Preparation and Characterization of Nanocrystalline TiO₂ on Microsericite for High-Efficiency Photo-Energy Conversion of Methanol to Hydrogen

Round 1

Reviewer 1 Report

Article contain interesting results which deserve for publication after serious revision. For the improve article please reply to my remarks:

1. First of all, should be  clearly shown what is new to this material from the point of view of crystallography: structure, method of production, etc.?

2. Similarly, please explain, whether the new use of the prepared crystaline  material  to  the photo conversion of methanol into  hydrogen.

3. You conclude that the  best hydrogen production was achieved by using the TiO2/sericite photocatalyst therefore please discuss:

- how is dependence of conversion efficiency of crystaline morphology (nanocrystalities size)

- please compare obtained result 7938 μmol/g after 6 h of UV-light irradiation with literature data - for example P25 or other structures.

- how is the influence   of the different radiations used  (UV-light irradiation) and the sunlight on the device efficiency? 

4. What is device  work stability - aging effects?

Author Response

Reviewer #1:

Article contain interesting results which deserve for publication after serious revision. For the improve article please reply to my remarks:

Response

We have carefully considered your comments, and have addressed detailed responses to your questions. Additionally, we have revised the manuscript accordingly. Thank you!

1. First of all, should be clearly shown what is new to this material from the point of view of crystallography: structure, method of production, etc.?

Response

The authors appreciate the reviewer’s comment. This study provides a facile method to prepare TiO₂/sericite composite materials with a higher conversion efficiency of methanol to hydrogen than TiO₂ or P25 (commercial TiO₂). Besides, many research focuses on the development of nanomaterials, but we want to highlight the disadvantages of nanosize materials, including particle aggregation, higher cost for production, an inhalation potential through the skin into the bloodstream. Therefore, we propose that nanomaterials should be loaded on a micron-size material employed as a substrate. Microsize materials would be safer than nanosize materials. Besides, we successfully demonstrated that the TiO₂/sericite (microsize) had higher photocatalytic efficiency than TiO₂ (nanosize).

We have mentioned this point of view in the manuscript (section of the introduction, line 70-79).

2. Similarly, please explain, whether the new use of the prepared crystalline material to the photo conversion of methanol into hydrogen.

Response

Many thanks for the reviewer’s suggestion. We observe that the additional amount of acetic acid would affect the crystallite size of the prepared crystalline materials, leading to the different distribution types of TiO₂ loaded on sericite. Such kinds of difference would further influence the performance of hydrogen production. As Fig. 2 shown, the crystallite size of pure TiO₂ would decrease as the amount of acetic acid addition increases. For TiO₂/sericite photocatalysts, the crystallite sizes are similar regardless of the amount of the acetic acid addition or not. However, the addition of acetic acid would improve the distribution of TiO₂ loaded on sericite, resulting in a smooth surface shown in Fig. 5_10A-TS.

3. You conclude that the best hydrogen production was achieved by using the TiO2/sericite photocatalyst therefore please discuss:

- how is dependence of conversion efficiency of crystalline morphology (nanocrystallites size)

Response

As shown in the Fig. 2 of the manuscript, adding acetic acid (0-10 mL) would not affect to the crystallite size (~11-12 nm) of TiO₂/sericite while a little change has been observed for TiO₂ (14-18 nm).

To directly discuss the dependence of conversion efficiency of nanocrystallites size, we have compared the photocatalytic activity of T and 10A-T photocatalysts (TiO₂ without adding acetic acid (the crystallite size of 18 nm) and TiO₂ with adding 10 mL acetic acid (the crystallite size of 14 nm)). The content is provided in the manuscript as follows: “For the case of TiO₂ photocatalyst, T and 10A-T, showed the similar performance of hydrogen production although the specific surface area of 10A-T was much higher than that of T. It might result from the fact that the crystalline size of 10A-T was smaller than that of T, leading to higher possibility of the boundary recombination of electrons and holes within the TiO₂ blocks [35,36].”

- please compare obtained result 7938 μmol/g after 6 h of UV-light irradiation with literature data - for example P25 or other structures.

Response

Many thanks for your kind suggestion. We have revised the manuscript as follows: “Although the conditions for conducting experiments (including power intensity and wavelength of UV-light, ethanol concentration, and the design of photocatalysts) are different, it is worth comparing the hydrogen production in terms of the hydrogen rate in the literature. Table R-1 (Table 3 in the manuscript) summarizes the recent photo-activity performance in the presence of CH3OH. So far, although many efforts have been made for promoting the photo-energy conversion of methanol to hydrogen, this approach still faces several challenging issues. Therefore, efforts shall pay attention to some topics as follows: (1) to develop better efficient photocatalysts (a wider optical absorption band, a lower recombination rate of e−/h+ pairs); (2) to elucidate the relationship between the structural architecture and the photocatalytic performances [1].”

Table R-1. The photo-activity performance over various photocatalysts

- how is the influence of the different radiations used (UV-light irradiation) and the sunlight on the device efficiency?

Response

We appreciate the reviewer’s comment. In this study, the photoreaction was only conducted by using UV-light irradiation. The reason is that the UV-Vis absorption spectra of the materials revealed that they were UV-responsive materials. Therefore, we did not conduct the reaction under sunlight-irradiation. We hope you agree with our direction.

4. What is device work stability - aging effects?

Response

We did not verify the aging effect yet. In this study, we would like to focus on the elucidation of the mechanism and the benefits of sericite as the support role. Based on your suggestion, we would pay attention to the stability-aging effects in the future study of this project.

Reference

1.         Li, D.; Yu, J.C.-C.; Nguyen, V.-H.; Wu, J.C.S.; Wang, X. A dual-function photocatalytic system for simultaneous separating hydrogen from water splitting and photocatalytic degradation of phenol in a twin-reactor. Appl. Catal. B 2018, 239, 268-279, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.apcatb.2018.08.010.

2.         Fontelles-Carceller, O.; Muñoz-Batista, M.J.; Conesa, J.C.; Kubacka, A.; Fernández-García, M. H2 photo-production from methanol, ethanol and 2-propanol: Pt-(Nb)TiO2 performance under UV and visible light. Mol. Catal. 2018, 446, 88-97, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.mcat.2017.12.023.

3.         Yang, X.; Salzmann, C.; Shi, H.; Wang, H.; Green, M.L.H.; Xiao, T. The Role of Photoinduced Defects in TiO2 and Its Effects on Hydrogen Evolution from Aqueous Methanol solution. J. Phys. Chem. A 2008, 112, 10784-10789, doi:https://0-doi-org.brum.beds.ac.uk/10.1021/jp804305u.

4.         Chiarello, G.L.; Aguirre, M.H.; Selli, E. Hydrogen production by photocatalytic steam reforming of methanol on noble metal-modified TiO2. J. Catal. 2010, 273, 182-190, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.jcat.2010.05.012.

5.         Majrik, K.; Turcsányi, Á.; Pászti, Z.; Szabó, T.; Domján, A.; Mihály, J.; Tompos, A.; Dékány, I.; Tálas, E. Graphite Oxide-TiO2 Nanocomposite Type Photocatalyst for Methanol Photocatalytic Reforming Reaction. Top. Catal. 2018, 61, 1323-1334, doi:https://0-doi-org.brum.beds.ac.uk/10.1007/s11244-018-0989-z.

6.         Mills, A.; Bingham, M.; O’Rourke, C.; Bowker, M. Modelled kinetics of the rate of hydrogen evolution as a function of metal catalyst loading in the photocatalysed reforming of methanol by Pt (or Pd)/TiO2. J. Photochem. Photobiol. A 2019, 373, 122-130, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.jphotochem.2018.12.039.

7.         Jones, W.; Martin, D.J.; Caravaca, A.; Beale, A.M.; Bowker, M.; Maschmeyer, T.; Hartley, G.; Masters, A. A comparison of photocatalytic reforming reactions of methanol and triethanolamine with Pd supported on titania and graphitic carbon nitride. Appl. Catal. B 2019, 240, 373-379, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.apcatb.2017.01.042.

8.         Han, B.; Hu, Y.H. Highly Efficient Temperature-Induced Visible Light Photocatalytic Hydrogen Production from Water. J. Phys. Chem. C 2015, 119, 18927-18934, doi:https://0-doi-org.brum.beds.ac.uk/10.1021/acs.jpcc.5b04894.

9.         Gu, Q.; Long, J.; Zhuang, H.; Zhang, C.; Zhou, Y.; Wang, X. Ternary Pt/SnOx/TiO2 photocatalysts for hydrogen production: consequence of Pt sites for synergy of dual co-catalysts. Phys. Chem. Chem. Phys. 2014, 16, 12521-12534, doi:https://0-doi-org.brum.beds.ac.uk/10.1039/C4CP01496K.

10.       Tálas, E.; Pászti, Z.; Korecz, L.; Domján, A.; Németh, P.; Szíjjártó, G.P.; Mihály, J.; Tompos, A. PtOx-SnOx-TiO2 catalyst system for methanol photocatalytic reforming: Influence of cocatalysts on the hydrogen production. Catal. Today 2018, 306, 71-80, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.cattod.2017.02.009.

11.       Zhang, Y.-H.; Li, Y.-L.; Jiu, B.-B.; Gong, F.-L.; Chen, J.-L.; Fang, S.-M.; Zhang, H.-L. Highly enhanced photocatalytic H2 evolution of Cu2O microcube by coupling with TiO2 nanoparticles. Nanotechnol. 2019, 30, 145401, doi:https://0-doi-org.brum.beds.ac.uk/10.1088/1361-6528/aafccb.

12.       Xu, F.; Zhang, L.; Cheng, B.; Yu, J. Direct Z-Scheme TiO2/NiS Core–Shell Hybrid Nanofibers with Enhanced Photocatalytic H2-Production Activity. ACS Sustain. Chem. Eng. 2018, 6, 12291-12298, doi:https://0-doi-org.brum.beds.ac.uk/10.1021/acssuschemeng.8b02710.

13.       Xin, Y.; Lu, Y.; Han, C.; Ge, L.; Qiu, P.; Li, Y.; Fang, S. Novel NiS cocatalyst decorating ultrathin 2D TiO2 nanosheets with enhanced photocatalytic hydrogen evolution activity. Mater. Res. Bull. 2017, 87, 123-129, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.materresbull.2016.11.027.

Author Response File: Author Response.docx

Reviewer 2 Report

This report introduces preparation of TiO2 photocatalysts with(or without) sericite supports in the presence of acetic acid as a size controlling agent. The data show that the 'average' size is controlled by the amount of acetic acid and the resulting catalysts showed enhanced photocatalytic hydrogen evolution rates for all the samples compared to that of p-25. However, the manuscript has insufficient data and explanation, and poor arrangement to support what they argued. It also needs extensive english editing before being published.

-Fig. 3 has very little information in it. The FTIR data can only suggest that there is sericite support or not. In addition, only for TS with acetic acid shows C-H stretching. Is there any reason for the residual isopropanol only for the acetic acid-TS samples (when isopropanol was used for all the other sample preparation)?

-Fig.4 should be presented in a form of Kubelka Munk form to determine the bandgap properly.

-Fig 5 SEM images are all low-resolution. it need high resolution images (x100,000 or higher) It does not show any single 20 nm sized TiO2 particles at all.

-photocatalytic hydrogen evolution rate should be presented in a unit of umol/h under given experimental condition. The use of umol/g cannot be supported and represent the system properly.

- for the comparison, sericite support without TTIP precursors in the presence of acetic acid should be also included for comparision of XRD, SEM as well as photoactivity.

- in conclusion " Whereas, the addition of acetic acid could 254 assist the TiO2 deposit onto the sericite more uniformly." -The authors did not show any data that can support uniformity of the prepared TiO2 nanoparticles (on sericite support ).

- In Fig. 6, the activity of TS is even lower than that of T when TS are generally argued to be more effective.  Also, T and 10A-T show similar activity when adding acetic acid can potentially be more beneficial. This is shown for the comparison of TS and 10A-TS. So, the role of acetic acid is basically not fully explained. Can the authors explain why?

Author Response

Reviewer #2:

This report introduces preparation of TiO2 photocatalysts with (or without) sericite supports in the presence of acetic acid as a size controlling agent. The data show that the 'average' size is controlled by the amount of acetic acid and the resulting catalysts showed enhanced photocatalytic hydrogen evolution rates for all the samples compared to that of p-25. However, the manuscript has insufficient data and explanation, and poor arrangement to support what they argued. It also needs extensive english editing before being published.

Response

Our sincere thanks to you for consideration and professionalism. Per your suggestions, we have now addressed point-by-point responses. The manuscript has been edited and considered to be improved in grammar, punctuation, spelling, verb usage, sentence structure, conciseness, general readability, writing style, and native English usage to the best of the editor’s ability. We trust that our responses are satisfactory to you and that it is now suitable for publication in Crystals.

-Fig. 3 has very little information in it. The FTIR data can only suggest that there is sericite support or not. In addition, only for TS with acetic acid shows C-H stretching. Is there any reason for the residual isopropanol only for the acetic acid-TS samples (when isopropanol was used for all the other sample preparation)?

Response

We would appreciate your kind suggestion. Indeed, the FTIR data suggests that the existence of sericite. While TiO₂ loaded onto sericite, the signals of sericite became smaller, indicating the coverage of TiO₂.

Regarding the reason for the residual isopropanol only for the TS samples, we propose a conjecture that the isopropanol has a strong interaction between sericite possibly due to their OH groups, causing the residual isopropanol existed within the TiO₂/sericite photocatalysts. This discussion is provided in the line 187-192 of the manuscript.

-Fig.4 should be presented in a form of Kubelka Munk form to determine the bandgap properly.

Response

Many thanks for your suggestion. The figure is updated as below (Fig. S-1). Based on the result of the Tauc plot, the band gaps of photocatalysts were identified. The band gaps of the T, 10A-T, TS, 10A-TS photocatalysts were 2.96, 2.97, 3.03, and 3.10 eV, respectively.

Fig. S-1. UV–Vis absorption spectra of the TiO₂ photocatalysts (T and 10A-T) and TiO2/sericite photocatalysts (TS and 10A-TS)

-Fig 5 SEM images are all low-resolution. it need high resolution images (x100,000 or higher) It does not show any single 20 nm sized TiO2 particles at all.

Response

In this study, we would like to highlight the formation of macro-size materials; hence, the resolution images should be enough to represent that the TiO₂ coating and the sericite substrate. For the crystallite size or grain size of TiO₂, it could be observed from the XRD data (Fig. 1 in the manuscript). Therefore, we did not use the high-resolution images (x100,000 or higher) for SEM. We hope you will consider accepting our designed experiment.

-photocatalytic hydrogen evolution rate should be presented in a unit of umol/h under given experimental condition. The use of umol/g cannot be supported and represent the system properly.

Response

We do agree. In the revised manuscript, we use the unit to μmol/g·h to present the hydrogen evolution rate.

- for the comparison, sericite support without TTIP precursors in the presence of acetic acid should be also included for comparision of XRD, SEM as well as photoactivity.

Response

The XRD of pure sericite has been shown in Fig. 1(b) of the manuscript. The SEM of pure sericite was shown below (Fig. S-2), indicating the surface of sericite was smooth. Since the sericite was not photo-responsive materials (Fig. S-3), we did not conduct the photoreaction.

Since the sericite almost could not absorb light, we do not conduct the photoreaction for the sericite support in the presence of acetic acid.

Fig. S-2. The SEM image of pure sericite

Fig. S-3. The UV-Vis spectra of pure sericite

- in conclusion " Whereas, the addition of acetic acid could assist the TiO2 deposit onto the sericite more uniformly." -The authors did not show any data that can support uniformity of the prepared TiO2 nanoparticles (on sericite support).

Response

The uniformity of the TiO₂ coating was speculated based on two indirect reasons. Firstly, the addition of acetic acid caused the smoothly TiO₂ coating without discontinuous films on the surface, as shown in SEM images. Secondly, the Ti/Si ratio of 10A-TS was much higher than that of TS, indicating that the addition of acetic acid could assist Ti to deposit onto the sericite. We speculate that TiO₂ of TS may partially aggregate, leading to a discontinuous TiO₂ film observed. Therefore, we proposed that 10A-TS has a better uniformity due to the smooth TiO₂ film shown in the SEM image and the higher Ti/Si signal obtained from EDS result.

- In Fig. 6, the activity of TS is even lower than that of T when TS are generally argued to be more effective. Also, T and 10A-T show similar activity when adding acetic acid can potentially be more beneficial. This is shown for the comparison of TS and 10A-TS. So, the role of acetic acid is basically not fully explained. Can the authors explain why?

Response

The activity of TS was lower than that of T photocatalyst, resulting from the fact that the actual amount of TiO₂ of TS was much lower than that of T. The average hydrogen production rate was calculated based on the total weight of photocatalyst. Lower amount TiO₂ leaded lower activity for the case of TS.

Besides, the discontinuous TiO₂ film reveals the partial aggregation of TiO₂, indicating the longer pathways for electron and hole pairs might be required for moving to the surface. On the contrary, TiO₂ of 10A-TS was uniformly coated on 10A-TS, resulting in the short route moving to the surface for photocatalysis.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript deals with the “Preparation and Characterization of Nanocrystalline TiO2 on Micro-sericite for the conversion of methanol in Hydrogen”. While the topic of the paper is interesting and deserve publication, many aspect of work still need further investigation and manuscript looks just a preliminary study, therefore I do not recommend the publication of the manuscript in the present form.

Hera are my detailed comments.

Generally speaking the Authors should better highlights the novelty of the work and compare the results obtained in hydrogen evolution to those reported in literature.

From the point of view of the synthetic approach:

- What is the advantage to use sericite? Is there any role of the support in enhancing the photocatalytic activity?

- Is there any homogeneously nucleated TiO2 (I mean not on sericite surface)?

- What is the amount of TiO2 on sericite?

- Is there any literature to support the proposed reaction mechanism and to account for the different trend in crystallite size for TiO2/sericite sample?

- DRS spectra: quantum size effect in TiO2 nanoparticles usually arise for diameters lower than 3 nm, the blu-shift of the absorption onset could be ascribed to other effect? Maybe scattering for instance? What about the spectra of the other samples?

- What about the BET of samples prepared with different amount of acetic acid?

- The magnification of SEM images is too low to resolve TiO2 nanoparticles. A TEM characterization with statistical determination of nanocrystals size as a function of reaction condition is necessary.

Photocatalytic experiments:

 - What is the light flux used

- Why the tests have been performed only on 10-T and 10-TS samples? What about samples prepared by adding 1 and 5 ml of acetic acids?

- The concencentration of TiO2 used is quite high (more than 1g/L). Based to my experience in this condition P25 lead to a milky suspension with strong shield effect that reduce the penetration of light. Indeed ISO standards recommend a TiO2 concentration of 0.1g/L for photocatalytic tests with suspended powder. This could not occur for catalysts prepared by calcination whose aggregates are usually larger (as can be also observed in SEM images). I strongly suggest to perform the experiments also at lower TiO2 concentration. 

- The Authors should replicate the experiments (at least five replicate) and report error bars in Fig 6

Comments for author File: Comments.pdf

Author Response

Reviewer #3:

The manuscript deals with the “Preparation and Characterization of Nanocrystalline TiO2 on Micro-sericite for the conversion of methanol in Hydrogen”. While the topic of the paper is interesting and deserve publication, many aspect of work still need further investigation and manuscript looks just a preliminary study, therefore I do not recommend the publication of the manuscript in the present form.

Hera are my detailed comments.

Generally speaking the Authors should better highlights the novelty of the work and compare the results obtained in hydrogen evolution to those reported in literature.

Response

We have re-written the introduction section to highlights the novelty of nanocrystalline TiO₂ on micro-sericite as following (line 70-79): “Although a nano-size photocatalyst has higher performance due to the above reasons, it causes some following disadvantages concerning nano-size one. The disadvantages include an issue of particle aggregation, higher cost for production, an inhalation potential through the skin into the bloodstream. With a micron-size material employed as a substrate [20,21], it is expected that nano-size photocatalysts can not only exhibit the high performance but also prevent the aggregation of nanoparticles and the danger of direct inhalation through the skin. On the other hand, Li et al. found that TiO2 grain size would be reduced while introducing the kaolinite, which could be ascribed to the carrier effect. In other words, natural minerals would be contributed to the size growth retardation, particle dispersion, and surface modification [20]. Therefore, the methods of preparing nano-TiO2 loaded on the micron-size materials are worthy of being developed.”

Thank you for your kind suggestion. We agree that although the conditions for conducting experiments are different, it is worth comparing the hydrogen production in terms of the hydrogen rate in the literature. Table R-1 (Table 3 in the manuscript) summarizes the recent photo-activity performance in the presence of CH₃OH that compare the hydrogen evolution results obtained in this study to those reported in the literature.

From the point of view of the synthetic approach:

- What is the advantage to use sericite? Is there any role of the support in enhancing the photocatalytic activity?

Response

Based on our study, sericite has provided support and dominated the hydrolysis reaction due to its OH group on the surface. The sericite predominated the crystallite size of TiO₂. Adding the acetic acid, the TiO₂ loaded on sericite could be deposited uniformly, which can be proved from the smooth surface and the higher Ti/Si signal. These results could be obtained from SEM and EDS, respectively.

- Is there any homogeneously nucleated TiO2 (I mean not on sericite surface)?

Response

We believe that there might also exist homogeneously nucleated TiO₂; however, we could not confirm by EDS and XRD results since these were similar to all the cases.

- What is the amount of TiO2 on sericite?

Response

In this study, we prepared the TiO₂: sericite with the molecular ratio of 2:1.

- Is there any literature to support the proposed reaction mechanism and to account for the different trend in crystallite size for TiO2/sericite sample?

Response

We appreciate the reviewer’s positive suggestion. We have proposed the reaction mechanism and to account for the different trend in crystallite size for TiO₂ and TiO₂/sericite samples as following (line 224-239): “We attempted to explain the mechanism clearly via Fig. S-4, and Fig. S-5 for the cases of TiO₂ formation without and with sericite, respectively.

Fig. S-4. The schematic concept of TiO₂ formation without and with acetic acid

For the case of TiO₂ formation without sericite and acetic acid addition, the grains or crystals would agglomerate together to form large particles, and the particles would further aggregate as shown in the SEM images. On the other hand, when the acetic acid was added into the system, the hydrolysis rate would be decreased due to the steric effect of molecular acetic acid [1], leading to the formation of smaller grains. The small grain would agglomerate easily to form the bulk and solid-like TiO₂, and the mechanism was shown in Fig. S-4. Li et al. also demonstrate that the acetic acid may decrease the surface free energy and form Ti-acetate coordination with Ti precursor, resulting in facilitating the crystallization and transformation [2].

Fig. S-5. The schematic concept of TiO₂/sericite formation without and with acetic acid

For the case of TiO₂ formation with sericite, the hydrolysis reaction occurred mainly on the surface of sericite, as shown in Fig. S-5. Therefore, the crystallite sizes did not change apparently since the sericite effect dominated. While the addition of acetic acid was involved in the preparing process, the molecular acetic acid would help the Ti(OH)x distributed on the sericite to generate a smooth and continuous TiO₂ on the surface. The mechanisms were proposed reasonably from the crystallite sizes obtained from the XRD, the morphologies observed by SEM, and the FTIR also provides the information of OH group.”

- DRS spectra: quantum size effect in TiO2 nanoparticles usually arise for diameters lower than 3 nm, the blu-shift of the absorption onset could be ascribed to other effect? Maybe scattering for instance?

Response

As the particle size increased, the peak blue-shifted. While the particle size was big enough (>20 nm), it would lose the quantum size effect [3]. Since our calculated crystallite sizes were smaller than 20 nm, the blue shift may be contributed to the quantum size effect.

We have now provided in the manuscript as follows: “The nano-size crystal would cause the band gap to become more extensive due to the quantum effect [3] or scattering effect [4].”

What about the spectra of the other samples?

- What about the BET of samples prepared with different amount of acetic acid?

Response

Since the crystallite sizes of samples prepared with different amount of acetic acid were similar, we choose the most significant amount of acetic acid to compare the effect of adding acetic acid.

Due to the budget limitation, we could only decide to analyze some essential samples and did not analyze all the samples.

- The magnification of SEM images is too low to resolve TiO2 nanoparticles. A TEM characterization with statistical determination of nanocrystals size as a function of reaction condition is necessary.

Response

As mentioned above, we would like to highlight the formation of macro-size materials; hence, the resolution images should be enough to represent that the TiO₂ coating and the sericite substrate.

For the crystallite size or grain size of TiO₂, it could be observed from the XRD data (Fig. 1 in the manuscript). Therefore, we did not use the high-resolution images (x100,000 or higher) for SEM or TEM characterizations. We hope the reviewer will consider accepting our designed experiment.

Photocatalytic experiments:

- What is the light flux used

Response

In this study, we used 200 W of the light source with the wavelength of 320-500 nm. We are sorry that we did not have light flux data due to the limit of the equipment.

- Why the tests have been performed only on 10-T and 10-TS samples? What about samples prepared by adding 1 and 5 ml of acetic acids?

Response

Since the crystallite sizes of samples prepared with different amount of acetic acid were similar, we decided to use the most massive adding amount of acetic acid to compare the effect of acetic acid.

- The concencentration of TiO2 used is quite high (more than 1g/L). Based to my experience in this condition P25 lead to a milky suspension with strong shield effect that reduce the penetration of light. Indeed ISO standards recommend a TiO2 concentration of 0.1g/L for photocatalytic tests with suspended powder. This could not occur for catalysts prepared by calcination whose aggregates are usually larger (as can be also observed in SEM images). I strongly suggest to perform the experiments also at lower TiO2 concentration.

Response

Many thanks for the kind suggestion. We have used the TiO₂ concentration of 1 g/L for photocatalytic tests with suspended powder. Based on the reviewer’s comment and experience, we would pay attention to this issue, and consider to perform the experiments at a lower TiO₂ concentration in the future.

- The Authors should replicate the experiments (at least five replicate) and report error bars in Fig 6.

Response

The reviewer is corrected to pointing out that this critical issue. Reproducibility tests were conducted and the data was updated in Fig. S-6 (Fig. 8 of the revised manuscript).

Fig. S-6. The average hydrogen production rate with 10 vol.% CH₃OH in 6 h photocatalysis reaction

Reference

1.         Fujimoto, M.; Ohno, T.; Suzuki, H.; Koyama, H.; Tanaka, J. Nanostructure of TiO2 Nano‐Coated SiO2 Particles. J. Am. Ceram. Soc. 2005, 88, 3264-3266, doi:https://0-doi-org.brum.beds.ac.uk/10.1111/j.1551-2916.2005.00583.x.

2.         Li, Y.; Wang, S.; Lei, D.; He, Y.-B.; Li, B.; Kang, F. Acetic acid-induced preparation of anatase TiO2 mesocrystals at low temperature for enhanced Li-ion storage. J. Mater. Chem. A 2017, 5, 12236-12242, doi:https://0-doi-org.brum.beds.ac.uk/10.1039/C7TA02361H.

3.         Ren, Y.; Zhao, L.; Zou, Y.; Song, L.; Dong, N.; Wang, J. Effects of Different TiO2 Particle Sizes on the Microstructure and Optical Limiting Properties of TiO2/Reduced Graphene Oxide Nanocomposites. Nanomaterial 2019, 9, 730, doi:https://0-doi-org.brum.beds.ac.uk/10.3390/nano9050730.

4.         Sahu, D.R.; Hong, L.; Wang, S.-C.; Huang, J.-L. Synthesis, analysis and characterization of ordered mesoporous TiO2/SBA-15 matrix: effect of calcination temperature. Microporous Mesoporous Mater. 2009, 117, 640-649, doi:https://0-doi-org.brum.beds.ac.uk/10.1016/j.micromeso.2008.08.013

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Article has been improved in satisfactory level, therefore I can recommend publication in present form. 

Author Response

Article has been improved in satisfactory level, therefore I can recommend publication in present form.

Response

We thank the reviewer for your valuable comments. These comments are very constructive and help us to improve the manuscript, specifically in terms of clarifying our methodology and contribution of this article.

Reviewer 2 Report

I don't have any further comment on this manuscript.

Author Response

I don't have any further comment on this manuscript.

Response

Our sincere thanks to you for consideration and professionalism. Your comments are all valuable and very helpful for revising and improving our article, as well as the critical guiding significance to our researches.

Reviewer 3 Report

I am sorry to say that my opinion about the manuscript “Preparation and Characterization of Nanocrystalline TiO2 on Micro-sericite for the conversion of methanol in Hydrogen” is still negative.
Indeed the manuscript underwent only minor modifications whereas the major criticisms arisen in the first round of revisions are still there:

- The characterization of the prepared samples is incomplete. No new information about sample 1x and 5x are reported.

- Higher magnification SEM image (at least) or TEM image are necessary to characterize nanoparticles being the title of the paper “Preparation and Characterization of NANOCRYSTALLINE TiO2….”. XRD is not enough to claim the nanoscopic regime of the particles since the crystallite size could differ from the particle diameter.

- Reporting the light flux is needed to give a frank account of the efficiency of the catalysts and it is necessary to compare the results reported in the manuscript with literature. It can be measured by actinometry without need of any special equipment

- The photocatalytic characterization of sample 1 and 5 has not been performed.

- The effect of the concentration of the catalyst has not been investigated in spite of my warning about the possible negative effect due to the shield effect in milky-like sospensions.

Thank into account the above reported considerations, I do not suggest the publication of the manuscript.

Author Response

I am sorry to say that my opinion about the manuscript “Preparation and Characterization of Nanocrystalline TiO2 on Micro-sericite for the conversion of methanol in Hydrogen” is still negative.

Indeed the manuscript underwent only minor modifications whereas the major criticisms arisen in the first round of revisions are still there:

Response

We appreciate your valuable comments. We have studied your suggestions carefully and have made correction, which we hope meet with approval. The leading corrections in the manuscript and the response to the reviewer’s comments are as flowing:

- The characterization of the prepared samples is incomplete. No new information about sample 1x and 5x are reported.

Response

The authors appreciate the reviewer’s comment. We added the SEM and EDS analysis for 1A-T, 5A-T, 1A-TS, and 5A-TS for comparison. The SEM images of 1A-T and 5A-T were similar to those of 10A-T (Figure 4, Page 6, Line 210). Similarly, the SEM images of 1A-TS and 5A-TS were also similar to those of 10A-TS. Regarding EDS analysis (Table 2, Page 7, Line 234), all the samples T, 1A-T, 5A-T, and 10A-T had similar chemical composition of Ti and O. However, when adding the acetic acid, the Ti (%) was raised from 5.71 % to 9.53 % ~ 13.20 %, indicating that the addition of acetic acid could improve Ti deposition on the sericite.

- Higher magnification SEM image (at least) or TEM image are necessary to characterize nanoparticles being the title of the paper “Preparation and Characterization of NANOCRYSTALLINE TiO2….”. XRD is not enough to claim the nanoscopic regime of the particles since the crystallite size could differ from the particle diameter.

Response

We appreciate the reviewer’s comment. We have conducted the HR-SEM for the 10A-TS sample (as shown in Figure R-1). However, due to the limit of instrument, we could not clearly observe the crystalline size. Therefore, we decide do not provide this data to the manuscript.

Fortunately, the crystallite size or grain size of TiO₂ could be observed from the XRD data (Fig. 1; Page 4, Line 149). We have used the Scherrer’s equation to calculate the TiO2 crystallite sizes of all photocatalysts further (as shown in Fig. 2; Page 5, Line 173). We hope the reviewer accepts our designed experiment.

Figure R-1. HRSEM of 10A-TS sample

- Reporting the light flux is needed to give a frank account of the efficiency of the catalysts and it is necessary to compare the results reported in the manuscript with literature. It can be measured by actinometry without need of any special equipment

Response

Many thanks for your kind suggestion. The light flux is 3.2 mW/cm² at a wavelength of 365 nm. This content is provided in the manuscript on Page 3, Line 133-134.

We have compared our results with the literature, the content as follows (Page 10, Line 312): “Although the conditions for conducting experiments (including power intensity and wavelength of UV-light, ethanol concentration, and the design of photocatalysts) are different, it is worth comparing the hydrogen production in terms of the hydrogen rate in the literature. Table R-1 (Table 3 in the manuscript) summarizes the recent photo-activity performance in the presence of CH3OH. So far, although many efforts have been made for promoting the photo-energy conversion of methanol to hydrogen, this approach still faces several challenging issues. Therefore, efforts shall pay attention to some topics as follows: (1) to develop better efficient photocatalysts (a wider optical absorption band, a lower recombination rate of e⁻/h⁺ pairs); (2) to elucidate the relationship between the structural architecture and the photocatalytic performances [1].”

Table R-1. The photo-activity performance over various photocatalysts

- The photocatalytic characterization of sample 1 and 5 has not been performed.

Response

We thank you for the reviewer’s suggestion. Based on the characterization results, the samples prepared with different amount of acetic acid show similar properties with TiO₂/sericite, including crystalline size (XRD), morphology (SEM), chemical composition (EDS), and surface functional group (FT/IR); therefore, we pick up the most considerable amount of acetic acid addition for comparing the effect of acetic acid addition.

- The effect of the concentration of the catalyst has not been investigated in spite of my warning about the possible negative effect due to the shield effect in milky-like sospensions.

Response

Many thanks for the kind suggestion. We understand your concern on the possible negative effect due to the shielding effect in milky-like suspensions. However, to the best of our knowledge, TiO₂ photocatalyst dosage (1 g/L), which has been used in our study, also been used in many previous studies, including photo-degradation of pharmaceuticals and personal care products (PPCPs) [14], photo-degradation of amoxicillin [15], photo-removal of complex wastewater [16], photo-production of benzaldehyde [17]. On the other hand, some studies also show that the optimal conditions of the photocatalyst dosage are 2 g/L [18], or even higher dosage 12.5 g/L [19]. This may have been attributed to the additional electrons and holes that were generated due to the increased photocatalyst dosage, resulting in increasing of the generation of reactive radicals.

Again, we are thankful the reviewer’s reminding, and we would pay attention to the suggested photocatalyst dosage from the ISO standards (0.1 g/L) for photocatalytic tests with suspended powder.

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Author Response File: Author Response.docx