Callens, Freddy

Damien, Hylke

Maes, Kwinten

Nevjestic, Irena

Vrielinck, Henk

Maes, KwintenUGent0000903532748020020235959797586653940000-0003-1668-06211F8F5098-F0EE-11E1-A9DE-61C894A0A6B4

Nevjestic, IrenaUGent000131218465802001696829975553698220830D98E8-4280-11E3-A709-765F10BDE39D

Damien, Hylke000150898755502C3302-5675-11E5-B03A-F334B5D1D7B1

Vrielinck, HenkWE048010010849420000-0003-4861-9630F503F252-F0ED-11E1-A9DE-61C894A0A6B4

Callens, FreddyUGent8010005040539722581271590000-0002-6504-6945F411202C-F0ED-11E1-A9DE-61C894A0A6B4

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Effects of gas exposure on the EPR spectrum of V(IV) doped into the metal-organic framework MIL-53(Al)

Ghent University Academic Bibliography

Effects of gas exposure on the EPR spectrum of V(IV) doped into the Metal-Organic Framework MIL-53(Al). K. Maes, I. Nevjestić, H. Damien, H. Vrielinck, F. Callens Ghent University, Dept. of Solid State Sciences, Krijgslaan 281/S1, 9000 Gent, Belgium Kwinten.maes@ugent.be Metal-Organic Frameworks (MOFs) are ordered porous crystalline materials constructed of metal ions connected by organic linkers. Because of their many interesting properties, a diverse scale of applications are being explored (e.g., catalysis, gas adsorption, separation and storage). For the research presented here we use MIL-53(Al), which consists of Al(OH) chains linked together by BDC (1,4-benzenedicarboxylate) creating a lattice with large one-dimensional pores. After activation (emptying the pores) the structure exhibits the breathing phenomenon: the framework can reversibly change from an open (large pore) to a closed (narrow pore) structure depending on conditions like temperature and pressure. EPR spectroscopy using V(IV) as a paramagnetic probe is able to distinguish between the large pore and the narrow pore state of V-doped MIL-53(Al). Recently the g and 51V A tensors for these dopant ions were determined in both states and the transition between both was investigated using EPR and XRD measurements.1-3 In the present study we investigate the changes to the structure when introducing different gases at various temperatures. First, the effect of air on the large pore structure was studied. Increasing air pressure leads to a clear broadening of the spectrum. Measuring the temperature dependence of this broadening showed increase of the linewidth with decreasing temperature, following an Arrhenius behaviour with an activation energy of 12 kJ/mole. Secondly, we found that exposure of the large pore structure to CO2 causes most of the sample to convert to the narrow pore state, with a non-negligible part still in the large pore state. Exposing the narrow pore state to CO2 and O2 has no effect on the EPR spectrum, which suggests that these gases cannot access the pores for this state. Figure 1: X-band EPR spectrum of V-doped MIL-53(Al) before and after exposure to CO2. The structure started in the large pore state and changed to mostly the narrow pore state. 1. I. Nevjestic, H. Depauw, K. Leus, V. Kalendra, I. Caretti, G. Jeschke, S. Van Doorslaer, F. Callens, P. Van Der Voort and H. Vrielinck, Chemphyschem 16 (14), 2968-2973 (2015). 2. I. Nevjestić, H. Depauw, K. Leus, G. Rampelberg, C. A. Murray, C. Detavernier, P. Van Der Voort, F. Callens and H. Vrielinck, The Journal of Physical Chemistry C 120 (31), 17400-17407 (2016). 3. I. Nevjestic, H. Depauw, P. Gast, P. Tack, D. Deduytsche, K. Leus, M. Van Landeghem, E. Goovaerts, L. Vincze, C. Detavernier, P. Van Der Voort, F. Callens and H. Vrielinck, Phys Chem Chem Phys 19 (36), 24545-24554 (2017). 300 350 400Field (mT) MIL-53(Al) 1% V vacuum MIL-53(Al) 1% V CO2 1,4 bar

https://biblio.ugent.be/publication/8567059/file/8567060

Effects of gas exposure on the EPR spectrum of V(IV) doped into the metal-organic framework MIL-53(Al)

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Ghent University Academic Bibliography