Preparation and Photocatalytic Activities of TiO₂-Based Composite Catalysts

Round 1

Reviewer 1 Report

The paper can be accepted after major revision regarding the following aspects:

Abstract :

I.-lines 16, 17, 18 „therefore, it exhibits inefficient photocatalysis when it irradiated with ultraviolet light (wavelength ≤ 387.5 nm) due to the high probability of photogenerated-carrier coupling.” –please clarify

 -lines 20 , 21”The morphology, size, and structure of a heterojunction can be altered through element doping leading to improved photocatalytic efficiency”.-–please clarify

II. Are the following references relevant for the text? Please, explain and improve the references

Line 166-169

[92] Liang H, Zhou S, Chen Y, et al. Diatomite coated with Fe2O3 as an efficient heterogeneous catalyst for degradation of organic 1093 pollutant. J Taiwan Inst Chem Eng. 2015, 49 ,105-12.

[95] Liu MY, Zheng L, Lin GL, et al. Synthesis and photocatalytic activity of BiOCl/diatomite composite photocatalysts: Natural 1099 porous diatomite as photocatalyst support and dominant facets regulator. Adv Powder Technol. 2020, 31(1), 339-50

Line 204-206

[107] Seo HO, Park EJ, Kim IH, et al. Influence of humidity on the photo-catalytic degradation of acetaldehyde over TiO2 surface 1124 under UV light irradiation. Catal Today. 2017, 295, 102-9.

Line 231-236

[115] Silva IMP, Byzynski G, Ribeiro C, et al. Different dye degradation mechanisms for ZnO and ZnO doped with N (ZnO:N). J Mol 1140 Catal A: Chem. 2016, 417, 89-100. 1141

[116] Sin J-C, Lam S-M, Lee K-T, et al. Preparation of cerium-doped ZnO hierarchical micro/nanospheres with enhanced 1142 photocatalytic performance for phenol degradation under visible light. J Mol Catal A: Chem. 2015, 409, 1-10.

Line 255-256

[121] Ramezanalizadeh H, Zakeri F, Manteghi F. Immobilization of BaWO4 nanostructures on a MOF-199-NH2: An efficient separable 1152 photocatalyst for the degradation of organic dyes. Optik. 2018, 174, 776-786. 1153

[122] Rao Z, Shi G, Wang Z, et al. Photocatalytic degradation of gaseous VOCs over Tm3+-TiO2: Revealing the activity enhancement 1154 mechanism and different reaction paths. Chem Eng J. 2020, 395, 125078. 1155

[123] Rezaei M, Habibi-Yangjeh A. Microwave-assisted preparation of Ce-doped ZnO nanostructures as an efficient photocatalyst. 1156 Mater Lett. 2013, 110, 53-6.

Author Response

he paper can be accepted after major revision regarding the following aspects:

Abstract :

I.-lines 16, 17, 18 „therefore, it exhibits inefficient photocatalysis when it irradiated with ultraviolet light (wavelength ≤ 387.5 nm) due to the high probability of photogenerated-carrier coupling.” –please clarify

Response: It has been revised in the text according to the suggestions of the reviewer.

 -lines 20 , 21”The morphology, size, and structure of a heterojunction can be altered through element doping leading to improved photocatalytic efficiency”.-–please clarify

Response: By doping composite photocatalysts of type I, type II, type III, schottky junction and type Z heterojunction structure, the specific surface area is increased, the electron hole separation efficiency is improved, and the light response range is expanded to improve the photocatalytic performance

1. Are the following references relevant for the text? Please, explain and improve the references

Line 166-169

[92] Liang H, Zhou S, Chen Y, et al. Diatomite coated with Fe2O3 as an efficient heterogeneous catalyst for degradation of organic 1093 pollutant. J Taiwan Inst Chem Eng. 2015, 49 ,105-12.

[95] Liu MY, Zheng L, Lin GL, et al. Synthesis and photocatalytic activity of BiOCl/diatomite composite photocatalysts: Natural 1099 porous diatomite as photocatalyst support and dominant facets regulator. Adv Powder Technol. 2020, 31(1), 339-50

Line 204-206

[107] Seo HO, Park EJ, Kim IH, et al. Influence of humidity on the photo-catalytic degradation of acetaldehyde over TiO2 surface 1124 under UV light irradiation. Catal Today. 2017, 295, 102-9.

Line 231-236

[115] Silva IMP, Byzynski G, Ribeiro C, et al. Different dye degradation mechanisms for ZnO and ZnO doped with N (ZnO:N). J Mol 1140 Catal A: Chem. 2016, 417, 89-100. 1141

[116] Sin J-C, Lam S-M, Lee K-T, et al. Preparation of cerium-doped ZnO hierarchical micro/nanospheres with enhanced 1142 photocatalytic performance for phenol degradation under visible light. J Mol Catal A: Chem. 2015, 409, 1-10.

Line 255-256

[121] Ramezanalizadeh H, Zakeri F, Manteghi F. Immobilization of BaWO4 nanostructures on a MOF-199-NH2: An efficient separable 1152 photocatalyst for the degradation of organic dyes. Optik. 2018, 174, 776-786. 1153

[122] Rao Z, Shi G, Wang Z, et al. Photocatalytic degradation of gaseous VOCs over Tm3+-TiO2: Revealing the activity enhancement 1154 mechanism and different reaction paths. Chem Eng J. 2020, 395, 125078. 1155

[123] Rezaei M, Habibi-Yangjeh A. Microwave-assisted preparation of Ce-doped ZnO nanostructures as an efficient photocatalyst. 1156 Mater Lett. 2013, 110, 53-6.

Response: Thank the reviewers for their valuable comments, and sort out the references systematically. The references of [92], [95], [107], [115], [116], and [121-123] were removed. At the same time, the references of [59], [106], [107], [119] and [120] are added, the references as follow.

[59] Linsebigler A L., Lu G, and Yates, Jr Jn T. Photocatalysis on Ti02 Surfaces: Principles, Mechanisms, and Selected Results, Chem. Rev. 1995, 95, 735-758

[106] Wang Y, Li X, and Liu Y, Preparation of TiO₂ Sol by Sol-gel Method, Chinese Syn Chem, 2008, 16, 705-708

[107] Liu S., Synthesis of TiO₂-gel by Sol-gel Method, Shandong Chem Industry, 2015, 20(44), 3-5

[119] Yamashita H., Harada M., Tanii A., Preparation of efficient titanium oxide photocatalysts by an ionized cluster beam (ICB) method and their photocatalytic reactivities for the purification of water, Catal. Today, 2000, 63, 3-69

[120] Pizem H., Sukenik C. N., Sampathkumaran U., et al., Effects of substrate surface unctionality on solution-deposited titania films, Chem. Mater.,2002, 14, 76-2485

Author Response File: Author Response.pdf

Reviewer 2 Report

The review article is seems to be good and it can be accepted after minor revision.

1. The comparison table is needed

2.  Several types of heterojunctions were made to improve the efficiency of TiO2. Therefore, the authors should discuss the heterojunction advantages in detail. 

3. Different mechanism scheme were proposed recent days, that also should be discussed in the revised article

Author Response

1. The comparison table is needed

Response: The comparison table is added in the text.

2. Several types of heterojunctions were made to improve the efficiency of TiO2. Therefore, the authors should discuss the heterojunction advantages in detail. 

Response: 1) The traditional heterojunction has three forms as shown in Figure 1, there are type-I, type-II and type-III.

Figure 1 Image of photogenerated carriers in traditional heterojunction photocatalysts: (a) type-I, (b) type-II, and (c) type-III heterojunctions

2) As shown in figure 2, there is also a p-n heterojunction combining a p-type semiconductor and an n-type semiconductor. On the one hand, the Fermi energy level is closer to the valence band in the p-type semiconductor, on the other hand, in the n-type semiconductor, it will move to the electric band. In type A semiconductor, it will move towards the electrical band. In p-n type semiconductor, it will move towards the electrical band.

 

Figure 2 Schematic diagram of the photogenerated charge carriers separation under the influnce of internal electric field of a p–n heterojunction photocatalyst under illumination

3)  Z-Scheme heterojunction: For these types of heterostructures mentioned above, due to the oxidation and reduction processes that occur on semiconductors with low oxidation and reduction potentials, the ability of the photocatalyst is reduced due to the oxidation and reduction processes that occur on the body. Researchers also found another type of heterojunction is Z-Scheme heterojunction photocatalysis system. The traditional Z-Scheme photocatalysis system consists of two semiconductors (the system consists of two semiconductors (SC - II and SC - I) and an electron acceptor) and a solution oxidation composed of an electron acceptor/donor (dissolution oxidation composed of a donor (A/D) pair) pair, as shown in Figure 3.

Figure 3 Diagrammatic representation of three main generations of Z-scheme photocatalysis: (a) Traditional Z-scheme photocatalytic system with shuttle redox mediators, (b) All-solid-state Z-scheme photocatalytic system with solid electron mediator, and (c) Direct Z-scheme photocatalytic system

 

3. Different mechanism scheme were proposed recent days, that also should be discussed in the revised article

Response: It has been revised in the text according to the comments of the reviewer

Author Response File: Author Response.pdf

Reviewer 3 Report

In the review paper entitled “Preparation and Photocatalytic Activities of TiO2-Based Composite Catalysts”, Yang and co-workers presented the state of the art of functionalization and application of titania-based photocatalysts. I am very impressed with the work done. In my opinion, the review can be published in Catalysts. However, some major issues should be added/explained/corrected:

1. Figure 2-1 should be redrawn to emphasize the electron transfer between VB and CB to understand the mechanism better.

2.      What are the numbers in brackets in Figure 2-2?

3. Whenever the Authors write about degradation rates of Methylene Blue, Rhodamine, or another organic compound – more details about these photodegradation studies need to be provided, e.g., light wavelength, time and dose of irradiation.

4.      The methods described in Section 3 should be concluded by a table/figure comparing the advantages and disadvantages of every one of them.

5.      Also, at the end of Section 4, the summarizing table or figure should be added.

6.      Please improve the Figure 5-2 quality for better visibility.

Author Response

1. Figure 2-1 should be redrawn to emphasize the electron transfer between VB and CB to understand the mechanism better.

Response: Figure 2-1 has been redrawn to emphasize the electron transfer between VB and CB as shown in the text.

2. What are the numbers in brackets in Figure 2-2?

Response: The numbers in brackets in Figure 2-2 was explained in the text. After processes 1 and 3 represent electron–hole pair separation, respectively. (processes 2 and 4 represent recombination of electron–hole pair on the surface or in the bulk, and the energy of the charge carriers is converted to vibrational energy of lattice atoms (phonons) or photons. Generally, the defect sites serve as recombination centers for processes 2 and 4, resulting in lowering the efficiency of the TiO₂ photocatalysis.

3. Whenever the Authors write about degradation rates of Methylene Blue, Rhodamine, or another organic compound – more details about these photodegradation studies need to be provided, e.g., light wavelength, time and dose of irradiation.

Response: The photodegradation conditions have been added in the text.

4. The methods described in Section 3 should be concluded by a table/figure comparing the advantages and disadvantages of every one of them.

Response: The advantages and disadvantages of the synthesis methods are compared in the text

5. Also, at the end of Section 4, the summarizing table or figure should be added.

Response: It has been summarized in the text

6. Please improve the Figure 5-2 quality for better visibility

Response:  The clarity of Figure 5 is improved according to the requirements of reviewers

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The work can be published in  present form

Reviewer 3 Report

I have no further comments. In my opinion, the paper can be accepted in its present form.