Crosslinked Facilitated Transport Membranes Based on Carboxymethylated NFC and Amine-Based Fixed Carriers for Carbon Capture, Utilization, and Storage Applications

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However, the aim of the paper is not clearly stated in the Introduction and this should be clarified and summarized to ease comprehension of the impact of the results.

Please see track changes in the last paragraph in part 1 of the manuscript about the clarification of the aim of the paper

For instance, the pathway of the reactions taking place in the facilitated transport membranes based on amine functional groups and carbamate and bicarbonate ions, is not clear, since it seems that half-reactions and overall reactions are mixed in the explanation. Please clarify and perhaps propose a scheme with the reactions expected in the particular membrane system reported in the present paper, as other authors in literature did (eg. Journal of Membrane Science 543 (2017) 202–211).

Please see track changes in the manuscript part 1 relative to the new figure of the reaction scheme

Please clarify why the membranes reported in this work are named as “bio-based”, only because nanofibrillated cellulose is used as structural polymer in a 80% proportion against 20 % PVAm? Bio-based and sustainable properties of these synthetic NFCs should be justified.

Indeed the membranes are bio-based since they are made of 80% of carboxymethylated cellulose nanofibrils (cmNFC). cmNFC are obtained from cellulose, a natural polymer extracted from wood. The biobased and sustainable properties of cmNFC are largely described in literature (references from 56 to 60)

The last paragraph of the introduction describes the characterization techniques described below in the experimental section instead of focusing in the aim and novelty of the present works in the state-of-the-art of the research literature and market on facilitated transport membranes.

Please see track changes in the last paragraph in part 1 of the manuscript about the clarification of the aim of the paper

Lines 230-231, why are the FTIR spectra containing NFCs normalized at 1105 cm-1 and what do the authors mean by “1 unit of absorbance”?

Among the experts about cellulosic materials, we agree on normalizing the FTIR spectra at 1105 cm-1 which corresponds to the peak of the C-O stretching vibration of the glucopyranose ring (that is not impacted by the chemical modification). The absorbance value is set to 1 for the intensity of this peak. This method allows us to qualitatively compare the intensity of the peaks from the different FTIR spectra (especially the intensity of the grafted moieties). Please see track changes in part 2.5

Lines 266-267, please show how the melting temperature and enthalpies are calculated from DSC data.

“The melting temperature (Tm) and enthalpy (Hm) were respectively determined as the temperature of the endothermic peak and by integrating the area under the endothermic curve.” Please see track changes in part 2.10

Lines 275-281, are EDX measurements carried out at the FESEM microscope? How many sample images are considered for each sample and how many data points per image?

Yes, EDX measurements were carried out using the FEG-SEM microscope. “The X mapping was carried out on one image and at low magnitude (x1000) for each sample to have an overview.” Please see track changes in part 2.12. EDX measurements were performed in another lab after service request.

Line 316, why the thickness of the membrane in equation (8) is represented by an “l” while it is an “e” in equation (5)? Please normalize nomenclature or clarify.

Please see modifications in equations 8

Line 348, Figure 3 is not the 29Si MAS NMR, but rather it seems the representation of the equation (10) with time, thus derivation of this should be explained and perhaps supported by the relevant NMR spectra in the Supporting information. Please revise.

In the submitted paper we don't talk about solid NMR (MAS means Magic Angle Spinning, and is in relation with solid NMR only). We described kinetics study followed with liquid 29Si NMR in situ (This is clearly indicated in the text). The title of Figure 3 is modified by "Hydrolysis-Condensation kinetics curves of AEAPTMS in acidic D2O/EtOH (20/80) medium followed by liquid 29Si NMR in-situ." NMR data are obtained from the studies previously made by the co-author Marie-Christine Brochier-Salon and the NMR spectra are already available in the references 79, 83 and 84.

Line 372, why the weight of the water uptake is given in g/m2? No standard deviation is provided in Table 2. How reproducible are these values? This should be checked since the values reported do not vary much from one sample to the other.

In line 372 (or Table 1. Characteristics of the amine-functionalized cmNFC-based crosslinked membranes) we don’t talk about the weight of the water uptake but the weight per surface unit of a 20-cm round membrane (usually named as grammage in paper sector). The same membrane was used to do all the analyses. So the value is an average for all the samples taken from the membrane. The goal was to obtain membranes with same weight per surface unit to properly compare them. We had standard deviations in this table for the thickness values.

In Table 2 (DSC results), we only performed one DSC analysis per sample.

Line 380, “amine bonding”, please indicate the type of bonding the authors are referring to.

We are referring to “secondary amide bonding resulting in the presence of more crosslinking of cmNFC with PVAm and/or AEAPTMS”. Please see track changes in part 3.2.

Line 401, what is the meaning of “dipping by water”? Is it water swelling? This is not reported in the manuscript and it could influence membrane integrated. Please revise.

In process B, the crosslinking between the nanofillers and the matrix was first carried out and then the grafting of the aminosilane was performed by dipping the crosslinked membranes inside the aminosilane solution.

Lines 436-438, where is the “visual swelling” expected to come from if the membranes are more hydrophobic and the water uptake, according to Cobb60 tests is kept constant at a value of 50 g/m2 (figures 6c and d)? Especially since the water swelling significantly improved the CO2/N2 separation performance of the membranes (Table 5). Please revise and clarify the aim of the membranes and the work.

Please see track changes in part 3.3 “Despite their hydrophobic surface, the membranes absorbed a large amount of liquid water, since PVAm has a good affinity to water. Moreover, a visual swelling of the membranes in presence of liquid water was observed while the integrity of the sample remained intact. This observation supports the crosslinking effect between the filler and the matrix as suggested.”

Line 494, define the degree of substitution of COOH as DSc in equation (11) before introducing the equation, if it is correct.

Please see track changes in part 3.4 regarding the definition of the degree of substitution

Line 503, should not the degree of substitution be a number between 0 and 1? What does it mean the number of 3 stated as maximum?

No, the degree of substitution (DS) is between 0 and 3 as there are 3 OH groups per anhydroglucose unit of the cellulose that could be substituted. For example, a DS equal to 1 means that average 1 OH per anhydroglucose unit is substituted. This explanation is taken into account in the DS calculation, as always described in the literature (references 76, 77, 81, 82).

Lines 421 and 453, can the reverse effect of cmNFC and aminosilanes on the barrier properties of the membranes be related with the nanopores observed in the surface? What is the purpose of these barrier properties to air for CO2 /N2 separation membranes?

Even if nanopores were observed for cmNFC, this material is highly barrier (i.e. air permeability results and literature [reference 59]). So it is difficult to make a relation between the barrier properties and the nanopores observed in the surface, since gas solubility and tortuosity mechanisms are also at stake when dealing with gas permeability. Since air is composed of 80% of N2, the air permeability could add information about CO2/N2 separation, especially for cmNFC-PVAm which has higher permeability to air. Please see track changes in part 3.5.