Highly Active Carbon Material Derived from Carica papaya Fruit Juice: Access to Efficient Photocatalytic Degradation of Methylene Blue in Aqueous Solution under the Illumination of Ultraviolet Light

Round 1

Reviewer 1 Report

Please see the attachment.

Comments for author File: Comments.pdf

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Author Response

Reviewer #1:

 

The authors prepared carbon material from Carica papaya fruit juice by a simple method. The carbon material was used for the photodegradation of methylene blue in aqueous solution. However, the study does not provide any novelty or meaningful advances. Thus, the quality of the manuscript is not enough for publication in Catalysts at this state.

 

We are thankful to the reviewer for the useful comments and suggestion in improving the quality of manuscript before publication.

 

1. The XRD pattern shows lots of interference signals. The reflection peaks of graphite are not clear. The authors should address it.

Ans. According to XRD analysis, carbon material exhibits closely related crystalline features of graphite, however the weak reflection suggested that the material is most likely exhibited amorphous phase. This has been added in the revised draft of manuscript.

The authors said that they prepared carbon dots from biomass. Could the authors provide any direct evidence for it?

Ans. We do not claim that our material is carbon dot, however it is only carbon based material prepared from the papaya and found to be very active towards the degradation of MB under the illumination of UV light

2. How to calculate the k value in Table 1?

Ans. The K value is calculated through the slope of linear fit of Ln (Co/Ct) against time.

3. The carbon catalyst shows a higher constant (k) with a dye concentration of 1.15.10-5 M. Why do the authors use the dye concentration of 2.30.10-5 M for further investigation? What is the catalytic activity of carbon material with other concentrations?

Ans. The low concentration of dye 1.15×10^-5 M has high K value, confirming  that the dye almost degraded into mineralized products like CO₂ and H₂O. This is the dye concentration where we can say that carbon material is highly effective in removing the MB form aqueous solution via oxidation of MB under the illumination of UV light. For the higher concentration 2.30×10^-5 M, the K value is acceptable but the dye removal is not complete and hence we used to describe that the optimum level of dye removal was found to be at 1.15×10^-5 M. Furthermore, we can say that if we go beyond the 1.15×10^-5 M dye concentration which is not required because at 1.15×10^-5 M concentration, the dye is approximately 100% degraded into harmless products.

4. The conclusions about the influence of the initial dye concentration, catalyst dose, and pH of dye solution are not novelty and meaningful

 

Ans. In the revised draft, we have updated the conclusion in terms of novelty, however the presence of initial dye concentration, catalyst dose and pH of dye solution was considered in terms of performance evaluation of carbon material but not the emphasis on the description of novelty of presented work.

 

Reviewer 2 Report

The article is interesting, novel and well written and discussed. However, since this is a photodegradation process where adsorption on carbonaceous materials is very important, the authors should show evidence of the contribution of the adsorption process and the photocatalytic process on the methylene blue decay curve.

In addition, the authors must show evidence of the generation of HO radicals in the system and of the degradation by-products generated. 

 

Author Response

The article is interesting, novel and well written and discussed. However, since this is a photodegradation process where adsorption on carbonaceous materials is very important, the authors should show evidence of the contribution of the adsorption process and the photocatalytic process on the methylene blue decay curve.

We are thankful to the reviewer for the useful comments and suggestion in improving the quality of manuscript before publication

 

In addition, the authors must show evidence of the generation of HO radicals in the system and of the degradation by-products generated.

 

Ans. A 2-3% adsorption would be expected by the presence of carbon material under the mechanical stirring. We have found that the carbon material was mainly involved in the photocatalytic oxidation of MB in the presence of UV light, whereas the adsorption phenomenon was highly limited. This has been added in the revised draft. For the evidence of HO hydroxyl radicals, we have carried out the trapping measurement and we found that EDTA was active to limit the degradation efficiency and it has been shown in previous studies that EDTA is evidently proven to be hydroxyl radical trapping agents, hence it is being highlighted in the revised draft of manuscript.

 

Reviewer 3 Report

The authors presented the synthesis of efficient photocatalyst from Carica papaya juice which is low cost, simple, and ecofriendly. 

Please do check the whole document for typos and spelling.

If possible, please improve the figures resolution.

 

High quality of English with some minor revisions required.

 

Author Response

The authors presented the synthesis of efficient photocatalyst from Carica papaya juice which is low cost, simple, and eco-friendly.

Please do check the whole document for typos and spelling.

If possible, please improve the figures resolution.

We are thankful to the reviewer for the useful comments and suggestion in improving the quality of manuscript before publication

 

 

High quality of English with some minor revisions required.

 

Ans. In the revised draft, we have polished and improved English language and remove the typo and grammatical errors. Also the quality of figures was improved.

 

Round 2

Reviewer 1 Report

The authors solved most of the problems. The manuscript could be published after minor revision.

In the introduction part, the authors specifically mentioned carbon quantum dots (properties, advantages, synthesis method). But, the authors answered that they did not prepare carbon quantum dots. So, the introduction part must be improved. 

Author Response

 

 

Reviewer 1

 

Comments and Suggestions for Authors

The authors solved most of the problems. The manuscript could be published after minor revision.

In the introduction part, the authors specifically mentioned carbon quantum dots (properties, advantages, synthesis method). But, the authors answered that they did not prepare carbon quantum dots. So, the introduction part must be improved. 

We are thankful to the reviewer for useful comments and suggestions in improving the quality of manuscript prior to publication

 

Ans. We have revised the introduction and following text has been with proper citatiosn have been added. In recent years, carbon materials have been considered as a potential candidate for the photocatalysis and adsorption applications, owing to their specific surface area, large porosity, and high activity. However, the drawback of these material is identified in view of low availability of standardized process along with the limited information about their specific applications. For instance, functionalized graphite material having diverse and typical functional groups, or doped graphitic material with certain dangling bonds are associated with adsorption of several ionic and molecular substances. This type of adsorption on the functionalized graphite surface is suggested as chemisorption. Whereas, the adsorption performed by the weak Vander Waal forces via π-π interaction between the aromatic molecules and the graphitic material simply follows the physical adsorption [2]. Graphene oxide is a typical carbon-based material that favors the attraction and hence the removal of cationic dye because of the presence of oxygenated groups in graphene oxide, however, pristine graphene may be able to adsorb both cationic and anionic dyes through π-π interaction [2]. The photocatalytic performance accompanied by the semiconducting material with rich defect chemistry and surface oxygenated groups or nitrogen doped fills the gap of sp2 on the carbon material [3]. The diversity of sp² of carbon material enables the surface modifications for the use in several applications. These surface modifications have shown the highly efficient role in driving both processes of adsorption and photocatalysis. The surface modification is carried out by making composite systems like metal/carbon composites [4-8] and metal oxide/carbon composites for photocatalytic reactions of both anionic and cationic dyes [9, 10].

 

 

Reviewer 2 Report

Authors have corrected the manuscript correctly. 

Author Response

 

 

Reviewer 2 2^nd round

 

Comments and Suggestions for Authors

Authors have corrected the manuscript correctly. 

 

We are thankful to the reviewer for the consideration of our paper in Catalysts for publication