Adsorption of arsenate on iron(III) oxide coated ethylenediamine functionalized multiwall carbon nanotubes

New criteria in assessing the quality of drinking water reduced the maximum permissible concentration of arsenic from 50 μg L−1 to 10 μg L−1, and set a requirement for the development of new technologies for arsenic removal. In this paper, ethylenediamine functionalized multiwall carbon nanotubes (e-MWCNT) were loaded with iron(III) oxide in the goethite form, by precipitation of adsorbed Fe3+ and oxidized Fe2+ using base, in that way e-MWCNT/Fe3+ and e-MWCNT/Fe2+ adsorbents, respectively, were obtained. The influence of pH on the As(V) and As(III) removal from drinking water was studied in a batch system, of pH range 3–10 and initial arsenic concentration 0.05–4 mg L−1. Time dependent As(V) adsorption and adsorption data can be described by pseudo-second-order kinetic model and by Freundlich isotherm, applying linear and non-linear fitting methods. The maximum adsorption capacities obtained from Langmuir model for As(V) on e-MWCNT/Fe2+ and e-MWCNT/Fe3+ were 23.47 and 13.74 mg g−1 at 25 °C, respectively. Thermodynamic parameters showed that the adsorption of As(V) was spontaneous and endothermic for both e-MWCNT/Fe2+ and e-MWCNT/Fe3+. Influences of the pH, iron(III) oxide loading and interfering ions were modeled by MINTEQ program, and good agreement between experimental and modeling data was obtained.

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► Iron(III)-oxide loaded e-MWCNT shows good sorption affinity for arsenic(V).
► The sorption pattern of As(V) fits well to the Freundlich model.
► As(V) adsorption is dependent to iron(III)-oxide content, pH and temperature.
► The sorption of As(V) and As(III) is a rather complex and spontaneous process.
► Creation of inner-sphere surface complexes are main sorption mechanisms.