| Summary: | The ternary nanocomposites Fe<sub>3</sub>O<sub>4</sub>/Ag/polyoxometalates (Fe<sub>3</sub>O<sub>4</sub>/Ag/POMs) with core−shell−core nanostructure were synthesized by coating [Cu(C<sub>6</sub>H<sub>6</sub>N<sub>2</sub>O)<sub>2</sub>(H<sub>2</sub>O)]H<sub>2</sub>[Cu(C<sub>6</sub>H<sub>6</sub>N<sub>2</sub>O)<sub>2</sub>(P<sub>2</sub>Mo<sub>5</sub>O<sub>23</sub>)]·4H<sub>2</sub>O polyoxometalates on the surface of Fe<sub>3</sub>O<sub>4</sub>/Ag (core−shell) nanoparticles. The transmission electron microscopy/high resolution transmission electron microscopy (HR-TEM) and X-ray powder diffraction (XRD) analyses show that the Fe<sub>3</sub>O<sub>4</sub>/Ag/POMs ternary nanocomposites reveal a core−shell−core nanostructure, good dispersibility, and high crystallinity. The vibrating sample magnetometer (VSM) and physical property measurement system (PPMS) demonstrated the good magnetic properties and superparamagnetic behavior of the nanocomposites at 300 K. The UV−vis spectroscopy displayed the broadband absorption of the Fe<sub>3</sub>O<sub>4</sub>/Ag/POMs with the maximum surface plasmon resonance of Ag nanostructure around 420 nm. The dye removal capacity of Fe<sub>3</sub>O<sub>4</sub>/Ag/POMs was investigated using methylene blue (MB) as a probe. Through adsorption and photocatalysis, the nanocomposites could quickly remove MB with a removal efficiency of 98.7% under the irradiation of visible light at room temperature. The removal efficiency was still as high as 97.5% even after six runs by magnetic separation of photocatalytic adsorbents after processing, indicating the reusability and high stability of the nanocomposites. These Fe<sub>3</sub>O<sub>4</sub>/Ag/POMs photocatalytic adsorbents with magnetic properties will hopefully become a functional material for wastewater treatment in the future.
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