The surprising oxidation state of fumed silica and the nature of water binding to silicon oxides and hydroxides

Wang TH; Gole JL; White MG; Watkins C; Street SC; Fang ZT; Dixon DA

Chemical Physics Letters, Vol.501, No.4-6, 159-165, 2011

DOI10.1016/j.cplett.2010.11.013 Export Citation

The surprising oxidation state of fumed silica and the nature of water binding to silicon oxides and hydroxides

Wang TH, Gole JL, White MG, Watkins C, Street SC, Fang ZT, Dixon DA

X-ray photoelectron spectroscopy (XPS) data demonstrate that the average formal oxidation state of silicon in fumed silica (CAB-O-SIL (R)) is +1 as opposed to the usual +4. Electronic structure calculations on model molecular clusters and comparison with XPS data for silicon compounds in known oxidation states suggest less hydrophilic character for CAB-O-SIL (R) than the oxides of silicon with Si in an average formal +3 or +4 oxidation state. Once the +3 oxidation state is formed, water on the fumed silica surface facilitates the ready conversion of the Si in an average +3 oxidation state to an average + 4 oxidation state. (C) 2010 Elsevier B.V. All rights reserved.