Pt-Modified Interfacial Engineering for Enhanced Photocatalytic Performance of 3D Ordered Macroporous TiO₂

Round 1

Reviewer 1 Report

The authors synthesized and characterized the macroporous Pt-loaded TiO₂ photocatalyst colloidal crystal-template method. They claimed that their synthesized catalysts possess uniform 3D ordered macroporous structure, high crystallinity and large porosity. The synthesized catalyst was shown to be efficient towards the photocatalytic degradation of Rhodamine B. While this work is not particularly novel, their synthesis method could be of interests to the photocatalyst community. However, some of the results and discussion need to be significantly improved before it is ready for publication. Here are some major concerns which need to be addressed

• The light intensity for photocatalytic experiments should be given in term of power/area (watt/m² for example). Only providing the intensity of the light source means nothing.
• In the case of FTIR data Figure 2(b), the authors are looking at transmittance, the downward peaks are only important. Not sure why they looked at upward peaks which are only significant if they are reporting FTIR data in terms of absorbance.
• The authors claimed that the pores of TiO2 structures are uniform and they only provided the average size of the pores. Uniformity can be only checked by looking at the standard deviation. They should provide that information.
• Any idea why there is a shift in peak position for the PL spectra (Figure 7(b) ) for Tio2/Pt in comparison to TiO2 alone?
• The accuracy of measuring bandgap from UV-vis diffuse reflectance is not good enough to differentiate between 3.01 eV and 2.96 eV. Any comments?
• Finally, how did they know that the enhanced performance of TiO2/Pt composites is not due to plasmonic or catalytic properties of Pt?

Author Response

Responses to Review

Reviewer #1:

The authors synthesized and characterized the macroporous Pt-loaded TiO₂ photocatalyst colloidal crystal-template method. They claimed that their synthesized catalysts possess uniform 3D ordered macroporous structure, high crystallinity and large porosity. The synthesized catalyst was shown to be efficient towards the photocatalytic degradation of Rhodamine B. While this work is not particularly novel, their synthesis method could be of interests to the photocatalyst community. However, some of the results and discussion need to be significantly improved before it is ready for publication. Here are some major concerns which need to be addressed.

 Response: Thank you very much for your positive comments and suggestions on our work. Following your valuable advice, we have further revised our manuscript to improve its overall quality. We hope that the revisions can be satisfactory and wish you a happy life.

1. The light intensity for photocatalytic experiments should be given in term of power/area (watt/m² for example). Only providing the intensity of the light source means nothing.

Response: Thanks for your good suggestion. Following your advice, we have provided the related light power density information in the revised version.

The corresponding modification in the revised manuscript is as follows:

Page 4: “…with a power density of 9.4 W/cm²…”.

2. In the case of FTIR data Figure 2(b), the authors are looking at transmittance, the downward peaks are only important. Not sure why they looked at upward peaks which are only significant if they are reporting FTIR data in terms of absorbance.

Response: Thanks very much for your professional comment. Following your suggestion, we have re-analyzed the FT-IR spectra (Fig. R1) and provided a reasonable interpretation of the corresponding peaks.

The corresponding description has been revised in the manuscript as follows:

Page 5: “The FT-IR spectra of TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples are shown in Figure 2b. Apparently, TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples demonstrate similar FT-IR characteristic peaks. The Ti–O stretching and Ti–O–Ti bridging stretching modes locate in the range of 400~750 cm⁻¹.^[29] The peak at 3335 cm^-1 is attributed to hydroxyl and water molecules adsorbed on the surface of the sample.^[30] In addition, the peak at 1592 cm^-1 corresponds to the O–H stretching and bending vibrations.^[30-32] These adsorbed OH groups and H₂O play an important role in the photocatalytic activity of 3DOM Pt/TiO₂. Compared to TiO₂, 3DOM Pt/TiO₂ sample does not show characteristic peaks of loaded Pt possibly due to the low loading amount of Pt species.”

Fig. R1 FT-IR spectra of TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples. (Now is new Fig. 2b in the revised manuscript.)

 3. The authors claimed that the pores of TiO₂ structures are uniform and they only provided the average size of the pores. Uniformity can be only checked by looking at the standard deviation. They should provide that information.

Response: Thanks for your good remarks. In this manuscript, we have combined SEM images (Fig. R2) and N₂ adsorption-desorption isotherms (Fig. R3) characterizations to further demonstrate that 3DOM TiO₂ is characterized by relatively homogeneous pores. The pore size distributions of 3DOM TiO₂ are concentrated in the range of 60~150 nm from the N₂ adsorption/desorption isotherms (Fig. 6b), exhibiting the macroporous type. All these results suggest the relatively good uniformity of 3DOM TiO₂ pores.

Fig. R2 SEM images of 3DOM TiO₂ and 3DOM Pt/TiO₂ samples. (Now is Fig. 3c-d in the revised manuscript.)

Fig. R3 Pore-size distributions of 3DOM TiO₂ and 3DOM Pt/TiO₂. (Now is Fig. 6b in the revised manuscript.)

4. Any idea why there is a shift in peak position for the PL spectra (Figure 7(b)) for TiO₂/Pt in comparison to TiO₂ alone?

Response: Thanks for your good question. Since the Fermi energy level of Pt is lower than the Fermi energy level of TiO₂. Therefore, when Pt is in contact with TiO₂, the Fermi energy level of Pt shifts upwards while TiO₂ undergoes a downward shift, allowing the Fermi energy levels of 3DOM Pt/TiO₂ to reach a new equilibrium (Figure 11b in the revised manuscript). As the visible light irradiation time increases, many photogenerated electrons in the conduction band of TiO₂ can gain enough energy to cross the Schottky barrier between the two and are captured by the Pt co-catalyst. The luminescence principle of PL is the radiative recombination of photogenerated electrons and holes to emit photons. The 3DOM Pt/TiO₂ photocatalyst has holes enriched in the valence band of TiO₂ and electrons enriched in the Pt Fermi energy level. 3DOM Pt/TiO₂ is constructed in a way that effectively changes the photon energy of the photogenerated carrier radiative complex. This results in a red-shift in the excitation position of the PL of 3DOM Pt/TiO₂ as also suggested by recent literatures such as doi:10.1016/S0045-6535(02)00201-1 and doi: 10.1039/c6pp00240d.

5. The accuracy of measuring bandgap from UV-vis diffuse reflectance is not good enough to differentiate between 3.01 eV and 2.96 eV. Any comments?

Response: Thanks for your question. Since the Fermi energy level of Pt is lower than the Fermi energy level of TiO₂. Therefore, when Pt is in contact with TiO₂, the Fermi energy level of Pt shifts upwards while TiO₂ undergoes a downward shift, resulting in a new equilibrium of the Fermi energy levels of 3DOM Pt/TiO₂ (Figure 11b in revised manuscript). Pt as a co-catalyst can effectively regulate the Fermi energy levels of 3DOM Pt/TiO₂ composite but does not change the positions of the conduction/valence bands of TiO₂ noticeably. Thus, the above results can explain the small difference in band gap width between TiO₂ (3.01 eV) and 3DOM Pt/TiO₂ (2.96 eV). Similar observation can also be found in few previous literatures such as doi: 10.3390/nano12030474 and doi: 10.1016/j.jece.2018.08.042.

6. Finally, how did they know that the enhanced performance of TiO₂/Pt composites is not due to plasmonic or catalytic properties of Pt?

Response: Thanks very much for your very good remarks. Your question has inspired us to further reconsider the underlying mechanism for enhanced catalytic property of our composite catalyst. After carefully thinking, we agree with you that the plasmonic and catalytic properties of Pt nanoparticles can also contribute to the enhanced catalytic activity. However, the exact contribution of each aspect is hard to be separated because they are coupled together and play synergistically. Nonetheless, the contribution of plasmonic or Pt alone is not dominant because of the following reasons: (1) plasmonic effect requires well-defined particle size, morphology, and particle distribution; (2) the high catalytic property of Pt needs a relatively high loading amount. However, in our case, the deposition amount of Pt on the 3DOM TiO₂ is low, and its size, morphology and particle distribution haven’t been well controlled yet. Therefore, to better answer this referee’s question, we have further revised the explanation of the catalytic performance enhancement part in our revised version by taking the referee’s comments inside as follows:

Page 10: “In addition, it is noted that the plasmonic effect due to the introduction of Pt nanoparticles and the catalytic function of Pt alone can contribute partly to the enhanced photocatalytic degradation of the RhB.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript ID: 1735546 General comments: In this manuscript "Pt-Modified Interfacial Engineering for Enhanced Photocatalytic Performance of 3D Ordered Macroporous TiO2 ", the authors have described the reparation of three-dimensionally ordered macroporous Pt-loaded TiO2 photocatalyst (3DOM Pt/TiO2) using a facile colloidal crystal-template method. The results described here show the good photocatalytic activity of the 3DOM Pt/TiO2 photocatalyst against RhB dye. The results are well supported by the characterization techniques. The work is adequate. The comments may be useful for the improvement of the manuscript. Minor revisions are needed to make the work acceptable. Some specific comments are as follows:

1. Please rewrite the abstract.
2. The degradation products of RhB should be characterized by the high-performance liquid chromatography (HPLC) and mass spectrometry (MS).
3. Please mention a few advantages of using colloidal crystal template method in the introduction.
4. Authors have not explained an FT-IR characteristic absorption peak at 2250 cm −1.
5. Dye adsorption study must also be including.
6. Cyclic stability study should be include explaining the parcticalability of the photocatalyst.
7. Why RhB was used as a pollutant.
8. There are many errors in the manuscript, like, "TiO2" and grammatical mistakes like "The result of photocatalytic degradation of rhodamine B (RhB) verified that 3DOM Pt/TiO2 degraded 88% of RhB under visible light irradiation (λ≥ 420 nm) for 100 min, while the degradation ratio was only 37% when using commercial TiO2 as the photocatalyst".
9. Radical scavenger tests must be include explaining the generation of radicals during the dye degradation process.
10. Are the synthesized photocatalysts active in the UV region?

Author Response

Responses to Review

Reviewer #2:

In this manuscript "Pt-Modified Interfacial Engineering for Enhanced Photocatalytic Performance of 3D Ordered Macroporous TiO₂ ", the authors have described the reparation of three-dimensionally ordered macroporous Pt-loaded TiO₂ photocatalyst (3DOM Pt/TiO₂) using a facile colloidal crystal-template method. The results described here show the good photocatalytic activity of the 3DOM Pt/TiO₂ photocatalyst against RhB dye. The results are well supported by the characterization techniques. The work is adequate. The comments may be useful for the improvement of the manuscript. Minor revisions are needed to make the work acceptable.

Response: Thank you very much for your positive comments and suggestions on our work. Following your valuable advice, we have further revised our manuscript to improve its overall quality. We hope that the revisions can be satisfactory and wish you a happy life.

1. Please rewrite the abstract.

Response: Thanks very much for your suggestion. Following your advice, we have rewritten the abstract section in the revised manuscript to make it more concise as follows:

 Page 1: “Narrowing the band gap and increase the photodegradation efficiency of TiO₂-based photocatalysts are very important for their wide application in environment-related fields such as photocatalytic degradation of toxic pollutants in wastewater. Herein, a three-dimensionally ordered macroporous Pt-loaded TiO₂ photocatalyst (3DOM Pt/TiO₂) has been successfully synthesize using a facile colloidal crystal-template method. The resultant composite combines several morphological/structural advantages including uniform 3D ordered macroporous skeletons, high crystallinity, large porosity, and internal electric field formed at Pt/TiO₂ interfaces. These unique features enable the 3DOM Pt/TiO₂ to possess a large surface for photocatalytic reaction and fast diffusion for mass transfer of reactants as well as efficient suppression of recombination for photogenerated electron-hole pairs in TiO₂. Thus, the 3DOM Pt/TiO₂ exhibits significantly enhanced photocatalytic activity. Typically, 88% of RhB can be degraded over the 3DOM Pt/TiO₂ photocatalyst under visible light irradiation (λ≥ 420 nm) within 100 min, much higher than that of the commercial TiO₂ nanoparticles (only 37%). The underlying mechanism for the enhanced photocatalytic activity of 3DOM Pt/TiO₂ has been further analyzed based on energy band theory and ascribed to the formation of Schottky-type Pt/TiO₂ junctions. The proposed method herein can provide new references for further improving the photocatalytic efficiency of other photocatalysts via rational structural/morphological engineering.”

2. The degradation products of RhB should be characterized by the high-performance liquid chromatography (HPLC) and mass spectrometry (MS).

Response: Thanks very much for your good suggestion. We agree with you that HPLC and MS tests play a key role in determining the photocatalytic activity of photocatalysts. However, unfortunately our lab does not have such high-level characterization instruments yet and we’re also unable to send our samples outside our city for outer evaluation due to the spreading of COVID-19 case and related strict control measures in Wuhan City at present. However, we do appreciate your good suggestions and keep it in mind for our future work where appliable.

 3. Please mention a few advantages of using colloidal crystal template method in the introduction.

Response: Thanks for your good remark. Following your advice, we have further discussed the advantages of the colloidal crystal template method for the sample synthesis in the introduction section in the revised manuscript as follows:

Page 2: “The colloidal crystal template method has been widely used for the preparation of various photocatalytic materials along with the advantages of simple preparation, high reproducibility, well-ordered structures and low cost.”

 4. Authors have not explained an FT-IR characteristic absorption peak at 2250 cm⁻¹.

Response: Thanks for your question. We measured the FT-IR spectrum in a transmittance mode. In this mode, the bands are directed towards the bottom of the graph. However, the position of the peak at 2250 cm^-1 is towards the top and thus does not belong to the peak of the FT-IR spectrum with a transmittance mode. Similar analysis can also be found in recent reference such as DOI: 10.1039/c4ta01922a (which is Ref. 17 in our manuscript.).

 5. Dye adsorption study must also be included.

Response: Thanks for your suggestion. Following your advice, we have supplemented the adsorption tests of TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ photocatalysts for RhB adsorption. The experimental details and conclusions of the adsorption tests have been described in the revised manuscript as follows:

Page 4 (Experimental section): “The adsorption properties of the samples were assessed by adsorption experiments of the RhB dye. 100 mg of the as-prepared photocatalyst was added to 100 ml of RhB solution (10 mg L^-1) and placed in the dark for magnetic stirring. 5 mL of the solution was extracted every 5 minutes and the mixed solution was centrifuged to obtain the supernatant. Finally, the RhB concentration was tested using a UV-Vis spectrometer. The adsorption capacity of the photocatalyst for RhB can be calculated by the following equation:

where Q_t (mg g⁻¹) represents the instantaneous (at time t) adsorption of RhB on per gram of the photocatalyst. C₀ and C_t represent the initial and t moment concentrations of RhB, respectively. M represents the mass of the photocatalyst, and V represents the volume of the solution.”

 Page 9 (Results and discussion section): “To evaluate the adsorption performance of the photocatalysts, we investigated the effect of TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ on the adsorption of RhB, respectively. Figure 10a shows that during the adsorption process within 50 min, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples can adsorb more RhB than TiO₂ due to the more adsorption sites on the 3DOM TiO₂ and 3DOM Pt/TiO₂ samples. The above results suggest that the 3DOM Pt/TiO₂ sample is favorable for mass transfer and capture of dye molecules, thus exhibiting higher photocatalytic activity.”

Fig. R1 Adsorption equilibrium plots of RhB solution (20 mg/L) with addition of TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂, respectively. (Now is new Fig. 10a in the revised manuscript.)

6. Cyclic stability study should be include explaining the parcticalability of the photocatalyst.

Response: We thank the reviewer’s great suggestion. Following your advice, we have measured the cyclic stability of the photocatalyst. The corresponding experimental details and discussion have been appended in the revised manuscript as follows:

Page 4 (Experimental section): “Cycling stability experiments were carried out under the same reaction conditions to further investigate the reusability and stability of the TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples. After every 100 min of photodegradation reaction, the centrifugally separated photocatalyst was washed and placed in a 100 ^oC oven to dry for 3 h and then placed in the same volume of fresh RhB solution (20 mg L^-1) for the next cycle of photocatalytic experiment.”

Pages 9-10 (Results and discussion section): “The cycling stability of the photocatalysts during photodegradation process was also evaluated. As shown in Figure10b, 3DOM Pt/TiO₂ exhibits high photocatalytic activity for the degradation of RhB. After three cycle tests, the photodegradation efficiency could still be maintained in the range of 80~88% within 100 min of visible light irradiation, indicating that the prepared 3DOM Pt/TiO₂ photocatalyst exhibits high cycle stability and may have good application prospects in water pollution treatment.”

Fig. R2 Recycling tests of RhB degradation with TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂, respectively within 100 min under visible-light irradiation. (Now is new Fig. 10b in the revised manuscript.)

 7. Why RhB was used as a pollutant.

Response: Thanks for your good question. Rhodamine B is often used as a fluorescent reagent due to its excellent coloring properties and has been widely used in the printing industry, colored glass, mining, and steel, and is a common alkaline dye. However, its strong toxicity, carcinogenicity and difficulty in degradation that accompany RhB have had a serious impact on the environment. Therefore, the development of an efficient green photocatalyst for the degradation of RhB has become very important.

8. There are many errors in the manuscript, like, "TiO₂" and grammatical mistakes like "The result of photocatalytic degradation of rhodamine B (RhB) verified that 3DOM Pt/TiO₂ degraded 88% of RhB under visible light irradiation (λ≥ 420 nm) for 100 min, while the degradation ratio was only 37% when using commercial TiO₂ as the photocatalyst".

Response: Thanks very much for your professional comments. Following your advice, we have carefully the whole manuscript again and tried out best to correct all possible typos and grammar issues. The corresponding modifications, including the listed one, have been highlighted in the revised version.

 9. Radical scavenger tests must be include explaining the generation of radicals during the dye degradation process.

Response: Thanks very much for your good suggestion. However, as our response to your 2^nd question, the current situation does not allow us to run more extra experiments though we agree that such experiments can indeed further strengthen the discussion section. However, on the other hand, TiO₂ has been intensively studied as a photocatalyst. Thus, its catalytic mechanism, including the generation of radicals during dye degradation process, can be sourced from recent literature. The main contribution of our current work lies in the rational design and synthesis of a 3DOM Pt/TiO₂ composite, which can combine both the morphology and heterostructure. However, your suggestions are very useful, and we’ll surely take your advice in our future work where appliable for in-depth structure and mechanism investigation.

 10. Are the synthesized photocatalysts active in the UV region?

Response: Thanks for your question. We think the photocatalysts are also active in the UV region because TiO₂ is a wide bandgap (~3.2 eV for anatase) semiconductor material and has been intensively investigated as a photocatalyst under illumination by UV light in early literature. However, the light of UV region in sunlight only occupies around 4%; thus, developing novel photocatalysts that can utilize the visible light is more important nowadays.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors report a very interesting work dealing with the fabrication of Pt-modified interfacial engineering for enhanced photocatalytic performance of 3D ordered microporous TiO2.

The paper is well written, and the results are consistent and widely discussed.

I suggest accepting the manuscript for publication on Crystals after major revisions.

• The authors should justify the use of a so expensive noble metal. In fact, the activity of TiO2-based materials in the visible part of the electromagnetic spectrum can be enhanced using cheaper metals. Moreover, in terms of CO2 production the thermal degradation of polystyrene spheres play a crucial role that is problematic from an environmental sustainability point of view.
• On page 2 line 46 the authors include Cu among noble metals. This is a mistake that must be corrected.
• One page 2 lines 57 and 58 the authors report “Moreover, decreasing the mean size or increasing surface area of Au nanoparticles…”. These are not two different parameters but they are consequence of each other. Please, rephrase this sentence.
• In the manuscript it is not clear if TiO2 used for comparison is a commercial product or if it is prepared by the authors. In the latter case, the synthetic process is not reported.
• In the paragraph “Characterization” SEM equipment is not reported.
• In the section “Results and Discussion” the authors report the formation of TiO2 micelles. How can micelles be formed in these conditions?
• On page 5 line 176 the authors report that Figure 2b shows the information on surface-related functional groups of these three photocatalysts. However, functional groups are characteristics of organic compounds, but they are not present in these inorganic materials. Moreover, the FT-IR spectra description is confusing. If the band at 480 cm-1 can be effectively described as a IR band, the other two bands at 1670and 3480 cm-1 are not IR band. In fact, in a transmittance spectrum the bands are directed towards the bottom of the graph, while in an absorbance spectrum, on the contrary, they go upwards. Here, the band at 480 cm-1 is directed towards the bottom correctly, whereas the other two bands are pointing upwards. Please, comment the IR spectra properly.
• On page 5 lines 182 and 183 the authors state “the adsorption of these -OH groups and H2O at 3DOM Pt/TiO2 can effectively decompose the contaminants”. Actually, OH groups and H2O are not able to decompose contaminants but participate in the production of active species.
• Figure 4 is of poor quality, in particular Fig 4 b. Moreover, what is the mean diameter of Pt NPs?
• Concerning the other results (very exiting), I would emphasize the extraordinary activity of 3DOM TiO2. In fact, the addition of Pt NPs, even if enhances a little bit the activity of the material, at the same time increases the cost terribly. In sight of this, the band energy of 3DOM TiO2 has to be added, as well as its UV-vis diffuse reflectance spectrum.
• Figure 10 can be removed.

Author Response

Responses to Review

Reviewer #3:

The authors report a very interesting work dealing with the fabrication of Pt-modified interfacial engineering for enhanced photocatalytic performance of 3D ordered microporous TiO₂. The paper is well written, and the results are consistent and widely discussed. I suggest accepting the manuscript for publication on Crystals after major revisions.

Response: Thank you very much for your positive comments and suggestions on our work. Following your valuable advice, we have further revised our manuscript to improve its overall quality. We hope that the revisions can be satisfactory and wish you a happy life.

1. The authors should justify the use of a so expensive noble metal. In fact, the activity of TiO₂-based materials in the visible part of the electromagnetic spectrum can be enhanced using cheaper metals. Moreover, in terms of CO₂ production the thermal degradation of polystyrene spheres plays a crucial role that is problematic from an environmental sustainability point of view.

Response: Thanks very much for your critical remarks. The reasons for using noble metal's as co-catalysts are based on the facts that they are stable and exhibit relatively better catalytic activity. Also, the use of PS spheres as template can ease the fabrication of 3DOM ordered structures. We’re sorry for the lack of deep thinking the possible large-scale fabrication process of our catalysts on an industry-scale. We hope that they can be OK from lab-scaled research. We also thank you for your very good suggestions and will take your advice seriously in our future work.

2. On page 2 line 46 the authors include Cu among noble metals. This is a mistake that must be corrected.

Response: Thanks for pointing out this mistake for us. We have corrected this in our revised manuscript and used a new Ref. as follows:

Page 2: “Some noble metals (e.g., Rh [14], Au [15], Ag [16], Pt [17] and Pd [18]) have been widely used as co-catalysts loaded on the surface of TiO2 because their Fermi energy levels are lower than that of TiO₂”

 Ref. 14. Balayeva, N. O.; Mamiyev, Z.; Dillert, R.; Zheng, N.; Bahnemann, D. W. Rh/TiO₂-Photocatalyzed Acceptorless Dehydrogenation of N-Heterocycles upon Visible-Light Illumination. ACS Catalysis 2020, 10, 5542-5553.

3. On page 2 lines 57 and 58 the authors report “Moreover, decreasing the mean size or increasing surface area of Au nanoparticles…”. These are not two different parameters but they are consequence of each other. Please, rephrase this sentence.

Response: We thank the reviewer’s question. Following your advice, we have modified the description of this sentence in the revised manuscript as follows:

Page 2: “Moreover, by reducing the average grain size of the Au nanoparticles, the specific surface area can be increased, leading to an increase in photocatalytic activity of the resultant Au/TiO₂.”

4. In the manuscript it is not clear if TiO₂ used for comparison is a commercial product or if it is prepared by the authors. In the latter case, the synthetic process is not reported.

Response: We thank the reviewer’s question. The samples we used were commercial TiO₂ and the types and specifications of commercial TiO₂ are described in the materials section of the revised manuscript as follows.

Page 3: “commercial TiO₂ powders (99.8%, with diameter of 40 nm) was provided by Aladdin Reagent Company (China)”

5. In the paragraph “Characterization” SEM equipment is not reported.

Response: We thank the reviewer’s question. We have provided the SEM equipment details in the characterization section and the corresponding descriptions have been revised in the manuscript as follows.

Page 3: “The morphologies and particle/pore sizes of the samples were observed by a scanning electron microscope (SEM, Hitachi S-4800) equipped with a field emission gun.”

6. In the section “Results and Discussion” the authors report the formation of TiO₂ micelles. How can micelles be formed in these conditions?

Response: We thank the reviewer’s question. We have explained the formation of TiO₂ micelles as follows:

 Page 4: “Then, tetrabutyl titanate was added and fully penetrated the voids of the as-prepared Pt-containing PS template and self-assembled to form Pt/PS@TBNT. Subsequently, the prepared Pt/PS@TNBT was exposed to air for 24 h, allowing the TNBT to be in full contact with water vapor in the air, and the hydrolysis reaction led to the formation TiO₂ micelles.”

 7. On page 5 line 176 the authors report that Figure 2b shows the information on surface-related functional groups of these three photocatalysts. However, functional groups are characteristics of organic compounds, but they are not present in these inorganic materials. Moreover, the FT-IR spectra description is confusing. If the band at 480 cm^-1 can be effectively described as a IR band, the other two bands at 1670 and 3480 cm^-1 are not IR band. In fact, in a transmittance spectrum the bands are directed towards the bottom of the graph, while in an absorbance spectrum, on the contrary, they go upwards. Here, the band at 480 cm^-1 is directed towards the bottom correctly, whereas the other two bands are pointing upwards. Please, comment the IR spectra properly.

Response: We thank the reviewer’s comment. At the suggestion of the reviewer, we have recalibrated the FT-IR spectra (Fig. 2b) and have provided a reasonable interpretation of the corresponding peaks. The corresponding description has been revised in the manuscript as follows:

 Page 5: “The FT-IR spectra of TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples are shown in Figure 2b. Apparently, TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples demonstrate similar FT-IR characteristic peaks. The Ti–O stretching and Ti–O–Ti bridging stretching modes locate in the range of 400~750 cm⁻¹.^[29] The peak at 3335 cm^-1 is attributed to hydroxyl and water molecules adsorbed on the surface of the sample.^[30] In addition, the peak at 1592 cm^-1 corresponds to the O–H stretching and bending vibrations.^[30-32] These adsorbed OH groups and H₂O play an important role in the photocatalytic activity of 3DOM Pt/TiO₂. Compared to TiO₂, 3DOM Pt/TiO₂ sample does not show characteristic peaks of loaded Pt possibly due to the low loading amount of Pt species.”

 8. On page 5 lines 182 and 183 the authors state “the adsorption of these -OH groups and H₂O at 3DOM Pt/TiO₂ can effectively decompose the contaminants”. Actually, OH groups and H₂O are not able to decompose contaminants but participate in the production of active species.

Response: We thank the reviewer’s good question. Following your comment, we have revised the discussion on this part in the revised manuscript accordingly as follows:

Page 5: “These adsorbed OH groups and H₂O play an important role in the photocatalytic activity of 3DOM Pt/TiO₂.”

9. Figure 4 is of poor quality, in particular Fig 4b. Moreover, what is the mean diameter of Pt NPs?

Response: Thanks for your question. We have replaced Fig. 4 with a clearer image and marked the size of the average pore diameter of 3D Pt/TiO₂ in Fig. 4a (~130 nm).

Fig. R1 TEM image of 3DOM Pt/TiO₂ (a); HRTEM image of 3DOM Pt/TiO₂ (b). (Now is new Fig. 4 in the revised manuscript.)

10. Concerning the other results (very exiting), I would emphasize the extraordinary activity of 3DOM TiO₂. In fact, the addition of Pt NPs, even if enhances a little bit the activity of the material, at the same time increases the cost terribly. In sight of this, the band energy of 3DOM TiO₂ has to be added, as well as its UV-vis diffuse reflectance spectrum.

Response: We thank the reviewer’s question. Following your advice, we have added the UV-Vis diffuse reflectance spectra and band energies of 3D TiO₂, as shown in Fig. 7(a). Meanwhile, we have marked the band gap widths (E_g) of the samples to facilitate reading and understanding.

Fig. R2 UV-vis diffuse reflectance spectra and plots of (αhʋ)^1/2 versus energy (hʋ) for TiO₂, 3DOM Pt/TiO₂ and 3DOM Pt/TiO_2. (Now is new Fig. 7a in the revised manuscript.)

 11. Figure 10 can be removed.

Response: We thank the reviewer’s great suggestion. We have removed Figure 10 from the manuscript and revised the corresponding discussion part in the revised manuscript as follows:

Page 9: “The calculated k_app values for TiO₂, 3DOM TiO₂ and 3DOM Pt/TiO₂ samples are 0.00414 min⁻¹, 0.01765 min⁻¹ and 0.02237 min⁻¹, respectively. The results suggest that the apparent rate constant of 3DOM Pt/TiO₂ is five times higher than that of TiO₂, indicating that 3DOM Pt/TiO₂ has a high photocatalytic activity.”

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

In my opinion the authors have enhanced the quality of their work and the manuscript can be accepted in the revised form.