Mixed-Valence Bimetallic Ce/Zr MOF-Based Nanoarchitecture: A Visible-Light-Active Photocatalyst for Ciprofloxacin Degradation and Hydrogen Evolution.

ABSTRACT

A mixed-valency bimetallic Ce/Zr MOF with Ce3+/Ce4+ ions incorporated and an oxygen vacancy-rich single-component photocatalyst have been designed through the one-step solvothermal route to harness photons from the visible-light spectrum for green energy (H2) generation and ciprofloxacin (CIP) degradation. The one-pot-engineered bimetallic Ce/Zr MOF shows visible-light-active characteristics accompanied by a narrower band gap, along with enhanced exciton separation and superior ligand-to-metal charge transfer (LMCT), due to the presence of an interconvertible Ce3+/Ce4+ ions pair in comparison to its pristine MOF counterpart. The Ce ion insertion led to increase in electron density around the Zr4+ ion, along with generation of some oxygen vacancies (OV), which cumulatively led to the rise in the photo-reaction output. The synthesized UNH (Ce/Zr 11) MOF displayed a boosted photocatalytic H2 production rate of 468.30 µmol h-1 (ACE = 3.51%), which is around fourfolds higher than that of pristine MOFs. Moreover, for CIP photodegradation, the UNH (Ce/Zr 11) shows an enhanced efficiency of 90.8% and follows pseudo-first-order kinetics with a rate constant of 0.0363. Typically, the active species involved in the photo-redox reaction of the CIP photodegradation follows the order hydroxyl radical (OH•) < superoxide radical (O2•-), as confirmed by the TA and NBT tests. Consequently, the bimetallic Ce/Zr MOF can be readily employed as a robust photocatalyst with enhanced tendencies towards CIP degradation and H2 evolution.