The Effect of Cu(II) Nanoparticle Decoration on the Electron Relaxations and Gaseous Photocatalytic Oxidations of Nanocrystalline TiO₂

Round 1

Reviewer 1 Report

The authors have studied the electron relaxations and gaseous effect of Cu(II) nanoparticle on TiO2 which can be consider as interesting focus of research. There are few comments in order for this paper to be accepted:

1) The CuO presence in modified sample should be detail analyzed via FESEM EDS/EDX or other detection methods for confirmation

2) XRD analysis should be included

3) The electron relaxation should be further confirmed with PL analysis

Thanks

Author Response

Please see the attachment 

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper disclosed the electron relaxations and photocatalytic activity of nano-TiO₂ with Cu(II) nanoparticle. The work should be interesting to the readership of Catalysts. The authors clearly deliver the aim, originality, importance, impact and scientific reliability of the work. Let me ask one question out of genuine interest.

One of the authors, Dr. Baoshun Liu, previously reports theoretical kinetic analysis of photocatalysis by TiO₂ nanotube arrays (Liu, B.; et al., The Journal of Physical Chemistry C 2012, 116, 7471-7479). Dr. Liu said “Based on this model, we can predict the optimized values of R, d, and L for nanotube arrays to have the best photocatalytic activity”. If we modify the optimized nanotubes with the Cu(II) nanoparticle, what kind of photocatalyst will we get?

Author Response

This paper disclosed the electron relaxations and photocatalytic activity of nano-TiO₂ with Cu(II) nanoparticle. The work should be interesting to the readership of Catalysts. The authors clearly deliver the aim, originality, importance, impact and scientific reliability of the work. Let me ask one question out of genuine interest.

Comment 1: One of the authors, Dr. Baoshun Liu, previously reports theoretical kinetic analysis of photocatalysis by TiO₂ nanotube arrays (Liu, B.; et al., The Journal of Physical Chemistry C 2012, 116, 7471-7479). Dr. Liu said “Based on this model, we can predict the optimized values of R, d, and L for nanotube arrays to have the best photocatalytic activity”. If we modify the optimized nanotubes with the Cu(II) nanoparticle, what kind of photocatalyst will we get?

Response: Thanks for this comment, we thought the modification of the optimized nanotubes with the Cu nanoparticles can also increase the electron relaxation rate. Similar to the current result, whether the photocatalytic activity can be increased should also rely on the photocatalytic types. It is possible that the loading of Cu(II) nanoparticles could decrease the acetone photocatalytic oxidation, although the electron transfer to O₂ can be increased. Maybe, the hydrogen generation can be increased.

Reviewer 3 Report

In this manuscript copper was used for modifying titanium oxide P25 as one of the effective ways to improve the photocatalytic activity of titanium oxide, which is very important and meaningful research. This study is worthy of publication, but authors should improve it as the following.

1) Please provide the real copper content of all samples, not theoretical values.

2) Crystallographic information for Cu(I), Cu(II) and/or Cu(0), including crystal size as well as XRD content. This information can help the reader to understand this study well.

3) It is well known that P25 titanium oxide is a typical mixed crystalline titanium oxide sample, include anatase, rutile and amorphous. Reports has been published to investigate the order of deposition of metal particles on different crystals as well as the different activities when metal deposited on different crystals. In the case of this study, is there also a preferential order of Cu deposition on different crystals? If the authors believe that there is no preferential order, please give the corresponding verification procedure.

4) Cu(I) is deposited on the surface of titanium oxide, which is very susceptible to be reduced or oxidized. For this study, if the situation for long-time irradiation or lifetime of sample by re-use was considered?

Author Response

Referee 3

In this manuscript copper was used for modifying titanium oxide P25 as one of the effective ways to improve the photocatalytic activity of titanium oxide, which is very important and meaningful research. This study is worthy of publication, but authors should improve it as the following.

 

Comment 1: Please provide the real copper content of all samples, not theoretical values.

Response:

The real copper contents of the Cu(II)/TiO₂ samples were checked with ICP-OES, please checked the revised manuscript, p4, line 168-169

 

Comment 2: Crystallographic information for Cu(I), Cu(II) and/or Cu(0), including crystal size as well as XRD content. This information can help the reader to understand this study well.

Response:

Due to the low loaded amount, the XRD does not reveal the existence of the Cu nanoparticles (Figure S1). The TEM analysis showed that the Cu nanoparticles have a narrow size distribution at ~ 3 nm, as shown in the inner of revised Figure 1. The crystalline structure of the Cu(II) nanoparticles should be amorphous, as revealed by the TEM analysis. This should be true as the sample were prepared at low temperatures. The Cu(I) species and Cu(0) species should be also amorphous, as they are in-situ formed from the Cu(II) nanoparticles. Furthermore, under the ultra-high vacuum condition, the Cu(II) can be reduced to Cu(I) during the TEM analysis, which also shows the amorphous structure. The fine structure of the Cu(II) nanoparticles had been already studied by means of XANES in literatures (J. Phys. Chem. C. 2009, 113, 10761–10766.), which shows that Cu(II) nanoparticles are incorporated in a distorted amorphous CuO-like structure, having a five-coordinated square pyramidal form.

 

Comment 3: It is well known that P25 titanium oxide is a typical mixed crystalline titanium oxide sample, include anatase, rutile and amorphous. Reports has been published to investigate the order of deposition of metal particles on different crystals as well as the different activities when metal deposited on different crystals. In the case of this study, is there also a preferential order of Cu deposition on different crystals? If the authors believe that there is no preferential order, please give the corresponding verification procedure.

Response: Based on the TEM and EDS measurements (revised Figure 1b), it can be seen that the Cu does not present a preferential deposition on different crystals, and they should tend to randomly distribute over all the TiO₂ nanocrystals. This is a good comment, we also considered the crystalline type should has an effect on the photochromism and electron relaxation kinetics. This should be an interesting topic, but it is not the focus of the current study, and we will investigate it in our future studies.

Comment 4: Cu(I) is deposited on the surface of titanium oxide, which is very susceptible to be reduced or oxidized. For this study, if the situation for long-time irradiation or lifetime of sample by re-use was considered?

Response: Not Cu(I), but Cu(II) nanoparticles were deposited on the TiO₂ surfaces. Yes, the Cu(II) nanoparticles can be reduced to Cu(I) and Cu(0) under UV light illumination in different atmospheres, as we showed in the paper. It is confirmed by the UV-Vis-NIR spectra that the reduced Cu/TiO₂ sample can be reoxidized to Cu(II) after exposing to O₂ and H₂O, which can be re-used in photochromism,  photoconductance, and photocatalytic measurement for long times and many times.