Sorption-reduction removal of Cr(VI) from aqueous solution by the porous biomorph-genetic composite of α-Fe2O3/Fe3O4/C with eucalyptus wood hierarchical microstructure

A porous biomorph-genetic composite of alpha-Fe2O3/Fe3O4/C (PBGC-Fe/C) with eucalyptus wood hierarchical microstructure was prepared and characterized. The result indicated that the PBGC-Fe/C material retained the hierarchical porous structure of eucalyptus wood with three different types of pores (widths 70-120, 4.1-6.4 and 0.1-1.3 mu m) originating from vessels, fibres, and pits of the wood, respectively. Batch experiments were conducted to evaluate the effects of different parameters on Cr(VI) adsorption systematically. With increasing initial concentration from 10 to 150 mg/L, the amounts of Cr(VI) adsorbed on the pulverized PBGC-Fe/C adsorbent (<0.149 mm) increased from 1.00 to 4.01 mg/g at 25 degrees C, from 1.00 to 4.22 mg/g at 35 degrees C, and from 1.00 to 4.52 mg/g at 45 degrees C. At the initial concentrations of 2, 10, and 50 mg/L, the adsorption capacities for the unpulverized PBGC-Fe/C adsorbent (>0.841 mm) were determined to be 0.20, 0.92, and 2.96 mg/g, respectively, which exhibited a similar average value to those of fine particles or nanoparticles of iron oxides. The adsorption followed Freundlich as well as Langmuir isotherms and could well be described by the pseudo-second-order kinetic equation. X-ray photoelectron spectroscopy studies showed that the main mechanism of Cr(VI) removal was a sorption-redox reaction between Cr(VI) and the PBGC-Fe/C adsorbent.