty of this adopted method and materials as compared to other reported in literature.

 As suggested, we have modified the introduction section.

 Comment 2: In fact, there are many similar examples in the preparation of modified biochar (https://doi.org/10.1016/j.jclepro.2021.130069; https://doi.org/10.1016/j.chemosphere.2021.132788; https://doi.org/10.1016/j.chemosphere.2022.134034; https://doi.org/10.1016/j.molliq.2022.118623 ) for remediation of water contaminated with dyes. What is the novelty in this developed biochar and significant advantages as compared to other modified biochar in real field application?

 By carefully reading the recommended references, we found that the references focus on the use of biochar's adsorption function for remediation of dye-contaminated wastewater. And this work focuses on biochar-catalyzed persulfate for degradation of dye-contaminated wastewater, and biochar as an efficient catalytic material. The specific surface area of the biochar prepared by us is 676.34 m²/g, which is much larger than that of other biochars without modification. The study found that LLC800 also has excellent adsorption performance, but its adsorption effect is not the focus of this article. We will conduct a detailed study on the adsorption performance of biochar in the future.

Comment 3: Author should mention every peaks in the images of XPS, XRD, EPR and FTIR analysisin before and after removal process.

 EPR is mainly used to study the mechanism of biochar activation of persulfate to degrade AO7, to capture the types of free radicals and non-radicals existing in the reaction, and to further prove the mechanism of degradation. Combined with the quenching experiment, it is explained that ¹O₂ is in AO7 its leading role in the explanation. Therefore, we do not think a before-and-after comparison is necessary, and similar studies are not mentioned.

We compared the FT-IR spectra of LLC800 before and after the reaction. The vibrational peaks of the surface functional groups of LLC800 did not change significantly before and after the reaction, but the peak area decreased, indicating that the functional groups were involved in the reaction. That is, the catalytic activity of LLC800 and its surface functional groups closely related. XPS and XRD did not compare before and after use, because the effect of pyrolysis temperature on the performance of biochar was studied. The article carried out XPS and XRD characterizations of the materials at three temperatures respectively, and explained the reasons for the excellent properties of LLC800 materials through characterization. In the follow-up research, a comprehensive comparison of XPS, XRD and FTIR will be conducted before and after the material is used.

 Comment 4: Authors should examine the pH of the point of zero charge of the developed biochar and correlate the observation of removal efficacy.

 There is little mention of the pH value of the zero charge point of biochar in the references on biochar-catalyzed peroxynitrite degradation of pollutants, which is mainly used for the study of the effect of pH change on adsorption of metallic biochar catalytic materials.

The material of this study was a non-metallic biochar catalytic material and also the effect of the change of solution pH on the experiment was carried out and it was found that the change of pH had almost no effect on the degradation efficiency.Subsequent studies will be carried out to enhance this work.
Comment 5: Sub-Section 3.2 and 3.5:Explanation about removal mechanisms effect of operating process variables and experimental conditions are very poor. Just repeating common trend. The both sub-section 3.2 and 3.5 should be revised with scientific analytical proof and mechanistic aspects.

As suggested, we have added operating process variables in sections 3.2 and 3.5. Section 3.2 focuses on the selection of optimal catalytic materials. And three materials, LLC700, LLC800 and LLC900, were experimentally prepared, and its origin is described in Section 2.2. The adsorption performance and catalytic performance of LLC700, LLC800 and LLC900 were investigated respectively, and the experimental results showed that LLC800 had the best adsorption and catalytic performance and was used for the subsequent experiments.

The poor effect of experimental conditions in part 3.5 indicates that the LLC800/PS system is resistant to interference, which is the advantage of non-metallic biochar catalysts. The LLC800/PS system in is a reaction dominated by non-radical ¹O₂ (Chem Eng J .2020.126090; Chem Eng J. 2020.124065; Sep Purif Technol. 2022. 120650).

Section 3.2 is not analyzed mainly because its purpose is mainly to select the optimal material, i.e., LLC800, for subsequent experiments.

The mechanism in section 3.5 has been modified.

 Comment 6: It will be better for readers and researchers if efficacy of the developed biochar will be examine in removal of dyes from real samples of printing and dyeing wastewater which is contaminated with dyes.

 Due to time constraints and effluent collection issues, we were not able to complete the dye effluent removal experiments in a short period of time. Moreover, dye wastewater is a mixed dye, which may contain unknown pollutants such as heavy metals, aniline, a large amount of humic acid and anions, and cannot only be removed with a single color to consider the performance of biochar and the dischargeability of dye wastewater. In the follow-up research, we will supplement the practical application experiments of biochar catalytic materials.

Comment 7: Desorption studies help to elucidate the mechanism behind of adsorption and recovery of the adsorbates and adsorbent. So desorption study of dyes should be provided in the revised form of manuscript.

 LLC800 is not a single adsorption material, but a catalytic material with adsorption properties. Desorption experiments were performed using acetonitrile, and the results showed that the dye was almost completely degraded rather than adsorbed on the LLC800 surface, so it is not specifically stated in the manuscript.

Round 2

Reviewer 1 Report

The manuscript is acceptable in the present form since authors have well addressed the questions proposed by referees

Reviewer 3 Report

The authors respond well to the reviewer's comments. I accept the authors' notes and amendments.