Design of Fe-MOF-bpdc deposited with cobalt oxide (CoOx) nanoparticles for enhanced visible-light-promoted water oxidation reaction

This work spotlights the facile method to deposit cobalt oxide (CoOx) nanoparticles as a cocatalyst on Fe-MOF-bpdc to enhance its photocatalytic activity for water oxidation reaction (WOR) under visible light irradiation to evolve gaseous O-2. Due to the soft conditions needed for the process developed, the framework structure of Fe-MOF-bpdc was maintained even after the deposition of CoOx. The optimized CoOx@Fe-MOF-bpdc composite showed enhanced activity towards visible-light-driven WOR as compared to pristine Fe-MOF-bpdc, the amount of evolved O-2 being increased by about 2 times at the maximum with CoOx loading of 2 wt% as Co metal. Investigations on the wavelength dependence of visible-light-driven WOR on CoOx@Fe-MOF-bpdc revealed that the direct photo-excitation of Fe-oxo clusters within Fe-MOF-bpdc plays an important role to initiate the reaction. Furthermore, it was found that the rate of 2-propanol oxidation reaction, which is a typical two-electron oxidation reaction, was hardly affected by CoOx deposition, suggesting that CoOx acts as a unique hole trapping site and more preferentially catalyse the four-electron oxidation reactions like WOR than the two-electron oxidation reaction.