Exploring the Influence of the Reused Methanol Solution for the Structure and Properties of the Synthesized ZIF-8
Round 1
Reviewer 1 Report
In this study, the synthesis of ZIF-8 by recycling solvent is demonstrated. However, a similar study was published in 2014. http://dx.doi.org/10.1016/j.micromeso.2014.07.052
The authors should include this relevant reference and others in the introduction and clarify the contribution of their study.
Author Response
Comments and Suggestions for Authors
In this study, the synthesis of ZIF-8 by recycling solvent is demonstrated. However, a similar study was published in 2014. http://dx.doi.org/10.1016/j.micromeso.2014.07.052
The authors should include this relevant reference and others in the introduction and clarify the contribution of their study.
Answer: Dear reviewer, thanks for your valuable comment. In this paper, we explored the influence of the reused methanol solution for the structure and properties of the synthesized ZIF-8. The results shows that the reused methanol solution does not change the phase, porous structure and BET surface area of ZIF-8. However, the particle size of ZIF-8 increases from 50 nm to 5 um and the productive rate decreases to 7.4% when the methanol solution is reused for four times. Nilay Keser Demir and his co-workers explored the effect of the methanol/Zn(NO3)2 molar ratio on the particle size, BET surface area and on the rate of the crystallization. Furthermore, the mother liquor was collected and reutilized to synthesize ZIF-8 crystal by adding only the initial amount of Zn2+ to the liquor. It is different from our study. We added Zn(NO3)2 and 2-methyl imidazole to the collected liquor. We explored the influence of the reused methanol solution for the structure and properties of the synthesized ZIF-8. However, we can learn a lot of from their report. We have cited their paper in our revised manuscript. Thank you very much.
Reviewer 2 Report
ZIF-8 was successfully synthesized in methanol solution and the collected methanol solution could be reused as dissolving to synthesize ZIF-8 at least for four times. The results are valuable considering the importance of sustainable development. However, minor reversions are needed before accepttance:
1. the only question is that in the reused methanol solution, how to control the actual molar content of zinc nitrate hexahydrate and C4H6N2. Data should be provided for the reused methanol.
there are some other suggestions for the presentation:
1. in the introduction Zn2+ should be Zn2+
2. the frames of figures 1, 3, and 5 are too thick.
Author Response
Reviewer #2:
ZIF-8 was successfully synthesized in methanol solution and the collected methanol solution could be reused as dissolving to synthesize ZIF-8 at least for four times. The results are valuable considering the importance of sustainable development. However, minor reversions are needed before accepttance:
1. the only question is that in the reused methanol solution, how to control the actual molar content of zinc nitrate hexahydrate and C4H6N2. Data should be provided for the reused methanol.
Answer: Dear reviewer, thanks for your kind reminding. In this experiment, ZIF-8 was synthesized by the following procedure. Firstly, 22.5 g of Zn(NO3)2·6H2O was absolutely dissolved into 100 mL of methanol. Secondly, the above solution was poured into another 100 mL of methanol containing 19 g of C4H6N2. The mixture was stirred 5 min and then aged at 60 oC for 15 h. Then, the white precipitate was centrifuged, washed by ethanol and dried at 60 oC to obtain the ZIF-8. Following, the above methanol solution was retrieved to synthesize ZIF-8 by the same method. 22.5 g of Zn(NO3)2·6H2O was absolutely dissolved into 100 mL of collected methanol. 19 g of C4H6N2 was absolutely dissolved into another 100 mL of collected methanol. They were mixed together and aged at at 60 oC for 15 h. Then, the white precipitate was centrifuged, washed by ethanol and dried at 60 oC to obtain the ZIF-8. In order to make comparison, the synthesized ZIF-8 was labeled as ZIF-8(X) (X represents the reused time of the methanol solution). It has been introduced in Part 2.2 (Synthesis of ZIF-8 by the reused methanol solution). If there are any problems about it, please do not hesitate to tell us. Thank you very much.
2. in the introduction Zn2+should be Zn2+
Answer: Dear reviewer, thanks for your kind reminding. We have modified it in our revised manuscript. Thank you very much.
3. the frames of figures 1, 3, and 5 are too thick.
Answer: Dear reviewer, thanks for your kind reminding. We have modified it in our revised manuscript. Thank you very much.
Reviewer 3 Report
In this work, authors have synthesized ZIF-8 using a methanol solution of Zinc nitrate hexahydrate and 2-methylimidazole as raw materials. Repeated retrieving of used methanol solution to synthesize new ZIF-8, comparing the structure, pore size property, BET surface area etc. of ZIF-8 synthesized by methanol solvents with different retrieving times (one to four times). With the increase of methanol using times, the pore size property and BET surface area of ZIF-8 remained unchanged, but the particle size of the product gradually increased and the yield gradually decreased. Under the premise of meeting the demand, the utilization rate of methanol is improved. However, there are still some points that need to be improved in the article, as described below:
1. Whether there is zinc nitrate hexahydrate or 2-methylimidazole in the methanol solution for repeated recovery, and what is the proportion of the content? In addition, the relationship between the number of methanol recovery and the yield of ZIF-8 decreases is suggested.
2. The size of ZIF-8 prepared by recovering methanol for three times cannot be reflected in the SEM of Figure 2C, but the size in the SEM is probably 2 um according to the scale.
3. The curves of four XRD pattern are not recommended to overlap, can be hierarchically distinguished and show peak heights.
4. There are some spelling mistakes in the article. The valence of zinc ion in the abstract should be placed in the top right corner. In addition, there are punctuation errors in key words and the second paragraph of the introduction.
Author Response
Reviewer #3:
In this work, authors have synthesized ZIF-8 using a methanol solution of Zinc nitrate hexahydrate and 2-methylimidazole as raw materials. Repeated retrieving of used methanol solution to synthesize new ZIF-8, comparing the structure, pore size property, BET surface area etc. of ZIF-8 synthesized by methanol solvents with different retrieving times (one to four times). With the increase of methanol using times, the pore size property and BET surface area of ZIF-8 remained unchanged, but the particle size of the product gradually increased and the yield gradually decreased. Under the premise of meeting the demand, the utilization rate of methanol is improved. However, there are still some points that need to be improved in the article, as described below:
1.Whether there is zinc nitrate hexahydrate or 2-methylimidazole in the methanol solution for repeated recovery, and what is the proportion of the content?In addition, the relationship between the number of methanol recovery and the yield of ZIF-8 decreases is suggested.
Answer: Dear reviewer, thanks for your valuable comment. It is a good question. During the experiment, we found that the molar ratio of Zn2+/methanol, Zn2+/2-methylimidazole and NO3-/2-methylimidazole has great influence on the structure and properties of the synthesized ZIF-8. However, in this paper, we just explored the influence of the reused methanol solution for the structure and properties of the synthesized ZIF-8. The reused methanol solution contains the Zn2+, NO3- or 2-methylimidazole. So it has great influence on the on the structure and properties of the synthesized ZIF-8. In the following research, we will explore the Zn2+/methanol, Zn2+/2-methylimidazole and NO3-/2-methylimidazole separately. If there are any problems about it, please do not hesitate to tell us. Thank you very much.
2.The size of ZIF-8 prepared by recovering methanol for three times cannot be reflected in the SEM of Figure 2C, but the size in the SEM is probably 2 um according to the scale.
Answer: Dear reviewer, thanks for your kind reminding. The particle size of ZIF-8(3) is about 2 um. It is our mistake. We have modified it in revised manuscript. Thank you very much.
3.The curves of four XRD pattern are not recommended to overlap, can be hierarchically distinguished and show peak heights.
Answer: Dear reviewer, thanks for your valuable comment. Figure 1 shows the XRD patterns of ZIF-8(1), ZIF-8(2), ZIF-8(3) and ZIF-8(4). All samples almost show the same XRD patters and exhibit six obvious peaks at 7.53°, 10.58°, 12.93°, 14.84°, 16.67° and 18.24°, corresponding to the (011), (002), (112), (022), (113) and (222) planes of ZIF-8, respectively. As you point out, the intensity of four XRD pattern can not be the same. However, it does not mean anything. As we know, the intensity of XRD patterns is influence by the placement position, moisture content and other thing. We can distinguish the phases from the XRD patterns. If there are any problems about it, please do not hesitate to tell us. Thank you very much.
4.There are some spelling mistakes in the article. The valence of zinc ion in the abstract should be placed in the top right corner. In addition, there are punctuation errors in key words and the second paragraph of the introduction.
Answer: Dear reviewer, thanks for your kind reminding. We have modified this in the revised manuscript. However, the punctuation of the key works are consistent with the requirement of this journal. Thank you very much.
Reviewer 4 Report
In this paper, the authors presented the synthesis of zeolitic imidazolate framework-8 (ZIF-8) by traditional synthesis method. The synthesized material was characterized by X-ray diffraction instrument (XRD), scanning electron microscope (SEM), specific surface area analyzer (BET) and Fourier Transform infrared spectroscopy (FT-IR).
General comments
The manuscript contains descriptions of studies that have been well planned, carried out and interpreted. There are sufficient details given to replicate the proposed experimental procedures for traditional synthesis of zeolitic imidazolate framework-8 (ZIF-8).
However, there are still some places that are not clear, and some comments are made below for the authors to further enhance their paper before its possible publication.
- Novelty or purpose of the study is not stated clearly. The authors' proposal is to collect the residual methanol and reuse it to obtain a new amount of ZIF-8. This is not really an element of novelty and efficient. While the methanol is reused, the other reagents required to obtain ZIF-8 are consumed. Which is the purity of the reused methanol?
- The introduction must be improved, and the novelty must clearly specified.
- The applicability of the synthesized material is not tested and discussed. I recommend additional experimental studies to highlight the applicability possibilities of ZIF-8 obtained by reusing methanol.
- Regarding the characterization of ZIF-8 obtained by the traditional method:
- there are no details regarding the characteristics of the devices and parameters.
- for XRD characterization must be indicated the JCPDS No for this type of MOFs. The indications given by another work are not sufficient.
- I recommend updating the bibliographic resources.
Author Response
Reviewer #4:
The manuscript contains descriptions of studies that have been well planned, carried out and interpreted. There are sufficient details given to replicate the proposed experimental procedures for traditional synthesis of zeolitic imidazolate framework-8 (ZIF-8).
However, there are still some places that are not clear, and some comments are made below for the authors to further enhance their paper before its possible publication.
1.Novelty or purpose of the study is not stated clearly.The authors' proposal is to collect the residual methanol and reuse it to obtain a new amount of ZIF-8.This is not really an element of novelty and efficient. While the methanol is reused, the other reagents required to obtain ZIF-8 are consumed. Which is the purity of the reused methanol?
Answer: Dear reviewer, thanks for your valuable comment. In this paper, we explored the influence of the reused methanol solution for the structure and properties of the synthesized ZIF-8. The results shows that the reused methanol solution does not change the phase, porous structure and BET surface area of ZIF-8. However, the particle size of ZIF-8 increases from 50 nm to 5 um and the productive rate decreases to 7.4% when the methanol solution is reused for four times. During the experiment, we found that the molar ratio of Zn2+/methanol, Zn2+/2-methylimidazole and NO3-/2-methylimidazole has great influence on the structure and properties of the synthesized ZIF-8. However, in this paper, we just explored the influence of the reused methanol solution for the structure and properties of the synthesized ZIF-8. The reused methanol solution contains the Zn2+, NO3- or 2-methylimidazole. So it has great influence on the on the structure and properties of the synthesized ZIF-8. In the following research, we will explore the Zn2+/methanol, Zn2+/2-methylimidazole and NO3-/2-methylimidazole separately. If there are any problems about it, please do not hesitate to tell us. Thank you very much.
2.The introduction must be improved, and the novelty must clearly specified.
Answer: Dear reviewer, thanks for your kind reminding. We have done our best to improve the introduction and specify the novelty. Thank you very much.
3.The applicability of the synthesized material is not tested and discussed. I recommend additional experimental studies to highlight the applicability possibilities of ZIF-8 obtained by reusing methanol.
Answer: Dear reviewer, thanks for your valuable comment. Zeolitic imidazolate framework-8 (ZIF-8) is constructed by Zn2+ and imidazole (Im) units, exhibits the zeolite sodalite (SOD) topology and generates a resistant structure with large cages interconnected via narrow 6-ring windows. ZIF-8 has been widely used in many fields, such as CO2 capture, H2 storage and catalysis, due to its outstanding properties. In this paper, we just explored the influence of the reused methanol for the structure and properties of the synthesized ZIF-8. As for the applicability of the synthesized ZIF-8, we will do more study and report it in the following research. Thank you very much.
4.Regarding the characterization of ZIF-8 obtained by the traditional method.There are no details regarding the characteristics of the devices and parameters.For XRD characterization must be indicated the JCPDS No for this type of MOFs. The indications given by another work are not sufficient.
Answer: Dear reviewer, thanks for your kind reminding. The details characteristics of the devices and parameters were added in the revised manuscript. Furthermore, the JCPDS No for ZIF-8 is JCPDS 00-062-1030. We have added it in the revised manuscript. Thank you very much.
5. I recommend updating the bibliographic resources
Answer:Dear reviewer, thanks for your kind reminding.The format of bibliographic resources is in consistent with the requirement of the Journal of Processes. Thank you very much.
Round 2
Reviewer 1 Report
The authors included a reference noted in the previous review. However, this study was not discussed in the introduction, nor were the differences and contributions made by the authors compared to previous studies. Thus, the introduction can be improved since it does not provide sufficient background.
Author Response
Dear reviewer, thank you for you comment. We have discessed it in the last paragraph of introduction in the revised manuscript. Thank you very much.
Reviewer 4 Report
The manuscript can be accepted in revised form.
The authors responded adequately to the observations and made the requested additions.
Author Response
Thank you very much.
