Ambient-dried anisotropic MOF-loaded cellulose aerogel for efficient removal of Pb(II).

Metal-organic framework (MOF)-loaded cellulose aerogels show considerable promise for remediating water polluted by heavy metal ions. However, their practical application has been limited by energy-intensive drying methods and suboptimal performance. Herein, a low-cost, scalable preparation strategy to fabricate a MOF-loaded cellulose aerogel (denoted as b-CAT-Z) via ambient drying, employing bidirectional freezing combined with solvent exchange, without the need for toxic crosslinking agents. Specifically, tannic acid (TA)-modified cellulose nanofibers (CNF) and aramid nanofibers (ANF) form a robust skeleton, while MOFs (ZIF-8) anchored via hydrogen bonding and coordination interactions serve as nanofillers to enhance Pb(II) adsorption. The optimized b-CAT-Z aerogel exhibited an ultra-low density (20.3 mg/cm3) and excellent mechanical properties, with a specific strength of 10.93 kN·m/kg. More importantly, benefiting from the construction of long-range ordered water transport channels, the b-CAT-Z aerogel prepared via bidirectional freezing demonstrates outstanding performance in adsorbing Pb(II), exhibiting a superior adsorption capacity (584.4 mg/g), removal efficiency (97.4%), and adsorption kinetics (reaching equilibrium within 180 min). These properties confer significant advantages over its counterparts prepared by random freezing (441.0 mg/g, 300 min) and unidirectional freezing (514.9 mg/g, 300 min). Remarkably, the b-CAT-Z aerogel still maintains a Pb(II) removal efficiency as high as 80.3% even after six adsorption-desorption cycles. Density Functional Theory (DFT) calculations revealed that the oxygen-containing and imidazole groups in b-CAT-Z strongly bind Pb(II), acting as efficient adsorption sites. The b-CAT-Z aerogel demonstrated favorable recyclability. This work presents an ambient-dried strategy for fabricating high-performance cellulose aerogels, providing valuable insights for designing next-generation heavy metal adsorbents.