Magnetic sedimentation of nonmagnetic TiO2 nanoparticles in water by heteroaggregation with Fe-based nanoparticles

Abstract A new approach to remove TiO 2 nanoparticles from water is studied. Composite Fe 3 O 4 -SiO 2 and Fe-C-SO 3 H nanoparticles with magnetic cores (5 nm) were designed to be used as flocculants for magnetic sedimentation of nonmagnetic TiO 2 nanoparticles in water. The sedimentation dynamics of heterogeneous water suspensions (starting solid phase concentration of 100 mg/l) of (TiO 2 ) 1− x (Fe 3 O 4 -SiO 2 ) x ( x  = 0.15–0.55) and (TiO 2 ) 1− x (Fe-C-SO 3 H) x ( x  = 0.01–0.17) was studied in a gradient magnetic field (B = 0.3 T, dB/dz  3 O 4 -SiO 2 , Fe-C-SO 3 H and TiO 2 nanoparticles in water after magnetic sedimentation. The hydrodynamic sizes of the heteroaggregates (d h ) depend on the pH value and on the mass content of the magnetic component, x . For the mixed (TiO 2 ) 1− x (Fe 3 O 4 -SiO 2 ) x water suspensions the maximum of d h  = 5 μm and the fastest sedimentation are reached for x  = 0.35–0.5 at pH = 3, 4, and for x  = 0.2 at pH = 5. At this regime, the highest efficiency of TiO 2 particles removal from water, that is, 99.7% for 30 min, was observed. For the mixed (TiO 2 ) 1−x (Fe-C-SO 3 H) x water suspensions the largest heteroaggregates and the fastest sedimentation were observed for the smaller mass content of the magnetic flocculant, x  = 0.03–0.05 at pH = 3, 4 and for x  = 0.03 at pH = 5. However, by adding Fe-C-SO 3 H nanoparticles flocculant the achieved minimum residual concentration of TiO 2 nanoparticles in water is two orders of magnitude higher. These results are discussed by assuming a specific distribution of Fe - based nanoparticles by heteroaggregation with TiO 2 nanoparticles.