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 inorganic organic 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-C 5 H 11 OH, n-C 10 H 21 OH) 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 cm 3 /g was achieved, with a specific surface area of 387 m 2 /g for the PHPS-derived amorphous silica chemically modified with n-C 10 H 21 OH at the Si/n-C 10 H 21 OH 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.

Synthesis of a Novel Polyethoxysilsesquiazane and Thermal Conversion into Ternary Silicon Oxynitride Ceramics with Enhanced Thermal Stability

“…In the ATR-IR spectrum for the sample after pyrolysis at 800 °C in N 2 (Figure 1), the characteristic peaks due to the organic substituents disappeared and the spectrum was similar to that of silica composed of a weak and broad band at 3000–3700 cm −1 and a strong band centered around 1010 cm −1 assigned to intermolecular hydrogen-bonded Si–OH groups and ν as Si–O in Si–O–Si linkage [27,28]. …”

Microporosity and CO2 Capture Properties of Amorphous Silicon Oxynitride Derived from Novel Polyalkoxysilsesquiazanes

“…Under inert atmosphere up to 800 °C, this polymer exhibited a unique thermal decomposition behavior: a cleavage of the oxygen–carbon bond of the EtO group to evolve ethylene as a main gaseous species formed in-situ, which led to the formation of amorphous Si–O–C–N with an extremely low carbon content (1.1 wt %) compared to the theoretical EtOSZ (25.1 wt %). Thus, the EtO group can be expected to act as a “sacrificial template” to afford a micro and mesoporous material as previously reported for the organo-substituted polysilazanes [22,23,25]. …”

“…ROSZ sample polymers with R = ( a ) Et [22]; ( b ) nPr; ( c ) nBu; ( d ) nHex; ( e ) iPr; ( f ) sBu; ( g ) sHex; ( h ) Cy and ( i ) DHNp.…”

“…During the crosslinking and subsequent high-temperature pyrolysis of polymer precursors, by-product gases such as CO 2 , CH 4 , NH 3 and H 2 were detected, and the microporosity in the amorphous PDCs could be assigned to the release of the small gaseous species formed in-situ [14,15,16,20,21,22,23]. …”