Upcycling Hazardous Fly Ash into High-Performance Lightweight Xerogels for Thermal Insulation, CO2 Adsorption, and Wastewater Purification

Each year, millions of tons of fly ash (FA), a hazardous byproduct of coal-fired power plants, are disposed of in landfills, causing serious environmental pollution and substantial health risks. Consequently, effective FA management has become critically important. Despite its popularity in the construction sector, FA has rarely been used to create multifunctional porous materials capable of addressing heat insulation, CO ₂ capture, and wastewater purification. This paper reports the successful development of highly durable, lightweight, flexible and multifunctional xerogels derived from FA. The FA was chemically modified and blended with cellulose nanofibers (CNFs), a binder, and a crosslinker to enhance structural stability and multifunctionalities. The resulting xerogel exhibited a compressive strength of 293.5 ± 9.6 kPa and a Young’s modulus of 264.1 ± 6.8 kPa at 70% strain, representing an increase of 86.6% in strength and 94% in modulus compared to pure CNF xerogel. Moreover, it exhibited excellent thermal conductivity of 32.1 mW/m.K, and a CO ₂ adsorption capacity of 1.67 mmol/g, superior to many contemporary materials. Interestingly, the xerogel also performed extremely well in selectively removing both cationic and anionic dyes from water. These results highlight the effectiveness of our formulation and design approach in producing a robust multifunctional xerogel. With its simple fabrication process, lightweight structure, mechanical robustness and multifunctionality, the developed xerogel emerges as an attractive solution for wastewater management, CO ₂ mitigation and building insulation.