title: Differentiating and characterizing geminal silanols in silicas by (29)Si NMR spectroscopy.
abstract: Single and geminal hydroxyl species in silicas have been characterized using solid-state (29)Si NMR spectroscopy. Differentiating hydroxyl types is important in understanding their roles in chemical toxicity mechanisms for inhaled crystalline silicas responsible for silicosis. (1)H-(29)Si cross polarization NMR spectroscopy has been employed to obtain (29)Si NMR chemical shift data and signal accrual and relaxation characteristics. Spectral deconvolution is used to examine relative single and geminal hydroxyl resonance areas for a series of representative silicas and silica gels. Silicon-containing materials examined include 1878a quartz, and 1879a cristobalite from the National Institute for Science and Technology, kaolin, and several widely used respirable silicas and silica gels. Geminal hydroxyls were observed in every case, with relative resonance areas accounting for 21-65% of total hydroxyl signals. Factors affecting relative areas measured as a function of contact time, relaxation, and surface area are discussed. Subsequent (29)Si and (31)P NMR studies of a silica coated with various sodium hydrogen phosphates show preferential single silanol-phosphate interaction for basic phosphates, and oligomerization products for acidic phosphates. Geminal hydroxyl resonance areas displayed significant error (4-17%) for low surface area silicas, limiting this method to studies exhibiting major changes in chemical or spectroscopic properties.
authors.affiliation: National Institute for Occupational Health and Safety, 1095 Willowdale Road, M/S 3030, Morgantown, WV 26505, United States. DMurray@cdc.gov
authors.forename: David K
authors.initials: DK
authors.lastname: Murray
mesh_terms: D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy; D012821:Silanes / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*
chemical_list: D007554:Isotopes; D012821:Silanes; C082343:silanol; D012825:Silicon