Post-synthetic modification approach for tandem functionalization of a 2D-layered Zn-coordination polymer: from exfoliated nanosheets to a 3D supramolecular structure with enhanced dye adsorption efficiency

Abstract

Post-synthetic modification (PSM) represents a promising approach for enhancing the properties of coordination polymers (CPs) and MOFs by introducing new functional groups and tailored surface chemistry. This study details a tandem PSM of a 2D Zn-coordination polymer (parent compound), [Zn(AIP)(DMSO)]_n (Zn-CP), to generate various functionalized structures. In the first step of PSM, Zn-CP-df was created through the removal of coordinated DMSO molecules from [Zn(AIP)(DMSO)]_n to form Lewis acid sites. Subsequently, the stacked layers of Zn-CP-df were exfoliated to Zn-CP-df-ex nanosheets. In the second step, Zn-CP-df was reacted with ethylenediamine (en) to generate a multilayered structure of [Zn(AIP)(en)]_n (Zn-CP-en), decorated with Lewis-base sites. In the third PSM step, the nanosheets were functionalized with Brønsted-acid groups (–SO₃H moieties) via the reaction of Zn-CP-en with 1,3-propanesultone (ps) to form [Zn(AIP)(en)(ps)]_n (Zn-CP-en-ps). In parallel with step two, Zn-CP-df layers were cross-linked by 1,3-diaminopropane (dap) to form a 3D supramolecular framework, [Zn(AIP)(dap)]_n (Zn-CP-dap), exhibiting distinct properties compared to the Zn-CP-en. The structures of the functionalized compounds were characterized by FT-IR, PXRD, CHNS, zeta-potential, FESEM, and TEM analyses. The adsorption performance of all synthesized compounds was evaluated for both anionic and cationic dyes to elucidate the structure–property relationships between the post-synthetic modifications and dye adsorption efficiency.