An in situ redox
process in microfluidic reactors
was developed to synthesize hybrid nanoparticles with amorphous metallic
cores and uniform metal oxide shells embedded with nanocrystallites
at large scale. For example, the fabricated Fe(B)@iron oxides nanoparticles
(NPs) exhibit permanent ferromagnetic properties at room temperature
due to the strong magnetic coupling between different parts and the
nanocrystalline pinning effect, providing an alternative design of
nanostructures to break out the superparamagnetic limit in ultratiny
particles. The NPs with amorphous metallic cores and uniform metal
oxide shells can be well maintained over 4–5 months. The dictated
novel microfluidic process provides a large-scale synthetic strategy
for metal@metal oxide core–shell NPs with uniform shells and
long-term stability and can be extended to a variety of material systems.
A new methodology based on core alloying and shell gradient-doping are developed for the synthesis of nanohybrids, realized by coupled competitive reactions, or sequenced reducing-nucleation and co-precipitation reaction of mixed metal salts in a microfluidic and batch-cooling process. The latent time of nucleation and the growth of nanohybrids can be well controlled due to the formation of controllable intermediates in the coupled competitive reactions. Thus, spatiotemporal-resolved synthesis can be realized by the hybrid process, which enables us to investigate nanohybrid formation at each stage through their solution color changes and TEM images. By adjusting the bi-channel solvents and kinetic parameters of each stage, the primary components of alloyed cores and the second components of transition metal doping ZnO or Al2O3 as surface coatings can be successively formed. The core alloying and shell gradient-doping strategy can efficiently eliminate the crystal lattice mismatch in different components. Consequently, varieties of gradient core-shell nanohybrids can be synthesized using CoM, FeM, AuM, AgM (M = Zn or Al) alloys as cores and transition metal gradient-doping ZnO or Al2O3 as shells, endowing these nanohybrids with unique magnetic and optical properties (e.g., high temperature ferromagnetic property and enhanced blue emission).
Simple programmed microfluidic processes show the precise morphology and crystal structure controlled synthesis of nanohybrids using Sn–SnO2 nanohybrids as models.
We have developed a core alloying and shell gradient doping strategy for the controlled surface modification of Fe or CoFe nanoparticles for enhanced magnetic resonance imaging.
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