Interactive metal ion–silicon oxidation/reduction processes on fumed silica

摘要: Fumed silica is shown to represent an active oxidation/reduction site. Arresting results demonstrate that the average oxidation state of silicon, at least surface fumed silica, +1 in contrast assumed value +4, thus allowing preparation with desired reduced silicon states without post-synthesis treatment. The nature this interface demonstrated by preparing Fe/silica and Cu/silica materials unprecedented control transition metal state. Supported iron or copper catalysts were prepared contacting anhydrous iron(III) chloride, nitrate nonahydrate, hydrated copper(II) chloride fumed, amorphous (CAB-O-SIL®) dry methanol room temperature. Subsequently, solids vacuum-dried (∼10−3 Torr) temperature for two hours. These solids, particular iron-silica interface, examined X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy, UV-vis diffuse reflectance (DRS), diffraction (XRD), transmission electron microscopy (TEM), colour analysis, water contact angle analysis. No discernible evidence was found indicated formation large crystallites metals. products interaction also investigated using phenanthroline complexation confirm presence Fe(II) ions. This body data showed compelling a portion ions lower while some observed be “oxidized” higher states. ratio over Fe(III) XPS deconvolution spectra matches well theoretical prediction based upon simple reaction between valent Si Fe doping deduced more likely axial position Si–O bond rather than equatorial. It remarkable these transitions ion occurred inherent simplicity technique general many reducible oxides, thus, its use preparations may provide new way controlling various elements.