Low-Cost Silica Aerogels from Waste-Derived Ashes via Atmospheric Pressure Drying: A Systematic Review of Synthesis Strategies, Properties, and Application
DOI:
https://doi.org/10.48048/tis.2026.13233Keywords:
Silica aerogel, Sol-gel process, Waste-derived ashes, Atmospheric pressure drying, Structure-property relationship, Low-cost synthesis, Systematic literature reviewAbstract
Silica aerogel (SA) is a very light porous material that has been widely explored for applications in thermal insulation, adsorption, catalysis, and environmental remediation, even in the health sector. SA in this review is made from waste-based ashes, which include coal fly ash and biomass ash. Silk aerogel from waste ash has been widely studied at the laboratory scale, but until now, it has not been adapted to the industrial scale due to the high processing costs and the complexity of the drying method used. In this case, atmospheric pressure drying (APD) is a possible alternative method for producing SA at a low cost and easier so that it can be applied on an industrial scale. This study presents a systematic literature review on the synthesis of silica aerogel from waste-based ashes with a special emphasis on the APD-based process along with a concise application carried out following the PRISMA 2020 guidelines, including the stages of identification, screening, and assessment of the eligibiliexpenses reputable journal articles. The discussion focuses on the silica extraction pathway through initial pretreatment, calcination, sol-gel process conditions, aging process, solvent exchange, surface modification strategies required to maintain the porous structure during drying at atmospheric pressure, and a brief discussion of the application of silica aerogels from waste-based ash. The results of the literature synthesis indicate that the character of the ash source determines the need for pretreatment, the pH of the sol-gel plays a crucial role in maintaining the stability of the hydrolysis-condensation reaction, the aging process is essential in establishing structural stability, and surface modification through silylation is crucial to prevent pore collapse and excessive shrinkage during APD. Optimization of the alkali fusion ratio and reaction conditions affects the efficiency of silica extraction, and last but not least, time and temperature are crucial in achieving the best SA. This review identifies challenges related to the evolution of pore structure during APD and highlights the need to develop sustainable and scalable APD protocols for industrial applications.
HIGHLIGHTS
- Systematically reviews low-cost silica aerogels derived from waste ashes with a specific focus on atmospheric pressure drying (APD) routes.
- Elucidates critical synthesis parameters (pH, feed rate, precursor chemistry, and surface modification) governing process–structure–property relationships.
- Establishes comparative insights between fly ash- and biomass-derived aerogels in terms of textural, physicochemical, and hydrophobic performance.
- Proposes a unified framework linking synthesis strategies, material properties, and application potential, while highlighting challenges in reproducibility, scalability, and performance standardization.
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