Controllable Synthesis of Amino-Functionalized Silica\nParticles via Co-condensation of Tetraethoxysilane and (3-Aminopropyl)triethoxysilane

Amino-functionalized\nsilica has attracted a great deal of interest\ndue to its high surface reactivity and potential for diverse applications\nacross various fields. While the classical co-condensation method\nis commonly used to synthesize amino-functionalized silica particles,\nthe mechanism of the reaction between (3-aminopropyl)triethoxysilane\n(APTES) and tetraethoxysilane under different conditions remains unclear,\nleading to unexpected self-nucleation or cross-linking between silica\nparticles and consequently hindering rational control over the extent\nof functionalization. To address this issue, we systematically explored\nthe co-condensation growth mechanism of amino-functionalized silica\nparticles in the Stöber method by investigating the effects\nof APTES concentration and water content on the hydrolysis and condensation\nof silanes. The experimental results revealed that APTES could decrease\nthe rate of hydrolysis/condensation, while the moderate water content\npromoted both the rate of hydrolysis/condensation and the overall\nquality of the silica particles. Consequently, we successfully demonstrated\nthe rational synthesis of amino-functionalized silica particles with\ndiameters ranging from 213 to 670 nm and a nitrogen content of ≤2.8\nwt %. The relationship between the APTES concentration and particle\nproperties exhibited a biphasic trend. At low APTES concentrations\n(≤2.0 mM), the particle size remained stable while the isoelectric\npoint increased rapidly. Further increasing the APTES concentration\nfrom 2.0 to 100.0 mM induced a decrease in particle size due to APTES’s\ninhibitory effect on silica growth, with nitrogen content continuing\nto increase even after the isoelectric point remained unchanged. These\nsilica particles, featuring varying surface amino group densities,\nwere utilized as matrices for loading Au nanoparticles. The resulting\nfunctionalized particles exhibited distinctive catalytic ability in\nthe reduction of 4-nitroaniline, demonstrating significant potential\nfor applications across various fields.