Functionalization of silica-coated magnetic nanoparticles as powerful demulsifier to recover oil from oil-in-water emulsion

Abstract

This study presents an innovative approach for the preparation of Fe3O4 nanoparticles covered with SiO2 shell (denoted as Fe–Si-MNP), which were used to recover oil recovery from oil-in-water emulsion (O/W-emul). The Fe–Si-MNP were prepared with differing silica layer thicknesses (5 nm [Fe–Si-1], 8 nm [Fe–Si-2], 10 nm [Fe–Si-3], and 15 nm [Fe–Si-4]) and tested for the percentage of oil separation (%Soil) under different dosages (DMNP), oil concentration (Doil), surfactant dosages (Dsur), and pH. The Fe–Si-MNP exhibited excellent %Soil, reliable stability, and high magnetization values ranging between 46.1 and 80.2 emu/g. adding a 5 nm silica layer on the surface of the Fe–Si-MNP (i.e., Fe–Si-1) protected them from oxidation conditions, extended their service life, and achieved a %Soil of ∼96.3%. The %Soil slightly decreased to ∼92% with an alkaline pH or when the thickness of the silica layer increased to ≥10 nm. The %Soil was 90.5%, 89.5%, and 87.5% for Fe–Si-2, Fe–Si-3, and Fe–Si-4, respectively. Increasing the water salinity from 0.1 to 0.5 M slightly improved the %Soil for the tests carried out with a Doil of 100 mg/L to 93.3%, 90.3%, and 86.3% for Fe–Si-2, Fe–Si-3, and FeSi-4, respectively. The highest %Soil achieved with Fe– Si-1 Fe–Si-2 and Fe–Si-3 was >95%, 95% and 92%, respectively. The Fe–Si-MNP exhibited a high recyclability for 9 cycles with the lowest %Soil ∼80%. The results suggest that the structure and properties of the Fe–Si-MNP can be manipulated to achieve a high oil recovery, easy separation, and extended service life.