The Sonocatalytic Activation of Persulfates on Iron Nanoparticle Decorated Zeolite for the Degradation of 1,4-Dioxane in Aquatic Environments

Round 1

Reviewer 1 Report

In this manuscript, Malkapuram et al. reported the synthesis and application of iron nanoparticles modified Zeolite as a catalyst coupled with ultrasound for the activation of persulfates for the degradation of 1,4-dioxane in aquatic environments. The catalyst material as well as the catalytic process were well characterized and researched. The synergy between the catalyst and the ultrasound was also studied. Overall, this work presents new and interesting results that can appeal to the readership of the journal Catalysts. However, the current manuscript requires further revision to meet the publication standards. The below detailed comments need to be properly addressed.

1. The Title needs revision. The authors claimed that the catalyst was made by “doping zeolite with iron nanoparticles (FeNP/Z)”. Then the title part “Zeolite doped iron nanoparticles” should be revised into “iron nanoparticles doped Zeolite” or “Zeolite doped with iron nanoparticles”. In addition, the authors need to reconsider the use of the wording “dope”. Other words like “decorate” or “modify” might be more appropriate, considering that dope usually refers to the substitution of an element into a structure (for example, nitrogen-doped carbon materials, lithium-doped cobalt oxide, etc.).

2. The Introduction is suggested to be revised. (1) The first 3 paragraphs of the Introduction focuses too much on the background information of dioxane and the traditional way to get rid of it from wastewater. It is suggested that the authors make this part more concise. This part also included almost 1/3 of the cited references, which should also be reduced (as they are not relevant to the AOPs to be discussed in the manuscript). (2) The authors need to provide more justification as to why Fe NPs are selected as the catalyst. They did not even mention the full name of Fe NPs in the Introduction section.

3. Related to above, to appeal to a broader readership, recent works about AOPs (e.g., ACS Sustainable Chem. Eng. 2022, 10, 1899-1909; Trends in Chemistry, 2019, 1, 410-424) are recommended to be referenced in the Introduction.

4. Fig. 1 (left part) included an ultrasonic experimental setup, which also appeared in Fig. 2. The one in Fig. 1 might be redundant and if this is the case then it needs to be deleted.

5. For comparison purpose, the XRD data of the sample “pure zeolite” should be included. Because the authors mentioned that “due to the adjustment of FeNPs in the zeolite matrix, peaks slightly shifted away from pure zeolite 2θ location”. With only one set of XRD data, it is difficult to see any shift.

6. Equation (1) was not balanced. A minus sign might be missing on the right side of the equation.

7. Fig. 6, for the XPS data of Fe 2p, why was the y axis called “Counts/s”? The unit for “Counts” is often cps, then what is this “s” after the “Counts”? In addition, if Fe is in the form of nanoparticles, why Fe⁰ species was not observed in the XPS spectra?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The herein manuscript 2371563 , entitled "Sonocatalytic Activation of Persulfates on Zeolite doped iron nanoparticles for the Degradation of 1,4-Dioxane in Aquatic Environments" deals with the application of Fe-zeolite nanoparticles with the combination of persulfate and ultrasounds as effective AOP. 

The study perfectly matches with the scope of the Catalysts, however, the quality of the work leaves to much desired, mainly because, it is similar to its prior study (https://doi.org/10.1016/j.wri.2022.100183). Therefore, it should not be accepted for publication.

Moreover: 

* The article is only based on 3 experiments. Additional experiments must be compulsory performed (adsorption; PS+cat and US+cat).

*As mentioned in line 249, this catalyst presents high surface area, therefore, the adsorption ability of the catalyst must be tested. 

*The iron species may act as persulfate activator into radicals species. The efficiency of the catalyst+persulfate (without applying ultrasounds) mus be given.

* The experiments US+Cat, as indicated in the manuscript, is confusing. PS is also added? If so, it should be name as US+PS+cat. 

Consequently, US+cat experiment (without adding PS) is needed.

* Figure 1 and 2 provide the same ultrasonic setup? Figure 1 has not a good quality and some words cannot be readable. Moreover, it is also included in the latest article (https://doi.org/10.1016/j.wri.2022.100183). The repetition could be avoided.

* According to line 198 "As shown in Figure 3, XRD patterns indicate that FeNPs have been impregnated on zeolite" cannot be guessed, because there is no XRD patterns to make the comparison.

* Figure 6 shows a XPS results, but only provides the Fe2p_1/2 peaks . The deconvolution of iron peaks also involves the Fe2p_3/2 core levels and satellite peaks (ex: https://www.thermofisher.com/pt/en/home/materials-science/learning-center/periodic-table/transition-metal/iron.html; https://doi.org/10.1016/j.apsusc.2007.09.063) 

* if there another previous study indicating that the optimum R_ox=4, why is then reduced to 2? In addition, as mentioned in the manuscript in line 240 "lower Rox couldn’t provide sufficient quantity of radicals". Lower Rox than what value? Everything should be explaining or supported with experiments with inhibitors.

* How has been calculated the degradation kinetics? They are typically represented with points and providing R-square values (ex: https://doi.org/10.1016/j.seppur.2014.12.035)

* This study also compares the efficiency with single-stage addition of persulfate and two-stage addition of persulfate (as previously carried out in the prior study). However, neither it is explained in the experimental section nor it is indicated the reason to use these two methods.

*  The reaction mechanism is supposed to be studied with IPA and TBA for "as scavengers for HO^• and SO4^•- respectively" (line 296). On the one hand, theses experiments are not described into the manuscript. On the other hand, TBA is also a HO^• scavenger as well as IPA is an SO₄^•- inhibitor. In fact, this is also discussed in their latest research. 

*Even so, the reaction mechanism is proposed in those study. The mechanism is then different than before?

* Finally, in the cost estimation section, the reference of the prices must be provided. (example: line 324 "cost of unit electricity is ₹ 6"; line 334, "wholesale cost of zeolite is ₹ 280/kg"). Where are theses values taken? how is the value of 46 ₹/m3 for the cost of persulfate (Rox = 2 )?

* Also, check the calculations or the values because if it is consider the value of ₹ 6.85 per 5mg of catalyst and if it is needed 5mg per 500mL, then, it is necessary 10000 mg for 1 m³. Therefore, the price for the proposed treatment would be :6.85*10000+1980+46= ca. 68.546)

* Minor mistakes in lines 127 and 322 (0.5 L instead of 0.5l). 

* The introduction is too long and could be summarized.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised manuscript is recommended for acceptance.

Author Response

Dear Reviewer

We are grateful for your previous comments which enriched the discussion and resulted in a better manuscript.

Thank you and best wishes from our team