A Stable Broad-Range Fluorescent pH Sensor Based on Eu3+ Post-Synthetic Modification of a Metal–Organic Framework

Via a facile and nondestructive post-synthetic modification (PSM) method applied to the metal–organic framework UiO-67-bpy (bpy = 2,2-bipyridine-5,5′-dicarboxylic acid), the lanthanide-functionalized hybrid material UiO-67-bpy-Eu-BTA (BTA = benzoyltrifluoroacetone) is prepared. The pristine neutral framework retains its high crystallinity and regular morphology after PSM. In addition, the hybrids display an exponential correlation between the luminescence intensity and the pH value of aqueous solutions over a broad range (from 1.05 to 9.85). Also, the stability, reusability, and luminescence response speed of the sensor have been studied to evaluate its performance. The possible sensing mechanism is also involved. These findings demonstrate that UiO-67-bpy-Eu-BTA has enormous potential in wide-range luminescent pH sensing in aqueous solutions.