Rice husk-derived extra-large-pore mesoporous silica foam for direct air capture of carbon dioxide
Abstract
The design of high-performance and cost-effective solid sorbents remains a critical challenge for the large-scale deployment of silica-based direct air capture (DAC) technologies. While silica-supported amine sorbents are leading candidates, conventional precursors impose substantial environmental and economic burdens, which limits their applicability. Herein, we report a cost-effective and sustainable extra-large-pore mesoporous silica foam (XL-MSiF) synthesized from rice husk-derived silica without the use of swelling agents or post-synthetic pore expansion processes. This architecture possesses an high pore volume (2.31 cm3 g−1) and large pore channels (18.01 nm), facilitating unobstructed gas transport even at high amine loadings. The synthesized sorbents exhibited CO₂ uptakes of 2.92 and 3.62 mmol g−1 under dry and humid (20% relative humidity, RH) conditions, respectively. Even at 50% RH, where competitive water adsorption reduces the maximum capacity, the sorbent retained a substantial CO2 uptake of 2.53 mmol g−1. Furthermore, a dynamic breakthrough experiment using real ambient air demonstrated a CO2 uptake of 2.43 mmol g−1, confirming effective CO2 capture under continuous-flow real-air conditions. The sorbent also demonstrated near-complete regeneration at mild temperatures (60–75°C) and maintained excellent cyclic stability, with less than 2.5% capacity loss over 20 consecutive adsorption-desorption cycles under both dry and humid conditions. Overall, this study establishes that rice husk-derived XL-MSiF can serve as a robust, energy-efficient, and environmentally sustainable support material for amine-based DAC processes.
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