Uranium Sequestration with Bisphosphonate-Grafted Mesoporous Silica: Sorption Behavior, Mechanistic Insights, and In Vitro Evaluation

A mesoporous silica-based sorbent, anchored with 2-amino-1-hydroxypropylidene-1,1-bisphosphonic acid onto mesoporous silica (MSNBP), was developed and employed for the sequestration of uranyl (VI) ions from aqueous solutions. The sorbent was characterized using physicochemical methods, such as TGA, XPS, BET surface area analysis, SEM, and FTIR, confirming its mesoporous structure with a surface area of 657.26 m2/g and a pore diameter of 3.57 nm. The adsorption behavior of MSNBP, compared to amine-functionalized mesoporous silica (MSN-NH2), was evaluated under varying uranyl concentration, pH, contact time, and temperature conditions. The functionalized material exhibited enhanced adsorption capacity, with maximum capacities of 36.67 mg/g and 291.37 mg/g for initial uranyl ion concentrations of 50 mg/L and 400 mg/L, respectively. Adsorption followed pseudo-second-order kinetics and conformed to the Freundlich isotherm, indicating multilayer adsorption on heterogeneous sites. XPS and FTIR analyses demonstrated that the adsorption mechanism involved complexation between uranyl ions and the bisphosphonate functional groups, with a 1:1 U to P stoichiometry established in the sorbed complex. Notably, the sorbent achieved 97.42% uranium removal at pH 8, maintaining its efficacy across the adsorption–desorption cycles with a recovery rate of 95.42%. The effect of coexisting ions on U(VI) adsorption by MSNBP showed minimal interference, while Ca2+ and HCO3– reduced adsorption due to competition for phosphonate sites and the formation of negatively charged U(VI) complexes. In vitro evaluation demonstrated that the hemolysis of MSNBP was less than 5%, verifying its hemocompatibility and suitability for applications involving biological interfaces. These findings position MSNBP as a promising and reusable material for uranium sequestration from aqueous environments, highlighting its potential for nuclear waste management.