Rapid preparation of terbium-doped titanium dioxide nanoparticles and their enhanced photocatalytic performance

Further applications of photocatalysis were limited by the high recombination probability of photo-induced electron–hole pairs in traditional titanium dioxide nanoparticles (TiO2 NPs). Herein, we modified them with rare earth metal via a facile sol–gel method, using tetrabutyl titanate as a precursor and terbium (III) nitrate hexahydrate as terbium (Tb) source. The resulting samples with different Tb doping amounts (from 0 to 2%) have been characterized by X-ray diffraction, UV–visible diffuse reflectance spectroscopy, X-ray photo-electron spectroscopy and a scanning electron microscope. The photocatalytic performance of Tb-doped TiO2 was evaluated by the degradation of methylene blue. The effects of Tb doping amount and initial pH value of solution were investigated in detail. The composite with Tb doping amount of 1.0 wt% showed the highest photocatalytic performance. It exhibited approximately three times enhancement in photocatalytic activity with a reaction rate constant of 0.2314 h−1 when compared with that of commercial P25 (0.0827 h−1). In addition, it presented low toxicity on zebrafishes with 96 h-LC50 of 23.2 mg l−1, and has been proved to be reusable for at least four cycles without significant loss of photocatalytic activity. A probable photocatalytic mechanism of Tb-doped TiO2 was proposed according to the active species trapping experiments. The high photocatalytic performance, excellent reusability and low toxicity of Tb-doped TiO2 indicated that it is a promising candidate material in the future treatment of dye wastewater.

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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. ********************************************** RSC Associate Editor: Comments to the Author: (There are no comments.) RSC Subject Editor: Comments to the Author: (There are no comments.) ********************************************** Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) In this MS, the authors described a sol-gel route for preparing Tb-doped TiO2 nanoparticles and investigated the photocatalytic performance to degrade MB. Since metal ions-doped TiO2 photocatalysts have been widely reported in the literature, the present work has no enough novelty from the synthetic methodology. Nevertheless, some findings are interesting such as biosafety. The present MS can be considered for publication in this journal after the below queries are answered. 1. According to Table 1, with the increase of Tb content the size of the product decreases. However, the crystallinity is irregular. Why? 2. The authors claimed that the presence of C peak was attributed to exogenous pollution. This is unclear description. In fact, the C peak is always detected in XPS survey spectrum. Is it polluted at all times? Moreover, the formation of Ti3+ was also attributed to the reduction of Ti4+. Then, please give related reaction equations. 4. The present expression of superoxide radicals is error. Please correct it. 5. English should be carefully checked to avoid many errors/mistakes.

Reviewer: 2
Comments to the Author(s) The manuscript reported the preparation and performance of Tb doped TiO2. I think it showed some interest and can be accepted after some revisions. 1. Fig. 1 is suggested to be deleted.

Recommendation?
Accept as is

Comments to the Author(s)
The present revised MS can be accepted.

Response to referees
Dear Editors and Reviewers, Thank you for your letter and for the reviewers' comments concerning our manuscript entitled "Rapid Preparation of Terbium Doped Titanium Dioxide Nanoparticles and Its Enhanced Photocatalytic Performance" (ID: RSOS-191077). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope to meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer's comments are as flowing: Reviewer: 1 1. According to Table 1, with the increase of Tb content the size of the product decreases. However, the crystallinity is irregular. Why?
Response:The crystallinity is related to the pH value of the reaction solution and the amount of Tb doped into the titanium dioxide lattice, in addition to the calcined process. However, since acetic acid was added during the preparation of samples, the pH value of the reaction solution varied dynamically depending on the amount of terbium(III) nitrate hexahydrate added. Besides, the amount of terbium doped into the titanium dioxide lattice or the surface was uncontrollable. In summary, due to the complexity of these two factors, the crystallinity of all samples was higher than 95%, but it didn't show obvious regularity.
2. The authors claimed that the presence of C peak was attributed to exogenous pollution. This is unclear description. In fact, the C peak is always detected in XPS survey spectrum. Is it polluted at all times? Moreover, the formation of Ti 3+ was also attributed to the reduction of Ti 4+ . Then, please give related reaction equations.
Response: We are very sorry that we have made a mistake for the explanation of C