Abstract
Wastewater containing heavy metal ions such as lead should be treated for cleanup before discharge to environment. This work reports new nanomaterials of orthohexagonal iron oxide for efficient removal of lead (II), which were doped with cobalt (CoFe2O3) or Nickel (NiFe2O3) ions through a simple method. The structure of adsorbents and adsorption mechanism were investigated by scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometer, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and so on. The results showed that the concentration of nitrate concentration has a tiny effect on the Pb(II) adsorption and the kinetic adsorption experiments showed that CoFe2O3 and NiFe2O3 took less time to achieve the equilibrium state than Fe2O3 without doping And the isotherm batch experiments showed that Langmuir model matched well with the data of Fe2O3, Freundlich model fitted well in CoFe2O3 and NiFe2O3 experiments data, indicating that cobalt/nickel doping changes the adsorption mechanism. XPS analysis showed that the hydroxyl at surface played an important role in Pb(II) removal and the hydrogen bond was replaced by metal-oxygen bond. Furthermore, the adsorption capacities of, CoFe2O3 and NiFe2O3 for Pb(II) removal were 136.0 mg/g and 97.5 mg/g respectively, which were superior to pristine Fe2O3 (93.9 mg/g). This study clearly showed that CoFe2O3 and NiFe2O3 are promising candidates for lead ion removal in aqueous solution.
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•Ortho-hexagonal iron oxides at nanometer scale have been synthesized through a cost-effective simple method.•The crystal structure of α-Fe2O3 was transformed into γ-Fe2O3 by doping with cobalt or nickel.•The doping with cobalt greatly enhanced the adsorption capacity of the iron oxides.•The adsorption mechanism of lead on the materials was extensively studied.