Polypyrrole Coating via Lemieux-von Rudloff Oxidation on Magnetite Nanoparticles for Highly Efficient Removal of Chromium(VI) from Wastewater.

An alternative way for the coating of polypyrrole (PPy) polymer on hydrophobic magnetite (Fe 3 O 4 ) nanoparticles is reported here to capture toxic chromium ions, Cr (VI), present in water. Iron oxide magnetic nanoparticles (Fe 3 O 4 ) were synthesized by the conventional coprecipitation technique using FeCl 3 ·6H 2 O and FeSO 4 ·7H 2 O iron precursors and subsequently modified with oleic acid (OA). Then OA-Fe 3 O 4 hydrophobic nanoparticles were oxidized using the Lemieux-von Rudloff reaction to transfer OA into hydrophilic azelaic acid (AA) (HOOC(CH 2 ) 7 COOH-modified magnetic nanoparticles (AA-Fe 3 O 4 ). Finally, a PPy polymer coating was formed by a seeded polymerization of pyrrole, using AA-Fe 3 O 4 as seeds. The average size of PPy/Fe 3 O 4 nanocomposites is 12.33 nm and is almost spherical in shape. The surface composition is confirmed by FTIR and thermogravimetry analyses. An X-ray diffraction study confirmed the formation of highly crystalline Fe 3 O 4 nanoparticles, and the crystallinity was retained after the surface modification. The adsorption study suggested that the Cr(VI) ion adsorption is highly pH-dependent and the maximum amount of adsorption is obtained at pH 2.0. The adsorption results revealed that the Langmuir model provided the best fit for the isotherm, with a maximum adsorption capacity reaching approximately 173.22 mg g -1 at 323 K. Spontaneous and endothermic adsorption processes were confirmed by evaluating the thermodynamic parameters obtained in this investigation. The kinetics study showed that the interaction between Cr(VI) ions and magnetic nanocomposites was directed by a pseudo-second-order rate process indicating chemisorption. The prepared PPy/Fe 3 O 4 nanocomposites would be promising adsorbents to purify water by eliminating Cr(VI) metal ions from wastewater.