Mesoporous silica nanoparticles for rapid removal of PFOA: Impact of surface functional groups on adsorption efficiency and adsorbent regeneration
Ahmed M.A. Abdelsamad, Navid Saeidi, Katrin Mackenzie
Abstract
This study explores mesoporous silica nanoparticles (MSN) synthesized via oil-water biphase stratification and functionalized with n-octyltrichlorosilane (OTS), 3-aminopropyltriethoxysilane (APTES), or both, yielding OMSN, AMSN, and OAMSN. All adsorbents rapidly removed perfluorooctanoic acid (PFOA) from water, reaching 95% adsorption equilibrium within 10 minutes. PFOA adsorption kinetics showed that OAMSN, with the largest pore size (14.4 nm), had the highest pseudo-second-order rate constant. Isotherm analysis indicated that both OAMSN and AMSN achieved higher equilibrium loadings across a broad equilibrium concentration range ( C e : 0.2 μg/L - 8 mg/L), which covers environmentally relevant concentration of PFOA. AMSN, with a positively charged surface (point of zero charge = 9), showed the highest maximum adsorption capacity ( q m = 208 mg/g), while OAMSN, combining hydrophobicity and positive charge, achieved a much higher adsorption coefficient ( K d = 1.4 × 10 5 L/kg at C e = 50 μg/L). OMSN, the most hydrophobic evaluated by water contact angel measurements, had a high K d at C e = 50 μg/L but the lowest q m . Pore filling calculations showed large variations (0.8% for MSN to 12% for AMSN) despite similar pore volumes, highlighting the dominant role of surface chemistry over pore structure. Hydrophobicity governs adsorption at low loadings, while electrostatic interactions become key approaching q m . Solvent extraction preserved adsorption efficiency in hydrophobic adsorbents (OMSN, OAMSN), while UV-activated persulfate degraded up to 87% of the loaded PFOA but impaired reuse, especially for functionalized materials. Thus, solvent extraction suits functionalized adsorbents, whereas UV/persulfate is better for regenerating non-functionalized ones.