Paddlewheel SBU based Zn MOFs: Syntheses, Structural Diversity, and CO<sub>2</sub> Adsorption Properties
oleh: Ting-Ru Lin, Cheng-Hua Lee, Yi-Chen Lan, Shruti Mendiratta, Long-Li Lai, Jing-Yun Wu, Kai-Ming Chi, Kuang-Lieh Lu
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2018-12-01 |
Deskripsi
Four Zn metal⁻organic frameworks (MOFs), {[Zn<sub>2</sub>(2,6-ndc)<sub>2</sub>(2-Pn)]·DMF}<i><sub>n</sub></i> (<b>1</b>), {[Zn<sub>2</sub>(cca)<sub>2</sub>(2-Pn)]·DMF}<i><sub>n</sub></i> (<b>2</b>), {[Zn<sub>2</sub>(thdc)<sub>2</sub>(2-Pn)]·3DMF}<i><sub>n</sub></i> (<b>3</b>), and {[Zn<sub>2</sub>(1,4-ndc)<sub>2</sub>(2-Pn)]·1.5DMF}<i><sub>n</sub></i> (<b>4</b>), were synthesized from zinc nitrate and <i>N</i>,<i>N</i>′-bis(pyridin-2-yl)benzene-1,4-diamine (2-Pn) with naphthalene-2,6-dicarboxylic acid (2,6-H<sub>2</sub>ndc), 4-carboxycinnamic acid (H<sub>2</sub>cca), 2,5-thiophenedicarboxylic acid (H<sub>2</sub>thdc), and naphthalene-1,4-dicarboxylic acid (1,4-H<sub>2</sub>ndc), respectively. MOFs <b>1</b>⁻<b>4</b> were all constructed from similar dinuclear paddlewheel {Zn<sub>2</sub>(COO)<sub>4</sub>} clusters and resulted in the formation of three kinds of uninodal 6-connected non-interpenetrated frameworks. MOFs <b>1</b> and <b>2</b> suit a topologic 4<sup>8</sup>·6<sup>7</sup>-net with 17.6% and 16.8% extra-framework voids, respectively, <b>3</b> adopts a pillared-layer open framework of 4<sup>8</sup>·6<sup>6</sup>·8-topology with sufficient free voids of 39.9%, and <b>4</b> features a <b>pcu</b>-type pillared-layer framework of 4<sup>12</sup>·6<sup>3</sup>-topology with sufficient free voids of 30.9%. CO<sub>2</sub> sorption studies exhibited typical reversible type I isotherms with CO<sub>2</sub> uptakes of 55.1, 84.6, and 64.3 cm<sup>3</sup> g<sup>−1</sup> at 195 K and <i>P</i>/<i>P</i><sub>0</sub> =1 for the activated materials <b>1′</b>, <b>2′</b>, and <b>4′</b>, respectively. The coverage-dependent isosteric heat of CO<sub>2</sub> adsorption (<i>Q<sub>st</sub></i>) gave commonly decreased <i>Q<sub>st</sub></i> traces with increasing CO<sub>2</sub> uptake for all the three materials and showed an adsorption enthalpy of 32.5 kJ mol<sup>−1</sup> for <b>1′</b>, 38.3 kJ mol<sup>−1</sup> for <b>2′</b>, and 23.5 kJ mol<sup>−1</sup> for <b>4′</b> at zero coverage.