Influence of Technical Parameters of the Pyrolysis Process on the Surface Area, Porosity, and Hydrophobicity of Biochar from Sunflower Husk Pellet

Round 1

Reviewer 1 Report

The issue discussed in the article fits well into the profile of the journal. It concerns the processing of waste into a value-added product that can be used in the processes of removing pollutants from water solutions. This a very topical topic because obtaining biochar dedicated to specific applications requires a lot of research in the field.

Critical remarks:
1. Please characterize biochar in terms of C, N, P content and micronutrient content - if the Authors conclude that they may affect the assimilation of micronutrients by plants.
2. The analysis of the surface chemistry of biochar produced under different parameters and the sorption experiment is missing. Do the authors plan to continue research in this direction?
3. What was the heating rate used?
4. Improve the quality of Fig. 5  (please use white text instead of blue)

Author Response

Thank you for your valuable comments and we hope that the changes will allow the publication of the article.

1. Please characterize biochar in terms of C, N, P content and micronutrient content - if the Authors conclude that they may affect the assimilation of micronutrients by plants.

A new subsection 3.4 - Content of selected biochar components and pH has been added to the manuscript.

 

2. The analysis of the surface chemistry of biochar produced under different parameters and the sorption experiment is missing. Do the authors plan to continue research in this direction?

The authors plan to continue research, including the chemistry of the surface of the produced biochar and the use of the produced biochar in the processes of removing pollutants from water solutions

3. What was the heating rate used?

Introduced into the manuscript in section 2.2.

“The applied heating rate for 480°C was 4.00 and 7.38°C·min^-1, for 530°C it was 4.42 and 8.15°C·min^-1 and for 580°C it was 4.83 and 8.92°C·min^-1. The residence time of the sam-ple at the set temperature was 10 and 60 minutes”

4. Improve the quality of Fig. 5 (please use white text instead of blue)           The authors decided to resign from placing the drawing due to its poor quality/readability after introducing white inscriptions.

Reviewer 2 Report

In this manuscript, the authors studied various parameters of the pyrolysis process of biochar from sunflower husk pellet, and tested their influence on the surface area, porosity, and hydrophobicity. However, the following problems should be addressed before further consideration of publication:

1. Scale bars should be added and clearly shown in Figure 1-2, and 5-8.

2. Figure 2 should be cropped with revised scale bars, and the labels in Figure 2d can be removed. The authors need to add SEM images of other typical samples, and thus Figure 2 can be revised as a large composite one for better comparison and demonstration.

3. For BET analysis, the N₂ adsorption−desorption isotherms of various samples should be contained. Thus, the detailed measurement of BET surface area, pore volume, and pore size can also be listed in detail in one table.

4. In Table 2, can the grain size be evaluated using the same numbers of measurement and shown in “average value ± standard deviation”? Figure 5 is also confusing, which needs to be revised with detailed description.

5. All the figures need to be revised with the consistent annotation and formatting. Some figures can be merged into a large one. In the caption of Figure 8, “biocar” was one wrong description.

6. FT-IR characterizations are suggested to investigate the functional groups of the biochar samples and the initial states for better comparison.

7. Table 4 should be revised, an appropriate unit of “mg/kg” can be used.

8. General applicability of the conclusion for other types of biochars can be discussed in the manuscript, and the main difference with other researches can be added.

Author Response

Thank you for your valuable comments and we hope that the changes will allow the publication of the article.

1. Scale bars should be added and clearly shown in Figure 1-2, and 5-8

AUTHORS- As suggested by the reviewer, scale bars were placed on the all figures

2. Figure 2 should be cropped with revised scale bars, and the labels in Figure 2d can be removed. The authors need to add SEM images of other typical samples, and thus Figure 2 can be revised as a large composite one for better comparison and demonstration.

AUTHORS- Figure 2 cropped and labels removed in Figure 2d. As suggested by the reviewer, to compare the surface morphology of biochar produced from sunflower husk pellets, SEM photos of the surface morphology from walnut shells were included. The aim was to show how the type of substrate used affects the nature and properties of biochar. Comparing both biochar, it is found that the biochar produced from a nut has a less developed microporous structure. In the case of biochar from sunflower husk pellets, the difference in surface morphology will be associated with a higher sorption potential.

3. For BET analysis, the N₂adsorption−desorption isotherms of various samples should be contained. Thus, the detailed measurement of BET surface area, pore volume, and pore size can also be listed in detail in one table.

AUTHORS-There are several procedures for determining the specific surface area of solids. As indicated in the review, one of the methods is the analysis of nitrogen adsorption isotherms at 77-78 K. In our research, BET surfaces were determined using the PoreMaster 33 Hg Porosimeter. It is an automatic pore size and volume distribution analyzer using the rapid mercury intrusion method. Therefore, due to the different methodologies, we are unfortunately unable to include the N2 adsorption-desorption isotherm in our studies.

4. In Table 2, can the grain size be evaluated using the same numbers of measurement and shown in “average value ± standard deviation”? Figure 5 is also confusing, which needs to be revised with detailed description.

AUTHORS- Table 2 has been corrected. Measurements are presented as "mean value ± standard deviation". The authors decided to resign from placing the fig.5 due to its poor quality/readability after introducing white inscriptions.

 

5. All the figures need to be revised with the consistent annotation and formatting. Some figures can be merged into a large one. In the caption of Figure 8, “biocar” was one wrong description.

AUTHORS- The authors have tried to maintain consistent annotation and formatting. According to the reviewer's proposal, Fig. 3 and Fig. 4 were combined in one drawing. The authors believe that the combination of other drawings would not be legible and clear. In Fig. 8, the word "biocar" has been corrected to "biochar".

6. FT-IR characterizations are suggested to investigate the functional groups of the biochar samples and the initial states for better comparison.

AUTHORS- The authors intend to expand the scope of research using FT-IR in the future. However, due to the lack of the required equipment in our Research Unit, it is planned to send samples to other institutes for analysis in the future. As noted by the reviewer, this will allow for a more thorough examination of the functional groups of the biochar samples.

7. Table 4 should be revised, an appropriate unit of “mg/kg” can be used.

AUTHORS- corrected in table 4

8. General applicability of the conclusion for other types of biochars can be discussed in the manuscript, and the main difference with other researches can be added.

AUTHORS- added in 3.1. and in summary

Reviewer 3 Report

The manuscript ''Influence of technical parameters of the pyrolysis process on the surface area, porosity, and hydrophobicity of biochar from sunflower husk pellet'' investigated on effect of change in temperatures functions on physical properties of biochar. There are some important points:

 

The abstract is NOT well structure and needs to be rewrite and a little more extent!

Keywords need to be special, NOT repeating words from title!

lines 54-68: Regard to effect of pyrolysis temperature on biochar surface characteristics I suggest to add these two new references that are fit to your scope: https://doi.org/10.3390/su142214722 and https://doi.org/10.1002/ldr.4464

line 118: ''...heating time, and reaction time, have already been described in the publication [40].''.--> Delete this types of sentences. Make the current work special one! This paper should be stand by itself, so bring any data that need to be present!

line 120: ''heating times (65 minutes and 120 minutes) and retention times (10 minutes and...''.-->  we have some common expressions that are usual in pyrolysis literature such as ''heating rate'' and ''residence time''. In your case, there are two important point: 1) heating times and retention times SHOULD be replaced with heating rate and residence time, respectively. 2) The unit of heating rate is ℃/min, NOT minutes that you mentioned. For instance when we say heating rate is 65 ℃/min, it means in each min the temperature will increase 65 ℃. Is it your mean?

line 146: what about CHNO and other chemical analyses?

line 151: scientific unit is wrong. ''m2/g''-->m2 g-1. check it across the text.

Table 1: Warm-up time? It's NOT clear!

line 228: Too high a rate of heating can cause a reduction...--> Need to be rephrased.

line 235: 480℃ --> 480 ℃

Check whole text for misspelling and grammer mistakes.

Reference style is NOT correct. Please check it base on instructures for authors. For example journal names should be abbreviation.

Good Luck!

Author Response

Thank you for your valuable comments and we hope that the changes will allow the publication of the article.

 

• The abstract is NOT well structure and needs to be rewrite and a little more extent!

                        The abstract has been corrected

• Keywords need to be special, NOT repeating words from title!

keywords have been changed

• lines 54-68: Regard to effect of pyrolysis temperature on biochar surface characteristics I suggest to add these two new references that are fit to your scope: https://doi.org/10.3390/su142214722 and https://doi.org/10.1002/ldr.4464

The manuscript was supplemented with information from very interesting articles proposed by the reviewer. Featured articles are [17] and [33] items in the reference list

• line 118: ''...heating time, and reaction time, have already been described in the publication [40].''.--> Delete this types of sentences. Make the current work special one! This paper should be stand by itself, so bring any data that need to be present!

All data/parameters were entered in the manuscript. The changes made are marked in yellow.

• line 120: ''heating times (65 minutes and 120 minutes) and retention times (10 minutes and...''.-->  we have some common expressions that are usual in pyrolysis literature such as ''heating rate'' and ''residence time''. In your case, there are two important point: 1) heating times and retention times SHOULD be replaced with heating rate and residence time, respectively. 2) The unit of heating rate is ℃/min, NOT minutes that you mentioned. For instance when we say heating rate is 65 ℃/min, it means in each min the temperature will increase 65 ℃. Is it your mean?

We agree and thank you very much for such valuable attention. Appropriate nomenclature has been introduced throughout the manuscript.

• line 146: what about CHNO and other chemical analyses?

AUTHORS- A new subsection 3.4 - Content of selected biochar components and pH has been added to the manuscript.

• line 151: scientific unit is wrong. ''m2/g''-->m2 g-1. check it across the text.

Corrected

• Table 1: Warm-up time? It's NOT clear!

Changed/corrected

• line 228: Too high a rate of heating can cause a reduction...--> Need to be rephrased.

Corrected

• line 235: 480℃ --> 480 ℃

corrected

• Check whole text for misspelling and grammer mistakes.

The text of the article has been corrected by a native speaker

• Reference style is NOT correct. Please check it base on instructures for authors. For example journal names should be abbreviation.

Corrected

Round 2

Reviewer 2 Report

I am satisfied with your responses. Good luck.

Reviewer 3 Report

The current manuscript was properly upgraded and met all mentioned points in the previous version. It potentially can be published!