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Description
HKUST-1 is a Cu(II)-based metal–organic framework constructed from copper paddlewheel units interconnected by benzene-1,3,5-tricarboxylate linkers [1]. Its high porosity and accessible coordinatively unsaturated Cu(II) sites support applications in adsorption, heterogeneous catalysis, environmental remediation, and biological or biomedical systems. However, its pronounced affinity toward water and limited hydrolytic stability restrict its use in aqueous and biologically relevant media. Moreover, the conventional synthesis frequently relies on N,N´-dimethylformamide (DMF), a solvent associated with significant toxicological and environmental concerns [2, 3]. This study therefore investigated how replacement or partial substitution of DMF with dimethyl sulfoxide (DMSO), ethanol, and water affects HKUST-1 formation, crystallinity, phase purity, and subsequent structural stability.
HKUST-1 materials were prepared solvothermally from copper(II) nitrate trihydrate and benzene-1,3,5-tricarboxylic acid at 120 °C for 20 h using H₂O/EtOH, DMSO/EtOH, DMSO/H₂O, DMSO/DMF, pure DMSO, and pure DMF solvent systems. After controlled cooling, the crystalline products were isolated, washed thoroughly with methanol, dried in air, and characterized primarily by powder X-ray diffraction (PXRD), supported by Fourier-transform infrared (FTIR) spectroscopy. The PXRD patterns of all samples displayed the characteristic reflections of HKUST-1 and agreed closely with the simulated pattern derived from its single-crystal structure, confirming successful framework formation and preservation of the HKUST-1 topology irrespective of solvent composition. The absence of additional diffraction reflections further indicated high phase purity and showed that neither solvent variation nor retained solvent coordination produced a detectable change in the crystalline framework. FTIR spectroscopy confirmed coordination of the benzene-1,3,5-tricarboxylate linker to Cu(II) through the characteristic carboxylate and Cu–O vibrations. In DMSO-containing samples, an additional sulfoxide stretching band revealed the presence of residual DMSO molecules after methanol washing. The structural stability of the prepared materials was subsequently evaluated in aqueous media over a broad pH range, in biologically relevant phosphate-buffered saline, tris(hydroxymethyl)aminomethane and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffers, physiological saline, and selected organic solvents. These findings demonstrate that solvent modulation, including the use of DMSO-containing systems, enables the preparation of phase-pure HKUST-1 and provides a suitable basis for assessing its applicability in aqueous and biologically relevant environments.
