Visible-Light-Active Doped Metal Oxide Nanoparticles: Review of their Synthesis, Properties, and Applications

Metal oxide semiconductors with a bandgap between 2 and 4 eV are an important class of compounds in the electronics industry and for photocatalysis. With the demand for these materials expanding rapidly, especially in the field of photocatalysis, the fabrication of nanoscale metal oxide particles, which increases the surface-to-volume ratio and thereby reduces the materials costs, is an emphasis of current research. For the purpose of photocatalysis, another important quality is the ability to absorb light efficiently. However, due to the wide bandgap of metal oxide semiconductors, the absorptions are limited to the UV region. Conveniently, a wider range of wavelengths and physical properties can be enabled by doping these metal oxide nanoparticles. Furthermore, the synthesis of doped metal oxides in nanoparticle form offers utility in an expansive array of systems, substrates, and dispersion media. However, the reliable synthesis of nanosized colloidal particles of doped metal oxides remains an ongoing challenge for materials researchers. This manuscript gives a concise overview of research conducted regarding the synthesis of visible-light-active doped metal oxide nanoparticles (NPs) and analyzes how doping impacts the optical properties, making them active in the visible to near-infrared regions. The effects of doping on applications are also summarized. Given that the most commonly doped metal oxide materials are TiO2 and ZnO, this review highlights both anion- and cation-doped TiO2 and ZnO nanoparticles. In addition, doped perovskite nanoparticles (e.g., BaTiO3 and SrTiO3) as well as some of the lesser studied doped metal oxide nanoparticle systems are covered. This work is intended to provide not only a broad overview of existing doped metal oxide nanoparticles but also a foundation for the development of semiconducting nanoparticle architectures for next-generation applications.