Structural, Optical and Photocatalytic Properties of Mn Doped ZnO Nanoparticles Used as Photocatalysts for Azo-Dye Degradation under Visible Light
, Ikram Daou 1, Hamou Moussout 2 and Joaquim C. G. Esteves da Silva 3Round 1
Reviewer 1 Report
In this paper, the authors synthesized different weight percentages of Mn-doped (1% to 10%) ZnO by precipitation method. Further photocatalytic degradation experiments showed that Mn-ZnO photocatalysts were able to degrade the target pollutant MO under visible light irradiation. While the concept of making efficient photocatalysts by doping with ZnO is exciting, there are several important issues with this study that prevent me from recommending it for publication.
1. The actual fluorescence intensity of the Mn-ZnO sample is significantly decreased with the increasing dope content of Mn in Figure 5. The authors need to explain the reason.
2. Why do the Mn-doped ZnO samples not have the K edge peak of Zn (8.5-9.5 KeV) in the EDS analysis, but exhibited in the ZnO sample? The authors should give a reasonable explanation.
3. Details of the reuse experiments should be presented in the experimental section.
4. The x%Mn-ZnO photocatalysts in Figure 7 can still degrade MO in the absence of light, The authors should include a reasonable explanation.
5. Authors should double-check their manuscripts before submitting a revision, there are so many errors. E.g. line446, “400–4000 cm-1”
6. Several additional articles on TiO2 photocatalysis modified by other strategies are suggested. (e.g., 10.1016/j.apcatb.2016.03.021, 10.3390/nano9030391, 10.1016/j.apcatb.2017.03.077).
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Recommendation: The manuscript may be publishable after a minor revision
Zegaoui O. and et al. report on the photocatalytic activity of ZnO nanoparticles doped with Mn ions using decomposition of methyl orange as a model reaction. This photocatalyst is active under visible light irradiation that is important for the development of industrial processes for wastewater decontamination. The development of cheap photocatalyst for dye degradations is placed among of most actual problems of modern environmental science and the article contributes to this field. The studies are carefully performed and article is well-written. Three materials were characterized using XRD, FTIR, UV-vis, PL and XPS techniques and scanning electron microscopy. Then, their photocatalytic activity was studied. The strategy to increase photoactivity of ZnO under irradiation by visible light using Mn ions as dopant is known (see ref in the article). Thus, the authors should compare their results with those reported elsewhere in the literature and discuss the advantage of their materials. This analysis is very brief in the present version and should be revisited before the final decision on the acceptance of the article to publication.
I recommend this manuscript to publication only after corrections of following points
1. Mn-doped ZnO materials were already studied (for examples ref 56 and 53). Please, discuss in the Introduction Part all methods which were used for preparation of these materials and explain the novelty of this work.
2. Page 1, lines 152-153. Please, give more details on the statement “These results are not similar to those reported by Yan et al. [56]. In contrast, they are comparable to those ob- tained Basnet et al. [53] for Mn-doped ZnO.” What it means “not similar “and “comparable”?
3. Page 9, lines 284-286. Please, give more details on these statement “ These results are comparable to those reported by several authors such as Li et al. [66], Basnet et al. [53] and Nithyab et al. [67] who reported that Mn-doped ZnO exhibited a better photocatalytic performance com- 286 pared to bare ZnO particles”. What it means comparable? For example, give the table in the Supporting Information with all details.
4. Page 14, line 475: “The UV light portion (λ<400 nm) was filtered by a 0.73 M NaNO2 475 solution [4].” Please give in the Supporting information the blanc spectrum of the lamp which was used for the experiments before and after filtration.
5. Page 9, line 316-317: « was also carried out by monitoring its chemical oxygen demand reduction (COD), which 316 is an effective index of water quality allowing the estimation of the degradation rate of the 317 organic compounds”. According to experimental part, COD was determined by UV-vis monitoring. Please, give COD0 and explain how CODt values were calculated. Give all information allowing to understand why this method is better in comparison with “monitored generally by a UV-vis spectrophotometer (line 312)”.
6. Please, complete the Experimental part and add all experimental conditions which were used in the study of pH dependence, scavengers and reusability experiments in the Experimental Part.
7. Table 1. R2 value: Please explain the meaning of R2 in the footnote.
8. Page 13, line 430. Please, add the scale of the experiments (precise the amount of compounds which were introduced in all synthesis).
There are also minor points to correct:
1. Page 1, line 20. Please, change “and” to “by“ (substitution of Zn by Mn)
2. Page 1, line 23. Please, explain the meaning of COD.
1. Page 1, line 151.Please, change the order of materials to correspond to the text (from small Mn content to high).
3. Page 8, line 264. Please add space after Figure 7.
4. Page 8, line 264. Please use minuscule for as “So, As....)
5. Page 9, line 336. Please explain the meaning of pHpzc
6. Figures 7 and 8. Please, add all experimental conditions in the caption of the figures to give readers a possibility to understand the figures without additional reading of the text.
7. Please, revisit eq 1: (Mn-ZnO) appears from both sides that seems be unclear.
8. Eq11 and 12. The transformation of MO to the final products (CO2?) should proceed through intermediate products. By-products cannot appear in this pathway according to the definition of “by product”.
9. Please, check all journal abbreviations in the reference list (Dyes Pigm., for instance).
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
My comments were addressed satisfactorily. The manuscript is much improved and I'd be happy to see it published in catalysts.
