Abstract
Silica aerogels have attracted tremendous interest due to their high specific surface area and the physical, chemical, and mechanical properties as promising materials for thermal insulation, chemical sensors, and energy storage devices. However, large-scale production of silica aerogels remains a challenge due to costly alkoxide precursors and energy-intensive supercritical drying processes. This paper analyzes the effect of acidity levels and feed rate on the porosity of rice husk aerogels with high specific surface area under ambient pressure. This synthetic approach is cost-effective, eco-friendly, and facilitates recycling. Rice husk ash, which consists of 92% amorphous pure silica, was produced by combustion. A process of solvent exchange and surface modification under ambient pressure at different pH levels was conducted for synthesis of the aerogel. The specific surface area of rice husk aerogel was confirmed as ranging from 385 to 861 m2/g under pH 1 to pH 9 and acid feed rate of 0.5 to 5.0 mL/min. The optimized aerogel had a specific surface area of 861 m2/g, a pore volume of 3.33 cm3/g, and an average pore diameter of 12 nm when synthesized at pH 1 and an acid feed rate of 2.5 mL/min. The aerogel was found to be highly hydrophobic, with a water contact angle of 156° up to about 340 °C.
Highlights
Silica aerogels are highly porous materials with a three-dimensional network of approximately 90% mesopores filled with air
The aerogels have been widely studied for potential applications in various fields due to properties such as high porosity (85%–99%), low density (0.03–0.3 g/cm3), high specific surface area (600–1000 m2/g), high transparency, low thermal conductivity (~0.015 W/m·K), low sound velocity (~100 m/s), low dielectric constant (~1.1), inflammability, and chemical stability [1]
The challenge of conventional aerogel synthesis in this study was overcome by extracting pure silica from rice husk (RH) using solvent exchange and drying it under ambient pressure
Summary
Silica aerogels are highly porous materials with a three-dimensional network of approximately 90% mesopores filled with air. The aerogels have been widely studied for potential applications in various fields due to properties such as high porosity (85%–99%), low density (0.03–0.3 g/cm3), high specific surface area (600–1000 m2/g), high transparency, low thermal conductivity (~0.015 W/m·K), low sound velocity (~100 m/s), low dielectric constant (~1.1), inflammability, and chemical stability [1] They have been investigated as thermal insulation materials to apply in the fields of building, industry, aerospace, and biomaterials. The challenge of conventional aerogel synthesis in this study was overcome by extracting pure silica from rice husk (RH) using solvent exchange and drying it under ambient pressure. This alternative synthetic method provides economic benefits for the mass production of aerogels as the process is at low pressure, uses low-cost raw materials, and the solvent in the solvent exchange can be recycled. The aim of this research is to develop an eco-friendly source of silica aerogels under ambient pressure using a cost-effective process with re-usable solvents
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