The 3rd International Symposium on Nanocellulosic Materials (3rd ISNCM)

2 / 2021-04-21 14:47:55

NANOCELLULOSE AEROGELS FOR HIGHLY EFFICIENT ADSORPTION OF URANIUM (Ⅵ) FROM AQUEOUS SOLUTION

Aerogel; Nanocellulose; Adsorption; Coordination mechanism; Uranium extraction

   Uranium is the most important source of nuclear energy, generating electricity with more millions of times than conventional fossil fuels without emitting greenhouse gases. However, uranium (U(VI)) can be transferred into the aquatic environment via nuclear-related processes. In the aquatic environment, uranium can be easily accumulated by various organisms by food chains. Excessive exposure to uranium may induce serious diseases such as DNA damage and cancer. In order to effectively address this issue, various technologies have been applied to separate and recovery uranium from the aqueous solution. Adsorption is regarded as one of the most promising method because of its low-cost and high efficiency. Cellulose nanofibers (CNF) were extracted from natural cellulose fibers, which showed higher specific surface area and richer hydroxyl/carbonyl functional groups, in addition to the cellulose features of ready availability, good hydrophilicity and environmental friendly. However, CNFs tend to loss when applied directly in aqueous solution. Here, three-dimensional network structured CNF aerogels were prepared via simple covalent crosslinking and freeze-drying method. The porous cellulose aerogel possessed ultra-high specific surface areas, good mechanical properties and high metal-chelating capacity, which showed fast adsorption kinetics and high adsorption capacity (440.60 mg g^-1) in static uranium adsorption, The adsorption was in good agreement with Langmuir (R² = 0.97), indicating the adsorption was a monolayer and homogeneous process. Pseudo-second-order kinetic model was used to describe the adsorption kinetic behavior (R² = 0.998), which was dominated by chemical adsorption. The CNF aerogels showed good selectivity to other competing ions. In addition, the CNF aerogels have excellent regenerability, and the elution efficiency remained higher than 90 % after five adsorption-desorption cycles. In the continuously dynamic filtration system, the maximum adsorption capacity reached 194 mg g^-1 with the initial concentration of 10 mg L^-1. In addition, the cellulose aerogel possessed excellent selectivity and regeneration ability for uranium adsorption. The integrated analyses of attenuated total reflection Fourier transform infrared (ATR-FTIR), X-Ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) suggested that the predominant UO₂²⁺ species formed inner-sphere surface complexes with two active carboxyl groups in the coordination model. This strategy may provide a sustainable route for development of efficient biomass-based adsorbents for uranium pollutant removal from aqueous solution or uranium extraction from seawater.