Selective Uranium Adsorption of Phosphorylated Silica Gel With High Capacity and Ultrafast Kinetics

A simple and scalable ultrasonic-acid-assisted grafting method was applied to synthesize phosphorylated silica gel adsorbent (SGB-P2), which significantly enhanced the adsorption capacity and selectivity for uranium. The obtained SGB-P2 exhibited a maximum uranium adsorption capacity of 400 mg·g^-1 greatly surpassing those of the unmodified sample (50.54 mg·g^-1), and achieved ultrafast adsorption equilibrium within just 1 min and retained over 80% efficiency after five adsorption-desorption cycles. The adsorption process followed the pseudo-second-order kinetics and Langmuir isotherm models, indicating chemisorption-dominated monolayer adsorption. Combined spectroscopic analyses and density functional theory (DFT) calculations revealed that the coordination between uranium and the phosphate groups (P─O/P═O) constitutes the primary adsorption mechanism. This study demonstrates great potential for practical application of silica gel in the treatment of uranium-contaminated wastewater.