Zirconium(IV) Metal Organic Frameworks with Highly Selective Sorption for Diclofenac under Batch and Continuous Flow Conditions
, Gerasimos S. Armatas 2 and Manolis J. Manos 1,3,*Round 1
Reviewer 1 Report
The reviewed paper reports a study on the application of two Zr-based MOFs to remove Diclofenac from the aqueous solutions. Essentially, the paper is well written and describes interesting research. After some minor amendments, the manuscript seems appropriate for publication in Crystals.
Namely, remove (错误!未找到引用源。) line 184. Moreover, the preparation of MOR-1-HA was reported in the ESI to the cited work (S. Rapti et al., Chem. Sci.,2016,7,2427.) but the other cited ref. 35 is hardly available, so it should be removed. Thus, the respective procedure for MOR-2 could not be found. In my opinion, the Authors should include the exact experimental methods for preparing both materials.
Author Response
Reviewer 1
Comments and Suggestions for Authors
The reviewed paper reports a study on the application of two Zr-based MOFs to remove Diclofenac from the aqueous solutions. Essentially, the paper is well written and describes interesting research. After some minor amendments, the manuscript seems appropriate for publication in Crystals.
Our response: We thank the reviewer for the positive comments.
Namely, remove (错误!未找到引用源。) line 184.
Our response: This is corrected in the revised manuscript.
Moreover, the preparation of MOR-1-HA was reported in the ESI to the cited work (S. Rapti et al., Chem. Sci.,2016,7,2427.) but the other cited ref. 35 is hardly available, so it should be removed. Thus, the respective procedure for MOR-2 could not be found. In my opinion, the Authors should include the exact experimental methods for preparing both materials.
Our response: Indeed, the reference 35 in the initial manuscript does not present the synthesis of MOR-2. This is corrected in the revised manuscript and now reference 38 reports the synthesis of MOR-2. We do not wish to include again the synthesis of these known materials, as the preparations are reported in detail in the cited papers (references 37 and 38 in the revised manuscript).
Author Response File: 
Author Response.docx
Reviewer 2 Report
The diclofenac removal from flowing water by Zr-MOF is a very impressive work. Anion/anionic dye separation by LDHs, MOFs are very common. However, the separations of the charge-neutral molecule, under a continuous flow of water, are very rare or unreported. In this regard, the following paper should be cited.
Adsorptive removal of pharmaceuticals from water using metal-organic frameworks: A review (DOI: 10.1016/j.jenvman.2020.111389)
Importantly, the papers therein should be scrutinized carefully before claiming that this is the first study of adsorbing drugs from flowing water.
Besides inflammatory drugs, the estrogenic pill is one of the biggest threats to water pollution (DOI:10.30919/es8d428 ; https://www.espublisher.com/journals/articledetails/428/). Several species are under survival threat. Such synthetic hormones are also charge-neutral molecules and removal of such pills costs beyond capability. This paper should be referred also to attract the researchers working on pill removal.
At line 103, the temperature unit is provided at K. There should be the same unit. (Either C or K)
The important peak positions in figure 8 should be depicted over the figure so that one can easily point out the compound easily.
There are some minor article/preposition mistakes that should be modified.
I think this is very nice work and I suggest the editor to accept the manuscript after a minor review.
Author Response
Reviewer 2
Comments and Suggestions for Authors
The diclofenac removal from flowing water by Zr-MOF is a very impressive work. Anion/anionic dye separation by LDHs, MOFs are very common. However, the separations of the charge-neutral molecule, under a continuous flow of water, are very rare or unreported.
Our response: We thank the reviewer for the positive comments.
In this regard, the following paper should be cited.
Adsorptive removal of pharmaceuticals from water using metal-organic frameworks: A review (DOI: 10.1016/j.jenvman.2020.111389)
Importantly, the papers therein should be scrutinized carefully before claiming that this is the first study of adsorbing drugs from flowing water.
Our response: The suggested reference was cited in the revised manuscript. We have checked carefully various papers cited in the review article and we found no study involving sorption of drugs under continuous flow conditions.
Besides inflammatory drugs, the estrogenic pill is one of the biggest threats to water pollution (DOI:10.30919/es8d428 ; https://www.espublisher.com/journals/articledetails/428/). Several species are under survival threat. Such synthetic hormones are also charge-neutral molecules and removal of such pills costs beyond capability. This paper should be referred also to attract the researchers working on pill removal.
Our response: The suggested reference was cited in the revised manuscript.
At line 103, the temperature unit is provided at K. There should be the same unit. (Either C or K)
Our response: We changed the temperature units to K in the revised manuscript.
The important peak positions in figure 8 should be depicted over the figure so that one can easily point out the compound easily.
Our response: In the revised manuscript we have added two more graphs showing the IR spectra from 1000 to 400 cm-1, in order to highlight the C-Cl band.
There are some minor article/preposition mistakes that should be modified.
Our response: We have done several corrections in the manuscript, as editor requested to rephrase various parts of the paper.
I think this is very nice work and I suggest the editor to accept the manuscript after a minor review.
Our response: We thank again the reviewer for the nice comments.
Author Response File: Author Response.docx
Reviewer 3 Report
The paper of Manolis J. Manos and co-authors is a fundamental and nearly industrial work on the selective sorption of diclofenac anions from water solution with a previously synthesized Zr-based MOFs. The authors showed that Zr MOFs can efficiently absorb diclofenac anions even in flow mode in a SiO2 covered with MOF column.
In the introduction, the authors state (line 33-25) “Diclofenac… is commonly found in the form of carboxylate anions (pKa ~ 4) in surface and ground water”. The pharmaceutical form of Diclofenac is a sodium salt, which was an object of the study. Based on the low value of pKa, it can be assumed that in nature water the counterion of diclofenac is not sodium, but magnesium/calcium/iron. It would be interesting whether the sorption of the MOF will depend on the choice of the starting salt?
Line 184 – didn’t understand hieroglyphs
“Crystals” for the most part studies the synthesis and structure of new compounds, monocrystal X-Ray structure is needed. The authors synthesized and studied the structure of discussed Zr MOFs earlier. In order for this article to be seen by more relevant specialists, I advise to resubmit or transfer to another MDPI Journal - Materials/Membranes/Water/ Sustainability
Author Response
Reviewer 3
The paper of Manolis J. Manos and co-authors is a fundamental and nearly industrial work on the selective sorption of diclofenac anions from water solution with a previously synthesized Zr-based MOFs. The authors showed that Zr MOFs can efficiently absorb diclofenac anions even in flow mode in a SiO2 covered with MOF column.
Our response: We thank the reviewer for the positive comments.
In the introduction, the authors state (line 33-25) “Diclofenac… is commonly found in the form of carboxylate anions (pKa ~ 4) in surface and ground water”. The pharmaceutical form of Diclofenac is a sodium salt, which was an object of the study. Based on the low value of pKa, it can be assumed that in nature water the counterion of diclofenac is not sodium, but magnesium/calcium/iron. It would be interesting whether the sorption of the MOF will depend on the choice of the starting salt?
Our response: This a nice suggestion by the reviewer. We believe, however, that Mg2+, Ca2+ will not have any influence in the sorption of diclofenac by the MOF, considering that these alkaline earths ions are strongly hydrated and thus, they have very weak interactions with diclofenac anions in aqueous solutions. In contrast, diclofenac may have strong interactions with the MOF via formation of Zr-carboxylate coordination bonds. In any case, it will be interesting to check sorption of diclofenac from real water samples (e.g. potable, groundwater, lake, river, seawater etc.), which contain a variety of cations and anions, by using various MOFs under batch and continuous flow conditions. Such studies may be included in a future work.
Line 184 – didn’t understand hieroglyphs
Our response: We have corrected this issue in the revised manuscript.
“Crystals” for the most part studies the synthesis and structure of new compounds, monocrystal X-Ray structure is needed. The authors synthesized and studied the structure of discussed Zr MOFs earlier. In order for this article to be seen by more relevant specialists, I advise to resubmit or transfer to another MDPI Journal - Materials/Membranes/Water/ Sustainability.
Our response: Indeed, the present paper did not include new crystal structures; however, we are presenting powder X-ray data including cell indexing and Le Bail refinement results. The paper is intended to be published in the special issue “Organic-Inorganic Hybrids: Synthesis, Property and Application” and we believe that it will be a nice contribution in this collection of articles in Crystals.
Author Response File: Author Response.docx
