Porous Hybrid PVDF/BiFeO₃ Smart Composite with Magnetic, Piezophotocatalytic, and Light-Emission Properties

Round 1

Reviewer 1 Report

In this manuscript, the authors reported the preparation of PVDF/BiFeO3 composite membrane and its piezophotocatalytic application in degrading MB. The manuscript is well organized and clearly written. I recommend it could be published in Catalysts after clarifying the following issues.

(1) In line 158, "Figure 4" could be "Figure 3"?

(2) As there are some impurity phases (Bi25FeO40, Bi2Fe4O9) existing in the PVDF/BFO composite, the authors are suggested to discuss whether these impurity phases could be coupled with BiFeO3 to form heterojunctions and whether they have effect on the piezophotocatalytic degradation performance.

(3) How about the adsorption of MB onto the PVDF/BiFeO3 composite? It is noted that the dye adsorption generally has an appreciable effect on its photocatalytic degradation.

(4) Is there an optimal ratio between PVDF and BiFeO3 to achieve the highest piezophotocatalytic performance of PVDF/BiFeO3 composites?

(5) The authors are suggested to draw a diagram to elucidate the piezophotocatalytic mechanism of PVDF/BiFeO3.

(6) To strengthen the research background, the papers related to the photocatalytic enhancement strategies are suggested to read and mentioned (Langmuir 39 (2023) 1159−1172, Dalton Transactions 51 (2022) 18652–18666, Colloids and Surfaces A 644 (2022) 128758).

Author Response

In this manuscript, the authors reported the preparation of PVDF/BiFeO₃ composite membrane and its piezophotocatalytic application in degrading MB. The manuscript is well organized and clearly written. I recommend it could be published in Catalysts after clarifying the following issues.

The authors are grateful to the reviewer for their careful review of the work, valuable recommendations, and questions.

(1) In line 158, "Figure 4" could be "Figure 3"?

Corrected

(2) As there are some impurity phases (Bi₂₅FeO₄₀, Bi₂Fe₄O₉) existing in the PVDF/BFO composite, the authors are suggested to discuss whether these impurity phases could be coupled with BiFeO₃ to form heterojunctions and whether they have effect on the piezophotocatalytic degradation performance.

Thank you for the question. In our previous works, we investigated the influence of synthesis parameters on the content of impurity phases and photocatalytic activity. We showed that annealing at 600°C after synthesis can minimize the content of impurity phase without losing photocatalytic activity. (Orudzhev, F. F., et al. "Synthesis and study of the properties of magnetically separable nanophotocatalyst BiFeO₃." Kimya Problemleri 4 (2018): 484-495. /// https://link.springer.com/article/10.1007/s10854-021-05911-9 ) It was shown that the difference in photocatalytic activity between the freshly synthesized sample with impurity phases (7%) and annealed at 600°C (3%) is practically absent. However, getting rid of impurity phases is a very difficult and still unsolved problem. In many samples, impurities are still present, but due to the detection limit of XRD, many represent the absence of impurity phase peaks as a single-phase material.

(3) How about the adsorption of MB onto the PVDF/BiFeO₃ composite? It is noted that the dye adsorption generally has an appreciable effect on its photocatalytic degradation.

Thank you for the question. Of course, adsorption plays a very important role. We checked the dark adsorption before catalysis. Since the sample is hydrophobic, adsorption was less than 5% in 60 minutes. Therefore, these data are not presented. We mentioned this in the text of the article (line 349).

(4) Is there an optimal ratio between PVDF and BiFeO₃ to achieve the highest piezophotocatalytic performance of PVDF/BiFeO3 composites?

Thank you for the question. In our work, we presented data with this mass loading because we were interested in comparing PVDF/BiFeO₃ composites obtained by different methods. In our previous work, we investigated the piezophotocatalytic properties of PVDF/BiFeO₃ composite synthesized by electrospinning method. (Orudzhev, F.; Sobola, D.; Ramazanov, S.; Částková, K.; Papež, N.; Selimov, D.A.; Abdurakhmanov, M.; Shuaibov, A.; Rabadanova, A.; Gulakhmedov, R.; et al. Piezo-Enhanced Photocatalytic Activity of the Electrospun Fibrous Magnetic PVDF/BiFeO₃ Membrane. Polym. 2023, Vol. 15, Page 246 2023, 15, 246, doi:10.3390/POLYM15010246.). In our next work, we will compare it with the PVDF/BiFeO₃ composite synthesized by the phase inversion method from a non-solvent (NIPS). Of course, the choice of the initial composition of the composite at 5% is based on preliminary experiments, which showed that 5% and 20% loading exhibit the same activity.

(5) The authors are suggested to draw a diagram to elucidate the piezophotocatalytic mechanism of PVDF/BiFeO3.

Thank you for the suggestion. We presented the scheme of piezo-enhanced photocatalysis in our previous article, so we believe that references to it will be sufficient not to burden the article. (Orudzhev, F.; Sobola, D.; Ramazanov, S.; Částková, K.; Papež, N.; Selimov, D.A.; Abdurakhmanov, M.; Shuaibov, A.; Rabadanova, A.; Gulakhmedov, R.; et al. Piezo-Enhanced Photocatalytic Activity of the Electrospun Fibrous Magnetic PVDF/BiFeO₃ Membrane. Polym. 2023, Vol. 15, Page 246 2023, 15, 246, doi:10.3390/POLYM15010246.)

(6) To strengthen the research background, the papers related to the photocatalytic enhancement strategies are suggested to read and mentioned (Langmuir 39 (2023) 1159−1172, Dalton Transactions 51 (2022) 18652–18666, Colloids and Surfaces A 644 (2022) 128758).

We thank you for drawing attention to good works. We have added references.

Reviewer 2 Report

The manuscript presents interesting results concerning piezophotocatalytic properties of PVDF-based composites. Before publication, a few details must be clarified:

1. The paper contains some typing mistakes and needs some English corrections.

2. Row 158 is Fig.3, not Fig.4.

3.  Please add DSC for PVDF film and discussed the data in relation to its characteristics.

4. In Table 1 add measurements unit.

5. The magnetic behavior of both BFO and PVDF/BFO is more like a ferrimagnetic than a ferromagnetic material.

6. It will be more interesting if you compare all the properties also with PVDF films.

Author Response

The manuscript presents interesting results concerning piezophotocatalytic properties of PVDF-based composites. Before publication, a few details must be clarified:

Dear reviewer, we are extremely grateful for your careful consideration of our results and valuable recommendations. We have made the necessary revisions to the article and are confident that it has improved the quality of our work. Below are all of our responses and comments.

1. The paper contains some typing mistakes and needs some English corrections.

Thank you, we revised the text and corrected the language

2. Row 158 is Fig.3, not Fig.4.

Corrected

3.  Please add DSC for PVDF film and discussed the data in relation to its characteristics.

Thanks for this recommendation. Here, we have presented only the data for the composite material to show that the synthesized material is highly crystalline, since the piezoelectric properties of the composite strongly depend on crystallinity. We did not want to show the difference between a pure polymer and a composite, since we do not study the piezophotocatalytic activity of a pure polymer in this work due to its lack of photosensitivity.

4. In Table 1 add measurements unit.

Corrected

5. The magnetic behavior of both BFO and PVDF/BFO is more like a ferrimagnetic than a ferromagnetic material.

Thanks for the question. It is quite difficult to conclude based only on M(H) magnetic loops within the framework of this study, because there are several factors affecting the magnetic properties of bismuth ferrite: the size of crystallites, impurity phases. They are strongly depend on the synthesis protocol and post heat treatment ( Nano Lett., Vol. 7, No. 3, 2007, MRS Advances   Vol 4 (28-29) 2019 pp. 1659-1665)  

Our research did not aim to study in detail the magnetic properties of bismuth ferrite nanoparticles, which was used as a magnetic fillers for the PVDF/BFO composite. The main purpose of the magnetic measurements was to determine how the magnetic properties (Ms, Mr, Hc) of the PVDF/ BFO composite change in comparison with the original bismuth ferrite nanoparticles. For more specific conclusions about the magnetic nature of bismuth ferrite, additional magnetic measurements are needed, including M(T) measurements. In paper, we just note that we observe behavior typical for soft ferromagnetic materials.

6. It will be more interesting if you compare all the properties also with PVDF films.

Thank you, we certainly compared with pure PVDF. The sample, as expected, does not show photocatalytic activity, so there was no point in showing piezophotocatalysis. Of course, if the article were devoted to piezocatalysis, we would undoubtedly have given data for pure PVDF too. Based on this, we decided not to load the work with data. This could make it difficult for readers to understand the results.