Phytic acid-modified porous organic polymer for efficient adsorption of U(VI) from aqueous solution and simulated seawater

Abstract

In this work, an amine functionalized porous organic polymer (POP-ABP-NH₂) was synthesized by one-step Friedel–Crafts alkylation reaction using 2-aminobiphenyl as an organic monomer and p-dichlorobenzyl as a crosslinker. Then, POP-ABP-NH₂ was functionalized with different concentrations of phytic acid (PA, 30% and 50%) through hydrothermal reaction, and new phytic acid-modified porous organic polymers (POP-ABP-PA-1 and POP-ABP-PA-2) were successfully synthesized. The adsorption performance of the adsorbents for U(VI) ions in aqueous solution and simulated seawater was studied. The results show that the higher PA concentration, the smaller the specific surface area (S_BET POP-ABP-PA-2 (185.84 m²/g) < S_BET POP-ABP-PA-1 (598.43 m²/g)). This may be because the high concentration of PA occupies more pore sites, resulting in a decrease in specific surface area. The adsorption kinetics of the materials for U(VI) conform to the pseudo-second-order kinetic adsorption model, and the adsorption isotherm conform to the Langmuir monolayer adsorption model. Under the optimal adsorption conditions, the maximum adsorption capacity of POP-ABP-PA-2 for U(VI) (q_max = 1372.2 mg/g) is much higher than that of POP-ABP-PA-1 (q_max = 769.2 mg/g). This may be because POP-ABP-PA-2 is connected to a high concentration of PA and has a high phosphorus and oxygen content, resulting in stronger coordination ability and higher adsorption capacity. Most importantly, in simulated seawater at pH = 8, POP-ABP-PA-2 exhibited a high theoretical adsorption capacity of 299.4 mg/g in 150 min. In addition, in a solution where many impurity ions coexist, POP-ABP-PA-2 can still exhibit excellent adsorption selectivity for U(VI), and after five adsorption–desorption cycles, the adsorption removal percentage of U(VI) can still be maintained at 90%. This study provides an important research idea for further developing phytic acid (PA) composites for U(VI) adsorption.