Sol-gel synthesis and microstructure analysis of amino-modified hybrid silica nanoparticles from aminopropyltriethoxysilane and tetraethoxysilane

Agglomerated amino-modified silica nanoparticles were prepared from a novel Stöber-like precursor system consisting of aminopropyltriethoxysilane (APTES), tetraethoxysilane (TEOS), ethanol, and water where the molar ratio APTES/TEOS was 0, 0.1, 1.0, and 2.0, and the molar ratio H₂O/- SiOC₂H₅ was about 20 to 60, or great excess amounts of H₂O were employed. APTES catalyzed the hydrolysis and condensation of both silanes. ²⁹Si magic angle spinning nuclear magnetic resonance spectra confirmed that the particles consisted of Qⁿ species (Si(OSi)_n(OH)_4-n; n=2, 3, 4) and Tⁿ species (NH₂(CH₂)₃-Si(OSi)_n(OH) _3-n; n=2, 3). The APTES content in the precursor solutions controlled the agglomerating spherical particle size and morphology: 0.1 in the ratio APTES/TEOS led to almost independent spheres of 300-400 nm, while the larger ratios 1 and 2 led to ∼250 and ∼150 nm spheres, respectively, that were largely agglomerated and some were fused to look like peanut-shells. When soaked in Kokubo's simulated body fluid, those amino-modified particles deposited apatite. The mechanisms of particle formation and apatite deposition were discussed in terms of an intraparticle hydrated layer.