Reticular Engineering of Multiscale MOF-Cellulose Nanofiber Aerogels for Sustainable Bicarbonate Capture From Water

Dissolved CO₂ in the form of aqueous bicarbonate (HCO₃¯) is the dominant inorganic-carbon species in natural waters and a primary driver of ocean acidification, yet its direct adsorptive removal remains essentially unexplored. Here, we introduce a systematic reticular exploration of MOF-biopolymer composite aerogels (AeroG) for sustainable capture of dissolved HCO₃¯ from water. Four isoreticular Zr^IV/Hf^IV-based MOFs namely UiO-66 (Zr & Hf) and MOF-808 (Zr & Hf), are integrated within renewable cellulose nanofiber scaffolds via directional freeze-casting into MOF-biopolymer aerogels. This multiscale design uses MOF functionalities as adsorption variables, while the nanofibers govern colloidal dispersion and freeze-casting defines the aligned macroporous transport network. Comprehensive adsorption studies indicate that the Zr(IV)-based aerogels systematically outperform Hf-counterparts, with saturation capacities following 66-Zr-AeroG (3.45 mmol g^{- 1}) > 808-Zr-AeroG (3.06 mmol g^{- 1}) > 66-Hf-AeroG (2.53 mmol g^{- 1}) > 808-Hf-AeroG (1.77 mmol g^{- 1}), surpassing previously reported MOF-sorbents for aqueous HCO₃¯ capture. Cradle-to-gate life cycle assessment (LCA) demonstrates that UiO-66 (Zr) incorporation reduces the performance-normalized climate change potential 31-fold, from 3.799 to 0.122 kg CO₂-equiv. mmol^{- 1}. Our work establishes a systematic assessment of the performance-sustainability trade-off across a reticular MOF composite family, with functional performance and environmental responsibility mutually reinforcing the outcomes of the proposed reticular aerogels.