Preparation of Fe 3 O 4 @polyoxometalates nanocomposites and their efficient adsorption of cationic dyes from aqueous solution

Abstract

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.