Synthesis of seashell-like amino-functionalized mesoporous silica nanoparticles for uranium adsorption

Amino-rich anionic mesoporous silica (AAMS) nanoparticles were synthesized using a binary Co-Structure Directing Agent (CSDA) strategy to enhance nitrogen incorporation while preserving mesostructural order for U(VI) adsorption. All synthesized materials were comprehensively characterized using TEM, N2-sorption analysis, FTIR, XPS, zeta – pH measurements, and nitrogen elemental analysis. The binary-CSDA APTMS/APTES material exhibited a distinctive sea-shell-like morphology, providing enhanced surface accessibility, well-defined mesopore exposure, and improved diffusion, thereby contributing to its superior adsorption performance. Compared to the single-CSDA sample (surface area 503.6 m2 g−1, pore volume 0.866 cm3 g−1, nitrogen content 1.61 wt%, capacity 30 mg g−1), the binary systems combining APTES (3-aminopropyltriethoxysilane) with APTMS (3-aminopropyltrimethoxysilane) or N3TPED (N-[3-(trimethoxysilyl)propyl]ethylenediamine) achieved higher nitrogen contents (2.82–3.25 wt%), while maintaining high surface areas (394.7–336.6 m2 g−1) and uniform pore sizes (~3.8 nm). As a result, their U(VI) adsorption capacities increased significantly to 80 mg g−1 (APTES/APTMS) and 116 mg g−1 (APTES/N3TPED). These capacities surpass those reported for recent amino-based silica adsorbents, such as amide/phosphorus functionalized silica (95 mg g-1), amidoxime-modified mesoporous silica (~57 mg g-1), and amino-functionalized hydroxylated SBA-15 (115 mg g−1). Adsorption kinetics followed the pseudo-second order model (R2 ≈0.99), and the uptake mechanism was governed primarily by electrostatic attraction and physical interactions between protonated amino groups and hydrolyzed U(VI) species. Thermodynamic parameters (ΔG° = –3 to −5 kJ mol−1; ΔH° = –15 to −23 kJ mol−1) confirmed a spontaneous, exothermic process, while the materials maintained ≥80% regeneration efficiency after seven cycles. Owing to their high amino density, surface charge, and stable mesoporous architecture, the binary CSDA-derived AAMS nanoparticles also show strong potential for the removal of other wastewater pollutants, including heavy metals, pesticides, and pharmaceutical contaminants.