Facile synthesis of polyethyleneimine-modified cellulose nanocrystal/silica hybrid aerogel for CO₂ adsorption

Cellulose nanocrystal (CNC)/silica hybrid aerogel (CSA) was synthesized from CNC and sodium silicate hybridization using the one-step sol–gel method under atmospheric drying. At a weight ratio of CNC to silica of 1:1, the obtained CSA-1 had a highly porous network, a high specific area of 479 m² g⁻¹, and a CO₂ adsorption capacity of 0.25 mmol g⁻¹. Then, polyethyleneimine (PEI) was impregnated on CSA-1 to improve CO₂ adsorption performance. The parameters governing CO₂ adsorption performance on CSA-PEI, such as temperatures (70–120 °C) and PEI concentrations (40–60 wt%), were investigated systematically. The optimum adsorbent (CSA-PEI50) exhibited an excellent CO₂ adsorption capacity of 2.35 mmol g⁻¹ at 70 °C and a PEI concentration of 50 wt%. The adsorption mechanism of CSA-PEI50 was elucidated by analyzing many adsorption kinetic models. The CO₂ adsorption behaviors of CSA-PEI at various temperatures and PEI concentrations had the goodness of fit with the Avrami kinetic model, which can correspond to the multiple adsorption mechanism. The Avrami model also showed fractional reaction orders in a range of 0.352–0.613, and the root mean square error is negligible. Moreover, the rate-limiting kinetic analysis showed that film diffusion and intraparticle diffusion resistance controlled the adsorption speed and dominated the subsequent adsorption stages, respectively. The CSA-PEI50 also exhibited excellent stability after ten adsorption–desorption cycles. This study illustrated that CSA-PEI was a potential adsorbent for CO₂ capture from flue gas. Graphical abstract: [Figure not available: see fulltext.]