Surface reactivity of ferrihydrite nanoparticles toward gaseous SO2

COLL 463

Daniel R. Strongin, dstrongi@temple.edu1, Gang Liu, gangliu8@temple.edu1, Sudeep Debnath, suddeb@temple.edu1, Kristian W. Paul, kpaul@UDel.Edu2, F. Marc Michel, fmichel@ic.sunysb.edu3, John B. Parise, john.parise@sunysb.edu4, and Donald Sparks, dlsparks@udel.edu2. (1) Department of Chemistry, Center for Environmental Molecular Science, Temple University, 1901 N. 13th St, Philadelphia, PA 19122, (2) Department of Plant and Soil Sciences, University of Delaware, 152 Townsend Hall, Newark, DE 19716, (3) Department of Geosciences, Center for Environmental Molecular Science, Stony Brook University, Stony Brook, NY 11794-2100, (4) Department of Geosciences, Department of Chemistry, Center for Environmental Molecular Science, Stony Brook University, Stony Brook, NY 11794-2100
Nanoparticles with nominal sizes of 3 and 6 nm were assembled within ferritin, an iron storage protein. The crystallinity and structure of the particles, after removal of the protein coat by heating to 373 K in a reactive ozone environment, were evaluated using electron microscopy and atomic force microscopy (AFM), and scanning tunneling microscopy (STM). Electron microscopy showed that both amorphous and crystalline nanoparticles were present, with the degree of crystallinity improving with increasing size of the particles. The dominant phase of the crystalline nanoparticles was ferrihydrite. The morphology and electronic structure of the nanoparticles supported on Au(111) were characterized using a combination of AFM and STM. Scanning tunneling spectroscopy (STS) measurements of the band gap associated with the 6 nm nanoparticles were consistent with bulk ferrihydrite, whereas a smaller band gap was measured for the 3 nm nanoparticles. The interaction of gaseous SO2 with the ferrihydrite nanoparticles was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and the results were interpreted with the aid of molecular orbital/density functional theory (MO/DFT) frequency calculations. The reaction of SO2 with the nanoparticles resulted in a variety of sulfur oxyanion surface species. In particular, the reaction led to the formation of a mixture of sulfite, bisulfite, sulfate and bisulfate. The relative ratio of sulfur oxyanions and the rate in which they formed was a sensitive function of the ferrihydrite particle size.

Environmental Interfaces
8:30 AM-12:40 PM, Wednesday, 13 September 2006 Sir Francis Drake -- Empire Room, Oral

Division of Colloid & Surface Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006