title: Removal of hexavalent chromium [Cr(VI)] from aqueous solutions by the diatomite-supported/unsupported magnetite nanoparticles.
abstract: Diatomite-supported/unsupported magnetite nanoparticles were prepared by co-precipitation and hydrosol methods, and characterized by X-ray diffraction, nitrogen adsorption, elemental analysis, differential scanning calorimetry, transmission electron microscopy and X-ray photoelectron spectroscopy. The average sizes of the unsupported and supported magnetite nanoparticles are around 25 and 15 nm, respectively. The supported magnetite nanoparticles exist on the surface or inside the pores of diatom shells, with better dispersing and less coaggregation than the unsupported ones. The uptake of hexavalent chromium [Cr(VI)] on the synthesized magnetite nanoparticles was mainly governed by a physico-chemical process, which included an electrostatic attraction followed by a redox process in which Cr(VI) was reduced into trivalent chromium [Cr(III)]. The adsorption of Cr(VI) was highly pH-dependent and the kinetics of the adsorption followed a pseudo-second-order model. The adsorption data of diatomite-supported/unsupported magnetite fit well with the Langmuir isotherm equation. The supported magnetite showed a better adsorption capacity per unit mass of magnetite than unsupported magnetite, and was more thermally stable than their unsupported counterparts. These results indicate that the diatomite-supported/unsupported magnetite nanoparticles are readily prepared, enabling promising applications for the removal of Cr(VI) from aqueous solution.
authors.affiliation: Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China. yuanpeng@gig.ac.cn
authors.forename: Peng
authors.initials: P
authors.lastname: Yuan
authors.forename: Dong
authors.initials: D
authors.lastname: Liu
authors.forename: Mingde
authors.initials: M
authors.lastname: Fan
authors.forename: Dan
authors.initials: D
authors.lastname: Yang
authors.forename: Runliang
authors.initials: R
authors.lastname: Zhu
authors.forename: Fei
authors.initials: F
authors.lastname: Ge
authors.forename: JianXi
authors.initials: J
authors.lastname: Zhu
authors.forename: Hongping
authors.initials: H
authors.lastname: He
mesh_terms: D000327:Adsorption; D002152:Calorimetry, Differential Scanning; D002857:Chromium / Q000302:isolation & purification*; D007692:Diatomaceous Earth / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D012996:Solutions; D013816:Thermodynamics; D014867:Water; D018508:Water Purification; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D012996:Solutions; D014867:Water; D002857:Chromium; C074702:chromium hexavalent ion; C000499:ferric oxide; D007692:Diatomaceous Earth; C033787:diatomite; D052203:Ferrosoferric Oxide