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

A multifunctional metal-organic framework (MOF), {(pbisoixH2)[Zn(mu 4-BDPFA)]<middle dot>2DMF<middle dot>4H2O} n (ESOGU-3) (BDPFAH4: N 1,N 4-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 BDPFA4- 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.