Advancing Biochar Applications: A Review of Production Processes, Analytical Methods, Decision Criteria, and Pathways for Scalability and Certification

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

The authors have made substantial improvements. The new resubmitted manuscript considers all previous comments, including the addition of comprehensive tables, and provides new sections and illustrations that help readers follow the text.

Hence, the new review has excellent standards in the field and will serve a broad range of disciplines including sciences, engineering, and material sciences. The article can be accepted without further revision.

Author Response

Response to Reviewer #1 Comments

The current review paper is interesting and it discusses one of the hot research topics related to sustainability. The manuscript can be accepted after the following major revision

Authors: We thank the Reviewer for the careful reading of the manuscript and the suggestions to improve the quality of our work. The work became clear and well-organized with the suggested modifications. We have tried to follow his/her remarks in the revised version of the paper.

The authors restructured some aspects to spell out the contributions of the work.

All the modifications can be seen in the document: Manuscript_Marked in orange color. In addition, the text was extensively reviewed and corrected for grammar, punctuation, and text clarity by a native English speaker.

We hope the corrections, changes, and edits suffice and the article can follow through for publication.

Notation:

• We use black color to reproduce the comments of the Reviewers.
• We use blue color for our responses and explanations.
• We use red color to report the actions that have been taken in the new version of the manuscript, following the suggestions of the Reviewer.

The responses to the specific questions are given below.

Reviewer Comment

Author’s Response

1. The authors have made substantial improvements. The new resubmitted manuscript considers all previous comments, including the addition of comprehensive tables, and provides new sections and illustrations that help readers follow the text. Hence, the new review has excellent standards in the field and will serve a broad range of disciplines including sciences, engineering, and material sciences. The article can be accepted without further revision.

no modifications asked. But, we modified and reviewed all the manuscript.

 

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The author has thoroughly revised according to the previous review, and I have no further suggestions. Attention should be paid to some references that display incorrect markings, such as lines 92, 135, etc., and the author needs to thoroughly review and revise them.

Author Response

Response to Reviewer #2 Comments

The review is well-written, logical, and systematic. I have a few suggestions.

Authors: We thank the Reviewer for the careful reading of the manuscript and the suggestions to improve the quality of our work. The work became clear and well-organized with the suggested modifications. We have tried to follow his/her remarks in the revised version of the paper.

The authors restructured some aspects to spell out the contributions of the work.

All the modifications can be seen in the document: Manuscript_Marked in orange color. In addition, the text was extensively reviewed and corrected for grammar, punctuation, and text clarity by a native English speaker.

We hope the corrections, changes, and edits suffice and the article can follow through for publication.

Notation:

• We use black color to reproduce the comments of the Reviewers.
• We use blue color for our responses and explanations.
• We use red color to report the actions that have been taken in the new version of the manuscript, following the suggestions of the Reviewer.

The responses to the specific questions are given below.

Reviewer Comment	Author’s Response
1. The author has thoroughly revised according to the previous review, and I have no further suggestions. Attention should be paid to some references that display incorrect markings, such as lines 92, 135, etc., and the author needs to thoroughly review and revise them.	References links have been revised and made, changes appear in orange color in the text.

 

Author Response File: Author Response.pdf

Reviewer 3 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

1. Language needs to be reorganized, such as Line 17-20; Line 33-39; Fig.1 and Fig.2 order; Line 164-177; Line 205-220.

2. Need references in Line 28-19.

3. Please check Line 155; Line 178; Line 304 ......

4. Table 4 requires more ref support.

5. Fig. 6 requires additional data for different temperatures，such as 300, 500, 600, 700.

6. English needs improvement.

 

Comments on the Quality of English Language

Improve

Author Response

Response to Reviewer #3 Comments

The study presented in the manuscript " Biochar from lignocellulosic biomass: the importance of physicochemical characterization and multi-criteria decision analysis for its application”.  However, the novelty and aim were limited. After an overall evaluation, this manuscript cannot be recommended for publication in this journal in its current form with some specific comments listed as follows:

Authors: We thank the Reviewer for the careful reading of the manuscript and the suggestions to improve the quality of our work. The work became clear and well-organized with the suggested modifications. We have tried to follow his/her remarks in the revised version of the paper.

The authors restructured some aspects to spell out the contributions of the work.

All the modifications can be seen in the document: Manuscript_Marked in orange color. In addition, the text was extensively reviewed and corrected for grammar, punctuation, and text clarity by a native English speaker.

We hope the corrections, changes, and edits suffice and the article can follow through for publication.

Notation:

• We use black color to reproduce the comments of the Reviewers.
• We use blue color for our responses and explanations.
• We use red color to report the actions that have been taken in the new version of the manuscript, following the suggestions of the Reviewer.

The responses to the specific questions are given below.

Reviewer Comment	Author’s Response	Revised Text
1. Language needs to be reorganized, such as Line 17-20; Line 33-39; Line 164-177 ; Line 205-220	Changes were made to improve the text's readability. Changes appear in Orange color.	Line 17-20: Although extensive research has been conducted on the physical and chemical properties of biochar, there remains a significant gap in evaluating its practical applications. This paper emphasizes the role of Multi-Criteria Decision Analysis (MCDA) as a valuable tool for optimizing both biochar production and its application strategies Line 33-39: Commonly known as coal, carbonaceous materials have been extensively studied and have reached a crucial stage of development, serving as precursors for widely used materials such as activated carbon. And with exceptional adsorption capabilities in both liquid and gas phases, these materials are highly versatile and can be tailored for specific applications, similar to traditional coal. Line 164-177: Established in 2010, the Chinese Biochar Network (CNB) has played a key role in advancing discussions on biochar within both academia and industry in China [45]. Alongside other organizations, CNB has also been instrumental in defining classification parameters for raw materials and biochar products deemed suitable for agricultural applications. Notably, the International Biochar Initiative (IBI) and the European Biochar Foundation (EBC) have contributed significantly to these efforts [46]. Similar to China, the United States has a strong agricultural sector and actively seeks innovative technologies to boost productivity while reducing environmental impacts, particularly greenhouse gas emissions. The US Biochar Initiative (USBI) has been pivotal in this context, expanding its activities and effectively coordinating the efforts of biochar producers nationwide. Additionally, the US has attracted investments in pilot plants dedicated to biochar production, focusing on three key objectives: soil enhancement, carbon sequestration, and greenhouse gas mitigation. These collective efforts represent a significant step toward sustainable agriculture and environmental conservation [47] Line 205-220: The proportion between these three fractions is influenced by experimental conditions such as temperature, heating rate, residence time, and pyrolysis type. The pyrolysis process can be classified into three main types: Slow pyrolysis: Occurs at temperatures between 300–650 ºC, with a residence time ranging from 5 minutes to 12 hours (longer duration) and a heating rate of 10–30 ºC min⁻¹. This process primarily yields a significant fraction of solids (biochar), accounting for 20–40% of the total products [50,53,54]; Fast pyrolysis: Takes place at higher temperatures (above 500 ºC) with an extremely short residence time (1–2 seconds) and a rapid heating rate (>1000 ºC min⁻¹). This method maximizes bio-oil production, with the gaseous phase comprising 50–70% of the output, while the liquid and solid residues account for 10–30% and 15–20%, respectively [46,54]; Flash pyrolysis: Operates at even higher temperatures (above 800 ºC) with an ultra-short residence time (<0.5 seconds) and a heating rate exceeding 1000 ºC min⁻¹[46]. Understanding these different pyrolysis systems is essential for analyzing how process parameters influence the distribution of products. Figure 3 illustrates the three possible fractions resulting from biomass pyrolysis: (i) a gas phase consisting of non-condensable gases (H₂, CO, CO₂, CH₄, and other light hydrocarbons); (ii) a liquid phase composed of organic acids, water, and lower molecular weight tar; and (iii) a solid phase consisting of biochar
2. 2. Need references in Line 28-19.	Reference added
3. Please check Line 155; Line 178; Line 304 ......	The links were corrected.
4. Table 4 requires more ref support.	More data were added to the table
5. Fig. 6 requires additional data for different temperatures， such as 300, 500, 600, 700.	Four FTIR spectra of silkworm biochar produced at temperatures of 300°C, 400°C, 500°C, and 600°C were added.
6. English needs improvement	It has been reviewed.

 

Author Response File: Author Response.pdf

Reviewer 4 Report (Previous Reviewer 4)

Comments and Suggestions for Authors

In the Introduction and Abstract, I believe it is necessary to reinforce how the work contributes to the area so that, whoever reads it, knows the orientation of the review. 

The suitability of biochar in energy applications is mentioned, but it would be useful to discuss its applicability in other fields so that this work can serve as a starting point for future research.

Future research directions, such as the optimization of production methods or emerging applications of biochar, need to be identified.

I suggest a grammatical revision of some parts per work. For example the paragraph: “This transformation is evidenced by a reduction in the O/C and H/C ratios, which strongly correlate with an increase in HHV [59,76], enhancing the biochar's suitability as an energy source” is not clear to me. 

Author Response

Response to Reviewer #4 Comments

The subject matter is interesting, and a review of these characteristics can contribute to concentrating on the different sources of information that exist. It has several strengths such as the importance given to the physicochemical characterization of biochar, the description of advanced characterization techniques such as FTIR, Raman, TGA, SEM, ssNMR, and XPS, and the attempt to cover aspects of chemistry, engineering, agriculture and environmental sciences, the article adopts a multidisciplinary approach. However, I believe that there are several aspects that need improvement.

Authors: We thank the Reviewer for the careful reading of the manuscript and the suggestions to improve the quality of our work. The work became clear and well-organized with the suggested modifications. We have tried to follow his/her remarks in the revised version of the paper.

The authors restructured some aspects to spell out the contributions of the work.

All the modifications can be seen in the document: Manuscript_Marked in orange color. In addition, the text was extensively reviewed and corrected for grammar, punctuation, and text clarity by a native English speaker.

We hope the corrections, changes, and edits suffice and the article can follow through for publication.

Notation:

• We use black color to reproduce the comments of the Reviewers.
• We use blue color for our responses and explanations.
• We use red color to report the actions that have been taken in the new version of the manuscript, following the suggestions of the Reviewer.

The responses to the specific questions are given below.

Reviewer Comment	Author’s Response
1. In the Introduction and Abstract, I believe it is necessary to reinforce how the work contributes to the area so that, whoever reads it, knows the orientation of the review.	It has been reviewed
2. The suitability of biochar in energy applications is mentioned, but it would be useful to discuss its applicability in other fields so that this work can serve as a starting point for future research.	In the section 4.5.4.Other applications it was pointed the possibilities of the use of biochar as: ·       Energy storage ·       Supercapacitor ·       Electrodes to detect heavy metals ·       non-enzymatic glucose sensing ·       electrochemical immunoassays for detecting viral proteins ·       environmental monitoring ·       Substitute for carbon black in batteries.
3. Future research directions, such as the optimization of production methods or emerging applications of biochar, need to be identified.	The final paragraph has been modified to make the future research directions clearer.
4. I suggest a grammatical revision of some parts per work. For example the paragraph: “This transformation is evidenced by a reduction in the O/C and H/C ratios, which strongly correlate with an increase in HHV [59,76], enhancing the biochar's suitability as an energy source” is not clear to me. "	It has been reformulated.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The current review paper is interesting and it discusses one of the hot research topics related to sustainability. The manuscript can be accepted after the following major revision

1-- Pls. provide proper references : “for functionalized mate- 49 rials applicable in chemical synthesis”

 

2-- Figure 3 is blurred. Pls. modify it.

3-- Provide one sample with both FTIR and Raman to illustrate the peaks of biochar, besides the table you provided.

4-- Although figure 2 provides the trend related to biochar during the past 11-12 years. However, it does not show the origin of biochar. Since this review is related lignocellulosic materials-based biochar, pls. provide another a similar figure that shows the origin of the biochar (i.e. lignocellulose, plastics, paper, egg shell waste, etc…)

4.1-- Likewise, pls. provide the main applications /trends for utilizing biochars based on web of science information - further to the brief discussion in page 3-  “biochar in different domains underscores its significance in contemporary studies, and  ongoing research continues to unveil more opportunities for its sustainable and effective  utilization in various applications (soil amendment [6–8], biofuel [9–11], adsorbent material [12–14] and wastewater treatment [15–17]) and as a support for functionalized mate- 49 rials applicable in chemical synthesis.”  You may take the data or overview from section 6.

 5-- Pls. address other applications including electrochemical sensors, optical sensors, etc….  (see this article: https://www.sciencedirect.com/science/article/pii/S0026265X20320452 )

 

Also, applications of biochars as an alternative to carbon black in batteries as well as energy storage devices  (see this article https://pubs.acs.org/doi/10.1021/acssuschemeng.2c02974  ); ( https://pubs.acs.org/doi/10.1021/acsomega.2c06054 ) ‘ ( https://www.mdpi.com/2313-0105/10/5/144 )

Recent applications in superwetting materials. Provide introduction about superhydrophobicity of biochars with some examples for its applications . examples are given below ( https://www.sciencedirect.com/science/article/pii/S0048969721015850 ) ( https://www.sciencedirect.com/science/article/pii/S0167732223005391  ) ( https://www.sciencedirect.com/science/article/pii/S0167732223005391  ) ( https://www.nature.com/articles/s41598-023-36589-0 ) ( https://www.mdpi.com/2571-8797/6/1/15 )

 6-- What about XRD patterns for biochars? Is it  useful for charecterization. Please comment and add section  if necessary.

 

 7-- It is highly recommended to add figures during the discussion for each application from recent literature. In the current state, the manuscript is not attractive for readers as there are no illustrations.

 

 8-- In the introduction, it is also recommended to mention the benifits of converting lignocellulosic waste into biochar to reduce the CO2 emissions by just burning as well as to avoid the increase of carbon content in the soil. 

 

 

 

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

The review is well-written, logical, and systematic. I have a few suggestions. The introduction section is too lengthy and could be condensed. Additionally, the content from Section 2, "Prospective study on biochar research," could be integrated into the introduction or deleted. I recommend deleting Section 3 to ensure the remaining content is more focused. This will enhance the overall focus of the review.

Reviewer 3 Report

Comments and Suggestions for Authors

The study presented in the manuscript " Biochar from lignocellulosic biomass: the importance of physicochemical characterization and multi-criteria decision analysis for its application”.  However, the novelty and aim were limited. After an overall evaluation, this manuscript cannot be recommended for publication in this journal in its current form with some specific comments listed as follows:

1. What is the motivation behind choosing multi-criteria decision analysis? As known, these methods are very conventional.

2. The authors need to present the key message specifically and unambiguously in abstract.

3. In manuscript, all figures are also not clear and the drawing standards are not consistent. The authors should revise it carefully and present it in a way that can be easily understood by a layperson.

4. Furthermore, the authors have not assessed the whole article, lacks logic. Such as Line 42-82.

5. Line 51-56, a Table should be needed.

6. The article seems to be comprehensive, but it is difficult for readers to get useful information.

 

Comments on the Quality of English Language

English needs to be improved.

Reviewer 4 Report

Comments and Suggestions for Authors

The subject matter is interesting, and a review of these characteristics can contribute to concentrating on the different sources of information that exist. It has several strengths such as the importance given to the physicochemical characterization of biochar, the description of advanced characterization techniques such as FTIR, Raman, TGA, SEM, ssNMR, and XPS, and the attempt to cover aspects of chemistry, engineering, agriculture and environmental sciences, the article adopts a multidisciplinary approach. However, I believe that there are several aspects that need improvement.

- The discussion on biochar applications, although extensive, is too general. I believe that the evaluation of each specific application should be further elaborated.

- The article does not present much original experimental data that would allow a detailed comparison between the cases analyzed.

- The section on Multicriteria Decision Analysis (MCDA) lacks details on how MCDA methods were applied and the specific results of this application.

The quality of the figures (resolution) should be improved.

- Emphasizing the number of publications on biochar may not be a strong indicator of the quality or relevance of research. This part should be removed.

- Although sustainability is mentioned, a detailed assessment of the environmental and economic impacts of biochar production and use may be lacking. There is much literature on this topic.

This article could benefit from a more explicit comparison between biochar and other alternative technologies or materials.

Discussions on the scalability and practical large-scale implementation of biochar have not been sufficiently developed.

Comments on the Quality of English Language

English quality has an academic focus, and technical vocabulary is widely used. No obvious typographical or spelling errors were detected; however, a final in-depth review of the grammar is recommended.