Speeding up the magnetic sedimentation of surface-modified iron-based nanoparticles

摘要

Nanoparticles with surface -modified shells are used for selective sorption of different impurities from water. Subsequent removal of nanoparticles from water can be strongly enhanced by using particles with magnetic core, providing their separation by sedimentation or filtration in magnetic field. The velocity of the magnetic sedimentation is strongly controlled by the particles aggregation which can be efficiently changed by interparticles interaction, in particular, by mixing the positively charged particles with negatively charged particles. The aggregation and sedimentation dynamics of the mixtures of the complex nanoparticles having the magnetite or the iron core, e.g., Fe3O4/SiO2, Fe3O4/SiO2-NH2 and Fe/C-NH2 in water were studied in a vertical gradient magnetic field B = 0.3 T, dB/dz = 0.13 T/cm. The sedimentation time is was measured using two independent methods: by optically registered turbidity and from residual particle concentration in water by Nuclear Magnetic Resonance Relaxometry (NMRR) method. The is reaches a minimum (7-10 min) for the (1:1) mixtures of the target Fe3O4/SiO2 and the seed Fe3O4/SiO2-NH2 nanoparticles. Adding of the seed Fe/C-NH2 nanoparticles to the target Fe3O4/SiO2 water suspension is more effective due to smaller sizes and to larger magnetic moments of the Fe-based particles. The sedimentation time of about (6-10) minutes is observed for rather small fraction (6, 15 mass%) of the added Fe/C-NH2 particles, which is important for application to reduce the residual sediment volume significantly. Preliminary exposure of the mixtures in the absence of magnetic field favors to more complete nanoparticles aggregation and, as a result, more rapid sedimentation of the nanoparticles in a vertical gradient magnetic field.