title: One-Pot synthesis, characterization and adsorption studies of amine-functionalized magnetite nanoparticles for removal of Cr (VI) and Ni (II) ions from aqueous solution: kinetic, isotherm and thermodynamic studies.
abstract: BACKGROUND
  Discharge of heavy metals such as hexavalent chromium (Cr (VI)) and nickel (Ni (II)) into aquatic ecosystems is a matter of concern in wastewater treatment due to their harmful effects on humans. In this paper, removal of Cr (VI) and Ni (II) ions from aqueous solution was investigated using an amino-functionalized magnetic Nano-adsorbent (Fe3O4-NH2).
  
  
  METHODS
  An amino-functionalized magnetic Nano-adsorbent (Fe3O4-NH2) was synthesized by compositing Fe3O4 with 1, 6-hexanediamine for removal of Cr (VI) and Ni (II) ions from aqueous solution. The adsorbent was characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), powder X-Ray Diffraction (XRD), and Vibrating Sample Magnetometry (VSM). Also, the effects of various operational parameters were studied.
  
  
  RESULTS
  According to our finding, Fe3O4-NH2 could be simply separated from aqueous solution with an external magnetic field at 30 s. The experimental data for the adsorption of Cr (VI) and Ni (II) ions revealed that the process followed the Langmuir isotherm and the maximum adsorption capacity was 232.51 mg g(-1) for Cr (VI) at pH = 3 and 222.12 mg g(-1) and for Ni(II) at pH = 6 at 298 °K. Besides, the kinetic data indicated that the results fitted with the pseudo-second-order model (R(2): 0.9871 and 0.9947 % for Cr (VI) and Ni (II), respectively. The results of thermodynamic study indicated that: standard free energy changes (ΔG(ɵ)), standard enthalpy change (ΔH(ɵ)), and standard entropy change (ΔS(ɵ)) were respectively -3.28, 137.1, and 26.91 kJ mol(-1) for Cr (VI) and -6.8433, 116.7, and 31.02 kJ mol(-1) for Ni (II). The adsorption/desorption cycles of Fe3O4-NH2 indicated that it could be used for five times.
  
  
  CONCLUSIONS
  The selected metals' sorption was achieved mainly via electrostatic attraction and coordination interactions. In fact, Fe3O4-NH2 could be removed more than 96 % for both Cr (VI) and Ni (II) ions from aqueous solution and actual wastewater.
authors.affiliation: Center for Water Quality Research, Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran ; Department of Environmental Health Engineering, School of Public Health Science, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Abbas
authors.initials: A
authors.lastname: Norouzian Baghani
authors.affiliation: Department of Environmental Health Engineering, School of Public Health Science, Tehran University of Medical Sciences, Tehran, Iran ; Center for Solid Waste Research, Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Amir Hossein
authors.initials: AH
authors.lastname: Mahvi
authors.affiliation: Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran ; Environmental Health Department, School of Public Health, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Mitra
authors.initials: M
authors.lastname: Gholami
authors.affiliation: Center for Air Pollution Research (CAPR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, 1417613151 Iran.
authors.forename: Noushin
authors.initials: N
authors.lastname: Rastkari
authors.affiliation: Environmental Health Department, School of Public Health, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Mahdieh
authors.initials: M
authors.lastname: Delikhoon
keywords: 1, 6 hexanediamine; Adsorption/desorption; Amino-functionalized; Fe3O4-NH2; Heavy metal ions; Thermodynamics