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 CO 2 gas from aqueous medium. First, oleic acid (OA) coated iron oxide magnetic particles (denoted as Fe 3 O 4 -OA) were prepared by a simple coprecipitation method. Then, the surface of the Fe 3 O 4 -OA particles was coated with silica by using tetraethyl orthosilicate. Finally, aminated Fe 3 O 4 /SiO 2 -NH 2 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 Fe 3 O 4 /SiO 2 -NH 2 particles with an average size of 15 and 68.6 nm, respectively. The saturation magnetization of Fe 3 O 4 /SiO 2 -NH 2 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 Fe 3 O 4 /SiO 2 -NH 2 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 Fe 3 O 4 /SiO 2 -NH 2 nanoparticles in aqueous medium. The produced magnetic Fe 3 O 4 /SiO 2 -NH 2 nanoparticles also exhibited efficient proton capturing activity (92%). The particles were used for magnetically recyclable adsorption of aqueous CO 2 at different pH values and temperatures. Fe 3 O 4 /SiO 2 -NH 2 nanoparticles demonstrated the highest aqueous CO 2 adsorption efficiency (90%) at 40 °C, which is clearly two times higher than that of nonfunctionalized Fe 3 O 4 -OA particles.