Porous carbon materials derived from rice husk pyrolysis with NaCl/Na2CO3 binary molten salt for CO2 capture

Abstract

CO₂ capture from flue gas by biomass-based porous carbons is a green and sustainable approach to reduce carbon emissions. In this study, NaCl/Na₂CO₃ binary molten salt was employed to prepare porous carbons from rice husk for CO₂ capture. Compared to direct pyrolysis, NaCl/Na₂CO₃ significantly reduced the ash content in rice husk derived porous carbons and etched the biochar matrix during pyrolysis, resulting in notable formation of micropores, mesopores, and macropores, along with the dominanted micropores around 0.65 nm. The molten salt was most pronounced at 800 °C, with MSPC-800 exhibiting the specific surface area of 922 m²/g and micropore volume of 0.318 cm³ /g. Meanwhile, MSPC-800 had a significant amount of surface basic oxygen-containing functional groups, mainly C-O-C/-OH and CO. These characteristics endowed MSPC-800 with good CO₂ adsorption capacity (4.84 mmol/g at 0 °C and 3.32 mmol/g at 25 °C), suitable isosteric heat of adsorption (22.4 kJ/mol), high CO₂/N₂ selectivity (33 at 0 °C and 19 at 25 °C), long breakthrough time (788 s at 25 °C), and excellent cycling stability (less than 1 % decay after 10 cycles). Overall, this work provided a reference for the preparation of porous carbons from high-ash-content biomass and the regulation of their CO₂ adsorption properties.