Kyushu Synchrotron Light Research Center（ Form: No.5）

Experiment Report for Prefectural Beamline
Proposal no. :2209082TBeamline no.: BL-11
Report date

: 07/11/2023

CO recognition using 2D nano CP
Biplab MannaIINA, Kumamoto University

１ ． Summary
In this preliminary report, we introduce a new kind of phase namely 2D nano stacked
coordination polymers (here after referred as 1 O P -2D-heated). The material is observed toshow nano level thickness and cont ain open metal-sites which recognize toxic gas like carbon
monoxide (CO) than that of other coordinating guests.

２．Purpose of experiment and background
CO is well known as major emission from large number of industrial process and later on it mixed with othergases like N2.1 Such mixture of gases on burning produces large amount of CO2, which gives an alarm to thewhole world an unprecedented rise in temperature throughout the planet. Hence recognition of CO remains amajor topic of research interests. Till now, chemisorption on low valent metal center has been extensively
utilized but requirement of very high temperature for CO desorption makes it much difficult. Apart from thatmetal-oxide based approach also required high temperature for detection.2,3 Porous coordination polymers(PCPs) / metal-organic frameworks (MOFs) is being well recognized for its adaptable porosity. 4 Apart fromother gases, literature reports on CO sorption were very rare owing its toxic nature. 5,6 Very recently, Mirica etal. showed chemo resistive detection of CO using a conductive two-dimensional MOF.7 But, designing a 2D
conductive PCP/ MOF using a conjugated ligand is quite difficult and is not cost effective. Hence, presentsituation demands a cost effective and feasible method for CO recognition. Here, we hypotheses 2D stacked

nano CPs/ MOFs with unsaturated metal centers which can be built from easily available precursors (Scheme1). These stacked 2D nano MOFs can be tailored into tunable thickness which eventually can adjust theirperformance.

Scheme 1: CO recognition by using unsaturation of metal node in 2D nano stacked CP/ MOF

３．Experimental
Here, we use a DUT-8(Ni) (denoted as 1op hereafter) as a starting MOF, that has been synthesized in ourlaboratory using a previously reported method.8 1op contains 2,6-napthalenedicarboxylate (NDC) and a pillar
linker (DABCO) represented as [{Ni2(NDC)2(DABCO)}.xG]n. The porosity of original phase wasconfirmed from its N2-adsorption isotherm. 1op-2D was synthesized from the water sonication of
the 1op. 1H-NMR of 1op-2D was analyzied with DCl/DMSO (1:9) following a protocol.9 Evacuatedphase of 1op-2D generates 1op-2D-heated (Figure 1). The surface morphological analysis wereperformed with 1op-2D and1op-2D-heated . EXAFS and XANES have been analysed using

BL-11 for 1op-2D-heated phase to know the coordination environment around metal centre.The
XRPD patterns were analyzed with the 1op, 1op-2D, 1op-2D-heated. The 1op-2D-heated waschecked with AFM analysis. Temperature programmed desorption (TPD) analysis of the above
vapors on 1op-2D-heated phase will be performed to elucidate the affinity and binding strength.
Other vapors (Aromatic (benzene, Toluene) and non-aromatic solvent (cyclohexane, hexane,heptane) adsorption are under consideration. HR-TEM and electron diffraction analysis of the1op-2D and 1op-2D-heated phases will be examined to investigate the lattice patterns.

In-situ-solid state UV and DRIFT under vapor exposure phases will be performed to understandthe detailed mechanisms of interactions. Theoretical insights using DFT analysis will bechecked.

Figure 1: Original MOF in the left (1op);2D nano stacked CP (model structure) in the right showing the ligand
chemical structure.

４．Results and Discussions
The water sonication of the 1op gives rise a 2D stacked sheet as observed in FE-SEM (Figure 2). 1H-NMR of
2D stacked sheet(1op-2D) evidenced the complete removal of the DABCO.

Figure 2: Morphology changes upon pillar linker removal from 1op to 1op-2D. Here, 1op-2D showed stacked 2D
sheets like morphology(right) whereas 1op exhibited brick like morphology(left).

The XRPD patterns showed a significant change in lattice structure with maintaining the surface morphology

(Figure 3a) but with a significant change in color. The AFM analysis of 1op-2D-heated exhibited a stacked
sheet nature with a height around 20nm (Figure 3b).

Figure 3: a) XRPD patterns 1op, 1op-2D and 1op-2D-heated indicating dynamic nature of 2D nano CP/ MOF;b) AFM images of 1op-2D-heated indicating stacked nature of 2D nano MOF. Height profile is shown to bearound 20nm.

Temperature programmed desorption (TPD) analysis of CO adsorptive was analyzed with the 1op-2D-heatedphase to elucidate the affinity and binding strength. The adsorption temperature of CO to the sample is -60oC.
We observed the sharp desorption peak at low temperature(-22oC) but no desorption peak was not detected atambient temperature. This indicated the strong affinity of CO to the OMS at low temperature of the adsorbent
1op-2D-heated (Figure 4).

Figure 4: TPD analysis of 1op-2D-heated. Low temperature adsorption was seen to occurred and desorption
peak came at -22oC. No TPD signal was detected at room temperature indicating no adsorption at RT on
1op-2D-heated.

５．Future issues
In future, we are looking forward to making devices that can sense CO selectively using MOF as template. But,for this, stability issues of 2D MOF, nano MOF could be addressed.
６．References
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Brunner, S. Kaskel, Phys. Chem. Chem. Phys. 2010, 12, 117789) B. Manna, H. Yokoi, A. Yamashita, S. Sato, J. Ohyama, M. Kunitake, S. Ida, Chem. Eur. J. 2022, 28,

10.1002/chem.202201665
７．Publications
Related articles:i)B. Manna, M. Asami, N. Hosono, T. Uemura, Chem. 2023, 10.1016/j.chempr.2023.05.041ii) B.Manna,* M.yamaguchi, H.setoyama, M.Fadil, M.Iwai, T.Kida* Manuscript under preparation, 2023
８．Keywords
Metal-organic framework, 2D materials, stacking, Molecular Recogniton