Adsorption performance of mixed metal-alkali metal-organic frameworks
Publication Date
December 12, 2023
Creator
Abstract
This work describes the solvothermal synthesis of zinc and lanthanum-based mixed metal-alkali metal-organic frameworks (MOF) with carboxylate linkers with benzene 1,4 dicarboxylic acid (H2BDC), 1,3,5-tris(4-carboxyphenyl) benzene (BTB), and 2,6-Naphthalenedicarboxylic acid (H2NDC). The successful synthesis of Zinc-Potassium (ZnKMOF), Zinc-Lithium (ZnLiMOF), and Lanthanum-Potassium (LaK) MOF was affirmed by several analytical techniques such as XRD, TGA, SEM, and EDX in this research. ZnKBTB MOF is a straightforward type 1 isotherm for Nitrogen and Hydrogen, indicating microporosity (width < 2nm) with a BET surface area around 200 m2 g-1 and pore volume ~ 0.17 cm3. While ZnKBTB and ZnLiBTB displayed strong CO2 adsorption capacity depicted by a concave curve at all temperature and relative pressure ranges, ZnKBDC and ZnKNDC MOFs displayed linear plot associated with Type III Isotherm indicating non-porosity for the adsorption of H2, N2 and CH4 gases at both 273K and 298K. Interestingly, ZnKBDC and ZnKNDC MOFs showed minimal Type I adsorption (described by a lower concave curve) at 77 K. We then deduced that the adsorption in this experiment is dependent on the ligand employed and on the probability of pore channel blockage by the alkali metal in the MOF. The study of the trend in CO2/N2 selectivity shows that the higher the CO2 adsorption capacity in both ZnKBTB and ZnLiBTB MOFs, the lower the CO2/N2 selectivity because ZnLiBTB possesses higher CO2/N2 selectivity of 32.32 while ZnKBTB was 24.13 at 800 mmHg and 298 K. Therefore, the adsorption capacity for CO2 increased in the order of K+>Li+. The heat of adsorption, Qst, falls in a range of 30.83 to 19.85 kJ/mol at high loading conditions (ZnKBTB; 34.38 - 30.83 kJmol-1 and ZnLiBTB; 29.17 kJmol-1 – 19.85 kJmol-1), thus exhibiting our MOFs with features favouring high loading of CO2 at low pressure and high heat of adsorptions, which are comparable to values attained by MOFs having open metal sites. The isosteric heat for CO2 on LaKBDC MOF shows that the carbon dioxide adsorption (CO2) on LaKBDC MOF exhibits a decreasing trend with higher uptake (thus higher pressure); this is common to all potassium-based MOFs studied. Selectivity studies show LaKBDC showed similar selectivity for CO2/N2 and CO2/H2 around 13.9 while displaying higher selectivity for CO2/CH4, thus predicting its useful separation potential for CO2/CH4.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Chemistry
eprints ID
76373
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Olukayode Adedayo Babarinde [14315759] PhD Thesis September 2023 AA.pdf
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