X-RAY PHOTOELECTRON-SPECTROSCOPY AS A TOOL TO DIFFERENTIATE SILICON-BONDING STATE IN AMORPHOUS IRON-OXIDES

An x-ray photoelectron spectroscopy (XPS) study was conducted to: (i) compare the Si (2p) and O (1s) peaks of selected Si-containing minerals, and (ii) evaluate the application of XPS in identifying probable Si-bonding environments in Si-containing ferrihydrites. For silica gel, the Si (2p) and O (1s) XPS peaks occurred at 104.0 and 534.2 eV, respectively; with biotite, these peaks occurred at 102.8 and 532.4 eV. The Si (2p) XPS peak for silicate adsorbed on ferrihydrite occurred at 100.9 eV. For ferrihydrite samples treated with an excess of Si (≥75 g kg-1), peaks attributable to a separate Si-rich phase were identified on decomposition of the Si (2p) and O (1s) XPS peaks. In the case of ferrihydrite coprecipitated with silicate at Si/Fe molar ratios ≥0.10, the Si (2p) peak occurred at approximately 102.8 eV, which is a position similar to that observed for layer silicates, indicating the possible presence of Si, i.e., the presence of -Fe-O-Si- bonds, within the ferrihydrite structure. -from Authors