Arsenite and arsenate adsorption on coprecipitated bimetal oxide magnetic nanomaterials: MnFe2O4 and CoFe2O4
ABSTRACT Bimetal oxide magnetic nanomaterials (MnFe2O4 and CoFe2O4) were synthesized and characterized with transmission electron microscope (TEM), X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). The adsorption of arsenic on these nanomaterials was studied as a function of pH, initial arsenic concentration, contact time and coexisting anions. The Langmuir and Freundlich isotherm models were applied to fit the adsorption data, and the maximum adsorption capacities of arsenite (AsIII) and arsenate (AsV) on MnFe2O4 were 94 and 90 mg g−1, and on CoFe2O4 were 100 and 74 mg g−1, respectively. MnFe2O4 and CoFe2O4 showed higher AsIII and AsV adsorption capacities than the referenced Fe3O4 (50 and 44 mg g−1, respectively) prepared by the same procedure. Quantificational calculation from XPS narrow scan results of O(1s) spectra of adsorbents indicated that the higher adsorption capacities of AsIII and AsV on MnFe2O4 and CoFe2O4 than on Fe3O4 might be caused by the increase of the surface hydroxyl (M–OH) species. Phosphate and silicate were powerful competitors with arsenic for adsorptive sites on the adsorbent. Desorption study showed that over 80% of AsIII and 90% of AsV could be desorbed from MnFe2O4 with 0.1 M NaOH solution.
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ABSTRACT: A novel magnetic nanomaterial was developed for gold recovery from dilute solutions. Fe3O4 nanoparticles were prepared by co-precipitation method, and SiO2 was coated on Fe3O4 nanoparticles by hydrolyzation of Na2SiO3 for protecting the core from being oxidized or dissolved under acid solution, and then thiol groups were modified on the Fe3O4@SiO2 through silanization reaction. Characterization with transmission electron microscope (TEM), energy-dispersive spectroscope (EDS), and X-ray photoelectron spectroscopy (XPS) proved that SiO2 and thiol groups were successfully covered on the surface of Fe3O4 nanoparticles to form Fe3O4@SiO2-SH adsorbent, which was readily separated from solution with a magnet because of superparamagnetism of Fe3O4 core. The formation of the stable Au-S bond between thiol group and gold element could be applied for gold recovery from solution. The adsorption behavior of Fe3O4@SiO2-SH for gold followed Langmuir isotherm model, and the maximum adsorption capacity was 84.75 mg/g at pH 5. When the initial concentration of gold was 5 mg/L, the gold in solution was completely adsorbed by Fe3O4@SiO2-SH, and when the gold concentration was 10 mg/L, 98.8% gold was adsorbed. With the solution pH increasing from 3 to 7, the adsorption capacity for gold showed a slight decrease, and the adsorbents still remained good adsorbability under high salinity condition. Gold loaded on the adsorbent could be easily desorbed by 1 mol/L or 2 mol/L HCl containing 2% of thiourea, and the adsorbents showed good reusability after 5 times recycle. (c) 2013 Elsevier B.V. All rights reserved.Separation and Purification Technology 09/2013; 116:391-397. DOI:10.1016/j.seppur.2013.06.018 · 3.07 Impact Factor
Journal of the Taiwan Institute of Chemical Engineers 02/2015; 47:190-196. DOI:10.1016/j.jtice.2014.10.014 · 2.64 Impact Factor
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ABSTRACT: Magnetic mesoporous iron cerium bimetal oxides (MMIC) with large surface area and pore volume was synthesized via the hard template approach. This obtained MMIC was easily separated from aqueous solution with an external magnetic field and was proposed as a heterogeneous Fenton-like catalyst for oxidation of As(III). The MMIC presented excellent catalytic activity for the oxidation of As(III), achieving almost complete oxidation of 1000ppb As(III) after 60min and complete removal of arsenic species after 180min with reaction conditions of 0.4g/L catalyst, pH of 3.0 and 0.4mM H2O2. Kinetics analysis showed that arsenic removal followed the pseudo-first order, and the pseudo-first-order rate constants increased from 0.0014min(-1) to 0.0548min(-1) as the H2O2 concentration increased from 0.04mM to 0.4mM. On the basis of the effects of XPS analysis and reactive oxidizing species, As(III) in aqueous solution was mainly oxidized by OH radicals, including the surface-bound OHads generated on the MMIC surface which were involved in Fe(2+) and Ce(3+), and free OHfree generation by soluble iron ions which were released from the MMIC into the bulk solution, and the generated As(V) was finally removed by MMIC through adsorption. Copyright © 2015 Elsevier B.V. All rights reserved.Journal of Hazardous Materials 01/2015; 287C:225-233. DOI:10.1016/j.jhazmat.2015.01.065 · 4.33 Impact Factor