Authors: Kaihua Wang | Yang Chen | Yi Wang | Jiuhong Chen | Jinping Li | Libo Li
Source: Chinese Science Bulletin (Chinese Version) (article, 2023-09-01)
Field: Chemistry — Inorganic Chemistry

Synthesis of metal organic frameworks based on multiazole ligands for adsorption and separation of acetylene <p indent="0mm">Acetylene (C<sub>2</sub>H<sub>2</sub>) production using the calcium carbide method produces several impurities, such as nitrogen, oxygen, and carbon dioxide. To obtain high-purity acetylene, research regarding the corresponding purification and separation is vital. Metal organic framework (MOF) materials have ultrahigh porosity and easy functionalization. Based on the specific characteristics of their pores, these materials typically possess large surface areas, abundant functional sites, and flexible and tunable pore structures. Thus, these materials demonstrate excellent performance in gas adsorption and separation. This study is based on MOF material construction using multiple nitrogen-containing imidazole ligands. A novel MOF material (Cu(Hptz)), named TYUT-15, was successfully synthesized using copper acetate monohydrate and 5-(4-pyridyl)-1H-tetrazole as raw materials. TYUT-15 has a basic structural unit comprising five-coordinated copper atoms linked to three different ligand units and two bridging oxygen atoms. Moreover, these units form a one-dimensional square channel structure with pore openings of approximately <sc>6.0 Å</sc>×<sc>6.0 Å</sc> and have a BET (Brunauer, Emmett and Teller) specific surface area of approximately <sc>416 m<sup>2</sup>/g.</sc> Considering the unique square-shaped pore structures and multiple nitrogen adsorption sites, TYUT-15 triggers the dipole moment synergistic adsorption among acetylene molecules in the pores, and it improves the adsorption capacity of acetylene under the joint action of host and guest. Single-crystal X-ray diffraction, thermogravimetric analysis, single-component gas adsorption, and a breakthrough test were performed to characterize the sample structure and gas adsorption/separation performance. The results indicate that TYUT-15 is structurally stable and possesses numerous microporous structures. The single-component gas adsorption test reveals that this material has a high C<sub>2</sub>H<sub>2</sub> adsorption capacity. The desorption isotherm of C<sub>2</sub>H<sub>2</sub> exhibits certain hysteresis compared to the desorption isotherms of other gases, indicating a stronger interaction between TYUT-15 and C<sub>2</sub>H<sub>2</sub>. GCMC simulation calculations also support this observation by demonstrating that the adsorption heat of C<sub>2</sub>H<sub>2</sub> is higher than that of CO<sub>2</sub>, providing further evidence of the stronger interaction between TYUT-15 and C<sub>2</sub>H<sub>2</sub>. Furthermore, TYUT-15 exhibits remarkably better adsorption capacity for C<sub>2</sub>H<sub>2</sub> compared to CO<sub>2</sub>/N<sub>2</sub>/O<sub>2</sub>, and its adsorption capacity surpasses those of many previously reported MOF materials, including BSF-1 <sc>(52.6 cm<sup>3</sup>/g),</sc> PCPs-mal <sc>(56.4 cm<sup>3</sup>/g),</sc> NTU-72 <sc>(41 cm<sup>3</sup>/g),</sc> and NbOFFIVE-1-Ni <sc>(53.8 cm<sup>3</sup>/g).</sc> The IAST selectivity calculation results for TYUT-15 at <sc>298 K</sc> and 1 bar for the equimolar gas mixture of C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub> (<italic>V</italic>/<italic>V</italic>=1/1) show that this material exhibits excellent C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub> selectivity (11.3). Moreover, the selectivity is superior to that of most C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub> separation materials, such as JNU-1 (3.6), UTSA-74 (9), DZU-11 (3.6), FJU-112 (4.2), and Ni-pz (10.3). The separation experiment results of the multicomponent mixed gas (C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub>/N<sub>2</sub>/O<sub>2</sub>) show that the retention time of C<sub>2</sub>H<sub>2</sub> is approximately twice that of CO<sub>2</sub>, indicating that TYUT-15 can directly capture C<sub>2</sub>H<sub>2</sub> from the four-component mixed gas of C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub>/N<sub>2</sub>/O<sub>2</sub>. Based on the structure construction of TYUT-15, this study utilizes the material’s special square-shaped cavity characteristics and multiple nitrogen adsorption sites to achieve efficient C<sub>2</sub>H<sub>2</sub> separation from mixed gases. This study proves that using multiazole ligands is feasible for building MOF materials for C<sub>2</sub>H<sub>2</sub> recognition and separation. Acetylene ; Metal-organic framework ; Adsorption ; Separation (statistics) ; Metal ; Chemistry ; Chemical engineering ; Materials science ; Inorganic chemistry ; Organic chemistry ; Computer science ; Engineering Metal-Organic Frameworks: Synthesis and Applications ; Zeolite Catalysis and Synthesis ; Sulfur Compounds in Biology