Experimental and computational investigation on interaction mechanism of Rhodamine B adsorption and photodegradation by zeolite imidazole frameworks-8

Abstract

The adsorption of Rhodamine B (Rh.B) was achieved by Zeolite imidazolate framework-8 (ZIF-8) in the dark condition, and the adsorption rate was noticeably increased under visible and UV light irradiations. According to fluorescence spectroscopic studies, ZIF-8 under UV light generated hydroxyl radicals for the effective degradation of Rh.B dyes. These featured mechanisms were systematically elucidated by investigating the zeta potentials of ZIF-8/Rh.B; blue-shifted pi-pi* transition of aromatic system; chemical shift of C-13 NMR spectra; FTIR spectra; and high surface area and abundant mesopores of ZIF-8. Furthermore, the interaction mechanism between Rh.B with ZIF-8 was studied using a density functional theory (DFT) coupled with a spectroscopic technique. Herein, nine ZIF-8 clusters and Rh.B molecules were optimized in aqueous solution using the polarizable continuum model to address the solvation effect. The DFT calculations suggested that pi-pi stacking interactions between the xanthene ring of Rh.B and the imidazole rings of ZIF-8 and electrostatic interactions between electron-deficient Zn centers and Rh.B predominantly contributed to the adsorption of Rh.B on the ZIF-8. The experimental and computations studies provide a new insight for the sophisticated design of ZIF-8 nanostructures for removing organic pollutants efficiently through the combined adsorption and degradation under solar light irradiation.