Preparation of Modified Biochar and Its Adsorption of Cr(VI) in Aqueous Solution
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Abstract:
1. Please revise the abstract to include more detailed data on some of the key results.
Introduction
1. I think the authors could include a comparison table that contrasts the performance of their adsorbent with other types of adsorbents.
2. The introduction contains too few references; the authors might consider adding more citations to bolster their arguments.
3. The authors stated that “Biochar has a relatively carbon-based structure, high porosity and large specific surface area. As a surface adsorbent, it is similar to activated carbon in some aspects. As an environmentally friendly material, biochar is widely used in water environment treatment. It is considered to be one of the important adsorbents for removing heavy metal ions and removing organic pollutants” Please support this text by adding the following reference: https://doi.org/10.1007/s11356-023-27688-6 and https://doi.org/10.1007/s13399-023-03904-8
Materials and Methods
2. Section 2.1.2. Determination of adsorption content of Cr ( VI ) in solution by native biochar at different temperatures: I have many concerns in this part, including:
A. The authors stated, “The residual concentration of Cr (VI) was determined according to the standard curve.” I did not get the point of the standard curve (UV-Vis or ICP or what). please write the Cr analysis method in detail
B. The authors present inconsistent results in this section; these results should be relocated to the 'Results and Discussion' section as part of a preliminary experiment.
Results and Discussion:
3. Section 3.1.2. BET and pore size analysis: Please combine Figures 3-2, 3-3, 3-4, and 3-5 in one Figure.
4. The surface area data tabulated in Table 3-1 appears to be inconsistent with the data shown in Figures 3-2 to 3-4. For example, the surface area of MB is listed as 1215.6153 in the table, while the highest volume shown in Figure 3-2 is 500. Could the authors please clarify this discrepancy?
5. The authors should show the EDS analysis for all the prepared samples and also should show the main content of each biochar.
6. IR analysis: the authors stated,” The absorption peak at 814 cm-1 is the symmetric stretching vibration absorption peak of Si-O-Si bond, the absorption peak at 464 cm-1 is caused by the bending vibration of Si-O bond, and the absorption peak at 1085 cm-1 is caused by the antisymmetric vibration of Si-O-Si. Please write the source of silicon in the prepared biochar and support your text with references.
7. IR analysis: Please support your text with references for all the assigned peaks.
8. Section 3.2.1, 3.2.2, 3.2.3: The authors should move the first paragraph to the experimental part.
9. Section 3.3. Adsorption kinetics experiment: The authors should write a deep discussion of the obtained results.
10. Section 3.4. . Isothermal adsorption experiments: This paragraph should be rewritten, and the authors should discuss every parameter obtained from the equilibrium models.
11. Section 3.4: Why did the authors not use other equilibrium models like Temkin and D-R to illustrate the type of the adsorption process?
12. Section 3.6.2. FTIR analysis after Cr(VI) adsorption: Three absorption peaks appear between 1000 and 1500 cm-1 after the adsorption of Cr. Could you please clarify why?
Author Response
Please see the attachment. Thank you.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
# 2.2.1.: on what basis the acid and alkali concentrations were determined? if the previous works are taken for reference, please cite. should FMB not be named FeMB? F stands for Fluorine.
# Fig 3-1 to 3-5: please set the same y-axis range for all figures for ease of comparison.
# Fig 3-10 onwards: resolution is bad.
provide the adsorption condition in the caption
# 3.5.: what is the elution % of Cr in the regeneration step? please add the elution profile along with the removal efficiency in each cycle.
# reduction of Cr(VI) during the course of adsorption onto biomass is a known observation. in this manuscript too, the similar might be the reason. also, gradual loss in the adsorption capacity indicates that some of the adsorbed Cr is reduced to Cr(IV) and has not been eluted well. a detailed discussion taking reference from past works is expected.
Author Response
Please see the attachment. Thank you.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
Please, address the following points:
1. Abstract. Please include the maximum Cr adsorption capacity achieved.
2. Introduction:
- The sentence "Compared with the above methods, the adsorption method has higher heavy metal adsorption" is not adequate since only adsorption method can have adsorption. Maybe, changing "heavy metal adsorption" to "heavy metal removal" will be better.
- The paragraph starting with "Biochar has a relatively carbon-based structure..." needs to be referenced.
- The sentence "Some researchers have made an in-depth research on the removal of heavy metals by biochar, and found that the adsorption capacity of traditional original biochar is poor." also needs a reference.
3. Materials and Methods.
- I guess that sub-section "2.1.2. Determination of adsorption content of Cr ( VI ) in solution by native biochar at different temperatures" are results and should be included in that section.
- Why samples were taken after 12 h? Did you test that the equilibrium was reached? In fact, in section "2.2.3. Adsorption experiments" the adsorption time was 24 h.
- Figure 2-1. Qe should be defined somewhere in the text.
- Section 3.2.1. The sentence " the adsorption sites are rich" is not clear, I guess you mean that there are many adsorption points, right?
- In: "Figure 3-11. Effect of dosage Cr(VI) adsorption by biochars." it would better changing to "Effect of Cr(VI) dosage on adsoprtion by biochars" or similar.
Comments on the Quality of English Language
In general the English is OK, only some minor changes are required.
Author Response
Please see the attachment. Thank you.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The authors have addressed the reviewers' comments and prepared a substantially improved manuscript. I recommend the publication of the manuscript.
Author Response
Thanks for the reviewer's comments, our research team will continue to work hard.
