Mesoporous silica SBA-15 functionalized with phosphonate and amino groups for uranium uptake

Mesoporous silicas have a very attractive ability of sorption and enrichment of metal ions due to their huge surface area and facile functionalization by organic ligands. In this work, phosphonate-amino bifunctionalized mesoporous silica SBA-15 (PA-SBA-15) as U(VI) sorbent was fabricated through post-grafting method. The obtained mesoporous silica was characterized by SEM, XRD, NMR and nitrogen sorption/desorption experiments, which revealed the existence of ordered mesoporous structure with uniform pore diameter and large surface area. The adsorptivity of PA-SBA-15 for U(VI) from aqueous solution was investigated using batch sorption technique under different experimental conditions. The preliminary results show that the U(VI) sorption by PA-SBA-15 is very quick with equilibrium time of less than 1 h, and the U(VI) uptake is as large as 373 mg/g at pH 5.5 under 95 °C. The sorption isotherm has been successfully modeled by the Langmuir isotherm, suggesting a monolayer homogeneous sorption of U(VI) in PA-SBA-15. The sorption is pH-dependent due to the pH-dependent charge of sorbent in the aqueous solution. The thermodynamics research shows that the sorption is a feasible and endothermic process. Based on these results, PA-SBA-15 could be a promising solid phase sorbent for highly-efficient removal of U(VI) ions from waste water and enrichment of U(VI) from a solution at a very low level.