Dynamics of Diffusion- and Immobilization-Limited Photocatalytic Degradation of Dyes by Metal Oxide Nanoparticles in Binary or Ternary Solutions
, Jonathan Hobley 3 and Anwar Usman 1,*
Round 1
Reviewer 1 Report
Dear Authors,
Manuscript catalysts-1952806 entiteled "Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface" and authored by Nurul Amanina A. Suhaimi , Cristina Pei Ying Kong , Nurulizzatul Ningsheh M. Shahri , Muhammad Nur , Jonathan Hobley , Anwar Usman targets a hot topic. The work is petentiually very interesting for the journal readers. while the overapll quality of the paper is acceptable few points needs to addressed:
1. Please change the current title "Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface" to a title that reflects more the current tendency in the field and that attracts more the readers.
2. The abstract needs to be reformulated to highlight major conclusions of the review ! in its current form this abstract will never attract the readers despite the impressive review work that have been conducted by the authors.
3. Introduction section: please add more data about damages that are caused by textile dyes. This part needs to be really improved.
4. In part 3 ". Synthetic dyes" please argument how dyes diversity is contributing to the the overall problem caused by dyes. Additionally please mention the effluents of synthetic dyes industries that are a mix of several dyes.
5. Conclusion have to be enriched and future directions in the field have to be highlighted.
I am really looking to read an imoproved version of this manuscript that addresses all these points and that I could recommend for publication.
Best regards
Author Response
Manuscript catalysts-1952806 entiteled "Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface" and authored by Nurul Amanina A. Suhaimi, Cristina Pei Ying Kong , Nurulizzatul Ningsheh M. Shahri , Muhammad Nur, Jonathan Hobley , Anwar Usman targets a hot topic. The work is potentially very interesting for the journal readers. while the overapll quality of the paper is acceptable few points needs to addressed:
- Please change the current title "Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface" to a title that reflects more the current tendency in the field and that attracts more the readers.
Our response:
We thank the referee for her/his kind suggestion. We have modified the title to be “Dynamics of diffusion- and immobilization-limited photocatalytic degradation of dyes by metal oxide nanoparticles in binary or ternary solutions”.
- The abstract needs to be reformulated to highlight major conclusions of the review ! in its current form this abstract will never attract the readers despite the impressive review work that have been conducted by the authors.
Our response:
We thank the referee for her/his kind suggestion. We have modified by adding the last three sentences in the Abstract.
- Introduction section: please add more data about damages that are caused by textile dyes. This part needs to be really improved.
Our response:
We thank the referee for her/his kind suggestion. We have modified the paragraphs #2 and #3 (line 51-66) in the Introduction. Accordingly, we have added a relevant reference (Ref. #9).
- In part 3 ". Synthetic dyes" please argument how dyes diversity is contributing to the overall problem caused by dyes. Additionally, please mention the effluents of synthetic dyes industries that are a mix of several dyes.
Our response:
We thank the referee for her/his kind comments and suggestion. Accordingly, we have added the discussion in the paragraph #1 and #2 in Section 3 (line 273-285):
“Amongst these chemically synthesized dyes, azo dyes containing auxochromes are widely used by textile, paper, leather, plastic, and rubber industries in large quantities, e.g. 60–70% of the total synthetic dyes, due to their push-full effect on intramolecular electron delocalization and, hence, intense light absorption, bright emission, and excellent fastness properties (Ref #9.83,84,86). The azo dyes are well known for their well solubility in water and for their harmful impacts on aquatic organisms (Ref #87) and human health (Ref #88), when discharged directly into water systems.
In the literature, there are still no reports of the effluents of synthetic dyes that are mixed in industrial wastewater, but it is believed that textile industries may use multiple coloring agents at the same time in the dyeing process, and produce multiple dyes in their wastewater (Ref. #11). Although the impacts of water containing multiple dyes have also not been reported, one could consider that possible synergistic effects of the dye effluents might cause more harmful health effects than wastewater of single solute solutions of dyes.”
- Conclusion have to be enriched and future directions in the field have to be highlighted.
Our response:
We thank the referee for her/his kind encouragement. We have modified the Conclusion by adding the future directions (line 515-5126).
Reviewer 2 Report
Comments to the Author
The authors reported an interesting review on “Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface”. In all, this review is interesting and meaningful. It can be recommended to be published after revisions.
1. Authors should include the effect of magnetism of the photocatalyst in the photocatalytic activity.
2. Authors should explain the adsorption contribution of the photocatalysts.
3. Authors can include the discussion about the diffusion process on the catalyst with other than the dyes for example diffusion process of pesticides
Author Response
The authors reported an interesting review on “Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface”. In all, this review is interesting and meaningful. It can be recommended to be published after revisions.
- Authors should include the effect of magnetism of the photocatalyst in the photocatalytic activity.
Our response:
We thank the referee for her/his kind encouragement and positive comments. We have added a new section (Section 5) highlighting the effect of magnetism of the photocatalyst in the photocatalytic activity. Accordingly, we have added relevant references (Refs. #104-108).
- Authors should explain the adsorption contribution of the photocatalysts.
Our response:
We thank the referee for her/his encouragement and positive comments. We have added the discussion on the contribution of adsorption on the photocatalysis of synthetic dyes in the last paragraph of Section 4 (line 411-421): “In other studies, the dynamics of immobilization of dyes has been anticipated, so that the effect of the adsorption of the dyes on their photocatalytic degradation was evaluated after keeping the mixture of dyes with TiO2 NPs in aqueous system in the dark [Ref. #104]. In this sense, the photocatalytic degradation of dyes effectively occurred after the mixture being kept for 48 h in the dark, suggesting that settling down the dyes onto the catalyst surface due to adsorption process plays on important role. In other words, photocatalysis of the preexisting dyes on the catalyst surface due to Le Chatelier’s equilibrium principle improves the degradation efficiency. However, during the photocatalytic degradation, it would be more reasonable to consider the dynamics of immobilization rather than the adsorption of the dyes onto the catalyst surfaces, as the adsorption-desorption equilibrium should be disrupted under light irradiation.”
- Authors can include the discussion about the diffusion process on the catalyst with other than the dyes for example diffusion process of pesticides
Our response:
We thank the referee for her/his suggestion. We have added the discussion on the diffusion process of pesticides on the photocatalysis in the last paragraph of Section 6 (line 490-499): “Based on the above argument, one could anticipate that the catalytic degradation of organic pesticides on photocatalysts should also be governed by diffusion of the pesticides onto the catalyst surfaces (110). However, the photocatalytic degradation of the organic pesticides was suppressed by the presence of activated carbon support (111). The organic compounds are well adsorbed and fill up the pore structures on the surfaces of the activated carbon/TiO2 composites NPs. The adsorption then hinders the diffusion of the organic compounds onto the catalyst surfaces. This has also been supported by lower degradation of organic pesticides at their higher concentrations, which acts as a driving force in the adsorption process, due most probably to the faster saturation of the composite surfaces (112).”
Reviewer 3 Report
The authors reported the review paper entitled "Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface" very well. The review article summarizes the importance of the dynamics of immobilization and reactivity of the dyes, as well as the vital roles of molecular conformation and functional groups on their diffusion onto the catalyst surface and photocatalytic degradation.This article is very useful to the scientific society but some points should be addressed before publication:
1.Novelty and objectives of the study must be clearly mentioned in the article.
2. What is the effect of scavengers on the photocatalytic degradation?
3. Author should also discussed about reusability and stability of different type of Metal oxide as photocatalysts.
4. Authors should highlight the scientific value of the present review with citing some journals such as Catalysts 2021, 11, 1025. https://doi.org/10.3390/catal11091025; Nanomaterials 2020, 10, 170; doi:10.3390/nano10010170; Journal of Hazardous Materials 409 (2021) 124840; Environmental Nanotechnology, Monitoring & Management, Volume 18, 2022, 100743, doi.org/10.1016/j.enmm.2022.100743.
5. It would be better if the author included in this review some diagrammatic illustration of the catalyst surface, with incorporation of metallic dopants which enhances and involved in the photocatalytic process of a metal based semiconductor photocatalyst material.
6. Author should comparing the efficiency rate of the photocatalytic degradation of different auxochromic dyes with binary or ternary solutions in parameters affecting the rate of photodegradation on different types of metallic dopants in table form.
7. It would be better if the author proposed a suggestion in conclusion section for the easy and safe waste disposal of the developed metal based photocatalyst material once the Photocatalytic degradation has been performed.
Author Response
The authors reported the review paper entitled "Photocatalytic degradation of synthetic dyes on metal oxide nanoparticles in binary or ternary solutions: The role of dye diffusion processes onto the catalyst surface" very well. The review article summarizes the importance of the dynamics of immobilization and reactivity of the dyes, as well as the vital roles of molecular conformation and functional groups on their diffusion onto the catalyst surface and photocatalytic degradation. This article is very useful to the scientific society but some points should be addressed before publication:
- Novelty and objectives of the study must be clearly mentioned in the article.
Our response:
We thank the referee for her/his comments and suggestions. We have revised the last paragraph of Section 1 (line 119-129): “These aspects on the photocatalytic degradation of the dyes are still deficient, while one could always consider the conventional non-fundamental factors, such as irradiation time, the ratio between dye concentration and the catalyst dosage, and the mediation of oxidative agents. This current review article summarizes the vital roles of crystal structure of catalysts on their photocatalytic activity. It also highlights the molecular conformation and functional groups of synthetic dyes that affect the rate and efficiency of photocatalytic degradation of the dyes, based on recently reported photocatalysis of dyes in single, binary, and ternary solute solutions. Therefore, the objective of this review article is to provide an insight the importance of the dynamics of immobilization dyes, which are attributed to their molecular conformation and functional groups, on their diffusion onto the catalyst surface and photocatalytic degradation.”
- What is the effect of scavengers on the photocatalytic degradation?
Our response:
We thank the referee for her/his comments and suggestions. We have added the discussion of the effects of H2O2 and scavengers on the photocatalytic degradation in Section 2, paragraph 6 (line 209-221) and paragraph 7 (line 222-231), respectively. Accordingly, we have cited several relevant papers.
- Author should also discussed about reusability and stability of different type of Metal oxide as photocatalysts.
Our response:
We thank the referee for her/his comments and suggestions. We have added the discussion of reusability and stability of different type of metal oxide as photocatalysts in Section 2, the last paragraph (line 244-261). Accordingly, we have cited several relevant papers (Refs. 76-81).
- Authors should highlight the scientific value of the present review with citing some journals such as Catalysts2021, 11, 1025. https://doi.org/10.3390/catal11091025; Nanomaterials 2020, 10, 170; doi:10.3390/nano10010170; Journal of Hazardous Materials 409 (2021) 124840; Environmental Nanotechnology, Monitoring & Management, Volume 18, 2022, 100743, org/10.1016/j.enmm.2022.100743.
Our response:
We thank the referee for her/his suggestions. These suggested papers are in line and support this current review. By adding these references, this review article is considerably improved. In particular, the sonophotocatalsysis is discussed in Section 2, paragraph #8 (line 236-243).
- It would be better if the author included in this review some diagrammatic illustration of the catalyst surface, with incorporation of metallic dopants which enhances and involved in the photocatalytic process of a metal based semiconductor photocatalyst material.
Our response:
We thank the referee for her/his encouragement and positive comments. We have added a schematic illustration of the photophysical processes in photocatalysts in Figure 1.
- Author should comparing the efficiency rate of the photocatalytic degradation of different auxochromic dyes with binary or ternary solutions in parameters affecting the rate of photodegradation on different types of metallic dopants in table form.
Our response:
We thank the referee for her/his encouragement and positive comments. Photocatalytic experimental conditions and observed photocatalytic degradation efficiency and rate of methylene blue, rhodamine B, and methyl orange in their single solute, binary, or ternary solutions in Table 1. In the table, the diffusion coefficient of the dyes is also summarized.
- It would be better if the author proposed a suggestion in conclusion section for the easy and safe waste disposal of the developed metal based photocatalyst material once the Photocatalytic degradation has been performed.
Our response:
We thank the referee for her/his encouragement. We have added a proposed suggestion in conclusion section for the easy and safe waste disposal of the developed metal based photocatalysts in the last part of Conclusion (line 518-526): “Another challenge in the future is recovery, regeneration, and reuse of the photoactive catalysts, as their crystal structures and surfaces should remain unchanged after the photoexcitation. Moreover, deriving nanostructured metal oxides from electronic waste, such as printed circuit boards and batteries is a challenging research area and opens up a new pathway of photocatalysis of recalcitrant dyes to be more efficient in terms of synthesis cost, environmental risks, electronic waste valorization, and waste disposal management, so that the photocatalysis keeps its records as the cleanest and ecofriendly process to remove dyes from wastewater.”
Round 2
Reviewer 1 Report
Dear Authors,
I could now recommand your manuscript for publication
Best regards
Reviewer 3 Report
The authors have revised the review article in light of the referees' comments nicely. Paper may be accepted in its current form.
