Adsorption behavior and mechanism of U(VI) on cetyltrimethylammonium bromide-modified bentonite-MOF composite

Seawater uranium extraction is a key technology for environmental sustainability with significant potential applications. For the first time, this work synthesized a CTAB/Bent-MOF808 with strong stability, abundant coordination functional groups, and low cost, and assessed its adsorption effectiveness for U (VI) in carbonate solutions. The study explores how pH, contact time, uranium concentration, temperature, carbonate, halide salts, phosphorus, and Ca/Mg ions influence uranium adsorption, with a focus on mechanistic insights through characterization and modeling. Under optimal conditions (temperature of 25 °C, pH 8.0, with a sodium bicarbonate concentration of 2 mmol L −1 and a U(VI) concentration of 50 mg L −1 ), which are similar to the real seawater environment, CTAB/Bent-MOF808 demonstrated superior uranium adsorption performance compared to MOF808 and CTAB/Bent in U(VI)–CO 3 solutions. Under high initial pH, NaHCO 3 , Ca/Mg ions, and halide ion concentrations, the complex's uranium adsorption capacity and removal rate are reduced due to competitive adsorption between ions, as well as increased electrostatic repulsion on the surface. The sorption process was identified as monolayer homogeneous chemical adsorption process by analyzing it with quasi second order kinetic models and Langmuir isotherm models. The inhibitory effect of halide ions is as follows: I −  > F −  > Br −  > Cl − . XPS suggested that the complexation of bromide anion with –COOH and electrostatic attraction could be crucial processes for uranium adsorption. This study offers theoretical insights into uranium extraction from natural uranium-bearing waters and highlights the expanded potential of MOF-based adsorbents in this process, enhancing both efficiency and application scope.