Controlling the microporosity of SBA-15 silicate material by background salt solution

Abstract

The structure of silicate material of the SBA-15 type has been studied under variable composition of a salt solution in synthesis. Ammonium and sodium chlorides, as well as ammonium fluoride, introduced into the composition of the reaction mixture both at the first stage of precipitation and at the second stage of the thermal treatment (TT), have been used as the salt additives. The mesostructure was controlled by X-ray diffraction, gas adsorption and transmission electron microscopy. It was found that the multiple increase of the ionic strength of the solutions in the presence of chloride salts disrupt the stoichiometry of the silicate-surfactant interaction at the first stage of formation of mesostructure and leads to the formation of an impurity of irregular structure. The ions of ammonium promote an increase in the microporosity of the silicate wall. The presence of sodium ions reduces microporosity. Small quantities of fluoride ions (F−: Si = 0.032) improve the ordering of the product at the stage of primary precipitation. At the ratio F−: Si = 0.16, the hexagonal mesostructure is not formed. The introduction of fluorides at the TT stage leads to a decrease of the silicate pore wall thickness, microporosity and hexagonality of the pore.