Facile Fabrication and Characterization of Amine-Functional Silica Coated Magnetic Iron Oxide Nanoparticles for Aqueous Carbon Dioxide Adsorption

Surface active amine-functionalized silica coated magnetic iron oxide nanoparticles were prepared by a simple two-step process for adsorbing CO₂ gas from aqueous medium. First, oleic acid (OA) coated iron oxide magnetic particles (denoted as Fe₃O₄-OA) were prepared by a simple coprecipitation method. Then, the surface of the Fe₃O₄-OA particles was coated with silica by using tetraethyl orthosilicate. Finally, aminated Fe₃O₄/SiO₂-NH₂ nanoparticles were concomitantly formed by the reactions of 3-aminopropyl triethoxysilane with silica-coated particles. The formation of materials was confirmed by Fourier transform infrared spectral analysis. Transmission electron microscopic analysis revealed both spherical and needle-shaped morphologies of magnetic Fe₃O₄/SiO₂-NH₂ particles with an average size of 15 and 68.6 nm, respectively. The saturation magnetization of Fe₃O₄/SiO₂-NH₂ nanoparticles was found to be 33.6 emu g^-1, measured by a vibrating sample magnetometer at ambient conditions. The crystallinity and average crystallite size (7.0 nm) of the Fe₃O₄/SiO₂-NH₂ particles were revealed from X-ray diffraction data analyses. Thermogravimetric analysis exhibited good thermal stability of the nanoadsorbent up to an elevated temperature. Zeta potential measurements revealed pH-sensitive surface activity of Fe₃O₄/SiO₂-NH₂ nanoparticles in aqueous medium. The produced magnetic Fe₃O₄/SiO₂-NH₂ nanoparticles also exhibited efficient proton capturing activity (92%). The particles were used for magnetically recyclable adsorption of aqueous CO₂ at different pH values and temperatures. Fe₃O₄/SiO₂-NH₂ nanoparticles demonstrated the highest aqueous CO₂ adsorption efficiency (90%) at 40 °C, which is clearly two times higher than that of nonfunctionalized Fe₃O₄-OA particles.