One-step cross-linking of amino-rich chitosan aerogels for efficient and selective adsorption of uranium from radioactive nuclear wastewater

Abstract

Extraction of uranium from radioactive wastewater is a critical challenge in the modern era of the prevalence of nuclear fuel. Herein, polyethyene polyamine/polydopamine modified carboxylated chitosan aerogels (PEPAx/PDAy-CMCSm-n) were obtained by a simple one-step cross-linking method for efficient and selective uranium adsorption. Carboxylation of chitosan substrates greatly improved solubility in water, which increased flexibility for biomass chitosan modification. More importantly, the PDA bonded coating avoided the problem of low availability of reactive sites caused by steric hindrance between CMCS and PEPA. The abundant –NH2 in the surface modifier PEPA endowed the chitosan aerogels with sufficient active sites, making it exhibit a high uranium adsorption capacity of 467.73 mg g−1. The optimal preparation scheme of aerogels was designed by comprehensive orthogonal experiments for the reactive monomer additive amounts. The obtained PEPA2.0/PDA0.7-CMCS3.5–250 showed prominent kinetics, excellent selectivity and superior regeneration performance. Importantly, reducing uranium concentration from 12.35 mg L-1 to 10 ug L-1 in simulated nuclear wastewater, which is below the Ministry of Environmental Protection of the People’s Republic of China uranium limit for drinking water (30 ug L-1). Besides, the density functional theory calculations revealed the binding mechanism and coordination mode between the adsorption unit and UO22+. Such efficient and low-cost adsorbed aerogels are extremely advantageous for uranium capture in real environments.