Visible Light-Driven Photocatalytic Degradation of Ciprofloxacin, Ampicillin and Erythromycin by Zinc Ferrite Immobilized on Chitosan
, Sherien Elagroudy 1,3 and Adewale Adewuyi 4,5,*Round 1
Reviewer 1 Report
This study investigated the synthesis of zinc ferrite immobilized on chitosan (ZnFe2O4@Chitosan) and its application in the photodegradation of ciprofloxacin (CIP), ampicillin (AMP) and erythromycin (ERY) in aqueous solution. The photodegradation study of CIP, AMP and ERY showed that both photodegradation and adsorption were taking place at the same time with the percentage degradation efficiency in the order CIP (99.80±0.20%)>AMP (94.50±0.10%)>ERY (83.20±0.20%). ZnFe2O4@Chitosan exhibited high stability with capacity >90% even at 15th regeneration cycle suggesting a viable economic value of ZnFe2O4@Chitosan. Therefore, this work is worth publishing, but this manuscript needs minor revision. My detailed comments are as follows:
1. In introduction, chitosan is not mentioned. Does it have any defects? By combining with ZnFe2O4, it can just make up for this part. Please add chitosan and cite relevant literature. Moreover, some works related to pollutant degradation and novel photocatalyst can be recommended and discussed. The author can refer to these papers, J. Hazar. Mater. 410, 2021, 124539. Chem. Eng. J. 409, 2021, 128185. Journal of Cleaner Production 360, 2022, 131948. 8. In addition, is it (ZnFe2O4@Chitosan) a core-shell structure?
2. In the experimental part, there are some small problems, such as “0.2M”no space.
3. There is no TEM, so it is recommended to add it to observe the morphology of the sample.
4. In Table 1. Comparison of the photodegradation of CIP, AMP and ERY by ZnFe2O4@Chitosan with other photocatalysts in literature. However, there is no comparison with the photocatalyst containing chitosan, and I hope to add a few.
5. If possible, the ESR experiments should be added to observe whether they are consistent with the results of free radical trapping experiments.
6. In Fig. 7a, the sun in the upper left corner is not beautiful. It is recommended to redo it.
Author Response
Comment 1
In introduction, chitosan is not mentioned. Does it have any defects? By combining with ZnFe2O4, it can just make up for this part. Please add chitosan and cite relevant literature. Moreover, some works related to pollutant degradation and novel photocatalyst can be recommended and discussed. The author can refer to these papers, J. Hazar. Mater. 410, 2021, 124539. Chem. Eng. J. 409, 2021, 128185. Journal of Cleaner Production 360, 2022, 131948. 8. In addition, is it (ZnFe2O4@Chitosan) a core-shell structure?
Response 1
We have included sentences on chitosan in the introduction. The suggested references are very helpful. Thank you.
Comment 2
In the experimental part, there are some small problems, such as “0.2M”no space.
Response 2
Thank you. This has been corrected
Comment 3
There is no TEM, so it is recommended to add it to observe the morphology of the sample.
Response 3
Yes, the TEM analysis will help reveal more information on morphology. However, the surface morphology has been evaluated using SEM in the study which showed the surface to be homogeneous. Presently, we do not have access to TEM but hopefully this will be considered in our future work. Thank you.
Comment 4
In Table 1. Comparison of the photodegradation of CIP, AMP and ERY by ZnFe2O4@Chitosan with other photocatalysts in literature. However, there is no comparison with the photocatalyst containing chitosan, and I hope to add a few.
Response 4
This is very true. Thank you. We have added a few chitosan based materials.
Comment 5
If possible, the ESR experiments should be added to observe whether they are consistent with the results of free radical trapping experiments.
Response 5
The Electron Spin Resonance (ESR) analysis is a spectroscopic technique which is very important, however, we have used a non-spectroscopic technic (vibrating sample magnetometry) which also gave an excellent result in understanding the magnetic property of ZnFe2O4@Chitosan. Kindly see figure 2d. Thank you.
Comment 6
In Fig. 7a, the sun in the upper left corner is not beautiful. It is recommended to redo it.
Response 6
Thank you for the observation. We have corrected it.
Thank you for the quality time you have spent in helping us to improve on the quality of our manuscript. This is highly appreciated.
Reviewer 2 Report
The following aspects need improvement, and the comments are expected to be discussed in the text before publication.
1. The current form of this manuscript lack of Control Experiment. Without justifying with control experiment it is very difficult to understand the quality of the ZnFe2O4@Chitosan catalyst. The authors synthesized ZnFe2O4 and ZnFe2O4@Chitosan but there is no data related ZnFe2O4 compound. They calculated the crystallite size, bandgap, surface area, and other values but they did not show any data related to ZnFe2O4. Then, how can the readers know ZnFe2O4@Chitosan is the better product? Therefore, I strongly recommended to add all the characterization and application data of the ZnFe2O4 sample and compared with ZnFe2O4@Chitosan.
2. The authors wrote, “The crystallite size for ZnFe2O4@Chitosan was found to be is 35.14 nm (Line 187-188)”. So, why this value is important must be explained with proper references.
3. The authors should carefully check the typo and space errors throughout the manuscript.
4. There are lots of papers already published regarding this same composite (ZnFe2O4@Chitosan) for photocatalytic application. Therefore, the authors should be clearly discussed the novelty of the present work.
5. The author should write the permissible limits for Fe and Zn in drinking water with proper references (Line 358-359).
6. The authors performed recycling experiments up to 15th times. Therefore, it should be added the stability of the catalyst (structural change) for practical application. It is highly recommended to the authors the structural changes of the catalyst after the photocatalytic reaction (after the 15th cycle) should add.
7. The authors did the pH experiment. But they should investigate the point of zero charges (PZC) of the ZnFe2O4@Chitosan catalyst for understanding the surface properties of that catalyst. It is highly recommended to investigate the PZC for the ZnFe2O4@Chitosan composite and correlate the results with pH experiments.
8. The authors should carry out LC-MS at least using one pollutant so that the possible degradation pathway of pollutant and possible degradation products are specified.
Author Response
REVIEWER 2
Comment 1
The current form of this manuscript lack of Control Experiment. Without justifying with control experiment it is very difficult to understand the quality of the ZnFe2O4@Chitosan catalyst. The authors synthesized ZnFe2O4 and ZnFe2O4@Chitosan but there is no data related ZnFe2O4 compound. They calculated the crystallite size, bandgap, surface area, and other values but they did not show any data related to ZnFe2O4. Then, how can the readers know ZnFe2O4@Chitosan is the better product? Therefore, I strongly recommended to add all the characterization and application data of the ZnFe2O4 sample and compared with ZnFe2O4@Chitosan.
Response 1
Thank you very much for the comment. The aim of the study is to synthesize ZnFe2O4@Chitosan catalyst for the degradation of AMP, CIP and ERY which are emerging contaminants of major concern globally most especially in Africa. The synthesis was achieved by immobilizing ZnFe2O4 on chitosan. The point raised is quiet understood but this is not the focus of the study. The aim is not to compare the activities of ZnFe2O4 and ZnFe2O4@Chitosan as catalyst.
Unfortunately, most ferrites like ZnFe2O4 aggregates after a while which is a drawback. This is the reason for the modification to produce ZnFe2O4@Chitosan. The use of chitosan helped stabilized the particles of ZnFe2O4 by reducing aggregation and helping to promote the recovery of ZnFe2O4 particles from solution. We have included more sentences in the manuscript in this regard.
The dark experiment which was conducted in the absent of light is considered as the control experiment to check for and establish photodegradation (photcatalysis) process.
Comment 2
The authors wrote, “The crystallite size for ZnFe2O4@Chitosan was found to be is 35.14 nm (Line 187-188)”. So, why this value is important must be explained with proper references.
Response 2
We have added information to address this in the manuscript. Thank you.
Comment 3
The authors should carefully check the typo and space errors throughout the manuscript.
Response 3
We have carefully read through the manuscript once again to correct all typo and space errors.
Comment 4
There are lots of papers already published regarding this same composite (ZnFe2O4@Chitosan) for photocatalytic application. Therefore, the authors should be clearly discussed the novelty of the present work.
Response 4
Yes, we have indicated this in the manuscript as catalyst for the degradation of ciprofloxacin (CIP), ampicillin (AMP) and erythromycin (ERY) in aqueous solution.
Comment 5
The author should write the permissible limits for Fe and Zn in drinking water with proper references (Line 358-359).
Response 5
We have included the values and reference in the manuscript. Thank you.
Comment 6
The authors performed recycling experiments up to 15th times. Therefore, it should be added the stability of the catalyst (structural change) for practical application. It is highly recommended to the authors the structural changes of the catalyst after the photocatalytic reaction (after the 15th cycle) should add.
Response 6
This is correct. Unfortunately, currently, we do not have access to XRD in our laboratory. We shall definitely consider this in our future collaboration with other coworkers.
Comment 7
The authors did the pH experiment. But they should investigate the point of zero charges (PZC) of the ZnFe2O4@Chitosan catalyst for understanding the surface properties of that catalyst. It is highly recommended to investigate the PZC for the ZnFe2O4@Chitosan composite and correlate the results with pH experiments.
Response 7
The study is mainly focused on photcatalytic degradation and not adsorption. In the case of adsorption, it is very important to determine the PZC in order to understand surface charges that may have been involved in the surface interaction (adsorption) which helps to understand the mechanism of interaction. However, in photocatalysis, the mechanism is based on the electron (e-) – hole (h+) generation. This is the reason for the “evaluation of reactive oxygen species scavenging capacity” in the study (see methods/experimental section). This experiment takes care of understanding the mechanism of the reaction. The pH study is for the establishment of the best reaction condition for the photocatalytic process.
Comment 8
The authors should carry out LC-MS at least using one pollutant so that the possible degradation pathway of pollutant and possible degradation products are specified.
Response 8
Absolutely correct. Unfortunately, we don’t have access to LC-MS or GC-MS currently but we are making effort in collaboration in our future study to get some of these analyses evaluated. Thank you.
Thank you for helping us to improve on the current status of our manuscript. We appreciate all the suggestions.
Reviewer 3 Report
The manuscript proposed by Mohammed et al. is well organized and structured, with an integral characterization of the material and correlation with the photocatalytic activity. Mechanistic insights are included, and a study of the radical species involved in the reaction. The efficiencies are competitive using a visible light active material such as zinc ferrite immobilized in an innovative chitosan substrate. The manuscripts shows high quality as presented and can be accepted for publication.
Author Response
Thank you for the quality time you have spent in revising our manuscript. This is highly appreciated.
Round 2
Reviewer 2 Report
The authors revised the manuscript and significantly improved in its quality. Hence, it is recommended to accept for publication in this journal.
