An Interpenetrated Anionic MOF Featuring Amide-Functionalized Pores for CO₂ and Methylene Blue Adsorption

A multifunctional metal-organic framework (MOF), {(pbisoixH₂)[Zn(μ₄-BDPFA)]·2DMF·4H₂O}_n (ESOGU-3) (BDPFAH₄: N¹,N⁴-bis(3,5-dicarboxyphenyl)fumaramide, pbisoixH₂: protonated form of 1,4-bis(2-isopropylimidazol-1-ylmethyl)benzene) was synthesized and thoroughly characterized using a variety of analytical techniques. X-ray crystallographic analysis revealed that the anionic 3D framework is constructed from Zn(II) ions coordinated with BDPFA^4- ligands, with the framework's negative charge balanced by protonated pbisoixH₂ counterions. The anionic frameworks interpenetrated each other to form a 2-fold interpenetrating porous 3D framework. Thanks to its porous architecture and stability in water, ESOGU-3 was evaluated for gas and dye adsorption performance. The single-component gas adsorption results showed that ESOGU-3 with a BET surface area of 805.73 m²/g displayed selective CO₂ adsorption (3.82 mmol/g at 100 kPa) over CH₄ and N₂ at 273 K. The enhanced CO₂ adsorption capacity was attributed to amide-functionalized groups within the framework. Furthermore, ESOGU-3, featuring an anionic framework, exhibited selective adsorption toward the smaller cationic methylene blue (MB), achieving a maximum adsorption capacity of 415.78 mg/g. This selectivity is attributed to favorable electrostatic interactions with MB over anionic dyes and size-exclusion effects that limit the adsorption of the larger rhodamine B (RhB) dye.