Cerium-based UiO-66 metal-organic framework for synergistic dye adsorption and photodegradation: A discussion of the mechanism

The recently developed Ce-UiO-66 was firstly used as adsorbent and photocatalyst to remove both cationic and anionic dyes. Compared with common Zr-UiO-66, the adsorption performance of Ce-UiO-66 for methylene blue (MB), methyl orange (MO), Rhodamine B (RhB) and acid orange 7 (AO7) increased by 3.02, 3.06, 4.38 and 4.02 times, respectively. Adsorption data was well described by the Langmuir isothermic and Pseudo-second-order kinetic models. And subsequently, RhB and AO7 adsorbed through chemical bonds were almost completely decomposed in 60 min of UV irradiation. The spectral analysis demonstrated that the light absorption range of Ce-UiO-66 is significantly red-shifted, indicating that it has the potential to utilize visible light energy. Moreover, its negative ligand-to-metal charge transfer energy (E-LMCT) accelerates the separation of electron-hole pairs, resulting in effective photolysis of organic dyes. The possible adsorption and photocatalytic mechanism of Ce-UiO-66 for removing organic dyes were proposed. This study provided a facile and feasible approach with excellent adsorption and photocatalytic activity in wastewater treatment.