Removing the Oxamyl from Aqueous Solution by a Green Synthesized HTiO₂@AC/SiO₂ Nanocomposite: Combined Effects of Adsorption and Photocatalysis

Round 1

Reviewer 1 Report

The article "Removing the oxamyl from aqueous solution by a composite of nano TiO₂@Green activated carbon: combined effects of adsorption and photocatalysis" is devoted to the synthesis of a composite material with photocatalytic and adsorption properties. The authors' idea is not new. There are a lot of such studies. In addition, the authors did not show the comparative advantages of their results.

The work is super voluminous; a lot of experiments were carried out by the authors. However, data are presented only for a small part. The work is written extremely carelessly. I believe that such is unacceptable for a journal of such a level as "Catalysts". I cannot recommend this work for publication, at least in its current form.

Here are some of the most significant comments:

1. Authors ignore subscripts and superscripts throughout the article. They do not adhere to the uniformity of terminology. This spoils the impression of the content of the work and misleads the reader. (For example, how the composite material is labeled. I counted at least 7 different ways of writing)
2. As for the experimental technique. Item "Preparation of activated carbon from rice straw". In the Carbonization step, how many samples were obtained carbonized under different conditions? (according to my calculations 15). The authors write that they were all characterized by SEM and adsorption. Unfortunately, I did not find these data in my work.
3. The item Activation step. The authors write "The highest iodine and methylene blue adsorption of obtained RSC was selected for the chemical activation step. "However, it is not clear which of the carbonated samples this is. According to my calculations, 48 samples should have been obtained at this stage. Again, the authors do not provide any data on these samples. The readers can only believe.
4. Clause "2.1. Synthesis of Nanocomposite TiO2 @ AC". It is unclear which of the 48 AC samples the authors used in this point. In this experiment, 6 samples of composite materials were obtained. What is meant by the decomposition of the AC? How was 5% determined? This data is also absent in the work.
5. What composition of the composite material was used in the PC experiments and why? Why were the experiments carried out under sunlight, since it is known that the band gap of anatase is 3.2 eV? How does the electronic structure of titanium dioxide in a composite change?
6. It can be seen from the experimental results that the difference between the efficiency in the dark and in the light is negligible. This indicates that sunlight is ineffective. Only the UV part of the solar spectrum works.
7. 7. Figure 1. Please add ticks on the axis. What exactly is the composition of the composite? At 25.29o I don't see the peak that the authors describe! If the authors write about the appearance of the rutile phase in other compositions, then it is necessary to provide evidence, I do not see these data in the work. It is known from the literature that a mixture of anatase and rutile exhibits better photocatalytic activity (for example, commercial P25) than the pure anatase phase. Why haven't the authors checked this?
8. Figure 2. Firstly, the quality of the picture is unacceptable. What composition is this image for? I do not see in the picture what the authors describe in the text. For example, the statement about the tetragonal form. I can clearly see the hexagonal structure. The EDX spectrum must be presented in an acceptable form as a continuous spectrum with marked peaks characteristic of the elements.

Author Response

Thanks, reviewer for your comments.

All comments have been done.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have taken into account the suggestions, the article is now publishable in the present form

Author Response

Thanks, reviewer.

Author Response File: Author Response.docx

Reviewer 3 Report

The present manuscript reports on the photocatalytic degradation and adsorption of the oxamyl over a nano-TiO₂@activated carbon composite catalyst. Although experimental conditions are well described, and kinetic studies are properly carried out, the presentation of the data is very approximate. Therefore, the manuscript may be accepted for publication after major revision. See details here below.

1. Please remove yellow highlights from the text, make formatting uniform and correct all typing errors (there are a lot of such errors, e.g. superscripts, subscripts).
2. Please mention in the introduction the employment of other biomass-derived carbonaceous materials (e.g., biochar) coupled with TiO₂ to produce composite materials showing a synergistic combination of reactant/product adsorption and catalytic degradation of organic pollutants. Please cite the following relevant and recent articles: DOI: 10.3390/catal11091048, DOI: 10.1016/j.chemosphere.2019.01.132, DOI: 10.1016/j.jenvman.2021.112937. The addition of these references should corroborate the proposed mechanism of action.
3. The results for iodine and methylene blue adsorption experiments (at least for the best materials) should be added in the supplementary file.
4. Please correct “3.1. Martial characterization” with “3.1. Material characterization”
5. (Figure 1) Please correct x-axis range (it should be 20-70°)
6. (Figure 2) “A point EDX spectrum acquired from the region indicated by a white circle is shown in Fig. 2”. However, no white circles can be found in Figure 2a.
7. (Figure 2a) The quality of the TEM image is very poor, and it does not provide any information. Please remove it or provide a high-quality image to support the discussion.
8. (Figure 2b) Please provide the complete EDX spectrum rather than a histogram plot that does not provide complete information regarding the potential presence of other elements besides Ti, C, O and F.
9. (Figure 4, adsorption desorption isotherm) Please improve the readability of this plot (e.g., y-axis title and numbers are overlapped)
10. There are two Figures labelled as “Figure 4”. Consequently, figures enumeration is wrong. Please fix this issue.
11. (Figure 4-Figure 9) Please explicit the acronym “R.R.%”
12. (Table 1) Please use the proper number of significant figures.

Author Response

Thanks, reviewer.

All comments have been done.

Author Response File: Author Response.docx

Reviewer 4 Report

My comments are listed in the following: 
- In my opinion, title is strange. From main text, I can find the sample name is HTiO2@AC/SiO2. But I can find the name is TiO2@AC. It’s basically different name.

- In Introduction part, it seems like review paper. Is it review paper or research paper ? From this part, Authors cited some published papers related to HTiO2@AC/SiO2 sample. What is originality and novelty?? It requires some more comprehensive description of the main purpose and research background.

- In Experimental part, I cannot completely understand the description for preparation procedures  “The highest lignin content was selected to go on to the carbonization step. The rice straw material was carbonized at 200, 300, 400, 500, and 600 °C in a furnace for 1, 2, and 3 h.”  Is it 15 kinds of samples? “The activation step was performed by reflux using 85% H3 PO4 and 85% KOH as an activating agent in the refluxing ratios of 1:8, 1:10, 1:15, and 1:20 w/v at 70, 80, 90, and 100 °C for 1, 2, and 3 h.” How many samples did you use for this study? I cannot believe temperature condition and the amounts of chemical reagents for the chemical activation.

- In the results and discussion part, it needs some clear interpretation with detailed discussion (deep academic discussion) for all of the data. And, this part needs some more verification of unique novelty with originality. Especially, it requires description of novel points.

- If HTiO2@AC/SiO2 has photocatalytic effect, it needs some more advanced data such as XPS, DRS and PL data.

Author Response

Thanks, Dr. for your comments.

All comments have been done.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Unfortunately, I have not received answers to my questions. Instead, the authors made clarifications that even more questions and confused me even more. I recommend that authors take a thorough approach to the revision of the article.

**Updated on email:**
"Dear editor, I have read the presented version of the article and the comments of the authors.
Much of what was indicated by me in the comments became clear.
I think the article can be accepted."

Author Response

Thanks, Dr. for your comments.

All comments have been done.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper can be accepted without any further changes.

Author Response

Thanks, Dr. for your comments

Reviewer 4 Report

As I described last comments, I cannot completely understand all of experimental procedure. And main manuscript not revised, yet.

Synthesis of activated carbon silica composite from rice straw

Rice straw samples were collected from a local farm. The rice straw was cut into small pieces, washed, and dried at 110 °C for 24 h. Rice straw material with moisture content lower than 5% was selected for further experiment. The rice straw material was ground and sieved to collect size 60 mesh particles. All solvents and chemicals used were either high-performance liquid chromatography (HPLC) grade or analytical grade and were purchased commercially from Sigma Chemical Company

From this step, I cannot find activation procedure. But authors used “activated carbon”. I cannot understand it. I think it’s one of precursor preparation step.

Carbonization step

The highest lignin content was selected to go on to the carbonization step. The rice straw material was carbonized at 500 °C in a furnace for 3 h. After carbonization, the obtained activated carbon/amorphous silica (AC/SiO₂ )was cooled down to room temperature in a desiccator. Before being investigated for Oxamyl adsorption.

In my opinion, this is carbonization step (Char step). How did you obtain activated carbon/amorphous silica (AC/SiO₂ ) ?? I think it's char/amorphous silica (Char/SiO₂ ).

Activation step

The activation step was performed by reflux using 85% H₃PO₄and 85% KOH as an activating agent in the refluxing ratios of 1:8 and 1:20 w/v at 100 °C for 3 h. Then, the obtained AC/SiO₂ samples were washed with hot water to remove residual acid and base. The neutral AC/SiO₂ samples were then dried at 110 °C for 24 h and cooled in a desiccator. The AC/SiO₂ sample was measured for Oxamyl adsorption.

I think it’s chemical activation step. Generally, we cannot obtain activated carbon in this temperature condition. For the obtaining of activated carbon, it requires some more high temperature condition. 

Author Response

All my greetings and thanks to the reviewer.

All comments have been discussed and responded.

Author Response File: Author Response.docx