Synthesis of a Novel Photocatalyst MVO4/g-C3N4 (M = La, Gd) with Better Photocatalytic Activity for Tetracycline Hydrochloride Degradation under Visible-Light Irradiation
Round 1
Reviewer 1 Report
The manuscript needs major revision before acceptance. The authors encouraged to consider the following comments.
1.The English of the text must be improved carefully. For example, the first sentence of the abstract is not clear.
2. What is TC in the title and in-text? Refine it in the text.
3.The quality of all figures is low. Provide more clear images. Especially, Figures 4,5 and 8
4. The conclusion part must be improved.
Author Response
Response to Reviewer 1 Comments
Point 1. The English of the text must be improved carefully. For example, the first sentence of the abstract is not clear.
Response 1: Thank you for your comments. The first sentence of the abstract did not declare the loading amounts of MVO4 and exist the problem of expression unclear. Therefore, the doping amount is marked after modification, and the relevant content of time data is clearly expressed. The first sentence has been amended to “In this study, a novel photocatalysts MVO4/g-C3N4 (M=La, Gd) were prepared by hydrothermal method, different loading amounts of 10%-50%MVO4 and g-C3N4 were mixed and ultrasonic oscillated to gain heterojunction catalysts.”, which is showed in Page 1 Line10 to Line 12.
Point 2. What is TC in the title and in-text? Refine it in the text.
Response 2: Thank you for your comments.TC is a short for tetracycline hydrochloride. The full name of TC in the article was not written for the first time, which is easy to cause misunderstanding to readers. TC has been changed to tetracycline hydrochloride now, which is showed in Page1 Line3 and Line17.
Point 3. The quality of all figures is low. Provide more clear images. Especially, Figures 4,5 and 8
Response 3: I'm sorry for the trouble caused to you due to the low resolution of the uploaded pictures. Now all the pictures have been modified to a resolution of 300, and the modified pictures are presented in the attachment.
Point 4. The conclusion part must be improved.
Response 4: Thank you for your comments. According to your suggestions, the conclusion has been revised as follows:
“In conclusion, a novel MVO4/g-C3N4(M = La, Gd) nanocomposite material was prepared by a facile hydrothermal method. This novel photocatalyst has the activity of initiating the decomposition of TC under visible light illuminate. As shown in XRD and FT-IR results, there is no impurity diffraction peaks were observed which confirmed the successful synthesis of MVO4/g-C3N4. We can also observe that, in the SEM and TEM results, both the pin-like LaVO4 and coral-like GdVO4 were successful loading on the sheet g-C3N4, respectively. And the results of DRS and PL characterization show that MVO has more efficient visible light response ability. In addition, it also exhibits excellent photocatalytic performance under ultraviolet light irradiation. The enhanced photocatalytic performance of GdVO4/g-C3N4 is not only related to the energy band potential of GdVO4 and g-C3N4, but also related to the interconnected nanocrystalline heterojunction of g-C3N4.This study may provide an important strategy for the designation and preparation of high-performance photocatalysts induced by visible light.”
which is shown in Page 10 Line 258.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is an interesting study that addresses novel g-C3N4 based MVO4/g-C3N4 (M=La, Gd) photocatalysts. Photocatalysts were prepared by a hydrothermal method, All the samples were characterized using XRD, SEM, TEM, FT-IR, XPS, Us-vis and PL. Thus, the hydrothermal method of synthesis and the prepared photocatalyst characterization of the synthesized semiconductors appears to be rigorous. While this manuscript could be good in terms of possible alternatives for photocatalytic conversion of tetracycline using visible light there are two main challenging issues that require clarification:
- a) Is 20mg/L tetracycline solution an expected TC contaminant concentration in water?
- b) Could the photocatalysts proposed have a harmful effect (toxicity) on humans? If this is the case, they should have to be removed from water which is unlikely to be fully achieved.
I have also concerns about the photoactivity experiments and the conclusions based on the following:
- There is no definition of standard deviations for experimental runs. Repeats and calculated standard deviations are needed to statistically validate experimental trends.
- First order kinetic parameters are not defined with confidence intervals. This is not adequate.
- Definition of photocatalytic reaction progress using the TC (tetracycline) conversion using UV–Vis spectrophotometer colour (absorption) changes at 356nm provides only partial information. The TC color (absorption) changes frequently describe the very first step of the complex TC photocatalytic conversion network. To provide a true test of TC conversion photoactivity, the total organic carbon (TOC) has to be measured at various irradiation times. Without total organic carbon (TOC) information it is difficult to reach a convincing conclusion about photoactivity. For more information, please refer to de Lasa et al, Photocatalytic Reaction Engineering 2005.
- As well, the performance comparison of various synthesized photocatalysts has to be done on the basis of Quantum Yields (QY) as,
QY= Moles of C in TC converted into CO2/Moles of photons absorbed.
Without QYs performance indicators is unlikely that the authors could conclude about claimed good performance of the photocatalysts studied.
In summary, in view of the comments above, this manuscript requires major clarifications before it can be accepted for publication.
Author Response
Response to Reviewer 2 Comments
Point 1. Is 20mg/L tetracycline solution an expected TC contaminant concentration in water?
Response 1: Thanks for your comments. The reason why 20mg/L concentration is chosen is that the concentration of TC in natural water is close to 20mg/L, and this study is to simulate the concentration of TC in natural seawater.[1]
Point 2. Could the photocatalysts proposed have a harmful effect (toxicity) on humans? If this is the case, they should have to be removed from water which is unlikely to be fully achieved.
Response 2: Thank you for your comments. After the degradation test, the catalyst in the aqueous solution will be centrifuged, washed, dried and recycled for reproducibility test. According to previous literature, g-C3N4-based photocatalyst can be used as an ideal material for water pollution treatment because their toxicity decreases dramatically due to mineralization under visible light conditions.[2]
Point 3. There is no definition of standard deviations for experimental runs. Repeats and calculated standard deviations are needed to statistically validate experimental trends.
Response 3: Thank you for your comments. For the stability of the catalyst, we conducted repeated experiment, as shown in the figure below, and the degradation result remained about 87% after six repeated experiments.
Point 4. First order kinetic parameters are not defined with confidence intervals. This is not adequate.
Response 4: Referred to previous literature, this paper chose to use first-order kinetic constant to summarize the degree of relationship between concentration and degradation rate.[3][4]
Point 5. Definition of photocatalytic reaction progress using the TC (tetracycline) conversion using UV–Vis spectrophotometer color (absorption) changes at 356nm provides only partial information. The TC color (absorption) changes frequently describe the very first step of the complex TC photocatalytic conversion network. To provide a true test of TC conversion photoactivity, the total organic carbon (TOC) has to be measured at various irradiation times. Without total organic carbon (TOC) information it is difficult to reach a convincing conclusion about photoactivity. For more information, please refer to de Lasa et al, Photocatalytic Reaction Engineering 2005.
As well, the performance comparison of various synthesized photocatalysts has to be done on the basis of Quantum Yields (QY) as,
QY= Moles of C in TC converted into CO2/Moles of photons absorbed.
Without QYs performance indicators is unlikely that the authors could conclude about claimed good performance of the photocatalysts studied.
Response 5： Thank you for your comments. Based on your suggestion, I have read a lot of relevant literature on TOC test after photocatalytic degradation experiment. However, due to the limited laboratory conditions, I am sorry that the TOC test has not been completed.
1. Wang, H.; Wu, Y.; Feng, M.; Tu, W.; Xiao, T.; Xiong, T.; Ang, H.; Yuan, X.; Chew, J.W. Visible-light-driven removal of tetracycline antibiotics and reclamation of hydrogen energy from natural water matrices and wastewater by polymeric carbon nitride foam. Water Res. 2018, 144, 215–225, doi:10.1016/j.watres.2018.07.025.
2. Wang, F.; Chen, P.; Feng, Y.; Xie, Z.; Liu, Y.; Su, Y.; Zhang, Q.; Wang, Y.; Yao, K.; Lv, W.; et al. Facile synthesis of N-doped carbon dots/g-C3N4 photocatalyst with enhanced visible-light photocatalytic activity for the degradation of indomethacin. Appl. Catal. B Environ. 2017, 207, 103–113, doi:10.1016/j.apcatb.2017.02.024.
3. Yang, C.; You, X.; Cheng, J.; Zheng, H.; Chen, Y. A novel visible-light-driven In-based MOF/graphene oxide composite photocatalyst with enhanced photocatalytic activity toward the degradation of amoxicillin. Appl. Catal. B Environ. 2017, 200, 673–680, doi:10.1016/j.apcatb.2016.07.057.
4. Du, X.; Bai, X.; Xu, L.; Yang, L.; Jin, P. Visible-light activation of persulfate by TiO2/g-C3N4 photocatalyst toward efficient degradation of micropollutants. Chem. Eng. J. 2020, 384, doi:10.1016/j.cej.2019.123245.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
The authors modified the text sufficiently and I can recommend it for publication.
Author Response
Dear reviewer,
Thank you for your comments.
In order to ensure the accuracy of the experimental data,
some changes have been made in the paper,
and TOC measurement data have been added in the paper
(page 7 of manuscript).
Author Response File: Author Response.docx
Reviewer 2 Report
Please refer to the enclosed file.
Comments for author File: Comments.docx
Author Response
Dear reviewer,
Thank you for your comments.
About TOC analysis, we did the TOC experiment last week.
The results were shown in manuscript (Page 7).
Author Response File: Author Response.docx
