Amidoxime-Functionalized Carbon Fibers for Efficient Adsorption of Uranium(VI) from Aqueous Solutions

A novel amidoxime-functionalized carbon fiber adsorbent (CFAO) was successfully fabricated via surface grafting modification for U(VI) removal. The sorption behaviors of the CFAO were systematically explored under various experimental conditions involving solution pH, contact time, initial U(VI) concentration, temperature, and complex competing ion environments. With a fixed adsorbent dosage of 10 mg in 30 mL solution, the maximum experimental equilibrium adsorption capacity was 56.25 mg/g at an initial U(VI) concentration of 60 mg/L, with sufficient contact time to attain full adsorption equilibrium. The Langmuir model yielded a theoretical saturated adsorption capacity of 63.78 mg/g. The adsorption process was well described by the pseudo-second-order kinetic and Langmuir isotherm models, while thermodynamic results confirmed the spontaneous and endothermic nature of U(VI) sorption. Benefiting from grafted amidoxime chelating groups, CFAO exhibited significantly improved uranium uptake compared with pristine carbon fibers. The material presented selectivity toward U(VI) in simulated seawater and nuclear wastewater, and retained over 90% of its original capacity after five adsorption–desorption cycles. With good recyclability and U(VI) selectivity, as reflected by the retained adsorption performance upon cycling, CFAO shows potential as a reusable adsorbent for U(VI) recovery from complex aqueous systems under laboratory batch conditions.