Microwave-Assisted Synthesis of Bismuth Niobate/Tungsten Oxide Photoanodes for Water Splitting

Abstract

We report the microwave-assisted synthesis of heterojunctions based on bismuth niobate (BiNbO4) and tungsten oxide (WO3). These architectures have been used as photoanodes for water splitting under simulated AM1.5G solar light. We show for the first time that by controlling temperature and irradiation power it is possible to tune the fraction of orthorhombic and triclinic phases in BiNbO4 nanoparticles, with strong consequences on the photocatalytic capabilities of the resulting heterojunctions. XRD patterns show that lower temperatures and irradiation power favor the formation of triclinic BiNbO4 arrangements, whereas the morphology of WO3 films is straightforwardly controlled by the addition of weak acids in the reactional medium that enable the formation of wrinkle-rod or cube-like particles. The orthorhombic symmetry of BiNbO4 is shown to decrease the bandgap energy, whereas wrinkle-rod nanoparticles of WO3 provides a rough surface that enhances the interaction between the semiconductors. This strategy leads to heterojunction able to generate photocurrent densities more than one order of magnitude higher than of bare WO3 film. Our findings demonstrate that the microwave-assisted route is a very attractive alternative to directly control crystalline structure and ultimately the photocatalytic performance of bismuth niobate- and tungsten oxide-based heterojunctions.