Formation of titanosilicate precursors of an active adsorption phase

Abstract

Micro-mesoporous titanosilicate precursors of the active absorption phase of a composite ceramic membrane are synthesized, and their textural and adsorption properties are investigated by means of low-temperature nitrogen adsorption/desorption. Low-temperature isotherms of nitrogen adsorption/desorption are analyzed using the BET, Langmuir, comparative t-plot, Barrett–Joyner–Halenda, and density functional theory methods. It is found that at high contents of silicon(IV) oxide, the resulting xerogels have surface areas of 656 and 890 m²/g according to the BET and Langmuir approaches, respectively, while the micropores’ inner and outer surfaces are 453 and 466 m²/g, respectively, according to the t-plot. According to the DFT distributions, the mesopore diameters of a sample can be adjusted in the range of 3–9 nm. By analyzing the type of capillary condensation hysteresis in the adsorption/desorption isotherms, it is shown that the pores in the samples are very bottle-like, even though their shape may be different in reality. It is found that in samples with high contents of titanium(IV) oxide, the pore throats are blocked during adsorbate desorption, due to the percolation effect. It is assumed that the stabilization of particles of titanium(IV) oxide by amorphous layers of silica protects the texture of titanosilicate xerogels from full contraction and the coalescence of particles during heat treatment ranging from 393 to 923 K.