Influence of the presence of RuO2 on the reactivity of Fe2O3 in the artificial photosynthesis reaction

Abstract

Surface Plasmonic Resonance (SPR) is the oscillation of free electrons on the surface of a metal or metallic particle upon irradiation with light of a certain frequency. The incorporation of Fe₂O₃ (a H₂O oxidising photocatalyst) with plasmonic RuO₂ nanoparticles to form a composite is studied. XRD results show that RuO₂ is formed in the rutile phase while Fe₂O₃ is rhombohedral and also suggests doping of the Fe₂O₃ lattice with Ru atoms in the composite. UV-Vis spectroscopy shows that RuO₂ exhibits a plasmon peak at 511 nm, and CO₂-TPD experiments show that RuO₂ adsorbs and desorbs CO₂. TEM also shows that the RuO₂ particles are spherical, as are the Fe₂O₃ particles with some irregular polyhedra present, too. The composite is a mixture of these two morphologies. The effect of composite formation on the activity of the materials in the artificial photosynthesis reaction is dramatic. Neither RuO₂ nor Fe₂O₃ alone produce significant quantities of gaseous CH₄ or CO products. However, the composite material produces both (as well as generating levels of unidentified adsorbed hydrocarbonaceous species). This reactivity is ascribed to the generation of a heterojunction in the composite material. It is suggested that the generation of holes in Fe₂O₃ is used to provide protons (from H₂O oxidation), and the decay of an SPR response on RuO₂ provides hot electrons, which together with the protons reduce CO₂ to produce CH₄, CO and adsorbed hydrocarbonaceous species.