Abstract
Titanium dioxide is a well-known photooxidation catalyst. It will oxidize mercury in the presence of ultraviolet light from the sun and oxygen and/or moisture to form mercuric oxide. Several companies manufacture self-cleaning windows. These windows have a transparent coating of titanium dioxide. The titanium dioxide is capable of destroying organic contaminants in air in the presence of ultraviolet light from the sun, thereby keeping the windows clean. The commercially available self-cleaning windows were used to sequester mercury from oxygen–nitrogen mixtures. Samples of the self-cleaning glass were placed into specially designed photo-reactors in order to study the removal of elemental mercury from oxygen–nitrogen mixtures resembling air. The possibility of removing mercury from ambient air with a self-cleaning glass apparatus is examined. The intensity of 365-nm ultraviolet light was similar to the natural intensity from sunlight in the Pittsburgh region. Passive removal of mercury from the air may represent an option in lieu of, or in addition to, point source clean-up at combustion facilities. There are several common band-gap semiconductor oxide photocatalysts. Sunlight (both the ultraviolet and visible light components) and band-gap semiconductor particles may have a small impact on the global cycle of mercury in the environment. The potential environmental consequences of mercury interactions with band-gap semiconductor oxides are discussed. Heterogeneous photooxidation might impact the global transport of elemental mercury emanating from flue gases.
Acknowledgments
Dr. Robert Thompson of Parsons Project Services, Inc. determined the mercury content of the titanium dioxide powders and glasses. Dr. John Baltrus of the United States Department of Energy deduced the form of mercury on the titanium dioxide powders and glasses. Evan Granite thanks Professor Klaus Lackner of Columbia University and Dr. Albert A. Presto of Carnegie Mellon University for their excellent input on the mass transfer limitations for both passive clean-up of pollutants from the air, and photo-catalytic transformations of mercury within the atmosphere. The outstanding work by Professor Pratim Biswas of Washington University in St. Louis on capture of mercury from flue gas by titanium dioxide provided inspiration to the authors.
Disclaimer
Reference to any specific commercial product or service is to facilitate understanding and does not imply endorsement by the United States Department of Energy.
