Ultralow thermal conductivity of robust vermiculite aerogels fabricated by fast trivalent cation induced nanosheet gelation

Low thermal conductivities and high fire resistance are highly desired for the materials used in energy-efficient buildings with high-level safety. Traditional inorganic insulating materials are either fragile or have high thermal conductivities, while organic insulating materials or hybrids with inorganic ones are limited by poor fire resistance and significant volume shrinkage after heating. Herein we report mechanically robust vermiculite aerogels with a thermal conductivity as low as 0.033 W/(m center dot K), excellent fire resistance, and robust structural stability at high temperatures. The aerogels were assembled from delaminated two-dimensional vermiculite nanosheets via trivalent cations, such as Al3+, Fe3+, and La3+, induced fast gelation. The nanosheet concentration and ion crosslinking play critical roles in forming monolithic and robust aerogels. The vermiculite aerogels can resist a hightemperature flame without disintegration and show almost no volume shrinkage after long-time heat treatment at 700 degrees C. The excellent robustness and super-insulating performance (0.021 W/(m center dot K)) remain and even are improved after heating at 900 degrees C for 1 h. The as-made vermiculite aerogels show low-bulk density, high-porosity, super-insulating performance, excellent fire resistance, and environmental safety, endowing them with great potential as ideal thermal insulators for various applications, such as energy-efficient buildings.