| Abstract
| - Ferrihydrite nanoparticles with nominal sizes of 3 and 6 nm were assembled within ferritin, an iron storage protein.The crystallinity and structure of the nanoparticles (after removal of the protein shell) were evaluated by high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and scanning tunnelingmicroscopy (STM). HRTEM showed that amorphous and crystalline nanoparticles were copresent, and the degreeof crystallinity improved with increasing size of the particles. The dominant phase of the crystalline nanoparticleswas ferrihydrite. Morphology and electronic structure of the nanoparticles were characterized by AFM and STM.Scanning tunneling spectroscopy (STS) measurements suggested that the band gap associated with the 6 nm particleswas larger than the band gap associated with the 3 nm particles. Interaction of SO2(g) with the nanoparticles wasinvestigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and results wereinterpreted with the aid of molecular orbital/density functional theory (MO/DFT) frequency calculations. Reactionof SO2(g) with the nanoparticles resulted primarily in SO32- surface species. The concentration of SO32- appearedto be dependent on the ferrihydrite particle size (or differences in structural properties).
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