Pt Deposites on TiO₂ for Photocatalytic H₂ Evolution: Pt Is Not Only the Cocatalyst, but Also the Defect Repair Agent

Round 1

Reviewer 1 Report

In this paper, the authors reported the photocatalytic H₂ evolution of TiO₂ with cocatalyst Pt employing three Pt sources with different charges (positive, negative, neutral). They found that the loaded Pt with slightly negative charged H₂PtCl₆ not only improved the H₂ evolution, but also acted as the defect repair agent to improve the stability of TiO₂.

The results reported in this paper supported by suitable experimental measurement such as XPS, Raman spectra, and photocurrent.

However, there are some comments as follows.

Comments

1. Line 77

2.2. Preparation of samples → 2.2. Preparation of samples

2. Line 118

The preparation of TiO₂-Pt⁴⁺ and TiO₂-PtCl₆^2- should be described at 2.2., if the description of the preparation can separate from that of photocatalytic H₂ evolution reaction.

3. Line 112

The detail process of the catalytic performance measurement should be descrived.

4. Line 213

2 nm → 20 nm         ?

5. Line 214-215

The letter size should be standardized.

6. Line 264

How many PtCl₆^2- species exist in the TiO₂-PtCl₆^2- catalyst system at photocatalytic H₂ evolution reaction?

Author Response

Reviewer # 1

Comments:

In this paper, the authors reported the photocatalytic H₂ evolution of TiO₂ with cocatalyst Pt employing three Pt sources with different charges (positive, negative, neutral). They found that the loaded Pt with slightly negative charged H₂PtCl₆ not only improved the H₂ evolution, but also acted as the defect repair agent to improve the stability of TiO₂.

The results reported in this paper supported by suitable experimental measurement such as XPS, Raman spectra, and photocurrent.

However, there are some comments as follows.

Response: Thank you for your suggestion. We have addressed all the comments raised by the reviewer and made all the requested changes, which helped improve the manuscript significantly.

1. Line 77

2.2. Preparation of samples → 2.2. Preparation of samples

Response: Thanks. We have made the suggested change.

Line 118

The preparation of TiO₂-Pt⁴⁺ and TiO₂-PtCl₆^2- should be described at 2.2., if the description of the preparation can separate from that of photocatalytic H₂ evolution reaction.

Response: The preparation of TiO₂-Pt⁴⁺ and TiO₂-PtCl₆^2- have been added in the description of the catalyst synthesis. The preparation process were as followed: “TiO₂-Pt⁴⁺ and TiO₂-PtCl₆^2-: 0.1 g TiO₂ photocatalyst was dispersed in 90 mL water, then stirred with 10 mL of triethanolamine adding. The 1.07 mL (2.5 g/L) positive charged Pt source PtCl₄ or 0.41 ml (10 g/L) negative charged Pt source H₂PtCl₆ were added into the above solution, which irradiated under 300 W xenon lamp for 2.5 h. Finally, TiO₂-Pt⁴⁺ and TiO₂-PtCl₆^2- samples were obtained, respectively.” The corresponding description have been added in the revised manuscript. (Page 2, Line 83-87)

Line 112

The detail process of the catalytic performance measurement should be descrived.

Response: Thanks. We have made the following change. 

TiO₂ and TiO₂-Pt⁰_: Photocatalytic H₂ evolution reaction was carried out under a 300 W Xe lamp (Perfect Light, Microsolar300, λ > 300 nm). Typically, 100 mg of sample was added to 100 mL of aqueous solution containing 10 mL triethanolamine as the sacrificial electron donor and kept it stirring vigorously. The hydrogen amount was periodically detected by an online gas chromatograph (GC, 4000) with a thermal conductivity detector (TCD) using Ar as a carrier gas. After reaction, the products were collected by centrifugation method and washed with ethyl alcohol for 3 times. The samples after the reaction were recorded as sample-A.

Line 213

2 nm → 20 nm         ?

Response: In TEM images (Figure 4), the dark spots were Pt nanoparticles, which were ca. 2 nm. While for the TiO₂ sample, its particle size is ca. 20 nm. The corresponding description have been added in the revised manuscript. (Page 6, Line 220, 221)

Line 214-215

The letter size should be standardized.

Response: Thank you for your suggestion. The corresponding letter size have been standardized in the revised manuscript. (Page 6, Line 222, 223). 

Line 264

How many PtCl₆^2- species exist in the TiO₂-PtCl₆^2- catalyst system at photocatalytic H₂ evolution reaction?

Response: In the TiO₂-PtCl₆^2- sample, the Pt metal was obtained via the reduction of the negative charged Pt source H₂PtCl₆. The result of ICP showed that the weight ratio of Pt/Ti is 0.66% in the TiO_2-PtCl₆^2- (Table S1). On the basis of that, the PtCl₆^2- species exist in the TiO₂-PtCl₆^2- catalyst system are 0.66 wt%.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. Please add more results from BET measurements - adsorption isotherms and pore size distribution of the samples.

2. Improve English text. For example, the title is unclear and requires correction.

“Pt deposites on TiO₂ for photocatalytic H₂ evolution: Pt not only the cocatalyst, but also the defect repair agent”

should be replaced with:

“Pt deposites on TiO₂ for photocatalytic H₂ evolution: Pt is not only the cocatalyst, but also the defect repair agent”

3. ‘Conclusion’ should be changed to ‘Conclusions’

4. Conclusions, row 303-304

“It was found Pt could only the cocatalyst, but also act as the agent to repair defects.”

Should be corrected as follows:

“It was found that Pt could be not only the cocatalyst, but also it acts as an agent which repair defects.”

5. Conclusions, row 304-306

“That is, the defects with positive charge gradually form on TiO₂ during the photocatalytic H₂ evolution, which are the recombination centers of electrons and holes, and then harmful to the stability.”

Should be replaced with:

“In summary, the defects with positive charge are gradually formed on TiO₂ during the photocatalytic H₂ evolution; these defects are centers for recombination of electrons and holes – process which leads to lower stability.”

6. Conclusions, row 306-307

“Owing to the charge interaction”

Better is:

“Due to the charge interaction”

7. References 7, 10, 19, 21, 25, 33, 35 are not full

Author Response

1. Please add more results from BET measurements - adsorption isotherms and pore size distribution of the samples.

Response: The BET measurements - adsorption isotherms and pore size distribution of the samples have been determined in Figure R1. Compared with the Pt/TiO₂ samples via three different Pt sources, it could be found that the results of pore size distribution and N₂-sorption isotherm are similar, which suggest that the difference in photostability is not mainly resulted from the pore structure and specific surface area. The corresponding explanation have been added in the revised manuscript. (Line 233-238, Fig. S3, 4).

Figure R1 (a) BJH pore size distribution and (b) N₂-sorption isotherm linear plots of the used Pt/TiO₂ samples via three different Pt sources.

2. Improve English text. For example, the title is unclear and requires correction.

“Pt deposites on TiO₂ for photocatalytic H₂ evolution: Pt not only the cocatalyst, but also the defect repair agent”should be replaced with:“Pt deposites on TiO₂ for photocatalytic H₂ evolution: Pt is not only the cocatalyst, but also the defect repair agent”

Response: Thank you for your suggestion. The title has been corrected in the revised manuscript and supporting information.

3. ‘Conclusion’ should be changed to ‘Conclusions’

Response: Thanks. We have made the suggested change.

4. Conclusions, row 303-304

“It was found Pt could only the cocatalyst, but also act as the agent to repair defects.”Should be corrected as follows:“It was found that Pt could be not only the cocatalyst, but also it acts as an agent which repair defects.”

Response: The corresponding conclusions have been corrected in the revised manuscript (Page 10, Line 315, 316).

5. Conclusions, row 304-306

“That is, the defects with positive charge gradually form on TiO₂ during the photocatalytic H₂ evolution, which are the recombination centers of electrons and holes, and then harmful to the stability.”Should be replaced with:“In summary, the defects with positive charge are gradually formed on TiO₂ during the photocatalytic H₂ evolution; these defects are centers for recombination of electrons and holes – process which leads to lower stability.”

Response: The corresponding conclusions have been corrected in the revised manuscript (Page 10, Line 316-318).

6. Conclusions, row 306-307

“Owing to the charge interaction”Better is:“Due to the charge interaction”

Response: The corresponding conclusions have been corrected in the revised manuscript (Page10, Line 318, 319).

7. References 7, 10, 19, 21, 25, 33, 35 are not full

Response: The corresponding references have been corrected in the revised manuscript. That are,  

7. Lu, W.J. Yin, K.L. Peng, K. Wang, Q. Hu, A. Selloni, F.R. Chen, L.M. Liu, M.L. Sui, Self-hydrogenated shell promoting photocatalytic H₂evolution on anatase TiO₂, Nat. Commun., 9 (2018) 2752-2760.
8. Yan, F. Yang, C. Tao, X. Luo, L. Zhang, Highly efficient and stable Cu₂O-TiO₂intermediate photocatalytic water splitting, Ceram. Int., 46 (2020) 9455-9463.
9. Xing, H.B. Jiang, J.F. Chen, Y.H. Li, L. Wu, S. Yang, L.R. Zheng, H.F. Wang, P. Hu, H.J. Zhao, H.G. Yang, Active sites on hydrogen evolution photocatalyst, J. Mater. Chem. A, 1 (2013) 15258–15264.

21.M.S. Ünlü, Digital Detection of Nanoparticles: Viral Diagnostics and Multiplexed Protein and Nucleic Acid Assays, MRS Proceedings, 4 (2015) 1720-1725.

25. Du, Q. Chen, Y. Wang, J. Hu, X. Meng, Synchronous construction of oxygen vacancies and phase junction in TiO₂hierarchical structure for enhancement of visible light photocatalytic activity, J. Alloys Compd., 830 (2020) 154649-154658.
26. Li, L. Niu, X. He, Enhanced visible-light activity of Ti³⁺self-doped TiO₂ with co-exposed {001} and {101} facets, Micro & Nano Letters, 13 (2018) 514–517.
27. H. Kim, M.-H. Oh, B.L. Yang, Photocorrosion of polyaniline-ZnS-ZnO photoelectrode for water splitting, Thin Solid Films, 693 (2020) 137678-137684.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In revised manuscript, several attempts were made to improve original one.

I think that revised manuscript is improved very much.