Polyphosphate-Functionalized PGMA-Grafted Mesoporous Silica Nanoparticles for Selective U(VI) Removal from Aqueous Solutions

Uranium(VI) contamination in aquatic environments poses significant environmental and public health concerns, creating a need for efficient and selective adsorbents. In this study, polyphosphate-functionalized poly(glycidyl methacrylate)-grafted mesoporous silica nanoparticles (PP-PGMA/MSNs) were successfully synthesized and evaluated for U(VI) removal from aqueous solutions. A key novelty of this work lies in the incorporation of phosphate-rich functionalities onto PGMA-grafted MSNs prepared via ATRP, together with the systematic investigation of their effects on U(VI) adsorption equilibrium and selectivity in multi-metal systems. Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) confirmed the successful incorporation of phosphate-containing functional groups onto the MSN surface. The adsorbent exhibited rapid adsorption, reaching equilibrium within 120 min, with optimum performance observed at pH 4–6. A maximum U(VI) removal efficiency of 73.81% was achieved at an initial concentration of 10 mg L−1, while the maximum adsorption capacity reached 114.94 mg g−1. Equilibrium data were well described by the Langmuir isotherm model (R2 = 0.9697), indicating predominantly monolayer adsorption on relatively homogeneous adsorption sites. Despite a substantial reduction in surface area following functionalization, the material maintained a high adsorption capacity, suggesting that uranium uptake is governed primarily by interactions at phosphate-containing active sites. Furthermore, the adsorbent exhibited preferential affinity toward U(VI) in multi-metal systems containing Cr, Ni, Cu, Zn, Cd, and Pb ions, demonstrating enhanced selectivity toward uranyl species. The adsorption behavior suggests that phosphate functionalities serve as the primary binding sites through surface complexation and coordination interactions. These findings demonstrate the potential of PP-PGMA/MSNs as selective adsorbents for U(VI) removal from complex aqueous systems and environmental remediation applications.