Synthesis and Characterization of Fe Doped Aurivillius-Phase PbBi2Nb2O9 Perovskite and Their Photocatalytic Activity on the Degradation of Methylene Blue
Round 1
Reviewer 1 Report
In this manuscript, Gu et al. prepared Fe-doped PbBi2Nb2O9 (PBNO) perovskites by a solid-state reaction and investigated them in the photocatalytic degradation of methylene blue (MB). I suppose that this manuscript could be published in Catalysts after the following revisions:
1. There are a few formatting and spelling mistakes, which should to be corrected.
2. It is necessary to provide in Section 2 the wavelength of the xenon lamp used for the photocatalytic experiments.
3. The authors should investigate the photocatalytic mechanism by trapping experiments. It would help to clarify the role of the main reactive oxygen species involved in the reaction.
4. The stability of the photocatalyst (e.g., PBNO-0.2F) remains unclear. It would be nice to study it as well.
5. (a) Did the authors study the adsorption capacity of the prepared materials? The authors should provide data on the adsorption of MB on the photocatalyst surface and explain how it affects the photocatalytic degradation of the dye.
(b) Is there a correlation between adsorption capacity and photocatalytic acitivity? In many cases, the adsorption capacity has a strong influence on the photocatalytic activity of simple and complex oxides (see please for consulting and citing: 10.1016/j.solidstatesciences.2022.106997).
6. What products were formed during the photooxidation of MB? It would be nice to study them using an HPLC technique.
7. The authors should include a table where a comparison of this study with other investigations will be presented. This could help to assess the promise of the developed photocatalyst.
8. The authors should refer to more new literature and keep abreast of the latest research trends related to the use of complex oxides in photocatalysis (10.1039/D1NJ04439G; 10.1016/j.cej.2021.128783), including Bi-containing perovskites (10.3390/pr10040789; 10.1016/j.jiec.2022.02.051).
Author Response
-Response to Reviewer #1
In this manuscript, Gu et al. prepared Fe-doped PbBi2Nb2O9 (PBNO) perovskites by a solid-state reaction and investigated them in the photocatalytic degradation of methylene blue (MB). I suppose that this manuscript could be published in Catalysts after the following revisions:
Response : We are grateful for the reviewer’s encouraging comments regarding our manuscript. The answers to the questions raised are as below.
- There are a few formatting and spelling mistakes, which should to be corrected.
Response: As suggested the whole manuscript has been completely overhauled.
- It is necessary to provide in Section 2 the wavelength of the xenon lamp used for the photocatalytic experiments.
Response: The specification of the xenon lamp was already given in Section 3 as below.
“Photoluminescence (PL) spectra of the as-synthesized PBNO and PBFNOs samples were collected using a Spectrofluorometer (Jasco International, FP-8500ST) equipped with a 150 W Xenon lamp and a photomultiplier tube detector and operated at a scan rate of 600 nm min-1 over the wavelength ranges of 260-480 nm with 250 nm excitation wavelength.”
- The authors should investigate the photocatalytic mechanism by trapping experiments. It would help to clarify the role of the main reactive oxygen species involved in the reaction.
Response: We strongly agree with the reviewer’s suggestion that the trap experiments using H2O2 (OH*) is important to justify the predicted reaction path of the degradation. However, the repreparation of identical photocatalysts for the experiment might require a large effort, which might be impossible within the short period of time for revision. Moreover, poor samples cannot guarantee a perfect replication of the findings from the study, which could potentially lead to misinterpretation of the kinetic behaviors. Therefore, it is very difficult to conduct further experiments in the current situation.
Since the similar phenomena has been discussed in literature below,
- Soltani and M. H. Entezari, J. Mol. Catal. A: Chem. 377, 197 (2013)
- Severino, H. C. Junquera, M. Guglliotti, D. S. Gabrielli, and M. S. Baptista, J. Photochem. Photobiol. A: Chem. 77, 459 (2003)
- -H. Lee, H. Kim, Y. Gu, D.-H. Lim, Nanoscience and Nanotechnology Letters, Volume 10, Number 9, September 2018, pp. 1179-1186(8)
- -H. Lee, J. Sim, D.-H. Lim, Energy Procedia 158 (2019) 534-540.
We consulted the importance of O2 species from the references instead of conducting additional experiments. Thus, the following sentence in the manuscript was revised as below. Note that, text in itallics is found in the manuscript, underlined text has been added in the revised version of the manuscript in response to comments, and strikeout text indicates text removed from the original manuscript.
“It is noted that the number of active sites on the surface of the PBNO-0.2F could be increased by increasing its amount. Many studies reported that the importance of O2 and H2O molecules absorbed on the PBNO surfaces to form hydroxyl radicals (OH•) and/or superoxide anions (O2-•).”
- The stability of the photocatalysts (e.g., PBNO-0.2F) remains unclear. It would be nice to study it as well.
Response: We also agree with the reviewers' suggestions, and think that the stability of the photocatalyst is also a very important part. However, according to previous studies by Kim et al. (H. Kim, D. Hwang, and J. Lee, J. Am. Chem. Soc. 2004, 126, 29, 8912–8913), the durability of the photocatalyst when Fe is not doped is already known, and the stability part is being additionally tested while conducting follow-up studies. Thus, we added stability of the PBNO and keep it open for future investigations. The following sentence was added.
“It is noted that the PBNO showed good structural stability during the water decomposition under the visible light. Although no defective Fe-doped PBNOs were found the experiments in the present study, the stability of Fe-doped PBNO needs further investigation.”
- (a) Did the authors study the adsorption capacity of the prepared materials? The authors should provide data on the adsorption of MB of the photocatalyst surface and explain how it affects the photocatalytic degradation of the dye.
The adsorption of MB onto the PBNO was studied in one of our previous studies (C.-H. Lee, H. Kim, Y. Gu, D.-H. Lim, Nanoscience and Nanotechnology Letters, Volume 10, Number 9, September 2018, pp. 1179-1186(8)). The study has found out that the MB adsorption was not significantly affected by the surface condition of as-synthesized PBNO, while it was higly affected by the pH of the alkaline solution due to the enhanced attractive forces between MB and PBNO surface. Since it is not a photocatalytic experiment according to pH change, it is predicted that the performance change regarding absorption is negligible. The following sentence regarding the adsorption capacity was added.
“The surface structure of as-synthesized PBNO did not significantly affect the MB adsorption efficiency, while the pH of the alkaline solution plays a key role for enhancing the adsorption capacity”
(b) Is there a correlation between adsorption capacity and photocatalytic activity? In many cases, the adsorption capacity has a strong influence on the photocatalytic activity of simple and complex oxides (see please for consulting and citing: 10.1016/j.solidstatescience.2022.106997).
Response: We have not investigated the relation between the adsorption and photocatalytic activity in the present study, and thank reviewer for providing the useful reference for this point (Belousov, A.S.; Suleimanov, E.V.; Parkhacheva, A.A.; Fukina, D.G.; Koryagin, A.V.; Koroleva, A.V.; Zhizhin, E.V.; Gorshkov, A.P. Regulating of MnO2 photocatalytic activity in degradation of organic dyes by polymorphic engineering. Solid State Sci. 2022, 132, 106997.). As suggested, we added following sentence by consulting and citing the suggested reference. Also, as suggested by the reviewer, related follow-up studies are being prepared to analyze the photocatalytic activity according to adsorption.
“Belousov et al., found that there is synergetic effect between various physicochemical properties such as adsorption ability, morphology, bond strength, and surface molar ratio, such that the adsorption capacity dictate the photocatalytic activity.”
- What products were formed during the photooxication of MB? It would be nice to study them using an HPLC technique.
Response: We thank the reviewer for this comment. It is a very good study to verify the reactants after the photocatalytic reaction by conducting HPLC analysis. According to Chemical Engineering Journal 157 (2010) 373–378 and Water Conserv Sci Eng (2017) 1:249–256, pH can affect the activity of the photocatalyst, but it does not affect the substances produced as MB decomposes in the photocatalyst. Therefore, we expect the substances produced after the decomposition reaction to be azure A, azure B, azure C, and thionine, and our experimental results are expected to be similar to this. However, due to the tight time frame, it is difficult to proceed with the proposed additional experiments.
- The authors should include a table where a comparison of this study with other investigations will be presented. This could help to assess the promise of the developed photocatalyst.
Response: We thank the reviewer for this comment. The latest research on MB decomposition using various photocatalytic materials has been summarized and added to Table 4.
In the revised manuscript “Table 4” was added in the revised manuscripts.
- The authors should refer to more new literature and keep abreast of the latest research trends related to the use of complex oxides in photocatalysts (10.1039/D1NJ04439G;10.1016/j.cej.2021.128783), including Bi-containing perovskites (10.3390/pr10040789; 10.1016/j.jiec.2022.02.051).
Response: We thank the reviewer for providing the latest studies in our research area. As suggested, the introduction of the newest development in the photocatalysts was added as below.
- Belsousov, A.S.; Suleimanov, E.V.; Parkhacheva, A.A.; Fukina, D.G.; Koryagin, A.V.; Titaev, D.N.; Lazarev, M.A. Synthesis and Characterization of Bi2WxMo1−xO6 Solid Solutions and Their Application in Photocatalytic Desulfurization under Visible Light. Processes 2022, 10, 789, doi: 10.3390/pr10040789
- Belousov, A.S.; Suleimanov, E.V.; Fukina, D.G. Pyrochlore oxides as visible light-responsive photocatalysts. New J. Chem. 2021, 45, 22531-22558, doi: 10.1039/D1NJ04439G
- Wei, K.; Faraj, Y.; Yao, G.; Xie, R.; Lai, B. Strategies for improving perovskite photocatalysts reactivity for organic pollutants degradation: A review on recent progress. Chem. Eng. J. 2021, 414, 128783, doi: 10.1016/j.cej.2021.128783
- Maniyazagan, M.; Hussain, M.; Kang, W.S.; Kim, S.J. Hierarchical Sr-Bi2WO6 photocatalyst for the degradation of 4-nitrophenol and methylene blue. J. Ind. Eng. Chem. 2022, 110, 168-177, doi: 10.1016/j.jiec.2022.02.051
“Recently comprehensive and systematic reviews regarding the use of photocatalysts have been conducted. Particularly, Belousov et al., [23] reemphasizes the importance of specific surface area in the development process of pyrochlore oxides as photocatalysts. Wei et al., [24] suggested various strategies to improve the perovskite light utilization, charge separation and creating more active sites. Several studies reported the outstanding catalytic activity of Bi-containing perovskites [19,25]. It it noted that the physico-chemical properties of photocatalyst strongly influence the reaction capability under visible light [19].
Reviewer 2 Report
Manuscript number: catalysts-2057806
Title: Synthesis and Characterization of Fe doped Aurivillius-phase PbBi2Nb2O9 perovskite and their photocatalytic activity on the degradation of methylene blue
The paper needs some rectifications/additions and clarifications before one can take a final decision:
1) The paper contains some grammatical errors and typo-mistakes that should be corrected.
2) Abbreviations should be opened when mentioned for the first time.
3) The Abstract part should be improved. It should contain some qualitative and quantitative results.
4) Details of reagents used in the synthesis (name of chemical formula, source, purity, number of moles, masses, etc.) should be provided within the manuscript.
5) SEM for non-doped sample should be added.
6) The EDX spectra and atomic percentages should be provided along with SEM images.
7) From the SEM images, it is not clear that the particle sizes of PBFNO decrease with increasing the Fe doping ratio.
8) Authors presented only SEM images and did not perform any analysis of grain size distribution, density, porosity, etc. It will be much more useful if the authors can add some analysis of microstructure.
9) Details on how crystallites size is determined should be reported in the text.
10) Related to the current compounds, none of the physical properties such as polarization, magnetization, dielectric or magneto-dielectric properties, and magnetoelectric coupling effect has been investigated.
11) XPS analysis is interesting for being investigated.
12) Graduation, Y-axis values, and units should be provided in Figures 4 and 5.
13) Absorbance graphs as a function of reaction time for all samples should be provided.
14) Photocatalytic results should be compared with those previously found in comparable compositions. Anyway, all samples do not reveal full degradation of MB even after 3 hours of irradiation time. What is the success of the current study accordingly?
15) There are excess uses of references. The references should be rechecked, and their numbers should be reduced.
Author Response
- Response to Reviewer #2
The paper needs some rectifications/additions and clarifications before one can take a final decision:
Response : We appreciate the reviewer for carefully reading our manuscript. Answers regarding the questions raised are given below.
- The paper contains some grammatical errors and typo-mistakes that should be corrected.
Response : As suggested the whole manuscript has been completely overhauled.
- Abbreviations should be opened when mentioned for the first time.
Response : The acronyms ‘SEM-EDX, XRD, UV-Vis-NIR, UV-Vis spectrophotometer’ used in both abstract and introduction were replaced by the original words “scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), ultraviolet (UV)-visible (Vis)-near infrared (NIR), UV-Vis spectrophotometer”
- The abstract part should be improved. It should contain some qualitative and quantitative results.
Response: We thank the reviewer for this comment. We modified the abstract part to include quantitative and qualitative information (see the bold line in text).
In the revised manuscript “A simple solid-state reaction was applied to synthesize Fe-doped perovskite-type PBFNO catalysts, and methylene blue decomposition studies were performed in the form of visible light according to changes in Fe doping content (0.4 to 1.9 mol ratio compared with Bi mol) and amount of catalyst used (0.05 to 0.2 g used). As the Fe doping content increases, the absorbance and bang gap energy of the PBFNOs sample rapidly increase and decrease, respectively, because the Fe dopant in the PBNO lattice acts as an intermediate band between the valence and conduction bands of PBNO and reduces the band gap energy. As a result, it showed a performance degradation of about 42% compared to the maximum performance. In addition, the presence of Fe dopants in the PBNO lattice greatly reduces the intensity of the photoluminescent lines. This is because the Fe dopant can play an important role in light-induced electron transfer and as a hole trap, reducing the recombination rate. Additionally, when too much photocatalyst was used (>0.1 g used), the Fe dopant played an important role as a light-induced electron transfer and hole trap, reducing the recombination rate and lowering the overall photocatalytic activity by 51%. In particular, 0.1 g of PBNO-0.2-F showed continuous catalytic activity even when the photocatalytic reaction proceeded for 180 minutes. Therefore, this study demonstrates that the Fe-doped aurivillius-phase PBFNO photocatalyst is very promising for the dye manufacturing industry.” was modified in the revised manuscripts in the abstract section.
- Details of reagents used in the synthesis (name of chemical formula, source, purity, number of moles, masses, etc.) should be provided within the manuscript.
Response: We thank the reviewer for this comment. We have added detailed reagent information.
In the revised manuscript “Lead(II) Oxide (PbO, >99%, ACS Reagent), Bismuth(III) Oxide (Bi2O3, >98.0%, purum), Iron(III) Oxide (Fe2O3, >99.995% Trace metals basis), and Niobium(V) Oxide (Nb2O5 (99.99%, Trace metal basis) were purchased from Sigma-aldrich, Korea.” was added in the revised manuscripts in the experimental section.
- SEM for non-doped sample should be added.
Response: We thank the reviewer for this comment We added FE-SEM images of the Fe-undoped photocatalyst at the same magnification.
In the revised manuscript “Figure S1” was added in the revised manuscripts.
- The EDX spectra and atomic percentage should be provided along with SEM images
Response: We thank the reviewer for this comment We added an EDX of the Fe-undoped photocatalyst at the same magnification in the revised manuscript.
In the revised manuscript “Table S1” was added in the revised manuscripts.
- From the SEM images, it is not clear that the particle size of PBFNO decrease with increasing the Fe doping ratio.
Response : Thank you for this comment. It is difficult to measure the particle size of PBFNO using the SEM images, the size was measured through FWHM (Full width at half maximum) using a Scherrer Equation. That results are shown in Table 1.
- Authors presented only SEM images and did not perform any analysis of grain size distribution, density, porosity, etc. It will be much more useful if the authors can add some analysis of microstructure.
Response : We also agree to perform additional analyzes for a detailed interpretation of the analytes following the photocatalytic reaction proposed by the reviewers.
- Details on how crystallites size is determined should be reported in the text.
Response The following sentences regarding the size of crystallites estimated by X-Rays were added.
“According to Scherrer Equation, the wavelength of X-Rays are in the range between 0.01nm to 10nm. Hence, the X-Rays can easily penetrate the crystal structure of most material to analyze its physical properties. The particle size is estimated by the Scherrer formula:
Scherrer Formula:
Dp = (0.94 Χ λ) / (β Χ Cosθ)
where, Dp = Average Crystallite size, β = Line broadening in radians, θ = Bragg angle, λ = X-Ray wavelength.”
- Related to the current compounds, none of the physical properties such as polarization, magnetization, dielectric or magneto-dielectric properties, and magnetoelectric coupling effect has been investigated.
Response : We thank the reviewer to provide the insightful suggestion and strongly agree with the needs of investigation of physical properties. However, we believe that without considering the physical properties the present study has already provided sufficient findings of the photocatalytic activity in terms of the Fe-doping ratio. We will keep in mind the reviewers’ suggestion which will be a great research topic for further investigation regarding the influence of physical properties on the preparation of photocatalyst and its activity.
- XPS analysis is interesting for being investigated.
Response : We also agree to carry out additional analysis for a detailed interpretation of the catalyst as suggested by the reviewer. However, as you can see from reviewer 1's answer, it is difficult to analyze within a limited time, so we ask for the reviewer's understanding.
- Graduation, Y-axis values, and units should be provided in Figures 4 and 5.
Response: Thank you for this comment. As requested by reviewers, we added graduation, Y-axis values, and units to Figures 4 and 5.
In the revised manuscript “Figures 4 and 5” was added in the revised manuscripts.
- Absorbance graphs as a function of reaction time for all samples should be provided.
Response: The Absorbance graphs as a function of reaction time was already given in Figure 7 and Figure 8.
- Photocatalytic results should be compared with those previously found in comparable compositions. Anyway, all samples do not reveal full degradation of MB even after 3 hours of irradiation time. What is the success of the current study accordingly?
Response: We thank the reviewer for this comment. As shown in Reviewer 1’s answer 8, The latest research on MB decomposition using various photocatalytic materials which has comparable compositions has been summarized and added to Table 4.
As mentioned in the abstract, the goal of this study is to see the difference in energy band gap and the change in photocatalytic performance according to Fe doping based on a material with aurivillius-phase, and these effects were confirmed through various experiments.
In the revised manuscript “Table 4” was added in the revised manuscripts.
- There are excess uses of references. The references should be rechecked, and their number should be reduced.
Response : Thank you for this comment. We have rechecked the reference list. The initial references were reduced, but the reference has increased slightly due to the reviesed manuscripts.
Round 2
Reviewer 1 Report
The authors have addressed all the comments I originally proposed. I would recommend the acceptance.
Reviewer 2 Report
The revised manuscript has been improved. I think that it can be now accepted for publication.
