Preparation of Fe(3)O(4)@polyoxometalates Nanocomposites and Their Efficient Adsorption of Cationic Dyes from Aqueous Solution

In this work, two magnetic adsorbents Fe(3)O(4)@1 and Fe(3)O(4)@2 were prepared by combining Fe(3)O(4) nanoparticles and polyoxometalate hybrids [Ni(HL)(2)](2)H(2)[P(2)Mo(5)O(23)]·4H(2)O (1), [H(2)L](5)H[P(2)Mo(5)O(23)]·12H(2)O (2) (HL = 2-acetylpyridine-thiosemicarbazone). The temperature-dependent zero-field-cooled (ZFC) and field-cooled (FC) measurements indicated the blocking temperature at 160 K and 180 K, respectively. The Brunauer–Emmett–Teller (BET) surface area of Fe(3)O(4)@1 and Fe(3)O(4)@2 is 8.106 m(2)/g and 1.787 m(2)/g, respectively. Cationic dye methylene blue (MB) and anionic dye methyl orange (MO) were investigated for selective dye adsorption on Fe(3)O(4)@1 and Fe(3)O(4)@2. The two adsorbents were beneficial for selective adsorption of cationic dyes. The adsorption efficiency of MB was 94.8% for Fe(3)O(4)@1, 97.67% for Fe(3)O(4)@2. Furthermore, the two adsorbents almost maintained the same adsorption efficiency after seven runs. The maximum MB adsorption capacity of Fe(3)O(4)@1 and Fe(3)O(4)@2 is 72.07 and 73.25 mg/g, respectively. The fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) spectra of the adsorbents collected after adsorption of MB are very similar to the initial as-synthesized Fe(3)O(4)@polyoxometalates indicating the high stability of the two adsorbents. The adsorption kinetics indicated that the MB removal followed the pseudo-second-order model. These results showed that the two adsorbents had a potential application in treating wastewater.