How the Carbonization Time of Sugarcane Biomass Affects the Microstructure of Biochar and the Adsorption Process?

Round 1

Reviewer 1 Report

The effect of different carbonization time on structure of biochar and its ability to be used as an adsorbent were investigated. the manuscript was written well and could be published after minor revisions. please consider the comments below;

1. Please clearly mention in the last paragraph of the introduction what is the importance of this work and what is the novelty?
2. Please add the sub-section in section 2 and explain the characterization setups used for your work.
3. It is recommended to add the results for BET analysis to confirm the porosity of your materials.
4. It is recommended to add the XRD results to confirm the structure of produced activated biochar.
5. It is suggested to add the highlight results in Abstract and conclusion sections.

 

Author Response

We would like to acknowledge the excellent suggestions from both reviewers for improving the revised version of our manuscript.

The suggested edits and comments made by the reviewers are shown below.

 

 

Reviewers' comments:


Reviewer #1

 

The effect of different carbonization time on structure of biochar and its ability to be used as an adsorbent were investigated. the manuscript was written well and could be published after minor revisions. please consider the comments below;

 

1. Please clearly mention in the last paragraph of the introduction what is the importance of this work and what is the novelty?

 

Response: We thank reviewer # 1 for the careful review of our manuscript and useful suggestions. We have changed the last paragraph of the introduction to attend to the reviewer's suggestion. The last paragraph is now (line 94-106): “Thus, it is important to search for new alternatives for the production of low-cost BC i.e., using low temperatures in the carbonization process without an inert atmosphere. There is a lack of information and research that concerns the influence of time in the carbonization of SCB for adsorption. Furthermore, researches with biomass in natura showed very good adsorption capacities for dyes in several studies [1], [2], [3], [4]; this brings the possibility of using the biomass itself as an adsorbent. Herein, BCs from SCB were prepared at different carbonization times (1-5 h) at 200 °C and characterized by microscopy and spectroscopy techniques, that provide insights into the structure. The novelty is related to evaluating the influence of carbonization of the SCB and identifying if it is an appropriate approach to improve the adsorption performance or the changes in the structure do not improve the adsorption. We performed batch adsorption with SCB and BCs adsorbents at various conditions, such as different initial dye concentrations, contact time, adsorbent dosage, MB solution pH, and temperature. Furthermore, we propose the mechanism of adsorption of MB onto SCB and BCs produced.”

 

1. Al-Ghouti, M.A.; Al-Absi, R.S. Mechanistic understanding of the adsorption and thermodynamic aspects of cationic methylene blue dye onto cellulosic olive stones biomass from wastewater. Sci. Rep. 2020, 10, 1–18, doi:10.1038/s41598-020-72996-3.
2. Bouhadjra, K.; Lemlikchi, W.; Ferhati, A.; Mignard, S. Enhancing removal efficiency of anionic dye (Cibacron blue) using waste potato peels powder. Sci. Rep. 2021, 11, 1–10, doi:10.1038/s41598-020-79069-5.
3. El-Naggar, N.E.A.; Rabei, N.H. Bioprocessing optimization for efficient simultaneous removal of methylene blue and nickel by Gracilaria seaweed biomass. Sci. Rep. 2020, 10, 1–21, doi:10.1038/s41598-020-74389-y.
4. Uddin, M.K.; Nasar, A. Walnut shell powder as a low-cost adsorbent for methylene blue dye: isotherm, kinetics, thermodynamic, desorption and response surface methodology examinations. Sci. Rep. 2020, 10, 1–13, doi:10.1038/s41598-020-64745-3.

 

 

1. Please add the sub-section in section 2 and explain the characterization setups used for your work.

 

Response: We add in section 2 more information about the characterization setups of the SCB and BCs to clarify those processes. The changes can be read in lines 118 and 131-133.

 

 

1. It is recommended to add the results for BET analysis to confirm the porosity of your materials.

 

Response: We tried to determine the porosity by using a long time of degasification, but even so it was not possible to achieve a good BET isotherm profile to determine the porosity. Perhaps, this occurs because the presence of others gases strongly adsorbed at biochar’s surfaces.

 

 

1. It is recommended to add the XRD results to confirm the structure of produced activated biochar.

Response: Some studies have reported that the lignocellulosic-biomass-derived biochars present turbostratic carbon crystallites in their crystalline structures. In the XRD pattern of biomass is observed cellulose I, cellulose II, and hemicellulose peaks [5], [6], [7], [8], [9], [10]. Thus, we think the experiments will be only for increment information, but do not bring more novelty to this article. If the referee, keeps this recommendation, we will need more time to carry XRD experiments, since we have no diffractometer in our institution.

5. Nanda, S.; Mohanty, P.; Pant, K.K.; Naik, S.; Kozinski, J.A.; Dalai, A.K. Characterization of North American Lignocellulosic Biomass and Biochars in Terms of their Candidacy for Alternate Renewable Fuels. Bioenergy Res. 2013, 6, 663–677, doi:10.1007/s12155-012-9281-4.
6. Mohanty, P.; Nanda, S.; Pant, K.K.; Naik, S.; Kozinski, J.A.; Dalai, A.K. Evaluation of the physiochemical development of biochars obtained from pyrolysis of wheat straw, timothy grass and pinewood: Effects of heating rate. J. Anal. Appl. Pyrolysis 2013, 104, 485–493, doi:10.1016/j.jaap.2013.05.022.
7. Kim, P.; Johnson, A.; Edmunds, C.W.; Radosevich, M.; Vogt, F.; Rials, T.G.; Labbé, N. Surface functionality and carbon structures in lignocellulosic-derived biochars produced by fast pyrolysis. Energy and Fuels 2011, 25, 4693–4703, doi:10.1021/ef200915s.
8. Meng, H.; Nie, C.; Li, W.; Duan, X.; Lai, B.; Ao, Z.; Wang, S.; An, T. Insight into the effect of lignocellulosic biomass source on the performance of biochar as persulfate activator for aqueous organic pollutants remediation: Epicarp and mesocarp of citrus peels as examples. J. Hazard. Mater. 2020, 399, 123043, doi:10.1016/j.jhazmat.2020.123043.
9. Xu, X.; Cao, X.; Zhao, L.; Zhou, H.; Luo, Q. Interaction of organic and inorganic fractions of biochar with Pb(ii) ion: Further elucidation of mechanisms for Pb(ii) removal by biochar. RSC Adv. 2014, 4, 44930–44937, doi:10.1039/c4ra07303g.
10. Paunovic, O.; Pap, S.; Maletic, S.; Taggart, M.A.; Boskovic, N.; Turk Sekulic, M. Ionisable emerging pharmaceutical adsorption onto microwave functionalised biochar derived from novel lignocellulosic waste biomass. J. Colloid Interface Sci. 2019, 547, 350–360, doi:10.1016/j.jcis.2019.04.011.

 

1. It is suggested to add the highlight results in Abstract and conclusion sections.

Response: The Abstract was adjusted to highlight the results (line 41). The Abstract is now:

“Biochar (BCs) are very versatile adsorbents, mainly, in the effectiveness of adsorption of organic and inorganic compounds in aqueous solutions. Here, the sugarcane biomass (SCB) was used to produce biochar at different carbonization times: 1, 2, 3, 4, and 5 hours, denominated as BC1, BC2, BC3, BC4, and BC5, respectively. The superficial reactivity was studied with adsorption equilibrium experiments and kinetics models; Methylene Blue (MB) was used as adsorbate at different pH values, concentrations, and temperatures. In summary, the carbonization time provides the increase of superficial area, with exception of BC4, which decreased. Equilibrium studies showed inflection points and fluctuations with different initial dye concentrations and temperatures; SCB showed the best adsorption capacity compared to the BCs at the three temperatures tested, varying with the increase of MB concentration, suggesting the dependence of these two main factors on the adsorption process. The proposed adsorption mechanism suggests the major influence of Coulomb interactions, H-bonding, and π-interactions on the adsorption of MB onto adsorbents, evidencing that the adsorption is led by physical adsorption. Therefore, the results led to the use of the SCB without carbonization at 200 °C, saving energy and more adsorbent mass, considering that the carbonization influences weight loss. This study has gone some way towards enhancing our understanding of the use of SCB in MB dye adsorption as a low-cost and eco-friendly adsorbent.”

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper presents an interesting strategy searching for new alternatives for the production of low cost biochar. The influence of carbonization time on sugarcane biomass and how it affects the microstructure of biochar and the adsorption process were investigated. The superficial reactivity was studied in details with adsorption equilibrium experiments and kinetics models. As adsorbate Methylene Blue was used at different pH values, concentrations, and temperatures.

Despite considerable works have been performed using different production alternative of low cost biochar, several points must be improved for the acceptance of this manuscript.

1. Why the adsorption pH was fixed to 7. How you chose value of 7 since the trials were done at 2, 4, 6, 8, 10?  In lines 266-268 you presented the pH 8 as best pH as following: “El‑Ahmady and Rabei reported that at pH 8 the seaweed biomass showed greater removal of MB, indicating that the surface of the adsorbent used also has protonation and deprotonation behaviour, depending on the pH of the solution (El Naggar and Rabei 2020)”
2. In line 295 you mentioned: At pH between 8 and 10, we saw that adsorption is favoured…..all this make me to wonder if the 7 value for the pH is the optimal one.
3. Also at pH 6, 8 and 10 (Figure 3b) the adsorption capacities of SBC is better that any BCs…in this respect I do not understand why to consume energy for 5 hoursto carbonize the sugarcane biomass and get the comparable result as in case of initial SBC. It is not clear which is the novelty of your research?
4. Please compare the adsorption capacities with the one presented in the research literature for similar adsorbents.
5. The conclusion section must be rewritten. The best optimal conditions, best adsorbent material and best adsorbent capacity must be presented in this section.
6. The references must be adjusted as written in the instructions of Sustainability https://www.mdpi.com/journal/sustainability/instructions

In the text, reference numbers should be placed in square brackets [ ], and placed before the punctuation; for example [1], [1–3] or [1,3]. For embedded citations in the text with pagination, use both parentheses and brackets to indicate the reference number and page numbers; for example [5] (p. 10). or [6] (pp. 101–105).

The reference list should include the full title, as recommended by the ACS style guide. Style files for Endnote and Zotero are available.

Based on these, I advise the authors to rectify the above mentioned errors and I hope to re-evaluate the revised manuscript.

Author Response

We would like to acknowledge the excellent suggestions from both reviewers for improving the revised version of our manuscript.

The suggested edits and comments made by the reviewers are shown below.

 

Reviewers' comments:

Reviewer #2

 

This paper presents an interesting strategy searching for new alternatives for the production of low-cost biochar. The influence of carbonization time on sugarcane biomass and how it affects the microstructure of biochar and the adsorption process were investigated. The superficial reactivity was studied in details with adsorption equilibrium experiments and kinetics models. As adsorbate Methylene Blue was used at different pH values, concentrations, and temperatures.

 

1. 
   Why the adsorption pH was fixed to 7. How you choose value of 7 since the trials were done at 2, 4, 6, 8, 10? In lines 266-268 you presented the pH 8 as best pH as following: “El‑Ahmady and Rabei reported that at pH 8 the seaweed biomass showed greater removal of MB, indicating that the surface of the adsorbent used also has protonation and deprotonation behavior, depending on the pH of the solution (El Naggar and Rabei 2020)”

 

 

Response: We appreciate the reviewer’s positive feedback on our manuscript. The modification has been made accordingly in the revised version of the manuscript.

 

Although the pH of 8 presented the best adsorption capacity between the pH studied (2, 4, 6, 8, 10), the pH_PZC trials gave us a middle result of 6.9 (line 237). Considering that when the pH value of the solution is below pH_PZC the adsorbent surface is positively charged, being more efficient in attracting anions [11]; therefore, there will be repulsion between the adsorbent surface and the MB molecules, since MB is a cationic dye. Also, MB solutions (20 mg L^-1) with pH 8 and 10 decreased after the adsorption process, keeping the pH value between 6 and 7.3 (Table 3S). This decrease probably occurs due to the interactions between H⁺ ions and the hydrolyzed form of MB (MB⁺) are weak; therefore, most of the H⁺ adsorbed on the surfaces of the adsorbents are released in solution [11]. We also observed that for BCs the removal efficiency did not change significantly with the change in pH values, demonstrating that electrostatic interactions are not the main factor in the removal of MB. With those results, we have chosen a pH of 7 for all the upcoming experiments.

2. 
   In line 295 you mentioned: At pH between 8 and 10, we saw that adsorption is favored… all this make me to wonder if the 7 value for the pH is the optimal one.

 

Response: The response above explains these comments also. 

3. 
   Also at pH 6, 8 and 10 (Figure 3b) the adsorption capacities of SBC are better that any BCs…in this respect I do not understand why to consume energy for 5 hours to carbonize the sugarcane biomass and get the comparable result as in case of initial SBC. It is not clear which is the novelty of your research?

 

Response: We have changed the Abstract and the last paragraph of the introduction to explain the novelty of this research. This research aimed to fill the gap of influence of carbonization time in the MB adsorption; however, we observed that even with 5 hours of carbonization the biochar does not show a significant increase in the adsorption capacity. In line 379 we described that: “Notwithstanding the decrease, SCB was still a better adsorbent than BCs under the same concentration conditions at 25 and 35 ºC. Fig 6 also reveals that the increase in temperature had a greater influence on the adsorption capacity of BC5, which proved to be the best adsorbent among BCs; however, the average adsorption capacity for BC5 at 25, 35, and 45 ºC were 13.9, 32.9, and 44.6 mg g-1, respectively, while for SCB it was 46.2, 49.4 and 46.9 mg g-1. This demonstrates that despite the carbonization time of five hours, increasing the surface area by 14x to SCB is still proved to be a better adsorbent for MB dye under the studied conditions. Besides, the similar SCB adsorption capacity between 25 and 45 ºC increases its applicability and is not dependent on the temperature of the effluent contaminated with MB dye.”

4. 
   Please compare the adsorption capacities with the one presented in the research literature for similar adsorbents.

 

Response: We have not compared the adsorption capacity with other studies because in our study we did not model the isotherms. Published studies often compare considering the q_e value given by the isotherm model. Notwithstanding, we explain the possibilities of the results observed, showing the possible reason why we do not model the isotherms. In line 121 (Supporting Information): “Due to the observed behaviors, we do not have an appropriate isotherm model for data modeling [12]. Nevertheless, the authors divided the curve into two parts for modeling; however, we did not do this with our data, because even dividing the points is not suitable for isotherm models. Research into solving this problem is already underway [13]; studied the insertion of predictive models based on neural networks for grouped adsorption data for adsorbent-adsorbate pairs in different concentrations of adsorbate [13]. The model developed by the authors was successfully applied to various equilibrium concentrations, regardless of the isotherm model used in the studies used.”

 

11. Li, X.Y.; Han, D.; Xie, J.F.; Wang, Z.B.; Gong, Z.Q.; Li, B. Hierarchical porous activated biochar derived from marine macroalgae wastes (: Enteromorpha prolifera): Facile synthesis and its application on Methylene Blue removal. RSC Adv. 2018, 8, 29237–29247, doi:10.1039/c8ra04929g.
12. Wang, P.; Wu, C.; Guo, Y.; Wang, C. SI - Experimental and theoretical studies on methylene blue and methyl orange sorption by wheat straw-derived biochar with a large surface area. Phys. Chem. Chem. Phys. 2016, 18, 30196–30203, doi:10.1039/c6cp04625h.
13. Zhang, K.; Zhong, S.; Zhang, H. Predicting Aqueous Adsorption of Organic Compounds onto Biochars, Carbon Nanotubes, Granular Activated Carbons, and Resins with Machine Learning. Environ. Sci. Technol. 2020, 54, 7008–7018, doi:10.1021/acs.est.0c02526.
14. 
    The conclusion section must be rewritten. The best optimal conditions, best adsorbent material and best adsorbent capacity must be presented in this section.
    
    Response: The conclusion was rewritten and the best conditions were described. The conclusion is now:

“In this study, BCs were produced at different carbonization times at 200 ºC to compare their adsorption capacities with SCB of the MB dye. Although the increase in superficial area with an increase in carbonization time, the results show that the SCB was still a better adsorbent than any BCs produced. We show that varying the MB initial concentration, the adsorption capacity shows inflection points and fluctuations, even at different temperatures; which predict the endothermic or exothermic nature of the adsorption process. SCB showed the better adsorbent capacity at all initial concentrations (10, 30, 60, 110, 150, 190, 230, and 270 mg L^-1) at 45 °C, and contact time of 360 minutes. With the proposed adsorption mechanism there is a predominance of physical adsorption, through Coulomb interactions, hydrogen bonds, and π-interactions. Therefore, the SCB is a low-cost alternative adsorbent for use in the treatment of wastewater contaminated with MB dye.”

 

1. The references must be adjusted as written in the instructions of Sustainability https://www.mdpi.com/journal/sustainability/instructions

 

Response: Thank you for this comment. The references were checked and corrected, and they are highlighted in the manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Congratulations on a great job. The author has made a substantial improvement for this article. The manuscript can be accepted for publication in the present form.