Abstract
Three kinds of metal-organic framework materials (MOF-5, MLI-101(Cr), UiO-66) are synthesized, which are based on transition metal (Zn, Cr, Zr) as the center ions, and terephthalic acid (H2BDC) as organic ligand. At the same time, three kinds of MOFs were characterized and analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectrometer (UV-Vis), and fluorescence spectrometer (PL). This article analyzes the fluorescence effects of these three MOFs and investigates the role of different transition metal ions in MOF luminescence. The results show that the ionic radii of Zn2 + and Zr4 + are similar, which are 0.074 nm and 0.072 nm, respectively. MOF-5 and UiO-66 have similar fluorescence effects, both of which emit blue-violet light. However, MIL-101 (Cr) fluorescence centers on Cr3 + with an ionic radius of 0.0651 nm emits yellow-green light, which is different from the foregoing MOFs. Therefore, the ionic radius of the transition metal has an important effect on the fluorescence effect of the MOF. For larger ionic radii, the fluorescence of MOF is generally in the blue-violet square region.
Highlights
Luminescence is a very rare phenomenon, which generally refers to the luminescence ability of the molecule when the ground state electrons in the molecule absorb energy to transition to the excited state and return to the ground state by means of radiative transition[1, 2]
The specific crystal structures of the MOFs are generally determined by powder X-ray diffraction analyses
UV absorption peak of UiO-66 is a broad singlet of 200-350 nm. With it excited at an excitation wavelength of 338 nm, MOF-5 produces a single emission of 400-500 nm
Summary
Luminescence is a very rare phenomenon, which generally refers to the luminescence ability of the molecule when the ground state electrons in the molecule absorb energy to transition to the excited state and return to the ground state by means of radiative transition[1, 2]. Luminescent metal-organic framework materials, due to their design of the main structure of the fusion of the two major properties of porosity and light, can show a relatively rich host-guest interaction, and get a wide range of attention[3,4,5,6]. The metal-organic framework material is a porous material composed of a metal ion or a metal oxygen cluster as a central node and an organic chain-like molecule ligand, which simultaneously possesses an inorganic block and an organic block, which may have luminescent properties, and the combination of inorganic blocks and organic blocks can form unique metal-ligand intramolecular charge transfer to induce new luminescence properties[7,8,9,10]. It is very meaningful to study the effect of transition metals on the
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