Amino-functionalized iron oxide nanoparticles designed for adsorption of naphthenic acids

Abstract

Amino-functionalized silica-coated iron oxide (Fe3O4/SiO2 NH2/C18) magnetic nanoparticles were synthesized, and amino-surface modification was performed with a high-pressure autoclave experiment and newly developed reflux procedure. The nanoparticles were tested for their ability to remove naphthenic acids from a model crude oil solution and for their magnetic separation properties. Grafting degrees onto the nanoparticle surfaces of 3-aminopropyltrimethoxysilane (APTMS) and n-octadecyltriethoxysilane (ODS) were calculated based on elemental analysis and specific surface area of the nanoparticles was measured by the Brunauer, Emmett and Teller (BET) method. Presence of a core-shell structure of separate nanoparticles as well as nanoparticle agglomerates was confirmed by the use of transmission electron microscopy (TEM) imaging. Average nanoparticle size and coating thickness were calculated based on a TEM size distribution analysis. The two amino-functionalization methods revealed similar results for the adsorption of 4-heptylbenzoic acid (HBA) dissolved in octane, and 2.7 times higher adsorption capacity compared to the unmodified silica-coated (Fe3O4/SiO2) nanoparticles.