Selective cationic dye sorption in water by a two-dimensional zinc-carboxylate coordination polymer and its melamine-formaldehyde foam composite

Abstract

A new two-dimensional zinc(II) coordination polymer of 5-aminoisophtalic acid (H2AIP), namely [Zn(AIP)(DMSO)]n (Zn-CP), has been successfully prepared via conventional heating at 100 ​°C in a (2:1) dimethyl sulfoxide/ethanol solvent mixture. The compound has been characterized by FT-IR spectroscopy, elemental and thermogravimetric analyses, powder and single-crystal X-ray diffraction techniques. Crystal structure of Zn-CP shows the presence of neutral layers of composition Zn(AIP) and 63-hcb topology, which are decorated only on one side with dangling DMSO molecules. Moreover, the composite Zn-CP@Foam has also been fabricated growing Zn-CP crystals on the 3D porous structure of a melamine-formaldehyde foam (MF) by immersion of pieces of MF in the precursor solution of the coordination polymer. Both Zn-CP and Zn-CP@Foam materials have been studied for the adsorption in water of cationic dyes, such as Crystal Violet (CV), Victoria Blue (VB) and Malachite Green (MG), and anionic dyes, such as Sunset Yellow (SY), Congo Red (CR) and Aniline Blue (AB). Results show selective sorption of cationic dyes only, with faster and larger adsorption capacity observed for the porous composite material which has an adsorption capacity for Victoria Blue (VB) (102 ​mg ​g−1) more than twice larger than that found for pristine Zn-CP powder (48 ​mg ​g−1). This selectivity towards cationic dyes is attributed to electrostatic interactions between the cationic dye molecules and the negatively charged surface of the zinc coordination polymer, which shows a zeta potential of −13.7 ​mV. Moreover, dye adsorbed Zn-CP and Zn-CP@Foam can be regenerated by immersion in a water/acetic acid solution (1:1) and reused with almost the same efficiency.