Efficient Photocatalytic Degradation of RhB by Constructing Sn₃O₄ Nanoflakes on Sulfur-Doped NaTaO₃ Nanocubes

Round 1

Reviewer 1 Report

The authors modified the band structure of NaTaO3 by sulfur doping. The authors also fabricated a heterojunction of S-doped NaTaO3 with Sn3O4 to further enhance the photocatalytic properties of NaTaO3, especially charge separation.  The topic and materials are interesting. This manuscript can be accepted after some revision. Below are comments for authors.

1. The authors mentioned that “… the interfacial charge transfer of the composites enhanced RhB photosensitization process under irradiation, which can effectively separate and transfer photogenerated carriers”. Additional experiments such as EIS, PL, etc., are needed to support the argument.
2. Trapping experiment is needed to support the proposed mechanism.
3. It is suggested to provide HR-TEM of Sn/NTO-S to observe the interface.
4. The authors can get some information related to photodegradation from these works. Applied Surface Science, Volume 533, 15 December 2020, 147506, J Am Ceram Soc. 2020; 103:2252–2261, Ceramics International 45 (2019) 23651–23657

Author Response

Point 1: The authors mentioned that “… the interfacial charge transfer of the composites enhanced RhB photosensitization process under irradiation, which can effectively separate and transfer photogenerated carriers”. Additional experiments such as EIS, PL, etc., are needed to support the argument.

Response 1: Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion. Figure 6 was in the revised manuscript.  

Figure 6. Room-temperature PL spectra of NaTaO₃, NTO-S, Sn/NTO, Sn/NTO-S, and Sn₃O₄ respectively.

To prove the rationality of the proposed reaction pathway and investigate the capabilities of photo-induced e-/h+ pairs in the semiconductors, PL emission spectra of NaTaO₃, NTO-S, Sn/NTO, Sn/NTO-S, and Sn₃O₄ were carried out, respectively. PL emission arises from the recombination of free carriers, and a higher PL intensity reveals a higher recombination rate of photo-generated e-/h+ pairs. On the contrary, a weaker PL intensity indicates a lower recombination rate of photo-excited e-/h+ pairs, and accordingly much more photo-induced carriers can participate in the photocatalytic reaction. As shown in Fig.6, the spectrum of NaTaO₃ nanocubes shows three peaks at around 395 nm, 451 nm, and 469 nm. The emission at 451 nm and 469 nm due to band-to-band mixing of Ta⁴⁺-O^- states in the octahedral TaO₆ motifs of NaTaO₃. After doping the S anion in NaTaO₃, the PL intensity of NTO-S was weaker than that of pure NaTaO₃. It indicated that the NTO-S can suppress the recombination of e-/h+ pairs. Noticeably, the intensities of PL spectra of Sn/NTO, Sn/NTO-S heterojunction photocatalysts strongly decreases with the Sn/NTO heterojunctions formed as compared to pure cubic NaTaO₃, it can be seen that the maximum PL intensity around 469 nm. The lower PL intensity implies the efficient inhibition of photo-generated pairs and therefore higher photocatalytic activity in the UV light region, which can effectively explain the variation of photocatalytic activities of different samples.

Point 2: Trapping experiment is needed to support the proposed mechanism.

Response 2: Thanks very much for the reviewer’s suggestion. As is well known, Rh B is often used as a photodegradable dye. In our references 40, Advanced Powder Technology 2020, 31 (7), 2921-2931. From Fig.12, the proposed mechanism had well explained. Hence, we had referred to it here. Furthermore, other similar literature is also cited as the proposed mechanism directly.

Point 3: It is suggested to provide HR-TEM of Sn/NTO-S to observe the interface.

Response 3: Thanks very much for the reviewer’s suggestion. We have done it. Please look at Figure R1. They are TEM and HR-TEM images of Sn/NTO-S. The lattice fringe with interplanar distances of 0.329 nm was ascribed to (111) plane of triclinic Sn₃O₄.

Figure R2. (a) TEM and (b) HR-TEM images of Sn/NTO-S.

Point 4: The authors can get some information related to photodegradation from these works. Applied Surface Science, Volume 533, 15 December 2020, 147506, J Am Ceram Soc. 2020; 103:2252–2261, Ceramics International 45 (2019) 23651–23657

Response 4: Thanks very much for the reviewer’s suggestion. We have already referred to these literatures, they are all very good articles. In the Pag 13 lines 445-450.

Author Response File: Author Response.docx

Reviewer 2 Report

“Efficient Photocatalytic Degradation of RhB by constructing Sn3O4 nanosheets on sulfur-doped NaTaO3 nanocube” by S. Chang et al. deals with synthesis and characterization of novel Sn3O4/NaTaO3 heterostructure. The authors well characterize the synthesized materials and demonstrate that coupled Sn3O4/NaTaO3 nanoparticles have better photocatalytic degradation capability than pure NaTaO3 or Sn3O4 nanocrystals.

I recommend to publish this work on Crystals after minor revisions.

In particular, the authors should address the following points:

• Pag 1 line 34: reference 8 is related to the application of halide perovskites (not perovskite-type oxide) in photovoltaic devices. I think it is not appropriate to cite it here.
• Pag 6 Figure 4a: can the authors explain why the diffuse reflectance spectrum of NaTaO3 (black curve) goes negative around 350 nm?
• Pag 6 line 192: spectrum --> spectra
• Pag 6 line 198: ‘emission’, I think the authors meant to say absorption
• Pag 7 lines 201-204: this sentence seems to be missing a piece or needs to be linked to the next sentence.

Author Response

Point 1: Pag 1 line 34: reference 8 is related to the application of halide perovskites (not perovskite-type oxide) in photovoltaic devices. I think it is not appropriate to cite it here.

Response 1: Thanks very much for the reviewer’s suggestion. I accept it and delete reference 8.

Point 2: Pag 6 Figure 4a: can the authors explain why the diffuse reflectance spectrum of NaTaO3 (black curve) goes negative around 350 nm

Response 2: Thanks very much for the reviewer’s suggestion. In fact, the diffuse reflectance spectrum of NaTaO₃ (black curve) goes negative around 350 nm shouldn’t be appeared. I think that should be the result of the test or experimental error because the reference and the sample to be measured are not completely parallel. If we move the black curve vertically up, the diffuse reflectance spectrum of NaTaO₃ will be some absorption behind 350 nm (Figure R1.)，which is not supposed to happen.

Figure R1.

Point 3: Pag 6 line 192: spectrum --> spectra

Response 3: Thanks very much for the reviewer’s suggestion. Sorry, that is my mistake. The spectra contain several samples, it should be using a plural form --> spectra.

Point 4: Pag 6 line 198: ‘emission’, I think the authors meant to say absorption

Response 4: Thanks very much for the reviewer’s suggestion. It should be “absorption”. Please look at the ordinate. Moreover, Pag 6 lines 199-200: The pure Sn3O4 can absorb the light irradiation as its optical absorption was determined to be around 473nm. We have revised it.

Point 5: Pag 7 lines 201-204: this sentence seems to be missing a piece or needs to be linked to the next sentence.

Response 5: Thanks very much for the reviewer’s suggestion. Pag 7 line 204, we will add a sentence: Accordingly, results are shown in Fig.4b, the bandgap energies of NaTaO₃, NTO-S, Sn₃O₄, Sn/NTO, and Sn/NTO-S are calculated to 4.03eV, 3.84eV, 2.62eV, 2.56eV, and 2.37eV, specifically.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have responded to all comments.  This manuscript can be accepted in present form.