Bi-functional CexZr1−xO2 semiconductor nanoparticles with UV light switch

• CexZr1−xO2 nanoparticles are synthesized with uniform size distribution (∼4 nm).
• CexZr1−xO2 nanoparticles act as photocatalyst under 302 nm, but not 365 nm UV light.
• Zirconium substitution increases the rate of photocatalysis reactions.
• CexZr1−xO2 nanoparticles can completely stop photocatalysis of Aeroxide® TiO2 P25.
• We proposed a mechanism for the unique bi-functionality of CexZr1−xO2 nanoparticles.

A series of CexZr1−xO2 nanoparticles were synthesized by reverse micelle method that acted bi-functionally as either photocatalysts or free radical scavengers. The switch was realized by illumination with light at different wavelengths. Dye degradation method was used to evaluate their photocatalytic activity compared to Aeroxide® TiO2 P25. The free radical scavenging capability was examined by photocatalysis of mixed particles. Our results demonstrated their ability to effectively remove free radicals created by the best photocatalysts in the UV-B region. When the excitation wavelength decreased to 302 nm CexZr1−xO2 nanoparticles acted as photocatalysts. This opens possible applications such as selectively killing of the disease cells with bi-functional particles using light as a switch. Dark sections will be protective to tissues via free radical scavenging while illuminated sections will be free radical formers that may cause cell death. Particle characterization revealed that the bandgap played a major role in the selectivity of light wavelength while bi-functionality should be attributed to the exchange between [Ce3+] and [Ce4+] valence state. We also conclude that ceria must be a superior free radical former at 302 nm compared to titania since it is capable of surpassing its own free radical scavenging ability. Further tuning of the bandgap is predicted to produce bi-functionality with longer wavelengths.

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