Synthesis of microporous amorphous silica from perhydropolysilazane chemically modified with alcohol derivatives

Abstract

Perhydropolysilazane (PHPS) was chemical modified with alcohol derivative (ROH, R = CH₃, i-C₃H₇, n-C₅H₁₁, n-C₁₀H₂₁) at the silicon (Si) of PHPS/ROH molar ratio of 4/1. The alkoxy group-functionalized PHPS was converted into amorphous silica powders by curing at 270°C to promote oxidative crosslinking, followed by pyrolysis at 600°C in air to complete the polymer/amorphous silica conversion. Thermogravimetric analysis in air of the 270°C-crosslinked PHPS showed an approximately 18% weight gain at 200 to 500°C. This weight gain was suppressed consistently with the number of carbon atoms of the alkoxy groups introduced to PHPS. Upon heating to 600°C, the PHPS modified with n-C₅H₁₁OH showed a total weight loss of 12%, and further weight loss of 31% was observed for the PHPS modified with n-C₁₀H₂₁OH. The nitrogen sorption analysis revealed that micropore volume of the polymer-derived amorphous silica increased consistently with the weight loss during the pyrolysis up to 600°C, and the amorphous silica derived from the PHPS modified with n-C₁₀H₂₁OH exhibited the highest micropore volume. Further increase in the micropore volume was achieved by increasing the Si/n-C₁₀H₂₁OH molar ratio from 4/1 to 2/1. The micropore volume and specific surface area of the resulting amorphous silica powders were 0.193 cm³/g and 370 m²/g, respectively.