Morphology-Controlled WO3 for the Photocatalytic Oxidation of Methane to Methanol in Mild Conditions
Round 1
Reviewer 1 Report
In order to explore this aspect of inefficiency in photocatalytic activity, the authors prepared five different morphologies of WO3 consisting of micron, nanopowder, rods, wires, and flowers were synthesized and characterized. In addition, the authors employed several electron capture agents/oxidizers to investigate effect of photogenerated charge separation. The photocatalytic activity of different morphologies was assessed via CH3OH formation rates. Based on their results, WO3 flowers produced the highest methanol productivity (38.17 ± 3.24 μmol/g-h) when 2 mM H2O2 was used, which is ~4 times higher in the absence of H2O2. This higher methanol production has been attributed to the unique structure-related properties of the flower-like structure. Photoluminescence emission spectra and diffuse reflectance data reveals that flower structures are highly catalytic due to their reduced electron/hole recombination and multiple light reflections via petal-like hollow chambers.
After careful evaluation of this manuscript, the authors performed all the experiments with enough care and attention. They presented the data in an elaborate and well narrated manner. Therefore, I recommend this manuscript for acceptance in methane Journal in the present form.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this work, the authors compared five different morphologies of WO3 samples with micron, nanopowder, rods, wires, and flowers for the photocatalytic oxidation of methane to methanol. The manuscript was well prepared; however, there are some questions need to be addressed. I recommend a minor revision before acceptance.
(1). Line 94, for the synthesis of WO3 rods, why the mixture was baked at 180oC first and then centrifuged? Generally, it was centrifuged first and then baked later. Does it calcine before the performance test?
(2). From the Fig. S1 in supplementary, it can be found that the WO3 diffraction peaks changed a lot for different WO3 samples, it is better to explain how the crystalline structure of WO3 contributed to the reaction?
(3). How about the binding energies of WO3 samples with different morphologies?
(4). The oxygen vacancy in the metal oxide play an important role in the reaction, how about the role of oxygen vacancy in WO3 samples with different morphologies?
(5). The variation of methanol formation rate in Fig. 4b is similar to that of the specific surface area in Table 1. Does the specific surface area contribute to the methanol formation?
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
This manuscript studies the effect of morphology of WO3 photoanode on the photocatalytic oxidation ability of CH4 to CH3OH. Several types of WO3 nanostructures are synthesized, based on which the authors demonstrate the flower-like structure exhibits the best productivity. Possible explanations for the higher photocatalytic activity are also provided. The manuscript is well written. I recommend the acceptance though there are a few minor comments.
· In the Results and Discussion section, why is the first figure spectrophotometry rather than nanostructure morphology? I think material morphology, specifically SEM image, is the most important in the current work. It would make readers confused when reading the legend in Figure 1 because no one has any idea about how it looks like at this point.
· The linear fitted line for identifying the bandgap value should be drawn in Figure 1.
· Please provide higher-resolution image for Figure 3. Some parts are not clear such as the holes in VB.
· Page7, Line 237: I agree that the visible light absorption does improve. But I don’t think it is “greatly” extended according to the absorption spectra.
Author Response
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Author Response File: Author Response.pdf
