Structural changes and CO2 adsorption performance in Zn2(BDC)2DABCO metal-organic framework under high-pressure and high-temperature conditions

As a class of novel hybrid porous materials, metal-organic frameworks (MOFs) exhibit highly diversified and reversible CO 2 adsorption capabilities. Zn 2 (BDC) 2 DABCO (BDC = 1,4-benzenedicarboxylate; DABCO = triethylenediamine) attracted extensive attentions as a flexible MOF, which exbibits structural changes stimulated by the interactions with different guests and the variation of temperature or pressure. Although the activated Zn 2 (BDC) 2 DABCO was reported to be amorphized at 0.1 GPa in non-penetrating pressure transmitting medium previously, this work successfully investigated the structural changes of this MOF at higher pressure by in situ synchrotron powder X-ray diffraction and Raman spectroscopies. An irreversible phase transition was observed at a pressure < 0.36 GPa, which was attributed to the flexibility of the BDC linker and Zn 2 paddle-wheel unit. Furthermore, as the CO 2 adsorption performance of MOFs could be enhanced by pressure induced structural changes, the CO 2 adsorption of Zn 2 (BDC) 2 DABCO was investigated under high pressure using in situ Raman and Fourier transform inferred spectroscopies. Continuous contraction of unit cell without obvious phase transition was observed, accompanied by the emergence of two CO 2 adsorption sites above 0.79 GPa. The CO 2 -loaded Zn 2 (BDC) 2 DABCO was also studied at 1.13 GPa with increasing temperature to the melting point of CO 2 where CO 2 adsorption enhancement was observed. These findings provide new insights into the mechanisms of pressure stimulated structural changes and the CO 2 adsorption of MOFs across a broad pressure–temperature range.