Influence of sulfate ions on the atomic-scale structure of β-FeOOH

Ordinary X-ray diffraction measurements by Mo K alpha radiation and anomalous X-ray scattering (AXS) measurements by synchrotron radiation below Fe K absorption edge were used for characterizing the atomic-scale structure of beta-FeOOH particles with and without sulfate ions. Fourier-transform infrared spectroscopy (FT-IR) was also used for analyzing a change of the bonding structure in the beta-FeOOH particles by addition of sulfate ions. The realistic atomic-scale structures of the beta-FeOOH particles with and without sulfate ions were estimated by fitting both the ordinary and environmental interference functions with model calculation using the reverse Monte Carlo (RMC) simulation technique. The results showed that the linkages of FeO6 octahedral structural units in the beta-FeOOH particles are distorted by addition of sulfate ions, although the structure of the beta-FeOOH particles with and without sulfate ions is fundamentally similar to the ideal beta-FeOOH structure. The structural distortion in the beta-FeOOH particles with sulfate ions is likely to arise from the incorporation of sulfate ions. The atomic-scale structures visualized for these beta-FeOOH particles were discussed coupled with the bonding structure observed in FT-IR.