Si₃N₄ Nanofibrous Aerogel with In Situ Growth of SiO_<i>x</i> Coating and Nanowires for Oil/Water Separation and Thermal Insulation

Abstract

Nanofibrous aerogels constructed by ceramic fiber components (CNFAs) feature lightweight, compressibility, and high-temperature resistance, which are superior to brittle ceramic aerogels assembled from nanoparticles. Up to now, in order to obtain CNFAs with stable framework and multifunctionality such as hydrophobicity and gas absorption, it is necessary to perform binding and surface modification processes, respectively. However, the microstructure as well as properties of CNFAs are deteriorated by the direct addition of binders and modifiers. To tackle these problems, we introduced a unique low-temperature (100 °C) chemical vapor deposition method (LTCVD) to achieve the cross-linking and hydrophobization of Si₃N₄ CNFA in only one step. More importantly, during the LTCVD process, SiO_<i>x</i> coatings and nanowire arrays were in situ formed via vapor-solid (VS) and vapor-liquid-solid (VLS) mechanisms on the surface and intersection of Si₃N₄ nanofibers, which cemented the aerogel framework, endowed it with hydrophobicity, and improved its oxidation resistance at high temperature. Compared to most of its counterparts, the Si₃N₄/SiO_<i>x</i> CNFA exhibited better mechanical properties, higher capability of oil/water separation (33-76 g·g^-1), lower thermal conductivity (0.0157 W/m·K^-1), and superior structural stability in a wide temperature range of -196-1200 °C. This work not only presents an excellent Si₃N₄/SiO_<i>x</i> CNFA for the first time but also provides fresh insights for the exquisite preparation strategy of CNFAs.