Preparation of Hydrophobic Octadecylphosphonic Acid-Coated Magnetite Nanoparticles for the Demulsification of n-Hexane-in-Water Nanoemulsions

To design more environmentally friendly, economical, and efficient demulsifiers for oily wastewater treatment, hydrophobic octadecylphosphonic acid (ODPA)-modified Fe3O4 nanoparticles (referred to as Fe3O4@ODPA) were prepared by condensation of hydroxyl groups between ODPA and Fe3O4 nanoparticles using the co-precipitation method. The prepared magnetite nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric/differential thermogravimetric (TG/DTG) analysis. The water contact angles (theta(W)) of Fe3O4@ODPA nanoparticles were more than 120 degrees, indicating hydrophobic nature, and the diameter of the obtained spherical-shaped magnetite nanoparticles was 12-15 nm. The ODPA coating amount (A(O)) (coating weight per gram Fe3O4) and specific surface area (S-O) of Fe3O4@ODPA were 0.124-0.144 g.g(-1) and 78.65-91.01 m(2).g(-1), respectively. To evaluate the demulsification ability, stability, and reusability, the magnetite nanoparticles were used to demulsify an n-hexane-in-water nanoemulsion. The effects of the magnetite nanoparticle dosage (C-S), pH value of nanoemulsion, and NaCl or CaCl2 electrolytes on the demulsification efficiency (R-O) were investigated. The R-O of Fe3O4@ODPA samples was found to be higher than that of bare Fe3O4 samples (S0, ST, and SN) under all C-S values. With the increase in C-S, the R-O of Fe3O4@ODPA samples initially increased and then approached equilibrium value at Cs = 80.0 g.L-1. A maximum R-O of similar to 93% was achieved at C-S = 100.0 g.L-1 for the Fe3O4@ODPA sample S2. The pH and two electrolytes had a minor effect on R-O. The Fe3O4@ODPA nanoparticles maintained high R-O even after being reused for demulsification 11 times. This indicates that the hydrophobic Fe3O4@ODPA samples can be used as an effective magnetite demulsifer for oil-in-water nanoemulsions.

Automated summary

To design more environmentally friendly, economical, and efficient demulsifiers for oily wastewater treatment, Fe3O4@ODPA nanoparticles were prepared and characterized. The Fe3O4@ODPA nanoparticles showed hydrophobic nature with water contact angles of more than 120 degrees and had a diameter of 12-15 nm. The demulsification efficiency (R-O) of Fe3O4@ODPA samples was higher than that of bare Fe3O4 samples, and it maintained high R-O even after being reused for demulsification 11 times.