Plasma–Liquid Synthesis of PLA/MXene Composite Films and Their Structural, Optical, and Photocatalytic Properties
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis work reported a novel one-step plasma-liquid synthesis method for fabricating advanced PLA/MXene composite films. The direct current discharge between metal electrodes (Ti, Mo) in a solution of carbon tetrachloride and PLA simultaneously generates MXene nanosheets (Ti2CClx, Mo2CClx, Mo2TiC2Clx) and incorporates them into the biodegradable polymer matrix. The composite films exhibited discernable photocatalytic activity in degrading dyes pollutants in water under visible light irradiation. If the following issues can be properly resolved, I believe this article can be published.
- On page 12, line 382-383, “……Polylactic acid (PLA) pellets (Mw = 40,000) were dissolved in 120 ml of dichloromethane to achieve a concentration of 2 wt%.” Is it dichloromethane or CCl4?
- It is suggested that the chemical structural formulas of PLA and the three dyes (MB, RhB and RR6C) should be provided in the main text.
- On page 14, line 433-434, “...The dye mixture was constantly stirred in the reaction vessel. Concentration changes of each dye were determined using an SF-56 spectrophotometer, covering the wavelength range of 350–750 nm”. However, the paper does not provide a graph showing the variation of the absorption spectra with the duration of light exposure. Therefore, in the revised main text, this degradation profile of the absorption spectra with reaction times must be presented. Are there no overlapping absorption peaks between three dyes? How to ensure the accuracy of the measurement?
Author Response
Reviewer 1
- On page 12, line 382-383, “……Polylactic acid (PLA) pellets (Mw = 40,000) were dissolved in 120 ml of dichloromethane to achieve a concentration of 2 wt%.” Is it dichloromethane or CCl4?
Reply: Thank you for your comment. There was a mistake in the manuscript, which has now been corrected.
- It is suggested that the chemical structural formulas of PLA and the three dyes (MB, RhB and RR6C) should be provided in the main text.
Reply: Thank you for your comment. Structural formulas of the dyes are included in the manuscript text, Table 3.
- On page 14, line 433-434, “...The dye mixture was constantly stirred in the reaction vessel. Concentration changes of each dye were determined using an SF-56 spectrophotometer, covering the wavelength range of 350–750 nm”. However, the paper does not provide a graph showing the variation of the absorption spectra with the duration of light exposure. Therefore, in the revised main text, this degradation profile of the absorption spectra with reaction times must be presented. Are there no overlapping absorption peaks between three dyes? How to ensure the accuracy of the measurement?
Reply: Thank you for your comment. The absorption spectra of the dye mixture solution after photocatalytic degradation and irradiation of different durations are shown in Figure S1 in the supplementary material file. Yes, there are overlapping absorption peaks between Rhodamine B and Reactive Red 6C. The distinct, well-separated peak of Methylene Blue (MB) at 667 nm can be measured with high accuracy, as it experiences minimal interference. The overlapping peaks of Rhodamine B (~554 nm) and Reactive Red 6C (~533 nm) were resolved by analyzing the specific shape of the combined peak within the 500–580 nm range. Each dye contributes to the overall absorbance at each wavelength according to its concentration and extinction coefficient, as described by the Beer-Lambert law. By solving a system of equations at multiple wavelengths, the individual concentrations were determined.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript "" deals with an interesting topic, a very innovative method of synthesizing MXenes is used, the research is well designed, conducted and discussed. I have only two minor objections:
The first concerns the discussion of the micrographs of the obtained samples, specifically Fig 2d. Namely, while in Fig 2b and 2c the pores are indeed clearly visible, this does not seem so certain to me for 2d. The authors probably made a larger number of micrographs and I believe they have one in which the pores are clearly visible. If they do, I suggest that they add it to the manuscript. Also, the MXene sheets, which are claimed to be clearly visible, do not seem so visible to me. Adding an arrow to point to where they are visible or a micrograph at higher magnification would help.
The second remark refers to the discussion of photoclatholytic activity. The mechanism of the entire catalytic process is described here in detail. A small part of that discussion is based on the results, but a large part is actually based on the literature. However, in the entire passage of more than a page and a half, not a single literary reference is given. So part of this section is purely speculative. I would advise the addition of some references that support the claims made.
One more detail, on the y-axis of the XRD patterns of the samples, "Intensity (a.u.)" should be added.
Kind regards
Author Response
Reviewer 2
- The first concerns the discussion of the micrographs of the obtained samples, specifically Fig 2d. Namely, while in Fig 2b and 2c the pores are indeed clearly visible, this does not seem so certain to me for 2d. The authors probably made a larger number of micrographs and I believe they have one in which the pores are clearly visible. If they do, I suggest that they add it to the manuscript. Also, the MXene sheets, which are claimed to be clearly visible, do not seem so visible to me. Adding an arrow to point to where they are visible or a micrograph at higher magnification would help.
Reply: Thank you for your comment. SEM image for sample 3 (Figure 2d) has been revised. It should be noted that the MXene sheets may be embedded within the polymer matrix; although some are visible on the surface of the film, they are indicated by arrows in the figure.
- The second remark refers to the discussion of photoclatholytic activity. The mechanism of the entire catalytic process is described here in detail. A small part of that discussion is based on the results, but a large part is actually based on the literature. However, in the entire passage of more than a page and a half, not a single literary reference is given. So part of this section is purely speculative. I would advise the addition of some references that support the claims made.
Reply: Thank you. We agree with the comment and have added several references to support the assumptions made in the manuscript.
One more detail, on the y-axis of the XRD patterns of the samples, "Intensity (a.u.)" should be added.
Reply: Thank you for your comment. The correction has been made.
Reviewer 3 Report
Comments and Suggestions for AuthorsReview report
This manuscript reports a novel one-step plasma-liquid synthesis method for fabricating polylactide (PLA)/MXene composite films with enhanced photocatalytic activity under visible light. The authors demonstrate simultaneous exfoliation and incorporation of MXene nanosheets (Ti2CClx, Mo2CClx, Mo2TiC2Clx) into a biodegradable PLA matrix, resulting in porous films with improved optical absorption and reduced band gaps (0.62–1.15 eV). The composites show efficient photocatalytic degradation of organic dyes. However, several critical issues need to be addressed before the manuscript can be considered for publication. Until these concerns are thoroughly addressed, I recommend major revision for Catalysts.
Please see the major comments below.
comment 1.
In the introduction part, to strengthen the manuscript’s narrative, consider focusing on PLA properties and characteristics that are most relevant to photocatalytic composite development with MXenes, rather than providing extensive details on unrelated applications. This will help maintain a clear and cohesive storyline throughout the manuscript.
comment 2.
Throughout the manuscript (lines 66, 87, 98, 243, 374, 382, 418), the full name “polylactide (PLA)” is repeatedly used even after the abbreviation is defined. For clarity and readability, use “PLA” consistently after the initial definition. Additionally, please clarify whether “polylactide” and “polylactic acid (PLA)” are intended to refer to the same material, as the manuscript sometimes seems to use both terms interchangeably.
Comment 3.
The manuscript attributes enhanced photocatalytic activity to improved charge transport and reduced recombination (line 305), based solely on band gap and activity data. However, these parameters alone are insufficient to support such claims. Direct measurements (e.g., photoluminescence, transient absorption spectroscopy, or electrochemical impedance) are needed to substantiate statements regarding charge separation and transport.
comment 4.
In line 308–324, the manuscript states that superoxide radicals are generated via electron transfer from the conduction band to oxygen, and that hydroxyl radicals are formed via holes in the valence band. However, hydroxyl radicals can also be generated through reduction processes involving the conduction band. To conclusively prove the radical generation pathways, electron paramagnetic resonance (EPR) experiments under anoxic conditions are needed. Furthermore, please clarify whether photocatalytic reactions were performed in air or pure O2. Direct radical detection (e.g., EPR) would strengthen the mechanistic claims.
comment 5.
Figures 4 and 6 show degradation rates that are slow at 30 min and then accelerate at 45 min. Is this due to calibration issues, experimental artifacts, or is it an expected result? The data are only shown up to 45 min—does degradation reach completion (below 0.3) after this point?
Comment 6.
In line 324, the statement that molybdenum-based MXenes (Mo2CTx) exhibit “exceptionally high metallic conductivity” compared to titanium-based MXenes is not substantiated with experimental or literature data. Please provide appropriate references or direct measurements to support this assertion.
Comment 7.
In lines 353–364, the conclusion that dye adsorption is driven by electrostatic interactions is not supported by direct evidence (e.g., zeta potential measurements). Comparative analysis of catalyst surface charge and dye properties would be necessary to justify this claim.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 3
comment 1. In the introduction part, to strengthen the manuscript’s narrative, consider focusing on PLA properties and characteristics that are most relevant to photocatalytic composite development with MXenes, rather than providing extensive details on unrelated applications. This will help maintain a clear and cohesive storyline throughout the manuscript.
Reply: Thank you for your comment. The introduction to the manuscript has been rewritten.
comment 2.
Throughout the manuscript (lines 66, 87, 98, 243, 374, 382, 418), the full name “polylactide (PLA)” is repeatedly used even after the abbreviation is defined. For clarity and readability, use “PLA” consistently after the initial definition. Additionally, please clarify whether “polylactide” and “polylactic acid (PLA)” are intended to refer to the same material, as the manuscript sometimes seems to use both terms interchangeably.
Reply: Thank you for the comment, corrections have been made, we mean polylactide in our manuscript.
Comment 3.
The manuscript attributes enhanced photocatalytic activity to improved charge transport and reduced recombination (line 305), based solely on band gap and activity data. However, these parameters alone are insufficient to support such claims. Direct measurements (e.g., photoluminescence, transient absorption spectroscopy, or electrochemical impedance) are needed to substantiate statements regarding charge separation and transport.
Reply: Thank you for your comment. We measured the photoluminescence spectra of the samples, the results are shown in Figure 3d.
comment 4.
In line 308–324, the manuscript states that superoxide radicals are generated via electron transfer from the conduction band to oxygen, and that hydroxyl radicals are formed via holes in the valence band. However, hydroxyl radicals can also be generated through reduction processes involving the conduction band. To conclusively prove the radical generation pathways, electron paramagnetic resonance (EPR) experiments under anoxic conditions are needed. Furthermore, please clarify whether photocatalytic reactions were performed in air or pure O2. Direct radical detection (e.g., EPR) would strengthen the mechanistic claims.
Reply: Thank you for your comment; this is a very valuable observation. Unfortunately, due to the limited time available for the review response, we cannot perform measurements using the electron paramagnetic resonance method. However, we have identified the active species involved in the scavenger methods. This information has been added to the manuscript text and the supplementary materials. It should also be noted that the photocatalytic reactions were conducted in air.
comment 5.
Figures 4 and 6 show degradation rates that are slow at 30 min and then accelerate at 45 min. Is this due to calibration issues, experimental artifacts, or is it an expected result? The data are only shown up to 45 min—does degradation reach completion (below 0.3) after this point?
Reply: Thank you for your comment. The acceleration of the photodestruction process after 30 minutes is due to the accumulation of intermediate reaction products in the solution—highly active substances such as benzaldehyde, 1,4-benzoquinone imine, p-benzoquinone, and 3-aminophenol. These compounds react with dye molecules and promote their decomposition. It should be noted that complete degradation of the dye mixture solution is achieved within one hour. The experiment duration was limited to 45 minutes to prevent excessive heating of the cell.
Comment 6.
In line 324, the statement that molybdenum-based MXenes (Mo2CTx) exhibit “exceptionally high metallic conductivity” compared to titanium-based MXenes is not substantiated with experimental or literature data. Please provide appropriate references or direct measurements to support this assertion.
Reply: Thank you. We agree with the comment, and the sentence has been corrected. Additionally, a reference to the relevant literature has been added.
Comment 7.
In lines 353–364, the conclusion that dye adsorption is driven by electrostatic interactions is not supported by direct evidence (e.g., zeta potential measurements). Comparative analysis of catalyst surface charge and dye properties would be necessary to justify this claim.
Reply: We thank the reviewer for this insightful comment. We agree that zeta potential measurements would provide direct evidence of electrostatic interactions. However, determining the surface charge of our composite films via zeta potential is technically challenging. To address the reviewer's concern and avoid overinterpretation, we have revised the relevant section of the manuscript. Specifically, we have removed the claim regarding electrostatically driven adsorption and instead rephrased the discussion to emphasize other well-established factors influencing photocatalytic degradation kinetics, such as molecular size, structural complexity, and diffusion limitations, which align with our observed results. We believe this revised explanation is more accurate and defensible based on the available data. We acknowledge this limitation and have noted in the revised text that the adsorption mechanism is multifactorial. Future work will aim to characterize the surface properties of similar composite films more thoroughly.
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsReview report
The revised manuscript entitled "Plasma-liquid synthesis of PLA/MXene composite films and their structural, optical, and photocatalytic properties" demonstrates substantial improvement in clarity, focus, and scientific rigor. The authors have addressed all major concerns from the initial review, and the addition of new data and clarifications (such as photoluminescence spectra and scavenger experiments) has strengthened the mechanistic discussion. Where direct experimental evidence was not available, the authors have appropriately acknowledged the limitations and revised the manuscript accordingly. Therefore, I recommend acceptance after minor revision in Catalysts.
Minor comment:
In the discussion of the scavenger experiments, particularly for Reactive Red 6C and Rhodamine B, the inhibitory effect of IPA is greater than that of EDTA. This suggests that hydroxyl radicals are not generated exclusively via hole mediated oxidation, but may also arise through alternative pathways (for example, through reduction of oxygen). Therefore, it would be more accurate to acknowledge the possibility of multiple generation mechanisms for hydroxyl radicals, rather than attributing their formation solely to holes.
Comments for author File: Comments.pdf
Author Response
Reviewer 3
Minor comment:
In the discussion of the scavenger experiments, particularly for Reactive Red 6C and Rhodamine B, the inhibitory effect of IPA is greater than that of EDTA. This suggests that hydroxyl radicals are not generated exclusively via hole mediated oxidation, but may also arise through alternative pathways (for example, through reduction of oxygen). Therefore, it would be more accurate to acknowledge the possibility of multiple generation mechanisms for hydroxyl radicals, rather than attributing their formation solely to holes.
Reply: We agree with the comment. The correction has been made to the text and highlighted in green. •OH radicals are identified as the primary agents responsible for oxidizing RR6C and RhB. The more pronounced inhibitory effect of isopropanol compared to EDTA suggests that •OH radicals are generated not only through hole-mediated oxidation of H2O/OH⁻ but also potentially via alternative pathways, such as the protonation of superoxide radicals (•O2⁻ + H⁺ → HOO•), followed by further reduction and decomposition. Meanwhile, •O2⁻ and h⁺ are the principal species responsible for the degradation of MB.
