Polymer-derived amorphous silica-based inorganic-organic hybrids having alkoxy groups: Intermediates for synthesizing microporous amorphous silica materials

Abstract

Alkoxy group-functionalized amorphous silica-based inorganicorganic hybrid materials were designed through polymer precursor route, in order to develop a novel route for the fabrication of microporous amorphous silica-based materials. Commercial perhydropolysilazane (PHPS) was chemically modified with alcohols (R-OH, R = n-C5H11OH, n-C10H21OH) at a PHPS (Si basis) to ROH molar ratio of 4/1, and subsequently oxidized to afford alkoxy group-functionalized amorphous silica by exposure to aqueous ammonia vapours at room temperature. Then, the oxidized materials were heat-treated at 600°C in air. Nitrogen sorption analysis revealed that micropore volume of the amorphous silica increased upon alkoxy group-functionalization prior to the heat treatment. As a result, higher micropore volume of 0.204 cm3/g was achieved, with a specific surface area of 387m2/g for the PHPS-derived amorphous silica chemically modified with n-C10H21OH at the Si/n-C10H21OH molar ratio of 2/1. The micropores evaluated by the SF method were in the size range of 0.43 to 1.6 nm, and the resulting micropore size distribution plot exhibited a peak at 0.43 nm. The in-situ formation of the microporosity was further studied by the simultaneous thermogravimetry-mass spectrometry analysis. The relationship between the number of carbon atoms in the alkoxy group, the evolution of gaseous species during the heat treatment and the resulting microporosity is discussed.