Co-Pd/BiVO4: High-performance photocatalysts for the degradation of phenol under visible light irradiation

Leaf-like monoclinic BiVO4 and yCo(x)Pd/BiVO4 (CoxPd loading (y) = 0.060 - 0.092 wt%; Co/Pd molar ratio (x) = 0.26 - 1.70) photocatalysts were prepared using the hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. The Co-Pd nanoparticles (NPs) with a size of 4-6 nm were well dispersed on the surface of leaf-like BiVO4. The bimetallic Co-Pd-loaded BiVO4 samples performed much better than the monometallic Co- or Pd-loaded counterpart, with the 0.062Co(1.70)Pd/BiVO4 sample showing the best photo-catalytic performance (the time for 90% phenol removal was 3 h under visible light irradiation) and good photocatalytic stability. The pseudo-first-order reaction rate constants (0.4753 - 0.8367 h(-1) obtained over yCo(x)Pd/BiVO4 were much higher than those (0.0619 - 0.3788 h(-1)) obtained over BiVO4, 0.058Co/BiVO4, and 0.083Pd/BiVO4, with the 0.062Co(1.70)Pd/BiVO4 sample possessing the highest rate constant. In-depth investigations of X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and photoelectrochemical measurements reveal that high dispersion of bimetallic Co-Pd NPs increased the surface Pd-0 and superoxide anion radical concentrations and suppressed the recombination of photoinduced electrons and holes (hence enhancing the photocatalytic activity of yCo(x)Pd/BiVO4). The partial deactivation of the 0.062Co(1.70)Pd/BiVO4 sample after 15 h of three recycle tests was mainly due to the decrease in adsorbed oxygen species concentration. In addition, the possible photocatalytic phenol degradation mechanism over the 0.062Co(1.70)Pd/BiVO4 sample was also proposed. We believe that the BiVO4-supported Co-Pd NPs have promising applications for the photocatalytic elimination of organic pollutants in wastewater.