A microporous, amino acid functionalized Zn(ii)-organic framework nanoflower for selective CO2 capture and solvent encapsulation

Abstract

A new homochiral metal organic framework, {[Zn₄(μ₃-OH)₂(D-2,4-cbs)₂(H₂O)₄]·5H₂O}_n (Zn-CBS), has been solvothermally synthesized using a new chiral amino acid based tricarboxylic acid ligand, (2-((4-carboxybenzyl)amino)succinic acid), H₃(D-2,4-cbs). Zn-CBS was characterized by various techniques like Fourier transform infrared spectroscopy (FTIR), UV-Vis solid-state diffuse reflectance spectroscopy, elemental microanalysis, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray analysis (EDX) and elemental mapping. The nanoflower arrangement in Zn-CBS is clearly seen from the FESEM and TEM images. Its microporous nature is established by the nitrogen adsorption measurements which exhibit a reversible type I isotherm with a BET surface area of 282 m² g⁻¹. Similarly, it shows a reversible type I isotherm for H₂ with an uptake of 0.5 wt% at 77 K. Based on its CO₂ sorption isotherm with an uptake of 85.9 cm³ g⁻¹ at 195 K, a high isosteric heat of adsorption (Q_st) of 35 kJ mol⁻¹ at zero coverage is obtained. This is illustrated by its high potential of selectivity towards CO₂ over N₂ and CH₄ under ambient conditions (298 K and 1 bar). With the help of configurational bias Monte Carlo molecular simulation, this selectivity is explained for an effective interaction between CO₂ and basic amine sites of the framework. The porous nature and functionality of Zn-CBS have also been utilized in encapsulating various small molecules, which is followed by FTIR, TGA and PXRD.