Synthesis of High Surface Area Phosphosilicate Glasses by a Modified Sol−Gel Method

Abstract

High surface area phosphosilicate glasses were synthesized by a new sol−gel method and characterized for structural, textural, and acid properties by X-ray diffraction, thermogravimetry/differential thermal analysis, IR spectroscopy (Fourier transform and diffuse reflectance Fourier transform), solid state 31P and 29Si NMR spectroscopy, N2 adsorption, and NH3 temperature programmed desorption. The glasses were synthesized by a sol−gel route hydrolyzing the precursors in an almost solely aqueous environment. Microstructural changes occurring during the conversion of the gels into the corresponding glasses were investigated. For all dried gels (383 K), the elimination of organic residues was complete at 673 K. After this heat treatment, ca. 80% of the phosphorus was present as free phosphoric acid except for the sample with the highest P content for which the percentage dropped to ca. 47%. Textural properties of samples treated at 673 K were greatly influenced by the composition. Surface area decreased and pore dimension increased with increasing phosphorus content, indicating a gradual transformation of the siloxane matrix from microporous to mesoporous. Brønsted acid sites of differing strength, mainly related to the presence of phosphoric acids, were found. The surface concentration and strength of acid sites increased with phosphorus content.

Multinuclear NMR study of phosphosilicate gels derived from POCl3 and Si(OC2H5)4

“…DTA/TG analysis of the gels shows that no significant weight loss occurs after 400°C, thus the phosphorus and silicon contents determined from these 1000°C heated samples is a true reflection of the composition of the samples heated to 400°C [17].…”

“…Significantly, marked differences were seen in the texture of the gel samples heated for 1 h at 400°C as a consequence of changing the composition. In particular the surface area decreased and pore dimension increased with increasing phosphorus content, indicating a gradual transformation of the siloxane matrix from microporous to mesoporous [17].…”

“…Consequently a modified sol-gel procedure was introduced to obtain mesoporous gel-derived glasses with a high specific surface area [17]. In particular, the possibility of hydrolyzing the organometallic precursors in an almost solely aqueous environment was explored, to facilitate the introduction of water soluble inorganic precursors into the synthesis [17]. Significantly, marked differences were seen in the texture of the gel samples heated for 1 h at 400°C as a consequence of changing the composition.…”

Anhydrous proton-conducting organic–inorganic hybrid membranes synthesized from tetramethoxysilane/methyltrimethoxysilane/diisopropyl phosphite and ionic liquid

“…The spectral bands within the wavenumber range 400-880 cm −1 can be attributed to the Si-O-Si bond bending vibrations and symmetric stretching vibrations of Si-O-Si bonds, respectively. The spectral bands observed at 1,135 and 1,261 and 1,277 cm −1 can be assigned to asymmetric stretching vibrations of Si-O-Si bridging sequences and O=P bond stretching, respectively [45]. The 880-cm −1 band can be assigned to stretching vibration of free silanol groups on the surface of the amorphous silica.…”

Sol–gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure–activity correlations in hybrid materials targeting Zn(II) antibacterial use

“…Over the last decade, several studies [24][25][26][27][28][29] have focused on the preparation of nanospheres. Silica nanobottles [38], silica nanospheres with a magnetic core and charged surface [39], fluorescent silica nanospheres [40], polypyrrolemagnetite-silica particles [41], CdS-SiO 2 core-shell particles [42] and silica nanospheres encapsulating enzymes [43] are among some of the most interesting examples in this area.…”