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

ABSTRACT

Dissolved CO ₂ in the form of aqueous bicarbonate (HCO ₃ ¯) 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 HCO ₃ ¯ 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 HCO ₃ ¯ 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 CO ₂ ‐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.