Synthesis And Properties Of Nanocomposites Based On Fe₃O₄ And Noble Metals

The hybrid nanoparticles formed by Fe3O4 and noble metals not only can integrate the excellent performance of each component,but also can make up for the defects of magnetic nanoparticles and noble metals in practical applications,and have significant application advantages in the fields of catalysis,magnetism,biology,medicine and other fields.Polyoxometalates(POMs)have wide application prospects in the fields of catalysis,electrochemistry,optics and biomedicine due to their rich structural composition,high charge density and reversible redox properties.Combining the hybrid nanoparticles formed by Fe3O4 and noble metals with polyoxometallates can obtain multifunctional nanocomposites with novel structure and unique properties.In recent years,the synthesis of nanocomposites with novel structures and wide applications through simple,safe and green preparation methods has become a hotspot in the field of nanomaterials research.In this paper,Fe3O4@Ag,Fe3O4/IrO2 and Fe3O4@IrO2 hybrid nanoparticles were first prepared by a simple and easy-to-operate microemulsion method,and then the multifunctional nanocomposites of Fe3O4@Ag@POMs and Fe3O4@IrO2/POMs based on Fe3O4 and noble metals were prepared by sonochemical method,and passed through transmission electron microscope/high resolution transmission electron microscope(HR-TEM),X-ray powder diffraction(XRD),scanning electron microscope-energy dispersive X-ray spectrometer(SEM-EDS),X-ray photoelectron spectroscopy(XPS),Vibration sample magnetometer(VSM)and physical performance measurement system(PPMS)and other instruments and equipment to conducted in-depth research on the structure and properties of the prepared hybrid nanoparticles and multifunctional nanocomposites based on Fe3O4 and noble metals.Fe3O4@Ag@POMs has good magnetic properties and high stability,which can quickly remove organic dyes through adsorption and photocatalysis,and can be easily recovered and reused under an external magnetic field.The nanocomposites of Fe3O4@Ag@POMs are expected to become a magnetic photocatalytic adsorption functional material for wastewater treatment.Fe3O4@IrO2 core-shell nanoparticles have good electrochemical stability and chemical stability,show good hydrogen and oxygen evolution activity under acidic and alkaline conditions,and are expected to become an electrocatalyst with bidirectional hydrolysis and high stability.The main research work of this paper is as follows:1.Synthesis,characterization and properties of Fe3O4@Ag@polyoxometalate nanocompositesThe microemulsion method was used to coat Ag on the magnetic Fe3O4 nanoparticles to obtain Fe3O4@Ag core-shell nanoparticles,and then the surface of the Fe3O4@Ag core-shell nanocomposite particles were coated with polyoxometalates([Cu(L)2(H2O)]H2[Cu(L)2(P2Mo5O23)]·4H2O,[Zn(L)2(H2O)2]2H2[P2Mo5O23]·2H2O,[Cd(L)2(H2O)2]2H2[P2Mo5O23]·2H2O,[Co(L)2(H2O)2]2H2[P2Mo5O23]·2H2O,L=Pyridine-2-carboxamide)by sonochemical method to synthesize Fe3O4@Ag@polyoxometalates(Fe3O4@Ag@POMs)nanocomposites with core-shell-shell nanostructures.Transmission electron microscopy/high resolution transmission electron microscopy(HR-TEM)and X-ray powder diffraction(XRD)analysis showed that Fe3O4@Ag@POMs nanocomposites have high crystallinity,near-spherical morphology,narrow particle size distribution and good monodispersity.Vibration sample magnetometer(VSM)and physical property measurement system(PPMS)proved that nanocomposites have good magnetic properties and exhibit superparamagnetic behavior at 300 K.UV-Vis spectra showed that Fe3O4@Ag@POMs nanocomposites have large surface plasmon resonance absorption around 420 nm.The dye removal capacity of Fe3O4@Ag@POMs was investigated using methylene blue(MB)as a probe.The results showed that at room temperature,nanocomposites can quickly remove MB with a removal rate of 98.7%through adsorption and photocatalysis.The removal efficiency was still up to 97.5%even after six runs by magnetic separation of photocatalytic adsorbents after process indicating the reusability and high stability of the nanocomposites.The Fe3O4@Ag@POMs photocatalytic adsorbents with magnetic properties and high stability are expected to become a functional material for wastewater treatment in the future.2.Synthesis of Fe3O4/IrO2 and Fe3O4@IrO2 hybrid nanoparticles and study on the properties of electrocatalytic hydrogen and oxygen evolutionThe Fe3O4/IrO2 hybrid nanoparticles and Fe3O4@IrO2 core-shell nanoparticles were synthesized by microemulsion method using two-phase dispersible PEO-PPO-PEO as surfactant.The formation of nanoparticles and their composition,structure,and morphology were analyzed by high-resolution transmission electron microscope(HR-TEM),X-ray powder diffractometer(XRD),scanning electron microscope-energy dispersive X-ray spectrometer(SEM-EDS),and X-ray photoelectron spectroscopy(XPS).The good magnetic behavior of nanoparticles at room temperature was demonstrated by vibrating sample magnetometer(VSM).The specific surface area of the synthesized nanoparticles was determined by a fully automatic chemical/physical adsorption apparatus,and the results showed that the nanoparticles had a large specific surface area.By studying the HER and OER activities of the synthesized nanoparticles under acidic and alkaline conditions,it was found that the calcined Fe3O4@IrO2 core-shell nanoparticles have good hydrogen evolution and oxygen evolution activities under acidic and alkaline conditions.Under the condition of constant control voltage,the stability of the calcined Fe3O4@IrO2 core-shell nanoparticles was tested in acidic and alkaline environments.The results showed that the current density hardly fluctuated after 20 h continuous operation,which proved that the nanoparticles had good stability under acidic and alkaline conditions.The synthesis of the nanoparticles opens the way for the development of bidirectional hydrolytic electrocatalysts at wide pH values.3.Synthesis and characterization of Fe3O4@IrO2/POMs nanocompositesFe3O4@IrO2 core-shell nanoparticles and POMs were organically combined by sonochemical method to form Fe3O4@IrO2/POMs nanocomposites.Transmission electron microscopy(TEM)and X-ray powder diffraction(XRD)proved that the nanocomposites are highly crystalline,basically spherical,with a narrow particle size distribution and an average particle size of～17.5 nm.The magnetic test proved that the nanocomposites exhibited ferromagnetism at room temperature,and the coercive force was about 37.8 Oe The dispersion and aggregation behavior of nanocomposites in water proved the good dispersion and magnetic manipulation behavior of nanocomposites in water.Fe3O4@IrO2/POMs nanocomposites have potential application value in the fields of magnetism,biomedicine and environmental protection.