Chemically Directed Assembly of Photoactive Metal Oxide Nanoparticle Heterojunctions via the Copper-Catalyzed Azide-Alkyne Cycloaddition Click Reaction

Metal oxides play a key role in many emerging applications in renewable energy, such as dye-sensitized solar cells and photocatalysts. Because the separation of charge can often be facilitated at junctions between different materials, there is great interest in the formation of heterojunctions between metal oxides. Here, we demonstrate use of the copper-catalyzed azide-alkyne cycloaddition reaction, widely referred to as click chemistry, to chemically assemble photoactive heterojunctions between metal oxide nanoparticles, using WO3 and TiO2 as a model system. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy verify the nature and selectivity of the chemical linkages, while scanning electron microscopy reveals that the TiO2 nanoparticles form a high-density, conformal coating on the larger WO3 nanoparticles. Time-resolved surface photoresponse measurements show that the resulting dyadic structures support photoactivated charge transfer, while measurements of the photocatalytic degradation of methylene blue show that chemical grafting of TiO2 nanoparticies to WO3 increases the photocatalytic activity compared with the bare WO3 film.