Efficient and selective capture of uranium by polyethyleneimine-modified chitosan composite microspheres from...

Uranium extraction from radioactive nuclear waste is vital for sustainable energy supply and ecological security. Herein, a polyethyleneimine-chitosan composite microspheres n-PEI/ECH-CTS (n = 0.1, 0.2, 0.3, 0.4, 0.5) were synthetized for efficient and selective uranium adsorption. The prepared chitosan microspheres with uniform size, uniform dispersion and good mechanical strength combine cost-effectiveness and environmental benefits. The 0.4-PEI/ECH-CTS exhibits the highest adsorption capacity of 380.65 mg g^-1 within only 4 h due to high nitrogen content of 6.57 mol kg^-1. The DFT calculations confirms that the optimal coordination mode of UO₂²⁺ and 0.4-PEI/ECH-CTS is one UO₂²⁺ chelated with two -NH₂ from two adsorption units, respectively. Adsorption efficiency of U(VI) from simulated nuclear wastewater achieves to 100%, and the K_d value is up to 1.1 × 10⁴ mL g^-1, which is 1.7 × 10⁴-6.1 × 10⁴ times that of coexisting ions. The C_U(VI) reduces in simulated wastewater from 10.98 mg L^-1 to 1 μg L^-1, which is well below the US Environmental Protection Agency uranium limits for drinking water (30 μg L^-1). Besides, 0.4-PEI/ECH-CTS still maintains above 95% adsorption efficiency after seven cycles. In short, the 0.4-PEI/ECH-CTS microspheres integrate high performance, practicality and cost-effectiveness, which has great advantages in practical industrial applications.