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

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.

Cellulose Nanofiber–Alginate Biotemplated Cobalt Composite Multifunctional Aerogels for Energy Storage Electrodes

“…From this, it is estimated that the supercritically dried gels have a 1:1 (w/w) ratio of inorganic to organic mass. The TGA data for the pyrolyzed sample show an immediate decrease in mass followed by a slight increase, consistent with a drying and buoyancy effect that has been observed previously in silica aerogels [97,98]. The second DTA peak in Figure 6b is consistent with the conversion of alginate to sodium carbonate [95].…”

“…The Co2p region can be difficult to interpret compared to other elements, owing to the multiple oxide species that can be present, the proximity of the XPS peaks with satellite peaks, the loss features and Auger peaks, and that the Co 2+ and Co 3+ XPS peaks exactly overlap [96,97]. The deconvoluted spectra for the Co2p region for each sample are shown in Figure 5d-f.…”

“…Other peaks in the spectrum correspond to Co Auger (776 eV) and satellite features (784-790 eV). Further discrimination between Co 2+ and Co 3+ is not possible since the XPS peaks overlap and, if Co3O4 is present, it is a mixed valence of 2+ and 3+ oxidation states [97]. Following pyrolysis, a metallic Co peak is detected at 780 eV in addition to the oxide peak at 781 eV in a 1:2 ratio, respectively.…”