BiVO₄-Based Systems Magnetron Sputtered with Silver Nanoparticles for the Artificial Photosynthesis Reaction

The incorporation of Ag nanoparticles onto BiVO₄ (a known H₂O oxidising photocatalyst) through magnetron sputtering to form a composite was studied. ICP-OES results showed that the loading of Ag on BiVO₄ was below 1% in all cases. UV-Vis DRS and CO₂-TPD analyses demonstrated that upon incorporation of Ag onto BiVO₄, an increase in the extent of visible light absorption and CO₂ adsorption was seen. TEM imaging showed the presence of Ag particles on the surface of larger BiVO₄ particles, while XRD analysis provided evidence for some doping of Ag into BiVO₄ lattices. The effect of the composite formation on the activity of the materials in the artificial photosynthesis reaction was significant. BiVO₄ alone produces negligible amounts of gaseous products. However, the Ag-sputtered composites produce both CO and CH₄, with a higher loading of Ag leading to higher levels of product formation. This reactivity is ascribed to the generation of a heterojunction in the composite material. It is suggested that the generation of holes in BiVO₄ following photon absorption is used to provide protons (from H₂O oxidation), and the decay of an SPR response on the Ag NPs provides hot electrons, which together with the protons reduce CO₂ to produce CH₄, CO, and adsorbed hydrocarbonaceous species.