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A novel castor oil/water/ethanol Pickering emulsion, stabilized by magnetic nanoparticles (NPs), was developed to allow on-demand demulsification by an external magnetic field for the extraction of ethanol from aqueous solution using the castor oil. The emulsion was stabilized by Fe3O4-coated cellulose nanocrystals (CNC@Fe3O4) and lignin-coated Fe3O4 NPs (lignin@Fe3O4). The stability of the emulsions was investigated at various castor oil to ethanol-water ratios (50/50 and 70/30), various NP concentrations, and ethanol concentrations in the aqueous phase. The magnetically controlled demulsification ability of the emulsions was investigated by using a permanent magnet. The results showed that the 70/30 emulsions were more stable than the 50/50 emulsions for all the ethanol concentrations. Moreover, increasing the NP concentration increased the emulsion stability and hence, 1 w/v% NPs concentration provided the more stable systems. However, all the emulsions were successfully broken by the permanent magnet. Yet, the presence of ethanol improves the ability of the external magnetic field to demulsify these dispersions. Furthermore, the used hybrid NPs were recovered and recycled for three cycles. The recycled NPs were characterized with X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) indicating that they retained their saturation magnetization and crystalline structure, demonstrating their lack of degradation over multiple recycling cycles. This study facilitates the exploration of innovative two-phase Pickering emulsions comprising three distinct liquid components and their utilization in liquid-liquid extraction processes.more » « less
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The ternary manganese pnictide phases, MnAs 1− x Sb x , are of interest for magnetic refrigeration and waste heat recovery due to their magnetocaloric properties, maximized at the Curie temperature ( T C ), which varies from 580–240 K, depending on composition. Nanoparticles potentially enable application in microelectronics (cooling) or graded composites that can operate over a wide temperature range, but manganese pnictides are synthetically challenging to realize as discrete nanoparticles and their fundamental magnetic properties have not been extensively studied. Accordingly, colloidal synthesis methods were employed to target discrete MnAs x Sb 1− x nanoparticles ( x = 0.1–0.9) by arrested precipitation reactions of Mn 2 (CO) 10 with (C 6 H 5 ) 3 AsO and (C 6 H 5 ) 3 Sb in coordinating solvents. The MnAs x Sb 1− x particles are spherical in morphology with average diameters 10–13 nm (standard deviations <20% based on transmission electron microscopy analysis). X-Ray fluorescence spectroscopy measurements on ensembles showed that all phases had an excess of Sb relative to the targeted composition, whereas energy dispersive spectroscopic mapping data of single particles revealed that the nanoparticles are inhomogeneous, adopting a core–shell structure, with the amorphous shell rich in Mn and O (and sometimes Sb) while the crystalline core is rich in Mn, As, and Sb. Magnetization measurements of the nanoparticle ensemble demonstrated the presence of both ferromagnetic and paramagnetic phases. By combining the magnetization measurements with precision chemical mapping and simple modeling, we were able to unambiguously attribute ferromagnetism to the MnAs x Sb 1− x crystalline core, whereas paramagnetism was attributed to the amorphous shell. Magnetization measurements at variable temperatures were used to determine the superparamagnetic transition of the nanoparticles, although for some compositions and particle sizes the blocking temperature exceeded room temperature. Preliminary magnetic studies also revealed a conventional dependence between core size and coercivity, in spite of variable compositions of the nanoparticles, an unexpected result.more » « less
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