Rational synthesis of isomorphic rare earth metal–organic framework materials for simultaneous adsorption and photocatalytic degradation of organic dyes in water

In recent years, the treatment of dye wastewater has attracted widespread attention. Metal-organic frameworks (MOFs) adopt ordered porous structures and abundant active sites, which endorses them promising photocatalysts for the degradation of organic pollutants. In this work, two rare earth MOFs were successfully synthesized by solvothermal method from the reaction of of Eu3+ and Tb3+ salts with an aromatic tetracarboxylic acid H4TPTC (3,3',5,5'-terphenyl tetracarboxylic acid). X-ray single crystal diffraction indicated that the isostructural MOFs exhibited unique di-nuclear [Eu2(COO)4] or [Tb2(COO)4] clusters to construct three-dimensional coordination frameworks with solvent accessible channels along the [110] direction. These two MOFs had good thermal stability up to 400 °C and pH stability in the pH range of 3-9. The negative Zeta potential on the surface of these two complexes were conducive to the selective adsorption and degradation of cationic and neutral dyes, especially the high removal rate of large RhB molecules. For the photocatalytic degradation, mechanism studies showed that ·OH and ·O2- enhanced the sensitization of dyes and the separation of photogenerated carriers, and promoted the efficiency of photocatalytic degradation. This work provides two isomorphic rare earth MOFs adsorbents as well as photocatalysts for the purification of dye wastewater.