Construction of Water Vapor Stable Ultramicroporous Copper-Based Metal–Organic Framework for Efficient CO₂ Capture

Round 1

Reviewer 1 Report

The manuscript by Yang et al. entitled as “Construction of water vapor stable ultramicroporous copper based metal organic framework for efficient CO₂ capture” demonstrated the synthesis and characterization of a Cu-MOF (SXU-5) and its ability to capture CO2 at ambient conditions. The authors have claimed the high CO₂ uptake capacity (99 cm³g^-1 and 56.6 cm³g^-1 at 273 K and 298 K respectively) as well as high selectivity over N₂ (118 at a scale of CO₂/N₂ 15/85, 298 K). The high uptake and selectivity of CO₂ was achieved through the combination of ultramicropore and high density of CO₂-philic sites without OMSs. The authors included theoretical calculations to demonstrate the role of the neighboring ketonic O atoms with suitable distance in enhancing the CO₂ uptake selectivity. The authors did not discuss anything about the synthesis and characterization of the ligand, 5-(1H-1,2,4-triazol-1-yl) isophthalic acid (H2TIPA). However, if I am not wrong, the same ligand has been used previously for the synthesis and characterization of a Cu-MOF which also exhibited selective CO₂ capture ability (180 cm³·g⁻¹) at 273 K (https://doi.org/10.1021/acs.inorgchem.1c00357 Inorg. Chem. 2021, 60, 6550−6558). In fact the previous Cu-MOF exhibited excellent acid-alkali resistance and thermal stability. I am wondering about the difference in between SXU-5 and the previously reported Cu-MOF. I think that the authors should have discussed whether there is any difference or not if the ligand is same. The manuscript needs a major revision to address the mentioned points properly. The following points also should be incorporated in the revised manuscript.

1. It is always better to provide a schematic view of the organic ligand.
2. The description of the synthesis and characterization of ligand should be described properly.
3. Provide a comparison table of the CO₂ uptake capacity of MOFs with literature report.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled " Construction of water vapor stable ultramicroporous copper based metal organic framework for efficient CO₂ capturee" presents a topic of great interest in flue-gas separation. The authors have carried out numerous gas sorption studies that offer some promise for CO2/N2 separation, although it should be noted that the total uptake of CO2 capacity and separation performances remain notably low. Additionally, the authors have yet to provide any experimental evidence to demonstrate that the material can function effectively under conditions that mimic flue gas. Therefore, substantial revisions are necessary before the manuscript can be deemed suitable for publication in the Processes.

1.      The authors need to explain better the significant differences of 12 degrees observed in the PXRD of the as-made and simulated materials (Figures 2b and 2b). They must also elaborate on why this peak is missing ~12/13 degrees and the reason behind its absence.

2.      The authors must also clearly explain the missing low-angle signal at ~9 and ~16 degrees. The authors have reported the absence of a low-angle signal at 9 degrees in the 100 C and 150 °C VT-PXRD, which reappeared in the 200 °C and 250 °C VT-PXRDs. To better understand the structural changes, the authors must measure SC-XRD at 150 °C and 200 °C. Additionally, if SC-XRD data is not available, they must provide the 150 °C and 200 °C powder patterns Rietveld refinements. The Rietveld refinement for the 150 °C and 200 °C powder patterns would also give a bulk phase purity and a better understanding of their structural changes.

3.      The authors must also provide PXRD patterns of water-soaked samples before and after soaking.

4.      The structural stability of MOFs cannot be conclusively determined from PXRD after soaking them in ambient air exposure or organic solvents. To support their claim of flue-gas capture, the authors must provide the water-soaked samples' CO2 and N2 sorption isotherms.

5.      Furthermore, they should measure water sorption isotherms at ambient conditions and 40C temperature, where the flue gas is typically present.

6.      It is difficult to observe PXRD signals in Figure 2b. The resolution of the PXRD in Figure 2b is inadequate and needs to be split into two separate figures.

7.      The authors must avoid repeating paragraphs in the manuscript, such as the one concerning the growing trend of strong CO₂-CO₂ interactions inside the narrow pores.

 

8.      The literature has widely documented the use of ultra-microporous MOFs for enhancing flue-gas capture and CO2 and CO2 separation from CH4 and N2. Therefore, the authors must cite the state-of-the-art MOFs (Science Advances 8 (44), eade1473 and Chemical Engineering Journal 446 (2022) 137101).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors agreed that the linker was used previously for the synthesis of Cu-MOFs, the synthesis conditions are different and led to a crystal structure with different space group in this present case. However the previous report also discussed about the CO2 adsorption properties of the Cu-MOFs. So the author should discuss the importance of this materials in terms of CO2 adsorption properties compared to the earlier Cu-MOFs. What is the significance of synthesizing new Cu-MOF with same linker? 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Based on a thorough examination, it has come to attention that the authors have omitted the inclusion of a highly significant reference relating to a recent ultramororous MOF for flue-gas separation (Science Advances 8 (44), eade1473). It is highly recommended that the reference be added to guarantee the thoroughness and comprehensiveness of the research work.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf