Palladium-Supported Zirconia-Based Catalytic Degradation of Rhodamine-B Dye from Wastewater

Round 1

Reviewer 1 Report

Reviewer #:  water-1231436 „Palladium- supported Zirconia-Based Catalytic Degradation of Rhodamine-B Dye from Wastewater” by Salma Jabeen, Muhamed Sufaid Khan, Rozina Khattak, Ivar Zekker *, Juris Burlakovs, Sergio S. dC Rubin, Makarand Madhao Ghangrekar, Anna Kallistova, Nikolai Pimenov, Muhammad Zahoor *

In this manuscript, the authors analysed the catalytic activity of Pd/ZrO2 in the removal of Rhodamine-B dye in the presence of hydrogen peroxide. As one of the conclusions, experimental conditions observed for the dye degradation were temperature effect, time effect, loading of catalyst. ( 0.050g catalyst, reaction time 5h, temp 333K, 1 mL hydrogen peroxide addition, 10 mL dye solution (15 mg/L) and agitation rate of 500 rpm). The reaction kinetics were followed by the pseudo-first-order for Rhodamine-B dye deg radiation.   The Freundlich isotherm was best fitted for this dye degradation.

The manuscript is, in general, properly written and organized, but authors before resubmission should consider to:

(i) Table 1, please add a citation as a reference to a source

(ii) Materials and Methods, please add a grade of chemicals

(iii) Figure 6. – What does it mean “original” in the legend for the figure?

(iv) Figure 11. The size of figure 11a) is smaller than 11b).

(v) Reference 5 – there is no information about the volume and pages.

(vi) Reference 6 – different citation styles.

The journal was selected correctly and due to the readers' interest, such work may be published in Water.

Author Response

Reviewer 01 #: 

water-1231436 „Palladium- supported Zirconia-Based Catalytic Degradation of Rhodamine-B Dye from Wastewater” by Salma Jabeen, Muhamed Sufaid Khan, Rozina Khattak, Ivar Zekker *, Juris Burlakovs, Sergio S. dC Rubin, Makarand Madhao Ghangrekar, Anna Kallistova, Nikolai Pimenov, Muhammad Zahoor *

In this manuscript, the authors analysed the catalytic activity of Pd/ZrO2 in the removal of Rhodamine-B dye in the presence of hydrogen peroxide. As one of the conclusions, experimental conditions observed for the dye degradation were temperature effect, time effect, loading of catalyst. (0.050g catalyst, reaction time 5h, temp 333K, 1 mL hydrogen peroxide addition, 10 mL dye solution (15 mg/L) and agitation rate of 500 rpm). The reaction kinetics were followed by the pseudo-first-order for Rhodamine-B dye degradation. The Freundlich isotherm was best fitted for this dye degradation.

The manuscript is, in general, properly written and organized, but authors before resubmission should consider to:

Table 1, please add a citation as a reference to a source.

• Dear reviewer, citation has been added to Table 1.

Materials and Methods, please add a grade of chemicals

• Dear reviewer, analytical grade chemicals have been used and required details have been incorporated in the respective section.
• Figure 6. – What does it mean “original” in the legend for the figure?
• Dear reviewer, the word “original” was deleted to avoided confusion. It was a mistake.

(iv) Figure 11. The size of figure 11a) is smaller than 11b).

• Dear reviewer, they were accordingly resized. Thanks you very much for pointing out the size differences.

(v) Reference 5 – there is no information about the volume and pages.

• Dear reviewer, we have corrected reference accordingly.

(vi) Reference 6 – different citation styles.

• Dear reviewer, corrected accordingly.

The journal was selected correctly and due to the readers' interest; such work may be published in Water.

• Thanks worthy reviewer for encouraging remarks.

Reviewer 2 Report

Some revisions should be made.

1. Why do you need H2O2? What if no H2O2 is used? Please test the catalytic performance as a function of H2O2 amount.
2. What are the degradation products and reaction intermediates? How to prove that?
3. How can you prove that the process is only thermal catalysis but not a combination of thermal catalysis and photocatalysis? Can the catalyst work in the dark?
4. Can the catalysts be used several times without losing activity? Show the data.
5. Can the catalyst be used in other reactions? Show the data.

Author Response

Reviewer 2:

Comments and Suggestions for Authors

Some revisions should be made.

1. Why do you need H₂O₂? What if no H₂O₂ is used? Please test the catalytic performance as a function of H₂O₂ amount.

• Hydrogen peroxide (H2O2) is often used as a ‘green’ oxidant to oxidize and decompose organic matters irrespective of their type. Hydrogen peroxide, produces highly reactive hydroxyl radical (OH.) In water that can oxidize and degrade the organic matter. Worthy reviewer, we have stopped working on this project (Adsorption stage) and we are unable to incorporate your valuable suggestion at this stage. From your valuable suggestion we have got a necessary insight into the process and in future studies will incorporate such important parameters.

2. What are the degradation products and reaction intermediates? How to prove that?

• Worthy reviewer, usually intermediates of degradation are separated through silica gel columns which are then confirmed through different spectroscopic techniques. However, in this case we are more concerned with adsorption where then on surface of catalyst dye decolorization encounters. In such studies initially adsorption parameters are evaluated and the then intermediates and mechanism of degradation are determined. Since we are at the preliminary stage and our focus is adsorption feasibility, and we have not determined the intermediate structures or mechanism, which we have planned to be published in later stages.

1. How can you prove that the process is only thermal catalysis but not a combination of thermal catalysis and photocatalysis? Can the catalyst work in the dark?

• Worthy reviewer, I used this catalyst as a thermal catalyst, but it is used as photocatalyst as well and yes it was used in dark.

1. Can the catalysts be used several times without losing activity? Show the data.

• Worthy reviewer, yes it is theoretically recoverable without losing their activity. But, unfortunately we have not performed these studies.

1. Can the catalyst be used in other reactions? Show the data.

Yes, it can be used and already in literature it has been used in synthesis per following Ref: Khalid Saeed, Mohammad Sadiq, Idrees Khan, Saleem Ullah, Nauman Ali & Adnan Khan. Synthesis, characterization, and photocatalytic application pf Pd/ZrO₂ and Pt/ZrO₂. Applied Water Science volume 8, Article number: 60 (2018). 

Reviewer 3 Report

This manuscript presents the application of Pd/ZrO2 as a catalyst for Rhodamine-B degradation. Even though the work is of interest, the paper needs a lot of improvement before publication.

Comments:

1. Please provide EDX mapping of your catalyst to identify Pd on zirconia.
2. Based on your SEM, there are large particles scattered/deposited on ZrO2. Assuming that they are Pd, why are they not detected on XRD? Then if they are not Pd, your synthesis process of ZrO2 should be  improved to get a more uniform ZrO2 particles.
3. Please index your XRD pattern.
4. I suggest you perform the degradation experiments with only ZrO2 or Pd to prove the activity of Pd/ZrO2 system.
5. The reviewer can't see any importance of adding kinetic studies in this paper. It is only logical that increasing the temperature and irradiation time will only lead to enhanced activities.

Author Response

Reviewer 3

Comments and Suggestions for Authors

This manuscript presents the application of Pd/ZrO2 as a catalyst for Rhodamine-B degradation. Even though the work is of interest, the paper needs a lot of improvement before publication.

Comments:

1. Please provide EDX mapping of your catalyst to identify Pd on zirconia.

• Worthy reviewer EDX of the sample is already there in manuscript (Figure 5).

1. Based on your SEM, there are large particles scattered/deposited on ZrO2. Assuming that they are Pd, why are they not detected on XRD? Then if they are not Pd, your synthesis process of ZrO2 should be improved to get a more uniform ZrO₂ particles.

• Worthy reviewer, as the amount of the Pd is much lower as compared to the Zirconia. Large particles are zirconia while smaller are Pd. Dear reviewer, the XRD graph was not explained properly. Now we have revised the figure and relevant details. Hopefully, it will be OK. Sorry for the mistake.

1. Please index your XRD pattern.

• The refractive indices were included in figure accordingly. Hope it will be OK now.

1. I suggest you perform the degradation experiments with only ZrO₂ or Pd to prove the activity of Pd/ZrO₂ system.

• Worthy reviewer, due to Pd support on zirconia it, increases its catalytic potential. Your suggestion is valuable, however, at this stage we stopped working on that phase of the project, therefore we are unable to incorporate your suggestion at this stage. From your valuable suggestion we have got a necessary insight into the process and in future studies will incorporate such important parameters.

1. The reviewer can't see any importance of adding kinetic studies in this paper. It is only logical that increasing the temperature and irradiation time will only lead to enhanced activities.

• Worthy reviewer, you are right but scientific proofs are necessary for readers and scientific community, therefore they have been incorporated.

Round 2

Reviewer 2 Report

good

Reviewer 3 Report

Some of the responses are still inadequate. But the paper can now be recommended for publication. Please recheck minor language errors.