Synthesis of silica spheres with neutral and ionic amphiphiles and their interaction with photosensitive spiropyrans

• Published in: Microporous and mesoporous materials Vol. 118; no. 1; pp. 121 - 133
• Main Authors: Domínguez, José M., Rosas, Raúl, Aburto, Jorge, Terrés, Eduardo, López, Alfonso, Martínez-Palou, Rafael
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-02-2009; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Imidazoline; Mesoporous silica spheres; Microwave-assisted synthesis; Neutral amphiphiles; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Porous materials; Single-particle analysis; Spiropyrans; Surface physical chemistry; Neutral amphiphiles; Spiropyrans; Mesoporous silica spheres; Single-particle analysis; Imidazoline; Microwave-assisted synthesis; Binary compound; High resolution; Support; Microwave; Alcohol; Silicates; Surfactant; Ionic surfactant; Density; Porous material; Silica; Particle; Organic synthesis; Synthesis; Molecular mass; Diameter; Clay; Organic dye; Ethanol; Pore structure; Propanol; Electron microscopy; Mesoporosity; Infrared spectrometry; Adsorption; Pore; Morphology; Spherical particle; Solid phase; Reflectance
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2008.08.040

A study was made on the influence of ionic and non-ionic amphiphiles, i.e., CTAB and 1-(2-aminoethyl)-2-heptadecyl-2-imidazoline (
1), on the pore hierarchy and morphology of siliceous particles synthesized with. The amphiphile (
1) leads to formation of spherical silica particles of about 250
nm
diameter, while the ionic surfactant (CTAB) led to porous silica spheres of about 750
nm
diameter. A single-particle analysis using High Resolution Electron Microscopy (HREM) and Optical Density Transforms (ODT) show the inner pore structure of the particles synthesized with CTAB and low molecular weight alcohols co-surfactants (ethanol and propanol) is oriented along the sphere radius, while silica particles synthesized with (
1) have a random-like pore structure. Both systems were used as supports for adsorption of a photosensitive spiropyran (i.e., Spiro-6) type compound (1’,3’,3’-trimethyl-6-nitrospiro-(2H-1-benzopyran- 2,2’indoline)) and their interaction with the silica surface was characterized by IR spectroscopy, showing a weak interaction with respect to other silicates (lamellar clays). These effects are potentially interesting for applications of biomarkers, stable photosensitive materials, solid-phase organic synthesis and dyes. The UV–vis reflectance spectra of the materials series impregnated with Spiro-6 indicated that siliceous IMP-type materials (i.e., prepared with CTAB and low molecular weight alcohols: Pr-1, Pr-2, Pr-3 and Et-1, Et-2) contained a small shoulder at 460
nm of the less conjugated protonated merocyanine form, together with a broad band at 517
nm, which corresponds to the merocyanine form. The incorporation of aluminum into the silica framework results in a single broad band at 435
nm corresponding to the protonated merocyanine form. Thus, the acidic sites created by aluminum incorporation into the silica spheres seem to favor the formation of protonated merocyanine instead of the basic merocyanine molecule.