Abstract
The synthesis of Mobil Composition of Matter 41 (MCM-41) mesoporous silica nanoparticles (MSNs) of controlled sizes and porous structure has been performed at laboratory and pilot plant scales. Firstly, the effects of the main operating conditions (TEOS –Tetraethyl ortosilicate– addition rate, nanoparticle maturation time, temperature, and CTAB –Cetrimonium bromide– concentration) on the synthesis at laboratory scale (1 L round-bottom flask) were studied via a Taguchi experimental design. Subsequently, a profound one-by-one study of operating conditions was permitted to upscale the process without significant particle enlargement and pore deformation. To achieve this, the temperature was set to 60 °C and the CTAB to TEOS molar ratio to 8. The final runs were performed at pilot plant scale (5 L cylindrical reactor with temperature and stirring speed control) to analyze stirring speed, type of impeller, TEOS addition rate, and nanoparticle maturation time effects, confirming results at laboratory scale. Despite slight variations on the morphology of the nanoparticles, this methodology provided MSNs with adequate sizes and porosities for biomedical applications, regardless of the reactor/scale. The process was shown to be robust and reproducible using mild synthesis conditions (2 mL⋅min−1 TEOS addition rate, 400 rpm stirred by a Rushton turbine, 60 min maturation time, 60 °C, 2 g⋅L−1 CTAB, molar ratio TEOS/CTAB = 8), providing ca. 13 g of prismatic short mesoporous 100–200 nm nanorods with non-connected 3 nm parallel mesopores.
Highlights
Since their discovery, mesoporous silica has been broadly employed in many fields thanks to a very convenient and regular porosity showing high specific surface areas
Regardless of the base employed, the resulting silanol groups are responsible of the TEOS condensation; at the expense of having significant variability depending on the base strength and concentration
We found that the nanoparticles obtained at laboratory scale average a circularity of 0.99 ± 0.009, suggesting a shape very similar to a sphere
Summary
Mesoporous silica has been broadly employed in many fields thanks to a very convenient and regular porosity showing high specific surface areas. The application of the developed technology in recent decades has permitted to synthesize a large number of materials (Santa Barbara Amorphous 15 and 16 –SBA-15 and SBA-16–, MCM-41, MCM-48, Fibrous silica nanospheres –KCC-1–, among others) with different pore sizes and geometries (hexagonal, cubic, radial, etc.) and particle morphologies (spheres, rods, layered, etc.). Their applications are consequences of their porous nature and robust chemical composition, which permit their use in many applications: water treatment [1], gas processing [2], and supported catalysis [3], amongst many others. The broader dendritic pore morphology of KCC-1 [29] MSNs is highly affected by the concentration of loaded molecules, oppositely to molecules (that can be a drug, prodrug, fluorophore, etc.) loaded in MCM-41, whose mass transport obeys a Fickian diffusion equation [30]
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