Increasing access to clean drinking water is a global sustainability goal1. Solar energy can disinfect water through the generation of reactive oxygen species (ROS), but current methods utilize ultraviolet (UV) light—only 5% of the solar spectrum—and make use of particulate suspensions which must be removed from the water post-disinfection. Visible-light-driven ROS generation is a promising alternative, but immobilized photocatalyst with strong visible light absorption, high quantum efficiency and proper redox energy positions are necessary.
Here, we report on the fabrication and characterization of metal-semiconductor-metal plasmonic photocatalysts for visible-light-driven water disinfection. Our plasmonic photocatalysts are immobilized on glass supports and composed of Au nanoparticles deposited on a thin ZnO film with an Al sub-layer for optical reflection and plasmonic coupling. These structures are broadband absorbers which currently capture 30% of the solar spectrum centered around 600 nm, though simulations show 90% absorbance is achievable through improved fabrication. We discuss the enhancement of visible-light absorbance and hot-electron production through our design.
We test the ability of our plasmonic photocatalysts to generate ROS and disinfect pathogens in 25 mL batch systems under UV filtered AM1.5G illumination. Our immobilized photocatalysts produce >5μM H2O2 in 20 minutes and show greater than 3.5 log (>99.95%) reduction of E. coli in water. We also demonstrate continuous water disinfection in the dark through the use of ZnO and propose the mechanism through which this occurs. We will present a potential reaction pathway for ROS generation and explore the impact of individual ROS (i.e., H2O2, ●OH, and O2-) on water disinfection. Lastly, we will discuss the performance and stability of our plasmonic photocatalysts, and the improvements necessary to realize real-world application.
1) World Health Organization. 2012. Progress on Drinking Water and Sanitation. Geneva, Switzerland: WHO Press.