Adsorption Equilibrium of CO₂ on Microporous Activated Carbon Produced from Avocado Stone Using H₂SO₄ as an Activating Agent

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript, the authors synthesized biomass-based activated carbons for CO2 adsorption. Some specific comments are as follows:

1. What is precursor of this work, in the title it is avocado seed, in the text, it is avocado stone, this should be consistent.

2. The yield of carbons should be given.

3. Do these carbons contain heteroatoms? will they affect the CO2 uptake?

4. In XRD, there shows some sharp peaks, why?

5. The authors only test the CO2 adsorption under 0C for all the samples, which is unrealistic in actual application. CO2 adsorption under 25C should be tested and compared with recent carbonaceous CO2 adsorbents. Some examples are: https://doi.org/10.1016/j.fuproc.2023.107854 

https://doi.org/10.3390/molecules28041772

 

6. Have the authors tested the morphology of these carbons?

 

 

Comments on the Quality of English Language

NA

Author Response

Dear Reviewer,

Thank you very much for your questions and comments. They made our manuscript  better. I have attached the file with the answers below.

best Regards

Michalkiewicz

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript on using avocado seeds to produce activated carbonate contains significant flaws in experimental designs. XRD has low sensitivity for amorphous/poorly crystalline materials. Using it as the sole method to characterize the "crystal structure" of the experimental product is inadequate. The authors did not address the sharp peaks ~ 28 and 40 degrees. Also, the authors did not provide the XRD pattern for the starting materials so it is impossible to compare. Further microscopy and spectroscopy experiments are needed to provide a reasonable characterization of the materials. Without careful characterization of the product, I would recommend rejection of this manuscript.

Author Response

Dear Reviewer,

Thank you very much for your questions and comments. They made our manuscript  better. I have attached the file with the answers below.

best Regards

Michalkiewicz

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

       This paper investigated the preparation of activated carbon (AC) products from avocado stones produced through chemical activation using sulfuric acid at temperatures (700-800°C).  Some serious comments were addressed as follows.

 

1.      The sources of biomass feedstock (avocado seeds) and its pretreatments (like particle size after shredding and screening) should describe in detail because they played an important factor in the properties of AC products.

2.      The description about the AC production was too simple.  The basic process conditions, including heating rate, residence time, batch amount, furnace type (vertical or horizontal in the tube furnace.  What are the sizes of the tube reactor?), should be described in the Sec. 2.1.

3.      The data on the thermochemical properties in the starting feedstock, especially in thermogravimetric analysis (TGA), elemental contents and proximate analysis, should be provided, because these values played a vital role in the selection of process conditions and the properties of resulting AC products. 

4.      The description about the adsorption isotherm equations in the Sec. 3.1 should be significantly reduced.

5.      Concerning the Rouquerol criteria for determining the BET surface area of microporous materials, the authors should summarize the correlation results of the BET equation, including relative pressure range, C, n_m and standard deviation (R²).

6.      In this work, only four AC products were used to measure the CO₂ adsorption by using ASAP 2460.  The authors should discuss the relationship between pore properties and process parameters elaborately.  For example, the authors should discuss their differences between the causes of carbonization and activation.

7.      According to my experience in the AC preparation, the data on the yields and pore properties of resulting AC products were not often consistent.  Thus, the repeatability of the data should be stated in detail.

8.      The pore properties of resulting AC were not significant for the effective adsorption of CO₂ at low concentrations (or pressure).  In this regard, the chemical activator (H₂SO₄) was not available in the chemical activation for producing AC.  Also, it is not a novel activator.

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

Dear Reviewer,

Thank you very much for your questions and comments. They made our manuscript  better. I have attached the file with the answers below.

best Regards

Michalkiewicz

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

Please check the uploaded document

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Please check the uploaded document

Author Response

Dear Reviewer,

Thank you very much for your questions and comments. They made our manuscript  better. I have attached the file with the answers below.

best Regards

Michalkiewicz

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript lacks the comparison with previously reported results.

Author Response

There was no comments

Reviewer 2 Report

Comments and Suggestions for Authors

I think the authors have addressed most of my concerns with the identification of amorphous/ low crystallinity using FTIR. I would think it is okay to be accepted.

Author Response

Reviewer 1

The manuscript lacks the comparison with previously reported results.

 

You are right we added the comparison in Table 4: CO2 adsorption of various carbons at 1 bar and 0°C and comment:

Tab. 4 presents a summary of CO2 adsorption outcomes for activated carbons derived from diverse carbon sources. While our CO2 adsorption results may not claim the top position, they remain competitive when juxtaposed with outcomes from alternative materials.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Although the authors raised the proper replies to my comments, the biomass-derived activated carbon (AC) has been extensively studied in the literature.  In addition, the pore properties of the resulting ACs are too low to remove the CO2 from the gas stream.   The authors may try to use other activating agents (e.g., potassium salts) in the production of high-surface-area ACs from the novel biomass (avocado seeds).

Author Response

We acknowledge your valid point regarding the extensive literature on biomass-derived activated carbon (AC) and the limitations of pore properties in our current ACs for CO2 removal from gas streams. You have provided us with valuable insights, and we are committed to addressing these concerns in our future work.

We understand the importance of exploring alternative activating agents, such as potassium salts, to enhance the surface area of ACs derived from novel biomass sources like avocado seeds. This indeed is an exciting avenue for research, and we are planning to delve into this area in our upcoming research projects.

Your feedback has underscored the need to expand our research scope and consider a wider range of activating agents to improve the CO2 adsorption capacity of our ACs. We believe that your suggestions will contribute significantly to the advancement of our work. We are going to applied a new series of sorbents activated K2CO3.

The primary objective of this publication was to focus on the utilization of H2SO4 as an activator and to develop an activation method that could result in higher textural parameters compared to the methodology described in reference [10.1021/ie402627d], where H2SO4 was also used as an activator.

Our research yielded a notable success, as the textural parameters were considerably higher and CO2 adsorption was possible. CO2 adsorption over AC produced from avocado seeds using H2SO4 as an activating agent is described for the first time by us.

Thank you for your valuable guidance, and we look forward to sharing our improved findings in subsequent publications.

 

The information was added: “The objective was to emphasize the utilization of H₂SO₄ as an activator and to devise an activation method that could yield higher textural parameters in contrast to the methodology delineated in reference [20], where H₂SO₄ was similarly employed as an activating agent.”

 

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

The article can be accepted

Author Response

There was no comments

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

Based on the reviewers' positive response, it can be accepted in current form.  It's better to extend the work for higher pore properties by other chemical activators like potassium salts.