(421h) Magnetically Induced Emulsification and Demulsification of Three-Component Castor Oil/Water/Ethanol Emulsions Stabilized By Cnc@Fe3O4 and Lignin@Fe3O4 Nanocomposites

Magnetically controlled emulsion systems have potential applications in low-energy liquid extraction separations. There are few studies conducted on multicomponent emulsion systems. In this work, a three-component magnetically-controlled castor oil/water/ethanol Pickering emulsion, stabilized by CNC@Fe₃O₄ and Lignin@Fe₃O₄ nanocomposites, was studied to extract ethanol from aqueous solutions to castor oil. Herein, superparamagnetic iron oxide (Fe₃O₄)-coated cellulose nanocrystals (CNC@Fe₃O₄) and kraft lignin-coated iron oxide multicore structures (Lignin@Fe₃O₄) were synthesized to formulate emulsions with magnetically controlled stability. Iron oxide NPs were deposited onto the surface of wood-pulp CNCs by a single one-step coprecipitation method. Similarly, lignin-coated iron oxide nanoparticles were assembled onto Fe₃O₄ nanocrystals by a pH-driven precipitation method. In addition, both CNC@Fe₃O₄ and Lignin@Fe₃O₄ NPs were characterized by transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), dynamic light scattering (DLS), and zeta potential measurements. Magnetite loading on CNC and lignin provided superparamagnetic properties to the nanocomposites, allowing them to induce demulsification using an external Neodymium permanent magnet. Moreover, the effect of nanocomposites (0.1 to 1 wt%) on the castor oil/ethanol solution interfacial tension was measured by an optical tensiometer using the pendant drop method.

The oil to water volume ratios of emulsions was first optimized using a binary castor oil/water system. With oil contents of 70% and 90% v/v, and addition of 1wt% CNC@Fe₃O₄ NPs of aqueous phase, the emulsions were water-in-oil (W/O) and were broken by an external magnet, while the CNC@Fe₃O₄ NPs were recovered and recycled. The 30 and 50% v/v oil emulsions were oil-in-water (O/W) and could not be broken by the magnet with CNC@Fe₃O₄, probably as a consequence of higher emulsion stability. Lignin@Fe₃O₄, however, broke the emulsions at 50 v/v% using an external magnet. To assess the effect of the CNC@Fe₃O₄ and lignin@Fe₃O₄ on the castor oil/water/ethanol Pickering emulsions, stabilized by the nanocomposites, emulsions were formulated by using a 70/30 volume ratio of castor oil rich and water-rich phases with added ethanol at the equilibrium composition. The emulsions were observed to be stable for a long time (at least 48 hours) without the presence of a magnet. Moreover, the composition of CNC@Fe₃O₄ NPs and lignin@Fe₃O₄ NPs was varied from 0, 0.1, 0.3, 0.5, and 1 wt% of the aqueous phase. In each case, the emulsions were water-in-oil (W/O) and were broken by an external magnet at equilibrium conditions in less than 24 hours. Emulsions stabilized with the NP concentration of 1 wt% of aqueous phase showed faster magnetic demulsification than the lower NP concentrations. The demulsification capability of the fabricated CNC@Fe₃O₄ and lignin@Fe₃O₄ have potential uses for magnetically-driven separations, oil recovery, or drug delivery.