The Influence of Anion-Stripped MIL-101(Cr) Dispersed in Thin-Film Polyvinyl Alcohol Membrane Matrix on the Methylene Blue Dye Separation

Comments and Suggestions for Authors

The paper entitled “The Influence of Anion-stripped MIL-101(Cr) Dispersed in Thin-Film Polyvinyl Alcohol Membrane Matrix on the Methylene Blue Dye Separation” is an interesting work on the preparation and assessment of composite membranes toward the removal of dyes. The work is interesting, however, needs to be improved in some aspects, namely grammar and formatting.

Authors must pay attention to the formatting throughout the manuscript. There are many small mistakes. Examples: 

Line 101 – “deionized” should be “Deionized”.

Line 115 – “Exchanging fluoride ions with chloride ions in M101 structure”. Is it a sub-topic? It should be numbered then.

Interpretation (I) #1:

The quality of the figures is poor, and it seems that the figures are flattened.

Answer (A) 1:

The quality of the figures has been improved

I #2:

There are some yellow highlighted texts.

A2:

Yellow highlights have been removed

I #3:

What is the calibration curve for the measurement of MB concentration, including the detection limit?

A3:

The calibration curve is provided for you here

I #4:

Grammar must be checked.

A4:

Done

Comments and Suggestions for Authors

In this manuscript, the authors investigated the production and performance of a novel nanofiltration membrane for removal of cationic dye (Methylene blue) and multivalent cations. The authors presetned interesting results and the manuscript can be accepted after minor revisions.

Interpretation (I) #1:

The conclusion section should be improved. The highlights of the work can be listed.

Answer (A) 1:

The conclusion was improved in the modified text. The highlights of the work are also listed here.

Highlights

·       A nanofiltration membrane was fabricated by incorporating MOF particles in thin layer of polyvinyl alcohol.

·       MIL-101(Cr) was synthesized by hydrothermal method, and modified to form a cationic state (Cl-MIL-101(Cr))

·       MIL-101(Cr) and its Cl-MIL-101(Cr) particles have been used as porous fillers in PVA solution, and were placed on the polysulfone substrate.

·       MIL-101(Cr) is compatible with the PVA matrix, and the displacement of F- anions with Cl- in its structure greatly increases the cationic dye rejection.

·       Cross-flow filtration indicates the maximum methylene blue rejection of 99.08%, and improvement of membrane performance, flux drop and cleaning properties.

I #2:

The presentation of Fig.3 should be improved.

A2:

It has been improved

I #3:

More literatures from Coating can be included in the reference list.

A3:

In addition to references 9 and 27, reference 3 is also given from the Coatings journal.

Comments and Suggestions for Authors

The manuscript entitled: "The Influence of Anion-stripped MIL-101(Cr) Dispersed in Thin-Film Polyvinyl Alcohol Membrane Matrix on the Methylene Blue Dye Separation" is an interesting work dealing with the fabrication and characterization of membranes for the removal of dyes from water. It is is an interesting article well written that can be revised in order to get accepted for publication.

Interpretation (I) #1:

SEM images are not of good resolution and the images need to be either retaken or corrected.

Answer (A) 1:

The resolution and quality of FESEM images have been improved.

I #2:

Please provide higher magnification of the membrane cross-section

A2:

A higher magnification of the membrane cross-section is presented here.

(a)

(b)

(c)

(d)

cross section images of (a) polysulfone substrate, (b) PM0.8, (c) PM0.8-15 and (d) PM0.8-15-2

I #3:

How did the authors evaluate the performance of the MOF particles in the separation process?

A3:

As mentioned in the text, these MOF particles have a partial positive charge due to having a mobile anion (Cl^-). The effect of these particles on the membrane surface charge has been proven by zeta potential analysis. On the one hand, membrane rejection increases due to the presence of like charges and the electrostatic repulsion between the dye particles and the membrane surface. On the other hand, the porosity of the MOF particles reduces the negative effect of particle loading on the flux.

I #4:

The morphology of the MOF particles is indeed stable however, for the evaluation of the particle performance, it will be interesting to have an idea about the type of adsorption that the particles are following. For this, a combination of experimental data and modeling of the data is necessary. Similar approaches can be found for MOFs and activated carbon particles in literature (e.g., https://doi.org/10.3390/polym10010051)

A4:

Your opinion is completely correct, but in the case of the mentioned article, which is also given in reference 31, active carbon particles act as an adsorbent, and therefore the isotherm and adsorption mechanisms were investigated by different models. In our work, MOF particles repel the dye particles and water passes through the membrane under the influence of transmembrane pressure. Here, the issue of pressure drop and fouling is proposed. We calculated the relevant parameters including R_r, R_ir, RFR and FRR in our work. It is possible to examine fouling models to find the dominant model, but it is defined as a separate work due to its wide content.