Review Reports - Assessment of Degradation Behavior for Acetylsalicylic Acid Using a Plasma in Liquid Process

Round 1

Reviewer 1 Report

The manuscript “Assessment of degradation behavior for acetylsalicylic acid using plasma in liquid process” deals with an interesting topic. Combination of plasma, TiO2 nanomaterials and other chemical used for ASA degradation was done nicely. I recommend for the publication of this paper with minor comments based on below.

Fig. 1 a. The graph between ln (C/C0) Vs reaction time-whether this generalized ln (C/C0) is applicable to all initial concentration over time?. For example, in the present case 50 ppm was taken initially and plotted ln (C/C0). If 500 ppm was used can we expect the similar values with rate constants?. Fig.1 d: The authors may include a typical OES spectrum measured for any sample reaction time for position identification of OH radicals and easy understanding. Also provide the photograph of the plasma generated when increasing the voltage or frequency values. In the plasma system diagram, what is the purpose of circulation system?. Throughout the experiments, the total amount of sample solution remains same or observed any evaporation due to plasma heating? Detail of the power supply was not given sufficiently. Manufacturer, AC or Dc operation, and other details etc. Fig. 1 e and f: Provide the duty ratio for 2-5µs pulse width operation at 30kHz. Sec. 2.3: Whether formation of UV was confirmed by OES? If yes please provide the spectrum.

Author Response

Revisions of manuscript

Ms. Ref. No.: catalysts-645921
Title: Assessment of degradation behavior for acetylsalicylic acid using plasma in liquid process

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Dear Editor and Reviewers

Thank you for allowing the opportunity to respond to reviewers’ comments regarding the above-referenced manuscript. The manuscript was revised according to the reviewer’s comments. Changes made in response to the comments are described below.

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Reviewers' comments:

Reviewer #1: The manuscript “Assessment of degradation behavior for acetylsalicylic acid using plasma in liquid process” deals with an interesting topic. Combination of plasma, TiO₂ nanomaterials and other chemical used for ASA degradation was done nicely. I recommend for the publication of this paper with minor comments based on below.

Fig. 1 a. The graph between ln (C/C₀) Vs reaction time-whether this generalized ln (C/C₀) is applicable to all initial concentration over time? For example, in the present case 50 ppm was taken initially and plotted ln (C/C₀). If 500 ppm was used can we expect the similar values with rate constants?

[Response] In this decomposition experiment, ASA was linearly decreased in concentration and assumed to be a first order reaction. Therefore, even if the initial concentration changes to 500 ppm, the rate constant does not change.

Fig.1 d: The authors may include a typical OES spectrum measured for any sample reaction time for position identification of OH radicals and easy understanding. Also provide the photograph of the plasma generated when increasing the voltage or frequency values.

[Response] The typical OES spectrum of PiL is shown in the previous literature, and the wavelengths for the peaks of chemical activated species, including hydroxyl radicals, are described further in the text. In addition, a photograph of the plasma reaction generation is provided in figure 7.

In the plasma system diagram, what is the purpose of circulation system?. Throughout the experiments, the total amount of sample solution remains same or observed any evaporation due to plasma heating?

[Response] The circulating cooling system was used to prevent the temperature rise of reaction solution by PiL reaction. Section 3.1. The part was revised and supplemented.

Detail of the power supply was not given sufficiently. Manufacturer, AC or Dc operation, and other details etc.

[Response] The power supply used in this study is described further in section 3.1.

Fig. 1 e and f: Provide the duty ratio for 2-5µs pulse width operation at 30kHz.

[Response] We have added information about the duty ratio between 2 µs and 5 µs.

Sec. 2.3: Whether formation of UV was confirmed by OES? If yes please provide the spectrum.

[Response] In the OES spectrum due to the light generated in the PiL reaction, an emission peak at 200 to 400 nm is formed, which is the wavelength range of UV light. OES spectra by the PiL reaction are described in the previous literature.

Reviewer 2 Report

Assessment of degradation behavior for acetylsalicylic acid using plasma in liquid process

Hye-Jin Bang 1, Heon Lee 1, Young-Kwon Park 2, Hyung-Ho Ha 3, Young Hyun Yu 3, Byung-Joo 4 Kim 4, Sang-Chul Jung 1,*

The paper is about the degradation behavior of acetylsalicylic acid popularly known as aspirin. Plasma in Liquid phase Process along with TiO₂ and H₂O₂ is used to enhance the reactivity rate. The paper could be accepted in the journal with the following corrections:

The experimental procedure should come before the results and discussion such that the reader can get an overall idea about the experiment conducted and results submitted based on it. I don’t see any part 4. The authors jump to part 5 which is the conclusion. It would be more interesting to read about OES methodology used to measure hydroxyl radicals such as why did you select the particular wavelength? Did you keep the plasma on throughout the reaction? In fig 1, the condition of the last bar in figure b, d and f are all same. It would be relatable if you could use a common color to all three. In section 2.2, what is the level of electric power? It is neither mentioned in the paragraph nor the graph. Can you elaborate more on the scavenging effect of case 0.100 M? Again, what is the plasma condition for section 2.3 and section 2.4? What is the concentration of TiO₂ and H₂O₂ used for PiLP-HT experiment? Is it the same as the one used for H and T experiment? In section 2.5, were you able to quantify the measurement? Is CO₂ and H₂O the final and desirable product of this experiment? Did you try to measure it? What is the percentage conversion of ASA and what is the yield of CO₂? In abstract 1^st line, you should mention you are using plasma for the photocatalyst? Line 60-61, H2O2 cannot be a powder, language to be corrected. Page 1. Section 2.3, add few sentences explaining how a photocatalyst is meant to work. What are the typical concentrations of ASA expected in real applications?

Author Response

Revisions of manuscript

Ms. Ref. No.: catalysts-645921
Title: Assessment of degradation behavior for acetylsalicylic acid using plasma in liquid process

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Dear Editor and Reviewers

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Reviewer #2: The paper is about the degradation behavior of acetylsalicylic acid popularly known as aspirin. Plasma in Liquid phase Process along with TiO₂ and H₂O₂ is used to enhance the reactivity rate. The paper could be accepted in the journal with the following corrections:

The experimental procedure should come before the results and discussion such that the reader can get an overall idea about the experiment conducted and results submitted based on it.

[Response] Modified according to the format required by Journal (Catalysts).

I don’t see any part 4. The authors jump to part 5 which is the conclusion.

[Response] Revised the number of conclusion section.

It would be more interesting to read about OES methodology used to measure hydroxyl radicals such as why did you select the particular wavelength? Did you keep the plasma on throughout the reaction?

[Response] Analysis of the peaks appearing at specific wavelengths in the OES spectrum allowed the analysis of chemical activated species in the PiL reaction, which is described in section 2.1. Plasma was continuously generated by PiL reaction during ASA degradation.

In fig 1, the condition of the last bar in figure b, d and f are all same. It would be relatable if you could use a common color to all three.

[Response] The last bar pointed out by the reviewer is the same as the maximum operating condition (250 V, 30 kHz, and 5 µs) of the electrical power supply, and the bar color is the same as yellow as suggested.

In section 2.2, what is the level of electric power? It is neither mentioned in the paragraph nor the graph.

[Response] As recommended, the electric power supply condition is further described.

Can you elaborate more on the scavenging effect of case 0.100 M? Again, what is the plasma condition for section 2.3 and section 2.4?

[Response] As recommended, corrected for that part.

What is the concentration of TiO₂ and H₂O₂ used for PiLP-HT experiment? Is it the same as the one used for H and T experiment?

[Response] As recommended, corrected for that part.

In section 2.5, were you able to quantify the measurement?

[Response] LC-MS analysis was used to examine by-products in ASA degradation reactions and to derive degradation mechanisms. No quantitative measurement of by-products was performed.

Is CO₂ and H₂O the final and desirable product of this experiment? Did you try to measure it? What is the percentage conversion of ASA and what is the yield of CO₂?

[Response] This study focused on the degradation rate and degradation pathway of ASA by PiLP and additives, and did not analyze the final product.

In abstract 1^st line, you should mention you are using plasma for the photocatalyst?

[Response] In this study, PiLP was used to decompose ASA, and hydrogen peroxide and TiO2 photocatalyst were used as additives to evaluate degradation effects.

Line 60-61, H₂O₂ cannot be a powder, language to be corrected.

[Response] As recommended, corrected for that part.

Page 1. Section 2.3, add few sentences explaining how a photocatalyst is meant to work.

[Response] In Section 2.3, the effects of TiO2 photocatalysts on ASA degradation efficiency are described as follows;

“The TiO₂ photocatalyst is activated by UV generated at the tungsten electrode, and the decomposition of ASA is achieved by hydroxyl radicals and strong oxidants generated on the activated photocatalytic surface”

What are the typical concentrations of ASA expected in real applications?

[Response] It is known that ASA can be detected up to 20 to 40 mg / L (ppm) in water environmental, and in this experiment, ASA initial concentration was 50 ppm.