Exploring 3,4-dihydroxybenzaldehydefunctionalized MIL-88A(In:Fe) towards the efficient adsorption of...

The incorporation of metal-organic frameworks (MOFs) towards the removal of organic pollutants has triggered increasing research over the past decade. This study investigated the impact of binary metal sites (Fe:M, where M = Co, Cd, Cu, Mn, Mg, Ni, and In) and secondary organic ligands (malonic acid, cinnamaldehyde, pyrrole-2-carboxylic acid, 3,4-dihydroxybenzaldehyde, and diethylenetriaminepentaacetic acid) on the MIL-88A material. For the first time, a flexible 3,4-dihydroxybenzaldehyde-In/Fe-MOF was used for the adsorption of tetracycline hydrochloride. Importantly, the adsorption was hinged on (i) the pore-filling effect of the MIL-88A mesoporous configuration and (ii) the chemical interactions (hydrogen bonding, electrostatic attraction, and pi-pi interactions) that were both enhanced by the In metal centers and the 3,4-dihydroxybenzaldehyde ligand. TCH adsorption stood at 97.88 %, with an adsorption capacity of 475.42 mg/g (towards 300 mg/L TCH) despite its low BET surface area of 15.48 m²/g. Notably, a wide adsorption working range was observed from pH = 2 (81.70 %, 490.21 mg/g) to even pH = 11 (93.35 %, 560.09 mg/g). Also, the kinetic studies correlated with both pseudo-second-order and pseudo-first-order fittings. Fe:In(25:75)-5 %-dhba had favorable adsorption even after five cycles. This work presents an outstanding MOF needed for the effective elimination of organic water pollutants.