HYDROTHERMAL CRYSTALLIZATION OF PORPHYRIN-CONTAINING LAYER SILICATES

Porphyrins and metalloporphyrins have been demonstrated as organic templates in the hydrothermal crystallization of layered silicate smectite clays. Two water-soluble free-base porphyrins, tetrakis(N-methyl-4-pyridiniumyl)porphyrin (TMPyP) and tetrakis(N,N,N-trimethyl-4-aniliniumyl)porphyrin (TAP), along with metallo derivatives like Fe(III)TAP, were utilized as their chloride salts. Aqueous gels consisting of a 0.0166:0.20:1.00:1.52 porphyrin:LiF:Mg(OH)2:SiO2 molar ratio heated at reflux temperature crystallized synthetic porphyrin-containing hectorite clays in just 2 days. X-ray powder diffraction (XRD) gave (001) reflections of 15.0, 16.7, and 16.4 angstrom for TMPyP-, TAP-, and FeTAP-hectorite, respectively, indicating that the organic macrocycles are intercalated parallel between the clay layers. Microanalysis data and UV-visible diffuse reflectance (DR) absorption spectra reveal that the porphyrin is incorporated intact. XRD and DR spectra also reveal that the free-base forms of the porphyrins dominate in hydrothermal crystallization products, while in ion-exchanged products the dication forms predominate. Small-angle neutron scattering (SANS) was used to follow the crystallization of these systems and to analyze interactions that exist when porphyrin is reacted with silica sol and magnesium hydroxide alone. Guinier analysis of the scattering curves yields structural information about the growth process of the clay system. Random network structures are observed for the porphyrin-silica system.