Director of Environmental Chemistry
U.S. Army Corps of Engineers
Dr. Don Cropek is the Director of the Environmental Chemistry Laboratory and the Synthetic Biology Laboratory at the U.S. Army Corps of Engineers, ERDC-CERL, in Champaign, IL. He received his Ph.D. in Analytical Chemistry from the University of Illinois, Urbana-Champaign (UIUC). Dr. Cropek is also affiliated with the Chemistry and Veterinarian Biosciences Departments at UIUC as well as with the Illinois Natural History Survey. Initially, his work addressed short- and long-term environmental and compliance issues at military installations, but has steadily moved to a focus on basic and applied research in biosensing and biomimetics. His group comprises molecular and cell biologists, tissue engineers, microbiologists, polymer and analytical chemists, and civil engineers that study integrated microfluidic systems, tissue engineering, novel environmental sensor design, innovative selective molecular beacons, and advanced oxidative treatment methods for contaminants.
FLASH POSTER PRESENTATION
Nanoscopic Photocatalysts for the Treatment of Organic Water Pollutants
Advances in nanoparticle-based photocatalyst design has opened the door for their widespread use in the removal of water pollutants. Photocatalysts have been used to degrade a wide variety of targets such as explosives and pesticides. The mechanism behind photocatalytic degradation is based on reactive oxygen species (ROS) production from irradiation of photocatalysts. ROS can attack and react with molecular contaminants in the environment to degrade unwanted compounds. Unfortunately, the ROS based photocatalytic reactions are limited by multiple factors, the first of which is ROS lifetime. These radicals only work in a short time domain, typically within few nanometers from the catalyst surface. Second, photocatalytic degradation tends to be non-selective, leading to collateral damage of untargeted species. Third, production of ROS by TiO2 requires illumination by fairly energetic photons. We focused on fabrication of a more sophisticated photocatalytic nanoparticle that overcomes these limitations.
We describe here a sol-gel synthesis and treatment process for TiO2 nanoparticles followed by a surface modification technique for hybrid photocatalysts with desired properties. First, this process results in significantly smaller 5 nm nanoparticles versus the ubiquitous 25nm Degussa P25 TiO2nanoparticles. The smaller nanoparticles have proven more efficient for degrading contaminants through greater specific surface area and higher surface activity, as confirmed by secondary ion mass spectroscopy. X-ray diffraction results showed the TiO2primary crystal phase to be anatase (>85%), which is favorable for organic molecule adsorption and ROS generation.
Greater numbers of surface hydroxyl groups permit facile surface modification for contaminant targeting. Surface modified photocatalysts can attract desired contaminants and also fixate the contaminants closer to the ROS domain at the surface, leading to selective degradation and greater catalytic activity. Spectroscopic surface analysis proves that our TiO2is far more amenable to modification than Degussa nanoparticles. Additionally, preliminary results show that the surface modifications also lead to better ROS production under visible light irradiation where standard TiO2 is far less efficient.
We show the function and activity of our hybrid organic-inorganic TiO2 photocatalysts for contaminant degradation. The benefits of these types of nanoparticles can be implemented in design and engineering a complete contaminant degradation system.