Synthesis and Structural Characterization of Amine-Functionalized Zinc- and Copper-Based Metal–Organic Frameworks (Zn-BDC-NH2 and Cu-BDC-NH2)

Abstract

Metal–organic frameworks (MOFs) functionalized with pendant amine groups are of growing interest as tunable, low-cost adsorbent platforms because their pore surfaces can be engineered to interact selectively with polar and ionizable pollutants. In this study, amine-functionalized zinc-based (Zn-BDC-NH2 MOF) and copper-based (Cu-BDC-NH2 MOF) metal–organic frameworks were synthesized from 2-aminoterephthalic acid (BDC-NH2) and the corresponding metal nitrate precursors using a simple, conventional solution-based route in ethanol buffered with sodium acetate at near-neutral pH. The two products were characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). FTIR spectra of both materials showed disappearance of the free carboxylic acid C=O stretch of the parent linker and its replacement by an asymmetric/symmetric carboxylate (COO−) doublet, together with new low-frequency bands assigned to Zn–O and Cu–O stretching, confirming metal–carboxylate coordination, while retained C–N bands confirmed that the –NH2 functionality survived framework assembly in both cases. XRD patterns confirmed the crystallinity of both products, with Cu-BDC-NH2 MOF displaying a greater number of well-resolved reflections extending to higher diffraction angles and a smaller Debye–Scherrer crystallite size (≈51 nm) than Zn-BDC-NH2 MOF (≈80 nm). SEM revealed markedly different morphologies: coarse, angular, plate-like aggregates for Zn-BDC-NH2 MOF versus fine, globular, densely packed nanoparticle clusters for Cu-BDC-NH2 MOF. Together, these results establish a reproducible, low-cost synthetic route to two structurally distinct amine-functionalized MOFs bearing free –NH2 groups, providing a structurally characterized platform for subsequent pollutant-adsorption applications.

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