Decolourization of crystal violet using nano-sized novel fluorite structure Ga2Zr2−xWxO7 photocatalyst under visible light irradiation

Fluorite-type Zr-based oxides with the composition Ga2Zr2−xWxO7 (x = 0, 0.05, 0.1, 0.15 and 0.2) were prepared using the citrate technique. Appropriate characterizations of all prepared materials were carried out. X-ray diffraction clarified that the undoped and W-doped Ga2Zr2O7 samples were crystallized in the cubic fluorite phase structure. The average particle size of the samples was in the range of 3–8 nm. The lowest band gap (1.7 eV) and the highest surface area (124.3 m2 g−1) were recorded for Ga2Zr0.85W0.15O7. The photocatalytic impacts of the prepared systems were studied by removal of crystal violet (CV) dye employing visible light illumination and taking into consideration the initial dye concentrations, duration of visible irradiation treatment, catalysts dose and the dopant concentration. The obtained results showed higher dye removal with the boost of the catalyst dosage. W doping shifted the absorption to the visible light range by decreasing the band gap from 4.95 eV for parent Ga2Zr2O7 to 1.7 eV for 15 mol% tungsten-doped Ga2Zr2O7 enhancing the photocatalytic decolourization of CV from 4.2% to 83.6% for undoped and 15 mol% W-doped Ga2Zr2O7, respectively, at optimum operating conditions (pH 9, 1 g l−1 catalyst dose and 300 min) while heavily doped W sample containing 20 mol% W showed lower removal than 15 mol% W-doped Ga2Zr2O7. Complete CV degradation using 15 mol% W-doped Ga2Zr2O7 was attained with the assistance of 25 mmol l−1 hydrogen peroxide. The reaction is aligned to pseudo-first-order kinetics. Different scavengers were introduced to decide the significance of the reactive species in CV degradation. O2−∙ and h+ had the major role in the degradation of CV by Ga2Zr2−xWxO7 system compared with HO•.

6. To investigate the main active species on the catalyst, trapping agents can contrast the different photocatalytic performance of Ga2Zr2-xWxO7 for the degradation of CV with or without adding isopropyl alcohol (IPA), or benzoquinone (BQ), under visible light irradiation. 7. Some references on material preparation and AOPs should be cited, such as Environmental Science & Technology 2018, 52, (19), 11297-11308;Chem 2019Chem , 5, 2195Environmental Science & Technology 2019, 53, 9725-9733 etc. Decision letter (RSOS-191632.R0) 06-Jan-2020 Dear Dr Nasr: Title: Decolorization of crystal violet using nano-sized novel fluorite structure Ga2Zr2-xWxO7 photocatalyst under visible light irradiation Manuscript ID: RSOS-191632 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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(1) Some tests, such as TEM, XPS, and so on, of the as-prepared samples should be tested and discussed.
(2) It should be given more discussions about the effect of W doping on the photocatalytic performance.
(3) It should be given more discussions about the W dopant concentration more than 0.15.

Reviewer: 2
Comments to the Author(s) The manuscript shows a nano-sized Ga2Zr2-xWxO7 photocatalyst prepared by the Pechini method. The material is prepared successfully in the cubic fluorite phase. As a promising catalyst, it also presents high photocatalytic activity and stability in the progress of removing crystal violet dye. The lowest band gap (1.7 eV) and the highest surface area determine the high efficiency. Therefore, I recommend that the manuscript is considered for publication in Royal Society Open Science after a minor revision. My comments are as followings: 1. Based on other people's results, O2-• and HO• are considered to be the active species in the decolorization of CV in haste. But further investigation needs to be done, such as electron paramagnetic resonance (EPR). At the end of abstract, instead of mentioning by-productions, you should talk more about the primary reactive species in the degradation. 2. In Fig. 6, the brackets are not presented in a proper form. 3. The survey XPS spectrum is needed to demonstrate the chemical composition difference in the products.
4. The aesthetics of plotting results needs to be improved. 5. If you draw an energy level diagram of Ga2Zr2-xWxO7, and its corresponding charge separation towards dye degradation under visible light illumination, this will make the manuscript more visual. 6. To investigate the main active species on the catalyst, trapping agents can contrast the different photocatalytic performance of Ga2Zr2-xWxO7 for the degradation of CV with or without adding isopropyl alcohol (IPA), or benzoquinone (

Comments to the Author(s)
The authors have addressed the significant points needed to be revised. I suggest this paper published in Royal Society Open Science.

11-Feb-2020
Dear Dr Nasr: Title: Decolorization of crystal violet using nano-sized novel fluorite structure Ga2Zr2-xWxO7 photocatalyst under visible light irradiation Manuscript ID: RSOS-191632.R1 It is a pleasure to accept your manuscript in its current form for publication in Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
The comments of the reviewer(s) who reviewed your manuscript are included at the end of this email.

Dear valuable and distinguishable reviewers.
Authors would like to thank you all for your effort in handling, reviewing and great inputs that really improve the quality of our manuscript.
Authors went through the comments and replied to all comments and did amended the manuscript according to the comments of our valuable reviewers. Authors hope that the manuscript in its current form is qualified to be published in the valuable Royal Society Open Science. All the corrected parts are highlighted in green.
Here is in the next table you can find the reply of all comments as well as its place in the manuscript

Comments
Reply Reviewer #1 Some tests, such as TEM, XPS, and so on, of the as-prepared samples should be tested and discussed.
Thank you for the comment. TEM is presented in the supplementary S4. IR spectra were recorded for all the samples and presented in Fig. 3. Electron paramagnetic Resonance (EPR) was performed for all the samples (Fig. 6 and Table 3). In Egypt there is only one XPS equipment which is unfortunately is down in this month and we waited for the whole time to be maintained but it does not work. As well, authors proved the chemical composition of the prepared samples by ICP/OES (Table 1) to determine the practical amount of Ga, Zr and W and compare it with the theoretical values that has been theoretically determined before the preparation. Moreover, the EPR (Fig 6 And Table 3) indicated presence of Zr +3 as a result of W doping. It should be given more discussions about the effect of W doping on the photocatalytic performance.
Thank you for the comment The effect of W doping on the photocatalytic performance was manifested at section 3.2.4 It should be given more discussions about the W dopant concentration more than 0.15 Thanks for the comment A sample containing x=0.2 (GA2Zr1.8W0.2O7) was prepared, fully characterized and introduced to the necessary parts in the manuscript. The discussion was amended to align with the presence of the new dopant concentration. Reviewer #2 Based on other people's results, O2-• and HO• are considered to be the active species in the decolonization of CV in haste. But further investigation needs to be done, such as electron paramagnetic resonance (EPR). At the end of abstract, instead of mentioning by-productions, you should talk more about the primary reactive species in the degradation.
Thanks for the comment EPR was performed as required by the valuable reviewer (Section 3.1). The reactive species experiment was performed by introducing scavenger effect experiment to the manuscript (section 3.2.9.) and then the abstract is modified.
In Fig. 6, the brackets are not presented in a proper form.
Thank you for the comment The caption of Fig 6 has been amended taking into account that the effect of time experiment was carried out before optimizing dose or pH. The survey XPS spectrum is needed to demonstrate the chemical composition difference in the products.
Thank you for the comment. In Egypt there is only one XPS equipment which is unfortunately is down in this month and we waited for the whole time to be maintained but it does not work. As well, authors proved the chemical composition of the prepared samples by ICP/OES (Table 1)