Zn(II)/Cd(II)-Based Metal–Organic Frameworks as Bifunctional Materials for Dye Scavenging and Catalysis of Fructose/Glucose to 5-Hydroxymethylfurfural

Abstract

Functional neutral metal-organic frameworks (MOFs) {[M(<b>5OH-IP</b>)(<b>L</b>)]}_<i>n</i> [M = Zn(II) for ADES-<b>4</b>; Cd(II) for ADES-<b>5</b>; <b>5OH-IP</b> = 5-hydroxyisophthalate; <b>L</b> = (<i>E</i>)-<i>N</i>'-(pyridin-3-ylmethylene)nicotinohydrazide) have been synthesized by a diffusion/conventional reflux/mechanochemical method and characterized by various analytical techniques. Crystals were harvested by a diffusion method, and single-crystal X-ray diffraction (SXRD) analysis revealed that an adjacent [M₂(COO)₂]_<i>n</i> ladder chain generates isostructural two-dimensional network motifs by doubly pillaring via <b>L</b>. The bulk-phase purity of ADES-<b>4</b> and ADES-<b>5</b> synthesized by a versatile synthetic approach has been recognized by the decent match of powder X-ray diffraction patterns with the simulated one. Both ADES-<b>4</b> and ADES-<b>5</b> showed selective adsorption of cationic dyes methylene blue (MB), methyl violet (MV), and rhodamine B (RhB) over anionic dye methyl orange (MO) from water with good uptake and rapid adsorption. Utilization of ADES-<b>4</b> as a chromatographic column filler for adsorptive removal of individual cationic dyes as well as a mixture of dyes has been demonstrated from the aqueous phase. Interestingly, ADES-<b>4</b> is reusable with good stability, and it showed a dye desorption phenomenon in methanol. The probable mechanism of cationic dye removal based on insight from structural information and plausible supramolecular interactions has also been explored. Both MOFs also showed efficient catalytic transformation of fructose and glucose into the high-value chemical intermediate 5-hydroxymethylfurfural of industrial significance.