Preparation of Fe3O4@polyoxometalates Nanocomposites and Their Efficient Adsorption of Cationic Dyes from Aqueous Solution

Abstract

In this work, two magnetic adsorbents Fe₃O₄@<b>1</b> and Fe₃O₄@<b>2</b> were prepared by combining Fe₃O₄ nanoparticles and polyoxometalate hybrids [Ni(HL)₂]₂H₂[P₂Mo₅O₂₃]·4H₂O (<b>1</b>), [H₂L]₅H[P₂Mo₅O₂₃]·12H₂O (<b>2</b>) (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 Fe₃O₄@<b>1</b> and Fe₃O₄@<b>2</b> is 8.106 m²/g and 1.787 m²/g, respectively. Cationic dye methylene blue (MB) and anionic dye methyl orange (MO) were investigated for selective dye adsorption on Fe₃O₄@<b>1</b> and Fe₃O₄@<b>2</b>. The two adsorbents were beneficial for selective adsorption of cationic dyes. The adsorption efficiency of MB was 94.8% for Fe₃O₄@<b>1</b>, 97.67% for Fe₃O₄@<b>2</b>. Furthermore, the two adsorbents almost maintained the same adsorption efficiency after seven runs. The maximum MB adsorption capacity of Fe₃O₄@<b>1</b> and Fe₃O₄@<b>2</b> 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 Fe₃O₄@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.