A functionalized phosphonate-rich organosilica layered hybrid material (PSLM) fabricated through a mild process for heavy metal uptake

Highlights: • Novel phosphonate-rich organosilica layered hybrid material (PSLM) fabricated through a mild xerogel process. • Surface Complexation Modeling reveals that PSLM bears 2 types of functional groups able to bind heavy metal. • Maximum metal uptake capacities were found 2.72 mmol g−1 for Cu2+, 1.67 mmol g−1 for Pb2+ and 1.00 mmol g−1 for Cd2+ at pH 7. • EPR spectroscopy reveals local coordination environment for Cu2+ ions. - Abstract: A phosphonate-rich organosilica layered hybrid material (PSLM) made of 3-(trihydroxysilyl)propyl methylphosphonate, monosodium salt, as the single silica source, has been obtained from its aqueous solution through a xerogel process and mild thermal aging. The method is simple, affording bulk quantities of powdered PSLM in a single-step. The hybrid is stable in water and possesses a high content of phosphonate groups fixed on the solid matrix. In addition, PSLM shows good thermal stability, which exceeds 300 °C in air. The material was characterized using SEM, TEM, XRD, FT-IR and TGA techniques. Potentiometric titrations show that PSLM bears high-surface density of phosphonate groups (3 mmol g−1). As a result, the material displays high metal uptake capacity for heavy metal ions such as Cu2+ (2.72 mmol g−1), Pb2+ (1.67 mmol g−1) and Cd2+ (1.00 mmol g−1) at neutral pH values e.g. the pH of natural waters. Detailed theoretical modeling using a Surface Complexation Model combined with Electron Paramagnetic Resonance (EPR) spectroscopy shows that the surface distribution of surface bound Cu2+ ions is rather homogeneous e.g. copper-binding phosphonate sites are arranged in average distances 5–8 Å