Direct conversion of fly ash into monolithic composite aerogels with robust heat-insulating and fire-resistant...

Fly ash poses a significant global challenge in solid waste management due to its massive production. Converting fly ash into high-performance aerogel materials provides an attractive means for its high-value utilization. However, the micron-sized fly ash particles pose significant challenges to achieving a stable aqueous dispersion and constructing a monolithic porous structure. Herein, we present a scalable, chemical-free strategy to directly convert fly ash into monolithic composite aerogels containing up to 75 wt% fly ash, exhibiting high porosity (>90 %), excellent thermal insulation, and superior fire resistance. Stable aqueous dispersions of fly ash were achieved through steric hindrance imparted by low-dimensional nanoclay. Only minimal polymer addition (∼8 wt%) was required to form a robust clay network, effectively preventing pore collapse with increased fly ash content. The resulting fly ash aerogels balance thermal insulation and thermal stability, exhibiting thermal conductivities ranging from 0.0334 to 0.0385 W/(m·K) and a compressive strength of up to 2.7 MPa at 80 % strain, while maintaining structural integrity under extreme temperatures of up to ∼1300 °C. This research significantly broadens the potential applications of fly ash and presents an optimal strategy for its high-value utilization.