Synthesis and Characterization of High Surface Area Transparent SiOC Aerogels from Hybrid Silicon Alkoxide: A Comparison between Ambient Pressure and Supercritical Drying.

Adane Muche Abebe,Vineet Tirth,Gian Domenico Soraru,Ali Algahtani,Dinsefa Mensur Andoshe,Ganesh Thothadri,Gulam Mohammed Sayeed Ahmed,Andrea Zambotti

doi:10.3390/ma15041277

Adane Muche Abebe, Vineet Tirth + Show 6 more

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https://doi.org/10.3390/ma15041277

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Abstract

In this article, highly porous and transparent silicon oxycarbide (SiOC) gels are synthesized from Bis(Triethoxysilyl) methane (BTEM). The gels are synthesized by the sol-gel technique followed by both ambient pressure and supercritical drying. Then, the portion of wet gels have been pyrolyzed in a hydrogen atmosphere at 800 and 1100 °C. The FT-IR spectroscopy analysis and nitrogen sorption results indicate the successful synthesis of Si-O-Si bonds and the formation of mesopores. From a hysteresis loop, the SiOC ceramics showed the H1 type characteristic with well-defined cylindrical pore channels for the aerogel and the H2 type for the ambigel samples, indicating that the pores are distorted due to the capillary stress. The produced gels are mesoporous materials having high surface areas with a maximum of 1140 m2/g and pore volume of 2.522 cm3/g obtained from BTEM aerogels. The pyrolysis of BTEM aerogels at 800 °C results in the production of a bulk and transparent sample with a slightly pale white color, while BTEM xerogels are totally transparent and colorless at the same temperature. At 1100 °C, all the aerogels become opaque brown, confirming the formation of free carbon and crystalline silicon.

Highlights

Aerogels have become one of the most interesting materials
The average bulk density of the Bis(Triethoxysilyl) methane (BTEM) xerogel is about 0.75 g/cm3, which is slightly more than twice the density of the BTEM aerogel
Fourier transform infrared (FT-IR) and nitrogen sorption results revealed the successful synthesis of silicon oxycarbide (SiOC) gels and the formation of mesoporous materials, respectively

Summary

Introduction

Aerogels have become one of the most interesting materials. They have outstanding properties, such as large specific surface area, high porosity, low density and thermal conductivity, which are attributed mostly to their mesoporous nanostructure [1,2]. These properties have made aerogels intriguing as thermal insulators, dielectrics for electronics [1,3,4], molecular sieves, catalysis supports, sensors and as energy storage media [5]. Kistler was the first to introduce aerogels in 1931 [6]. Given the desired chemistry of the aerogels (e.g., SiO2 , SiOC), the selected precursors are dispersed in a solvent and allowed to gel, forming a continuous network of solid particles throughout the liquid, called wet gel

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