Sustainable aerogels using byproducts, waste and recycled materials as reagents

The increasing pressures imposed by climate change, environmental pollution and inefficient waste management have intensified the demand for sustainable material strategies grounded in circular economy principles. In this context, the valorization of waste streams, through the recovery of raw materials, to produce high-performance materials represents a critical pathway towards resource efficiency and the mitigation of environmental impacts. Aerogels, known for their exceptionally high porosity, low density, and outstanding thermal, acoustic, and adsorption properties, have traditionally been synthesized from high-purity commercial precursors, limiting their economic and environmental sustainability. Recent advances, however, demonstrate that a wide range of low-value feedstocks - including recycled polymers, biomass residues, and industrial byproducts - can be successfully transformed into functional aerogels with competitive or even superior properties. This review provides a critical and comparative analysis of aerogel synthesis routes derived from waste and secondary resources, highlighting the underlying chemical mechanisms, structure-property relationships, and performance trade-offs associated with different precursor classes. By systematically assessing the technological readiness, scalability challenges, and application potential of waste-derived aerogels in areas such as thermal insulation, environmental remediation, and energy storage, this work advances beyond descriptive surveys in the literature and offers a consolidated framework for guiding future research and industrial implementation of circular aerogel technologies.