Application of Functionalized Fe3O4 Magnetic Nanoparticles Using CTAB and SDS for Oil Separation from Oil-in-Water Nanoemulsions

Using magnetic nanoparticles (MNPs) for emulsified oilseparationfrom wastewater is becoming increasingly widespread. This study aimsto synthesize MNPs using amphiphilic coatings to stabilize the MNPsand prevent their agglomeration for efficiently breaking oil-in-waternanoemulsions. We coat two different sizes of Fe3O4 nanoparticles (15-20 and 50-100 nm) using cetyltrimethylammoniumbromide (CTAB) and sodium dodecyl sulfate (SDS) with surfactant-to-MNPmass ratios of 0.4 and 0.8. We study the effect of various variableson the demulsification performance, including the MNP size and concentration,coating materials, and MNP loading. Based on the oil-waterseparation analysis, the smaller size MNPs (MNP-S) show a better demulsificationperformance than the larger ones (MNP-L ) for a 1000 ppm dodecane-in-wateremulsion containing nanosized oil droplets (250-300 nm). Forsmaller MNPs (MNP-S) and at low dosage level of 0.5 g/L, functionalizingwith surfactant-to-MNP mass ratio of 0.4, the functionalization increasesthe separation efficiency (SE) from 57.5% for bare MNP-S to 86.1%and 99.8 for the SDS and CTAB coatings, respectively. The highestSE for MNP-S@CTAB and the zeta potential measurements imply that electrostaticattraction between negatively charged oil droplets (-55.9 +/- 2.44 mV) and positively charged MNP-S@CTAB (+35.8 +/- 0.34 mV)is the major contributor to a high SE. Furthermore, the reusabilitytests for MNP-S@CTAB reveal that after 10 cycles, the amount of oiladsorption capacity decreases slightly, from 20 to 19 mg/g, indicatingan excellent stability of synthesized nanoparticles. In conclusion,functionalized MNPs with tailored functional groups feature a highoil SE that could be effectively used for oil separation from emulsifiedoily wastewater streams.